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28073 PE-1852 STORMWATER DRAINAGE REPORT STORMWATER DRAINAGE REPORT for the proposed plat of STRAWTHER'S ADDITION located in the City of Spokane Valley in the NW '/4 of Section 33, T. 25 N., R. 44 E.W.M. Spokane County, Washington Original Draft: July 1, 2003 Amended (basin maps): September 29, 2003 Final Draft: February 17, 2004 ' Project Applicant: Donna Strawther 16326 North Castlebrook Lane Spokane, WA 99208 (509) 467-7581 ~gE.s Report Prepared By: ~04 w~s ' ~ Simpson Engtineers, Inc. ~ North 909 Argonne Road Spokane, Washington 99212 (509) 926-1322 A~' ' rEXPIF;Es ' 7/17/ 0 5 ENGINEER'S CERTIFICATION . The design improvements shown in this set of plans and calculations conform to the applicable editions of the Spokane County Standards for Road and Sewer Construction and the Spokane County Guidelines for Stormwater Management. I approve these plans for construction. CONTENTS Paize A. Proj ect Location . . . . . . . . . 2 B. Existing Site Topography. . . . . . . . 2 C. Project Description . . . . . . . . 2 ' D. Previous Reports . . . . . . . . . 3 ' E. Soils Description . . . . . . . . 3 F. Geo-Hazard Evaluation . . . . . . . . 3 G. Drainage Concept . . . . . . . . 4 H. Rainfall Data & Design Tools . . . . . . . 5 1. Drainage Basins . . . . . . . . . 5 ' J. Pre- vs. Post-Development Analysis . . . . . . 8 APPENDIX: SupplementalInformation 1. Site in Relation to Spokane County Aquifer Sensitive Area (Spokane County Guidelines for Stormwater Management, Figure 6, p. 6-9) ' 2. Site Viciruty and Mapped Soils (excerpted from USDA Soil Conservation Service, Soil Survey of Spokane County, Washington, March 1968, Sheet Number 75) , 3. Runoff Coefficients for Storm Sewers (Spokane County Guidelines for Stormwater Management, Table 1, p. 6-2) 4. Rational Formula Hydrology Calculations (4 sheets) (Basin E 1= Existing Conditions, and Basins P2, P3 & P4 = Proposed Conditions) ' 5. Proposed Culvert Capacity Calculations (2 sheets) 6. Pre-Development Drainage Basin fold-out map 7. Post-Development Drainage Basins fold-out map 8. TR-55/PondPack Computations dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 02/17/04 Page 1 , PROJECT LOCATION The Strawther's Addition project site is located within the newly-formed City of Spokane Valley, on the northeasterly side of Dishman-Mica Road and on the west side of Pierce Road (extended), between 38th Avenue and 40th Avenue. The site is located in the southwest quarter of the northwest quarter of Section 33, Township 25 North, Range 44 East, W.M., in Spokane County, Washington. The site lies near the south limit of the Spokane-Rathdrum Aquifer, and is within the Spokane County Aquifer Sensitive Area and the Priority Sewer Service Area. EXISTING SITE TOPOGRAPHY The site is bounded on the southwest by Dishman-Mica Road, a two-lane Principal Arterial within a 60-foot right-of-way. To the east are existing single-family houses, platted as Chester Field Addition, and to the north are existing single-family houses, platted as Short Plat 743-92. Aside from the existing duplex near the southeast corner of the plat, the remainder of the site is covered with Ponderosa pine trees, native grasses and brush. A natural drainage gully extends through the site, from an existing drainage easement on the north side of the site to an existing 18"-diameter CMP culvert under Dishman-Mica Road, draining to an apparent wetland area on the southwest side of the road. A proposed drainage easement through the site will connect the existing drainage easement to the existing culvert along the existing drainage course. The site has topographic high areas on the east and west portions, with the existing drainage gully in-between. On-site slopes range from very gentle to approximately 14%, facing primarily to the west, east and south. The local high points are located near the eastem plat boundary, where the proposed cul-de-sac will be located, and in the west portion of the site. The lowest area on the site is in the drainage gully at the entrance to the existing culvert underlying Dishman-Mica Road. ' Refer to the Strawther's Addition Stormwater Draina e Plan maP for locations of existin S g contours and proposed features described in this report. ' PROJECT DESCRIPTION The proposed plat of Strawther's Addition will subdivide approximately 3.24 acres of mostly undeveloped land into seven residential lots, which will vary in size. The project site is irregular in shape, with the southeasterly portion occupied by an existing duplex. The duplex is accessed off 40 Avenue, while the remainder of the plat will be accessed off an existing cul-de-sac at the west end of 38th Avenue at Pierce Road, from which a proposed private cul-de-sac will extend southward onto the site. The proposed cul-de-sac will provide direct access for the three lots nearest to the northeast corner of the site, while the three westerly lots of the plat will be accessed via a private driveway, to be located within an ingress-egress easement extending to the west off the west side of the on-site cul-de-sac. dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 07/01 /03 Page 2 PREVIOUS REPORTS A ConceDtual Stormwater Manazement Plan was prepared for Strawther's Addition by J. Paul Ramer & Associates, Inc. in 1998. The general concepts presented in that plan are maintained in the present drainage plan for the proj ect. A report letter titled Summarv ofResults of Limited Geotechnical EnaineeYina Studv, dated April 29, 1998, was prepared for this site by Cummings Geotechnology. The findings from that study are used herein for soils-related aspects of the present drainage plan. Any specific conclusions or data from that study that are used herein are referenced as such. SOILS DESCRIPTION Soi1s at the site are mapped as being almost completely Clayton sandy loam (map symbol CuB), with the contact with Springdale gravelly sandy loam (map symbol SxB) located near the east plat boundary, as per Soil Survey of Spokane County, Washington: USDA Soil Conservation Service (now the Natural Resources Conservation Service), March 1968. Springdale soils are listed by Spokane County as being acceptable for standard drywell practice, but Clayton soils are not. However, soils testing performed by Cummings Geotechnology at the location of a proposed drywell at the northwest side of the proposed cul-de-sac (as specified by J. Paul Ramer & Associates, Inc.) indicates soils having a permeability of "several hundred inches per hour," with the recommendation that "a Type B drywell could function adequately as long as it is embedded at least 5 feet into the clean gravelly coarse sand" that was found at a depth of "6 feet to greater than 10 feet." Refer to the attached excerpt from the S.C.S. soils map (Sheet Number 75) for location of the site ' relative to mapped soils. ' GEO-HAZARD EVALUATION "Geologically Hazardous Areas," as classified according to the characteristics described per the Spokane County Critical Areas Ordinance, include those areas prone to erosion and landslide hazards. Based on our initial field investigation of the proj ect site, we have determined that this site is not a Geologically Hazardous Area, due to the site having the following characteristics: a. Slopes at the site are all substantially less than 30% grade, with the steepest slopes being about 14% for a small, limited area in the southwest portion of the site, on the northwest side of the existing drainage course above the existing culvert under Dishman-Mica Road. b. Neither the Clayton sandy loam nor the Springdale gravelly sandy loaxn soils mapped at this site are identified by the USDA S.C.S. (now the Natural Resources Conservation Service) as having a"severe" potential for erosion (as listed in Appendix H of the Spokane County Critical Areas Ordinance). Clayton soils generally have moderate stability and moderate to dhc:Projects/14470-drn.doc Simpson Engineers, lnc. 06/26/03 Page 3 low resistance to erosion, while Springdale soils generally have moderate to high stability • and moderate to low resistance to erosion. Our observations at the site did not reveal any evidence of erosion having occurred recently to any significant degree. c. The only significant hydraulic factor to consider at this site is the well-defined drainage channel crossing through the site, leading to the existing culvert under Dishman-Mica road. However, it does not contain a perennial stream, and was observed this spring to be dry and to drain a limited basin area in the immediate vicinity. There are no known springs, and no wet areas observed on the site. d. This site is not a landslide-prone area; no evidence of landslides was observed on the site, and the site soils are not alluvium, not landslide deposits, and not Latah formation. ' e. This site is not an area of uncompacted fill. f. The site is not unstable due to stream or streambank erosion. DRAINAGE CONCEPT The proposed drainage design for this project is fairly straightforward and generally follows the recommendations established in Spokane County's Cruidelines for Stormwater Management. The developed site is proposed to be regraded such that all runoff water from the proposed asphalt surfacing will be collected and drained to a proposed drainage swale (grassed percolation area) for treatment and disposal. The swale is located near the northeast corner of the site, adjacent to the proposed access roadlcul-de-sac. The intention is to position the swale in the location where soils testing was performed by Cummings Geotechnology, as described above (see "Soils Description"). The proposed site plan will result in two primary points of discharge: the existing culvert under Dishman-Mica Road, and the proposed drainage swale by the proposed cul-de-sac. Runoff under both existing (pre-platting) and proposed (post-platting) conditions were analyzed to assess the irnpacts of the site improvements on flows at the existing culvert, using a 50-year storm event for the basins that include off-site areas. Runoff flowing to the proposed drainage swale, which only ' occurs under proposed conditions and only includes on-site areas, is analyzed using a 10-year storm event. The total areas of drainage basins involved is the approximately the same under both existing and proposed conditions. ' . The plan includes a private access dnve to serve three of the proposed lots. The road will transect the existing drainage gully which drains to the existing culvert under Dishman-Mica Road, so a new culvert will be constructed under the private drive. Flows to the existing culvert under existing conditions, and to both the existing culvert and the new culvert under proposed conditions, are analyzed. The drainage basins are named as shown on the StoYmwater Drainage Plan and detailed on the following pages. Refer to the Stormwater Drainage Plan for locations of drainage features described in this report. dhc:Projects114470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 4 ' RAINFALL DATA & DESIGN TOOLS The rainfall intensity-duration-frequency curve for both 10-year and 50-year recurrence intervals for the Spokane-Med.ical Lake-Reardon-Cheney-Rockford area, as presented in the February 1998 Addendum to Spokane County's Guidelines for Stormwater Management, in Figure 2, page 6-3, was adapted into tabular form for the rational formula hydrology calculations for the drainage basins under existing and proposed conditions. 1'he intention in designing stormwater drainage facilities for this project was to follow the procedures, methods and referenced data in Spokane County's Guidelines for Stormwater Management (1998). Computations were performed using Spokane County-accepted methods and software programs, including rational formula hydrology for calculations of peak discharge to the culverts, and bowstring methodology for ponding volume vs. drywell outflow, adapted into an MS Exce12000 spreadsheet. The existing topography and proposed features and grades shown on the Stormwater Drainage Plan map were drawn, and some of the areas were calculated, using AutoCAD Land Development. Runoff coefficient ("C") values are based on 2% to 10% slopes, as per "Runoff Coefficients for Storm Sewers" (Guidelines, February 1998, Table 1, p. 6-2). For Proposed conditions, new houses are assumed to be 2,000 sq. ft. and new concrete driveways are assumed to be 1,000 sq. ft. Separate hydrology calculation sheets for all described basins and conditions are included in this report. DR:AINAGE BASINS Drainage Basin Name: Basin E1 Condition: Earisting Basin Description: Area drainulg to existing culvert under Dishman-Mica Road under existing conditions. ~ Total Area of Basin: 157,920 sq. ft. = 3.625 acres Impervious Areas: Asphalt (N. %2 D.-Mica Rd.) = 10,230 sq. ft. = 0.235 acre (~a, C= 0.90 House Roofs = 5,000 sq. ft. = 0.115 acre na, C= 0.90 Concrete Driveways = 1,500 sq. ft. = 0.034 acre Q C= 0.80 Pervious Areas: Road Shoulder = 3,720 sq. ft. = 0.085 acre Q C= 0.50 Natural (on-site) = 110,395 sq. ft. = 2.534 acre na, C= 0.22 Lawn/Landscaping (off-site) = 27,075 sq. ft. = 0.622 acre a, C= 0.15 Point of concentration: Entrance to existing culvert under Dishman-Mica Road. 50-year Storm Discharge: QSo =(C) (iso) (A) = 3.79 c.f.s. (see hydrology calculation sheet) dt,c:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 5 DR.AINAGE BASINS - continued Drainage Basin Name: Basin P1 Condition: Proposed Basin Description: Area draining to proposed drainage swale by proposed cul-de-sac. Total Area of Basin: 30,355 sq. ft. = 0.697 acres Impervious Areas: Asphalt (new cul-de-sac) = 8,500 sq. ft. = 0.195 acre Q, C= 0.90 Concrete Curb & Gutter = 720 sq. ft. = 0.017 acre na, C= 0.80 House Roofs = 3,000 sq. ft. = 0.069 acre a, C= 0.90 Concrete Driveways = 3,000 sq. ft. = 0.069 acre a, C= 0.80 Pervious Areas: Lawn/Landscaping = 15,135 sq. ft. = 0.347 acre (~a, C= 0.15 Water Quality Treatment Area: (8,500 + 720 + 3,000) = 12,220 sq. ft. Water Quality Treatment Volume: (12,220 sq. ft.) x(1/2") x(1 ft./12") = 509 cu. ft. Point of concentration: Curb Inlet to proposed Drainage Swale 1. 10-year Storm Discharge: Qlo =(C) (i,o) (A) = 1.08 c.f.s. (see hydrology calculation sheet) * * * Provosed Stormwater TreatmentlDisposal Facilitv Name: Drainage Swale 1 ' Swale Location: Near northeast comer of the site, on northwest side of proposed cul-de-sac. Swale Floor Area =(24' x 26') +(16' x 10') +'/4 7E(16')2 = 624 + 160 + 201 = 985 sq. ft. Swale Floor Perimeter = 125 LF with 3:1 slopes on all sides. Water Oualitv Treatment Capacitv ' Swale Volume @ 6" Depth. . _(0.5 ft. depth)(swale floor area) +(1/2 x 0.5 x 1.5)(swale floor perimeter) ' = 0.5 (985) + 0.375 (125) = 492 + 47 = 539 cu. ft. 539 cu. ft. provided > 509 cu. ft. required for entire Basin P1 Drainage Swale 1 is OK for runoff treatment of entire Basin P 1@ 6" depth Outflow StoraQe Capacitv Swale Volume @ 8" Depth: _(0.67 ft. depth)(swale floor area) +(1/2 x 0.67 x 2.0)(swale floor perimeter) = 0.67 (985) + 0.67 (125) = 656 + 83 = 739 cu. ft. 739 cu. ft. provided > 397 cu. ft. required with 0.3 c.f.s. outflow Drainage Swale 1 is OK for storage @ 8" depth w/outflow via one Type "A" drywell (Note: Type "B" specified on plans, so drywell can be set deeper into coarse soil) dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 07/01/03 Page 6 ! DRAINAGE BASINS - continued Drainage Basin Name: Basin P2 Condition: Proposed Basin Description: Area draining to proposed culvert under proposed driveway access road. Total Area of Basin: 74,485 sq. ft. = 1.710 acres Impervious Areas: Asphalt Pavement = 0 sq. ft. = 0.000 acre Q, C= 0.90 House Roofs = 10,000 sq. ft. = 0.230 acre e, C= 0.90 Concrete Driveways = 3,500 sq. ft. = 0.080 acre (~a, C= 0.80 Pervious Areas: N. %2 Gravel Access = 1,500 sq. ft. = 0.034 acre (~a, C= 0.55 Lawn/Landscaping (on-site) = 32,410 sq. ft. = 0.744 acre Q C= 0.15 Lawn/Landscaping (off-site) = 27,075 sq. ft. = 0.622 acre Q C= 0.15 Point of concentration: Entrance to proposed culvert under driveway access road. 50-year Storm Discharge: Q50 =(C) (iso) (A) = 1.86 c.f.s. (see hydrology calculation sheet) * * * Drainage Basin Name: Basin P3 Condition: Proposed Basin Description: Area draining d.irectly to existing culvert under Dishman-Mica Road only, under proposed conditions (excluding flow through proposed culvert). Total Area of Basin: 53,080 sq. ft. = 1.219 acres Impervious Areas: Asphalt (N. '/Z D.