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HomeMy WebLinkAbout20060447 Ver 2_Preliminary Stormwater Plan_20080826O CD WITHERS RAVENEL Olde Towne Rec. Center Preliminary Stormwater Management Plan Raleigh, North Carolina Prepared By: WITHERS & RAVENEL, INC 111 MacKenan Drive Cary, North Carolina 27511 WR Project # 02080510 July 2008 i • i 02M2 (Ab iii INTRODUCTION Olde Towne Recreation Center is a ±14.48-acre, site located in the City of Raleigh, North Carolina. The site is located within the Neuse River Basin. The purpose of this study is to document calculations of the pre- and post-development peak stormwater discharges for the 2-, and 1o-year storm events as well as the BMP sizing calculations and Nitrogen Export rates for the site. Figure 1 Site Outlined in Red on Aerial Photography Per City of Raleigh regulations the site will be required to mitigate post-development flows to less than or equal to the pre-development flows in the 2-, and so-year 24-hour storm events. The site will also be required to reduce nitrogen export rates to less that 1o.o lbs/ac/yr. A single extended detention wetland is proposed to satisfy The City of Raleigh detention requirements and the nitrogen export requirements. Currently, the site and surrounding drainage area are primarily open space and woods, and contain predominantly Hydraulic Soil Group B soils. AUG E 6 2006 OENR -WATER QUALI'JY WET, 4ND 8T09MWATER BRANCH 01de Towne Rec. Cent. i W&R Project 2o80510 Pond Report July 2oo8 • METHODOLOGY The stormwater study was conducted using the natural drainage features as depicted by field survey, LIDAR topography (i-ft contours) and proposed development within the drainage areas. The scope of work included the following analyses: • Hydrolos;y ? Simulation of the 2-year, zo-year, and loo-year rainfall events for the Raleigh area ? Formulation of the 2-year, io-year, and Soo-year flood hydrographs for the pre- and post- development drainage areas • Hydraulic ? Routing the 2-year, io-year, and ioo-year flood hydrographs for post development runoff through the proposed extended detention wetland. • The results of the hydrology calculations are used in the hydraulic analyses. The hydraulic design requires the development of stage-storage and stage-discharge functions for the wetland. The rainfall/runoff hydrographs, stage-storage and stage-discharge functions have been compiled to • create a routing computer simulation model using Haestad Methods PondPack vio.o software. This PondPack model was then used to assess the impact of the peak discharges for the design rainfall events. • HYDROLOGY The SCS Method was used to develop runoff hydrographs in the Raleigh area. The 24-hour duration • rainfall curves are determined using the NOAA Atlas 14 rainfall data for Raleigh-Durham International Airport for the 2-year, io-year, and ioo-year storm events. This method requires three basic parameters: a curve number (CN), time of concentration (Q, and drainage area. Curve numbers were based on soil type and land use. Soil types were delineated from the USDA Web Soil Survey. Land use for existing conditions was based on the most recent Wake County aerial photographs. Post development land use is based on the proposed site plan. Times of concentration were calculated using methods described in the SCS publication "Urban Hydrology for Small Watersheds, TR-55" and based on Wake County topographic maps and field • survey data. The post-development time of concentration was estimated at 5 minutes due to the effect of piped drainage systems. The curve number data, time of concentration calculations and PondPack output