Loading...
The URL can be used to link to this page
Your browser does not support the video tag.
27238 PE-1684F RIDGEMONT EST N
1 I 4 I~ L7 z 0 I fN fL 07 I I I I J I W IL I 11 Uj s I° m LiJ U I ro ~ I U.S. STANDARD SIEVE SIZES C] O W_ W.- M L Q N 100 0 90 10 80 20 Q Z 1..,_.! (A 70 30 Z C/) Q 60 40 W F L~ z 50 50 ~ : 11111 1 11 1 z C ) L.j 1 40 so 1 1 W - - I U LtJ 30 70 CK 20 80 10 90 0 100 10 1 0.1 0.01 0.001 GRAIN SIZE (INCHES) PROJECT NAME: RNgemont Estates Seventh PROJECT NO.: SIMENG S9701A DATE: March 10, 1997 SAMPLE LOCATION: Unknown - Sampled by CI' SAMPLE DESCRIPTION: Dark Brown Silty Gravel GM PERCENT PASSING #4: 41X PERCENT PASSING M#200: 22X TEST METHOD: AST D-422, D-1140 REFERENCE NO.: SL2452 REMARKS/DEVIATIONS: In-Situ Moisture Content = 9.2saQ SIEVE ANALYSIS RESULTS 0;ee 5 T r'Z 2a i a OEOTECHNiCAL ENOINEERINO & MATERIALS TESTINO PLATE LOCAL ACCESS PAVEMENT STRUCTURES AVERAGE DAILY TRAFFIC SOIL TYPE 0 - 200 200-600 600+ Gw 20@/6" 2"/6" 218/6" GP 211/6" 21117" 211/7" CGN4) 211/6" 2"/7",,l 2"/8" GC 21117" L"/Q"! 311/611 J Sw 2"/6" 21117" 2 "/7" SP 2"/6" 211/7" 2"78" S M 201/711 211/611 311/611 SC Pavement Design ML 3176" 311/8"! 4"/6" CL Pavement Design OL 411/7" 511/71' 5"781' MH Pavement Design OH Pavement Design PT Pavement Design 1) Soil type is classified by the Unified Soil Classification System. 2) Required thickness is given as inches of asphalt concrete pavement over inches of crushed surfacing. SPOKANE COUNTY ALTERNATE PAVEMENT DESIGN (INTERIM) J Stormwater Drainage Report III. ROADWAY SURFACING DESIGN: The Spokane County Alternative Pavement Design (Interim) for Local Access Pavement Structures was used for design of the roadway surfacing. From the table, Local Access Pavement Structures, the following information is needed to determine the required surfacing depths. 1) The type of street must be local access. 2) Soil type (as classified by the United Soil Classification System) 3) The average daily traffic, ADT Street Tyne: Limerick Drive, Rotchford street and Moore Court are designated as local access (residential). Soil Type: In accordance with "Soil Survey, Spokane County, Washington" by United States Department of Agriculture, Soil Conservation Service, 1968, the soil found at the site is categorized as: GmB, Garrison very gravelly loam, similar to Garrison gravelly loam, except that the surface layer is very gravelly. Average Daily Traffic. ADT: Limerick Drive will have average daily traffic counts of less than 200. In the future, this road will be extended north and will connect to 16th Avenue, and the ADT count will probably increase to the 200-600 range. Therefore, this road will be constructed at 100% build out for the future condition. The remaining roads, Moore Court and Rotchford Street, will be cul-de-sacs or short cross streets each with average daily traffic counts of less than 200. Design From the table, 2 inches of asphalt concrete pavement over 7 inches of crushed surfacing is required for Limerick Drive. From the table, 2 inches of asphalt concrete pavement over 6 inches of crushed surfacing is planned for Rotchford Street and Moore Court. Try a depth of 1.2' V=1.486 R2/3 S 1/2IR = Area n } Wetted perimeter = 2'x1.21+(2x1.2xl.2) - 5.28 s.f. 2 +2(1.22+2.42) : • 7.36 ft., J • is R - .717 V - 1.486 (.717)2/3(.02)l/2- 5.61 fps .03 Q - VA - 5.61 fps x 5.28 of - 29.6 cfs . - 30 cfs . . d - 1.2' Solve Dc: Try 1.3' 9 Lb '+Z DO '7 D. 3/2 b+20Dc Q 32.2 (2+2x1.3)3 X 1.33/2= 30.9 cfs (2+2X2X1.3) - ti 30.9 cfs - 30 cfs do = 1.3' Dc > Dn, flow is supercritical. Since the flow is supercritical, care should be taken to provide a proper de- sign at points where horizontal and/or vertical alignment change. A free board of .30d should be applied D - .30 X 1.2 - 1.56' V - 5.6 fps > maximum allowable. Provide rip rap. (Refer to Section 4.5. ) 4-4 _ Detention/.Retention Systems - The peak rate of run-off from an existing site shall not be increased due to the proposed development for a given design storm. Therefore, a retention/deten- tion facility on-site will be required. Date: 4/4/84 4-4.2 Drywells - Precast concrete dry- wells, as shown on County standard drawings, may be used to retain storm drainage in.soils with a very rapid per- meability. Types A and B Drywells in the following soils may 'be designed to infiltrate a rate of flow of 0.3 cfs and 1.0 cfs respectively: Bong Marble Bonner Phoebe Garrison Springdale agan The locations of these soil types are shown in the Soil Conservation Service Soil Survey for Spokane County. The drainage, report shall include a copy of the;SCS map with the subdivision plotted thereon. The County Engineer shall re- quire the developer to provide a sieve analysis and soil type test from a soils laboratory acceptable to the County En-. gineer if there is a question regarding the above soil types. In rural areas, as defined in Spokane County Road Standards, open gravel dry- wells may be permitted in lieu of the precast concrete drywells. Precast concrete drywells proposed for use in other soils than those shown above and all open gravel drywells shall be designed according to percolation rates determined by a field test con- forming to the Manual of Septic tank practice. A County inspector shall be present during all percolation tests. A percolation test calculation sheet signed and sealed by a registered civil engineer shall be submitted. The per- colation rate shall be equal to or greater than 72 inches per hour to be acceptable for drywell construction. 4-4.2 Storage Facilities - Detention storage facilities may be used to regulate flow rates. An overflow type storage system which regulates the rate of outflow shall be used. See Figures •4-3, 4-4, 4-5, and 4-6 for suggested details. Landscaped facil- ities such as parks, playfields, tennis courts, etc. are recommended for 4-15 Or ~t Q O\ti - DEPTH OF FLOW - y1,e, 01 .02 .03 -04 OR not nft in S 6 1 11 I I 1 I + I I 'I I ~ i F I I I ~ I I I I ~ ~ I' ~ IiL l l i i l I I I I I I I I I I I I I I -I- I I (I j I:'I I- I I ~ ~ I I I -7-7 I !ooX -------I-f- r-~- I I I I I I~ I -i- I I~~ I I I I I I V I I I I I i I II~ j~ I I I I, I I( I I I I I ~ I I I I I V I I I I I I I• I I I ~ I (a) DISCHARGE PER FOOT OF LENGTH OF CURB OPENING INLETS WHEN INTERCEPTING 100% OF GUTTER FLOW I(b) PARTIAL INTERCEPTION RATIO FOR INLETS OF LENGTH LESS THAN La I I I ~ I a/ - - - - ° ~ L I I I .a I L I - alb I -r I I I ~ I i 0 ti- i I I I i I -L I I I I i I I i I I rt I I 1 I .01 1.0 A .6 .S 4 D 3 Q a x- io .OS .06 .06 .10 2 .S .4 .S .6 .e 1.0 L/La CAPACITY OF CURB OPENING INLETS ON CONTINUOUS GRADE 6-39 FIGURE 16 Stormwater Drainage Report H. STORMWATER DRAINAGE CALCULATIONS: (continued) Basin D Curb Opening at Low Point_ E.R. 0+38, left, Rotchford Street h = 8 in. = 0.67 ft. Total height of opening H = 0.156 ft. Depth of water at entrance Q = 0 68 cfs Total peak rate of flow Q = 3.087(L)(H)3'2 for H/h < 1, 0.166/0.67=0.25<1 L = Q _ (3.087)(H)312 = 0.68 _ (3.087)(0.166)32 = 3.26 ft Construct Curb Opening; 5 ft. wide, 8 in. deep Basin E Curb Opening at Low Point, Sta. 29+00, right, Limerick Drive h = 8 in. = 0.57 ft. Total height of opening H = 0.1905 ft. Depth of water at entrance Q = 1.12 cfs Total peak rate of flow Q = 3.087(L)(H f2 for Hlh e 1, 0. 1905/0.67 = 0.28 < 1 L = Q - (3.087)(H)3"2 = 1 12 -i- (3.0$7)(0.1905)3'2 = 4.36 ft. Construct Curb Opening; 5 ft. wide, 8 in. deep Basin F Curb Opening at Law Point. E.R. 0+38, right, Rotchford Street h = 8 in = 0.67 ft. Total height of opening H = 0.196 ft. Depth of water at entrance Q = 1.20 cfs Total peak rate of flow Q = 3.087(L)(H)3'2 for Hlh c 1, 0.196/0.67=0.29<1 L = Q - (3.087)312 = 1.20 - (3.087)(0 196)"2 = 4 48 ft. Construct Curb Opening; 5 ft. wide, 8 in deep Ridgemont Estates North. 7th Addition: Stormwater Drainage Report i II. STORMWATER DRAINAGE CALCULATIONS. (continued) Basin A Curb Opening on Continuous Grade, Sta. 24+58 to 24+65, left,' Limerick Drive a = 2 in. = 0.17 ft. Flowline depression at opening y = 0.119 ft. Depth of flow in normal gutter Q = 0 55 cfs Design discharge Qa/La = 0.079 From Fig 16(a), page 6-39 "Spokane County Guidelines for Stormwater Management" L = QI(QafLa) = 0.55]0.079 = 6.96 ft. Construct Curb Opening; 7 ft. wide, 8 in. deep Basin B Curb Opening on Continuous Crrade, Sta. 24+53 to 24+60, right, Limerick Drive a=tin =0.17ft y = 0.129 ft. Q=0.58cfs Qa1La = 0.086 Flowline depression at opening Depth of flow in normal gutter Design discharge From Fig 16(a), page 6-39 "Spokane County Guidelines for Stormwater Management" L = Qi(Qa/La) = 0.5810.086 = 6.74 ft. Construct Curb Opening; 7 ft. wide, 8 in. deep Basin C Curb Opening at Low Point, End of Cut-de-sac, Moore Court h = 8 in. = 0.67 ft. Total height of opening H = 0.1955 ft. Depth of water at entrance Q 1.36 cfs Total peak rate of flow Q = 3.087(L)(H)"" for H/hh < 1, 0.1955/0.67=0.29<1 L = Q - (3.087)(M"2 = 1.36 - (3.087)(0.1955)3!2 = 5.1O'~ ft. Construct Curb Opening; 6 ft. wide, 8 in. deep I, RATIONAL FORMULA HYDROLOGY 8 BOWSTRING METHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 50 YEAR STORM EVENT Date: 03131197 Design: K.W.M. Disk Fife. B5.Uxaw3tmyL5+ 1 716.wb1 Basin Name: Basin F Pond Name: Basin F Project Name: Ridgemont Estates North 7th Addition Project Number: 1271+6 Site Location: SE. Cor. 16th and Sullivan Basin Description: 1 Swale Location: : RotC o Point of Concentration:, Sta. 0+44 SUBAREAS: ___caa: acaaaa: axaaa=a aaaa :,m aanaaaa acaacca Description Acres C A*C Ashalt/Roofs/Drnres 0.209 0.90 0.188 Grass 0.801 0.15 4.120 Total Basin Area, acres= 1.010 Composite Runoff Coefficient = 0.305 Combined (Area * Runoff Coefficient) = 0.31 "208" DRAINAGE PARAMETERS: Imperious "208" Area = 6090 sq. ft. "208" Volume Provided = 396 cu. ft. Storm Storage Provided = 530 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #6 #7 Time Time Intensity ❑ dev. Vin V out Storage Inc. Inc. (min.) (sec.) (inJhr) (cfs) (cu. ft.) (cu. ft.) (cu. ft.) (tt1 W) WC**3) (OW *Q) (#5-a6) .