-Mica Rd.) = 10,230 sq. ft. = 0.235 acre Q, C= 0.90 House Roofs = 3,000 sq. ft. = 0.069 acre (a~ C= 0.90 Concrete Driveways = 1,000 sq. ft. = 0.023 acre Q C= 0.80 Pervious Areas: S. %2 Gravel Access = 1,500 sq. ft. = 0.034 acre Q C= 0.55 Road Shoulder = 3,720 sq. ft. = 0.085 acre Q C= 0.50 Lawn/Landscaping (on-site) = 33,630 sq. ft. = 0.772 acre cr, C= 0.15 Point of concentration: Entrance to existing culvert under Dishman-Mica Road. 50-year Storm Discharge: Qso =(C) (iso) (A) = 1.89 c.f.s. (see hydrology calculation sheet) dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 7 ' PRE- VS. POST-DEVELOPMENT ANALYSIS Under existing conditions, an area of approximately 3.6 acres drains to the existing culvert under Dishman-Mica Road. Of that drainage basin ("Basin E 1"), about 0.8 acres is off-site and adj acent ' to fihe subject project site, consisting of existing houses and yards, and the remaining 2.8 acres is on-site (in an undeveloped condition). Of that 2.8 acres on-site, an area of about 0.7 acres will be removed from the area draining to the existing culvert, so that even after construction of houses ~ and drivewaYs, the calculated flow to the existing culvert under Dishman-Mica Road is not substantially affected (see tables below for comparison using two methods of analysis). For the 0.7 acres referenced above ("Basin P 1"), the proposed plan calls for construction of an asphalt road and cul-de-sac, which will be graded to dxain to a proposed drainage facility ("Swale 1"). All proposed asphalt will drain to this swale for stormwater treatment and disposal. Although the calculations show that a Type "A" drywell would be sufficient, a Type "B" drywell is specified on the plans so that it extends sufficiently into the coarser soils (per the recommendation by Cummings Geotechnology - see section titled Soils Description on page 3 of this report). Table 1: Pre-Development & Post-Development Peak 50-year Flows to Existing Culvert Calculated via Rational Method Hydrology , Drainage Basin Storm Point of Calculated Basin Name Condition Event Concentration Peak Discharge E 1 J Existing L 50-year. ExistingCulvert ~ 3.79 cfs P 2--_ Proposed ~ 50-year ~ Proposed Culvert ~ 1.86 cfs ' P 3 ~ Proposed ~ 50_year ~ Existing Culvert ~ 1.89 cfs P 2+ P 3 ~ Proposed ~ 50-year ~ Existing Culvert ~ 3.75 cfs Note: Basin P2 drains through the proposed culvert, then to the existing culvert. Basin P3 is the area that drains directly to the existing culvert only, after development. Calculated net impact on existing culvert under Dishman-Mica Road: 50-year peak discharge is basically unchanged (decreased slightly from 3.79 c.f.s. to 3.75 c.f.s.). ' (Note: Actually, time of concentration for P2 and P3 differ slightly, so the combined peak is actually slightly lower than 3.75 c.f.s.) ' Table 2: Pre-Development & Post-Development Runoff Volumes to Existing Culvert Calculated via Runoff Curve Number Method using PondPack Drainage Basin Storm Calculated Calculated Basin Name Condition Event Peak Runoff Hydrograph Vol. . E(= same as E1) ~ Existing ~ 50-year ~ 1.63 cfs ~ 0.12 acre-ft P(= P2+P3) ~ Proposed ~ 50-year ~ 1.65 cfs ~ 0.11 acre-ft As shown in Table 2, peak runoff and hydrograph volume are essentially unchanged by this project. In conclusion, it is our opinion that construction of houses and associated improvements in this plat (as assumed per the modeled drainage basins) should not cause any significant change or impact on stormwater runoff at the "downstream" plat boundary (the existing culvert under Dishmars-Mica Road). dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 02/17/04 Page 8 ,f242E R43E R44E R45E , Spokane Caunty T 29 Aquifer Sensitive Area T 29 t N N ~ 1 \ •I E 4 } ~ ~ ~ + = t • ~ ~ f ; t ~ j • ~ T T 2c~3 28 j ~ a i - ~ y I• N N -i i ' T a-H ; 2 7 27 = ~ qr' ~ (njp~ f ! ! t N T 26 .T N ~ ~ ` ~-~j-• ~ - r f I ~i I 1 l - - T ~ 25 , ~ a7 L 25 ~ N t ~ -v ► • ~ i ~ f j-• ! f t . ; ` ri r . _ ~r ~ . ~ T 7 T 2 4 ~ „ 2 4 N _..13 ~ , ~ _ 4 , ~ i ~ ; • ~ ~ • ` ~ ~ ` I ` ~ ' ` ' ~ i 1 ~ . ~ ' ~ ~ ~ ~ ; 1 ; . • ~ , { ' 1 T 23 T ; ~ , -v ~ / ~ E ` ~ ~^"_i ~ E + t ~ ~ i , : ' iV \ 2 3 t y ~ f , • ~ 3 ( ! ' ~ ' , ' ! ' ~ ~t s ~ ~ , { a{-~ a ~ ~ ~ ~ ~ ~ ~ f ° ~ t ~ T , 22 T rl Z? 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B~ e B a B B h D - • T ~ , ~ .~~L . ~MaCStC ` f,~~: _ ~y~ Ci~BY` ~N~ud"~-s - J ~ ' ~'•~~~'3 , . ~'•_~.2,~'~¢.'~._ G 0 V2 1 Mile ' " i Scale 1: 20 000 ~ 0 1 1 TAB LE 1 RUNOFF COEFFICIENTS FOR STORM SEWERS ROLLING HILLY FLAT 2Z - 10% OVER 10% Pavement and Roof s . . . . . . . . . . . . . . 0.90 co 90) 0.90 Earth Shoulders . . . . • . . . . . . . . . . 0.50 (0. SU 0.50 Drives and Walks . . . . . . . . . . . . . . . 0.75 0.80 U.85 Gravel Pavement . . . . . . . . . . . . . . . 0.50 U.55 0.60 City Business Areas . . . . . . . . . . . . . 0.80 0.85 0.85 Lawns, Sandy Soil . . . . . . . . . . . . . . 0.10 01_15 0.20 Lawn, Heavy Soil . . . . . . . . . . . . . . . 0.17 0.22 0.35 Grass Shoulders . . . . . . . . . . . . . . . 4.25 0.25 0.25 Side Slopes, Earth . . . . . . . . . . . . . . 0.60 0.60 0.6U Side Slopes, Turf . . . . . . . . . . . . . . 0.30 0.30 0.30 Median Areas, Turf . . . . . . . . . . . . . . 0.25 0.30 0.30 Cultivated Land, Clay and Loam 0950 0.55 0.60 y Cultivated Land, Sand and Gravel 0.25 U.30 U.35 ' Industrial Areas, Light . . . . . . . . . . . 0.50 0.7U 0.80 Industrial Areas, Heavy . . . . . . . . . . 0.60 U.80 0.90 Parks and Cemetaries . . . . . . . . . . . . . 0910 0.15 0.25 ~ . Playgrounds . . . . . . . . . . . . . . . . . 0.20 0.25 0.30 Woodland and Forests . . . . . . . . . . . . . 0.10 QO.30' 0.20 ' Meadows and Pasture Land . . . . . . . . . . . 0.25 0.35 *SINGLE FAMILY RESIDENTIAL (Dwelling Unit/Gross Acre) I (Treez ~ U,ec.~,s~ , (Sandy and Gravelly Soil) ~ ' U-1. U DU/GA . . . ' . . . , . . . 0.15 1.0-1.5 DU/GA . . . . . . . . . - 0. 2U" 1.5-3.0 DU/GA . . . : . . . . : . 0.25 3. 0-3. S DU/GA . . . . . . . . . . .0. 30 3.5-4.0 DU/GA . . . . . . . . . . 0.35 4.0-6.0 DU/GA . . . . . . . . . 0.40 6. U-9. U DU/GA . . . . . . . . . . 0.60 9. 0-15. U" DU/GA . . : . . . . . . . 0.70 * Assumes flat lot plus one-half width bf abutting street. Other configurations . should be checked by combining individual runoff-factors for each various surface. ' Date 4/4/84 TAB LE 1 6-2 ~ 1 RATIONAL FORMULA HYDROLOGY , Drainage Basin Analysis for 50-year Storm Return Frequency Event Project Name: Strawthers Addition , Project: 14470 Drainage Basin Name: Basin E1 Condition: Existing Designer. DHC Basin Description: Total area draining to existing culvert Date: 26-.lun-03 Point of Concentration: Entrance to existing culvert under Dishman-Mica Road Disk File: 14470.xls RAINFALL INTENSITY-DURATION 50-Year Storm Retum Frequency SUBAREAS Time Time Stortn Description Acres C A'C Incrmnt. Incrmnt. Intensiry (minutes) (secofts) (nmr.) Asphalt Pavement 0.235 0.90 0.212 Tc = 8.33 500.0 3.66 = Intensity aQ Tc Road Shoulder 0.085 0.50 0.043 5 300 4.58 House Roofs 0.115 0.90 0.104 10 600 3.20 Concrete Ddves 0.034 0.80 0.027 15 900 2.47 Landscape (offsite) 0.622 0.15 0.093 20 1200 1.98 Natural (on-site) 2.534 0.22 0.557 25 1500 1.67 30 1800 1.46 Total Acres = 3.625 35 2100 1.30 Composite Coefficient (C)= 0.29 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION (Tc), minutes 55 3300 0.92 - 60 3600 0.87 Overland flow Channel flow 65 3900 0.82 70 4200 0.80 Seament A: L2 = 170 75 4500 0.77 Ct = 0.15 Z1 = 10 80 4800 0.75 L1(A) = 260 Z2 = 13 85 5100 0.72 N(A) = 0.4 B= 5 90 5400 0.70 S(A) = 0.03 n= 0.03 95 5700 0.68 Tc (A) = 6.97 s= 0.018 100 6000 0.67 d= 0.24 Seamenf B: L1(B) = 0 Tc (ch) = 1.36 Explanation: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (overland) + Tc (channel) S(B) = 0 Tc(tot.) = 8.33 Note: Tc (total) = 5 minutes minimum Tc (B)= 0.00 Intensity = 3.66 Ct = 0.15 = Coefficient for overland flow L1 = Length of ovedand flow segment(s), in feet Calculated Channel Flow Data: N = overland friction factor S= average slope of overtand flow, in ft./ft. Area = 1.83 Sq. Ft. Tc (overland) = Ct'(L1'N/S^0.5)^0.6) W.P. = 10.47 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.17 Ft. Z1 = inverse of cross slope of backslope of channel V= 2.08 FtJSec. ' Z2 = inverse of cross slope of foreslope of channel Tc(ch) = 1.36 Minutes B= Bottom width of channel (gutter or ditch), in feet Q(est) = 3.80 C.F.S. n= Manning's friction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = 1.06 d= depth of flow in channel, in feet Flow Regime = Supercridcal Flow Tc (channel) = L / ((1.486/n)'R^0.67s^0.5) / 60 Area = d*B+d^2/2'(Z1+Z2) Calculated Flow Depth in Channel: W.P. = B+d'(1/sin(atn(1/Z1))+1/sin(atn(1/Z2))) R= Hydraulic Radius = Area/ Wetted Perimeter ~ d= 0.24 Feet ~ V = Velocity = 1.486/n`R^.667+s^.5 Tc (ch) = Length (ft) ! Velocity (fps) / 60 Calculated Peak Discharge, 50-Year Storm: Q(est) = EsGmated Flow (verifies depth, d) = V'A Froude Number = V/(g'O.Sd)"0.5 ~ Q= 3.79 C.F.S. ~ Peak Discharge = Q= C'I'A (cubic ft. per sec.) Simpson Engineers, 1nc. 909 N. Argonne Road, Spokane, WA 99212 (509) 926-1322 Fax: (509) 926-1323 14474hyd • B35in E1 RATIONAL FORMULA HYDROLOGY & BOWSTRING CALCULATIONS DRAINAGE BASIN ANALYSIS & DESIGN for 10 YEAR STORM EVENT S/mpson Engineers, Inc. 909 N. Argonne Road, Spokane WA 99212 Date: 07/01/03 Sponsor Name: Donna Strawther Design: Doug Christenson Project Name: Strawther's Addition Project: 14470 Site Lacation: 38th Avenue, north side of Dishman-Mica Road Basin Name: Basln P1 Basin Description: Area draining to proposed swale by cul-de-sac G.P.A. Name: Sw81e 1 G.P.A. Location: Northeast portion of site Site Cflndition: Proposed Point of Concentration: Cub Inlet into proposed swale SUBAREAS: T1ME OF CONCENTRATION (minutes): Description Acres C A•C Tc (ovedarrd flow) Tc (gutter ffow) Asphaft Pavement 0.195 0.90 0.176 House Roofs 0.069 0.90 0.062 Ct = 0.15 L2 = 150 Concrete Curb & Gutter 0.017 0.80 0.014 Z1 = 50 Concrete Driveways 0.069 0.80 0.055 L1(A) = 70 Z2 = 0.167 Gravel Surfacing 0.000 0.55 0.000 N(A) = 0.3 B= 0 Pervious/Landscaping 0.347 0.15 0.052 S(A) = 0.01 n= 0.013 s = 0.01 Tc (A) = 3.71 d = 0.15 Total Basin Area, acres = 0.697 Composite Runoff Coefflaent = 0.514 L1(B) = 150 Tc (gut) 1.26 Combined (Area' Runoff Coefficient) = 0.358 N(B) = 0.016 Tc(A+B) : 4.59 S(B) = 0.016 Tc total 5.84 Intensity : 3.02 RUNOFF WATER QUALITY PARAMETERS: Tc (B) = 0.9 Holding 5.34 Impervious Treatment Area = 12,220 sq. ft. Treatment Volume Generated = 509 cu, ft. Q(estimated @ d) = 1.09 c.f.s. Time of Concentration = 5.84 minutes DRAINAGE FACILITY DATA for Swale 1 Total Swale Floor Area = 985 sq. ft. Swale Floor Perimeter @ 3:1 = 125 lin. ft. ' PEAK DISCHARGE, 10 YEAR STORM: Treatment Volume Provided @ 6" = 539 cu. ft. Storm Storage Provided @ 8" = 739 cu. ft. Q= C' I" A= ~ 1.08 C.F.S. ~ BOWSTRING CALCULATIONS NUMBER and TYPE of DRYWELLS PROPOSEO: #1 #Z #3 #4 #5 #8 #7 Time Time Intensiiy Q dev. V in V out Storage 1 Single-8arrel (City of Spokane Type 1) Incnnnt. Incrmnt. 0 Double-BaRel (City of Spokane Type 2) (min.) (sec.) (in./hr) (cfs) (cu. ft,) (cu. ft.) (cu. ft.) (01•60) (A•c-rxi) (ouv.•tt2) (a~s) Outflow Provided: 0.3 c.f.s. 5.84 350.80 3.02 1.08 509 105.18 404 5 300 3.18 1.14 458 90 368 10 600 2.24 0.80 577 180 397 15 900 1.77 0.63 647 270 377 WATER QUALITY TREATMENT VOLUME. 20 1200 1.45 0.52 686 360 326 25 1500 1.21 0.43 702 450 252 Required G.P.A. ponding volume: 30 1800 1.04 0.37 715 540 175 Impervious °208° Area x 1/2" = 509 cu. ft. 35 2100 0.91 0.33 724 630 94 volume provided at 6" depth = 539 cu. ft. 40 2400 0.82 0.29 740 720 20 ConGusion: OK 45 2700 0 74 0.27 748 810 -82 50 3000 0.68 0.24 760 900 -140 55 3300 0.64 0.23 784 990 -206 STORM STORAGE VOIUME: 60 3600 0.61 0.22 813 1080 -267 85 3900 0.60 0.22 864 1170 -306 Maximum storage required = 397 cu. ft. 70 4200 0.58 0.21 898 1260 -362 volume provided at 8" depth = 739 cu. H. 75 4500 0.58 020 927 1350 -423 Conclusion: OK 80 4800 0.53 0.19 935 1440 -505 85 5100 0.52 0.19 973 1530 -557 90 5400 0.50 0.18 989 1620 -631 DRYWELL REQUIREMENTS: 95 5700 0.49 0.18 1022 1710 -688 100 6000 0.48 0.17 1053 1800 -747 1 Single (fype 1) 0 Double (Type 2) Simpson Englneers, lnc. 909 North Argonne Road, Spokane, WA 99212 Phone: (509) 926-1322 Fax: (509) 926-1323 Basin P1 ' RATIONAL FORMULA HYDROLOGY Drainage Basin Analysis for 50-year StoRn Retum Frequency Event Project Name: Strawthers Addition Project: 14470 Drainage Basin Name: Basin P2 Condition: Proposed Designer. DHC Basin Description: Area draining to proposed cuivert under access road Date: 26-.lun-03 Point of Concentration: Entrance to proposed culvert under gravel road Disk File: 14470.xls RAINFALL INTENSITY-DURATION 50-Year Storm Retum Frequency SUBAREAS Time Time Storm Description Acres C A'C Incrmnt. Incrmnt. Intensity (minutes) (seconds) (in.mr.) Asphalt Pavement 0.000 0.90 0.000 Tc = 7.96 477.9 3.76 = Intensity aQ Tc N. 1/2 Gravel Road 0.034 0.55 0.019 5 300 4.58 House Roofs 0.230 0.90 0.207 10 600 3.20 Concrete Drives 0.080 0.80 0.064 15 900 2.47 Lawn/Landscape 1.366 0.15 0.205 20 1200 1.98 25 1500 1.67 30 1800 1.46 Total Acres = 1.710 35 2100 1.30 Composite Coefficient (C)= 0.29 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION (Tc), minutes 55 3300 0.92 60 3600 0.87 Overland flow Channel flow 65 3900 0.82 70 4200 0.80 Se4ment A: L2 = 100 75 4500 0.77 Ct = 0.15 Z1 = 10 80 4800 0.75 L1(A) = 260 7-2 = 13 85 5100 0.72 N(A) = 0.4 B= 5 90 5400 0.70 S(A) = 0.03 n= 0.03 95 5700 0.68 Tc (A) = 6.97 s= 0.018 100 6000 0.67 d= 0.16 Se4ment B: L1(B) = 0 Tc (ch) = 1.00 Explanation: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (overland) + Tc (channel) S(B) = 0 Tc(tot.) = 7.96 1Vofe: Tc (total) = 5 minutes minimum Tc (B) = 0.00 Intensity = 3.76 Ct = 0.15 = Coefficient for overiand flow L1 = Length of overiand flow segment(s), in feet Calculated Channel Flow Data: ' N = overland friction factor S= average slope of overland flow, in ft./ft. Area = 1.10 Sq. Ft. Tc (overland) = Ct'(L1'N/S^0.5)^0.6) W.P. = 8.72 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.13 Ft. Z1 = inverse of cross slope of backslope of channel V= 1.67 Ft./Sec. Z2 = inverse of cross slope of foreslope of channel Tc(ch) = 1.00 Minutes B= Bottom width of channel (gutter or ditch), in feet Q(est) = 1.85 C.F.S. n= Manning's friction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = 1.04 d= depth of flow in channel, in feet Flow Regime = Supercritical Flow Tc (channel) = L / ((1.486/n)'R:'0.67s^0.5) / 60 Area = d'B+d^2/2"(Z1+Z2) Calculated Flow Depth in Channel: W.P. = B+d'(1/sin(atn(121))+1/sin(atn(1/Z2))) R= Hydraulic Radius = Area/ Wetted Perimeter ~ d= 0.16 Feet ~ V = Velocity = 1.486/n'R^.667's^.5 Tc (ch) = Length (ft) / Velocity (fps) / 60 Calculated Peak Discharge, 50-Year Storm: Q(est) = Estimated Flow (verifies depth, d) = V•A Froude Number = V/(g'0.5d)^0.5 ~ Q= 1.86 C.F.S. ~ Peak Discharge = Q= C'I'A (cubic ft. per sec.) Simpson Engineers, Inc. 909 N. Argonne Road, Spokane, WA 99212 (509) 926-9322 Fax: (509) 926-1323 1e4704,yd • easi, wt RATIONAL FORMULA HYDROLOGY Drainage Basin Analysis far 50-year Storm Retum Frequency Event Project Name: Strawther's Addition Project: 14470 Drainage Basin Name: Basin P3 Condition: Proposed Designer. DHC Basin Description: Area draining to existing culvert only (not via new culvert) Date: 26-Jun-03 Point of Concentration: Entrance to existing cutvert under Dishman-Mica Road Disk File: 14470.xts RAINFALL INTENSITY-DURATION 50-Year StoRn Return Frequency SUBAREAS Time Time Storm Description Acres C A`C Incrmnt. Incrmnt. Intensity - (minutes) (seoonds) (tr,.mr.) Asphalt Pavement 0.235 0.90 0.212 Tc = 6.97 418.0 4.04 = Intensity Q Tc Road Shoulder 0.085 0.50 0.043 5 300 4.58 House Roofs 0.069 0.90 0.062 10 600 3.20 Concrete Drives 0.023 0.80 0.018 15 900 2.47 LawNLandscape 0.772 0.15 0.116 20 1200 1.98 S. 1/2 Gravel Road 0.034 0.55 0.019 25 1500 1.67 30 1800 1.46 Total Acres = 1.218 . 35 2100 1.30 Composite Coefficient (C)= 0.39 , 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION (Tc), minutes 55 3300 0.92 - ~ 60 3600 0.87 Overland flow Channel flow 65 3900 0.82 70 4200 0.80 Seament A: L2 = p 75 4500 0.77 Ct = 0.15 Z1 = 0 80 4800 0.75 L1(A) = 300 Z2 = 0 85 5100 0.72 N(A) = 0.4 B= p 90 5400 0.70 S(A) = 0.04 n= 0 95 5700 0.68 Tc (A) = 6.97 s= 0 100 6000 0.67 d= 0.00 ' Sepment B: L1(B) = 0 Tc (ch) = 0 Exolanation: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (overland) + Tc (channel) S(B) = 0 Tc(tot.) = 6.97 Note: Tc (total) = 5 minutes minimum Tc (B) = 0.00 Intensiry = 4.04 Ct = 0.15 = Coefficient for overland flow L1 = Length of overland flow segment(s), in feet Calculated Channel Flow Data: N = overland friction factor S= average slope of overland flow, in ft./ft. Area = 0.00 Sq. Ft. Tc (averland) = Ct'(L1'N/S110.5)^0.6) W.P. = 0.00 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.00 Ft. Z1 = inverse of cross slope of backslope of channel V= 0.00 Ft./Sec. ' Z2 = inverse of cross slope of foreslope of channel Tc(ch) _ 0.00 Minutes B= Bottom width of channel (gutter or ditch), in feet Q(est) - 0.00 C.F.S. n= Manning's friction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = N.A. ~ d= depth of flow in channel, in feet Flow Regime = N.A. Tc (channel) = L / ((1.486/n)*R^0.67s^0.5) / 60 Area = d+B+d^2/2'(Z1+Z2) Calculated Flow Depth in Channel: W.P. = B+d'(1/sin(atn(121))+1/sin(atn(122))) R= Hydraulic Radius = Area/ Wetted Perimeter ~ d= 0.00 Feet ~ V = Velocity = 1.486/n'R^.667's^.5 Tc (ch) = Length (ft) / Velocity (fps) / 60 Calculated Peak Dlscharge, 50-Year Storm: Q(est) = Estimated Flow (verifies depth, d) = V`A Froude Number = V/(g"O.Sd)^0.5 ~ Q= 1.89 C.F.S. ~ Peak Discharge = Q= C*I'A (cubic ft. per sec.) Simpson Engineers, Inc. 909 N. Argonne Road, Spokane, WA 99212 (509) 926-9322 Fax: (509) 926-1323 1aa70-n,a - easM P3 Circular Channel Analysis & Depign , Solved with Manning's Eguation ppen Charmel - Uniform flow Worksheet Name: Strawthex'z Addition Comment : Progased Culvert under access driveway Solve For Actual Depth Gi:ven Irtput Data : Di.ameter.......... 