summaries are • included in the appendices of this report. HYDRAULICS • Computer simulated reservoir routing of the 2-year, io-year, and loo-year design storms utilized stage-storage and stage-discharge functions. Stage-storage functions were derived from the proposed contours for the wetland. A non-linear regression relation for surface area versus elevation was derived for the detention basin. This relation estimates the incremental volume of the basin to the stage or elevation of that basin. Stage-discharge functions were developed to size the outlet structure for the wetland. • 01de Towne Rec. Cent. 2 W&R Project 20805-10 • Pond Report July 2oo8 CONCLUSIONS Based on the routing study, the post development peak discharge from the entire site after improvements is less than pre-development levels for the 2-year, and 1o-year design storms. The attached sheets summarize the preliminary peak attenuation results and general design information. Summary of Results Storm Event Pre-Development cfs Post-Development* cfs Difference (cfs) 2-Year 5.72 5.73 0.01 io-Year 19.77 16.63 -3.14 Extended Detention Wetland inflow (cfs) Outflow (cfs) WSE (ft) 2-Year 29.66 o.6 195-72 1o-Year 6.61 9.911 196.28 loo-Year 65.26 2.68 196.78 Pond Outlet Summary: 5'x 5' Inlet Box, Weir Crest @ 196.oo, Top of Dam @ 197.50 6" Diameter Orifice @ 195.00, 2" Diameter Inverted PVC,@194.00 36" Diameter Outlet Barrel Invert out =190.30' * Note: Post Development flows include 3.37 acres of off-site area. 01de Towne Rec. Cent. 3 MR Project 2o80510 Pond Report July 2008 Background Information Pond Pack Results • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Post to Wetland Predev-Site D a Q • CL 5 ?• X 7c N O O Pre-Out Pond 10 Post Bypass D a Q x 0 Post-Out • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Table of Contents Table of Contents ********************** MASTER SUMMARY ********************** Watershed....... Master Network Summary ............. 1.01 ****************** DESIGN STORMS SUMMARY ******************* RDU NOAA 14 Desi Design Storms ...................... 2.01 RDU NOAA 14 Desi 2 Design Storms ...................... 2.02 ********************** TC CALCULATIONS ********************* POST BYPASS..... Tc Calcs ........................... 3.01 POST TO WETLAND Tc Calcs ........................... 3.03 PREDEV-SITE..... Tc Calcs ........................... 3.05 ********************** CN CALCULATIONS ********************* POST BYPASS..... Runoff CN-Area ..................... 4.01 POST TO WETLAND Runoff CN-Area ..................... 4.02 PREDEV-SITE..... Runoff CN-Area ..................... 4.03 *********************** POND VOLUMES *********************** POND 10......... Vol: Elev-Area ..................... 5.01 i S/N: Bentley PondPack (10.00.027.00) 2:41 PM Bentley Systems, Inc. 7/8/2008 Table of Contents ii Table of Contents (continued) ******************** OUTLET STRUCTURES ********************* Outlet 1........ Outlet Input Data .................. 6.01 Composite Rating Curve ............. 6.04 SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 • • • • • • • • • • • • • • • • • • • • • • Type.... Master Network Summary Page 1.01 Name.... Watershed File.... K:\08\08-C)510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw MASTER DESIGN STORM SUMMARY Network Storm Collection: RDU NOAA 14 Desi Total Depth Rainfall Return Event in Type RNF ID ------------ 2 ------ 3.4400 ---------------- Time-Depth Curve ---------------- RDU NOAA 2yr 10 4.9800 Time-Depth Curve RDU NOAA 10yr 100 7.3700 Time-Depth Curve RDU NOAA 100yr MASTER NETWORK SUMMARY SCS Unit Hydrograph Method (*Node=Outfall; +Node=Diversion;) (Trun= HYG