-ca=seams aaaaaaa am=ccoaa aBaa==a saes=cm =rsc.sc=.: ss====sa= 7.70 461.79 3.84 1.18 731 461.79 269 5 300 47W 1.41 567 300 267 10 600 3.20 0.90 746 600 146 15 900 2.47 0.7+6 804 900 -96 20 1200 1.98 0.61 828 1200 -372 25 1500 1.67 0.51 852 1500 -648 30 1840 1.45 0.45 884 1800 -920 35 2100 1.30 -0.40 904 2100 -1196 40 2400 1.18 0.35 929 2400 -1471 45 2700 1.07 0.33 942 2700 -1758 50 3000 1.00 0.31 972 3000 -2028 55 3300 0.92 0.28 980 3300 -2320 60 3600 0.87 0.27 1007 3600 -2593 65 3900 0.82 0.25 1025 3900 -2875 70 4200 0.80 0.25 1074 4200 -3126 75 4500 0.77 0.24 1105 4500 -3395 80 4800 0.75 0.23 1145 4800 -3655 85 5100 0.72 0.22 1166 5100 -3934 90 5400 0.70 0.22 1198 5400 -4202 TIME OF CONCENTRATION (minutes): asaasama=a=cam aaaacc: aacccc:aa=ca4,: Tc (overland flow) Tc (gutter flow) Ct = 0.15 L2 = 120 Z1 = 0.172 L1 (A) = 180 202 = 36 N(A) = 0.3 B= 0 S(A) = 0.01 in = 0.016 S = 0.008 Tc (A) = 6.54 d = 0.1945 L1 (B) W 0 Tc (gut) 1.16 N(B) = 0 Tc(A+B) 6.54 S(B) = 0 Tc total 7.70 Tc (B) = 0.0 Intensity 3.84 Holding 4.28 Q (est) 1.18 c.f.s. Time of Concentration = 7.70 minutes PEAK DISCHARGE, 50 YEAR STORM: Q= C i I` A= 1.18 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 0 Singls-tiarr+ei (Spokane County Type A) 1 Double-Barrel (Spokane County Type B) Outflow Provided 1 c.f.s. "208" TREATMENT VOLUME: i Required G.P.A. ponding volume: Impervious "208" Area x 1C2" = 254 cu. ft. volume provided at 6" depth = 396 cu. fit. OK1 STORM STORAGE VOLUME: Maximum storage required c 267 cu. ft. volume provided at 8" depth = 530 cu. ft. OKI Stormwater Drainage Report H. STORMWATER DRAINAGE CALCULATIONS: (continued) Basin F~~ ! r~si ~e [ice e'1 + sit ndlueiwm°p'~`d) Area Total= 44,400 sq ft. - 1.01 acre Pavement = Limerick Drive = (110')(18') = 1,980 sq. ft. Ratchford Street (140')(18') = 2,520 sq ft (1/4)(7c)(45')2 = 1_590 sq. ft 6,090 sq. ft. Roofs and Driveways = I roofs at 2,000 sq. ft./house = 2,400 sq. ft. 1 drives at 1,000 sq. ft./house = 1,000 sq ft 3,000 sq. ft Impervious = 6,090 sq. ft. + 3,000 sq. ft. = 9,090 sq. ft. - 0.2087 acre Grass Lawns = 44,000 sq. ft. -9,090 sq. ft. = 34,910 sq ft. - 0.8014 acre Storage Required: a) "208" Storage Required = (6,090 sq. ft. )(112"=12 in. per ft.) = 254 cu. ft. b) Bowstring = 267 cu. ft. + 1 Double Barrel Drywell, Type B (1.0 cfs out) Storage Provided: Pond, 6" deep; (788 ft.')(0.5') = 394 cu. ft. > 254 Pond, 8" deep; (788 ft.2)(0.67') = 528 cu. ft. > 267 ernoni estates North 1TN Add►~►oti 1Z"116 Gvtte.r F low W iajl S 3 ~z.~ 19l Y-W M M a z O.tO 6 wtt ~r 'C ~vV! . W.i ~ t~_=- 1.19 ~ l2 0 kqy.... - - RATIONAL FORMULA HYDROLOGY & BOWSTRING METHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date: 03/06/97 Project Name: Ridgemont Estates North 7th Add. Project Number: 12716 Design: KWM. Site Location: NW 1/4 of Sec 25, T25N, R44E MDsk Fie: 65Ab wstm9%10%1271e.wb1 Basin Name: F Description: Limerick/Rotchford Pond Name: F SUBAREAS: TIME OF CONCEN TRATION (minutes): Description Acres - C - A"C Tc (overland flow) Tc (gutter flow) Asphalt -Pavement _ 0.210 0.90 0.189 Ct = 0.15 _1-2 = 287 Roofs and Driveways 0.210 0.90 0.189 Z1 = 0.172 Grass Lawns 0.590 0.15 0.0885 L1 (A) = 100 Z2 = 36 N()= 0.4 B= 0 S(A) = 0.01 n= 0.016 S = 0.008 Total Basin Area, acres- 1.010 Tc (A) = 5.46 = d 0.1955 Com C posite Runoff Coefficient = 0.462 • L1 ((B) = 0 Tc (gut.) 2.76 om bined (Area Runoff Coefficie nt) = 0.47 N(B) = 0 Tc(A+B) 5.46 S(B) = 0 Tc total 8.22 Tc (B) = 0.0 Intensity 2.57 "208" DRAINAGE PARAMETERS: Holding Q (est) 10.23 1.20 c.f.s. Impervious "208" Area = 9330 sq. ft. "208" Volume Provided = 396 cu. ft. Storm Storage Provided = 530 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #6 #7 Time Time Intensity Q dev. V in V out Storage Inc. Inc. (min.) (sec.) (nJhr) (cfs) (cu. ft) (cu. ft.) (cu. ft.) W 160) (A-cw) (md.*82) (mss) aa: a=a=aai =aaaaaaac=a~aaaaz==ez=aaa=aaaacaaaaa 8.22 493.21 2.57 1.20 794 493.21 301 5 3~U 3.18 - -f.W 596 300 296 10 600 2.24 1.04 802 600 202 15 900 1.77 0.83 882 900 -18 20 1200 1.45 0.68 925 1200 -275 25 1500 1.21 0.56 941 1500 -559 30 1800 1.04 0.49 955 1800 -845 35 2100 0.91 0.42 963- 2100 -1137 40 2400 0.82 0.38 982 2400 -1418 45 2700 0.74 0.35 990 2700 -1710 50 3000 0.68 0.32 1005 3000 -1995 55 3300 0.64 0.30 1035 3300 -2265 60 3600 0.61 0.28 1072 3600 -2528 65 3900 0.60 0.28 1139 3900 -2761 70 4200 0.58 0.27 1182 4200 -3018 75 4500 0.56 0.26 1219 4500 -3281 80 4800 0.53 0.25 1228 4800 -3572 85 5100 0.52 0.24 1278 5100 -3822 90 5400 0.50 0.23 1299 5400 -4101 95 5700 0.49 0.23 1341 5700 -4359 100 6000 0.48 0.22 1381 6000 -4619 ===a=_. a anaa=. a==eaaz as===a: a=a=ez e: xaaaa=. =aa==a=a Time of Concentration = 822 minutes PEAK DISCHARGE, 10 YEAR STORM: Q =C'I'A = 1.20 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 0 Single-Barrel (Spokane County Type A) 1 Double-Barrel (Spokane County Type B) Outflow Provided 1 c.f.s. "208" TREATMENT VOLUME: Required G.P.A. ponding volume: Impervious "208" Area x 12" = 389 cu. ft volume provided at 6" depth = 396 cu. ft. OKI STORM STORAGE VOLUME: Maximum storage required = volume provided at 8" depth = DRYWELL REQUIREMENTS: 0 Single (Type A) 296.35 cu. ft. 530 cu. ft. OKI Double (Type B) Stormwater Drainage Report 11. STORMWATER DRAINAGE CALCULATIONS: (continued) Basin I± EM= t 11 v ed level w• e li Area - ~Total = 44,000 sq. ft. - 1.41 acre Pavement= Limerick Drive = (290')(18') = 5,220 sq. ft. Rotchford Street = (140')(18') = 2,520 sq. ft. (1J4)(n)(45')2 = 1,590 sg ft 9,330 sq ft. Roofs and Driveways = 3 roofs at 2,044 sq. ft./house = 6,000 sq. ft. _ 3 drives at 1,000 sq. ft./house = 3,000 sq. ft 9,000 sq. ft. Impervious = 9,330 sq. ft. + 9,000 sq. ft. = 18,334 sq. ft. - 0 42 acre Grass Lawns = 44,040 sq. ft. - 18,330 sq. ft = 25,670 sq. ft. 0.59 acre Storage Reguired_ a) "208" Storage Required = (9,330 sq ft. )(1 f2 12 in. per ft.) = 389 cu. ft. b) Bowstring = 296 cu_ ft. + 1 Double Barrel Drywell, Type B (1.0 cfs out) StoWe_Proyided: Pond, 6" deep; (788 ft.2)(0.5') = 394 cu. ft. > 389 Pond, 8" deep, (788 ft.2)(0.67') = 528 cu. ft. > 296 (114)(n)(15')2= 176 sq ft. (31')(12') = 372 sq. ft. z (15')(16') = 240 sq. ft. 788 sq ft. P l a r• : P'DV► d ~ -Q o r RATIONAL FORMULA HYDROLOGY 8 BOWSTRING DRAINAGE BASIN ANALYSIS for 50 Date: 03/31197 Project Name: Rids Design: K.W.M. Project Number: 127 DwkFide 85:V*wshTQW11271e.wb1 Site Location: BE. Basin Name: Basin E Basin Description: Pond Name: Basin E Swale Location: Point of Concentration: SUBAREAS: .,..-s aa:rs ~ a a rs~ca•cz=z=x xz:~ssx~atas =aa~z:z ~ax3~~~ W Description Acres C A*C AshaWRoo%/Drives 0.187 0.90 0.168 Grass _ 0.447 0.15 0.067 Total Basin Area, acres = 0.634 Composite Runoff Coefficient= 0.371 Combined (Area' Runoff Coefficient) = 023 "208" DRAINAGE PARAMETERS: Impervious "208" Area - 5130 sq. ft. "208" Volume Provided = 392 cu. ft. Storm Storage Provided = 551 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #6 #7 Time Time Intensity Q dev. V in V out Storage Inc. Inc. (min.) (sec.) (inJhr) (cfs) (cu. ft.) (cu. ft) (cu. ft.) ate: a.-amass=: ~=~aaa: a~,aarsai ways G:~~: aaax:cma: ~~as:aax~a 9.11 546.35 3.45 0.81 593 163.90 429 5 300 4.58 1.08 433 90 343 10 600 320 0.75 591 180 411 15 900 2.47 0.58 630 270 360 20 1200 1.98 0.47 645 360 285 25 1500 1.67 0.39 662 450 212 30 1800 1.46 0.34 681 540 141 35 2100 1.30 0.31 698 630 68 40 2400 1.18 0.28 717 720 -3 45 2700 1.07 0.25 726 810 -84 50 3000 1.00 0.23 749 900 -151 55 3300 0.92 0.22 754 990 -236 60 3600 0.87 0.20 774 1080 -306 65 3900 0.82 0.19 787 1170 -383 70 4200 0.80 0.19 824 1260 -436 75 - 4500 0.77 -0.18 848 1350 -502 80 4800 0.75 0.18 879 1440 -561 85 5100 0.72 0.17 894 1530 -636 90 5400 0.70 0.16 919 1620 -701 95 5700 0.69 0.16 954 1710 -756 100 6000 0.67 0.16 974 1800 -826 DETENTION BASIN DESIGN STORM EVENT Estates North 7th Addition . 16th and Sullivan 11M 9 . 