1.00 ft = 12 Slope . . . . . . . . . . . . . 0.0200 ft/ft _ o,8'14a L-F Manning`s n....... 0.024 ~ zMp Discharge . . . . . . . . . 1.86 cf s _ q,o gps+N Pz- ~ Computed Results : Degtn 0.61 ft Velocity.......... 3.74 fps Flow Area 0.50 s f Critical Depth.... 0.58 f-t Critical S1oge.... f?.0227 ft/ft . Percent Full...... 60.57 0 Fu ll Cap-aci ty . . . . . 2.73 c f s QMA,X @ . 94D . . . . . . . . 2.94 cf s Froude Number..... 0.92 (flaw is Subcritical ) Open Channel Flow Module, Version 3.21 (c_) 1990 Haestad Metnods-, Inc. * 37 Brookside Rd * W-aterbury, Ct 96708 eircular Channel Analysis & Design Solved with Manning's Equation Open Channel - Uniform flow . Worksheet Name: Strawther's Addition Comrnent : Proposed eulvert under access driveway Solve For Full Flow Capacity Giverr fnput Data : Diameter.......... 1.0a ft Slope 0.0200 f.t/ft Manning 's n . . . . . . . D.024 Discharge . . . . . . . . . 2.73 cf s - ~PPe°x. ~ • Q'° . . c,u COTC1ptIt2C~ F~E S`tll t S : Full Flow-Cagacity..... 2.73 cf s Full Flow Depth........ 1.00 ft Velacity........... 3.47 fps Flow Area......... 0.79 sf Critzc-al- Ueptn 0.71 f t Critical Slope.... 0.0277 f t/ft . ~ Percent Full . . . . . . 100.00 Full Capacity..... 2.73 cf s QNAX L&. 34D . . . . . . . . 2.94 cf s Froude Number..... FULL ~ Open Channel Flow Module, Versi:on 3.21 (c) 1990 Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct 06708 37TH AVENUE - - . ~ ~ ~ 1 ~ - \ 1 \ 1 \ _ ~ ~ ~ E~. Havse ~opprox, oc 1 i \ ~ ~ ~ _J . ~ ~ ~ ~ ~ ♦ ~ . ~ . ~ ~ - - - - - - _ Basin boundary within private pro ert - C P Y . - was mapped by visual approximation. NORTH . ~ \ Ex. H u~e ~ ~ n (apPr loa) . ` 1 I ~ L / / ~ ~ / N T S ~ ~ OT 0 CALE \ .r a~ y . o / Q`p' ~ ~ _ \ Q~ ~ / ~ ~ o~~ / ~ - ~ ~ I ~ ~ go~ / A~/ / / ~ ~ ` ~ / ~ \ / ~ ~ ~7- ~ b ~ ~ r i ~ 38TH AVENUE a 1 \ J I ~ ~ \ Ex. uee \ a r loc. . ~ ~ PP ) \ ~ • ~ 1 5 1 E 24 . 0 record ~ ~ ( ) \ ~ \ ~ ~ ~ ~ , / \ . \ ~ ~ ~ \ . ~ a / s ` . ~ \ p~ N . . . ~0\ 0 / ' ~ ~ ~A 0 ~ ~ ~ - \ b 1 p ~ ~ R! ti ~ ti'0 ~ ~ . . ~ / `~`T . B ~ ~ 0 \ . ~ F \ \ t . ~ \ ~ ~ J ~ E~isting 1B' ~ ~ CbIP Culvut ~ \ / \ zoo~.< NE P- e opment drai ag ba 'n b ndar / I.E. 2006J ~SW; / ~ / \ ~ ~ / ~ , ~ ~ o ' ~ ~ o ~ ~ ` , \ ~ W ,f~ ~ ~ , - \ / ~ t!~ \ N \ ✓ M J , ~ ~r \ o ~ / Z ~ 9\ ~ \ \ / ~ \ ~ ~ \ ~ ~r \ ~ . y \ I ~ . \ ~ \ ~ ~ - ~ ~ - - s ~ \ Ex. Duplex 'Q (approx. loc.) ~o \ I I ~ ~ ~ ~ i ~ ~ o ~ ~ 1 ~ ~ ~ t \ ror the ~ ~ \ SE caner SW1/4 NW1/4 South line of the SW1/4 of the NW1/4 § \ . - - - - - - - - . ~ ~ 40TH AVENUE ~ . ~ . - ~ o . . ^ 7 1 I CALL BffORE YOU ~ I I • ~ DAIUN ~ SCALE ~ o~te CALL BEFORE YOU D1G 456-8000 ~ ~ ~ , 1YPE OF 14PROVE~IFNT: ~ ~ ~ ~ ~m~ ~ STRAWTHER S ADDITI~ ~ I~,,w DRAINAGE ~ ~ ADDITIDN ~ i i ~ E1'S, 111C. ~ i i so~4.ss I~ ~ ~ ~ ~ ~ PRE-DEVELOPMENT DRAINAGE I ~ I DRAINAGE BASIN ~ i i I + I CIV1L ENGINEERS dc LAND SURVEYORS I I +,o~m, RR Spke h~ Po~wr Pd~ 78tl N. of I,~ Na 909 ARGONNE R~AD, SP~KANE WA„ 99212-2789 Sw 1 4 OF SBCTION S9 T.26 N R.44 ~ I / , ~ g PH@I~ (509) 926-1~2 FAX (50~ 926-1323 14470 1 OF 1 SPO&A►B CoU IldsglNCTOx , T.25 N. R.44 B.II.Jf. I~~rz I RE1+15109JS / AS BUILT ~Otl+ Ave, East dde oi Dl~marlllca Rood 6 ( ~ vA oanvn_"rnAv ••wair -;s _ 37TH AVENUE _ ~ , . ~ ~ . ~ r ~ ~ ~ ON ~ ~ ~~1TJ 1 ~ yD ~ST . , ~ ~R FIE ~ ~ ~ HE T C 1 ~ ~ ~ ~ r , i ~ I Ex. House 1 I npDrax. loc~ / \ 1 / I I ~ ~ ~ ~ ~ ~ , I I I ~ ~ ~ ~ I I I . Basin boundar within rivate ro ~ -J---~--L---- ~ Y P p perty _ ~ C was mapped by visual approximation. ~ ~ / ~ - ~ , NORTH \ ~ I E~. H se I . \ \ IoPPr . loc.} \ ~ \ L _J ~ . ~ . / ~ T NOT TO SCALE ~ ~ / \ ~ o ~q. / ~ Q" d~ ~ -92 ' ~ ~ ~ al / ~ / PLAT ~743 / ~ _ \ o~ ~ SN~R % \ / ~ y . ~ c~ ~ . \ ~ 1~` / !r / ~ \ o• ~ ~r , \ ~9 a ~ i ~ ~ ~ ~ ~•~ti ~ ~ , ~ e~ °o r--~ ' ~ ~~~j ~ ~ - - vU11~ ~ • tiLil _ ~ J _ LEGEND p~ Ew ~use I I ~ u~ ~ \ J ~ r I. ~ I 2u ~ ~QAP °C ) ~ ~ ~ L__J ~ ~ \ \ ~ o _ ~ ~ f - - - - - - Pro ect Site Pro ert i ~ 1~ PROPOSED SWAIE 1. I P Y L ne \ ~ t ~ 2 ecor 10 r . ~i ~ ~ ~ n ~n , 85 aq.ft. 0 ~ev. 2020.0 ne ~ / ~C ~ Ofiset 6 from face of curb ~ = Other Parcel Unes a rox. \ 0 ~ PP ) ~ ~ \ ~,e~~ / ~ 3~ ~Double-Barrel Drywdl, T~pe 8 rox.) ~ a / , Met~ Frame dc Grate, Type 4 , ~ a ~ / - . ~ o~° ~ ~ui i~ okane County Standarde ~on9- Exlsting Ground Contour (1 fntervals) 11 ' intervals) \ '2 ~ ~ F ~ - r o ~ ~ To ot cte EIe~. 2ozo.5 ~ ~ ~ r „ ~ ~ ~ r--~ . . ~ ~ / ° , o . i ~ = House: Existin a rox. location . location) ~ ~ a. I I 9~PP ) ~ 9 x I i . I ~ 0~ I ~ . 5kp~ gutts to a[6or rwoff ~ ~ o ~ , . i nio ~ ~ _ _ ~ or Proposed (assumed) . a, ~ ~T ~E I Iwl I ~ isumed) , \ ~a , „ ~ m ,t0 f3 ~ ..n ~o ~ ~ ~ ~ ~ Q ~ ~i - ~ Proposed Concrete Curb ~ °i ~ Q ~ i / s , ~ ~ b~ ~ i~ ' ~~i. ~ _ . r , ~ ~ i/ ~ v Proposed Conc Cu b Inlet e \ ~ ° i~°1 ~ ' i. ~ - - , ~ ~ e Floor ~ o r z = Proposed Drainage Swale Floor e - N ,r a~e at ~ / - - - - - - ~ . . ~ - - - - µ 1 f Cr~ ~ - F ~ ~ i ~ ~ - Proposed Drywell . . „ o~ o y ~ ~ ~ 4~i , a ~ unun a ~ ~ / , ~ ~ BASIN P2_ _ Drainage Basin Boundar T ~ ~ - ' ~ - - - - - BASIN PJ y J y - euo ~ r' . Y EKhttng 18" n o tlllty ent ~ • i cuv aiK.t .E I I ~ T-5 ` d i~: 2o00oe:i ~s"w~ ~ ~~E _ m ~ o~ ~ --OT-+4 ~ LT6 , ~ ~ \ ( ti cv ~ o D ~ 0~1 ~ ` ~ I ~ 3 \ \ ~ ~ E ~ ~ \ ~ =m • o ~ ~ I : Pos- e ~ ~ ~n'~ ~ ~Dve~ m t ~0 3W dr~ age basin oun arie / ~ ~ ~ M B~oac , \ \ ~ ~ d ~ ~ ~ -o-~n - - - - -ad ~ \ \ ' rY in o p1T~ \ / ~ : i o P~ ~ ~ i . Q z ~D . s ~ \ ° ~ ~ O F1E ~ ° ~ \ \ , o o ~ ~ \ ~ z Es~ , \ \ / K N ~~t a 3 ~ ~ ~ ~ ~ . ~ ~ / ~ C~ \ ~ y \ \ --+%d ~ \ ' ~ . \ ~ i ~ ~ \ Ez. ~u lex ~ $ ~ ~ ~ I p I L ~ IoDPro~.loc.) I o ~ ~ ~ P ~ I I~ -1 4 ~ ~04-~ ~ ~ ~ ~ ~ s \ ~ \ ~ , < . ,~d , s j \ ~ y I ~ \ ~ ~ ~ ~ Ca1c poeitlon fa tl~e a ~ SE eaner SYA/4 NW1/4 b South line of the SW1/4 of the NW1/4 \ \ i,~ . M \ .1 , ~ ~ ~ ~ ~ , _ ~ 40TH AVENUE ~ _ _ _ ~ ~ ~ . CALL BEFORE rot1 DIG 456-8400 7 I I I CALL BEFaRE YOU $ I I DATUM ~ $CA~ ~ aa I $ IYPE dF IYPROVDENT. ~ ~ ~ ~ ~ z~ ~ F~^°°°'o'° STRA i~THER S ADDITII ,a~ xn ~„~,RN r~ m s~ I oHC DRAINAGE ~ au+~ ~ . ► ADDITIDN • I I I ~ y SOR ~ ~ B1'$ 11'tC. ~~A~ 2014.85 I,~ ~ ~ ~ ~ ~ ~ POST-DEVELOPMENT DRAINAGE a ~ ~ I ~ L I qV1L EN6INEERS dc LAND SURVEYORS ~ ..i . ~ I I ' N, 909 ARGUNNE ROAD, SPDKANE WA„ 99212-P789 ~ouM« RR SoOn In Po~ar Pd4 180' or ~,~vnra~m S1I J I OF SBCTION 33, T.25 N, R.44 ! ~ P ~ g I PI~PE (509> g26-1322 FAX (909) 926-1323 14470 ~ aF ~ SPOBANB COU1Y7'}', ~ASEINCTON ~ ~n I REVI90NS AS BUILT 40tl~ Ava East dde ol DI[ ,~IGa Raad s ~ ~ I i ~ ' ' Quick TR-55 Ver.5.46 S/N_ Exeeutec~:• 16-:40:00 02~~-E}-F~ 2-Q04 ' Strawther's Addition E}ve-ra-1 1 8ra-i-nage- An&l yai s ' Pre- Development (Existing) Condition Bas-in F- (Actua-1. A-reas ) 6 • RUNOFF CURVE NUMBER DATA Composite Area: Basin E AREA CN SURFACE DESCRIPTION (acres) Impervious (asph/roof) HSG B 0.38 98 Gravel/road shoulder HSG B 0.09 85 Natural trees/brus-Ir HSG R- 2A3 65 Lawn & Landscaping HSG B 0.62 61 COM-PO&I-T-E- AR-EA > 3.63 -68--. 3 E 68 ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ : : . ' 1 ' 1 ' ' Quick TR-55 Ver:5.46 S/N: Bxeeuted 16-: 41 . 59 02 -.E}6--.-2 Q04 ~!~-~r`t ~ -E x . ►t1 Strawther's Addition 0-v-e-r-a-1-1- D-&ina-ge- Ana-lyais Pre- Development (Existing) Condition Bas-i-n F~ ( C 1-a4--x- Axeas ) , RUNOFF CURVE NUMBER DATA t Composite Area: Basin EX AREA CN SURFACE DESCRIPTION (acres) Impervious (asph/roof) HSG B 38.40 98 Gravel/road shoulder HSG B 8.50 85 ' Natural treesf-brtrsrr HSG B- 253.40 65 Lawn & Landscaping HSG B 62.20 61 E0P4Pas-I'F~£- ARRA- - - - > ..3.6-2 . 5 0 .6-8-. 3- ( 68 ) . r . . . • • . • . . . • . r~.• ~ r•.••r-r r r • • . . • • . . • • . . •'r--r ~ ' Quick TR-5-5 Ver.5.46 S/N: Executed: 10:35:26 02-09-2004 C:\pondpack\14470-E.TCT S t ravutYrer'-s-- ~Yc~c~z t-i on Analysis-of-Flow,to,Existi.ng-Culvezt , Pre -Devel o~nient E~~r-s~ in -Condi t ion g? Basin E - Tc CMPUTAT-E}NS F4R:- gas}n E SHEET FLOW (Applicable to Tc only), Segment I D--- E 1 Surfaee description pervious-- M-annrng..i. s- roughne s s°coe-€ n- E} : 4 0 0 0 Flow length, L(total < or = 3.00) ft 10.0 'Fw-a-yr 24 -hr rainf al-1, P2 r-rt 1.230 Land slope, s ft/ft 0.0300 0.8 .007 * (n*L) Yirs- 0.08 = P.08 0.5 0.4 P-2- _ s SHALLOW CONCENTRATED FLOW S-egme~rt Ia. E2 Surface (paved or unpaved)? Unpaved F-1-ow-, length, L - €t 250 . 0 Watercourse slope, s ft/ft 0.0340 ' 0..5 Avg.V = Csf * (s) ft/s 2.9751 where-: - Unpaved C s f---16-: 3 4 5 Paved Csf = 20.~282 T= L/- (-3600*V) -rrrs-•- 0.02 = 0.02 CHANNEL FLOW ' Segment ID- E3 Cross Sectional Flow Area, a sq.ft 1.83 Wet-ted perimeter, Pw - ~t 10 . 47 Hydraul i c radius, r= a/ Pw f t-0.17 5 ' Char-m-el s 1 ope , s f-t /f t. 0.0180 Manning's roughness coeff., n 0.0300 , 1.49 * r 2/3 * s 1/2 V*,- ftf s- 2-.0831 n - F~~~~ len-gth; L ° f-t 170 T= L /(3600*V) hrs 0.02 = 0.02 TOTAL TIME (hrs ) • 9--.12- Quick TR-55 Version: 5.46 S/N: Page 1 , Return Frequerrcy.:- 5a. pT ars TR-55 TABULAR HYDROGR.APH METHOD 'FY-pe- Il. Di s-trib!~i on (24 hr. Duration Storm) Exeetrt ed-:-- 0-2- E}9---- 2-9-0-4,• 11-: 06: 0 5 Watershed file: C:\PONDPACK\1447D-EX.MOP Hydrograph f il2-: C: ~POAFDRACK\144-70 -EX . HYD , Strawther's Addition- Analysrs o-€~ Pl-o~t- tQ- E-xzst-zflg- Culvert Pre--Development Condition Ba si-n FX- ~Ba-s1n- Fr @- 1-0-0-x~ - a-r• ea s) , Input Pararneters Used to Compute Hydrograph Subarea AREA CN Tc * Tt Precip. Runoff Ia/-P De s-c ript i-on-... ( ac re s) f-hm-s-r- (-hrs-) ( in ) f in-Y- 'rnptrtl-qsed Bas in EX. 362.50 2. 4 s ~ 0-.3-7... . 3 s * Trave-1- tzme.. f-rom subarea -aut€a11- to- compos-z-te. Watershed outfa-1-1 p~int. I-- Subarea where user specified interpolation between Ia/p tables. Total area =•3-6-2-. 5-E-}- a-cres- Qr- 0.5664 sq. mi Peak discharge = 163 cfs Computer Modrfrcatroercs o-€ Input- P-arameters c«« Input Values Rounded Values Ia/p Subarea Tc * Tt Tc * Tt Interpolated Ia/p Dese r- rpt i arr- fh-r--> ( hr.)-- Fh-r-}- {.h-r-} ( Ye s/ No ) Agess age s ~Basi-n EX ~ 0.12 0 : M "a . -Z0 011-.- G'91 Ye s - - * Travel time from subarea outfall to composite watershed outfall point. Quick TR-55 Version: 5.46 S/N: Page 2 Return Frequencr.- ~E} p~ars TR-55 TABULAR HYDROGR.APH METHOD 'Fype~. II-. D-i-s-~ ri-bu~i on (24 hr. Duration Storm) Exe ctrt ed--- 0-2-- E}9-- 2-&E}4- - 1-1: 0 6: 0 5 Watershed file: C:\PONDPACK\-14470-EX.MOP I-lydrograph f iI-e-: E:\-PONDPAEK-\ 14 4 7 0- EX . HYD Strawther's Additzon Analysi~s- a€ F-1-ow to-- Exr-stzng- Culvert Pre--Development Condition Bas i-nm FrX FBa-s-in.. E-, C... I-44x- areas ) Summary of Subarea Times to Peak p,e-&k-- D-r,s~e-ha7rge-- at Time to- Peair., at Composite Outfall Composite Outfall Suba-rea (.e€s4- (hrs) B.as.i.n... EX L63. 12.1 Compos.i-t @ Wat er shed 1.6 .I.- 12- .1-- ~ ' , POND-2 Version: 5.21 S/N: Page 1 Exeeuted02--a9-2404 1-1- : 1-~ : 4 7 * * * * * Mul-t rgly Hydrog-rap-h- by.. CQn-s tant * * * * * Unit HYD File: 14470-EX.HYD - Output H-y.drograph : 1-4470--E- ~ HYD Multiplier Constant: .01 T FME- Uni t Mtirl-t ip--I ier Output HydraTyaph (hrs ) Ordinates Constant ( cf s ) 11.00 0.00 x 0.010 = 0.00 11.10 0.00 x 0.010 = 0.00 11.20 0.00 x 0.010 = 0.00 11...3.0. Q._.Q 0 x... 0-0-10. 11.44 o-.. oO-- x- o- . 0.00 11.50 0.00 X 0.010 - 0.00 11'. 6 o- T. m-- x o*'. oTrr, = 0.00 11.70 6.00 x 0.010 = 0.06 1-1. 8-&• 13- : 04- 2t E}•. o-ro- - = 0.13 11.90 19.00 x 0.010 = 0.19 12 : 7 T. 90- x T. QrY = 0.77 12.10 163.00 x 0.010 = 1.63 (o 0 12-. 2-0~- 97. 0-0-- x 0-1. 0-19-.- = 0.97 12.30 44.00 x 0.010 = 0.44 I-2' . 4-9- 3 G.(70° x 0--. Q10° = P.36 12.50 32.00 x 0.010 = 0•32 1-2- .6-o-- 2T. o-a x o--: o-10- = 0.27 12.70 23.00 x 0.010 = 0.23 12". $0'- 2 T-. x T. cr Ia. ~-20 21 .1a.9o Zo.oo X o.o1o 1 9--. o-o- X 0.19 13.10 18.00 x 0.010 = 0.18 r~-. 2-o... 171. (YT x o-. alo, 0.17 13.30 16.00 x 0.010 = 0.16 13-A~d- 16-. ao-.- x E?-. 0-16 = 0.16 13.50 15.00 x 0.010 = 0.15 I 37'. 6 0-- 14*. 00 ' x C": 0710 = 0.14 13.70 14.00 x 0.010 = 0.14 1-3- . 8-0- 13 . 0 F}- - X @°. 010- _ - 0 .13 13.90 12.00 x 0.010 = 0.12 T-T. p'pF 12 . 0 0 x 0-. O 10 = "0.12 14.10 12.00 x 0.010 = 0.12 14--.2-0-- 11.00 x o-:oso - b.ll 11.00 X 0.010 14.30 14. 40 11. 00- x 0-. O10 = 11 14.50 11.00 x 0.010 = .11 14-. 6-f}.. 11. 0 0 )e E)--. 010 14. = Q 11 70 11.00 x 0.010 = 0.11 1 4. 8-0.. . 10 . 0 0-- x 0': 010 0.10 14.90 10.00 x 0.010 = 0.10 1 s--. o-o-- r o-. o,o- x- Q--. Q-1-o. = 0.10 15-. ~ 010 &0 x 0-. 0•10- = 0.1•0 POND-2 Version: 5.21 S/•N:- - Pape 2- Executed 02-09-2004 11:18:47 1 , * * * * * Mul-ti:p~-r Ifydrogragh by- Cons tant * * * * * Unit HYD File: 14470-EX.HYD -E}utput Hydrograph : -144-70--E- . HYD Multiplier Constant: .01 'FIME- Uni:t. Agu1-t ig~ier °Output ~~Hydrvg~aph ' _(hrs) OrdinatesConstant (cf s) 15.20 10.00 x 0.010 = 0.10 15.30 9.00 x 0.010 = 0.09 15 . 4 0 9.00 x 0.010 = .--0 . 0 9 lri _5.0 . 9....0.0_ x. Q,._.Q1Q. = 0.09 -15. 6a, . 9..1. OFU x 0-. tTZ-O- = 0.09 15.70 9.00 x 0.010 = 0.09 8-&- 8--. 00- x 0-: 4-10- = 0.08 15.90 8.00 x 0.010 = 0.08 ' r6-. (70- T. Qrr- x a: crrcr- = 0.08 16.10 8.00 x 0.010 0.08 16-. 2o-- 8--. o~ 3-it o-. o-ro... - 0.08 16.30 8.00 x 0.010 = 0.08 rS.4ro-' 8--. cro- x cr. 071-c)- = 0.08 16.50 8.00 x 0.010 = 0.08 1-6-. 6-&- 8--. o-e- x o-. 0-1-0- = 0.08 16.70 8.00 X 0.010 = 0.08 rG-. $T T": 0-0- X or'. o-ro - = 0.07 16.90 7.00 x 0.010 = 0.07 o-o-- T. o-o- x o-. o-i-a- 0.07 17.10 7.00 x 0.010 = 0.07 r7-. 2'0- T. 0r0"' x 0-. t7IT = 0.07 17.30 7.00 x 0.010 = 0.07 ' 1-7--. 4-a- 7-. o-o-- x o-% al-o- = 0.07 17.50 7.00 x 0.010 = 0.07 o 7 17'.60.-.. 7. orQ-- X T. Qz o... = E.07 l7.7o 7.oo x o.oio 1 T. a-a. 7. o-o-- x o-. a-1-o = -o . o 7 17.90 7.00 X 0.010 = 0.07 r-T. o'o 7. o o-- X c~ I . az'o = ..P.07 18.10 7.00 X 0.010 = o.o~ 1&-.-2.o-. 7--: o-o-- X, o--: o 1o = -,o . o 7 18.30 7.00 x 0.010 = 0.07 18--. 4 0 7. o,O--' X p. 0 7 3-8.50 6.00 x 0.010 = 0.06 18-•:6-E}- 6.00 x- 0-.010 = 0.06 18.70 6.00 x 0.010 = 0.06 18'. $0 6. 00 x (Y': 0 10 = " 0. 06 1$.90 6.00 x 0.010 = 0.06 afl.... 6. o-E}- X- E)-. 010 = - 0 . 0 6 19.10 6.QQ x 0.010 = 0.06 19-. 2 0 6'. CIT x POND-2 Version: 5.21 S/N: Page 3 Ex-ectrted- 0-2 -0,a- H-Q4 11-18 : 4 7 mtti-tzply Hy-drOTraph- by- CCTita taRt- * * * Unit HYD File: 14470-EX.HYD 4utpvi-t Ry6rograph-: 1-4-4-7 0- -E-- . HYD Multiplier Constant: .01 'F fKE- Unr t Agtrl-tip- re-r Otrtp~t liy&ragyaph (hrs ) Ordinates Constant ( cf s ) 19.30 6.00 x 0.010 = 0.06 19.40 6.00 x 0.010 = -0.06 19.50 6.00 x 0.010 = 0.06 x Q-Q.lQ_. = 0.05 5-_QQ x. 0-_Q1Q_ = 0.05 , 19.80 5.00 x 0.010 = 0.05 1-9~. 9.Q- X- 0-. 0-1 E}- 0.05 20.00 5.00 x 0.010 = 0.05 24-.1 0- 5... 0-4- x- 0.05 20.20 5.00 x 0..010 = 0.05 2-E3--. 3-(Y- a G-- x- &I.E} . 0.05 20.40 5.00 x 0.010 = 0.05 20- . 50- 5--. 4-4- x- 0-. 4-0- _ - 0.05 20.60 5.00 x 0.010 = 0.05 2-E}-: 70-- 5-. E}E?-- x- E)-. &-1-0 - 0.05 ' 20.80 5.00 x 0.010 ~ 0.05 2.0.-. 9-0- 5-. 40-• x- 0-. 4--~-4-- 0.05 21.00 5.00 x 0.010 = 0.05 27-1.1-0•- o-o-- x 0-1 E}- _ 0.05 21.20 5.00 x 0.010 = 0.05 21,.3-0-. 5. Qa- x 0--. 8-14- = 0.05 21.40 5.00 x 0.010 - 0.05 21.50- e-o- )t 0.05 21.60 5.00 x 0.010- = 0.05 21.70-. 5- . 0-4- X. 0.05 21.80 5.00 x 0.010 = 0.05 ' 2-1-. 9-0--- 5-. 0-&-- X 0-. 0.05 22.00 5.00 x 0.010 = 0.05 22•. 1-4- 5• _ 0-9- X-- Q-. 9-14... - 0.05 22.20 5.00 x 0.010 - 0.05 2,-2-. 3-0- 5-. U-0- x 0-. 0-r8- = 0.05 22.40 4.00 x 0.010 = 0.04 22. .S,a. 4-.. ao--- x- 0.04 22.60 4.00 x 0.010 = 0.04 2-2-. 7 0- 4--. E}0- x- F}-. E)-rE}- = 0.04 22.80 4.00 x 0.010 = 0.04 2 a. 9 0-.- 4-. 4-4 x- 01. 0-14- = 0.04 23.00 4.00 x 0.010 = 0.04 2-a-. 10- 4--. o-o- x o-. o-.10- - 0.04 ~ 23.20 4.00 x 0.010 _ 0.04 2 3- . 30-- 3--. QO- x- 4-. 4-1-4- 3 POND-2 Version: 5.21 S/N: Page 4 Executed 02-09-2004 11:18:47 * * * * * Multipl-y- Hydrograprh-by Constant * * * * * Unit HYD File: 14470-EX.HYD - Ou~put Hydrograph : 14-4•7-0--E-- . HYD Mul tiplier Constant: .01 'FIPq-E-- Unit AgtrJ~-t-zp-11er Output- Hyd-ra~~aph (hrs ) Ordinates Constant ( cf s ) 23.40 3.00 x 0.010 = 0.03 23.50 3.00 x 0.010 = 0.03 23.60 3.00 x 0.010 = 0.03 2.1_. 7 Q. 3....,.QQ. 0_ 0.03 2-3.. 8-4-- 3--. 0~}- ~ 4--. 910- 1 = 0.03 , 23.90 3.00 x 0.010 = 0.03 2-,T,. 0,0'° 2. O-CI" x T. Q,z°fJ = 0.02 24.10 2.00 x 0.010 = 0.02 2-4-. 2-E3... 2.. a.f}. X• 0-. 0-1-0- = 0.02 24.30 2.00 x 0.010 = 0.02 2-. Q Q'' x Q"- . t1z..(7.. - 0.02 24.50 2.00 x 0.010 = 0.02 2-4,. &o-- 2-. o-o-- X, o-: o-ra-- = 0.02 24.70 2.00 x 0.010 = 0.02 24 St~- 2"°. 0'0- x T. CFz 0- = Q 0 2 24.90 1.00 x 0.010 = ~0.01 25.10 1.00 x 0.010 = .01 25. 2"Q" 1. 00" x Q" . QTor = 01 25.30 1.00 x 0.010 = ~-.01 4.a... I-. o-o-- x- ' o- : 0-1-0- = 9.01 25.50 1.00 x 0.010 = -0.01 ' 2-5 . 6 0"- 0". a0 ~ x Q'°. Bz 0 00 25.70 0.00 x 0.010 = 9-.00 2-5-. a-o-- 0.00 x a-. 0-1-0 = - o. o 0 ' 25-. gfl- 0.00 x o-. o1o - ...o-: oa- ~ POND-2 Version: 5.21 S/N: Executed 0,2---o-9--20•0 4 11-: 2-3-:14 Summaz'y of Hydrograph Volume Hydrograph-!.~ 1447-0--E- . HYD Volume = 5,054 cu.ft. o- . 12- a-e-- € t Sv E L npEn ~ ~ Quick TR-55 Ver.5.46 S/N: , Executed: 16:38:50 02-0-6-2-aQ4 t 44_rt o - F . P-c ,j Strawther's Addition Ove-r-al-l- apa-inage---A.na-3.ys i s Post-Development (Proposed) Condition Bas-ins- F2f-P-3- (Acttxal A3:eas ) RUNOFF CURVE NUMBER DATA Composite Area: Basin P AREA CN SURFACE DESCRIPTION (acres) Impervious ( asphf raa£~ H&G... B.... 0.64 98 Gravel/road shoulder HSG B 0.15 85 Lawn & Lands caprrrg - I+SG R--- 2.14 61 COMPOSITE AREA 2.93 70.3 ( 70 ) ~ ' Quick TR-55 Ver. 5. 