Truncation: Blank=None; L=Left; R=Rt; LR=Left&Rt) Max Return HYG Vol Qpeak Qpeak Max WSEL Pond Storage Node ------ ID ------- ---- Type ---- Event ------ ac-ft Trun ---------- -- hrs --------- cfs -------- ft -------- ac-ft --------- - POND 10 IN POND 2 1.368 12.1000 29.66 - - POND 10 IN POND 10 2.446 12.1000 46.61 POND 10 IN POND 100 4.245 12.1000 65.26 POND 10 OUT POND 2 .845 15.0000 .64 195.72 .914 POND 10 OUT POND 10 1.922 12.3500 9.91 196.28 1.242 POND 10 OUT POND 100 3.720 12.2000 42.68 196.78 1.547 POST BYPASS AREA 2 .362 12.1000 5.73 POST BYPASS AREA 10 .900 12.1000 16.11 POST BYPASS AREA 100 1.971 12.1000 30.73 POST TO WETL AND AREA 2 1.368 12.1000 29.66 POST TO WETL AND AREA 10 2.446 12.1000 46.61 POST TO WETL AND AREA 100 4.245 12.1000 65.26 *POST- OUT JCT 2 1.207 12.1000 5.73 *POST- OUT JCT 10 2.822 12.1000 16.63 *POST- OUT JCT 100 5.691 12.1500 66.04 S/N: Bentley PondPack (10.00.027.00) 2:41 PM Bentley Systems, Inc. 7/8/2008 Type.... Master Network Summary Page 1.02 Name.... Watershed File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\OldeTowneRec.ppw MASTER NETWORK SUMMARY SCS Unit Hydrograph Method (*Node=Outfall; +Node=Diversion;) (Trun= HYG Truncation: Blank=None; L=Left; R=Rt; LR=Left&Rt) Return HYG Vol Qpeak Qpeak Max WSEL Node ID --------------- Type -- -- Event ac-ft Trun hrs cfs ft *PRE-OUT -- JCT ------ 2 ---------- -- .475 --------- 12.2000 -------- -------- 5.72 *PRE-OUT JCT 10 1.320 12.1500 19.77 *PRE-OUT JCT 100 3.092 12.1500 41.61 PREDEV-SITE AREA 2 .475 12.2000 5.72 PREDEV-SITE AREA 10 1.320 12.1500 19.77 PREDEV-SITE AREA 100 3.092 12.1500 41.61 Max Pond Storage ac-ft ------------ S/N: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Design Storms Name.... RDU NOAA 14 Desi Page 2.01 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw Title... Project Date: 6/26/2008 Project Engineer: DLee Project Title: Watershed Project Comments: DESIGN STORMS SUMMARY Design Storm File,ID = RDU NOAA 14 Desi Storm Tag Name = 2 Data Type, File, ID Storm Frequency Total Rainfall Depth Duration Multiplier Resulting Duration Resulting Start Time Time-Depth Curve RDU NOAA 2yr 2 yr 3.4400 in 1 23.9904 hrs .0000 hrs Step= .0833 hrs End= 23.9904 hrs Storm Tag Name = 10 Data Type, File, ID = Time-Depth Curve RDU NOAA 10yr Storm Frequency = 10 yr Total Rainfall Depth= 4.9800 in Duration Multiplier = 1 Resulting Duration = 23.9904 hrs Resulting Start Time= .0000 hrs Step= .0833 hrs End= 23.9904 hrs Storm Tag Name = 100 Data Type, File, ID = Time-Depth Curve RDU NOAA 100yr Storm Frequency = 100 yr Total Rainfall Depth= 7.3700 in Duration Multiplier = 1 Resulting Duration = 23.9990 hrs Resulting Start Time= .0000 hrs Step= .0833 hrs End= 23.9990 hrs SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Design Storms Page 2.02 Name.... RDU NOAA 14 Desi Event: 2 yr File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\OldeTowneRec.ppw Storm... RDU NOAA 2yr Tag: 2 DESIGN STORMS SUMMARY Design Storm File,ID = RDU NOAA 14 Desi Storm Tag Name = 2 Data Type, File, ID = Time-Depth Curve RDU NOAA 2yr Storm Frequency = 2 yr Total Rainfall Depth= 3.4400 in Duration Multiplier = 1 Resulting Duration = 23.9904 hrs Resulting Start Time= .0000 hrs Step= .0833 hrs End= 23.9904 hrs Storm Tag Name = 10 Data Type, File, ID = Time-Depth Curve RDU NOAA 10yr Storm Frequency = 10 yr Total Rainfall Depth= 4.9800 in Duration Multiplier = 1 Resulting Duration = 23.9904 hrs Resulting Start Time= .0000 hrs Step= .0833 hrs End= 23.9904 hrs Storm Tag Name = 100 Data Type, File, ID = Time-Depth Curve RDU NOAA 100yr Storm Frequency = 100 yr Total Rainfall Depth= 7.3700 in Duration Multiplier = 1 Resulting Duration = 23.9990 hrs Resulting Start Time= .0000 hrs Step= .0833 hrs End= 23.9990 hrs SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Tc Calcs Name.... POST BYPASS Page 3.01 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw ........................................................................ ........................................................................ TIME OF CONCENTRATION CALCULATOR ........................................................................ ........................................................................ Segment #1: Tc: User Defined Segment #1 Time: .0830 hrs ------------------------------------------------------------------------ Total Tc: .0830 hrs Calculated Tc < Min.Tc: Use Minimum Tc... Use Tc = .0833 hrs S/N: Bentley PondPack (10.00.027.00) 2:41 PM Bentley Systems, Inc. 7/8/2008 Type.... Tc Calcs Name.... POST BYPASS Page 3.02 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw ------------------------------------------------------------------------ Tc Equations used... ------------------------------------------------------------------------ ___= User Defined ______----- ________________ Tc = Value entered by user Where: Tc = Time of concentration SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Tc Calcs Name.... POST TO WETLAND Page 3.03 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw ........................................................................ ........................................................................ TIME OF CONCENTRATION CALCULATOR ........................................................................ ........................................................................ Segment #1: Tc: User Defined Segment #1 Time: .0830 hrs ------------------------------------------------------------------------ ------------------------- Total Tc: .0830 hrs Calculated Tc < Min.Tc: Use Minimum Tc... Use Tc = .0833 hrs S/N: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Tc Calcs Name.... POST TO WETLAND Page 3.04 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\OldeTowneRec.ppw ------------------------------------------------------------------------ Tc Equations used... ------------------------------------------------------------------------ User Defined -------- T c = Value entered by user Where: Tc = Time of concentration SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 • • • • • • • • • • • • • • • • • Type.... Tc Calcs Name.... PREDEV-SITE Page 3.05 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw ........................................................................ TIME OF CONCENTRATION CALCULATOR ........................................................................ ........................................................................ Segment #1: Tc: TR-55 Sheet Mannings n .1000 Hydraulic Length 100.00 ft 2yr, 24hr P 3.6000 in Slope .074000 ft/ft Avg.Velocity .42 ft/sec Segment #2: Tc: TR-55 Shallow Segment #1 Time: .0660 hrs Hydraulic Length 274.00 ft Slope .037000 ft/ft Unpaved Avg.Velocity 3.10 ft/sec Segment #2 Time: .0245 hrs ----------------------------------------------------------------------- Segment #3: Tc: TR-55 Channel Flow Area 16.0000 Wetted Perimeter 12.00 Hydraulic Radius 1.33 Slope .019000 Mannings n .0500 Hydraulic Length 532.00 sq.ft ft ft ft/ft ft Avg.Velocity 4.98 ft/sec Segment #3 Time: .0297 hrs ------------------------------------------------------------------------ Total Tc: .1202 hrs SIN: Bentley PondPack (10.00.027.00) 2:41 PM Bentley Systems, Inc. 7/8/2008 Type.... Tc Calcs Name.... PREDEV-SITE Page 3.06 