95 r rlde-ML1lU Limerick Drive Sta. 29+00 TIME OF CONCENTRATION (minutes): :=a c. a. a =aaac ~a seas: a _ =====a Tc (overland flow) Tc (gutter flow) Ct = 0.15 L2 = 105 Z1 = 4.172 L1 A) = 225 Z2 » 36 N(A) 0 6 = 0.0 8 n = 0.01 S = 0.008 Tc (A) = 7.99 d = 0.169 L1 (B) = 0 Tc (gut.) 1.11 N(B) = 0 Tc(A+B) 7.99 SIB) = 0 Tc total 9.11 Tc (B) = 0.0 Intensity 3.45 Holding 3.74 Q (est) 0.81 c.f.s. Time of Concentration a 9.11 minutes PEAK DISCHARGE, 50 YEAR STORM: Q=C*I*A= 0.81 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 1 Single-Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c f.s. "208" TREATMENT VOLUME: Required G.P.A. ponding volume: Impervious "208" Area x 112" = 214 cu. ft. volume provided at 6" depth = 392 cu. ft. OKI STORM STORAGE VOLUME: Mauamum storage required = 411 cu. ft. volume provided at 8" depth = 551 cu. ft. OKI DRYWELL REQUIREMENTS: 1 Single (Type A) 0 Double (Type B) Stormwater Drainage Report II STORMWATER DRAINAGE CALCULATIONS: (continued) Basin E Ip : O n i e (deve[ pedl + OO ffsi re and Mel ~ ~ e ) Area Total = 27,600 sq. ft. - 0.63 acre Pavement= Limerick Drive = (285')(18') = 5,130 sq. ft. Driveways = 3 driveways at 1,000 sq. ft./house = 3,000 sq. ft Impervious = 5,130 sq. ft. + 3,000 sq. ft. = 8,130 sq. ft. - 0.1866 acre Grass Lawns = 27,600 sq. ft. - 8,130 sq. ft. = 19,470 sq. ft. 0.4470 acre Storage Required: a) "208" Storage Required = (5,130 sq. ft. )(1/2"=12 in. per ft.) = 214 cu. ft b) Bowstring = 411 cu. ft. + 1 Single Barrel Drywell, Type A (0.3 cfs out) Storage Provided: Pond, 6" deep; (28')(28')(0.5') = 392 cu. ft. > 214 Pond, 8" deep; (28.68')(28.68')(0.5') = 551 cu. ft. > 411 ui ~id9evao►n~ ~.sta}es Nor~ln 1~N Adc1►}~ch ~Z11G Gvt}er Flow W id~~+s 31~-g ~9~ MI M • 6.83'.- _ Z 18W. Z•l8'7• ' Gaiter -FIoYJ._.~nlidt~±~=. G•83~. ~ ~Z, b.kw..------- - - - I - RATIONALFORMULA HYDROLOGY & BOWSTRINd'METHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date 06/25196 Project Name: Ridgemont Estates North 7th Add. Project Number: 12716 Design: KWM. Site Locabon: NW 114 of Sec 25, T25N, R44E Dsk !F le. 134 lbow mglIM12716.wh1 Basin Name: E Description: Limerick Drive Fond Name- E SUBAREAS: Description Acres C AC Asphalt Pavement 0.200 0.90 0.18 Roofs and Driveways 0.140 0.90 0.126 Grass Lawns 0.290 0.15 0.0435 Total Basin Area, acres = 0.630 Composite Runoff Coefficient= 0.555 Combined (Area ' Runoff Coefficient) = 0.35 "208" DRAINAGE PARAMETERS: TIME OF CONCENTRATION (minutes): Tc (overland flow) Tc (gutter flow) Ct = 0.15 L2 = 330 Z1 = 0.172 L1 (A) = 37 Z2 = 36 N (A) = 0.4 B = 0 S(A) = 0.01 n = 0.016 S = 0.008 Tc (A) = 3.01 d = 0185 Li (B) = 0 Tc (gut.) 3.29 N(B) = 0 Tc(A+B) 3.01 S(B) = 0 Tc total 6.30 Tc (B) 00 Intensity 2.94 Holding 11.76 Q (est) 1.03 c.f.s. Impervious "208" Area = 9000 sq. ft. "208" Volume Provided = 392 cu. ft. Storm Storage Provided = 551 cu. ft. BOWSTRING CALCULATIONS #1 #2 03 #4 #5. #6 #7 Time Time Intensity Q dev. V in V out Storage Inc. Inc. (min.) (sec.) QnJhr) (cfs) (cu. ft.) (cu. ft.) (cu ft.) - (#1'60) (A'CV3) (outf'02) (#546) 6.30 377.91 2.94 ---1.03 520 113 37 406 5 300 3.1811 447 99 357 10 600 2.24 0.78 570 180 ' 390 15 900 1.77 0.62 636 270 366 20 1200 1.45 0.51 673 360 313 25 1500 1.21 0.42 689 450 239 30 1800 104 0.36 701 540 161 35 2100 0.91 0.32 709 630 79 40 2400 0.82 0.29 725 720 5 45 2700 0.74 0.26 732 810 -78 50 3000 0.68 0.24 744 900 -156 55 3300 0.64 0.22 767 990 -223 60 3600 0 61 0.21 795 1080 -285 65 3900 0.60 0.21 845 1170 -325 70 4200 0.58 0.20 877 1260 -383 75 4500 0.56 0.20 906 1350 -444 80 4800 0.53 0.19 913 1440 -527 85 5100 0.52 0.18 950 1530 -580 90 5400 0.50 0.17 966 1620 -654 95 5700 0.49 0.17 998 1710 -712 100 6000 0.48 0.17 1028 1800 -772 Time of Concentrabon = 6.30 minutes PEAK DISCHARGE, 10 YEAR STORM: Q =C'I'A 1.03 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 1 Single-Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c.f.s. "208" TREATMENT VOLUME: Required G.P A, ponding volume: Impervious "208° Area x 112" = 375 cu ft. volume provided at 6" depth = 392 cu. ft. O K! STORM STORAGE VOLUME. Maximum storage required = 390.32 cu. ft volume provided at 8" depth = 551 cu. ft. OK! DRYWELL REQUIREMENTS: 1 Single (Type A) 0 Double (Type B) Stormwater Drainage Report 11. STQRMWATER DRAINAGE CALCllLATIONS: (continued) Basin E ~1ID'tnnsitliCd+~lid~lt7isitlc ve~eloned43', Arga Total = 27,600 sq. ft. - 0.63 acre Pavement= Limerick Drive = (500')(18') = 9,000 sq. ft. Driveways = 6 driveways at 1,000 sq f}./house = 6,000 sq. ft. Impervious = 9,000 sq. ft. + 6,000 sq. ft. = 15,000 sq. ft. - 0 34 acre Grass Lawns = 27,600 sq. ft. - 15,004 sq. ft. = 12,600 sq. ft. - 0.29 acre Storage Required: a) "208" Storage Required = (9,000 sq. ft. )(1J2"-12 in. per ft.) = 375 cu. ft, b) Bowstring = 390 cu. ft. + 1 Single Barrel Drywell, Type A (0.3 cf's out) Storage Provided: Pond, 6" deep; (28')(28')(0.5') = 392 cu. ft.. 375 Pond, 8" deep, (28.68')(28.68')(05') = 551 cu ft > 390 33.36 ft. 2.68 ft, 20 30 ft. 4.1 \ 16"=05ft. 8"=0.67 ft.! / 4.1 26 fL Pond floor r (30 + 26)12 = 28' and (31 36 + 26)!2 = 28.68' ~4c~gev++ont jr-Stak'les NOvtk IAN A, 4(ikt;t ~ ~z~►6 Y~ W M a = o xt Gv~'k~e.r ~C lvw . wi ate ~.lza C lz~ v ~qy RATIONAL. FORMULA HYDROLOGY & BOWSTRING METHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date: 03/08197 Project Name: Ridgemont Design: KWM. Site Location: NW 114 of,' Basin Name: D Description: LimericktRi Pond Name: D SUBAREAS: w.».._..........saWas a==aaar rsaaa_aaaaa=__. _aac_aa Description Acres C A"C Asphalt Pavement 0.180 0.90 0162 Roofs and Driveways 0.020 0.90 0.018 Grass Lawns 0.270 0.15 0.0405 Total Basin Area, acres = 0.470 Composite Runoff Coefficient = Combined (Area' Runoff Coeffici "208" DRAINAGE PARAMETERS: Impervious "208" Area = "208" Volume Provided = Storm Storage Provided = 0.469 ent) a 0.22 7836 sq. ft. 340 cu. ft. 456 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #6 #7 Time Time Intensity Q dev. Vin V out Storage Inc. Inc. (min.) (sec) {in./hr) (cfs) (cu. ft.) (cu. ft.) (cu. ft.) 01.60) (A•c*#3) [ouu.-a 2] (oS sus] asses.aaaaaaacaaaaaaaaaasxaaacascaasc~sasaasaaa=aaa 5.44 326.30 3.10 0.68 299 97.89 201 5 300 X18' 0.70 282 90 192 10 600 224 0.49 359 180 171 15 900 1.77 0.39 395 270 125 20 1200 1.45 0.32 419 360 59 1 25 1500 1.21 0.27 430 450 -20 30 1800 1.04 0.23 438 540 -102 35 2100 0.91 0.20 444 630 -186 40 2400 0.82 0.18 454 720 -266 45 2700 0.74 0.16 459 810 -351 50 •3000 0.68 0.15 466 900 -434 55 3300 0.64 0.14 481 990 -509 60 3600 0.61 0.13 499 1080 -581 65 3900 0.60 0.13 531 1170 -639 70 4200 0.58 0.13 551 1260 -709 75 4500 0.56 0.12 569 1350 -781 80 4800 0.53 0.12 574 1440 -866 85 5100 0.52 4.11 597 1530 -933 90 5400 0.50 011 ' 608 1620 -1012 95 5700 0.49 0.11 628 1710 -1082 I 100 6000 0.48 0.11 647 1800 -1153 ates North 7th Add. Project Number: 12715 25, T25N, R44E Disk File 65:lbnsars k10%1271&wb1 TIME OF CONCENTRATION (minutes): rats..._._.:.-... a........._..._.___---._000000 Tc (overland flow) Tc (gutter flow) Ct = 0.15 L2 = 198 Z1 = 0.172 L1 (A) = 37 Z2 = 36 N(A) = 0.4 B= - 0 S(A) = 0.01 n = 0.016 S = 0.0061 Tc (A) = 3.01 d = 0.166 L1 B) = 0 Tc (gut.) 2.43 ) Tc(A+B) 3.01 = S(B 0 TC total 5.44 Tc (B) = 0.0 Intensity 3.10 Holding 7.05 ❑ (est) 0.68 c.f.s. Time of Concentration = 5.44 minutes PEAK DISCHARGE, 10 YEAR STORM: Q = C 'I' A = 0.68 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 1 Single-Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c.f.s. "208" TREATMENT VOLUME: Required G.P.A. ponding volume: Impervious "208" Area x 112" = 327 cu. ft. volume provided at 6" depth = 340 cu. ft. OKI STORM STORAGE VOLUME: Mabmum storage required = 191.88 cu. IL volume provided at 8" depth = 456 cu. fL OKI DRYWEL.L. REQUIREMENTS: 1 Single (Type A) 0 Double (Type B) i Storrnwater Drainage Report II. STORMWATER DRAINAGE CALCULATIONS: (continued) Basin D Area Total= 20,400 sq. ft. - 0.47 acre Pavement = Limerick Drive (207')(18') = -3,726 sq. ft. Rotchford Street= (140')(18') = 2,520 sq. ft.i (114)(7E)(45')2 = 1.590 ft, o. 7,836 sq ft.l Driveways = 1 driveway at 1,000 sq. ft./house = 1,000 sq,!ft, Impervious = 7,836 sq. ft. + 1,000 sq. ft. = 8,836 sq. ft. 0.20 acre i Grass Lawns = 20,400 sq. ft. - 8,835 sq. ft. = 11,554 sq. ft. 0.27 acre i Storage Required: a) "208" Storage Required = (7,836 sq. ft. )(1J2 12 in. per ft.) = 326 cu. ft. b) Bowstring = 192 cu. ft. + 1 Single Barrel Drywell, Type Storage Provided: Pond, 5" deep; (680 ft.2)(0.5') = 340 cu. ft. > 325 Pond, 8" deep; (680 ft.2)(0.57') = 456 cu. ft. > 192 (I MX} x)(15') = 176 sq. ft. (27')(12') = 324 sq. ft. (15')(12') = 180180 sa ft. 680 sq. ft. Tlaw_ Yo~-,a F loot I '~ic~gen~on~ fCSt~~ea North Aba~~r~ch 1~.'1~~ Gutfer F kow i~~}4►s 3I-L8 I'll 9.. Gut-~~..~ .~`I~~w_ ~►.~t~= .~•r.