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Home My WebLink AboutSW8021204_COMPLIANCE_20030213STORMWATER DIVISION CODING SHEET POST -CONSTRUCTION PERMITS PERMIT N0. SW DOC TYPE El CURRENT PERMIT ❑ APPROVED PLANS ❑ HISTORICAL FILE COMPLIANCE EVALUATION INSPECTION DOC DATE o�uiJO�J� YYYYMMDD WET DETENTION POND ANALYSIS FILE NAME: G:IDATAIWPDATAIWQSIPOND1021204.WK1 PROJECT #: SW8 021204 REVIEWER: L. Lewis PROJECT NAME: Dollar General Bell St. Wilmington DATE: 13-Feb-03 Receiving Stream: UT Cape Fear River Class: SC Drainage Basin: Cape Fear Index No. CPF17 18-(71) Site Area 1.50 acres Drainage Area '.65340 00` square feet Area in Acres 1.50 IMPERVIOUS AREAS Buildings Parking SW TOTAL SURFACE AREA CALCULATION Rational C 12685.00 square feet 1.00 26011.00 square feet 1.00 2072.00 square feet 1.00 square feet square feet square feet 4068 00>'' square feet Rational Cc= 0.70 % IMPERVIOUS 62.39% SA/DA Ratio 3.52% Des, Depth 6 Req. SA 2300 sf TSS: 90 Prov. SA _ .:2fi82': sf VOLUME CALCULATION Rational ?* Des. Storm 1 fly:: inches Rv= 0.612 Bottom 17 msl Perm. Pool 23 Off;; msl ................................. Design Pool 24.1 msl Storage met @elev 24.05 msl Req. Volume ;;;<;330 cf Vol. Prov. at DP >541211 cf ORIFICE CALCULATION * place a "1" in the box if Rational is used FOREBAY Perm. Pool Volume= �Isj Req. Forebay Volume= I69300 Provided Volume= J 557 Percent= -51V Elevation Area Inc. Vol. Acc. Vol. 23.00 2682.00 0.00 24.10 3631.00 3472.15 3472.15 COMMENTS Surface Area , Volume and Orifice are within Design Guidelines 11 /22/2002 CDC Total Drainage Area s . ft. acres 65,340 1.50 Impervious Area Land Use s .ft. I acres buildings 12.685 0.29 arkin !as halt 26.011 0.60 sidewalks 2,072 0.05 Future 0 0.00 Total 40,768 0,94 Stormwater Calculations: Time of Concentration: Hydraulic Length (L) = 600 ft. change in Height (H) = 2 ft. Tc = (L' 1H)'! 128 9.68 min. Flow for 2 year, 6 hour Storm (Q2): QPRE _ (CPRE) x (Ito) x (Area) 1.59 cis QPosT = (CPosr) x (110) x (Area) 4,40 cfs Jon Jiora a Lapaciq Tor L year worm: CN = (98)(°% imp.) + (60)(1-°% imp.) = 84 P = 3.30 in. fof2yr, 6 hr storm S = 1000ICN - 10 1.90 Depth (D)= [P-(0.2)(S)]2 f [P+(0.8)(S)j = 1.77 in. Time to Peak Flow: TP = [(43.5)(D)(Area)] ! Q7 26.20 min. Detention Pond Design: Pond Size: Elevation (ft . Surface Area (sq. ft. Normal Pool 23.00 202 Flood Pool 24.10 3,631 Top of Bank 25.50 4,935 Bottom of Pool 17.00 1 35 Dollar General Bell St. Stormwater Calculations °% impervious = 0.624 = 62.4°% say 6.2 CPRE = 0.25 CPosT = (°% imp.)(.95)+(1-0% imp.)