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw ------------------------------------------------------------------------ Tc Equations used... ------------------------------------------------------------------------ ___= SCS TR-55 Sheet Flow ____ Tc = (.007 * ((n * Lf)**0.8)) / ((P**.5) * (Sf**.4)) Where: Tc = Time of concentration, hrs n = Mannings n Lf = Flow length, ft P = 2yr, 24hr Rain depth, inches Sf = Slope, a ___= SCS TR-55 Shallow Concentrated Flow =----------------- Unpaved surface: V = 16.1345 * (Sf**0.5) Paved surface: V = 20.3282 * (Sf**0.5) Tc = (Lf / V) / (3600sec/hr) Where: V = Velocity, ft/sec Sf = Slope, ft/ft Tc = Time of concentration, hrs Lf = Flow length, ft SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... To Calcs Name.... PREDEV-SITE Page 3.07 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\OldeTowneRec.ppw ___= SCS Channel Flow R = Aq / Wp V = (1.49 * (R**(2/3)) * (Sf**-0.5)) / n To = (Lf / V) / (3600sec/hr) Where: R Aq Wp V Sf n To Lf Hydraulic radius Flow area, sq.ft. Wetted perimeter, ft Velocity, ft/sec Slope, ft/ft Mannings n Time of concentration, hrs Flow length, ft SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Runoff CN-Area Name.... POST BYPASS Page 4.01 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw RUNOFF CURVE NUMBER DATA .......................................................................... .......................................................................... Impervious Area Adjustment Adjusted Soil/Surface Description - ---------- - CN --- acres --------- °C %UC ----- ----- CN ------ ----------------- ---- Impervious Areas - Paved parking to 98 .350 98.00 Woods - good 55 1.720 55.00 Open space (Lawns,parks etc.) - Goo 61 5.890 61.00 COMPOSITE AREA & WEIGHTED CN ---> .................................... .................................... .... .... 7.960 .......... .......... ............ ............ 61.33 (61) ............. ............. SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Runoff CN-Area Name.... POST TO WETLAND Page 4.02 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw RUNOFF CURVE NUMBER DATA .......................................................................... .......................................................................... Impervious Area Adjustment Adjusted Soil/Surface Description -------------------------------- - CN --- acres --------- %C %UC CN ----- ----- ------ Impervious Areas - Paved parking to 98 3.390 98.00 Open space (Lawns,parks etc.) - Goo 61 3.130 61.00 Off-Site Impervious 98 1.930 98.00 Off-Site Open 61 1.440 61.00 COMPOSITE AREA & WEIGHTED CN ---> .................................... .................................... .... .... 9.890 .......... .......... 80.90 (81) ......................... ......................... SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Runoff CN-Area Name.... PREDEV-SITE Page 4.03 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw RUNOFF CURVE NUMBER DATA .......................................................................... .......................................................................... Impervious Area Adjustment Adjusted Soil/Surface Description - ---------- - CN --- acres --------- °C %UC CN ----- ----- ------ -------------------- - Open space (Lawns,parks etc.) - Goo 61 4.757 61.00 Woods - good 55 8.632 55.00 Woods - grass combination - good 58 1.091 58.00 COMPOSITE AREA & WEIGHTED CN ---> .................................... .................................... .... .... 14.480 .......... .......... 