46 S/TV : Exeeuted-:- 16-:43:49 - E}2---a&----2Q04 I 41 r~ v- Strawther's Addition ave~a-11 Drainage-Pcnalys.is Post-Development (Proposed) Condition Bas-ins- P-2-+-~3, (@- 1-0-0~ A-reas ) RUNOFF CURVE NUMBER DATA Composite Area: Basin PX AREA CN SURFACE DESCRIPTION (acres) Impervious (asph/roof) HSG B 63.70 98 Gravel/road shoulder HSG B 15.30 85 L- awn & Landscaping.- HSG B-- 213 . 80 61 COMPOSITE AREA 292.80 70.3 ( 70 ) , ' Quick TR`55 Ver:5.46 S/N: Executed.. 10--.39. 11 02-09--2-GE}4 e.-\pondpack\14470-P.TCT , Strawther's Addition Analysis- Erf PI-ow- to-- E-xi-stzng Culvert Post-Development (Proposed) Condition Pasin. P , Tc COMPUTATIONS FOR: Basin P SHE-E-'F. FbW- (Appl-icable to.._ Te- only) Segment ID pl SLrr€ a-ee- des c rip t i on pervi: ou s , Manning's roughness coeff., n 0.4000 F-~ow- length, L(total. c-or 3~}€t 10.0 Two-yr 24-hr rainfall, P2 in 1.230 Lan-d- slope-; s - ftfft 0: 0300 0.8 .007 * (n*L) T.. _ hrs-- 0.08 - = 0.08 ' P2- 0.5 s 0.4 * SHALLOW CONCENTR.ATED FLOW ' Seqmen.t. I•D - P2 Surface (paved or unpaved) ? Unpaved F1Qw- length, L - €t 250.0 ' Watercourse slope, s ft/ft 0.0300 0.5 Avg.V = Csf * (s) ft/s 2.7946 whe-re-.: - Unpaved C s f= Paved Csf = 20.S282 'F =--Ex- f- (3-600*V) - hr--s 0.02 0.02 ' CHANNEL FLOW S-e gmez`rt f-D P 3 Cross Sectional Flow Area, a sq.ft 1.10 Wet-ted pe~-ime-te r, Pw... €t-- 8.72 Hydraulic radius, r- a/Pw , ft 0.126 eltarrnel s-l-ope , s € t/f t 0 . 018 0 Manning's roughness coeff., n 0.0300 2/3 1/2 1.49 * r * s ftf-s- 1.6760 n FI.Gvi-. I-eflgth , L € t 170 T= L/(3600*V) hrs 0.03 = 0.03 TOTAL TIMF- EIvrs-} 9-:-1 3- ' Quick TR-55 Version: 5.46 S/N: Page 1 Return FrequenEy: 50-ypars TR-55 TABULAR HYDROGR.APH METHOD ' Type-• f -1. ar str-z•brx-~ i on (24 hr. Duration Storm) Executed: N-- 0-9-2-0-0-4- 1.1-:15 : 3 0 ' Watershed file: C:\PONDPACK\14470-PX.MOP Hydrograph f i 1e-:- C~--\-Fpif&PACK-\-1-4-4-7-0 - PX . HYD Strawther's Addition- Analys-i-s- o-€ F-1-ow to- F}xisting- Culvert Post-Development Condition Baai•a RK (-Basr-ia. P- C- 14-4x.• a-reas ) Input Parameters Used to Compute Hydrograph , , Subarea AREA CN Tc * Tt Precip. . Runoff Ia/-P ae-scrigti vrr- ( a c re s) f~~rrrs~~ (.-rrrs.) ( in ) - f±n'r' irrput-f~sed 1 -Bas---in----PX 2-9-2--. -0 3-----5-- 8------ 7-0-. -0----- 0-. -10 0-. -0 0----- 2--. --45----j---0--. -43 I-. -5 .3 * TratieL. time.. from subarea oii t.fall_ t.a._ cam~.o.s.ite. watershed. outfal.L point. I-- Subarea where user specified interpolation between Ia/p tables. Tota1 area or- a. 4 5 7 5 sq. mi Peak discharge = 165 cfs Computer Agodi€-re-atr-orns- o-€ I-nput P-arameter-S <;c«< Ir-pu-t Values-- Rounded. v-a-l-u€ s- I a/p ' Subarea Tc * Tt Tc * Tt Interpolated Ia/p Dese r ipt-ron- (-hr (hr-Y - (-hr>-- Ehr-}- (Ye s / No ) A9Eess,~ige s ' Rasjl1_px - - - - - - - - -a-~- - - -0__QQ_ - - - -a-~- - - -Q__QQ.. - - - - - - -Yes-------------- * Txave~ ~ime f.ronv subarea- opat€a-~1- to- Eomposite watershed-- outf&11 po-int. ' ' Quick TR-55 Version: 5.46 S/N: Page 2 Return. Frequ-ency-: 5-0-- y~ears , TR-55 TABULAR HYDROGR.APH METHOD Type-11. Dr atrzb I i on , (24 hr. Duration orm) Exeeu•ted.: 4-2-0-9 -2Q04- 1-1:1.5..: 3 0 Watershed file: C:\PONDPACK\14470-PX.MOP I~d-rograph f i~e-: - - C:--~Pf}ND€~~~~~1-4~470--PX . HYD Strawther's Addition ~ Analysi-s— o-€ F-Iow- to- P~is-ting Ctrlvert Post-Development Condition a~s,in- PX- (Pras-in- P-- @- 10-0x a-re4s) Summary of Subarea Times to Peak Peal - D--rs-ehanrSe- at- Time— ta ge~ at Composite Outfall Composite Out-fall Gubaxe,& - (e €s-)- (,hr s ) . .Basin 'PX, iG5 , , 12.1 ~ + ! Composite Watershed 165 12.1 ' • POND-2 Version: 5.21 S/N: Page 1 Exeeut ed- 4~ - 0-3 - 2-0-0 4 - 11: 1,9 :19 , * * * * * N4tt'ltipTly- HydrOgraph" ~'7y° C031st drit * * * * * Unit HYD File: 14470-PX.HYD Otrtput Ifydrograph :-Z4~?-0-- P-.- S ITYD Multiplier Constant: .01 TIME- Uni-t- Mu-1-t rp-1rer--- Output I~~dr-oSFaph ( hrs ) Ordinates Constant ( cf s) 11.00 0.00 x 0.010 = 0•0fl 11.10 0.00 x 0.010 = -0.00 11.20 0.00 x 0.010 = 0.00 11...3 0. 0.0.0 x..._ Q-Q1D_ = 0.00 z z'.40 0..: 0ra' x Q-. (TI. 0 = P 0 0 11.50 0.00 x 0.010 = 0.00 i.r .&o-. o-: aa., X o-. o--ra- = 0.00 11.70 8.00 X 0.010 = 0.08 rrl: 8-0-- 15 .a0- x 9'. QrOr, = 0.15 11.90 23.00 x 0.010 = 0.23 1-2--. o-a-- 87-: a0- x- o--: aio = - 0.87 12.10 165 . 00 x 0.010 = 1. 65 fO° 12--. 2'0- 9 6. fJT x Q.'. 0'I.4".- = 0.96 12.30 42.00 x 0.010 = 0.42 3 4 12--. 4 0~ 3-4 . ao-- ~-o-.-. 0-1-01. = 9:30 12.50 2 5 30.00 x 0.010 12u. 6(Y,- 2-5 . Q-0- x 0-1. 0-10- = 9:22 12.70 22.00 x 0.010 1- 2- .8 o--- 2 a-. Q.o-- X- o--. o-i- a = 0.20 12.90 19.00 x_ 0.010 = 0.19 _ 1*3 . Qt7 18". QOW x 17. Qz.O.... _ 0.18 13.10 17 . 00 x 0.070 = 0•17 13-: 2-E?- lfr : o-Q~. x- Q-: a~o-= 0.16 13.30 15.00 x 0.010 = 0.15 I3: 40- 14°'. fTO- x or. t1't0r" = 0.14 ~ 13.50 14.00 x 0.010 = 0.14 ~ 3-. 66 13- 0-E}- x- 0- . 0-1-0-- = 0.13 13.70 12.00 x 0.010 = 0.12 13". S0" 12. ~cr, x T. O-To = 0.12 13.90 12.00 x 0.010 = 0.12 14.. 4-E}-. 11... 0-01.- x a°. 0-1.0- = t 11 14.10 11.00 x 0.010 = 11 1:4-. Z*O* 1(7'. ftor- x T. 0-I0, _ ° 0.10 14.30 10.00 x 0.010 = 0.10 14-. 40... 10--. 00- x 0--. E}1.0- _ - 0.10 14.50 10.00 x 0.010 = 0.10 14.60 10r':' Q(7' x C1r. Qz'O' _ 0.10 14.70 10.00 x 0.010 = 0.10 14 .a0-- 9°~ o-a-- x- o-. E}i0 = - 0. 09 14.90 9.00 x 0.010 = 0.09 15. 0 0** J. 0'0r x 0-.crI 0- = 0.09 15, 10 9-.00-- x 0.0-10-- _0-.09- POND- 2.. Versi~on : 5.21 S/P~:-- P-~ge 2 Executed 02-09-2004 11:19:19 * * * * * Mu-1 tigly- Hydrograph- by. Constant * * * Unit HYD File: 14470-PX.HYD Outptrt Hydrograph : 1-44-7 a- P-- . HYD Multiglier Constant: .01 T I-YIE- Unr-t Mul,tip-lre-r-- Output HydrmgTaph (hrs) Ordinates Constant (cfs) 15.20 9.00 x 0.010 = 0.09 15.30 8.00 x 0.010 = 0.08 . 15.40 8.00 x 0.010 = .,4•08 7r5_....5.Q. 8.....QQ_ x.. Q.-Ql.Q .0. 0 8 ~.5... 6-p-. 8. 0-a X. 4--. 0-1-0 • = 0.08 15.70 8.00 x 0.010 = 0.08 I-15. 8.Q... 7. 00.... x 0-. 0'z 0' = Q 0 7 15.90 7.00 x 0.01~ = U•0`1 I-Er. 0-4 7: E}0 - X• 0-. aI-0 = 0.07 16.10 7.00 x 0.010 = 0.07 16.20-- T. 4rO- x 07.: tTZO'. 0.07 16.30 7.00 x 0.010 = 0.07 16-: 4-o-- T. aa- x- o-: 0-10... = 0.07 16.50 7.00 x 0.010 = 0.07 1: 6-. 6 0.,. T. M" x T. ar0* = 0.07 16.70 7.00 x 0.010 = 0.07 16--. 8-F} , f}&-- x E1: (}10 = 0.06 16.90 6.00 x 0.010 = 0.06 Z7". 0'0' G-. 0-0-- x T. 0°rT = 0.06 17.10 6.00 x 0.010 = 0.06 1.7.: 2.0. F~.: E}4° X- E~ . 0.06 17.30 6.00 x 0.010 = 0.06 ' r7 .zrtT... 6-. aDr- x 0-. QTT = 0.06 17.50 6.0,0 x 0.010 = 0.06 1T: 6-E}° G-. 0-0- x 0-: 4-1-01. 0.06 17.70 6.00 x 0.010 = 0.06 17"870F 6'.0-0- x 0° . f')TT = 0.06 17.90 6.00 x 0.010 = 0.06 0.E}. fr. &f}- X. E}--. 4-I-a = 0.06 18.10 6.00 x 0.010 = 0.06 1,8.... 270'° 6. Q.Q.. x T. Q7'0' _ ` 0. 0 6 18.30 6.00 x 0.010 = 0.06 4.o-... 6. 0-0- X, 0--. 03.0 = - 0. 0 6 18.50 6.00 x 0.010 = 0.06 z~-. 6 0'._ 5. Q'O- x 0-. 01~0 0.05 18.70 5.00 x 0.010 = 0.05 18---. 8-a,. 5. 0 0- x- E}-. O 10 = 0. 0 5 18.90 5.00 x 0.010 = 0.05 1:,9". 0'0-. 5. 0Or' x (7 : QI0 = -0. O S 19.10 5.00 x 0.010 = 0.05 19-. 2 0- 5-. 0•0-- x- 4• : o-ro- - o. 0.5 POND-2 Version: 5.21 S/N: Page 3 Executed,02-09-2004 11:19:19 * * * * * Mul t i-pl-y Hydrog-r-a~~- by- Constant * * * * * Unit HYD File: 14470-PX.HYD Otr~ ~ut Hydrogr aph :--1-4 4-7a-- P-- . HYD Multiplier Constant: .01 TIMBT uait Mu--tipl-ier - Output ~Hydro~faph (hrs) ordinates Constant (cfs) 19.30 5.00 x 0.010 = 0.05 19.40 5.00 x 0.010 = ~0.05 19 . 50 4.00 x 0.010 = -,0. 04 lg. _.~..Q.. 4--QQ. 0.04 ~-a- 4-. o o-- 0.04 19.80 4.00 x 0.010 = 0.04 19-. 9-0-- 4-. 0-4- x- 8- . 0-1-.0.... = 0.04 20.00 4.00 x 0.010 = 0.04 4.. a.o-. X a-: 0,1-0-- = 0.04 20.20 4.00 x 0.010 = 0.04 2.0-.. ~0- 4-. aaw x- Q-. 0.10- - = 0.04 20.40 4.00 x 0.010 = 0.04 2o-. 50- 4--. o-o- x- o-. o-1 o- - = 0.04 20.60 4.00 x 0.010 = 0.04 2.0..., 7- a- 4: QO~. xv- 0_1, 0.1.p.. = 0.04 20.80 4.00 x 0.010 = 0.04 2.0-.. 9-f}- 4... 0-&-- x E}-. 0.1-10- = 0.04 21.00 4.00 x 0.010 = 0.04 21. 1-o.. 4. oa X.- a. a-1o 0.04 21.20 4.00 x 0.010 = 0.04 2°1. 3-{}-- 4... o o- x- 011. a-110 = - 0. 0 4 21.40 4.00 x 0.010 = 0.04 ' 21. 5 0- 4.. o-a- _x- 0-1. 04 o- _ - o. 0 4 21.60 4.00 x 0.010 = 4•04 2.1.n.... 4. 4-4-- X- a-. 010- = 0.04 ~ 21.80 4.00 x 0.010 _ 0.04 2.1.. 9-4-- 4. 0-9... x. 4... 0-10 - .0. 04 22.00 4.00 x 0.010 = 0.04 2-2--: 1-0- 4. Q0° E}--. 0-10 = --0 . 04 22.20 4.00 x 0.010 = 0.04 2.2.. , 3.p. 4.. Q4,.. X- 0,910 Q10 = 0.04 22.40 4.00 x 0.010 = 0.04 2-2--. 5o-- oo-le a.1. o-i a = - 0.04 22.60 3.00 x 0.010 = 0.03 2.2 -.7 4.- I. aa x- a, 0~ 4-- = 0.03 22.80 3.00 x 0.010 = 0.03 2-2-. ga X- E}: 01-0. _ -0. 03 23.00 3.00 x 0.010 = 0.03 a 3. 1. 0-- 3-.Q4. x- 4-. 0-10- = 0.03 23.20 3.00 x 0.010 = 0.03 2-3-.aE}• 0~-0 ~ p.., p3.... POND-2 Version: 5.21 S/N: Page 4 Pxeeuted. 0-2-09-2004 -•..11 : 1,9 : 19 * * * ML'rj-~.i~r1-y- I-lpd-rOgr?plt br-COY1starit * * * Unit HYD File: 14470-PX.HYD E?txt-put .-Hydr-ograph : 1-447-E}--P- . HYD Multiplier Constant: .Ol 'FIMR- Urt-it mtz-ltrgl-ier Output Hyeiroq~'aph (hrs) Ordinates Constant (cfs) ~ 23.40 3.00 x 0.010 = 0.03 23.50 2.00 x 0.010 = 0.02 23.60 2.00 x 0.010 = 0.02 21...7 0... 2_.Q0- x.. Q_0.10L. = 0.02 23". $0.. . 2': QO- x a:(TIO" = 0.02 23.90 2.00 x 0.010 = 0.02 24-. o-o-~ 2% NaY x o--. a}o-.. = 0.02 24.10 2.00 X 0.010 = 0.02 ~*~T'. n" z'. 0'0*' X T. az G- = 0.02 24.30 2.00 x 0.010 = 0.02 2-,4- . 4,o-~- 2... o-o- X- o-. 0-1-0- = 0.02 24.50 2.00 x 0.010 = 0.02 01 2-;T' . ~~o- z~ : crc~- X rrz-cr-~ = ~_.01 2470 1.00 X 0.010 24 8-&-- r-. o-o- x- a.: o~o--- = tol o 1 24.90 1.00 x 0.010 2-5.OrQ'" T". Or0F x T. GZ'Q" = 01 25.10 1.0*0 x 0.01D = 9:01 2--cr-: 2o-- 1.. o-o- X-- o-. 0-1.0... = 01 25.30 1.00 X 0.010 = ~_.01 25.4.o.... r-. (yo-- X v-. o-1o- = 01 25.50 0.00 x 0.010 = ~_.00 25-. 6-o-- o-.. o-a- x a..,. 0.10 - = 0.00 25.70 0.00 x 0.610 = 0.00 2-5.$tY T. 0'o-' x 071. GzT = 0.100 25-. 9-0-, 0-. 0-0- X. 0-. 010 = 0.00 POND-2 Version: 5.21 S/N: Executed 02-09-2004 11:24.:12 » » » » Summary Of Hydrograph Volume « « « « Hydrograph: 14470-P .KXD Volume = 4,684 cu.ft. 0-.1 1-- a-E - f t ~ STORMWATER DRAINAGE REPORT for the proposed plat of STRAWTHER'S ADDITION located in the NW '/4 of Section 33, T. 25 N., R. 44 E.W.M. Spokane County, Washington Original Draft: July 1, 2003 - Amended (basin maps): September 29, 2003 Project Applicant: ~ ~UC ~up~~ . OONZIR'S Donna Strawther ORIG1NqL 16326 North Castlebrook Lane PR°~# 1) _ Spokane, WA 99208 suBWnn,~ # PE_ i&5z (509) 467-7581 lO 5 N. cHR,s Report Prepared By: ' . - Simpson Engineers, Inc, o North 909 Argonne Road Spokane, Washington 99212 s9010 ~O~' ~ qFCrsTe (509) 926-1322 ~SSlO{~AL~~ - EXPiRES 4/10/ B5' ~ ENGINEER'S CERTIFICATION - The design improvements shown in this set of plans and calculations conform to the applicable editions of the Spokane County Standards for Road and Sewer Construction and the Spokane County Guidelines for Stormwater Management. I approve these plans for construction. CONTENTS PaRe ' A. Proj ect Location . . . . . . . . . 2 B. Existing Site Topography. . . . . . . . 2 C. Proj ect Description . . . . . . . . 2 D. Previous Reports . . . . . . . . . 3 ' E. Soils Descnption . . . . . . . . 3 F. Geo-Hazard Evaluation . . . . . . . . 3 G. Drainage Concept . . . . . . . . 4 H. Rainfall Data & Design Tools . . . . . . . 5 I. Drainage Basins . . . . . . . . . 5 J. Summary & Conclusion . . . . . . . . 8 APPENDIX: SuuplementalInformation 1. Site in Relation to Spokane County Aquifer Sensitive Area (Spokane County C,'ruidelines for Stormwater Management, Figure 6, p. 6-9) 2. Site Vicinity and Mapped Soils (excerpted from USDA Soil Conservation Service, Soil Survey of Spokane County, Washington, March 1968, Sheet Number 75) 3. Runoff Coefficients for Storm Sewers ' (Spokane County Guidelines for Stormwater Management, Table 1, p. 6-2) 4. Rational Formula Hydrology Calculations (4 sheets) t (Basin E1 = Existing Conditions, and Basins P2, P3 & P4 = Proposed Conditions) 5. Proposed Culvert Capacity Calculations (2 sheets) 6. Pre-Development Drainage Basin fold-out map 7. Post-Development Drainage Basins fold-out map d hc: Projects/1 4470-dm.doc Simpson Engineers, Inc. 09/29/03 Page 1 ' . . ' PROJECT LOCATION . The Strawther's Addition project site is located within the newly-formed City of Spokane Valley, on the northeasterly side of Dishman-Mica Road and on the west side of Pierce Road (extended), between 38th Avenue and 40th Avenue. The site is located in the southwest quarter of the northwest quarter of Section 33, Township 25 North, Range 44 East, W.M., in Spokane County, Washington. ' The site lies near the south limit of the Spokane-Rathdrum Aquifer, and is within the Spokane County Aquifer Sensitive Area and the Pnonty Sewer Service Area. EXISTING SITE TOPOGR.APHY The site is bounded on the southwest by Dishman-Mica Road, a two-lane Principal Arterial within a 60-foot right-of-way. To the east are existing single-family houses, platted as Chester Field Addition, and to the north are existing single-family houses, platted as Short Plat 743-92. ' Aside from the existing duplex near the southeast corner of the plat, the remainder of the site is covered with Ponderosa pine trees, native grasses and brush. A natural drainage gully extends through the site, from an existing drainage easement on the north side of the site to an existing 18"-diameter CMP culvert under Dishman-Mica Road, draining to an apparent wetland area on the southwest side of the road . A proposed drainage easement through the site will connect the existing drainage easement to the existing culvert along the existing drainage course. The site has topographic high areas on the east and west portions, with the existing drainage gully in-between. On-site slopes range from very gentle to approximately 14%, facing primarily to the west, east and south. The local high points are located near the eastem plat boundary, where the proposed cul-de-sac will be located, and in the west portion of the site. The lowest area on the site is in the drainage gully at the entrance to the existing culvert underlying Dishman-Mica Road. . Refer to the Strawther's Addition Stormwater Drainage Plan map for locations of existing contours and proposed features described in this report. PROJECT DESCRIPTION ' - The proposed plat of Strawther,s Addition will subdivide approxunately 3.24 acres of mostly undeveloped land into seven residential lots, which will vary in size. The project site is irregular in shape, with the southeasterly portion occupied by an existing duplex. The duplex is accessed off 40th Avenue, while the remainder of the plat will be accessed off an existing cul-de-sac at the west end of 38~h Avenue at Pierce Road, from which a proposed private cul-de-sac will extend - southward onto the site. The proposed cul-de-sac will provide direct access for the three lots nearest to the northeast corner of the site, while the three westerly lots of the plat will be accessed via a private driveway, to be located within an ingress-egress easement extending to the west off the west side of the on-site cul-de-sac. dhc:Projects/14470-dm.doc Simpson Engineers, Inc. 07/01 /03 Page 2 1 PREVIOUS REPORTS ' A ConceDtual Stormwater ManaQement Plan was prepared for Strawther's Additlon by J. Paul Ramer & Associates, Inc. in 1998. The general concepts presented in that plan are maintained in the present drainage plan for the project. A report letter titled Summarv ofResults ofLimited Geotechnical Enaineerinz Studv, dated April 292 1998, was prepared for this site by Cummings Geotechnology. The findings from that study are used herein for soils-related aspects of the present drainage plan. Any specific conclusions or data from that study t.hat are used herein are referenced as such. SOILS DESCRIPTION Soils at the site are mapped as being almost completely Clayton sandy loam (map symbol CuB), with the contact with Springdale gravelly sandy loam (map symbol SxB) located near the east plat . boundary, as per Soil Survey of Spokane County, Washington: USDA Soil Conservation Service (now the Natural Resources Conservation Service), March 1968. Springdale soils are listed by Spokane County as being acceptable for standard drywell practice, but Clayton soils are not. However, soils testing performed by the location of a proposed drywell at the northwest side of the proposed cul-de-sac (as specified by J. Paul Ramer & ' Associates, Inc.) indicates soils having a permeability of "several hundred inches per hour," with the recommendation that "a'could function adequately as long as it is embedded at that was found at a depth of 1~■f~' Refer to the attached excerpt from the S.C.S. soils map (Sheet Number 75) for location of the site relative to mapped soils. ' GEO-HAZARD EVALUATION "Geologically Hazardous Areas," as classified according to the characteristics described per the ' Spokane County Critical Areas Ordinance, include those areas prone to erosion and landslide hazards. Based on our initial field investigation of the project site, we have determined that this site is not a Geologically Hazardous Area, due to the site having the following characteristics: a. Slopes at the site are all substantially less than 30% grade, with the steepest slopes being about 14% for a small, limited area in the southwest portion of the site, on the northwest side of the existing drainage course above the existing culvert under Dishman-Mica Road. b. Neither the Clayton sandy loam nor the Springdale g,ravelly sandy loam soils mapped at this