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Home My WebLink About20140874 Ver 1_Stormwater Management Plan_20140813Stormwater Management Plan Cedar Ridge Tract Subdivision & Virginia Waters Drive Roadway Improvements Town of Rolesville, North Carolina 502 Southtown Cir, Rolesville, NC 27571 (919) 556 -3506 Contents Include: Project Description Project Area and Stormwater Runoff characteristics Proposed Stream, wetland and buffer impacts. Pre and Post development runoff Nitrogen Reduction and TSS Treatment Ditch calculations Erosion Control Measures and Rip Rap calcs Site Area Map SCS Soils Map Flood Map Drainage Area Map (culverts) Drainage Area Map (BMP) (1� 64� ?� --X/-/'S '4V SEAL 24951 8 -05 -14 Aiken & Yelle Associates, PA Professional Engineers and Land Survey 3755 Benson Drive Raleigh, North Carolina 27609 Phone: (919) 877 -9992 Fax: (919) 877 -9979 Project Description The project includes transportation improvement and subdivision of the 70 acre parent tract. The proposed improvements include a 2700 feet of a 36' wide curb and guttered roadway. The roadway is part of the Town's collector street system that has been deemed to be critical for the town's transportation infrastructure system. The tract will be subdivided into 4 pod tracts that ultimately will be subdivided into 117 low density residential lots. Tract Subdivision Stormwater Runoff characteristics The 70 acre property is zoned low density residential. The predominant soil type is Louisburg characteristic of sandy loam surface soil to a 2 feet depth and granite type bedrock at 2 -5 foot depth. The property is wooded primarily with pines. The property will be limited to less than 24% post development. Project Stream Impact Area and Stormwater Runoff characteristics: Virginia Waters Drive is located through a the 70 acre. The area to be used for this roadway and associated stormwater controls is 7.00 acres. There will be 79,130 sf. of impervious area associated with the Virginia Waters Drive extension project. The stormwater runoff generated consists of typical street and residential runoff. The location of the roadway is such that most offsite (outside of right of way) runoff is directed away from the street. There are 2 stream crossings of Harris Creek associated with this roadway. Stream crossing #1 occurs at station 12 +80 + -. Stream crossing #2 occurs at station 39 +00 + -. The stream has been designated as a perennial stream at both locations. Stream crossing 1 will be managed by a 60 inch concrete pipe culvert with a buried invert. The drainage area to this culvert is 25.0 + - acres. The length of the culvert is 137.0'. Stream crossing #2 will be managed by a ConSpan concrete bridge 25'(w) x 10'(h) culvert. The ConSpan Bridge is used due to the presence of granite rock at this stream crossing location. The drainage area to this culvert is 240.0 + - acres. Each culvert crossing is located in only location possible as dictated by topography and location of existing streams and ponds in the area. Due to the vertical design criteria of the proposed roadway and the steep topography large fill area are required at the stream crossing locations. All efforts have been made to minimize and or avoid wetland and stream impacts and still maintain public health, safety and welfare. The runoff volumes for culvert sizing were estimated using SCS 24 hr Type II storm and based on current zoning full build out conditions. The estimated runoff flows at each stream crossing are as follows: Stream crossing 1- Q2 =14.5 cfs., Q10 =36.8 cfs., Q100 =77.3 cfs. Stream crossing 2- Q2= 53.8 cfs., Q10= 145.2 cfs., Q100= 373.4 cfs. Proposed Stream, wetland and buffer impacts. There are no proposed wetland impacts proposed for the proposed tract subdivision or roadway improvements being requested at this time. As noted above there are 2 locations of stream and buffer impacts. The impacts area as follows: Stream crossing #1 occurs at station 12 +80 137 if stream impact including dissipater 514 sf of stream impact 8,431 sf of NRB Zone 1 impact 2,791 sf of NRB Zone 2 impact (north of stream) 2,694 sf of NRB Zone 2 impact (south of stream) Stream crossing #2 occurs at station 39 +00 +- 0 if