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HomeMy WebLinkAboutSW8030425_COMPLIANCE_20030611STORMWATER DIVISION CODING SHEET POST -CONSTRUCTION PERMITS PERMIT NO. --L_ SW _so)3AA,,5 DOC TYPE ❑ CURRENT PERMIT ❑ APPROVED PLANS ❑ HISTORICAL FILE COMPLIANCE EVALUATION INSPECTION DOC DATE �CD30Gl( YYYYMMDD WET DETENTION POND ANALYSIS FILE NAME: PROJECT #: SW8 030425 PROJECT NAME: Dutch Square Storage G :IDATAIW P DATAIWQSIP O N D\0 30425. W K 1 REVIEWER: LSMunn DATE: 11-Jun-03 Receiving Stream: Smith Creek Class: C-SW Drainage Basin: Cape Fear Index No. Site Area 2.90 acres Drainage Area 2fi324 04 : square feet Area in Acres 2.90 IMPERVIOUS AREAS Rational C building 46290.00 square feet parking 41976.00 square feet sidewalk 395.00 square feet square feet square feet square feet TOTAL t3B6-- 4-- square feet Rational Cc- 0.06 SURFACE AREA CALCULATION % IMPERVIOUS 70.19% Des. Depth 6 TSS: 90 SA/DA Ratio 3.91 % Req. SA 4943 sf Prov. SA ::,::8205< sf VOLUME CALCULATION * place a "1" in the box if Rational is used Req. Volume 717E cf Vol. Prov. at DP ORIFICE CALCULATION FOREBAY Perm. Pool Volume= Req. Forebay Volume= Provided Volume= Percent= #111lOi Elevation Area Inc. Vol. 39.00 8205.00 40.00 9628.00 8916.50 IN Acc. Vol. 8916.50 Avg. Head = 0.47 ft Q2 Area = 1.81 sq. inches Flow Q2, cfs 0.042 cfs Q5 Area = 0.73 sq. inches Flow Q5, cfs 0.017 cfs Orifice Area 1.77 sq. inches No. of Orifices 1',: Q= 0.040 cfs Diameter, inches :, . 1.5(J weir H x W :'.:.:.. <. rn x :.. rn Drawdown = 1' > days Surface Area @DP = 9628 sq. ft. Falling Head Drawdown = 3.5 days COMMENTS Surface Area , Volume and Orifice are within Design Guidelines. Suv2) 03 0L4Z5 _Datr_k 5e6 UCL4e STORMWATER SUBMITTAL REQUIREMENTS DETENTION POND A. Site Plan ✓ I . Development/Project Name 2. Designer=s seal, signature, name and firm. +/ 3. Legend 4. North Arrow 5. Location Map with direction, distance to named streets, NCSR numbers. ✓ 6. Scale 7. Date 171~ 8. Revision number and date. 9. Original contours, proposed contours, spot elevations, finished floor elevations. ✓ 10. Existing drainage, including off -site. Provide a map of any offsite areas. 11. Property/Project boundary lines, dimensioned. ��- 12. Mean High Water Line, if project is adjacent surface waters. Drainage easements, catch basins, pipe sizes, inverts. Wetlands delineated, or a note on the plans that none exist. Ponds may not be located in a wetland. 15. Details of the road, parking, cul-de-sacs, including sidewalks, curb and gutter.. Drainage area to each pond delineated. el7. ` Dimensions of the permanent pool. �- 17 Vegetated filter detail if using 85% TSS. This is NOT a connector ditch. �le 19. Dimensions of the road, parking cul-de-sacs, sidewalks,,and curb and gutter. 20. Unit footprint with dimensions and concrete wood deck areas noted.for apartments or condo development. 21. Forebay at each inlet. (Prefer one inlet) 22. Inlets located such that entire pond is used for treatment and no short-circuiting. 23. Pond/forebay section detail with: Bottom elevation Permanent pool elevation PP Storage pool elevation SP —� Slopes: 3:1 above permanent pool _ Vegetated shelf located below permanent pool, 6:1 slope, with begin and end elevations around main pond. (Not required inside forebay) Forebay bottom elevation, 3:1 slopes, Forebay weir elevation between PP and DP. 24. Outlet structure detail with trash rack and orifice size specified. Maximum trash rack y ; 2 P opening size is 4". Note on plans that all roof drains must be directed so as to be picked up by the pond. A 3:1 L: W ratio has been provided for the pond. ^� 27. Maximum ave. rag, pond depth of 6. (Parts of pond may be deeper -up to 7.5') 28. Vegetation requirements for pond slopes and wetland species for the 6.1 shelf are listed. Weeping Love grass is not suitable for use in North Carolina. t CFF In C. STORMWATER SUBMITTAL REQUIREMENTS DETENTION POND (cont) Calculations 1. 85% or 90% TSS Chart noted. 2. Pond depth. 3. SA/DA ratio calculation. 4. Required surface area at permanent pool. 5. Provided surface area at permanent pool (Based on pond dimensions) 6. Provided surface area at temporary design pool. 7. Required volume calculation. 8. Provided volume calculation. 9. Orifice size based on required 1" volume, using average head to design pool elevation. 