(.25) 12 = 4.25 in/hr 110 = 4.92 inlhr Row for 10 year, 6 hour Storm (010): QP9E _ (CPRE) x (125) x (Area) 1.85 cfs 0PosT= (C'PosT) x (125) x (Area) = 5.09 cfs Soil Storage Capacity for 10 vear Storm: CN = (98)(°% imp.) + (60)(1-°% imp.) = 84 P = 4,82 in. for 10 yr, 6 hr storm S = 10001CN - 10 1.90 Depth (D)= [P-(0.2)(S)12 ! (P+(0.8)(S)] 3.11 in. Time to Peak Flow: 7 = [(43.5)(D)(Area)] f 010,Posr 39.80 min. Pond side slopes = 3 :1 Depth below N.P. = 6 ft. SAIDA = 0.0355 (Chart for 90 % TSS Removal for Wet Detention SA = ft. State Volume Required for Storage of first 1" of runoff: Provided Storage Volume: Rv = .05+ .009(°% imp) Voi. _ [(Normal pool SA + Flood Pool SA) 1 21 = 0,611543 x (F.P. elev. - N.P. elev.):1 V= (Design rainfalf)(Rv)(Drainage Area) 3,472 cu. ft. 11ml//,, = 3,330 cu. ft. 02057 `\�`\��ao��, CAR Roll l RECEIVED ,:pFSEA 9.� SEAL 17374 DEC 0 6 2002 FNc{E�?'AQ DWQ PROJ 07- I Z 0 ¢ fffrrtt ti IZ'"' 'CAL 02057pond 1 of 3 11 /22/2002 CDC Dollar General Bell St. Stormwater Calculations Pond Volume: Bottom SA = 35 sq. ft. Normal Pool SA = 2,682 sq. ft. Vol. = [(N.P. $A + Bottom $A) 121 x (N.P. el. - Bottom el.) = 8,151 cu. ft. Forebay: Required Volume Vol. = 20% of storage volume = 1,630 cu. ft. Outlet Structure Design: Flow for 2-day drawdown: for 1 st 1" of stormwater, Q = Required Vol. 1 172,800 sec. (2-days) 0.019 cfs Required Area of Pipe for 2-day drawdown A= Q/ [Cd x SQ RT(2 x g x h)] Cd = 0.6 g = 32.2 Rdsz h = (F.P, elev.- N.P. elev.)12 = 0,55 ft. A = 0.0054 sq, ft. Diameter of Pico for 2-dav drawdown: DIA. = SQRT[(A x 4) ! pi] = 0.0829 ft. 0.99 in. 'Use: 0.75 in diameter pipe Outlet Structure Check: Using a 4' x 4' Basin, Perimeter L = 16 ft. Q = CIA C = (% imp.)(.95) + (1-% imp.)(.25) = 0,69 1 = 4,92 in, for a 25 yr. Storm A = 1.50 Acres 5.09 cfs Q= CwxLxH"s H = [Q 1 (Cw x L)]'n Cw = 3 = 0.22 ft. Peak elevation = flood pool elevation + H 24.32 ft. Provided Volume 02057 Bottom SA = 225 sq, ft. Normal Pool SA = 813 sq, ft, Vol. = [(N.P. SA + Bottom SA) 12] x (N,P, ef. - Sam 1,557 cu. ft, Flow for 5-day drawdown: for 1st 1" of stormwater, Q = Required Vol. / 432,000 sec. (5-days) 0.008 cfs Required Area of Pipe for 5-day drawdown: A= Q I [Cd x SQRT(2 x g x h)] Cd = 0.6 g = 32.2 ft.ls2 h = (FP. elev. - N.P. elev.) 1 2 = 0.55 ft. A = 0.0022 sq. ft. Diameter of Pipe for 5-day drawdown: DIA. = SQRT[(A x 4) / pi] = 0.0524 ft. 0.63 in. 02057pond 2of3 December 6, 2002 Stormwater Narrative Dollar General — Bell Street Wilmington County, NC TE 02057 The proposed site for Dollar General Bell Street is 1.50 acres and is an existing vacant car lot. A proposed building of 12,685 sf, 26,011 sf of asphalt parking and 2,072 sf of concrete sidewalk are proposed. The site meets high density requirements. Runoff will be treated by wet detention. The system will treat the total 1.50 acres with 40,768 sf of impervious area. The system is sized to meet the State's 1" and the City's pre -post requirement. Runoff from the site will drain to a tributary of the Cape Fear River, classification C-SW.