°►` ~ ~i - RATIONAL FORMULA HYDROLOGY & BOWSTRING METHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date- 06125196 Design: KWM. Basin Name: C Pond Name: C Project Name: Ridgemont Estates North 7th Add. Project Number: 12716 Site Location NW 114 of Sec 25, T25N, R44E Disk Fde. im Lbov rng11 1311 2 7 1 6 rvbl Description: Moore Court SUBAREAS: TIME OF CONCENTRATION (minutes): Description Acres C k c Tc (overland flow) Tc (gutter flow) Asphalt Pavement 0.304 0.90 0 27 Ct = 0.15 L2 = 306 Roofs and Driveways 0.140 0.90 0.126 Z1 = 0.172 Grass Lawns 0 310 0.15 0.0465 L1 (A) = 37 72 = 36 N(A) = 0.4 S = 0 S(A) = 0.01 n = 0.016 S = 0.4103 Tc (A) = 3.01 d = 0.1955 Total Basin Area, acres = 0.750 Composite Runoff Coefficient = 0.590 L1(5) = 0 Tc (gut) 2 59 Combined (Area * Runoff Coefficient) = 0.44 N(B) = 0 Tc(A+H) 3.01 S(B) = 0 Tc total 5.60 Tc (B) = 0.0 Intensity 3.07 Holding 10.90 "208" DRAINAGE PARAMETERS: Q (est) 1.36 c.f.s. Impervious "208" Area = 13256 sq. ft. °208" Volume Provided = 560 cu. ft. Time of Concentration = 5.60 minutes Storm Storage Provided = 781 cu. ft. PEAK DISCHARGE, 10 YEAR STORM- BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #6 #7 Time Time Intensity Q dev. V to V out Storage Inc. Inc. (min.) (sec.) (inJhr) (cfs) (cu. ft) (cu. ft.) (cu ft.) (#1'613) (A-C-03) (outt '#2) (#54A6) 5.60 335.98 ---3.07 ^--1.36+ 611 100.80 r~ 510r~ 5 300 3.18 1 41 566 90 476 10 600 2.24 0.99 708 180 528 15 900 1.77 0.78 794 270 524 20 1200 1.45 0.64 843 360 483 25 1500 1.21 0.54 864 450 414 30 1800 1.04 0.46 881 540 341 35 21100 0.91 0.40 892 630 262 40 2400 4.82 0.35 912 720 192 45 2700 0.74 0.33 922 810 112 50 3000 0.68 0.30 937 900 37 55 3300 0.64 0.28 967 990 -23 60 3600 0.61 0.27 1003 1480 -77 65 3900 4.64 0.27 1066 1170 -144 70 4200 0.58 0.26 1107 1260 -153 75 4500 0.56 0.25 1143 1350 -207 80 4800 0.53 0.23 1153 1440 -287 85 5100 0.52 0.23 1200 1530 -330 90 5400 0.50 0.22 1220 1620 -400 95 5700 0.49 0.22 1261 1710 -449 100 6000 0.48 0.21 1299 1800 -501 Q=C*I*A= 1.36 CFS. NUMBER and TYPE of DRYWELLS PROPOSED: 1 Single-Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c.f.s. '208" TREATMENT VOLUME: Required G PA. ponding volume- Impervious "208" Area x 112" = 552 cu. ft. volume provided at 6" depth = 560 cu. ft. OKI STORM STORAGE VOLUME: Maximum storage required W 527.95 cu. ft. volume provided at 8" depth = 781 cu. ft. OK! DRYWELL REQUIREMENTS: 1 Single (Type A) 0 Double (Type B) Ridgemont Estates North 7th Addition: Stormwater Drainage Report 11. STORMWATER DRAINAGE CALCULATIONS: (continued) Basin C Area Total = 32,600 sq. ft. 0.75 acre Pavement= Limerick Drive= (109')(18') = 1,962 sq ft. Moore Court = (137')(36') = 4,932 sq. ft (n)(45'Y 6.352 sn. ft. 13,255 sq. ft. Driveways = .6 driveways at 1,000 sq. ft./house = 6,000 sq. ft. Impervious = 13,256 sq. ft. + 5,000 sq. ft. = 19,256: sq. ft. - 4.44 acre Grass Lawns = 32,600 sq. ft. - 19,255 sq. ft. = 13,344 sq. ft. - 0.31 acre Storage required: a) "208" Storage Required= (13,256 sq. ft. )(1J2"-12 in. per ft.) = 552 cu. ft. b) Bowstring = 528 cu. ft. + 1 Single Barrel Dryweli, Type A (0.3 cfs out) Storage Provided: Pond, 6" deep; (28')(40')(0.5') = 560 cu. ft. > 552 Pond, 8" deep, (28.68')(40.68')(4.67') = 781 cu. ft. 7 528 43-36+ _ a ~pNz g.~Y _ ~'n i 1 l' t Fond F floor 17 3 266 L OIA4 door, (30 + 26)!2 = 28' and (31.36 + 25)12 = 28.68' (42 + 38)12 = 40' and (43.36 + 38)!2 = 40.58' f Ali ~1t~~errv►ov►~ rG5'~0.'~~s NO~t~ `~~K Ac~ai}'ivln 17."11G C,u~ter taw is~ ~s 3 we I C u ser ~t~aw_ ~a#1,. 4.~8` 1~ ok ao~ KA-FIONAL FORMULA HYDROLOGY & BOWSTRING METHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date: 06/25196 Project Name: Ridgemont Design: KWM. She Location: NW 114 of ates North 7th Add. Project Number: 12716 25, T25N, R44E W Chsk File 54 lbowstm9%10%1271& wbt Basin Name: B Description: Limerick Pond Name: B SUBAREAS: Description Acres C A *C Asphalt Pavement 0.110 0 90 0.099 Roofs and Driveways 0.070 0,90 0.063 Grass Lawns 0 170 0.15 0.4255 Total Basin Area, acres = 0.350 Composite Runoff Coefficient = 0.536 Combined (Area " Runoff Coefficient) = 0.19 "208" DRAINAGE PARAMETERS: TIME OF CONCENTRATION (minutes): Tc (overland flow) Tc (gutter flow) Ct = 0.15 L2 = 280 Z1 = 0.172 Li (A) = 37 Z2 = 36 N(A) = 0.4 B= 0 S (A) = 0.01 n = 0.016 S = 0.0175 Tc (A) = 3.01 d = 0.129 Li (B) = 0 Tc (gut.) 2.40 N(B) = 0 Tc(A+B) 3,01 S(B) = 0 Tc total 5.41 Tc (B) = 0.0 Intensity 3.10 Holding 9.98 ❑ (est) 0.58 c f.s. Impervious 0208" Area = 5040 sq. ft. "208" Volume Provided = 220 cu. ft. Storm Storage Provided = 314 cu. ft. BOWSTRING CALCULATIONS Time Time Intensity ❑ dev. V In V out Storage Inc. Inc. (min.) (sec.) (inJhr) (cfs) (cu. ft.) (cu. ft.) (cu. ft.) (#1"6D) (A'C`93) (autt-a2) (#5-#6) 5.41 -324.53 3.10 0.58 253 T^97.36 - --156 - 5 300 3.18 0.64 240 90 150 10 600 2.24 - 0.42 298 180 118 15 900 1.77 0.33 335 270 65 20 1200 1.45 0.27 356 360 -4 25 1500 1.21 0.23 365 450 -85 30 1800 1.04 0.20 373 540 -167 35 2100 0.91 0.17 377 630 -253 40 2400 0.82 0.15 386 720 -334 45 . 2700 0.74 0.14 390 810 -420 50 3000 0.68 0.13 397 900 -503 55 3304 0.64 0.12 409 990 -581 60 3600 0.61 0.11 424 1080 -656 65 3900 0.60 0.11 451 1170 -719 70 4200 0.58 0.11 469 1260 -791 75 4500 0.56 0.11 484 1350 -866 80 4800 0.53 0.10 488 1440 -952 85 5100 0.52 0.10 508 1530 -1022 90 5404 4.50 0.09 517 1620 -1103 95 5700 0.49 0.09 534 1710 -1176 100 6000 0.48 0.09 550 1800 -1250 Time of Concentration = 5.41 minutes PEAK DISCHARGE, 10 YEAR STORM: © = C * I ' A = 0.58 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 1 Single-Barre! (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c.f.s "208" TREATMENT VOLUME: Required G.P.A. ponding volume: Impervious "208" Area x 112" = 210 cu. ft. volume provided at 6" depth = 220 cu ft_ OK! STORM STORAGE VOLUME: Mabmum storage required = 149.69 cu. ft. volume provided at 8" depth = 314 cu. ft. OK! DRYWELL REQUIREMENTS: 1 Single ("Type A) 0 Double (Type B) i I Ridgemont Estates North 7th Addition: Stormwater Drainage keport i H. STQRMWATER DRAINAGE CALCULATIONS: (continued) I Basin B ALe-a -Total- 15,400 sq. ft. - 0.35 acre Pavement = Limerick Drive = _(280')(18') = 5,444 sq. ft, Driveways = 3 driveways at 1,444 sq. ft./house = 3,040 sq. ft. I Impervious = 5,444 sq. ft. + 3,404 sq. ft. = 8,444 sq. ft. 0.18 acre Grass Lawns = 15,444 sq. ft. - 8,440 sq. ft. = 7,350 sq. $1. 4.17 acre Stora a Re uire& a) "208" Storage Required (5,040 sq. ft. )(112"--12 in. per it.) = 210 cu. ft. b) Bowstring = 150 cu. ft. + I Single Barrel Drywell, Type A (0.3 cfs out) Storage Provided: Pond, 6" deep; (21')(21')(0.5') = 220 cu. ft. > 210 Pond, 8" deep; (21.68')(21.68')(0.67') = 314 Cu. ft. 24.35 ft. 2 23 ft. 2.68 4:1 \ 16" = 0.5 ft. 8" = 0.67 ft. I / 4:1 19 ft. Pond Floor (23 + 19)12 = 2 1' and (24.36 + 19)12 = 21.69' F-113eYY1vhi SSiaJe.S Nori~l Aaai~iah IZ"lt C Voter ~ 1ow V~ i~~~nS 3 jz8 r 97 TL ~ 8 - - Z gel. - - - - - - - - 0 k-Ay r RATIONAL FORMULA HYDROLOGY & BOWSTRINGMETHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date: 06/25196 Project Name: Ridgemont Estates North 7th Add. Project Number: 12716 Design: KWM. Site Location: NW 114 of Sec 25, T25N, R44E WlDisk I=sle B41bowstrngX10u2716.wb1 Basin Name: A Description: Limerick Drive Pond Name: A SUBAREAS: TIME OF CONCENTRATION (minutes): Description Acres C A*C - Tc overland flow) Tc utter flow Asphalt Pavement 0.070 0.90 0.063 Ct = 0.15 L2 = 168 Roofs and Driveways 0,070 0.90 0.063 Z1 - 0.172 Grass Lawns 0.320 0.15 0.048 L1 (A) = 37 Z2 = 36 N(A) = 0.4 B= 0 S (A) = 0.01 n = 0.016 S = 0.0235 Tc (A) = 3.01 d = 0.119 Total Basin Area, acres = 0.460 Cornposrte Runoff Coefficient = 0.378 LI (B) = 0 Tc (gut) 1.31 Combined (Area * Runoff Coefficient) = 0.17 N(B) = 0 Tc(A+B) 3.01 S(B) = 0 Tc total 5.00 Tc (B) = 0.0 Intensity 3.18 Holding 5.99 "208" DRAINAGE PARAMETERS. 0 (est) 0.55 c.f.s. Impervious "208" Area = 3060 sq. ft. "208" Volume Provided = 128 cu. ft. Storm Storage Provided = 186 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 05 #6 #7 Time Time Intensity 0 dev. Vin V out Storage Inc. Inc (min.) (sec.) (in./hr) (cfs) (cu. ft.) (cu. ft) (cu. ft.) (81.60) (A-CV3) (md--#2) (95-96) 5.00 300.00 3.18 _ T0.55 ~ 222 - 90.00 - -132^! 