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Home My WebLink AboutSW8021205_COMPLIANCE_20030228STORMWATER DIVISION CODING SHEET POST -CONSTRUCTION PERMITS PERMIT NO. SW nilau�rOJ DOC TYPE ❑CURRENT PERMIT ❑ APPROVED PLANS ❑ HISTORICAL FILE COMPLIANCE EVALUATION INSPECTION DOC DATE o�LAl30��dS� YYYYMMDD WET DETENTION POND ANALYSIS FILE NAME: G:IDATAIWPDATAIWQSIPOND1021205.WK1 PROJECT #: SW8 021205 REVIEWER: L, Lewis - PROJECT NAME: Strick's LP Gas DATE: 28-Feb-03 Recei' i'ng Stream: UT Prince George Creek Class: CS w,L Drainage Basin- Cape Fear Index No. CPF23 18-74-53 ry Site Area 2.00 acres Drainage Area 87.12Q 00 square feet Area in Acres 2.00 IMPERVIOUS AREAS Rational C Building 4000.00 square feet Parking 17276.00 square feet Existing grave 4036.00 square feet Concrete 2127.00 square feet square feet TOTAL 2 A ,:I O square feet square feet Rational Cc= -0:14 SURFACE AREA CALCULATION % IMPERVIOUS 31.50% SAIDA Ratio 2.82% Des. Depth 4 Req, SA 2456 sf TSS: 90 Prov. SA 5572: sf VOLUME CALCULATION Rational ?* Des. Storm OQ: inches Rv= 0.333 Bottom 90.9 msl Perm. Pool .::,»::94.00' msl Design Pool 95.7 msl Storage met @elev 95.29 msl Req. Volume .., 2421; cf Vol. Prov. at DP k cf * place a "1" in the box if Rational is used Perm. Pool Volume= Req. Forebay Volume= Provided Volume= Percent= Elevation Area 94.90 5572.00 95.70 6717.00 11744 2348.8 2468.00 Inc. Vol. Acc. Vol. 0.00 4915.60 4915.60 ORIFICE CALCULATION Avg. Head = 0.38 ft Q2 Area 0.68 sq. inches Flow Q2, cfs 0.014 cfs Q5 Area = 0.27 sq. inches Flow Q5, cfs 0.006 cfs Orifice Area 0.44 sq. inches No. of Orifices Q= 0.009 cfs Diameter, inches ....... ;ti 75: weir H x W x in Drawdown = 31: days Surface Area @DP = 6717 sq. ft. Falling Head Drawdown = 8.6 days COMMENTS Surface Area , Volume and Orifice are within Design Guidelines • . , 2/19/2003 CDC Strick's L.P. Gas Stormwater Calculations 02096 Total Drainage Area s . ft. acres 87,120 2.00 Impervious Area Land Use sq. ft. acres building 4,000 0,09 asphalt 17,276 0,40 existing ravel 4,036 0.09 concrete 2,127 0.05 Total 27,439 1 0.63 Stormwater Calculations: Time of Concentration'. Hydraulic Length (L) = 350 ft. hange in Height (H) = 2 ft. Tc = (L' IH)"" 1 128 5.19 min. Flow for 10 year, 6 hour Storm (Q10): QPRE '- (CPRE) x (110) x (Area) = 3.15 cfs QPOST - (CPOST) x (I10) x (Area) = 6.05 cfs Detention Pond Design: Pond Size: Elevation ft. Surface Area (sq. ft.) Normal Pool 94.90 5,572 Flood Pool 95.70 6,717 Top of Bank 98.00 10,583 Bottom of Pool 90.90 300 Total Provided Storage Volume: Vol. _ [(Normal pool SA + Flood Pool SA) / 21 x (F.P. elev. - N.P. elev.) 4,916 cu, ft. RECEIVED FEB 2 0 2003 DWQ PROJ # 1(A);F0Z12U5 _ 02096POND % impervious = 0.315 = 31.5% say 32.0% CPRE = 0.25 CPOST = (% imp.)(,95)+(1-% imp.)