site are identified by the USDA S.C.S. (now the Natural Resources Conservation Service) as having a"severe" potential for erosion (as listed in Appendix H of the Spokane County Critical Areas Ordinance). Clayton soils generally have moderate stability and moderate to dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 3 low resistance to erosion, while Springdale soils generally have moderate to high stability and moderate to low resistance to erosion. Our observations at the site did not reveal any evidence of erosion having occurred recently to any significant degree. c. The only significant hydraulic factor to consider at this site is the well-defined drainage channel crossing through the site, leading to the existing culvert under Dishman-Mica road. However, it does not contain a perennial stream, and was observed this spring to be dry and to drain a limited basin area in the immed.iate vicinity. There are no lalown springs, and no wet areas observed on the site. d. This site is not a landslide-prone area; no evidence of landslides was observed on the site, and the site soils are not alluvium, not landslide deposits, and not Latah formation. e. This site is not an area of uncompacted fill. f. The site is not unstable due to stream or streambank erosion. DR;AINAGE CONCEPT The proposed drainage design for this project is fairly straightforward and generally follows the recommendations established in Spokane County's Guidelines for Stormwater Management. The developed site is proposed to be regraded such that all runoff water from the proposed asphalt surfacing will be collected and drained to a proposed drainage swale (grassed percolation axea) for treatment and disposal. The swale is located near the northeast corner of the site, adjacent to the proposed access road/cul-de-sac. The intention is to position the swale in the location where soils testing was performed by Cummings Geotechnology, as described above (see "Soils Description'). _ The proposed site plan will result in two primary points of discharge: - * and the Runoff under both existing (pre-platting) and proposed (post-platting) conditions were analyzed to assess the impacts of the site improvements on flows at the existing culvert, using a 50-year storm event for the basins that include off-site areas. Runoff flowing to the proposed dxainage swale, which only ~ occurs under proposed conditions and only includes on-site areas, is analyzed using a 10-year storm event. The total areas of drainage basins involved is the approximately the same under both existing and proposed conditions. The plan includes a private access drive to serve three of the proposed lots. The road will transect the existing drainage gully which drains to the existing culvert under Dishman-Mica Road, so a new culvert will be constructed under the private drive. Flows to the existing culvert under existing conditions, and to both the existing culvert and the new culvert under proposed conditions, are analyzed. The drainage basins are named as shown on the Stormwater Drainage Plan and detailed on the following pages. Refer to the Stormwater Drainage Plan for locations of drainage features described in this report. dnc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 4 RAINFALL DATA & DESIGN TOOLS The rainfall intensity-duration-frequency curve for both 10-year and 50-year recurrence intervals for the Spokane-Medical Lake-Reardon-Cheney-Rockford area, as presented in the February 1998 Addendum to Spokane County's Guidelines for Stormwater Management, in Figure 2, page 6-3, was adapted into tabular form for the rational formula hydrology calculations for the drainage basins under existing and proposed conditions. The intention in designing stormwater drainage facilities for this project was to follow the procedures, methods and referenced data in Spokane County's Guidelines for Stormwater Management (1998). Computations were performed using Spokane County-accepted methods and soflware programs, including rational formula hydrology for calculations of peak discharge to the culverts, and bowstring methodology for ponding volume vs. drywell outflow, adapted into an MS Exce12000 spreadsheet. The existing topography and proposed features and grades shown on the Stormwater Drainage Plan map were drawn, and some of the areas were calculated, using AutoCAD Land Development. Runoff coefficient ("C") values are based on as per "Runoff Coefficients for Storm Sewers" (Guidelines, February 1998, Table l, p. 6-2). For Proposed conditions, new houses are assumed to be 2,000 sq. ft. and new concrete driveways are assumed to be 1,000 sq. ft. Separate hydrology calculation sheets for all described basins and conditions are included in this report. DR:AINAGE BASINS Drainage Basin Name: Basin E1 Condition: Existine Basin Description: - Total Area of Basin: 157,920 sq. ft. = 3.625 acres Impervious Areas: , Asphalt (N. %z D.-Mica Rd.) _ 10,230 sq. ft. = 0.235 acre (a), C_ 0.90 H o u s e R o o f s - 5,000 s q. ft. = 0. 115 a c r e a, C- 0.90 Concrete Driveways = 1,500 sq. ft. = 0.034 acre (cr, C= 0.80 Pervious AYeas: Road Shoulder = 3,720 sq. ft. = 0.085 acre a, C= 0.50 Natural (on-site) = 110,395 sq. ft. = 2.534 acre Q C= 0.22 Lawn/Landscaping (off-site) = 27,075 sq. ft. = 0.622 acre Q C= 0.15 Point of concentration: Entrance to existing culvert under Dishman-Mica Road. 50-year Storm Discharge: Q50 =(C) (iso) (A) (see hydrology calculation sheet) dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 5 DR.AINAGE BASINS - continued Drainage Basin Name: Basin P1 Condition: ProQosed Basin Description: ~r 1T11T1~~rrnnnePr~ r1,-zLn~no ~x ~ .,,,;,~~~~~•b~pe~vel~a~ Total Area of Basin: 30,355 sq. ft. = 0.697 acres Impervious Areas: Asphalt (new cul-de-sac) = 8,500 sq. ft. = 0.195 acre (a~ C= 0.90 Concrete Curb & Gutter = 720 sq. ft. = 0.017 acre (~a, C= 0.80 House Roofs = 3,000 sq. ft. = 0.069 acre (~a, C= 0.90 Concrete Driveways = 3,000 sq. ft. = 0.069 acre a, C= 0.80 Pervious Areas: Lawn/Landscaping = 15,135 sq. ft. = 0.347 acre nu, C= 0.15 Water Quality Treatrnent Area: (8,500 + 720 + 3,000) = 12,220 sq. ft. V Water Quality Treatment Volume: (12,220 sq. ft.) x(1/2") x(1 ft./12") = 509 cu. ft. Point of concentration: Curb Inlet to proposed Drainage Swale 1. 10-year Storm Discharge: Q10 =(C) (i,o) (A) - (see hydrology calculation sheet) ~ * * Provosed Stormwater Treatment/Disposal Facilitv Name: DrainaLre Swale 1 Swale Location: Near northeast corner of the site, on northwest side of proposed cul-de-sac. Swale Floor Area =(24' x 26') +(16' x 10') +'/4 n(16')2 = 624 + 160 + 201 = 985 sq. ft. Swale Floor Perimeter = 125 LF with 3:1 slopes on all sides. S Water Oualitv Treatment Capacitv ~ wale Volume @ 6~~ Depth: _(0.5 ft. depth)(swale floor area) +(1/2 x 0.5 x 1.5)(swale floor perimeter) = 0.5 (985) + 0.375 (125) = 492 + 47 = 539 cu. ft. 539 cu. ft. provided > 509 cu. ft. required for entire Basin P1 Drainage Swale 1 is OK for runoff treatment of entire Basin P1 @ 6" depth Outflow StoraQe Capacitv Swale Volume @ 8" Depth: _(0.67 ft. depth)(swale floor area) +(1/2 x 0.67 x 2.0)(swale floor perimeter) = 0.67 (985) + 0.67 (125) = 656 + 83 = 739 cu. ft. 739 cu. ft. provided > 397 cu. ft. required with 0.3 c.f.s. outflow Drainage Swale 1 is OK for storage @ 8" depth w/outflow via one Type "A" drywell (Note: Type "B" specified on plans, so drywell can be set deeper into coarse soil) dhc:Projects/14470-dm.doc Simpson Engineers, Inc. 07/01/03 Page 6 DR.AINAGE BASINS - continued Drainage Basin Name: Basin P2 Condition: Proposed Basin Description: A.rea draining to proposed culvert under proposed driveway access road. Total Area of Basin: 74,485 sq. ft. = 1.710 acres Impervious Areas: Asphalt Pavement = 0 sq. ft. = 0.000 acre Q C= 0.90 House Roofs = 10,000 sq. ft. = 0.230 acre (a) C= 0.90 Concrete Driveways = 3,500 sq. ft. = 0.080 acre 0, C= 0.80 Pervious Areas: N. %2 Gravel Access = 1,500 sq. ft. = 0.034 acre Q C= 0.55 Lawn/I,andscaping (on-site) = 32,410 sq. ft. = 0.744 acre e, C= 0.15 Lawn/Landscaping (off-site) = 27,075 sq. ft. = 0.622 acre (~a, C= 0.15 Point of concentration: Entrance to proposed culvert under driveway access road. 50-year Storm Discharge: QSp =(C) (iso) (A) , (see hydrology calculation sheet) * * ~ r Drainage Basin Name: Basin P3 Condition: Proposed Basin Description: Area draining directly to existing culvert under Dishman-Mica Road only, under proposed conditions (excluding flow through proposed culvert). Total Area of Basin: 53,080 sq. ft. = 1.219 acres ' Impervious Areas: Asphalt (N. %2 D.-Mica Rd.) = 10,230 sq. ft. = 0.235 acre (a), C= 0.90 , House Roofs = 3,000 sq. ft. = 0.069 acre a, C= 0.90 Concrete Driveways = 1,000 sq. ft. = 0.023 acre (d~ C= 0.80 Pervious Areas: S. %2 Gravel Access = 1,500 sq. ft. = 0.034 acre (~a, C= 0.55 Road Shoulder = 3,720 sq. ft. = 0.085 acre (~a, C= 0.50 Lawn/Landscaping (on-site) = 33,630 sq. ft. = 0.772 acre (~a, C= 0.15 Point of concentration: Entrance to existing culvert under Dishman-Mica Road. 50-year Storm Discharge: Q50 =(C) (iso) (A) see hydrology calculation sheet) dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 7 ' SUMMARY & CONCLUSION Under existing conditions, an area of approximately 3.6 acres drains to the existing culvert under Dishman-Mica Road. Of that drainage basin ("Basin E1"), about 0.8 acres is off-site and adjacent to the subj ect proj ect site, consisting of existing houses and yards, and the remaining 2.8 acres is , on-site (in an undeveloped condition). Of that 2.8 acres on-site, an area of about 0.7 acres will be removed from the area draining to the existmg culvert, so that even after construction of houses and driveways, the calculated flow to the existing culvert under Dishman-Mica Road is not substantially affected (see table below). For the 0.7 acres referenced above ("Basin P 1"), the proposed plan calls for construction of an asphalt road and cul-de-sac, which will be graded to drain to a proposed drainage facility ("Swale 1"). All proposed asphalt will drain to this swale for stormwater treatment and disposal. Although the calculations show that a Type "A" drywell would be sufficient, a Type "B" drywell is ' specified on the plans so that it extends sufficiently into the coarser soils (per the recommendation by Cummings Geotechnology - see section titled Soils Description on page 3 of this report). Table 1: Comparison of Pre-Development & Post-Development Flows to Existing Culvert Drainage Basin Storm Calculated Point of ' Basin Name Condition Event Peak Discharqe Concentration E 1 ~ Existinq 50-year ~ 3.79 ~ Existmg Culvert P 2 ~ Proposed 50-year ~ 1.86 ~ Proposed Culvert ~ P 3 ~ Proposed 50-year ~ 1.89 ( Existinq Culvert P 2+ P 3 ~ Proposed ~ 50-year ~ 3.75 ~ Existing Culvert ' Note: Basin P2 drains through the proposed culvert, then to the existing culvert. Basin P3 is the area that drains directly to the existing culvert only, after development. ' Calculated net imPact on existing culvert under Dishman-Mica Road: 50-year peak discharge is basically unchanged (decreased from 3.79 c.f.s. to 3.75 c.f.s.). 1 (Note: Actually, rime of concentration for P2 and P3 differ slightly, so the combined peak would actually be lower than 3.75 c.f.s.). In conclusion, it is our opinion that construction of houses and associated improvements in this plat (as assumed per the modeled drainage basins) should not cause any significant increase in stormwater runoff at the "downstream" plat boundary, and therefore should not cause nor exacerbate any runoff-related problems that may exist or occur downstream of this site. dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 8 .R44E 45 E R42E R43E T 29 ~ }~-c` ; q t - ; ~ . • ~ ~4 o~e C,ounty i Up er S~ns'tiVe A~ 29 Aq 7 28 i , t { ~ ~ i ~ , ~r t t { 1, ~ ~ t} 1 28 t~ 27 ~ T , t ~ , ; ► ~I ? 7 30 z' T 26 , Ar T 26 T r ~ 1 1 ~ ~ ~ ` 25 i ~ fl f ` ~ ~ 1 S 7- 25 ~ 1 t ~ ~ • .t r~ t t ~ ~ Min/ ~ ~ . ~ • ~ } ~ 1 - . - ~ ~ ~ ~ ; ~ ; T 2¢ t . i ~ ~ ~ ~ ~ ~ ~ 1 q ~ ; _7 i_.- F T 24 1' ~ 23 T t ~ i ` , ; ~ ~ ~ , , ~ s ~ ~ • 23 ~ 1~ ~ 4 ~ ~ ~ ~ ~ i ~ , • ~ ~ t ' T 22 1V 22 -7 1 T N `=9 ` ` F ! ''t , i s . r • 1 ~ 21 t i ~ i~ ~ ~ ' ~t~ < <'~1. 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M ~ . ` ~ s,o . ~r0 r~-. ► • O ' TA.B LE 1 RUNOFF COEFFICIENTS FOR STORM SEWERS ~4 ~ ROLLING HILLY FLAT 2% - 10% OVER 10% Pavement and Roofs . . . . . . . . . . . . . . 0.90 Co-9U 0.90 Earth Shoulders . . . . . . . . . . . . . . . 0.50 CO .SU) 0.50 Drives and Walks . . . . . . . . . . . . . . . 0.75 0.80 0.85 Gravel Pavement . . . . . . . . . . . . . . . 0.50 CO-55 0.60 City Business Areas . . . . . . . . . . . . . 0.80 0.85 0.85 ~ Lawns, Sandy Soil . . . . . . . . . . . . . . 0.10 ~_15) 0.20 Lawn, Heavy Soil . . . . . . . . . . . . . . . 0.17 0.22 0.35 Grass Shoulders . . . . . . . . . . . . . . . 0.25 0.25 0.25 Side Slopes, Earth . . . . . . . . . . . . . . 0.60 0.60 0.60 Side Slopes, Turf . . . . . . . . . . . . . . 0.30 0.30 0.30 Median Areas, Turf . . . . . . . . . . . . . . 0.25 0.30 U.30 Cultivated Land, Clay and Loam 0.50 0.55 U. 6U s Cultivated Land, Sand and Gravel 0.25 U.30 0.35 Industrial Areas, I+ight . . . . . . . . . . . 0.50 0.70 0.80 Industrial Areas, Heavy . . . . . . . . . U.60 U.80 0.90 Parks and Cemetaries . . . . . . . . . . . . . 0.10 0.15 0.25 ~ . Playgrounds . . . . . . . . . . . . . . . . . 0.20 0.25 0.30 Woodland and Forests . . . . . . . . . . . . . 0.10 0.15 0.20 Meadows and Pasture Land . . . . . . . . . . . U.25 0.30 0.35 *SINGLE FAMILY RESIDENTIAL. , 001.ik,.r~~ " 9ro"d- (Dwelling Unit/Gross Acre) (Sandy and Gravelly Soil) 0-1. U DU/GA . . . ' . . . . . . . 0.0 S 1.0-1.5 DU/GA . . . . . . . .-0.20- 1. 5-3. 0 DU/ GA . . . : . . . . : . 0.25 3.0-3. S DU/GA . . . . . . . . . . .U. 30 3. S-4.U DU/GA . . . . . . . . . . U•35 ~ 4. U-6. U DU/GA . . . . . . . . . 0.40 6. U-9. U DU'/GA . . . . . . . . . . 0.60 9. 0-15. U' DU/GA . . . . . . . . . . 0.70 * Asswaes flat lot plus one-half widCh bf abutting street. Other configurations . should be checked by combining individual runoff'factors for each various surface. Date 4/4/$4 " • TAB LE 1 6-2 ' ' RATIONAL FORMULA HYDROLOGY Drafnage Basin Malysis for ' 50-year Storm Retum Frequency Event Project Name: Strawther's Addition Project: 14470 Drainage Basin Name: Basin E1 Condition: Existing Designer. DHC Basin Description: Total area draining to existing culvert Date: 26-Jun-03 Point of Cancentration: Entrance to existing culvert under Dishman-Mica Road Disk File: 14470.xls RAINFALL INTENSITY-DURATION 50-Year Storm Retum Frequency__ SUBAREAS Time Time StoRn Description Acres C A'C IncRnnt. Inumnt. Intensity (minutes) (seoonds) (in_mr.) Asphalt Pavement 0.235 0.90 0.212 Tc = 8.33 500.0 3.66 = Intensity @ Tc Road Shoulder 0.085 0.50 0.043 5 300 4.58 House Roofs 0.115 0.90 0.104 10 600 3.20 Concrete Drives 0.034 0.80 0.027 15 900 2.47 Landscape (offsite) 0.622 0.15 0.093 20 1200 1.98 Natural (on-site) 2.534 022 0.557 25 1500 1.67 30 1800 1.46 Total Acres = 3.625 35 2100 1.30 Composite Caefficient (C)= 0.29 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION (Tc), minutes 55 3300 0.92 60 3600 0.87 Overiand flow Channel flow 65 3900 0.82 70 4200 0.80 Seament A: L2 = 170 75 4500 0.77 Ct = 0.15 Z1 = 10 80 4800 0.75 L1(A) = 260 Z2 = 13 85 5100 0.72 N(A) = 0.4 B= 5 90 5400 0.70 S(A) = 0.03 n= 0.03 95 5700 0.68 Tc (A) = 6.97 s= 0.018 100 6000 0.67 d= 0.24 Seqment B: L1(B) = 0 Tc (ch) = 1.36 Explana6on: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (overland) + Tc (channel) S(B) = 0 Tc(tot.) = 8.33 1Vofe: Tc (total) = 5 minufes minimum Tc (B) = 0.00 Intensity = 3.66 Ct = 0.15 = Coefficient for overland flow L1 = Length of overland flow segment(s), in feet Calculated Channel Flow Data: N = overland frictfon factor , S= average slope of overland flow, in ft./ft. Area = 1.83 Sq. Ft. Tc (overland) - Ct'(L1'N/S"0.5)^0.6) W.P. = 10.47 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.17 Ft. 21 = inverse of cross slope of backslope of channel V= 2.08 FtJSec. ' Z2 = inverse of cross slope of foreslope of channel Tc(ch) = 1.36 Minutes B= Bottom width of channel (gutter or ditch), in feet Q(est) = 3.80 C.F.S. n= Manning's friction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = 1.06 d= depth of flow in channel, in feet Flow Regime = Supercritical Flow Tc (channel) = L / ((1.486/n)'R^0.67s^0.5) / 60 Area = d'B+d^2/2'(Z1+Z2) Calculated Flow Depth in Channel: W.P. = B+d'(11sin(atn(11Z1))+1/sin(atn(1/Z2))) • R= Hydraulic Radius = Area/ Wetted Perimeter ~ d= 0.24 Feet ~ V = Velocity = 1.486/n'R^.667's".5 Tc (ch) = Length (ft) / Veloclty (fps) / 60 Calculated Peak Discharge, 50-Year Storm: Q(est) = Estimated Flow (verifies depth, d) = V'A Froude Number = V/(g'0.5d)`0.5 ~ Q= 3.79 C.F.S. ~ Peak Discharge = Q= C'I'A (cubic ft. per sec.) Simpson Engineers, lnc. 909 N. Aigonne Road, Spokane, WA 99212 (509) 926-1322 Fax: (509) 926-1323 144704ryd - Basln Et ' RATIONAL FORMULA HYDROLOGY & BOWSTRING CALCULATIONS DRAINAGE BASIN ANALYSIS 8 DESIGN for 10 YEAR STORM EVENT Sfmpson Eng/neers, lnc. 909 N. Argonne Road, Spokane WA 99212 I' Date: 07101/03 Sponsor Name: Donna Strawther Design: Doug Christenson Project Name: Strawther's Addition Project. 