5 300 3.18 0.55 222 90 132 10 600 2.24 0.39 274 180 94 15 900 1.77 0.31 309 270 39 20 1200 1.45 0.25 328 360 -32 25 1500 1.21 0.21 337 450 -113 30 1800 1.04 0.18 344 540 -196 35 2100 0.91 0.16 349 630 -281 40 2400 0.82 0.14 357 720 -363 45 2700 0.74 0.13 361 810 -449 50 3000 0.68 0.12 367 900 -533 55 3300 0.64 0.11 379 990 -611 60 3600 0.61 0.11 393 1080 -687 65 3900 0.60 0.10 418 1170 -752 70 4200 0.58 0.10 434 1260 -826 75 4500 0.56 0.10 448 1350 -902 80 4800 0.53 0.09 452 1440 -988 85 5100 0.52 0.09 471 1530 -1059 90 5400 0.50 0.09 479 1620 -1141 95 5700 0.49 0.09 495 1710 -1215 100 6000 0.48 0 08 510 1800 -1290 Time of Concentration = 5.00 minutes PEAK DISCHARGE, 10 YEAR STORM: Q = C * I * A = 0.55 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 1 Single-Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c.f.s. "208" TREATMENT VOLUME: Required G.PA. ponding volume: Impervious "208" Area x 112" = 128 cu. ft. volume provided at 6" depth = 128 cu. ft. OKI STORM STORAGE VOLUME: Maximum storage required = 132 43 cu. fL volume provided at 8" depth = 186 cu. ft. OKI DRYWELL REQUIREMENTS: 1 Single (Type A) 0 Double (Type B) Ridgemont Estates North 7th Addition: Stormwater Drainage Report II. STQRMWATER DRAINAGE CALCULATIONS: Basin A Area Total = 20,200 sq. ft. - 0.46 acre Pavement = Limerick Drive = (170')(18') = 3,060 sq. ft. Roofs and Driveways = 1 roof at 2,000 sq. ft./house = 2,0,00 sq. ft. I drive at 1,000 sq. ft./house = 1,000 sq. ft 3,000 sq. ft. Impervious = 3,060 sq. ft. + 3,000 sq. ft. = 6,060 sq. ft. - 0.14 acre Grass Lawns = 20,200 sq. ft. - 6,060 sq. ft. = 14,140 sq. ft. - 0.32 acre Storage RQuired: a) "°208" Storage Required = (3,060 sq. ft. )(1 /2",;- 12 in. per ft.) = 128 cu. ft. h) Bowstring = 132 cu. ft. + 1 Single Barrel Drywell, Type A (0.3 cfs out) Storage Provided: Pond, 6" deep; (16')(16')(0.5') = 128 cu. ft. = 128 Pond, 8" deep, (16.68')(16.68')(0.67') = 186 cu. ft. > 132, 19.36 ft 2.0 ft. 4.1 \ 16"=0.5ft. 8"=0.67ft.I / 4:1 14 ft. Pond Floor (18 + 14)12 = 16' and (19.36+ 14)/2 = 16.68' Stormwater Drainage Report, Ridgemont Estates North 7th Addition 1. SUMMARY. The development is divided into six (6) basins; A, B, C, D, E, and F. See Drainage Map for Ridgemont Estates North 7th Addition Each basin is composed of two subareas; 1) grass lawns, and 2) impervious roofs, driveways, and asphalt paved streets. Stormwater flows overland across roofs, grass lawns, and driveways and into grass drainage ponds Stormwater from asphalt streets flaws along the curb gutters and into the grass drainage ponds through curb openings located at low points in the curb profile. The grass percolation areas (drainage ponds) were calculated 11o hold the first 1/2" of rainfall runoff over the asphalt street areas. Figure 2, page 6-3, of the "Guidelines for Stormwater Management", by Spokane County Engineers, was used for rainfall intensity and duration occurring at a 10-year storm frequency for onsite drainage. The Rational and Bowstring Methods were used to calculate the peak stormwater runoff for each basin, and the type and number of drywells needed for each basin based on the storage capacity of the pond. In accordance with "Soil Survey, Spokane County, Washington", 1968, the soil is categorized as: GmB, Garrison very gravelly loam, similar to Garrison gravelly loam, except that the surface layer is very gravelly. Figure 2, page 6-3, of the "Guidelines for 5tormwater Management", by Spokane County Engineers, was used for rainfall intensity and duration occurring at a 10-year storm frequency. STDRMWATER DRAINAGE CALCULATIONS FOR RIDGEMONT ESTATES NORTH 7TH ADDITION NW 114 of Sec. 25, T. 25 N., R. 44 E. W.M. Spokane County, Washington March 31, 1997 Prepared by: Simpson Engineers, Inc. RECEIVED North 909 Argonne Road APR 0 2 1997 Spokane, Washington 99212 WOKANE COUNTY ENGINEER The design improvements shown in this set of plans conform to the applicable editions of the Spokane County standards for road and sewer construction and Spokane County guidelines for stormwater management. All design deviations have been approved by the Spokane County Engineer I approve these ? F plans for construction S00KANE CCU4ENC)INEEFR'S OFFICE OR GI'N,'A L PROJECT 4 Sl}BMITTAL k I. Summary RETURN TO COUNTY ENGINERA II. Stormwater Drainage Calculations for Basins A, B, C, D, E, and F of Ridgernont Estates North 7th Addition III. Attachments: * Soils Map and Tables * Roadway Surfacing Design Sto=wa w lkasn vkvpwbt 12716 RIDGElV ONT ESTATES NORTH 7TH ADDITION TEMPORARY {CUL-DE-SAC EASEMENT DESCRIPTION That portion of the NW'/a of Section 25, T. 25 N., R. 44 E.W.M. described as follows: Begin at the NE corner of Lot 1 Black 3 of RIDGEMONT ESTATES NORTH 7.i ADDITION; thence S 56°18'15"W, along the Northerly line of said lot 1, 60 00 feet to the True Point of Beginning of said described easement; thence N 33°41'45"W 95.00 feet; thence S 56°18' 15"W 97.17 feet; thence S 33°41'45"E 119.90 feet to the NE corner of Lot 8 Block 1 of said 7`h Addition; thence, N 33°19'57"E 63.79 feet to the NW corner of said Lot 1 Block 3; thence N 56°;1$'15"E 38.43 feet to the True P.O.B. Situate in the County of Spokane, State of Washington, o Temporary Easement .9 O s o 1 0 4 . eO~. py ~--Building Setback r~1~0Utility Easement 'r 15 'j 1 j ~ p L r r' 0- -yCf , 5 ~ r ~ ~ X5`1 f 10 f 10' Utility Eosemeipt i0- F O ~.J r IX 10-b '51 ' GRAPHIC SCALE (IN FEET) is ,rr - 0 25 so 104 r r r ,r, ipWW6 i~ bimpson Engineers, Inc. CIVIL ENGINEERS do LAND SURVEYDRS N909 ARGONNE ROAD ! SPOKANE. WA 99212 PH 926-1322 6impson Engir*.ers, Inc. CIVIL ENGINEERS AND LANG SURVEYORS N. 909 Argonne Road ■ Spokine, WA 99212 (509) 926-1322 • Fax: 926-1323 TO: Deav% Fr qnz akctia@ :C o4Ki Eh , neers SUBJECT: i~ e~hstate~ tlatrfk Add►``~`~~, - DATE: MarcL% 'a i 119-1 ~ tr►ciuAet] -ur Mgur rev% -wr are, -Vwro se-fs a r'at's of ~►e. rey;se4 5iree+ a &ctincL laK(s . Also yK e. d,,J J (-T Ck co 0 e rev ise.A r ai~~ e. aic+~~~t ar~~ a~, c~ i es 04 11 1 ►5@,c! ~!z ]C l1" 4►tis~iV i r@.u 11 t0 ~ ' ~a1~S car l~e. i ~f tt [ l a11'QI v%cL e. guvAs Pleakre- y . r ezV s5 wt r av ee~h W e t e to w1. Co ikp- h^ a o a 1 ow K e.►- .s W h 1" C7 P. Y• ar t e. 1-'Ae -sae earet-meK+ i.3 i+,iv(&A:.A, e,Q ~ Murc~ 7-G LR 7 c OW Itr t Since e 1 'I v APR I !,,Signed - - - GJ V) z 0 LU s R] LU 1J_ I l m 7 v ua z c.7 U.S. STANDMI) SIEVE SIZES Q Wk 0 Q 4 0 Nil IIII- } In q- 1 00 0 90 1 C~ C 80 20 U) 70 30 Li ~ < 80 F-~ CL 40 EI SC] _ i so Li t ll F 1 40 LY ' 80 W LLJ 30 lu [ (L 70 W 20 CL 80 i0 a H 9 Il - 77 10 100 GRAIN SIZE (INCHES) PROJECT NAME, Ridggernont Estates Seventh PROJECT NO.; SIMENG S9701A DATE: March 10, 1997 SAMPLE LOCATION: Unknown - Sampled by CI' t SAMPLE DESCRIPTION. Dark Brawn Silty Gravel GM , PERCENT PASSING 4: 4~1x PERCENT PASSING 200; 22% i TEST METHOD: A D-422 D-1140 , REFERENCE NO.; SL2452 REIVIARKS/DEVIATIONS: In-Situ Moisture Content 9.~a SIEVE ANALYSIS RESULTS J OEQTECIAMCAL EWQNVEERINo 6 MATMAJ.9 TESTING PLATIC i I LOCAL ACCESS PAVEMENT STRUCTURES AVERAGE DAILY TRAFFIC SOIL TYPE 0 - 200' 200-600 600+ GW 2"/6" 211/6" 2"16" GP 2"/6" 2"/7" 20'/7" GM 211/6" 27711 2178" GC 211R" 2"/8" 3176" SW 211/611 211/71' 211/711 SP - 211161' 2177" 2"/8" SM 211/7" 211/8" 317611 SC Pavement Design ML 311/6" 3"/8" 41#/6" CL Pavement Design O L 4111711 517711 518/811 MH Pavement Design OH Pavement Design PT Pavement Design 1) Soil type is classified by the Unified Soil Classification System. 2) Required thickness is given as inches of asphalt concrete pavement over inches of crushed surfacing: SPOKANE COUNTY ALTERNATE PAVEMENT DESIGN (INTERIM) J . Ridgemont Estates North 7th Addition- Stormwater Drainage Report 111. ROADWAY SURFACING DESIGN- The Spokane County Alternative Pavement Design (Interim) for Local Access Pavement Structures was used for design of the roadway surfacing From the table, Local Access Pavement Structures, the following information is needed to determine the required surfacing depths 1) The type of street must be local access. 4 2) Soil type (as classified by the United Soil Classification System) 3) The average daily traffic, ADT treet T e Limerick Drive, Rotchf'ord street and Moore Courtiare designated as local access (residential) Soil Tyne: In accordance with "Soil Survey, Spokane County, Washington" by United States Department of Agriculture, Soil Conservation Service, 1968, the sail found at the site is categorized as: Gans, Garrison very gravelly loam, similar to Garrison gravelly loam, except that the surface layer is very gravelly. The Unified Soil Classification System classifies the soil as- GM1, silty gravels, gravel-sand-silt mixture (See S.C.S soils map included) Average Daily Traffic. ADT- Limerick Drive will have average daily traffic counts of less than 200 In the future, this road will be extended north and will convect to 16th Avenue, and the ADT count will probably increase to the 200-600 range. Therefore, this road will be constructed at 100% build out for the future condition. The remaining roads, Moore Court and Ratchford Street, will be cul-de-sacs or short cross streets each with average daily traffic counts of less than 200. De- 5 g-n: From the table, 2 inches of asphalt concrete pavement over 7 inches of crushed surfacing is required for Limerick Drive. From the table, 2 inches of asphalt concrete pavement over 6 inches of crushed surfacing is planned for Rotchford Street and Moore Court i i i i i i i i i i i i i i i i i i SPOKANE COUNTY I Isopluvials of 10 year 24 hour precipitation in tenths of an inch. 20 2 4 26 JA 26 26 Deer Pork i !9 i 30 26 24 _ 22 SPOKANE g.106EMoK1 ~S7ACES . ROF-T H ,7N ADD. - j. 22 • Ch¢ne Spangle 1 20 i Is 6-6 • Lotoh I i L FIGURE 4 Sheet `I `I `I Try a depth of 1.2' t 2/3 1/2r V-1.486 R S IR - n :I Area Wetted perimeter 2'x1.2'+(2x1.2x1.2 - 5.28 s.f. 2 +2(1.22+2.42) 7.36 ft.. R - .717 V - 1.486 (.717)213(.02)1/2- 5.61 fps .03 Q - VA - 5.61 fps x 5.28 sf - 29.6 cfs =30efs d-1.2' Solve Dc: Try 1.3' Q - g (b + 0 Dc)3 Dc 3/2 b + 2E Dc Q -,,/32.2 (2+2x1.3)3 x 1.33/2- 30.9 cfs (2+2x2x1.3) 30.9 cfs - 30 cfs . do a 1.3' Dc > Dn, flow is supercritical. Since the flow is supercritical, care should be taken to provide a proper de- sign at points where horizontal and/or vertical, alignment change. A free board of .30d should be applied D - .30 X 1.2 - 1.56' V - 5.6 fps > maximum allowable. Provide rip rap. (Refer to Section 4.5. ) 4-4 Detention/Retention Systems - the peak rate of runoff from an existing site shall not be increased due to the proposed development for a given design storm. Therefore, a retention/deten- tion fatility on-site will be required. Date: 4/4/84 4-15 4-4.1 Drywells - Precast concrete dry- wells, as shown on County standard drawings, may be used to retain storm drainage in soils with a very rapid per- meability. Types A and B Drywells in the, following soils may 'be designed to infiltrate a rate of flow of 0.3 cfs and 1.0~cfs respectively: Song Marble Bonner Phoebe arrison Springdale ~ a an The- locations of these soil types are shown in the Soil Conservation Service Soil Survey for Spokane County. The drainage. report shall include a copy of the',SCS map with the subdivision plotted theiteon. The County Engineer shall re- quire the developer to provide a sieve analysis and soil type test from a soils lab6ratory acceptable to the County En gineer if there is a question regarding thelabove soil types. In jrural areas, as defined in Spokane County Road Standards, _open gravel dry- wells may be permitted in lieu of the precast concrete drywells. Precast concrete drywells proposed for usel in other soils than those shown above and all oven eravel drvwells shall be Edesigned according to percolation rates determined by a field test con- forming to to the Manual of Septic tank practice. A County inspector shall be present during all percolation tests. A percolation test calculation sheet signed and sealed by a registered civil engineer shall be submitted. The per- colation rate shall be equal to or greater than 72 inches per hour to be acceptable for drywell construction. 4-4912 Storage Facilities - Detention storage facilities may be used to regulate flow rates. An overflow typo storage system which regulates the ratd of outflow shall be used. See Figures 4-3, 4-4, 4-5, and 4-6 for suggested details. Landscaped facil- ities such as parks, playfields, tennis courts, etc. are recommended for Pull E i! ti f DEPTH OF FLOW - y{ (o) DISCHARGE PER FOOT OF LENGTH OF CURB OPENING INLETS WHEN INTERCEPTING 100 % OF GUTTER FLOW (6) PARTIAL INTERCEPTION RATIO FOR INLETS OF LENGTH LESS THAN La r I I-VJ I I ~ ~f F .00 I I I I I ~ _ a` " r I r I I I I I I I y I 000 r I / a Of I I I L I I i I P I ~ r to e 01 La a' A 7rr s .s 4 D 3 a x oS 06 .00 .10 rQ 2 .3 4 .3 6 .9 30 L/L(j CAPACITY OF CURB OPENING INLETS ON CONTINUOUS GRADE ~ 6-39 FIGURE IG Stormwater Drainage Report II. STORMWATER DRAINAGE CALCULATIONS: (continued) Basin D Curb Opening at Low Point, E.R. 0+38, left, Rotchford Street h = 8 in. = 0.67 ft. Total height of opening H = 0.166 ft. Depth of water at entrance Q = 0.68 cfs Total peak rate of flow Q = 3.087(L)CH)32 for H/h < 1, 0.166/0.67=0.25<1 L = Q - (3.087)(H)32 = 0.68 _ (3.087)(0.166)32 = 3.26 ft. Construct Curb Opening; 5 ft. wide, 8 in. deep Basin E Curb Opening at Low Point. Sta. 29+00, right, Limerick Drive h = 8 in. = 0.67 ft. Total height of opening H = 0.1905 ft. Depth of water at entrance Q = 1.12 cfs Total peak rate of flow Q = 3.087(L)(H)32 for H/h < 1, 0.1905/0.67 = 0.28 < 1 L = Q = (3.087)(H)32 = 1.12 _ (3.087)(0.1905)32 = 4.36 ft. Construct Curb Opening; 5 ft. wide, 8 in. deep Basin F Curb Opening at Low Point E.R. 0+38, right, Rotchford Street h = 8 in. = 0.67 ft. Total height of opening H = 0.196 ft. Depth of water at entrance Q = 1.20 cfs Total peak rate of flow Q = 3.087(L)(H)32 for H/h < 1, 0.196/0.67 = 0.29 < 1 L = Q _ (3.087)(H)32 = - 1.20 _ (3.087)(0.196)32 = 4.48 ft. Construct Curb Opening; 5 ft. wide, 8 in. deep Ridgemont Estates North 7th Addition- Stormwater Drainage Report 11. STORMWATER DRAINAGE CALCULATIONS: (continued) Basin A Curb Opening on Continuous Grade, Sta 24+58 to 24+65, left, Limerick Drive a=tin =017ft. y=0119ft. Q=055 cfs Qa/La = 0 079 Flowline depression at opening Depth of flow in normal gutter. Design discharge From Fig 16(a), page 6-39 "Spokane County Guidelines for Stormwater Management„ L=QI(Qa/La)=0.5510 079=6 96 ft Construct Curb Opening, 7 ft. wide, 8 in. deep Basin B Curb Opening on Continuous Grade, Sta. 24+53 to 24+60, right, Limerick Drive a = 2 in. = 0.17 ft. I~lowline depression at opening y = 0 129R Depth of flow in normal gutter Q = 0 58 cfs Design discharge Qa/La = 0 086 From Fig. 16(a), page 6-39 "Spokane County Guidelines for Stormwater Management" L = Q/(Qa/La) = 0 5810 086 = 6.74 ft. Construct Curb Opening; 7 ft wide, 8 in deep Basin C Curb 012ening at Low Point, End of Cul-de-sac, Moore Couri h = 8 in = 0.67 ft, Total height of opening H = 0.1955 ft. Depth of water at entrance Q = 1 36 cfs Total peak rate of flow Q = 3 087(L)(H)3'2 for HIh E 1, 0.1 95510 67 = 0.29 < 1 L = Q (3 087)(H)3 = 1 a6 = (3.087)(0.1955)3 = 5.10 ft Construct Curb Opening,; 6 ft wide, 8 in deep RATIONAL FORMULA HYDROLOGY & BOWSTRING METHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date: 03/06/97 Project Name: Ridgemont Estates North 7th Add. Project Number: 12716 Design: KWM. Site Location: NW 1/4 of Sec 25, T25N, R44E Wf DiskFlo: B5A)owstmg%10%12716.wb1 Basin Name: F Description: Limerick/Rotchford Pond Name: F SUBAREAS: TIME OF CONCENTRATION (minutes): Description Acres C A'C Tc (overland flow) Tc (gutter flow) Asphalt Pavement 0.210 0.90 0.189 Ct = 0.15 L2 = 287 Roofs and Driveways 0.210 0.90 0.189 21 = 0.172 Grass Lawns 0.590 0.15 0.0885 L1 (A) = 100 Z2 = 36 N(A) = 0.4 B = 0 S(A) = 0.01 n= 0.016 S = 0.008 = Tc (A) 5.46 = d 0.1955 Total Basin Area, acres = 1.010 Com posite Runoff Coefficient = ' 0.462 L123) ~ 0 Tc (gut.) 2.76 Com bined (Area Runoff Coefficie nt) = 0.47 N( ) = 0 Tc(A+B) 5.46 S(B) 0 Tc total 8.22 Tc (B) = 0.0 Intensity 2.57 Holding 10.23 "208" DRAINAGE PARAMETERS: Q (est) 1.20 c.f.s. Impervious "208" Area = 9330 sq. ft. 208" Volume Provided = 396 cu. ft. Storm Storage Provided = 530 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #6 #7 Time Time Intensity Q dev. V in V out Storage Inc. Inc. (min.) (sec.) (inJhr) (cfs) (cu. ft.) (cu. ft.) (cu. ft.) (01'60) (A-C-03) (oLd." i2) (#S-#6) 8.22 493.21 2.57 1.20 794 493.21 301 29 10 600 2.24 1.04 802 600 202 15 900 1.77 0.83 882 900 -18 20 1200 1.45 0.68 925 1200 -275 25 1500 121 0.56 941 1500 -559 30 1800 1.04 0.49 955 1800 -845 35 2100 0.91 0.42 963 2100 -1137 40 2400 0.82 0.38 982 2400 -1418 45 2700 0.74 0.35 990 2700 -1710 50 3000 0.68 0.32 1005 3000 -1995 55 3300 0.64 0.30 1035 3300 -2265 60 3600 0.61 0.28 1072 3600 -2528 65 3900 0.60 0.28 1139 3900 -2761 70 4200 0.58 0.27 1182 4200 -3018 75 4500 0.56 0.26 1219 4500 -3281 80 4800 0.53 0.25 1228 4800 -3572 85 5100 0.52 0.24 1278 5100 -3822 90 5400 0.50 0.23 1299 5400 -4101 95 5700 0.49 0.23 1341 5700 -4359 100 6000 0.48 0.22 1381 6000 -4619 Time of Concentration = 822 minutes PEAK DISCHARGE, 10 YEAR STORM: 1.20 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 0 Single-Barrel (Spokane County Type A) 1 Double-Barrel (Spokane County Type B) Outflow Provided 1 c.f.s. "208" TREATMENT VOLUME: Required G.P.A. ponding volume: Impervious "208" Area x 1/2" = 389 cu. ft. volume provided at 6" depth = 396 cu. ft. OK! STORM STORAGE VOLUME: Mapmum storage required = 296.35 cu. ft. volume provided at 8" depth = 530 cu. ft. OKI DRYWELL REQUIREMENTS: 0 Single (Type A) 1 Double (Type B) Stormwater Drainage Report H. STORM WATER DRAINAGE CALCULATIONS: (continued) Basin F Area Total= 44,400 sq. ft 1.01 acre Pavement= Limerick Drive = (290')(18') = 5,220 sq. ft. Ratchford Street = (140')(18') = 2,520 sq. ft (1r4)(n)(45 ,)2 = 1 590 Aq, ft 9,330 sq ft Roofs and Driveways = .3 roofs at 2,000 sq. ft./house = 6,000 sq. ft. 3 drives at 1,000 sq, ft./house = 3_,000 sq. ft. 9,000 sq ft. Impervious = 9,330 sq. ft. + 9,000 sq ft. = 18,330 sq. ft 0.42 acre Grass Lawns = 44,000 sq. ft. - 18,334 sq. ft. = 25,670 sq. ft. - 0.59 acre Stara a Required: a) "208" Storage Required = (9,330 sq. ft )(11'2"-12 in. per ft.) = 389 cu. ft. b) Bowstring = 296 cu. ft. + 1 Rouble Barrel Drywell, Type B 0.0 cfs out) Storage Provided: Pond, 6" deep, (788 ft.2)(0.51 = 394 cu. ft. a 389 Pond, 8" deep; (788 ft 0(0.67') = 528 cu. ft > 296 (114)(n)(15' )2 = 176 sq. ft (31')(12') = 372 sq. ft. (15')(16')=240 sa ft 788 sq. ft. P1av%: Pov,A Fl~ar RATIONAL FORMULA HYDROLOGY & BOWSTRING METHOD DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 0 YEAR STORM EVENT Date: 06125196 Project Name: Ridgemont Estates North 7th Add. Project dumber: 12716 Design- KWM Site