57.20 (57) ......................... ......................... SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Vol: Elev-Area Name.... POND 10 Page 5.01 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw Elevation Planimeter Area Al+A2+sgr(Al*A2) Volume Volume Sum (ft) ------------ (sq.in) (sq.ft) --------------------- (sq.ft) ----------------- (ac-ft) --------- (ac-ft) ------ 194.00 ----- 21529 0 .000 ------- .000 195.00 ----- 23451 67449 .516 .516 196.00 ----- 25429 73300 .561 1.077 197.00 ----- 27464 79320 .607 1.684 POND VOLUME EQUATIONS * Incremental volume computed by the Conic Method for Reservoir Volumes. Volume = (1/3) * (EL2-EL1) * (Areal + Areal + sq. rt. (Areal*Area2) ) where: ELI, EL2 = Lower and upper elevations of the increment Areal,Area2 = Areas computed for ELI, EL2, respectively Volume = Incremental volume between ELI and EL2 S/N: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Outlet Input Data Name.... Outlet 1 Page 6.01 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw REQUESTED POND WS ELEVATIONS: Min. Elev.= 194.00 ft Increment = .10 ft Max. Elev.= 197.00 ft OUTLET CONNECTIVITY ---> Forward Flow Only (UpStream to DnStream) <--- Reverse Flow Only (DnStream to UpStream) <---> Forward and Reverse Both Allowed Structure No. Outfall E1, ft E2, ft Inlet Box RO ---> CO 196.000 197.000 Orifice-Circular 00 ---> CO 195.000 197.000 Culvert-Circular CO ---> TW 190.300 197.000 TW SETUP, DS Channel SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Outlet Input Data Name.... Outlet 1 Page 6.02 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw OUTLET STRUCTURE INPUT DATA Structure ID = RO Structure Type ------------ = Inlet Box ------ # of Openings ------------ = 1 ------ Invert Elev. = 196.00 ft Orifice Area = 25.0000 sq.ft Orifice Coeff. _ .600 Weir Length = 20.00 ft Weir Coeff. = 3.000 Transition Elev. = 197.00 ft Transition Ht. _ .00 ft Crossover Elev. = 196.00 ft (weir = orifice) K, Reverse = 1.000 Mannings n = .0000 Kev,Charged Riser = .000 Weir Submergence = No Structure ID = 00 Structure Type = Orifice-Circular ------------------------------------ # of Openings = 1 Invert Elev. = 195.00 ft Diameter = .5000 ft Orifice Coeff. _ .600 SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 Type.... Outlet Input Data Name.... Outlet 1 Page 6.03 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\O1deTowneRec.ppw OUTLET STRUCTURE INPUT DATA Structure ID = CO Structure Type = Culvert-Circular ------------- ----------------- No. Barrels ------ = 1 Barrel Diameter = 3.0000 ft Upstream Invert = 190.30 ft Dnstream Invert = 190.00 ft Horiz. Length = 60.00 ft Barrel Length = 60.00 ft Barrel Slope = .00500 ft/ft OUTLET CONTROL DATA... Mannings n = .0130 Ke = .5000 Kb = .007228 Kr = .5000 HW Convergence = .001 (forward entrance loss) (per ft of full flow) (reverse entrance loss) +/- ft INLET CONTROL DATA... Equation form = 1 Inlet Control K = .0098 Inlet Control M = 2.0000 Inlet Control c = .03980 Inlet Control Y = .6700 T1 ratio (HW/D) = 1.158 T2 ratio (HW/D) = 1.304 Slope Factor = -.500 Use unsubmerged inlet control Form 1 equ. below T1 elev. Use submerged inlet control Form 1 equ. above T2 elev. In transition zone between unsubmerged and submerged inlet control, interpolate between flows at T1 & T2... At Tl Elev = 193.77 ft ---> Flow = 42.85 cfs At T2 Elev = 194.21 ft ---> Flow = 48.97 cfs Structure ID = TW Structure Type = TW SETUP, DS Channel ------------------------------------ FREE OUTFALL CONDITIONS SPECIFIED CONVERGENCE TOLERANCES... Maximum Iterations= 40 Min. TW tolerance = .01 ft Max. TW tolerance = .01 ft Min. HW tolerance = .01 ft Max. HW tolerance = .01 ft Min. Q tolerance = .00 cfs Max. Q tolerance = .00 cfs SIN: Bentley PondPack (10.00.027.00) 2:41 PM Bentley Systems, Inc. 7/8/2008 Type.... Composite Rating Curve Name.... Outlet 1 Page 6.04 File.... K:\08\08-0510\080510-Olde Towne - The Residence Ctr\H-H\OldeTowneRec.ppw ***** COMPOSITE OUTFLOW SUMMARY **** WS Elev, Total Q Notes -------- -------- ----- --- Converge ------------------------- Elev. Q TW E lev Error ft -------- cfs ------- f ----- t +/-ft --- Contributing Structures 194.00 .00 Free ----- Outfall -------------------------- (no Q: RO,OO,CO) 194.10 .00 Free Outfall (no Q: RO,OO,CO) 194.20 .00 Free Outfall (no Q: RO,OO,CO) 194.30 .00 Free Outfall (no Q: RO,OO,CO) 194.40 .00 Free Outfall (no Q: RO,OO,CO) 194.50 .00 Free Outfall (no Q: RO,OO,CO) 194.60 .00 Free Outfall (no Q: RO,OO,CO) 194.70 .00 Free Outfall (no Q: RO,OO,CO) 194.80 .00 Free Outfall (no Q: RO,OO,CO) 194.90 .00 Free Outfall (no Q: RO,OO,CO) 195.00 .00 Free Outfall (no Q: RO,OO,CO) 195.10 .02 Free Outfall O0,C0 (no Q: RO) 195.20 .09 Free Outfall OO,CO (no Q: RO) 195.30 .19 Free Outfall OO,CO (no Q: RO) 195.40 .31 Free Outfall OO,CO (no Q: RO) 195.50 .47 Free Outfall O0,C0 (no Q: RO) 195.60 .56 Free Outfall O0,C0 (no Q: RO) 195.70 .63 Free Outfall OO,CO (no Q: RO) 195.80 .70 Free Outfall O0,C0 (no Q: RO) 195.90 .76 Free Outfall OO,CO (no Q: RO) 196.00 .82 Free Outfall O0,C0 (no Q: RO) 196.10 2.77 Free Outfall RO,OO,CO 196.20 6.29 Free Outfall RO,OO,CO 196.30 10.82 Free Outfall RO,OO,CO 196.40 16.18 Free Outfall RO,OO,CO 196.50 22.27 Free Outfall RO,OO,CO 196.60 28.99 Free Outfall RO,OO,CO 196.70 36.28 Free Outfall RO,OO,CO 196.80 44.12 Free Outfall RO,OO,CO 196.90 52.45 Free Outfall RO,OO,CO 197.00 61.20 Free Outfall RO,OO,CO S/N: Bentley PondPack (10.00.027.00) 2:41 PM Bentley Systems, Inc. 7/8/2008 Appendix A Index of Starting Page Numbers for ID Names A-1 ----- 0 ----- Outlet 1... 6.01, 6.04 ----- P ----- POND 10... 5.01 POST BYPASS... 3.01, 4.01 POST TO WETLAND... 3.03, 4.02 PREDEV-SITE... 3.05, 4.03 ----- R ----- RDU NOAA 14 Desi... 2.01, 2.02 ----- W ----- Watershed... 1.01 SIN: Bentley Systems, Inc. Bentley PondPack (10.00.027.00) 2:41 PM 7/8/2008 BMP Sizing Project Name: Olde Towne Rec. Cent. City/State: Raleigh, NC Project #: 2080510 Date: 30-Jul-08 Table 1.1 Surface Area to Drainage Area Ratio for Permanent Pool Sizing for 85% Pollutant Removal Efficiencv in the Piedmont % Impervious Cover Permanent Pool Depth (feet) 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 0.59 0.49 0.43 0.35 0.31 0.29 0.26 20 0.97 0.79 0.70 0.59 0.51 0.46 0.44 30 1.34 1.08 0.97 0.83 0.70 0.64 0.62 40 1.73 1.43 1.25 1.05 0.90 0.82 0.77 50 2.06 1.73 1.50 1.30 1.09 1.00 0.92 60 2.40 2.03 1.71 1.51 1.29 1.18 1.10 70 2.88 2.40 2.07 1.79 1.54 1.35 1.26 80 3.36 2.78 2.38 2.10 1.86 1.60 1.42 90 3.74 3.10 2.66 2.34 2.11 1.83 1.67 Source: NCDENR/DWQ Stormwater Best Management Practices, Table 10-2, July 2007 STORMWATER BMP 1 - STORMWATER WETLAND (40% TN Removal) Land Use Area (ac) % IA Imp. Area (ac) Impervious 5.32 98 5.2 Open Space 4.57 0 0.0 Totals 9.89 5.2 Total % Impervious Surface Area = 53.8% Surface Area of Permanent Pool: Assumed depth = 3 feet SA/DA ratio = 2.19 % From Table 1.1 Minimum pond surface area (SA) = (DA * SA/DA ratio)/100 SA = 0.216 acres 9430 sq. ft. Normal pool elevation = 194.0 feet Surface area provided = 0.494 acres 21529 sq. ft. 1-Inch Runoff Volume Calculation Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987) Rv = 0.05 + 0.9(I) where, Rv = Runoff coefficient, in./in. = Percent impervious Rv = 0.53 in./in. Total runoff volume from 1-inch precipitation: Runoff volume, S = (Design rainfall) (Rv) (Drainage Area) S = 0.440 acre-ft 19175 cu. ft. Water quality pool elevation= 195.00 