(.25) 0.48 110 = 6.30 in/hr 150 = 7.79 in/hr Flow for 50 year, 6 hour Storm (Q50): QPRE - (CPRE) x (I1o) x (Area) 3.90 cfs QPosT = (CPosT) x (110) x (Area) 7.48 cfs State Surface Area Reauirement at normal pool: Pond side slopes = 3 :1 Depth below N.P. = 4 ft. SA/DA = 0.0286 (Chart for 90% TSS Removal for Wet Detention Pond without Vegetative Filter Required SA = (SA/DA) x (Total Drainage Area) = 2,492 s . ft. State Volume Reauirement for Storaae of first 1" runoff: Vol. _ [(1/12) x (DA) x (% imp.)] + 1(1/12) x (DA) x (1-% imp.) x C] C = 0.2 3,281 cu. ft. oF�SSib y..9 ' aQ SEAL? 17374 P. ��IOREGIO�,,`��O` 1 of 2 2/19/2003 CDC Pond Volume: Strick's L.P. Gas Stormwater Calculations Bottom SA = 300 sq. ft. Normal Pool SA = 5,572 sq. ft. Vol. = [(N.P. SA + Bottom SA) / 21 x (N.P. el. - Bottom el.) = 11,744 cu. ft. Forebay_: Required Volume Vol. = 20% of storage volume 2,349 cu, ft. Provided Volume Bottom SA = 135 sq. ft. Normal Pool SA = 1,510 sq. ft. Vol. = [(N.P. SA + Bottom SA) / 21 x (N.P. el. - Bottom el.) 2,468 cu. ft. depth = 3 ft. Outlet Structure Design: Flow for 2-day drawdown: for 1st 1" of stormwater, Q = Required Vol. / 172,800 sec. (2-days) 0.019 cfs Reauired Area of Pipe for 2-dav drawdown: A= Q/[Cd xSQRT(2xgxh)] Cd = 0.6 g = 32.2 ft./s2 h = (F.P. elev.- N.P. elev.) /2 0.4 ft. A = 0.0062 sq. ft. Diameter of Pipe for 2-dav drawdown: DIA. = SQRTI(A x 4) / pi) — 0.0891 ft. = 1.07 in. Use. 75" orifice Outlet Structure Check: Using a 4' x 4' Basin Perimeter L = 16 ft. Q = CIA C = (% imp.)(.95) + (1-% imp.)(.25) 0.48 1 = 6.30 in, for a 10 yr. Storm A = 2.00 Acres 6.05 cfs Flow for 5-day drawdown: for 1st 1" of stormwater, Q = Required Vol. 1432,000 sec, (5-days) 0.008 cfs Keoulrea Area of Hoe Tor 5-aav araWdOWn: A= Q/(Cd xSQRT(2xgxh)] Cd = 0.6 g = 32.2 ft./52 h = (F.P. elev. - N.P. elev.) / 2 = 0.4 ft. A = 0.0025 sq. ft. Diameter of Pipe for 5-day drawdown: 7= SQRT[(A x 4) / pi] = 0.0564 ft. 0.68 in, Q= CwxLxH H = IQ / (Cw x L)]2f3 Cw = 3 = 0.25 ft. Peak elevation = flood pool elevation + H = 95.95 ft. WZY1 02096POND 2 of 2 TRIPP ENGINEERING, P.C. 419 Chestnut Street Wilmington, North Carolina 28ZI01 Phone: (910) 763-5100 • FAX: (910) 763-5631 RIF, DFC December 4, 2002 NCDENR 1` Division Water Quality 127 Cardinal Drive Wilmington, NC 28405-3845 Attn: Ms. Linda Lewis Re: Strick's L.P. Gas New Hanover County, NC TE 02096 Dear Linda: Enclosed please find two (2) sets of plans, one (1) signed original and one (1) copy of the application form with narrative, one (1) wet detention basin supplement, two (2) sets of calculations and one check for the application fee. Please review for approval and contact us with any questions or comments. Thank you. Sincerely, Tripp Engineering, P.C. jwv�f �01pu Jennifer Rohde JLR:dcb Enc. December 4, 2002 Stormwater Narrative Strick's L.P. Gas New Hanover County, NC TE 02096 Strick's LR Gas is an existing 2.0 acre vacant tract of land. A commercial retial building and asphalt parking area are proposed. The building of 4,000 sf and parking area of 23,139 sf total 27,139 sf or 31.2% impervious area. A wet detention pond is designed to treat both the State's 1" requirement and New Hanover County's 25-year pre -post requirement. Outflow from the pond will be routed to and unnamed tributary of Denny's Creek, classification C-SW.