Location, NW 114 of Sec 25, T25N, R44E Disk Fide 84 U)DwStM9%10%12716 wb1 Basin Name. E Description: Limerick Drive Pond Name: E SUBAREAS Description Acres C A*C Asphalt Pavement 0200 0.90 0.18 Roofs and Driveways 0 140 0 90 0 126 Grass Lawns 0 290 0.15 0.0435 Total Basin Area, acres = 0 630 Composite Runoff Coefficient = 0.555 Combined (Area' Runoff Coefficient) = 0 35 "208" DRAINAGE PARAMETERS: TIME OF CONCENTRATION (minutes): Tc (overland flow) Tc (gutter flow) Ct = 015 L2 = 330 Z1 = 0.172 L1 (A) = 37 Z2 = 36 N(A) = 04 8 = 0 S (A) = 0.01 n = 0.016 S = 0.008 Tc (A) = 3 01 d = 0.185 L1 (B) = 0 Tc (gut.) 3.29 N(5) = 0 Tc(A+B) 3 01 S(B) = 0 Tc total 6.30 Tc (B) = 00 Intensity 2 94 Holding 11.76 Q (est) 1.03 c.f.s. Impervious "208" Area = 9000 sq ft. "208" Volume Provided = 392 cu. ft. Storm Storage Provided = 551 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #I6 #7 Time Time Intensity Q dev. V to V out Storage Inc Inc (min.) (sec.) (in./hr) (cfs) (cu ft.) (cu. ft) (cu. ft.) ;91160) (A'C'#3) (outf '92) (#5-#6) 6 30 377.91 2.94 1.03 520 113.37 406 5 300 3.18 1 11 447 - 9T 357 10 600 2.24 0 78 570 180 390 15 900 1.77 0 62 636 270 366 20 1200 145 0.51 673 360 313 25 1500 1.21 0.42 689 450 239 30 1800 1.04 0.36 701 540 161 35 2100 0.91 0.32 709 630 79 40 2400 0.82 0.29 725 720 5 45 2700 0.74 0 26 732 810 -78 50 3000 0.68 0 24 744 900 -156 55 3300 0.64 0.22 767 990 -223 60 3600 0.61 0 21 795 1080 -285 65 3900 0.60 0.21 845 1170 -325 70 4200 0 58 0 20 877 1260 -383 75 4500 0.56 0.20 906 1350 -444 80 4800 0 53 0.19 913 1440 -527 85 5100 0 52 0.18 950 1530 -580 90 5400 0.50 0.17 966 1620 -654 95 5700 0.49 017 998 1710 -712 100 6000 0 48 0 17 1028 1800 -772 Time of Concentration = 6.30 minutes PEAK DISCHARGE, 10 YEAR STORM. Q=C*I*A= 1.03 C,F.'S. NUMBER and TYPE of DRYWELLS PROPOSED- 1 Single-Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c.f.s. "208" TREATMENT VOLUME: Required G.P A. ponding volume: Impervious "208° Area x 112" = 375 cu ft. volume provided at 6" depth = 392 cu ft. OK! STORM STORAGE VOLUME: Maximum storage required = 390.32 cu. ft. volume provided at 8" depth = 551 cu. ft. OK! DRYWELL REQUIREMENTS. 1 Single (Type A) 0 Double (Type B) Ridgemont Estates North 7th Addition Stormwater Drainage Report II. STDRMWATER DRAINAGE CALCULATIONS- (continued) Basin E Area Total = 27,600 sq ft. - 0.63 acre Pavement= Limerick Drive = (500')(18') = 9,000 sq. h Driveways = 6 driveways at 1,000 sq, ft /house = 6,006 sq ft Impervious 9,000 sq. ft. + 6,000 sq. ft. = 1 £],000 sq. ft. - 0,34 acre Grass Lawns = 27,600 sq ft - 15,000 sq ft = 12,600!sq ft. - 0.29 acre Storage Required: a) "208" Storage Required = (9,000 sq. ft. )(1!2"-12 in. per ft,) = 375 cu. ft. li) Bowstnng = 390 cu ft + I Single Barrel Drywell, Type A (0 3 cfs out) Storage Provided Pond, 6" deep; (28')(28')(0.5') = 392 cu. ft, > 375 Pond, 8" deep; (28,68')(28,68')(0,5') = 551 cu. ft. > 390 31.36 ft. 2.68 ft. 30 ft. 41 I6"=05ft 811 -0.67 / 4:1 1. 26 ft. Pond Floor f (30 + 26)12 = 28' and (31.36 + 26)12 = 28.68' RATIONAL FORMULA HYDROLOGY & BOWSTRING METHOD: DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 1 0 YEAR STORM EVENT Date: ON06197 Project Name: Rkigemont Estates North 7th Add. Project Number: 12716 Design: KWM. Site Location: NW 114 of Sec 25, T25N, R44E Dmk Fdo 65 >i mgi1M12T16.,b1 Basin Name: D Description: LimerickiRotchford Pond Name: D SUBAREAS: TIME OF CONCENTRATION (minutes): Description Acres C A*C Tc (overland flow) Tc [gutter flow] Asphalt Pavement 0.180 0.90 0.162 Roofs and Driveways 0.020 0.90 0.018 Grass Lawns 0.270 0.15 0.0405 Total Basin Area, acres = 0.470 Composite Runoff Coefficient 0.469 Combined (Area * Runoff Coefficient) = 0.22 "208" DRAINAGE PARAMETERS: Ct = 0.15 L1 (A) = 37 N(A) = 0.4 S(A) = 0.01 Tc (A) = 3.01 L1 (B) = 0 N(B) = 0 S(B) = 0 Tc (B) = 0.0 Time of Concentration = L2 = 198 Z1 = 0.172 Z2 = 36 8= 0 n 0.016 S = 0-0061 d = 0.166 Tc (gut.) 2.43 Tc(A+B) 3.01 Impervious "208" Area = 7836 sq. ft. "208" Volume Provided - 340 cu. ft. Storm Storage Provided = 456 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #I6 #7 Time Time Intensity Q dev. V in V out Storage Inc. Inc. (min.) (sec-) (in./hr) (cfs) (cu. ft.) (cu. ft.) (cu. ft.) (#1'e6) (A'C`#3) (OLd **2) (#541%) ======3======: 5.44 326.30 3.10 0.68 299 97.89 201 5 3017 _T_18 0. FO 282 90 192 10 600 2.24 0.49 351 180 171 15 900 1.77 0.39 395 270 125 20 1200 1.45 0.32 419 360 59 25 1500 1.21 027 430 450 -20 30 1800 1.04 0.23 438 540 -102 35 2100 0.91 020 444 630 -186 40 2400 0.82 0.18 454 720 -266 45 2700 0.74 0.16 459 810 -351 50 3000 0.68 0.15 466 900 -434 55 3300 0.64 0.14 481 990 -509 60 3600 0.61 0.13 499 1080 -581 65 3900 0.60 0.13 531 1170 -639 70 4200 0.58 0.13 551 1260 -709 75 4500 0.56 0.12 569 1350 -781 80 4800 0.53 0.12 574 1440 -866 85 5100 0.52 0.11 597 1530 -933 90 5400 0.50 0.11 608 1620 -1012 95 5700 0.49 0.11 628 1710 -1082 100 6000 0.48 0.11 647 1800 -1153 Tc total 5.44 Intensity 3.10 Holding 7.05 Q (est) 0.68 c.f.s. 5.44 minutes PEAK DISCHARGE, 10 YEAR STORM: Q = C * I * A = 0.68 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED: 1 Single-Barrel (Spokane County Type A) 0. Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c.f-s. "208" TREATMENT VOLUME: Required G.P.A. ponding volume: Impervious "208" Area x 112" = 327 cu. ft. volume provided at 6" depth = 340 cu. ft. OKI STORM STORAGE VOLUME: Mabmum storage required = 191.88 cu. ft. volume provided at 8" depth = 456 cu. ft. OKI DRYWELL REQUIREMENTS: 1 Single (Type A) 0 Double (Type B) Stormwater Drainage Report 11 STQRMWATER DRAINAGE CALCULATIONS: (continued) Basin D Area Total = 20,400 sq. ft. a- 0.47 acre Pavement = Limerick Drive = (207')(18') = 3,726 sq. ft. Ratchford Street= (140')(18') = 2,520 sq. ft. (114)(,x)(45')' = 1,590 Sq. ft 7,836 sq. ft. Driveways = 1 driveway at 1,000 sq. ft./house = 1,000 sq, ft. Impervious = 7,836 sq. ft. + 1,000 sq. ft. = 8,836 sq. ft. - 0.20 acre Grass Lawns = 20,400 sq. ft. - 8,836 sq. ft. = 11,554 sq. ft. - 0.27 acre Storage Rewired: a) "208" Storage Required = (7,836 sq. ft. )(112"-12 in. per ft.) = 325 cu. ft. b Bowstring = 192 cu. ft. + 1 Single Barrel D ell Type A (0.3 g ryw cFs out) Storage Provided Pond, 6" deep, (680 ft.)(0.5') = 340 cu. ft. > 326 Pond, 8" deep; (680 ft. )(0 67') = 456 cu. ft. > 192 (114)(n)(15' )2 = 176 sq ft. (27')(12') = 324 sq. ft. (15')(12') = 180180 sq ft. 680 sq. ft. Tlan: Pc,.-, d f kvor I -,A 1 e7- 1 N RATIONAL FORMULA HYDROLOGY & BOWSTRING METHOD. DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date 06125196 Protect Name: Ridgemont Estates North 7th Acid. Project Number 12716 Design. KWM. Site Location: NW 114 of Sec 25, T25N, R44E Disk File 84A1xw%rn9M12716.wb1 Basin Name C Description. Moore Court Pond Name. C SUBAREAS: ❑escraptran____-------.'Acres C----- R'C- TIME OF CONCENTRATION (minutes): Tc (overland flow)~~ To (gutter flow) Asphalt Pavement 0.300 0 90 0 27 Roofs and Driveways 0.140 0 90 0.126 Grass Lawns 0.310 0.15 00465 Total Basin Area, acres = 0.750 Comosite Runoff Coefficient = 0.590 ComEined (Area " Runoff Coefficient) = 0 44 "208" DRAINAGE PARAMETERS: Impervious "208" Area = 13256 sq ft. "208" Volume Provided = 560 cu ft Storm Storage Provided = 781 cu ft BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #6 #7 Time Time Intensity Q dev Vin V out Storage Inc. Inc. (min.) (sec.) (in./hr) (cfs) (cu ft) (cu. ft.) (cu ft) (*1 "60) (A-C-93) (outr -92) (9546) 5.60 335 98 - 3.07 --r1.36 - 611 100.80 - 510^- 5 300 3.18 1.41 566 90 476 10 600 2 24 0.99 708 180 528 15 900 177 0.78 794 270 524 20 1200 1.45 0.64 843 360 483 25 1500 121 0.54 864 450 414 30 1800 1.04 0.46 881 540 341 35 2100 0 91 0.40 892 630 262 40 2400 0 82 0.36 912 720 192 45 2700 0 74 0.33 922 810 112 50 3000 0 68 0.30 937 900 37 55 3300 0.64 0.28 967 994 -23 60 3600 0 61 0 27 1003 1080 -77 65 3900 0.50 0.27 1066 1170 -104 70 4200 0.58 0 26 1107 1260 -153 75 4500 0.56 0 25 1143 1350 -207 80 4800 0 53 0.23 1153 1440 -287 85 5100 0.52 023 1200 1530 -330 90 5400 0 50 0.22 1220 1620 -400 95 5700 0 49 0.22 1261 1710 -449 100 6000 0 48 0.21 1299 1800 -541 Ct = 0.15 L2 = 306 Z1 = 0.172 Li (A) = 37 Z2 36 N(A) = 04 B = 0 S(A) = 0.01 n = 0 016 S = 0.0103 Tc (A) = 3 01 d = 0.1955 Li (B) = 0 To (gut.) 2.59 N(B) = 0 Tc(AtB) 3.01 S(B) = 0 Tc total 5 60 To (B) = 0.0 intensity 3.07 Holding 10.90 Q (est) 1.36 c.f.s Time of Concentration = 5.60 minutes PEAR DISCHARGE, 10 YEAR STORM: Q = C . I . A = 1.36 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED- 1 Single-Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0 3 c f.s. "208" TREATMENT VOLUME. Required G P.A ponding volume. Impervious "208" Area x 112" = 552 cu. ft volume provided at 6" depth = 56+0 cu. ft. OKI STORM STORAGE VOLUME: Maximum storage required = 527.95 cu. ft. volume provided at 8" depth = 781 cu ft OKI DRYWELL REQUIREMENTS- 1 Single (Type A) 0 Double (Type B) Ridgemont Estates North 7th Addition: Stormwater Drainage Report II