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Home My WebLink AboutSW8051012_COMPLIANCE_20060504STORMWATER DIVISION CODING SHEET POST -CONSTRUCTION PERMITS PERMIT NO. SW Lof XB1A DOC TYPE ❑CURRENT PERMIT ❑ APPROVED PLANS ❑ HISTORICAL FILE �7 COMPLIANCE EVALUATION INSPECTION C DOC DATE W2�9Xo0 Vd, YYYYMMDD WET DETENTION POND ANALYSIS FILE NAME S IWQSIPONDX051012 WK1 PROJECT # SWS 051012 REVIEWER L Lewis PROJECT NAME Noland Properties DATE 04-May-06 Lot 1 Royal Creek IP (SW8 000308) Receiving Stream UT New River Class Drainage Basin White Oak Index No Site Area 261 acres Drainage Area 119711 00 square feet Area in Acres 275 Onsite DA 114654 Offsite DA 505400 IMPERVIOUS AREAS Rational C Buildings 1000000 square feet Parking 4271900 square feet SW rr,, 203400 square feet -L"erbce55R4 411600 square feet Future 100000 square feet Offsite street 492200 square feet 112 of Frontier Way square feet TOTAL 1111,11111 64791 00, square feet Rational Cc= 009 SURFACE AREA CALCULATION % IMPERVIOUS 54 12% SA/DA Ratio 3 83% Des Depth 5 Req SA 4585 sf TSS 90 Prov SA 5011 sf VOLUME CALCULATION * place a "1" in the box if Rational is used Rational ?* Des Storm ;,'',,,; ;100 inches Rv= 0 537 Bottom 365 msl Perm Pool d 111 l',I 401 S0 msl Design Pool 41 52 msl Storage met @elev 4146 msl Req Volume �li'llll',�' 5358 jcf Vol Prov at DP �'11 ,1'`i 5664 jcf ORIFICE CALCULATION FOREBAY Perm Pool Volume= 9713 Req Forebay Volume= 19426 Provided Volume= 204300 Percent= 1121' 0%Ili!II1il1' Elevation Area Inc Vol Acc Vol 4050 5011 00 000 4152 609400 566355 566355 Avg Head = 049 ft Q2 Area = 1 33 sq inches Flow I cfs 0 031 cfs Q5 Area = 0 53 sq inches Flow Q5, cfs 0 012 cfs Orifice Area 0 79 sq inches No of Orifices i lli h 1 Q= 0 018 cfs Diameter, inches weir H x W jlIli '1'1'141'11' Id l in x in Drawdown = „',,,,, 13'4 days Surface Area @DP = 6094 sq ft Falling Head Drawdown = 4 9 days C 331 L= -0 098 COMMENTS Surface Area, Volume and Orifice are within Design Guidelines RECETVED MAR 0 2 2006 �ROd # S W SO��- 1 PROJECT DESCRIPTION Design Calculations Stormwater Treatment Facilities for Noland Properties, Inc. located In Jacksonville, N.C. III 111 1 CA o� QPOF S ,a[_ _ 1 48 The Project consists of a proposed businesses on a 2 47 acre tract and associated sitework 2 COMPUTE POND AREA REQUIRED a Compute Percent Impervious Impervious Areas On -Site Buildings On -Site Streets On -Site Parking On -Ste Sidewalks Other on -site Off -site Sub -Total FUTURE FUTURE(reserved) Total Total Area Drainage to Pond Percent Impervious = b Compute Pond Surface Area Existing Propsed Total 10,000 SF ,y4021' cfv;u u}t 4,922 SF 42,719 SF 2,034 SF 4,116 y} ivi$r`Jv�tV�rt+{��i},�Yv 0 Jn ry} 4,922 58,869 63,791 SF 0� 1,000 1,000 SF 0 59,869 64,791 SF 119,711 SF 0 541 or 541 % Using Surface Area to Drainage Area Ratio Chart for 90% TSS Removal (copy attached) and assuming ;;} ry;;°„ ;{foot pond depth SAIDA% (interpolated) Therefore Surface Area = SAIDA x Drainage Area 4,683 SF say '„ >„ 5,[ 1,1 SF I 0 c Compute Minimum Pond Dimensions Assume rectangular shape with 3 1 Length (L) to Width (W) Ratio Length = 122 61 feet Width = 40 87 feet Site conditions, however, dictate Hydr Length =�Yas ' { '$ feet so, Hydr Width 36 0 feet (avg) Actual L/W = 3 9 (irregular shape) 3 DETERMINE VOLUME TO BE CONTROLLED FROM 1" STORM Using Schuler "Simple Method" Rv = 0 05 + 0 009(I) where I = percent impervious Rv = 0 537 in/in Control Volume = Design Rainfall x Rv x Drainage Area Control Volume = 5,358 CF say'} #1# CF 4 DETERMINE REQUIRED STORAGE DEPTH Assume 3 1 side slopes solving for depth (d) by trial & error d= 101 5. DETERMINE ORIFICE SIZE Control Volume must be drawn down over a 2 day - 5 day period Using orifice equation, solve for Diameter (D) that results in 3-1/2 day period D=(Q/0026(h)5)5 Where Q = (Control Volume / 3 5 days x 86,400 sec/day) 0 019 cfs h= d / 2 =051 Solving for D D = 100 Use `w s. `uv,v," pipe Actual Drawdown with actual drawdown pipe diameter (using orifice equation) Q= 0 018 cfs Draw Down Period = 3 51 days OK, < 5 0 6 SELECT OUTLET STRUCTURE DIAMETER Size outlet structure such that depth of Q10 flow <1 0 feet Using Rational Formula (Q=CIA) where Cimper r Y v}n Cpery Ccum = 050 i4 C} A = 2 75 ac Q10 = 9 85 cfs Assuming 112 circumference is used as weir and using Francis Formula (Q=3 331-1-11' S) to solve for L such that H = 1 0 L = 2 96 Feet Min 24 inch diameter outlet structure Use 36 inch diameter outlet structure 7 DETERMINE Q10 STAGE 010 = 9 85 cfs Using Francis Formula (Q=3 33LH' S) solve for H H 10 = 0 73 feet 8 DETERMINE Q100 STAGE (ELEV OF EMERGENCY SPILLWAY) Using Rational Formula (Q=CIA) where Ccum = 050 1100 _;, m/hr A= 275 ac Q100 = 1168 Using Francis Formula (Q=3 331-114 5) solve for H i H 100 = 0 82 feet 9 DETERMINE 0100 STAGE OVER EMERGENCY SPILLWAY (TOP BERM ELEV ) Assume primary spillway blocked (i e , emergency spillway to accommodate Q100) Emergency spillway shall be a broad crested earthern weir designed to pass 100 year storm Using broad crested weir equation H = (Q/Cw x Lr where Q = Q100 11 68 cfs Cw=30 Length - nV `5 $ " z'' feet H = 0 26 feet 10 FOREBAY SIZING Compute Actual Pond Volumes (using average end method) Avg Incr Incr Cum Main Bay Volume . Pond Bottom Elevation Area 3660 (SF l Ama 216 (SF Depth (FT Vol (CE Vol (CE Bottom Veg Shelf 3883 4,613 865 333 2,879 2,879 Normal Pond 40,50 4,226 2,870 1 67 4,792 7,671 Main Bay Volume = 7,671 CF Forebay Volume, Pond Bottom Elevation Area 3550 (SF 1 Area �2 -(SF l Depth (FT l Vol (CF l Vol (CF} Normal Pond 4050 786 400 500 2,043 2,043 Forebay Volume = 2,043 CF Total Pond Volume = 9,713 CF Forebay Volume equates to 21 0 % of Total Volume Imp. Storage Volume, Normal Pond Elevation Area 4050 (SF] Area 5,011 (SF De tAhh (FT) Vol (CE Vol (CE Temp Pond Level 4tU 6A4 5,553 1 02 5,664 5,664 Temp Pool Volume = 5,664 CF Elution Area (SF) Area (SE)Depth (FT) Vol (CF) Vol (CF-) Temp Pond Level 4152 6,094 Temp Pond Level 42,25 61683 5,839 073 4,281 4,281 Temp Pool Volume = 100 Yr Storage Volume . Temp Pond Level Temp Pond Level Temp Pool Volume = 11 SUMMARY Pond Elevations Top Berm (minimum) 100-Yr Flood 10-Yr Flood 1-inch Storage 4,281 CF Elevation Area -(SF } Area (SE Depth (FT) Vol (CF) Vol (CF) 4152 6,094 42,$4 -6,601 5,878 082 4,828 4,828 4,828 CF H= 0 26 H100 = 0 82 H10= 073 storage depth = 102 Permanent Pool pond depth = 5 Pond Bottom 12 WET DETENTION BASIN SUPPLEMENT Basin Bottom Elevation 3550 Perm Pool Elevation 4050 Temp Pool Elevation 41 52 Perm Pool Surface Area 5,011 SF Drainage Area 2 75 AC Impervious Area 1 49 AC Perm Pool Volume 9,713 CF Temp Pool Volume 5,664 CF Forebay Volume 2,043 CF SAIDA 39123 Diameter of Orifice 100 Design Rainfall 1" Relative Awl 710 4260 684 42 34 (emerg weir elev) 076 4225 602 4152 (primary weir elev) 600 40 50 (invert out elev) 0 tiv+ vu} Wf } JYnti Y k I Design TSS Removal r 90% N