10. Designer—s seal. 11. Built -upon area to each pond. 12. Forebay designed to hold 20% of the permanent pool volume. (Range of 18-22 OK.) 13. Non -erosive flow for 10 yr. storm in the vegetated filter, if using 85% TSS. Supporting Documentation l . Completed permit application and supplement. a. is the person who signed the landowner or a leasee? Must be landowner. b. All sections and blanks completely filled in. C. Check signature per .1003 (e). Make sure title is provided. d. If agent signs, signatory authorization from owner. e. Wet detention supplement sheet provided. f. Mailing address & phone of applicant- no CIO. g. Verify water body classification. h. Justifications for,not meeting a design requirement. i. If a modification, include Designer=s Certification. j. Hand initial design requirements. 2. Proposed deed restrictions 6 V'(_"Iju;'� Krv-4d"(e, H�SOb C,q zo ) - -S q q C6-0 6-Y ) ( ; () ) :- Cq I (�o 3/11 /2003 CDC Dutch Square Storage Stormwater Pond Calculations 02084 Total Drainage Area s q. ft. I acres 126,455 1 2.90 Impervious Area Land Use s q, ft, acres building 46,290 1.06 asphalt 41,976 0.96 ravel 0 0.00 concrete 395 0.01 Iota I 1 88,661 1 2.04 Stormwater Calculations: Time of Concentration: Hydraulic Length (L) = 600 ft. hange in Height (H) = 2 ft. Tc = (L° IH)''..' / 128 9.68 min. Flow for 10 year, 6 hour Storm (Q10): QPRE - (CPRE) x (110) x (Area) 4.57 cfs QPosr = (CPosr) x (110) x (Area) 13.72 cis Detention Pond Design: Pond Size: Elevation ft. Surface Area (sq. ft. Normal Pool 39.00 8,205 Flood Pool 40.00 9,628 Top of Bank 42.50 13,282 Bottom of Pool 33.00 333 Total Provided Storage Volume: Vol. _ [(Normal pool SA + Flood Pool SA) / 2] x (F.P. elev, - N.P. elev.) 8,917 cu. ft. % impervious = 0.701 = 70.1% say 71.0% CPRE = 0.25 CPo,T= (%imp,)(.95)+(1%imp.)(.25) 0.75 110 = 6.30 inlhr 150 = 7.79 in/hr Flow for 50�year, 6 hour Storm (Q50) QPRE (CPRE) x (119).x (Area) 5.65 cfs QPosT = (CPosT) x (110) x (Area) 16.96 cfs JCdlt9 JUI IdGC HIBd MtLAVII CI IIen[ dl IIUI IIIdI Pond side slopes = 3 :1 Depth below N.P. = 6 ft. SA/DA = 0.0397 (Chart for 90% TSS Removal for Wet Detention Pond without Vegetative Filter Required SA = (SA/DA) x (Total Drainage Area) = 5,020 s . ft. State Volume Requirement for Storaae of first 1" runoff: Vol. = [(1/12) x (DA) x (% imp.)] + [(1/12) x (DA) x (1-% imp.) x C] C = 0.2 8,018 cu. ft. `\`\w��`o`�Z�, o�ESS/0 :Q SEAL 9•' - ,e'; 17374 a {�•'`�yGlNE��••Q �. +aREGfl,��`���``� !�•d7 02084POND 1 of 2 3/11 /2003 CDC Pond Volume: Dutch Square Storage Stormwater Pond Calculations Bottom SA = 333 sq. ft. Normal Pool SA = 8,205 sq. ft. Vol [(N.P. SA+ Bottom SA)1 2] x (N.P. el. - Bottom ei.) - 25,614 cu. ft. Forebaw Required Volume Vol. = 20% of storage volume = 5,123 cu. ft. Provided Volume Bottom SA= 1,063 sq. ft. Normal Pool SA = 2,575 sq. ft. Vol. _ [(N.P. SA + Bottom SA) 2] x (N.P. el. - Bottom el.) - 5,457 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) — 0.046 cfs Neouired Area oT i we Tor 2-aav drawdown: A= Q/ [Cd x SQRT(2 x g x h)] Cd = 0.6 g = 32.2 ft./sz h= (F.P. elev.-N.P. elev.)12 = 0.5 ft. A = 0,0136 sq. ft. Diameter of Pioe for 2-dav drawdown: DIA. SQRT[(A x 4) / pi] I` 0.1317 ft. 1.58 in. Use 1.5" orifice Outlet Structure Check: Using a 4' x 4' Basin, Perimeter L = 16 ft. Q = CIA C = (% imp.)(.95) + (1-% imp.)(.25) 0,75 1 = 6.30 in. for a 10 yr. Storm A = 2.90 Acres 13.72 cfs Flow for 5-day drawdown: far 1st 1" of stormwater, Q = Required Vol. 1432,000 sec. (5-days) 0.019 cfs uirea Area oT r�11Je Tor b-dav drawdown: A= Q/[CdxSQRT(2xgxh)] Cd = 0.6 g = 32.2 ft./S2 h = (F. P. elev. - N.P. elev.) / 2 0.5 ft. A = 0.0055 sq, ft. Diameter of Pipe for 5-day drawdown: DIA. = SQRT[(A x 4) / pi] 0.0833 ft. — 1.00 in. Q= CwxLXH' H [Q 1 (Cw x L)]2r3 Cw = 3 0.43 ft. Peak elevation = flood pool elevation + H 40A3 ft. 02084 02084POND 2 of 2 April 16, 2003 Stormwater Narrative Dutch Square Storage New Hanover County, NC TE 02084 Dutch Square Storage is an existing 2.90 acre site proposed for a high density RV storage facility. Runoff will be treated by wet detention. The pond will treat both the State 1" requirement and the County 25-year pre -post requirement. The pond is designed for 70.1% impervious coverage. 46,290 sf of building, 41,976 sf of parking and 395 sf of concrete sidewalk are proposed. Outflow from the pond will be to Smith Creek, classification C-SW.