feet Storage volume provided = 0.510 acre-ft 22216 cu. ft. Project Name: Olde Towne Rec. Cent. i /State: Raleigh, NC STORMWATER BMP - WETLAND (40% TN Removal) Orifice Calculator Q =Cd*A*(2gh)^(1/2) Variables WQ Volume: Head: Draw down time: 0.51 Acre-ft 1.00 ft 83 hrs 22215.6 cf 0.5 ft 298800 s Orifice Area = 0.021837 sq. ft Orifice Diameter = 2.000947 in 3.144566 sq. in Project #: 2080510 Date: 9-j u 1-08 Constants g = 32.2 ft/sz Cd = 0.6 USE 2 INCH DIAMETER ORIFICE Nitrogen Calculations Nitrogen Control Plan Commercial / Industrial / Residential Sites with Known Impervious Area Project Title: Olde Towne Rec. Site PartL Riparian Buffers Area includes riparian buffers? [ ] No [ X ] Yes [ ] Exempt If yes, [ X ] 50 foot [ ] 100 foot River Basin? [ X ] Neuse [ j Cape Fear Basis for Exemption Show buffers on site plan. Part II. Nitrogen Calculations (Method 2, Appendix C): a. Site Information Total Area of Property incl. R/W 14.48 Denuded Area 14.48 Impervious Area incl. R/W 3.91 Managed open space 8.85 Protected open space 1.72 b. Pre-development loading: Type of Land Cover Permanently protected undisturbed open space (forest, unmown meadow) Permanently protected managed open space (grass, landscaping, etc.) Impervious Area TOTAL Nitrogen Loading Rate (Ibs/ac/yr) _ c. Post-development loading; acres acres acres acres acres TN Export Area TN export coeff from use (acresl (Ibs/ac/vrl (Ibs/vrl 14.48 0.6 8.69 0 1.2 0 0 21.2 0 14.48 8.69 0.60 TN Export Area TN export coeff from use lacresl Hhs/ac/vrl (Ihs/vrl Type of Land Cover Permanently protected undisturbed open space (forest, unmown meadow) Permanently protected managed open space (grass, landscaping, etc.) Impervious Area TOTAL Nitrogen Loading Rate (Ibs/ac/yr) _ 1.72 0.6 1.03 8.85 1.2 10.62 3.91 21,2 82.89 14.48 94.54 6.53 Proposed BMP(s) Wetland Nitrogen Load after BMPs = 4.21 Ibs/ac/yr Nitrogen Load offset by Payments = 0.61 Ibs/ac/yr Estimated Buy Down = $7,456 Net change in on-site N Load = 2.93 Ibs/ac/yr • • Nitrogen Control Plan Commercial / Industrial / Residential Sites with Known Impervious Area Towne Project Name: Olde Towne Rec Site Project #: 2080510 TOTAL TRACT Total Area 60,7. T3. sqft. = 14.48 ac. Impervious sgft. = 3.91 ac. Natural Open Space Area. ` 2855 966- sgft. = 8.85 ac. Managed Open Space Area: ? ' '74,43> sqft. = 1.72 ac. Estimated Pre-Development TN Loading Date: 7/10/2008 Computed by: DBH Type of Land Cover Acres TN Export Coeff. TN EXPORT (Ibs/yr) (Ibs/ac/yr) Permanently Protected Undisturbed Area 14.48 0.6 8.69 Permanently Protected Managed Area 0.00 ' 1.2 0.00 Impervious Surface .0.00 21.2 0.00 Totals 14.48 0.6 8.69 Estimated Post-Development TN Loading Drainage Area I: Type of Land Cover Acres TN Export Coeff. TN EXPORT (Ibs/yr) (Ibs/ac/yr) Permanently Protected Undisturbed Area 0.00 0.6 0.00 Permanently Protected Managed Area 3.13 1.2 3.76 Impervious Area 3,39 21.2 71.87 Totals 6.52 75.62 Estimated UMN Keducllon Tor VVetland: 4u Estimated Drainage Area I Nitrogen Loading Reduction: 30.25 Ibs/yr Drainage Area II: Type of Land Cover Acres TN Export Coeff. (Ibs/ac/yr) TN EXPORT (Ibs/yr) Permanently Protected Undisturbed Area 1.72 0.6 1.03 Permanently Protected Managed Area 5.89 1.2 7.07 Impervious 0:35 21.2 7.42 Totals 7.96 15.52 Estimated rsMr reduction: u io Estimated Drainage Area II Nitrogen Loading Reduction: 0.00 Ibs/yr Total Area: 14.48 Acres Estimated Project Pre-BMP TN Export: 91.14 Ibs/yr Estimated Project BMP TN Removal: 30.25 Ibs/yr Estimated Project TN Load Rate After BMPs: 4.21 Ibslac/yr Estimated Project Composite Nitrogen Loading Rate Reduction: 33.19 % Estimated Project Buy Down: $7,455.82