STOPWWATER DRAINAGE CALCULATIONS: (continued) Basin C Area Total = 32,640 sq. ft. - 4.75 acre Pavement = Limerick Drive = (109')(18') = 1,962 sq. ft. Moore Court = (137')(36') = 4,932 sq. ft (7c)(45 )2 = 6,362 sq ft 13,256 sq. ft. Driveways = 6 driveways at 1,000 sq, ftJhouse = 6,000 sq ft. Impervious = 13,256 sq ft. + 6,400 sq. ft. = 19,256 sq. ft - 0.44 acre Grass Lawns = 32,600 sq. ft - 19,256 sq. ft = 13,344 sq. ft. - 0 31 acre Storage Required_ a) "208" Storage Required = (13,256 sq. ft. )(112"~ 12 in, per ft ) = 552 cu ft b) Bowstring = 528 cu ft. + 1 Single Barrel DrywelI, Type A (0.3 cfs out) Storage Provided: Pond, 6" deep, (28')(40')(0 5') = 560 cu. ft > 552 Pond, 8" deep, (28.68')(40.68')(0 67') = 781 cu. ft > 528 S k. 34' i r r - NILC ~'onc] F loor Pend Floor (30 + 26)12 = 28' and (31 36 + 26)12 = 28 68" (42 + 38)12 = 40' and (43.36 + 38)!2 = 40 68' RATIONAL FORMULA HYDROLOGY 8 BOWSTRING METHOD DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date: 06/25196 Project Name: Ridgemon Design KWM. Site Location. NW 114 of Basin Name B Description- Limerick Pond Name B SUBAREAS- Description Acres C A *C Asphalt Pavement 0.110 Roofs and Driveways 0.070 Grass Lawns 0.170 Total Basin Area, acres = 0 350 Composite Runoff Coefficient= Combined (Area ' Runoff Coeffii 0 90 0.099 0.90 0 063 015 0.0255 0.536 cent) = 0.19 "208" DRAINAGE PARAMETERS- Impervious "208" Area = 5040 sq. ft "208" Volume Provided = 220 cu. ft. Storm Storage Provided = 314 cu. ft. BOWSTRING CALCULATIONS #1 #2 #3 #4 #5 #6 #7 Time Time Intensity Q dev. V in V out Storage Inc. Inc (min.) (sec) (in./hr) (cfs) (cu. ft) (cu ft.) (cu. ft.) - [#1 160] - (A-C-93) (outt'#2) i#546) 5.41 324 53 310 0.58 ^ 253 -W97 36 ---156 5 3G0 318 0.60 240 90 150 10 600 2 24 0 42 298 180 118 15 900 177 0.33 335 270 65 20 1200 145 0.27 356 360 -4 25 1500 1.21 0 23 365 450 -85 30 1800 1.04 0.20 373 540 -167 35 2100 0.91 017 377 630 -253 40 2400 0.82 0,15 386 720 -334 45 2700 0.74 0 14 390 810 -420 50 3000 0.68 013 397 900 -503 55 3300 0.64 012 409 990 -581 60 3600 0.61 0.11 424 1080 -656 65 3900 0.60 011 451 1170 -719 70 4200 0 58 0.11 469 1260 -791 75 4500 0.56 011 484 1350 -866 80 4800 0.53 010 488 1440 -952 85 5900 0.52 010 508 1530 -1022 90 5400 0.50 0.09 517 1620 -1103 95 5700 0.49 0 09 534 1710 -1176 100 6000 0.48 0.09 550 1800 -1250 ates North 7th Add. Project Number; 12716 25, T25N, R44E WI Disk File B4 WowsLrng%10%12716 wb1 TIME OF CONCENTRATION (minutes) Tc (overland flow)Tc (gutter flow) Ct= 015 L1 (A) = 37 N(A) = 04 S(A) = 0.01 Tc (A) = 3.01 L2 = 280 Z1 = 0.172 7-2 = 36 B= 0 n = 0.016 S = 0.0175 d = 0.129 Lt (B) = 0 N(B) = 0 S(B) = 0 Tc (B) = 0.0 Time of Concentration = Tc (gut.) 2.40 Tc(A+B) 3 01 Tc total 5.41 Intensity 3.10 Holding 9.98 Q (est) 0 58 c f.s. 5.41 minutes PEAK DISCHARGE, 10 YEAR STORM: 0 = C * I * A = 0.58 C.F.S. NUMBER and TYPE of DRYWELLS PROPOSED. 1 Single-Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0.3 c f.s "208" TREATMENT VOLUME: Required G P.A. ponding volume: Impervious "208" Area x 112" = 210 cu. ft volume provided at 6" depth = 220 cu. ft. OK! STORM STORAGE VOLUME Maximum storage required = 149.69 cu. ft. volume provided at 8" depth = 314 cu. ft. OK! DRYWELL REQUIREMENTS 1 Single (Type A) 0 Double (Type 8) Ridgemont Estates North 7th Addition: Stormwater Drainage Report II. STORMWATER DRAINAGE CALCULATIONS (continued) Basin B Area Total = 15,400 sq ft. 0 35 acre Pavement= Limerick Drive = (2801')(18') = 5,040 sq. ft. Driveways = 3 driveways at 1,000 sq. ft./house = 3,000 sq. ft Impervious = 5,040 sq ft + 3,000 sq. ft. = 8,040 sq. ft. 0.18 acre 1 Grass Lawns = 15,400 sq ft. - 8,040 sq. ft. = 7,3601 sq ft - 0.17 acre Storage Required: a) "208" Storage Required = (5,040 sq ft )(1/2"-12 in per ft } p 210 cu. ft. b) Bowstring = 150 cu ft + 1 Sin 0, Barrel Drywell, Type A (0 3 cfs out) Storage Provided; ' Pond, 6" deep, (21')(21')(0.5') = 220 cu ft f 210 Pond, 8" deep, (21 68')(21.68')(0.67') = 314 cu ft > 150 ft. 2.68 f1. 23 ft, 4:1 ``t 16"=0.5ft 8"=067ft.I / 4:1 19 ft. Pond Floor (23 + 19)12 = 2 1' and (24.36 + 19)12 = 21.68' RATIONAL FORMULA HYDROLOGY & BOWSTRING METHOD` DETENTION BASIN DESIGN DRAINAGE BASIN ANALYSIS for 10 YEAR STORM EVENT Date, 06125/96 Project Name* Ridgemont Estates North 7th Add. Project Number: 12716 Design KWM. Site Location: NW 1 /4 of Sec 25, T25N, R44E WI Disk File 54.1bowstm9M\12716 wb1 Basin Name A Description- Limerick Drive Pond Name A SUBAREAS: Description Acres C A *C Asphalt Pavement 0.070 0.90 0 063 Roofs and Driveways 0.070 0.90 0 063 Grass Lawns 0.320 015 0 048 Total Basin Area, acres = 0.460 Composite Runoff Coefficient= 0.378 Combined (Area • Runoff Coefficient) = 0,17 "208" DRAINAGE PARAMETERS: TIME OF CONCENTRATION (minutes): Tc (overland flow) Tc (gutter flow) Ct = 0.15 L2 = 168 Z1 = 4.172 L1 (A) = 37 7-2 = 36 N (A) = 04 B= 0 S(A) = 0.01 n = 0 016 S = 0.0235 Tc (A) = 3.01 d = 0,119 LI(B) = 0 Tc (gut.) 1.31 N(B) = 0 Tc(A+B) 3.01 S(B) = 0 Tc total 5.00 Tc (B) = 00 Intensity 3.18 Holding 5.99 Q (est) 0 55 c f.s Impervious "208" Area = 3060 sq. ft, "208" Volume Provided = 128 cu, ft. Storm Storage Provided = 186 cu. ft. BOWSTRING CALCULATIONS Time Time Intensity Q dev Vin V out Storage Inc Inc, (min ) (sec.) (tn./hr) (cfs) (cu. ft.) (cu, ft.) (cu. ft.) [#1'~iD) (A'C'#3) (outf.'92) (*5-96) 5.00 300.00 318 0.55 222 90.00 132 5 300 3.18 0 55 222 90 132 10 600 224 0,39 274 180 94 15 900 1,77 0 31 309 270 39 20 1200 145 0.25 328 360 -32 25 1500 1.21 0.21 337 450 -113 30 1+800 1.04 0.18 344 540 -196 35 2100 0.91 0,16 349 630 -283 40 2400 0 82 0,14 357 720 -363 45 2700 0 74 013 361 810 -449 50 3000 0 68 012 367 900 -533 55 3300 0.64 0.11 379 990 -611 60 3600 0.61 0.11 393 1080 -687 65 3900 0.60 0.10 418 1170 -752 70 4200 0.58 0.10 434 1260 -826 75 4500 0.56 0.10 448 1350 -902 80 4800 0 53 0 09 452 1440 -988 85 5100 0 52 0 09 471 1530 -1059 90 5400 0.50 0.09 479 1620 -1141 95 5700 0.49 0.09 495 1710 -1215 100 6000 0,48 0 08 510 1800 -1290 Time of Concentration = 5.00 minutes PEAK DISCHARGE, 10 YEAR STORM: Q = C ' I ' A = 0 55 C.F S. NUMBER and TYPE of DRYWELLS PROPOSED 1 Single-'Barrel (Spokane County Type A) 0 Double-Barrel (Spokane County Type B) Outflow Provided 0 3 c.f.s. °208" TREATMENT VOLUME: Required G.P.A. ponding volume: Impervious '"208" Area x 112" = 128 cu. ft. volume provided at 6" depth = 128 cu. ft. OK! STORM STORAGE VOLUME: Maximum storage required = 132 43 cu. ft. volume provided at 8" depth = 186 cu. ft, OK! DRYWELL REQUIREMENTS: 1 Single (Type A) 0 Double (Type B) Ridgemont Estates North 7th Addition: Stormwater Drainage Report H. STDRMWATER DRAINAGE CALCULATIONS: Basin A Area Total 20,200 sq. f} - 0.46 acre Pavement = Limerick Drive = (170')(18') = 3,060 sq. ft. Roofs and Driveways = 1 roof at 2,000 sq. ft./house = 2',000 sq. ft. 1 drive at 1,000 sq ft,/house = 1,000 sq. ft 3,000 sq. ft. Impervious = 3,060 sq ft. + 3,000 sq. ft. = 6,060 sq. ftll - 0.14 acre Grass Lawns = 20,200 sq ft. - 6,060 sq. ft. = 14,140 sq. ft. - 0.32 acre i Storage Required: a) IL208" Storage Required = (3,060 sq ft. )(112 12 in, per ft.) = 128 cu ft b) Bowstring = 132 cu ft + 1 Single Barrel Drywell, Type A (0 3 cf's out) Storage Provided- Pond, 6" deep, (16')(16')(0,5') = 128 cu. ft. = 128 Pond, 8" deep; (16.68'){16.68')(0.67') = 186 cu. ft. > 13,2 19.36 ft 2.68 ft. 1811. 4 1 \ 16"=0.5ft. 8"=0.67ft i / 4:1 14 ft. Pond Floor (18 + 14)12 = 16' and (19.36 + 14)/2 = 16 68' Stormwater Drainage Report; Ridgemont Estates North 7th Addition I SUMMARY: The development is divided into six (6) basins; A, B, C, 1a, E, and F. See Drainage Map for Ridgemont Estates North 7th Addition, Each basin is composed of two subareas; l} grass lawns, and 2) impervious roofs, driveways, and asphalt paved streets. Stormwater flows overland across roofs, grass lawns, and driveways and into grass drainage ponds Stormwater from asphalt streets flaws along the curb gutters and into the grass drainage ponds through curb openings located at low points in the curb profile. The grass percolation areas (drainage ponds) were calculated to hold the first 112" of rainfall runoff over the asphalt street areas. Figure page 6-3, of the "Guidelines for Stormwater Management", by Spokane County Engineers, was used for rainfall intensity and duration occurring at a I0-year storm frequency for onsite drainage. The Rational and Bowstring Methods were used to calculate the peak stormwater runoff' for each basin, and the type and number ofdrywells needed for each basin based on the storage capacity of the pond. In accordance with "Soil Survey, Spokane County, Washington", 1968, the soil is categorized as- GmB, Garrison very gravelly loam, similar to Garrison gravelly loam, except that the surface layer is very gravelly. Figure 2, page 6-3, of the "Guidelines for Stormwater Management", by Spokane County Engineers, was used for rainfall intensity and duration occurring at a l0-year storm frequency