14470 Site Location: 38th Avenue, nortfi side of Dishman-Mica Road Basin Name: Basin P1 Basin Description: Area draining to proposed swale by cuWe-sac G.P.A. Name: Swale 1 G.P.A. Location- Northeast portion of site Site Condition: Proposed Point of Concentration: Curb Inlet into proposed swale SUBAREAS: TIME OF CONCENTRATION (minutes): Description Acres C A'C Tc (overland flow) Tc (gutter flow) Asphalt Pavement 0.195 0.90 0.176 House Roofs 0.069 0.90 0.062 Ct = 0.15 L2 = 150 Concrete Cufi & Gutter 0.017 0.80 0.014 Z1 = 50 Concrete Driveways 0.069 0.80 0.055 L1(A) = 70 Z2 = 0.167 Gravel Surfacing 0.000 0.55 0.000 N(A) = 0.3 B= 0 Pervious/Landscaping 0.347 0.15 0.052 S(A) = 0.01 n= 0.013 s = 0.01 Tc (A) = 3.71 d = 0.15 Total Basin Araa, acres = 0.697 Composite Runoff Coefficient = 0.514 L1(B) = 150 Tc (gut) 1.26 Combined (Area' Runoff Coefficient) = 0.358 N(B) = 0.016 Tc(A+B) • 4.59 S(B) = 0.016 Tc total 5.84 Intensiry : 3.02 RUNOFF WATER QUALITY PARAMETERS: Tc (B) = 0.9 Holding 5.34 Impervious Treatment Area = 12,220 sq. ft. Treatment Volume Generated = 509 cu. ft. Q(estimated @ d) = 1.09 c.f.s. Time of Concentration = 5.84 minutes DRAINAGE FACILITY DATA for Swale 1 Total Swale Floor Area = 985 sq. ft. Swale Floor Perimeter Q 3:1 = 125 lin. ft. PEAK DISCHARGE, 10 YEAR STORM: Treatment Volume Provided @ 6" = 539 cu. ft. Storm Storage Provided @ 8" = 739 cu. ft. Q= C' I' A= ~ 1.08 C.F.S. ~ BOWSTRING CALCULATIONS NUMBER and TYPE of DRYWELLS PROPOSED: #1 t#2 #3 #4 #5 #6 #7 Time Time Intensity Q dev. V in V out Storage 1 Single-Sarrel (City of Spokane Type 1) Incrmnt. Incrmnt. 0 Double-Barrel (City of Spokane Type 2) (min.) (sec.) (in.mr) (cfs) (cu. ft.) (cu. ft.) (cu. R.) (ai•so) (A•c-us) (oun.'xz) 0sas OutFlow Provided: 0.3 af.s. 5.84 350.60 3.02 1.08 509 105.18 5 300 3.18 1.14 458 90 368 10 600 224 0.80 577 180 397 15 900 1.77 0.63 647 270 377 WATER QUALITY TREATMENT VOLUME: 20 1200 145 0.52 686 360 326 25 1500 1.21 0.43 702 450 252 Required G.P.A. ponding volume: 30 1800 1.04 0.37 715 540 175 Impervious "208" Area x 1/2" = 509 cu. ft. 35 2100 0.91 0.33 724 630 94 volume provided at 6" depth = 539 cu. ft. 40 2400 0.82 0.29 740 720 20 Conciusion: OK 45 2700 0.74 0.27 748 810 -62 50 3000 0.68 0.24 760 900 -140 4104 55 3300 0.64 0.23 784 990 -206 STORM STORAGE VOLUME: 60 3600 0.61 0.22 813 1080 -267 o/ 65 3900 0.60 0.22 864 1170 -306 Maximum storage required = ".397 cu. ft. 70 4200 0.58 0.21 898 1260 -362 volume provided at 8" depth = 739 cu. ft, 75 4500 0.56 020 927 1350 -423 Conclusion: OK 80 4800 0.53 0.19 935 1440 -505 85 5100 0.52 0.19 973 1530 -557 90 5400 0.50 0.18 989 1620 -631 DRYWELL REQUIREMENTS: 95 5700 0.49 0.18 1022 1710 -688 100 6000 0.48 0.17 1053 1800 -747 1 Single (Type 1) 0 Double (Type 2) Simpson EngTneers, lnc. 909 Norih Argonne Road, Spokane, WA 99212 Phone: (509) 926-1322 Fax: (509) 926-1323 easin Pt RATIONAL FORMULA HYDROLOGY Drainage Basin Malysis for ' 50-year Storm Retum Frequency Event Project Name: Strawther's Addition Project 14470 Drainage Basin Name: Basin P2 Candition: Proposed Designer: DHC Basin Description: Area draining to proposed culvert under access road Date: 26-Jun-03 Point of Concentration: Entrance to proposed culvert under gravel road Disk File: 14470.xls RAINFALL INTENSITY-DURATION 50-Year Storm Retum Frequency SUBAREAS Time Time Storm Descriptfon Acres C A'C IncRnnt. Incrmnt. Intensity (minutes) (seconds) (in.lhr.) Asphalt Pavement 0.000 0.90 0.000 Tc = 7.96 477.9 3.76 = Intensity Qa Tc N. 1/2 Gravel Road 0.034 0.55 0.019 5 300 4.58 House Roofs 0.230 0.90 0.207 10 600 3.20 Concrete Drives 0.080 0.80 0.064 15 900 2.47 Lawn/Landscape 1.366 0.15 0.205 20 1200 1.98 25 1500 1.67 30 1800 1.46 Total Acres = 1.710 35 2100 1.30 Composite Coefficient (C)= 0.29 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION_ c, minutes 55 3300 0.92 60 3600 0.87 • Overland flow Channel flow 65 3900 0.82 70 4200 0.80 Seament A: LZ = 100 75 4500 0.77 Ct = 0.15 Z1 = 10 80 4800 0.75 L1(A) = 260 Z2 = 13 85 5100 0.72 N(A) = 0.4 B= 5 90 5400 0.70 S(A) = 0.03 n= 0.03 95 5700 0.68 Tc (A) = 6.97 s= 0.018 100 6000 0.67 d= 0.16 Seament 8: L1(B) = 0 Tc (ch) = 1.00 Explanation: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (overland) + Tc (channel) S(B) = 0 Tc(tot.) = 7.96 Note: Tc (total) = 5 minufes minimum Tc (B) = 0.00 Intensiry = 3.76 Ct = 0.15 = Coefficient for overland flow L1 = Length of ovedand flow segment(s), in feet Calculated Channel Flow Data: N = overland friction factor ' S= average slope of overland flow, in ft./ft. Area = 1.10 Sq. Ft. Tc (overland) = Ct'(L1'N/S110.5)^0.6) W.P. = 8.72 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.13 Ft. Z1 = inverse of cross slope of backslope of channel V= 1.67 Ft./Sec. Z2 = inverse of cross slope of foreslope of channel Tc(ch) = 1.00 Minutes B= Bottom width of channel (gutter or ditch), in feet Q(est) = 1.85 C.F.S. n= Manning's friction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = 1.04 d= depth of flow in channel, in feet Flow Regime = Supercritical Flow Tc (channel) = L / ((1.486/n)'R^0.67s^0.5) / 60 Area = d'B+d^2/2'(Z1+Z2) Calculated Flow Depth in Channel: W.P. = B+d'(1/sin(atn(121))+1/sin(atn(122))) R= Hydraulic Radius = Area/ Wetted Perimeter V = Velocity = 1.486/n'R^.667's^.5 Tc (ch) = Length (ft) / Velocity (fps) ! 60 Calculated Peak Discharge, 50-Year Storm: Q(est) = Estimated Flow (verifies depth, d) = V'A Froude Number = V/(g'0.5d)^0.5 ~ Q= 1.86 C.F.S. ~ Peak Discharge = Q= C'I"A (cubic ft. per sec.) Simpson Engineers, Inc. 909 N. Argonne Road, Spokane, WA 99212 (509) 926-1322 Fax: (509) 926-1323 , aa7o-ryo . easin P2 RATIONAL FORMULA HYDROLOGY Drainage Basin Analysis for 50-year Stortm Retum Frequency Event Project Name: SVawther's Addition Project: 14470 Orainage Basin Name: Basin P3 Condition: Proposed Designer: DHC Basin Description: Area draining to existing culvert only (nat via new culvert) Date: 26-Jun-03 Point of Concentration: EnUance to existing culvert under Oishman-Mica Road Disk File: i4470.xls RAINFALL INTENSITY-DURATION 50-Year Storm Retum Frequencv SUBAREAS , Time Time Storm Description Acres C A'C Incrmnt. Incrmnt. Intensity (minutes) (seconds) (tn.mr.) Asphalt Pavement 0.235 0.90 0.212 Tc = 6.97 418.0 4.04 =lntensiry @ Tc Road Shoulder 0.085 0.50 0.043 5 300 4.58 House Roofs 0.069 0.90 0.062 10 600 3.20 Concrete Drives 0.023 0.80 0.018 15 900 2.47 Lawn/Landscape 0.772 0.15 0.116 20 1200 1.98 S. 112 Gravel Road 0.034 0.55 0.019 25 1500 1.67 30 1800 1.46 Total Acres = 1.218 • 35 2100 1.30 Composite Coefficient (C)= 0.39 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION ffcl, minutes_.. 55 3300 0.92 60 3600 0.87 Overland flow Channel flow 65 3900 0.82 70 4200 0.80 Seament A: L2 = 0 75 4500 0.77 Ct = 0.15 Z1 = 0 80 4800 0.75 L1(A) = 300 Z2 = 0 85 5100 0.72 N(A) = 0.4 B= 0 90 5400 0.70 S(A) = 0.04 n= Q 95 5700 0.68 Tc (A) = 6.97 s= 0 100 6000 0.67 d= 0.00 Seament B: L1(B) = 0 Tc (ch) = 0 Exolanation: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (overtand) + Tc (channel) S(B) = 0 Tc(tot.) = 6.97 Note: Tc (fotal) = 5 minutes minimum Tc (B) = 0.00 Intensity = 4.04 Ct = 0.15 = Coefficient for overland flow L1 = Length of overland flow segment(s), in feet Galculated Channe! Flow Data: N = overland friction factor S= average slope of overland flow, in ft./ft. Area = 0.00 Sq. Ft. Tc (overiand) = Ct'(L1"N/S110.5)110.6) W.P. = 0.00 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.00 Ft. Z1 = inverse of cross slope of backslope of channel V= 0.00 Ft./Sec. Z2 = inverse of cross slope of foreslope of channel Tc(ch) = 0.00 Minutes B= Bottom width of channel (gutter or ditch), in feet Q(est) = 0.00 C.F.S. n= Manning's friction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = N.A. d= depth of flow in channel, in feet Flow Regime = N.A. Tc (channel) = L / ((1.486/n)'R^0.67s"0.5) / 60 ~ Area = d'B+d^2i2'(Z1+72) Calculated Flow Depth in Channel: W.P. = B+d'(1/sin(atn(1/Z1))+1/sin(atn(1/Z2))) R= Hydraulic Radius = Area/ Wetted Perimeter ~ d= 0.00 Feet ~ V = Velocity = 1.486/n`R^.667's^.5 Tc (ch) = Length (ft) / Velocity (fps) / 60 Calculated Peak Discharge, 50-Year Storm: Q(est) = Estimated Flow (verifies depth, d) = V'A Froude Number = V/(g"0.5d)^0.5 ~ Q= 1.$9 C.F.S. ~ Peak Discharge = Q= C'I'A (cubic ft. per sec.) Simpson Engineers, lnc. 909 N. Argonne Road, Spokane, WA 99212 (509) 926-9322 Fax: (509) 926-1323 14474Ayd • Basln P3 ' Circular Cnannel Rnalysis & Depign Solved with.Manning's Eguation Open Channel - Unif-orm flow Worksheet Name : Strawthes'-s Addition Comment : ProgQSed Culvert under access driveway Solve For Actual Depth Giv-en Input Data: , Uiameter.......... 1. 010, f t : r 2 Slope . . . . . . . . . . . . . 0 . 0200 ft/ft ~ o .a' /4e L.F Manning's n....... 0.024 Discharge . . . . . . . . . 1.86 cf s q~a ~ gps~N PZ eomputed Resul t s : DeptYr . . . . . . . . . . . . . 0.61 f t Velocity . . . . . . . . . . 3 . 74 .f_ps Floar Are-a . . . . . . . . . 0.50 s f Critical Depth.... 0.58 f-t Cri ti cal S 1 oge 0.0227 f t/ f t Percent Full...... 60.57 0 Full Cap-acr ty . . . . . 2.73 c f s QMAX @.94D........ 2.94 cf s Froude Number..... 0.92 (flov is Subcritical ) ' Open Channel Flow Module, Version 3.21 (c) 1990 Haestad Met-nods-, Inc. * 37 Broakside Rd *Wat-erbury, et U6708 Circular Channel Analysis & Design Solved with Manning's Equation Open Cnannel - Unitorm flow ' Worksheet Name: Strawther's Addition . Comment : Progosed Ctzlvert under access driveway Solve For Full Flow Capacity Given Input Data : Diameter 1.00 f t Slope............. 0.0200 f.t/ft Manr~zng~s n....... 0.024 Discharge . . . . . . . . . 2.73 cf s . C.c~ t-vERT O eomputed Results: Ful1 FLlow- Capacz ty 2.73 c f s Full Flow Depth........ 1.00 ft velQCity........... 3.47 fps Flow Area......... 0.79 sf Cri t i c-a 1- Depth 0.71 f t Critical Slope.... 0.0277 ft/ft Percent Ful l . . . . . . 100.00. o Full Capacity..... 2.73 cfs QMPsX g. J41Y . . . . . . . . 2.94 c f s Froude Number..... FULL Open Cnannel Flow Module, Version 3.21 (c) 1990 Haestad Methods, Inc. * 37 B-rookside Rd * Waterbury, Ct 06708 37TH AVENUE - - ~ ~ ~ 1 ~ . - \ 1 \ ~ 1 \ _ ~ ~ ~ ~ Ex. Houee a roz. loc. 1 i ~ PP I \ \ ~ _ J ~ I ~ / ~ \ / \ ~ ~ \ / / ~ - - - - _ _ _ Basin boundar within rivate ro ert ~ - Y P P P Y ~ - was mapped by visual approximation. NORTH ~ ~ ~ Ex. H uae ~ / ~ I ~aPPr x. loc.)I \ ,J 1 ~ L- / / gQ~(~ \ ~ / ~ NOT TO SCALE ~ \ ~ ~ a~ . o / \ ~Q ~a ti ~ ~ ~ ~ ~ oQ / / ~ ~ ~ ~ i _ ~ 9~'~ ~ a~ ~ ~ ~ ~ \ 1 ,y~ ~ ~ \ \ / ~ \ ~ h ~ ~ 38TH AVENUE _ ~ 1 \ a J ~ ~ Ez. use f ~ \ \ (appr .loc,) l \ I { L J ~ ~ 1 5 1 E 242. 0(record) ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ . ~i ~ ~ ti / ~ ~ ~ , .r-- ~ / ~ q ~ . , o /`i ~ O ti a ~ •~b ~ ~ • \ ~ ' ~ \ ~ ~ \ . ~ F ~ \ ~ ~ \ J ~ Existing 18" / ~ CMP Culvert ~ \ / \ ~.E. zoo~.a NE Pr - e opment drai ag ba 'n b ndar / I.E. 2006J ~SW; ~ ~ \ ~ ~ / v \ \ i u ~ n ~ ~ / ~i W • \ , \ \ • - - ° - - - - . . vf~n \ / V' \ ~ . ~ / ~ ~r ~ ° . ~ / ° ~ '9 ~ Z ~ \ \ / \ ~ ~r \ ~ \ ~ . . y \ / \ - - • ~ ~ ~ ~ \ s Q \ Ex. DupleK _ f_. ~oPPrax. loc.) \ I I \ ~ \ \ ~ ~ d ~ ~ ~ ~ ~ $ ~ Cotc poalcim ror the ~ ~ ~ SE oana SWI/4 NWI/4 ° South line of the SW1/4 of the NW1/4 . ~ \ . - - - - - - - - Y ~ ' ~ ~ ~ 40TH AVENUE ~ - - ~ - x 0 ~ + ~ ~ CALL BEFOViE Yq CALL BEFME YOU DIG 456-8000 I I ~ DANM ~ SCALE ~ wte ~ ENI: , ~ I I Faiptd~d 191e IM~~ ~ ~ ~ ~ I~x~ m~ ~r~~ DRAINAGE STRA iYTHER S ADDITI I . I ~ ~ ~ ~ ' son 8 I~c. S ADDITION ~ I I ~[uv~na 2014.95 ~~atnrx lataao awaT ~u 9ar wisrt PRE-DEVELOPMENT DRAINAGE I I I I + I CIVIL ENGINEERS dc LAND SURVEYORS ' DRAINAGE BASIN ~ ~ i N, 909 ARGONNE R~AD, SP~KANE WA„ 99212-2789 lio~,noi tat sok. b Pas Pah, 78C N. of urnic~rr Sl1 / 4 Ol SBCTION 33 f:26 X R.~4 I I ~ ~ ~ !5 y a►o~ csos> sz6-i3zx Fax csog~ ~2~-i~ 14470 1 OF 1 SPO1~I1vg coUxTY, 1Id581NCTON 6 er o~l[ I REVI90NS / AS BUILT /OM Aw, Eo~t dd~ ot DhM~m-Yko Rood ' L T.26 N. R.44 H.W.M. ~ I _ 37TH AVENUE . - ~ ~ ~ 1 ~ rlox I I nnh1 1 ~ LD 1ST I ER FjE I 1 \ HE T . C 1 ~ ~ ~ ~ r ~ ~ Ex. House 1 I I ~ opprox. loe~ / ~ ~ 1 / ~ L--J I ~ i ~ ~ ,i ~ ~ , ~ ~ ~ ~ ~ ` i ~ ~ ~ ~ Basin boundar within rivate ro ert J-- --L---- ~ Y P P P Y ~ ~ C was mapped by visual approximation. ~ ~ - ~ NORTH . ~ ~ Ex. H uee ~ ~ I (appr . loc.)I \ ~ o ~ ~ \ L -J ~ ~ ~ ~ > ~ T NOT TO SCALE ~ / ~ / \ ~ o ~ ~A ~ \ Q ~ ~ as-sz ~ Ja o~~~ ~ ~HORT PI.A7' #7 ~ ~ ~ \ ~ ~ . S ~ ~ \ ~ y ~ ~ , ~ / / \ o• 9 . `~S . ~ ~ ~9 0 / ~rr i _ I ~ • \ , ,y1,~ 1~•~, : „ ~ c ~p J ,~i,y~~j ~ °o r " - - sLL~TIL ~ r ~ 4~ U~'' ~ 1 _ LEGEND ~ ` p. Ex. F ouee ~ ~ ~ ` \ ` y/ J I a r la, I II ~ u . ~ ~ PP ~ ) ~ . ~ 11 ~ L-_J ` ~ ~Q \ \ ~ _ ~ I - Pro' ct Site Pro ert Line ine ~ . , . ~ PROPOSED SWALE 1: ~ P Y ~ ~ ~ ~,31 2 J recor ~ ti ~ ~ 1 n ~ ` 85 sq.ft. 0 Elev. 2020.0 \ ~ \ /'J ~ ~ Offaet 6 from face of curb _ ~ / 0 . Other Parcel Lines (approx.) . ~ ~ \ ~a~~ ~ r i 3~ ~Double-Barrel Drywell, T~p e B wox.) \ a ~ t Meta1 Froma dc Grote, Type 4 < 6 / ~ ' ~ ` \ ~~o ~o' utai mt i~ S okane Caunty Stondarda 2ao9 - Existing Ground Contour (1 intervals) ~ , P - r m s ~ To of rate Elev. 2020.5 (1' intervals) ~ r ~ ~ P ~ r--~ \ ~ ~ ° ~ , i ~ ~ House: Existin a rox. location ~ / ~ , a I I 9~PP ) A +tn .,l -~r sasaY_. ~ p~~ ~ I _ ~ ~ 9 o p e q u t t x t o d l o n n m o f f , _ ~ ` a` o~ L T E ~ '1' ~ to p o ~ a to w e e t - o r P r o p o s e d ( a s s u m e d) ` , / m ~ ~ ~ , \ p \ ~ ~1 7 n I m T3 - _ ~ ' V . w 13* 1s ~ ~ o ~ i • ~ ~i~ ~ g ~ ~ r~i = Proposed Concrete Curb ~ a ~v J ~ ~ / > ~ I ~ ~ Y / Q/ ~ ~ r o~ ~ ; ^ ~ g~' i ~ ~ ~ Vi . ~ = Proposed Conc, Curb Inlet s \ ~ i'Z ~ , i ,1 - - , ~ ~ o~~ ` is~ a~e c~t r 2 = Proposed Drainage Swale Floor '~9• - - - - a ~ det . - M 1 i 2 ~ ~ f~,i _ F , ~ ~i / ~ - Propased Drywell le Floor 7 D ~ ~ O ~a ~ Y ~ M~ / , unun ~ \ _BASIN P2_ _ Draincge Basin Boundary • ENt ~ = r o, J r ^ ~o ~ ~ . - - - - _ BASIN P3 y ~ .y . Exisling iB' ~ m o ~ ~t ~ I CMP Culvert .E ( I I ~ T- 5 ---_~r~ ~ I.E. 2007.4 NE I.E 7 = l - ~.E. z~s,, f s~3 _ ~ r m~ ~ or ~a ~ . \ L T 6 ; „ o ~ ~ I pl r ~ N~ ~ d 9 m o~ ~ ~ ` ' I 3 \ \ L'~ J E ~ o'' ~ ~ H \ ~ ~ L \ . ~ ~ ~ . o _ i ~ ~ ~ _ Pos~ Deve~ m t 3 W d►~ a g e b a s i n o u n a r i e / ~ M B ~ o a c ~ \ \ ~ ~ g . d \ ~ b~ ;o-M - - - - ~iot~ ~ \ \ ~ a 9t \ ~ / ~ D ~ p o P ~ ~ i . z L~ \ ~ \ ~ o ~E ~ o F ~ . ~ , r ~ Eg ~ ~ ~ , z ES~ \ ~ ~ / F N 4 ~ ~ ~ ~ ~ ~ , ~r' \ ~ / ~ Cs \ 9~ ~ o \ ' ~ ''~i ~ ~ ~ ~ N ~ \ ~ Ez. Duplez ~ ~ \ I IL . ~ ~ (oppro~. ~oc.) ~ ~ ~ ~ ~ \ I . ~ ~04-~ ~ , ~ ~ ~o , ~ ~ ~ ~ a ~ ~ ~ 5 ~ ti . ~ ~ ~ ~ ~ \ ~ ° \ ~ j` Ca1e poatifan ta the 7 ~ SE cana SWI/~ NWI/4 South line of the SW1/4 of the NWt/4 \ \ ~ . - - - - . \ _ ~ ~ 40TH AVENUE ~ ~ ~ 7 I I CALL BEF~tE YOU , ~ ~ ~ DANM I ( I ' Trae a r. ~ ~I~RDV~1D~ ~ CALL BEFORE YOU QIG 456-8000 ~ ; ; „~w ~i~i~ iauidid1°'° DRP,INAGE STRAi~THER S ADDITI~ I I I I . ~ ~ ~ ~ ' htC, ~ ADDITION POST-DEVELOPMENT DRAINAGE ~ I I Euv~nai 201~.A5 Iw~nrx Id~ I I ~ + qNl ENGINEERS dc LAND SURVEYORS ~ ~ ~ ~ k, h p,w, p,i ~ w N, 909 ARGUNNE ROAD, SP~KANE VA., 99212-2789 SII 1~ 0!' SBCTION 39 T.2b N R.I< i DRAINAGE BASINS , ~ IAGTIaI ~ A 0t I IPPlOM* I ~ ~ / g PI~NE 609) 926-132P vax csos~ sz~-i~ 14470 1 OF 1 SPOIIlVB COI/JV7'Y, ~AS87NCTON ~ m I at[ I REVISIONS / AS BUILT I 40Th Ar~. Eat ~ ot DhNnrn-IAoo Rood 6 I I I -T.,Zb N. R.44 N.W.M. o veyn1nn v I . Submittal Checklist - Sulbmittal # 2 for Road & Drainage Projects in Spokane Valley - Plats/Short Plats This form needs to be inclacded with each plan submittal to the Spokane Valley Engineer's Office. Proj ect Name: S TR&-ArTN m~ S AbD IT1 o rJ Spokane Valley Project No.: pE- Date: Proj ect Engineer: G 1-tvCIL S c KPS vr-l , P• E. Phone: 9Z4 -13?.Z Project Applicant: r>pNNOt STeAwTme*, Phone: "1- ? 58 ( A. Preliminary Process Prior to submittal of road and drainage plans, the following events are to have already occurred: At least one Pre-Design Meeting has been held with City staff at the Engineer's Office. B. Road and Drainage Plan Submittal The items listed below need to be provided as a minimum with each road and drainage plan submittal. Item Description (Yes) Road and drainage plans, one set. Yes Each plan sheet of record is signed and dated by the project applicant. (Ze:~ Drainage report, one copy. )~e The plans, drainage report, basin maps, and any other calculations are stamped, signed and dated by an engineer licensed in Washington. Mes) Prev* N/A Inspection agreement between the project applicant and its engineer. es Prev N/A Geotechnical report, one copy (Include all soil test pit/boring logs). Yes Prev 1q7 elX Structural pavement calculations, one set. Yes Prev %A) Cross-slope grade calculations - for road widening projects. ('Yes Prev N/A Fire district approval for private roads. es, Prev N/A Lot Plans (required for every lot with drainage easements). Yes Prev Any applicable State and Federal permits were obtained (i.e. HPA, JARPA, etc.) and a copy of the conditions is included in the plan submittal. ~ Yes Prev ~N/A,) Maintenance manual and sinking fund calculations for privately maintained facilities. Yes Prev (N/~ A draft copy of the Homeowner's Association CC&R's. Yes Prev 47TA-) Draft easement document for any easements. es NIA Erosion Control Plan to be included lan submittal. ~ (1 D ~ Yes Prev C/X) Sight distance analysis. *Prev = Previously accepted by the City Engineer QCT 3 0 2GO3 D _ , ~ I . STORMWATER DRAINAGE REPORT for the proposed plat of STRAWTHER'S ADDITION located in the NW of Section 33, T. 25 N., R. 44 E.W.M. Spokane County, Washington July 1, 2003 Project Sponsor: Donna Strawther (509) 467-7581 ti~ W~qsj , ~ Report Prepared By: ~ , ~o ~S-07 Simpson Engineers, Inc. North 909 Argonne Road Spokane, Washington 99212 ~~RES ~7/1 % ~ (509) 926-1322 ENGI NEER'S CERTI FlCA TION The design improvements shown in this set of plans and calculations conform to the applicable editions of the Spokane County Standards for Road and Sewer Construction and the Spokane County Guidelines for Stormwater Management. I approve these plans for construction. . CONTENTS Paize A. Proj ect Location . . . . . . . . . 