stream impact including dissipater 0 sf of stream impact 8,330 sf of NRB Zone 1 impact 3,098 sf of NRB Zone 2 impact (east of stream) 2,595 sf of NRB Zone 2 impact (west of stream) Pre and Post development runoff Tract subdivision: In the pre development and post development runoff patterns are basically unchanged. Most of the runoff from the residential subdivision will be disconnect runoff. The street runoff is being managed by grass bio retention areas prior to release into the buffer areas. The runoff into the buffer areas is managed to the 1 year storm event. The crass bioretention areas servinc the future subdivision are as follows: Cedar Ridge Bioretentio n area no. Drainag a area (sq ft) Drainag a area (ac) Imperviou s area (sq ft) la Rv Provided WQV (cu ft) WQV by Simple Method (cu ft) 1 18,700 0.43 5,400 0.29 0.310 693 483 2 60,300 1.38 35,500 0.59 0.580 2870 2,914 3 90,600 2.08 37,870 0.42 0.426 3210 3,218 4 24,400 0.56 16,800 0.69 0.670 1,588 1,362 5 84,500 1.94 26,959 0.32 0.337 2635 2,374 6 53,500 1.23 28,800 0.54 0.534 2338 2,383 7 31,400 0.72 9,600 0.31 0.325 938 851 8 43,100 0.99 9,100 0.21 0.240 1719 862 9 84,700 1.94 29,000 0.34 0.358 3080 2,528 10 82,900 1.90 17,500 0.21 0.240 1688 1,658 See plans for further details Pre and Post development runoff Virginia Waters Drive: In the pre development and post development runoff patterns are basically unchanged. All post development runoff entering the streams at the culvert crossing will be managed by 4 grass bioretention basins. The Bioretention basins are to be located in public drainage easements. The bioretention areas have been designed to accommodate F runoff volume. The runoff in excess of the WQV will be directed to the downstream headwall of each crossing via a flow split manhole. The grass bioretention areas are to be located as follows: Bio area 1 Station 12 +10 north 50' Bio area 2 Station 14 +50 north 50' Bio area 3 Station 37 +50 north 60' Bio area 4 Station 38 +15 south 62' Virginia Waters Drive Rolesville NC DS PIP E SLOP E V Dia Bioretent ion area no. Drainage area (sq ft) Draina ge area (ac) Imperviou s area (sq ft) la Rv WQV Provided (cu ft) WQV by Simple Method (cu ft) inlet velocity (fps) Draw down time (hours) 1 18,700 0.43 5,400 0.29 0.310 693 483 4.32 1.50 2 60,300 1.38 35,500 0.59 0.58 2,870 2,914 3.53 6.25 3 90,600 2.08 37,870 0.42 0.426 3,210 3,218 4.99 2.80 4 24,400 0.56 16,800 0.69 0.670 1,588 1,362 4.99 3.00 Totals 194,0002 1 4.45 1 95,570 17.6 14.93 18 0.015 RCP SMH #61B The Bioretention outflow for all storm events in excess of the first 1 inch of runoff including the Q1OO storm are managed via a flow splitting manhole. The outflow of the manhole will be tied into the adjacent headwalls to minimize buffer impacts associated with high velocity flows due to steep topography. The flow chart below demonstrates the require pipe sizes to manage the Q1OO storm event. PIPE SECTION Q100(c fs) Q100(cf s) RIM US DS PIP E SLOP E V Dia Dia use n TYP E FROM TO SUB TOTAL ELEV INV INV (it) % fps regd (in) SMH #10 HW #75 3.50 3.50 387.5 383.7 370.50 80 16.56 18.5 7.42 15 0.015 RCP SMH #13 HW #75 18.98 18.98 385.5 378.0 370.50 64 11.72 17.6 14.93 18 0.015 RCP SMH #61B HW #76 11.92 11.92 352.0 346.0 332.00 78 17.95 19.3 11.58 15 0.015 RCP SMH #64 HW #77 5.25 5.25 345.5 338.7 332.00 41 16.46 18.4 8.65 15 0.015 RCP Nitrogen Reduction and TSS Treatment: The nitrogen loading reductions and TSS removal is provided by the Bioretention areas shown on plan. We have not provided loading calculations with this submittal. Ditch calculations No ditches are proposed with this project. Erosion Control Measures The tract subdivision shall comply with all applicable standards for sediment and erosion control. The project erosion control will be provided by skimmer type sediment basins. The sediment basins will be temporarily located in the same location as the proposed bioretention location. The pipe sizing calculations for Q1O storm events are on the site plans are the basis of the culvert rip rap aprons. Rip rap dissipation is provided at HW 75, HW 77 has no dissipation requirements due to the proposed ConSpan bridge at this location . Sizing calculations are as follows: HW 75 