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Home My WebLink AboutWPO201300029 Calculations 2016-02-14 MINIMUM STANDARD 3.10 CHAPTER 3 It has been shown that porous pavement is more skid-resistant than conventional pavement in rainy weather and that the markings on a porous pavement are easier to see on rainy nights. In addition, studies have suggested that porous asphalt pavement is sufficiently strong and able to withstand freeze-thaw cycles and will last as long, structurally, as conventional pavement. Typically, porous pavement is slightly more expensive than regular pavement. Additional costs associated with critical installation procedures and the availability of the asphalt mix may be offset by eliminating the need for curb and gutter, inlets, and conveyance systems. Availability is a consideration, since asphalt producers may not be willing to provide porous asphalt for small projects due to the demand for conventional asphalt mixes.For the production of a porous pavement mixture,the asphalt plant must be cleaned out to remove the fines not wanted in the porous mix. The cost of the stone reservoir and filter fabric associated with porous pavement is offset by the amount that would be spent on a stormwater facility elsewhere on the site. Installation requires a very high level of workmanship throughout the construction process;porous pavement must be handled with great care in order for it to retain its porous qualities. Many pavement contractors and pavement engineers have limited experience in designing and constructing porous pavement. Improper installation can render a porous pavement design inoperative from the outset. The biggest drawback to porous pavement is its tendency to clog if improperly maintained. Once it is clogged, it may have to be completely replaced since rehabilitating it is difficult and costly. On going maintenance of the pavement surface and specific limitations on the methods of snow and ice removal are often ignored and/or forgotten over time and with transfers of ownership. Clogging of the pavement surface from construction-related erosion can be prevented by waiting until all other phases of construction are complete and vegetation is stabilized before installing the pavement. Clogging of the pavement surface from natural circumstances is best prevented by installing it in areas that do not have highly erodible soils or steep slopes adjacent to the paved area. Certain features can be incorporated into the design of porous pavement facilities to prolong the effective life of the system. One such feature is to "daylight" the aggregate base along the downslope edge of the pavement, forming a chimney drain into the stone storage under the pavement. The runoff can flow into the stone storage through the chimney drain if the pavement clogs. If slow infiltration rates in the subgrade exist, porous pavement systems can be designed with an underdrain or collector system. When the collector system has a restriction plate on the outlet that controls the discharge, the stone reservoir can be designed as an underground stone-storage detention facility. Evidence suggests that pollutants adsorb to the aggregate material, while particulates settle to the bottom of the aggregate layer.However,the target removal efficiency of 50%to 65%,as presented in Table 3.10-1 for infiltration facilities, is too high for a stone-storage facility. Therefore, a 3.10D- 3 MINIMUM STANDARD 3.10 CHAPTER 3 porous pavement facility with a stone storage underdrain system that provides positive drainage will be considered an extended-detention or detention facility. Its target pollutant removal efficiency will be based on the storage and release rate characteristics of these facilities as presented in Minimum Standards 3.07,Extended-Detention; and 3.08,Detention Basins,until more information is collected to support the use of a higher pollutant removal efficiency. Design Criteria The purpose of this section is to provide recommendations and minimum criteria for the design of porous pavement intended to comply with the runoff quality requirements oftheVirginia Stormwater Management programs. The general design criteria for the porous pavement stone reservoir area and the underlying soils are the same as for infiltration trenches. Additional design is required for determining the porous pavement thickness. The design of the pavement is dependent on the strength of the sub-base soil, the projected traffic intensities, and the storage capacity of the reservoir and base. A thorough examination of the site is of primary importance to the prover design and functioning of porous pavement. Soil and climate conditions,expected surface wear,and the use objectives of the porous surface should all be considered before designing the pavement. The following represents a general list of design elements that should be considered in any porous pavement design: 1. Anticipated traffic intensities, defined by the average daily equivalent axle load(EAL). 