2 B. Existing Site Topography. . . . . . . . 2 C. Project Description . . . . . . . . 2 D. Previous Reports . . . . . . . . . 3 E. Soils Description . . . . . . . . 3 F. Geo-Hazard Evaluation . . . . . . . . 3 G. Drainage Concept . . . . . . . . 4 H. Rainfall Data & Design Tools . . . . . . . 5 ' I. Drainage Basins . . . . . . . . . 5 J. Summary & Conclusion . . . . . . . . 8 APPENDIX: SupplementalInformation 1. Site in Relation to Spokane County Aquifer Sensitive Area (Spokane County C'ruidelines for Stormwater Management, Figure 6, p. 6-9) 2. Site Vicinity and Mapped Soils (excerpted from USDA Soil Conservation Service, Soil Survey of Spokane County, Washington, March 1968, Sheet Number 75) 3. Runoff Coefficients for Storm Sewers (Spokane County Guidelines for Stormwater Management, Table 1, p. 6-2) 4. Rational Formula Hydrology Calculations (4 sheets) (Basin E 1= Existing Conditions, and Basins P2, P3 & P4 = Proposed Conditions) 5. Proposed Culvert Capacity Calculations (2 sheets) dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 1 ~ PROJECT LOCATION The Strawther's Addition project site is located within the newly-formed City of Spokane Valley, on the northeasterly side of Dishman-Mica Road and on the west side of Pierce Road (extended), between 38th Avenue and 40th Avenue. The site is located in the southwest quarter of the northwest quarter of Section 33, Township 25 North, Range 44 East, W.M., in Spokane County, Washington. The site lies near the south limit of the Spokane-Rathdrum Aquifer, and is within the Spokane County Aquifer Sensitive Area and the Priority Sewer Service Area. EXISTING SITE TOPOGRAPHY The site is bounded on the southwest by Dishman-Mica Road, a two-lane Principal Arterial within a 60-foot right-of-way. To the east are existing single-family houses, platted as Chester Field Addition, and to the north are existing single-family houses, platted as Short Plat 743-92. Aside from the existing duplex near the southeast corner of the plat, the remainder of the site is covered with Ponderosa pine trees, native grasses and brush. A natural drainage gully extends th.rough the site, from an existing drainage easement on the north side of the site to an existing 18"-diameter CMP culvert under Dishman-Mica Road, draining to an apparent wetland area on the southwest side of the road. A proposed drainage easement through the site will connect the existing drainage easement to the existing culvert along the existing drainage course. The site has topographic high areas on the east and west portions, with the existing drainage gully in-between. On-site slopes range from very gentle to approximately 14%, facing primarily to the west, east and south. The local high points are located near the eastern plat boundary, where the Proposed cul-de-sac will be located, and in the west portion of the site. The lowest area on the site ' is in the drainage gully at the entrance to the existing culvert underlying Dishman-Mica Road. ' Refer to the Strawther's Addition Stormwater Draina e Plan ma for locations of existin g P g contours and proposed features described in this report. PROJECT DESCRIPTION , . The proposed plat of Strawther's Addition will subdivide approxunately 3.24 acres of mostly undeveloped land into seven residential lots, which will vary in size. The project site is irregular in shape, with the southeasterly portion occupied by an existing duplex. The duplex is accessed off 40th Avenue, while the remainder of the plat will be accessed off an existing cul-de-sac at the west end of 38`" Avenue at Pierce Road, from which a proposed private cul-de-sac will extend southward onto the site. The proposed cul-de-sac will provide direct access for the three lots nearest to the northeast corner of the site, while the three westerly lots of the plat will be accessed via a private driveway, to be located within an ingress-egress easement extending to the west off the west side of the on-site cul-de-sac. dnc:Projects/14470-drn.doc Simpson Engineers, lnc. 07/01/03 Page 2 ' PREVIOUS REPORTS , ' A Conceptual StoYmwater Manazement Plan was prepared for Strawther's Addition by J. Paul Ramer & Associates, Inc. in 1998. The general concepts presented in that plan are maintained in the present drainage plan for the project. A report letter titled Summary ofResults ofLimited Geotechnical Enzineerin-a Studv, dated April 29, 1998, was prepared for this site by Cummings Geotechnology. The findings from that study are used herein for soils-related aspects of the present drainage plan. Any specific conclusions or data from that study that are used herein are referenced as such. SOILS DESCRIPTION Soils at the site are mapped as being almost completely Clayton sandy loam (map symbol CuB), with the contact with Springdale gravelly sandy loam (map symbol SxB) located near the east plat boundary, as per Soil Survey of Spokane County, Washington: USDA Soil Conservation Service (now the Natural Resources Conservation Service), March 1968. Springdale soils are listed by Spokane County as being acceptable for standard drywell practice, but Clayton soils are not. However, soils testing performed by Cummings Geotechnology at the location of a proposed drywell at the northwest side of the proposed cul-de-sac (as specified by J. Paul Ramer & ' Associates, Inc.) indicates soils having a permeability of "several hundred inches per hour," with the recommendation that "a Type B drywell could function adequately as long as it is embedded at least 5 feet into the clean gravelly coarse sand" that was found at a depth of "6 feet to greater than , 10 feet." Refer to the attached excerpt from the S.C.S. soils map (Sheet Number 75) for location of the site relative to mapped soils. ' GEO-HAZARD EVALUATION "Geologically Hazardous Areas," as classified according to the characteristics described per the , Spokane County Critical Areas Ordinance, include those areas prone to erosion and landslide hazards. Based on our initial field investigation of the project site, we have determined that this site is not a Geologically Hazardous Area, due to the site having the following characteristics: a. Slopes at the site are all substantially less than 30% grade, with the steepest slopes being about 14% for a small, limited area in the southwest portion of the site, on the northwest side of the existing drainage course above the existing culvert under Dishman-Mica Road. b. Neither the Clayton sandy loam nor the Springdale gravelly sandy loam soils mapped at this site are identified by the USDA S.C.S. (now the Natural Resources Conservation Service) as having a"severe" potential for erosion (as listed in Appendix H of the Spokane County Critical Areas Ordinance). Clayton soils generally have moderate stability and moderate to dnc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 3 low resistance to erosion, while Springdale soils generally have moderate to high stability and moderate to low resistance to erosion. Our observations at the site did not reveal any evidence of erosion having occurred recently to any significant degree. c. The only significant hydraulic factor to consider at this site is the well-defined drainage channel crossing through the site, leading to the existing culvert under Dishman-Mica road. However, it does not contain a perennial stream, and was observed this spring to be dry and to drain a limited basin area in the immediate vicinity. There are no known springs, and no wet areas observed on the site. d. This site is not a landslide-prone area; no evidence of landslides was observed on the site, and the site soils are not alluvium, not landslide deposits, and not Latah formation. e. This site is not an area of uncompacted fill. f. The site is not unstable due to stream or streambank erosion. DR.AINAGE CONCEPT The proposed drainage design for this project is fairly straightforward and generally follows the recommendations established in Spokane County's Guidelines for S'tormwater Management. The developed site is proposed to be regraded such that all runoff water from the proposed asphalt surfacing will be collected and drained to a proposed drainage swale (grassed percolation area) for treatment and disposal. The swale is located near the northeast corner of the site, adjacent to the ' proposed access road/cu1-de-sac. The intention is to pos1t1on the swale in the location where soils testing was performed by Cummings Geotechnology, as described above (see "Soils Description"). The proposed site plan will result in two primary points of discharge: the existing culvert under Dishman-Mica Road, and the proposed drainage swale by the proposed cul-de-sac. Runoff under both existing (pre-platting) and proposed (post-platting) conditions were analyzed to assess the impacts of the site improvements on flows at the existing culvert, using a 50-year storm event for the basins that include off-site areas. Runoff flowing to the proposed drainage swale, which only occurs under proposed conditions and only includes on-site areas, is analyzed using a 10-year storm event. The total areas of drainage basins involved is the approximately the same under both existing and proposed conditions. The plan includes a private access drive to serve three of the proposed lots. The road will transect the existing drainage gully which drains to the existing culvert under Dishman-Mica Road, so a new culvert will be constructed under the private drive. Flows to the existing culvert under existing conditions, and to both the existing culvert and the new culvert under proposed conditions, are analyzed. The drainage basins are named as shown on the Stormwater Drainage Plan and detailed on the following pages. Refer to the Stormwater Drainage Plan for locations of drainage features described in this report. dnc:Projects/14470-dm.doc Simpson Engineers, Inc. 06/26/03 Page 4 , R:AINFALL DATA & DESIGN TOOLS The rainfall intensity-duration-frequency curve for both 10-year and 50-year recurrence intervals for the Spokane-Medical Lake-Reardon-Cheney-Rockford area, as presented in the February 1998 Addendum to Spokane County's Guidelines for Stormwater Management, in Figure 2, page 6-3, was adapted into tabular form for the rational formula hydrology calculations for the drainage basins under existing and proposed conditions. ' The intention in designing stormwater drainage facilities for this project was to follow the procedures, methods and referenced data in Spokane County's Guidelines for Stormwater Management (1998). Computations were performed using Spokane County-accepted methods and software programs, including rational formula hydrology for calculations of peak discharge to the culverts, and bowstring methodology for ponding volume vs. drywell outflow, adapted into an MS Exce12000 spreadsheet. The existing topogxaphy and proposed features and grades shown on the Stormwater Drainage Plan map were drawn, and some of the areas were calculated, using AutoCAD Land Development. Runoff coefficient ("C") values are based on 2% to 10% slopes, as per "Runoff Coefficients for Storm Sewers" (C'ruidelines, February 1998, Table 1, p. 6-2). For Proposed conditions, new houses are assumed to be 2,000 sq. ft. and new concrete driveways are assumed to be 1,000 sq. ft. Separate hydrology calculation sheets for all described basins and conditions are included in this report. DRAINAGE BASINS Drainage Basin Name: Basin El Condition: Existing Basin Description: Area draining to existing culvert under Dishman-Mica Road under existing conditions. Total A.rea of Basin: 157,920 sq. ft. = 3.625 acres Impervious Areas: V0Kk,_1_ dO Asphalt (N. %2 D.-Mica Rd.) = 10,230 sq. ft. = 0.235 acre na, C= 0.90 House Roofs = 5,000 sq. ft. = 0.115 acre a, C= 0.90 Concrete Driveways = 1,500 sq. ft. = 0.034 acre Q C= 0.80 r , Pervaous Areas: Road Shoulder = 3,720 sq. ft. = 0.085 acre Q C= 0.50 Natural (on-site) = 110,395 sq. ft. = 2.534 acre Q C= 0.22 Lawn/Landscaping (off-site) = 27,075 sq. ft. = 0.622 acre Q C= 0.15 Point of concentration: Entrance to existing culvert under Dishman-Mica Road. 50-year Storm Discharge: Q50 =(C) (i50) (A) = 3.79 c.f.s. (see hydrology calculation sheet) dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 5 DRAINAGE BASINS - continued 1 Drainage Basin Name: Basin P1 Condition: Proposed Basin Description: Area draining to proposed drainage swale by proposed cul-de-sac. Total Area of Basin: 30,355 sq. ft. = 0.697 acres Impervious Areas: Asphalt (new cul-de-sac) = 8,500 sq. ft. = 0.195 acre Q C= 0.90 Concrete Curb & Gutter = 720 sq. ft. = 0.017 acre (~a, C= 0.80 House Roofs = 3,000 sq. ft. = 0.069 acre (~a, C= 0.90 Concrete Driveways = 3,000 sq. ft. = 0.069 acre (cr, C= 0.80 ' Pervious Areas: Lawn/Landscaping = 15,135 sq. ft. = 0.347 acre (a) C= 0.15 Water Quality Treatment Area: (8,500 + 720 + 3,000) = 12,220 sq. ft. Water Quality Treatment Volume: (12,220 sq. ft.) x(1/2") x(1 ft./12") = 509 cu. ft. Point of concentration: Curb Inlet to proposed Drainage Swale 1. 10-year Storm Discharge: Qlo =(C) (i,o) (A) =1.08 c.f.s. (see hydrology calculation sheet) ' ~ * * Proposed Stormwater Treatment/Disposal Facility Name: Drainne Swale 1 ' Swale Location: Near northeast corner of the site, on northwest side of proposed cul-de-sac. Swale Floor Area =(24' x 26') +(16' x 10') +'/4 7c(16')2 = 624 + 160 + 201 = 985 sq. ft. Swale Floor Perimeter = 125 LF with 3:1 slopes on all sides. Swale Volume @ 6" Depth: Water Qualitv Treatment Capacitv 1 . _(0.5 ft. depth)(swale floor area) +(1/2 x 0.5 x 1.5)(swale floor perimeter) ' = 0.5 (985) + 0.375 (125) = 492 + 47 = 539 cu. ft. 539 cu. ft. provided > 509 cu. ft. required for entire Basin P1 Drainage Swale 1 is OK for runoff treatment of entire Basin P1 @ 6" depth Outflow StoraQe Capacitv Swale Volume @ S" Depth: _(0.67 ft. depth)(swale floor area) +(1/2 x 0.67 x 2.0)(swale floor perimeter) = 0.67 (985) + 0.67 (125) = 656 + 83 = 739 cu. ft. 739 cu. ft. provided > 397 cu. ft. required with 0.3 c.f.s. outflow Drainage Swale 1 is OK for storage @ 8" depth w/outflow via one Type "A" drywell (Note: Type "B" specified on plans, so drywell can be set deeper into coarse soil) dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 07/01 /03 Page 6 DRAINAGE BASINS - continued Drainage Basin Name: Basin P2 Condition: Proposed Basin Description: Area draining to proposed culvert under proposed driveway access road. Total Area of Basin: 74,485 sq. ft. = 1.710 acres Impervious Areas: Asphalt Pavement = 0 sq. ft. = 0.000 acre a, C= 0.90 House Roofs = 10,000 sq. ft. = 0.230 acre (a), C= 0.90 Concrete Driveways = 3,500 sq. ft. = 0.080 acre Q C= 0.80 Pervious Areas: N. %2 Gravel Access = 1,500 sq. ft. = 0.034 acre na, C= 0.55 Lawn/Landscaping (on-site) = 32,410 sq. ft. = 0.744 acre (~a, C= 0.15 Lawn/Landscaping (off-site) = 27,075 sq. ft. = 0.622 acre na, C= 0.15 Point of concentration: Entrance to proposed culvert under driveway access road. 50-year Storm Discharge: QSp =(C) (iso) (A) = 1.86 c.f.s. (see hydrology calculation sheet) * * * Drainage Basin Name: Basia P3 Condition: Proposed Basin Description: Area draining directly to existing culvert under Dishman-Mica Road only, under proposed conditions (excluding flow through proposed culvert). Total Area of Basin: 53,080 sq. ft. = 1.219 acres Impervious Areas: Asphalt (N. %2 D.