Estimation of Stone Size and Dimensions For Culvert Aprons Step 1) Compute flow velocity N -' at culvert or pared channel outlet. Step 2) For pipe culverts D. is diameter. For pipe arch, arch and box culverts, and paved channel outlets. Do = A. where A. = cross - sectional area of flow at outlet. For multiple culverts, use D. = 1.25 x Do of single culvert. Velocity (ft /s) 9.23 Opening type Pipe Culvert Single or multiple openings? Single Outlet pipe diameter, Do (ft) 5.0 NOTE 1: If opening type is anything other than "Pipe Culvert ", Do =Ao (Cross - sectional area of flow at outlet). NOTE 2: If multiple openings, Do =1.25 x Do of single culvert. Step 3) For apron grades of 10 % or steeper, use recommendations For next higher zone. (Zones 1 through b). Zone 2 Figure 8.06c Will apron have >/ =10% grade? No NOTE: For apron slopes equal to or greater than 10 %, use next higher Zone in Figure 8.06d to determine apron length. Apron length (ft) 10 Figure 8.06d Drainage Area map Culverts Attached here in Drainage Area map BMPs Attached here in and in plan set IN ad IN IN Nj cn % I / ♦ \1 1 \\ / wr I _ O I Cedar Rida St- Stora.. Grass Biorete=n area Drainage area Drainage area Impervious area Reported WQV WQV by Simple Method inlet velocity 1 18,700 0.43 &400 0.29 0,310 693 483 4.32 2 60,300 1.38 35,500 0.59 0.580 2870 2 914 3.53 3 90,600 2.08 37,870 0.42 0.426 3210 3,218 4.99 384.75 810 693 344.75 2.970 2635 374.75 1.362 3080 385.25 905 429 345 3.200 771 375 4.130 956 6 53,500 113 28 800 0.54 0.534 2338 2.383 4.32 8 41100 0.99 9,100 0.21 0,240 1719 862 3.95 Elev Area Volume Elev Area Volume I I Elev Area Volume 10 82 900 1.90 17,500 0.21 0.240 1688 1 658 3.22 Bio Area St- Stora.. 1 Bev Area Volume Elev Area Volume Bev Area Volume 383.75 575 343.75 2.300 373.75 2.640 384.75 810 693 344.75 2.970 2635 374.75 3.520 3080 385.25 905 429 345 3.200 771 375 4.130 956 1121 3406 4036 z Elev Area Volume Elev Area Volume I I Elev Area Volume 380 450 347 1.250 381 3 290 2870 354.75 700 2338 348 2125 1688 3 81.25 3,410 838 348.25 2 620 593 3708 3076 2281 3 Eley Area Volume Eley Area Volume 5068 1263 a Area Volume Elev Area Volume 438.75 960 440 1,580 1588 372 2,028 1719 440.25 1 880 430 37225 2 210 530 2018 1 2249 PERENNIAL STREAM 41 .-Ac./ / 5 PU 91555 �� /-/ / I err ! rI -IO_\ � \r ♦� / x \ ___ / / / / ♦ y AuN 8-05-1 IF PIP BEAVER _ WETLAND :EXISTING PUN /, i/! // /, i/! // //' ! �..: -ii/ -� �___ .ux... \ \. •. �\� - � \` �\�� s PERENNIAL STREAM /�/ / , // , / / / / !/ / , /� /' \� �-`� •YNl" r, `'\ _ ! �\�\,n fe$1' }$B� _ - ;'� / � �' � /'1 1 i� �� '� '- -- - � \ -� s .� /f'\ � 75 /" /•\ � \\ t /tee. dye\ \ *� / \ /• � l \ \\ / ,/, / i, \' . 1 i ��;i /'� t -.. ,. ,� °'' iii � /' <\ / !\ /� �\ � �\ �,� Z /' I I \\ \ / a/ ,� / j� \ \ • / �/ 1 / '1, / u , - 1 1 11 \ \ I '�\ Ll > / \ / / -�, $ PER EN AL STREAM r fi0 -- - - -� I I / / �� 1 I I l�r+; 1 +Itl C'�• � I'` /'�e i /� /� \'� i /'_ ! 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ALL STOLE WATER CONTROL MEAMM AD M MEASURES SIDEH EKDI SHALL E PETALLiL AREAS xsnNVD sr misRNxnax AND OF RUM xm NoTwlm E PAYED ON \ \ i Y \ \ / / Y v��Iy✓/ � i ' .`� \' , ` 'h - / / J W 1" SP7fDmU CONFILETION ON OF GR DINS AONWEL uE HE#1 a MOSSE Sl ACCORDANCE 1�1 ,L O'/' '• " \ \YV1 \\ ",��My�\\ / 2L CONIRACIWT SHALL CLEAR AND WNE ILD1 IITI//RS SERNI 1001 E AL NEEECRM // \ ^� / / \ ( �' • = _ 2a IE 0100 940CM ER EEVATNN FOR Ill CllWF6 ORASIO + OR MOLE AWES DES Nor THIS PLAN COMPLIES WITH TOWN OF ROLESMLLE 24. wl° l�H'M.R,,u MYR eE Ixm OF THE RIEDE NPARw WRIER WITH CRAW TES C� O / �� STORM WATER ORDINANCE EFFECTIVE IN 2008 R THERE Is Ar cwanwla WITHIN a0 FET s THE EDGE E nE as as SIM I I /a / �I %/ \ \ �_,0d I dill\ -mss THIS PLAN COMPLIES WITH TOWN OF ROLESVILLE 22L 25. THESE ARE NO WATER MEMOS AND OL1�E�W ARE NOT M'ROIO TO E INSTALLED IN ? / \ \ \ i �If F " 1 111M11 Z` BMRON I mYEMYS a SIEWUxs w /,y I. // /� RUBY .,902 STORM WATER ORDINANCE EFFECTIVE IN 2009 PER SECTION 7.5. J. 2 GRAPHIC SCALE PROP09ED ANNIYRWS 911EAE sl w w sEERAx: Iwa�LaeN a lall, Ac> Toro FYDraED AFVeYVaa aNaADE maem E bs m Aq (~ F,Yaospp x A,IFAMNR ,Sep AC / Aal Ao- 24.2RL ( • uR s 9AEp p aDp s FNnYNT, ,w s x Wnc pRYE AE SWRAN. 1 110 . ]Op �• SHEET 2D OF