-Mica Rd.) = 10,230 sq. ft. = 0.235 acre Q, C= 0.90 House Roofs = 3,000 sq. ft. = 0.069 acre (~a, C= 0.90 Concrete Driveways = 1,000 sq. ft. = 0.023 acre (~a, C= 0.80 Pervious Areas: S. '/2 Gravel Access = 1,500 sq. ft. = 0.034 acre (~a, C= 0.55 Road Shoulder = 3,720 sq. ft. = 0.085 acre na, C= 0.50 Lawn/Landscaping (on-site) = 33,630 sq. ft. = 0.772 acre Q C= 0.15 Point of concentration: Entrance to existing culvert under Dishman-Mica Road. 50-year Storm Discharge: QSp =(C) (iso) (A) = 1.89 c.f.s. (see hydrology calculation sheet) dnc:Projects/14470-dm.doc Simpson Engineers, Jnc. 06/26/03 Page 7 , SLMMARY & CONCLUSION Under existing conditions, an area of approximately 3.6 acres drains to the existing culvert under Dishman-Mica Road. Of that drainage basin (`Basin E1"), about 0.8 acres is off-site and adjacent to the subject project site, consisting of existing houses and yards, and the remaining 2.8 acres is on-site (in an undeveloped condition). Of that 2.8 acres on-site, an area of about 0.7 acres will be removed from the area draining to the existing culvert, so that even after construction of houses and driveways, the calculated flow to the existing culvert under Dishman-Mica Road is not substantially affected (see table below). For the 0.7 acres referenced above ("Basin P 1"), the proposed plan calls for construction of an asphalt road and cul-de-sac, which will be graded to drain to a proposed drainage facility ("Swale 1"). All proposed asphalt will drain to this swale for stormwater treatment and disposal. Although the calculations show that a Type "A" drywell would be sufficient, a Type "B" drywell is specified on the plans so that it extends sufficiently into the coarser soils (per the recommendation by Cummings Geotechnology - see section titled Soils Description on page 3 of this report). Table 1: Comparison of Pre-Development & Post-Development Flows to Existing Culvert Drainage Basin Storm Calculated Point of Basin Name Condition Event Peak Dische Concentration _ Culvert E 1 Existing r 50_year ~ 3.79 _-]--Existinq P 2 ~ Proposed ~ 50-year ~ 1.86 Proposed Culvert P 3 1 Proposed J_ _ 507year 1.89 Existing Culvert _ P 2+ P 3~ Proposed ~ 50-year ~ 3.75 ~ Existinq Culvert Note: Basin P2 drains through the proposed culvert, then to the existing culvert. Basin P3 is the area that drains directly to the existing culvert only, after development. ' Calculated net impact on existing culvert under Dishman-Mica Road. 50-year peak discharge is basically unchanged (decreased from 3.79 c.f.s. to 3.75 c.f.s.). (Note: Actually, time of concentration for P2 and P3 differ slightly, so the combined peak would actually be lower than 3.75 c.f.s.). In conclusion, it is our opinion that construction of houses and associated improvements in this plat (as assumed per the modeled drainage basins) should not cause any significant increase in stormwater runoff at the "downstream" plat boundary, and therefore should not cause nor exacerbate any runoff-related problems that may exist or occur downstream of this site. dhc:Projects/14470-drn.doc Simpson Engineers, Inc. 06/26/03 Page 8 -R ft43E R44E R45E T 29 Spokane CountY T p,quifer Sensitive Ama 29 ~ F 11 T ; • : : 7$ ,~1 t , 1 1 ~ ~ • ! ~ ' ~ i , 2 g `v T 2 7 . i 7` i ~ ~ . 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' . . - - ~ ' r $tCi • Sf ,,~.L.~.~ . _ - ; . ~ B r►o..~ ~ , . ~ • ~ ,.r : 1 , Bag BhD MaC~.~ StC\ 1 Nlile scale l: 20 000 ' fr a, ^.f -i.~af.".~~in.t.sQ ,r~ 3.~ Y . = , ~•JPC ~ • x~`,`~~~, ~-.1 - ~ 0 ~ f TAB LE 1 RUNOFF COEFFICIENTS FOR STORM SEWERS ~ ROLLING HILLY FLAT 2°6 - 10% OVER 10`6 Pavement and Roofs . . . . . . . . . . . . . . 0.90 Cu.9U) 0.90 Earth Shoulders . . . . . . . . . . . . . . . 0.50 CO-50 0.50 Drives and Walks . . . . . . . . . . . . . . . 0.75 CO .80 U.85 Gravel Pavement . . . . . . . . . . . . . . . 0.50 CO-55) 0.60 City Business Areas . . . . . . . . . . . . . 0.80 0.85 0.85 Lawns, Sandy Soil . . . . . . . . . . . . . . 0.10 CO.15) 0.20 Lawn, Heavy Soil . . . . . . . . . . . . . . . 0.17 0.22 0.35 Grass Shoulders . . . . . . . . . . . . . . . 0.25 0.25 0.25 Side Slopes, Earth . . . . . . . . . . . . . . 0.60 0.60 0.60 Sfde Slopes, Turf . . . . . . . . . . . . . . 0.30 0.30 0.30 Median Areas, Turf . . . . . . . . . . . . . . 0.25 U.3U U.30 Cultivated Land, Clay and Loam 0.50 0.55 0.60 ~ Cultivated Land, Sand and Gravel 0.25 U.30 U.35 Industrfal Areas, Light . . . . . . . . . . . 0.50 0.70 0.80 Industrial Areas, Heavy . . . . . . . . . . . U.60 U.80 0.9U Parks and Cemetaries . . . . . . . . . . . . . U.10 0.15 0.25 ~ Playgrounds . . . . . . . . . . . . . . . . . 0.2U 0.25 0.30 Woodland and Forests . . . . . . . . . . . . . 0.10 0.15 0.20 Meadows and Pasture Land . . . . . . . . . . . 0.25 0.30 0.35 , ~ts e 0, *SINGLE FAMILY RESIDENTIAL (Dwelling Unit/Gross Acre) ' (Trees (Sandy and Gravelly Soil) ~ ' 0-1. U DU/GA . . . ' . . . . . . . U.1.5 1. 0-1.5 DulGA . . . . . . . . . _ o. 20" 1.5-3.0 DU/GA . . . : . . . . : . U.25 3. 0-3. S DU/GA . . . . . . . . . . .0. 30 3. S-4. U DU/GA . . . . . . . . . . U. 35 4.0-6.0 DUlGA . . . . . . . . . . 0.40 6. U-9. U DU/GA . . . . . . . . . . 0.60 9. 0-15. U' DU/GA . . . . . . . . . . 0.70 * Assumes flat lot plus one-half width bf abutting street. Other configurations . should be checked by combining individual runoff-factors for each various surface. Date 4/4/84 - TAB LE 1 6-2 1 ' RATIONAL FORMULA HYDROLOGY Drainage Basin Anaysis for 50-year Storm Retum Frequency Event Project Name: Strawther's Addition Project: 14470 Drainage Basin Name: Basin E1 Condition: Existing Designer: DHC Basin Description: Total area draining to existing culvert Date: 26-Jun-03 Point of Concentra6on: Entrance to existing cufvert under Dishman-Mica Road Disk File: 14470.xls RAINFALL INTENSITY-DURATION 50-Year Storm Retum Frequency SUBAREAS Time Time Storm Description Acres C A'C Incrmnt. Incrmnt. Intensity (minutes) (seconds) (in.mr.) Asphalt Pavement 0.235 0.90 0.212 Tc = 8.33 500.0 3.66 = Intensity Q Tc Road Shoulder 0.085 0.50 0.043 5 300 4.58 House Roofs 0.115 0.90 0.104 10 600 3.20 Conc,rete Drives 0.034 0.80 0.027 15 900 2.47 Landscape (offsite) 0.622 0.15 0.093 20 1200 1.98 Natural (on-site) 2.534 0.22 0.557 25 1500 1.67 30 1800 1.46 Total Acres = 3.625 35 2100 1.30 Composite Coefficient (C)= 0.29 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION (Tc), minutes 55 3300 0.92 60 3600 0.87 Overland flow Channel flow 65 3900 0.82 70 4200 0.80 Seament A: L2 = 170 75 4500 0.77 Ct = 0.15 Z1 = 10 80 4800 0.75 L1(A) = 260 Z2 = 13 85 5100 0.72 N(A) = 0.4 B= 5 90 5400 0.70 S(A) = 0.03 n= 0.03 95 5700 0.68 Tc (A) = 6.97 s= 0.018 100 6000 0.67 d= 0.24 Seament B: L1(B) = 0 Tc (ch) = 1.36 Exolanation: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (overland) + Tc (channel) S(B) = 0 Tc(tot.) = 8.33 IVote: Tc (total) = 5 minutes minimum Tc (B) = 0.00 Intensity = 3.66 Ct = 0.15 = Coefficient for ovedand flow L1 = Length of overland flow segment(s), in feet Calculated Channel Flow Data: ' N = overiand friction factor S= average slope of overland flow, in ft./ft. Area = 1.83 Sq. Ft. Tc (overland) = Ct'(L1*N/S^0.5)^0.6) W.P. = 10.47 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.17 Ft. Z1 = inverse of cross slope of backslope of channel V= 2.08 Ft./Sec. ' Z2_ inverse of cross slope of foreslope of channel Tc(ch) = 1.36 Minutes B Bottom width of channel (gutter or ditch), in feet Q(est) = 3.80 C.F.S. n= Manning's friction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = 1.06 ' d= depth of flow in channel, in feet Flow Regime = Supercritical Flow Tc (channel) = L / ((1.486/n)+R^0.67s^0.5) / 60 Area = d'B+d^2/2"(Z1+Z2) Calculated Flow Depth in Channel: W.P. = B+d'(1/sin(atn(1/Z1))+1/sin(atn(1/Z2))) R= Hydraulic Radius = Area/ Wetted Perimeter ~ d= 0.24 Feet ~ V = Velocity = 1.486/n'R^.667*s^.5 Tc (ch) = Length (ft) / Velocity (fps) / 60 Calculated Peak Discharge, 50-Year Storm: Q(est) = Estimated Flow (verifies depth, d) = V*A Froude Number = V/(g*0.5d)^0.5 ~ Q= 3.79 C.F.S. ~ Peak Discharge = Q= C'I"A (cubic ft. per sec.) ' Simpson Engineers, Inc. 909 N. Aigonne Road, Spokane, WA 99212 (509) 926-1322 Faar: (509) 926-1323 14474hyd - Basm E t , ' RATIONAL FORMULA HYDROLOGY & BOWSTRING CALCULATIONS DRAINAGE BASIN ANALYSIS & DESIGN for 10 YEAR STORM EVENT Simpson Engineers, Inc. 909 N. Arganne Road, Spokane WA 99212 Date: 07101l03 Sponsor Name: Donna Strawther Design: Doug Christenson Project Name: Strawther's Addition Project: 14470 Site Location: 38th Avenue, nortfi side of Dishman-Mica Road Basin Name: Basin P1 Basin Description: Area draining to proposed swale by cul-de-sac G.P.A Name: Swale 1 G.P.A. Location: Northeast portion of site Site Condition: PrOposed Point of Concentration: Curb Inlet into proposed swale SUBAREAS: TIME OF CONCENTRATION (minutes): Description Acres C A'C Tc (overland Row) Tc (gutter flow) Asphalt Pavement 0.195 0.90 0.176 House Roofs 0.069 0.90 0.062 Ct = 0.15 L2 = 150 Concrete Curb & Gutter 0.017 0.80 0.014 Z1 = 50 Concrete Driveways 0.069 0.80 0 055 L1(A) = 70 Z2 = 0.167 Gravel Surfacing 0.000 0.55 0.000 N(A) = 0.3 B= 0 , Pervious/Landsqping 0.347 0.15 0.052 S(A) = 0.01 n= 0.013 Tc (A) = 3.71 d 0.~5 Total Basin Area, acres = 0.697 Composite Runoff Coefficient = 0.514 Li (B) = 150 Tc (gut.) 1.26 Combined (Area ' Runoff Coefficient) = 0.358 N(B) = 0.016 Tc(A+B) • 4.59 S(B) = 0.016 Tc total 5.84 Intensity : 3.02 RUNOFF WATER (1UALITY PARAMETERS: Tc (B) = 0.9 Holding 5.34 Impervious Treatment Area = 12,220 sq. ft. Treatment Volume Generated = 509 cu. ft. 0(es6mated @ d) = 1.09 c.f.s. Time of Concentration = 5.84 minutes DRAINAGE FACILITY DATA for Swate 1 Total Swate Floor Area = 985 sq. ft. Swale Floor Perimeter Q 3:1 = 125 lin. ft. PEAK DISCHARGE, 10 YEAR STORM: Treatment Volume Provided Qa 6" = 539 cu. ft Storm Storage Provided @ 8" = 739 cu. ft. Q= C' I' A= ~ 1.08 C.F.S. ~ BOWSTRING CALCULATIONS NUMBER and TYPE of DRYWELLS PROPOSED• #1 #2 it3 #4 it5 #6 #7 , Time Time Intensity Q dev. V in V out Storage 1 Single-Barrel (City of Spokane Type 1) Incrmnt. Incrmnt. 0 Double-Barrel (City of Spokane Type 2) (min.) (sec.) (in./hr) (cfs) (cu. k.) (cu. ft.) (cu. ft.) 01•60l (A`c•0) (outf.•uz) c"sl ' Outflow Provided: 0.3 c.f.s. 5.84 350.60 3.02 1.08 509 105.18 404. 5 300 3.18 1.14 458 90 368 ' 10 600 2.24 0.80 577 180 397 15 900 1.77 0.63 647 270 377 WATER QUALITY TREATMENT VOIUME: 20 1200 1.45 0.52 686 360 326 25 1500 1.21 0.43 702 450 252 Required G.P.A. ponding volume: 30 1800 1.04 0.37 715 540 175 Impervious "208" Area x 1/2" = 509 cu. ft. 35 2100 0.91 0.33 724 630 94 volume provided at 6" depth = 539 cu. ft. 40 2440 0.82 0 29 740 720 20 Conclusion: OK . 45 2700 0 74 0.27 748 810 -62 50 3000 0.68 0.24 760 900 -140 55 3300 0.64 0.23 784 990 -206 STORM STORAGE VOLUME: 60 3600 0.61 0.22 813 1080 -267 65 3900 0.60 022 864 1170 -308 Maximum storage required = 397 cu. ft. 70 4200 0.58 0.21 898 1260 -362 volume provided at 8" depth = 739 cu. R. 75 4500 0.56 0.20 927 1350 -423 Conclusion: OK 80 4800 0.53 0.19 935 1440 -505 85 5100 0.52 0.19 973 1530 -557 90 5400 0.50 0.18 989 1620 -631 DRYWELL REQUIREMENTS: 95 5700 0.49 0.18 1022 1710 -688 100 6000 0.48 0.17 1053 1800 -747 1 Single (Type 1) 0 Double (Type 2) Slmpson Englneers, Inc. 909 North Argonne Road, Spokane, WA 99212 Phone: (509) 926-1322 fax: (509) 926-1323 Basin P1 1 RATIONAL FORMULA HYDROLOGY Drainage Basin Anaysis for 50-year Storm Retum Frequency Event Project Name: Strawther's Addition Project: 14470 Drainage Basin Name: Basin P2 Condition: Proposed Designer: DHC Basin Description: Area draining to proposed culvert under access road Date: 26-Jun-03 Point of Concentration: Entrance to proposed culvert under gravel road Disk File: 14470.xls RAINFALL INTENSITY-DURATION 50-Year Storm Return Frequency SUBAREAS Time Time Storm Description Acres C A`C Incrmnt. Incrmnt. Intensity (minuces) (seconds) Or,.mr.) Asphalt Pavement 0.000 0.90 0.000 Tc = 7.96 477.9 3.76 = Intensity Q Tc N. 1/2 Gravel Road 0.034 0.55 0.019 5 300 4.58 House Roofs 0.230 0.90 0.207 10 600 3.20 Concrete Drives 0.080 0.80 0.064 15 900 2.47 Lawn/Landscape 1.366 0.15 0.205 20 1200 1.98 25 1500 1.67 30 1800 1.46 Total Acres = 1.710 35 2100 1.30 Composite Coeffic+ent (C)= 0.29 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION (Tc), minutes 55 3300 0.92 60 3600 0.87 Overiand flow Channel flow 65 3900 0.82 70 4200 0.80 Seament A: L2 = 100 75 4500 0.77 Ct = 0.15 Z1 = 10 80 4800 0.75 L1(A) = 260 Z2 = 13 85 5100 0.72 N(A) = 0.4 B= 5 90 5400 0.70 S(A) = 0.03 • n= 0.03 95 5700 0.68 Tc (A) = 6.97 s= 0.018 100 6000 0.67 d= 0.16 Seament B: L1(B) = 0 Tc (ch) = 1.00 Exolanation: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (overland) + Tc (channel) S(B) = 0 Tc(tot.) = 7.96 Nofe: Tc (total) = 5 minutes minimum Tc (B) = 0.00 Intensity = 3.76 Ct = 0.15 = Coefficient for overland flow L1 = Length of overland flow segment(s), in feet Calculated Channel Flow Data: N = overiand friction factor S= average slope of overland flow, in ft./ft. Area = 1.10 Sq. Ft. Tc (overland) = Ct'(L1*N/S^0.5)^0.6) W.P. = 8.72 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.13 Ft. Z1 = inverse of cross slope of backslope of channel V= 1.67 Ft./Sec. Z2 = inverse of cross slope of foreslope of channel Tc(ch) = 1.00. Minutes B= Bottom width of channel (gutter or ditch), in feet Q(est) = 1.85 C.F.S. n= Manning's friction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = 1.04 d= depth of flow in channel, in feet Flow Regime = Supercritical Flow Tc (channel) = L / ((1.486/n)*R^0.67s^0.5) / 60 Area = d`B+d^2/2"(Z1+Z2) Calculated Flow Depth in Channel: W.P. = B+d`(1/sin(atn(121))+1/sin(atn(122))) R= Hydraulic Radius = Area/ Wetted Perimeter ~ d= 0.16 Feet ~ V = Velocity = 1.486/n'R^.667's^.5 Tc (ch) = Length (ft) / Velocity (fps) / 60 Calculated Peak Discharge, 50•Year Storm: Q(est) = Estimated Flow (verifies depth, d) = V'A Froude Number = V/(g'0.5d)^0.5 ~ Q= 1.86 C.F.S. ~ Peak Discharge = Q= C"I*A (cubic ft. per sec.) Simpson Engineers, Inc. 909 N. Argonne Road, Spokane, WA 99212 (509) 926-1322 Fax: (509) 926-1323 1ea704,ya - easin PZ RATIONAL FORMULA HYDROLOGY Drainage Basin Maysis for 50 year Storm Retum Frequency Event Project Name: Strawther's Addition Project: 14470 Drainage Basin Name: Basin P3 Condition: Proposed Designer: DHC Basin Description: Area draining to existing culvert only (not via new culvert) Date: 26-,lun-03 Point of Concentration: Entrance to existing culvert under Dishman-Mica Road Disk File: 14470.xls RAINFALL INTENSITY-DURATION 50-Year Storm Retum Frequency SUBAREAS Time Time Storm Description Acres C A'C Incrmnt. IncRnnt. Intensity (minutes) (seconds) (in.fir.) Asphalt Pavement 0.235 0.90 0.212 Tc = 6.97 418.0 4.04 = Intensity aQ Tc Road Shoulder 0.085 0.50 0.043 5 300 4.58 House Roofs 0.069 0.90 0.062 10 600 3.20 Concrete Drives 0.023 0.80 0.018 15 900 2.47 Lawn/Landscape 0.772 0.15 0.116 20 1200 1.98 S. 1/2 Gravel Road 0.034 0.55 0.019 25 1500 1.67 30 1800 1.46 Total Acres = 1.218 35 2100 1.30 Camposite Coefficient (C)= 0.39 40 2400 1.18 45 2700 1.07 50 3000 1.00 TIME OF CONCENTRATION (Tc), minutes 55 3300 0.92 60 3600 0.87 Overland flow Channel flow 65 3900 0.82 70 4200 0.80 Sepment A: L2 = 0 75 4500 0.77 Ct = 0.15 Z1 = 0 80 4800 0.75 L1(A) = 300 Z2 = 0 85 5100 0.72 N(A) = 0.4 B= 0 90 5400 0.70 S(A) = 0.04 n= • 0 95 5700 0.68 Tc (A) = 6.97 s= 0 100 6000 0.67 d= 0.00 Seament B: L1(B) = 0 Tc (ch) = 0 Explanation: N(B) = 0 Tc(A+B) = 6.97 Tc (total) = Tc (ovedand) + Tc (channel) S(B) = 0 Tc(tot.) = 6.97 Note: Tc (total) = 5 minutes minimum Tc (B) = 0.00 Intensity = 4.04 Ct = 0.15 = Caefficient for overland flow L1 = Length of overland flow segment(s), in feet Calculated Channel Flow Data: N = overland friction factor S= average slope of overland flow, in ft./ft. Area = 0.00 Sq. Ft. Tc (overland) = Ct*(L1*N/S"0.5)^0.6) W.P. = 0.00 Ft. L2 = Length of flow in channel (gutter or ditch), in feet R= 0.00 Ft. Z1 = inverse of cross slope of baclcslope of channel V= 0.00 Ft./Sec. Z2 = inverse of cross slope of foreslope of channel Tc(ch) = 0.00 Minutes B= Bottom width of channel (gutter or ditch), in feet Q(est) = 0.00 C.F.S. n= Manning's fiction factor (0.016 for asphalt) s= longitudinal slope of channel, in ft./ft. Froude Number = N.A. d= depth of flow in channel, in feet Flow Regime = N.A. Tc (channel) = L / ((1.486/n)"R^0.67s^0.5) / 60 Area = d"B+d^2/2'(Z1+Z2) Calculated Flow Depth in Channel: W.P. = B+d'(1/sin(atn(1/Z1))+1/sin(atn(122))) R= Hydraulic Radius = Area/ Wetted Perimeter ~ d= 0.00 Feet ~ V = Velociry = 1.486/n'R^.667's^.5 Tc (ch) = Length (ft) / Velocity (fps) / 60 Calculated Peak Discharge, 50-Year Storm: Q(est) = Estimated Flow (verifies depth, d) = V*A Froude Number = V!(g"O.Sd)^0.5 ~ Q= 1.89 C.F.S. ~ Peak Discharge = Q= C"I•A (cubic ft. per sec.) Simpson Engineers, lnc. 909 N. Argonne Road, Spokane, WA 99212 (509) 926-1322 Fax: (509) 926-1323 1u7047yd - easi, a3 Circular Cnannel Analysis & Design , Solved with.Manning's Equation Open Channel - Uniform flow Worksheet Name : Strawthe,r'.s Addition Comment : Proposed Culvert under access driveway Solve For Actual Depth Given Input Data : Diameter 1.00 f t ~ ~Z Slope . . . . . . . . . . . . . 0 . 0200 f t f ft ~ o ,at l4o r-.F MarrMing ` s n . . . . . . . 0 . 024 = e-MI? Discharge......... 1.86 cfs = q,o PZ- ~ Computed Results : Deptn 0.61 ft Velocity.......... 3.74 fps FZ ow Area . . . . . . . . . 0. 5.Q s f Critical Depth.... 0.58 f-t Critical Slope.. . . 0.0227 ft/ft Percent Full...... 60.57 0 Fzll Capacity 2.73 cf s QMAX @.94D........ 2.94 cfs Froude Number..... 0.92 (flow is Subc-ritical ) Open Channel Flow Module, Version 3.21 (c) 1990 Haestad Metnods, Inc. * 37 SrQOkside Rd *Waterbury, Ct 06708 i~ Circular ehannel Analysis & Design Solved with Manning's Equation Open Channel - Uniform flow Worksheet Name: Strawther's Addition Comment: Froposed C'ulvert under access driveway Solve For Full Flow Capacity Given Input Data: I?iameter.......... 1. Oa f t Slope 0.0200 f.t/ft Marrrting t s rt 0.024 Discharge......... 2.73 cfs = APFROx, ~•5X Q~o . , Cu LvEf~T ~ ~ Computed Results: Full Flovr Capacity 2.73 cf s Full Flow Depth........ 1.00 ft Velocity.......... 3.47 fps Flow Area......... 0.79 sf erztzcal Depth.... 0.71 ft Critical Slope.... 0.0277 ft/ft Fercent Full . . . . . . 100.00 0 Full Capacity..... 2.73 cfs QMAX @.34II........ 2.94 cfs Froude Number..... FULL ' Open Channel Flow Module, Version 3.21 (c) 1990 Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct 06708