2. California Bearing Ratio (CBR) of the soils. 3. Susceptibility of the soils to frost heave. Due to the complexity of its design,a step-by-step procedure to engineer a porous pavement section will not be presented in this manual. A professional engineer, with training and experience in porous pavement design and construction,should design the pavement section and supervise during the paving operation. Specific design requirements for a satisfactory porous asphalt pavement section equivalent to a conventional pavement design are available through the U. S. Department of Transportation's Federal Highway Administration and through other references listed at the end of this standard. Specific design requirements for a satisfactory porous concrete pavement section are available through the Florida Concrete and Products Association, 649 Vassar Street,Orlando,Florida 32804. Other references are also listed at the end of this standard. 3.10D - 4 5/17/2013 u Internal Water Zone Bioretention Cell Schematic tt tt. s Bowl . Sandy Fill '. "; " ' Drainage Media 4 Internal Water yz ` St Under r ins;, Upturned Elbow i� 44C.".t � 4•,P1� In-situ Soil Exfiltration In-situ Sod CSUCIEUNIVERSITY What is an Internal Water Storage Zone? • Internal Water Storage = IWS • Originally developed to improve nitrate reduction in N-sensitive watershed — Bottom of cell remains saturated 4 anaerobic conditions created to reduce nitrate TN • Main benefit - "Infiltration Enhancer" — Biggest impact in sandy in-situ soils • Outflow - rare www.bae.ncsu.edu/stormwater &A 2 5/17/2013 ,. How is an Internal Water Storage Zone Created? • Elevating the outlet with a 90° PVC elbow to force water to be ponded in bottom layer. 3u s qq� c F , :04W (' T 9 9A/'. www.bae.ncsu.eduJstormwater Most ommon Inst- Method: Upturned Pipe in Outlet m ,,,,elfr o ; 1i t@ www.bae.ncsu.eduJstarmwater y wm 3 5/17/2013 Looking down into the Overflow Basin • otr- 4-t , • Bio8c‘-'N,14' www.bae.ncsu.edu/stormwater NICSIAIEUNIMSITY What can you do when WT restricts piping/ conveyance network? 41.1 - • „-ib - www.bae.ncsu.edu/stormwater Bl*k4 4 5/17/2013 lightMEUVAMTY Retrofit Ease / Cost Savings rye;, 17ELig, ;,,Temporary— [�A.,n�-1m.. 7WS V3tiF L<'�ngth A({1t P'V`^`�' ;"�a9 44174Z2145-- gf C>..t t,�na1Pl»lngth=i swam a www.bae.ncsu.eduf stormwater txcrettnr� gi NC STATE U.1NNERSITY Cost Savings • Tie into existing landscape easier b/c elev. drop from underdrain to outlet is less — Fewer materials (pipe/drain tube) — Length of trench to outlet underdrain is shorter • Best applied in where little change in elevation is accessible — Coastal plain (flat lands) — Retrofits www.bae.ncsu.edu/stormwater 4 f-Ac !:.:6 1 f !E A 5 5/17/2013 Retrofit Ease / Cost Savings AA Unable to o ri .. Existing Storm 'inonvindo www.bae.ncsu.edu/stormwater 8c. £o NG STATE UNWERSITY Retrofits • Easy to tie in underdrain outlet — Less elevation change to worry about — Save $$$ on trenching and pipe cost — Avoid underground power lines (often 1m deep) • Incorporating IWS makes some design scenarios feasible www.bae.ncsu.edu/stormwater .f 6 c O L U C s Jewaa m d 3 V co (up)awll,Moll a CD ccoo o w CO M o 0 - 0 0 0 0 0 CJ O O 0 0 (sdl)(llooleA'A CD N--. C o CO N V. CO 1 CO 0) 0) V Ir) 0 a N In 0) In 0 co M Nco O co O CO (sio)Alloede0 Moil Ilnd ,n0 v o 0. 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N- c0D o 0 (D cD 10 (O CO 0 (D cD 0 (up)-ouoo to auiy'01 o a) N v u 0 0 0 0 0 u') iri ui cD I .i ICC Vi Iri IC) T palelnwnooe wns yo N co <0o 0) o c a CO CD rn O) 0 0 0 0 0 0 0 0 0 O �- O T- lUawaJ�U�y'J N o CO N O O O O co co = 0 0 0 0 0 0 0 0 0 0 T - w •lja0)leU0neJ'0 N. o n N- o o m rn 0 0 0 0 0 0 0 0 0 0 W (sane) M O O M O O O 71 .ID uID < ea)e a6euleJp'y Co 0 0 0 0 0 0 o O o 0 —ci Y Z rl� 7 V aJnlorulS 6uipu3 ¢ ¢ ¢ a ,- x o w '^ pa U) 0 W ^_ O — Q Q m O W cm d LU a alnlonJlS 6upJelg ` ¢ a Q ¢ ` m ` v w o o a a a 0. 0. 0. 0. a a a a 'a STORM STRUCTURE SCHEDULE STRUCT. STRUCT. STRUCT. RIM INVERT INVERT PIPE ppgg# �y TYPE LENGTH ELEV.d �z IN OUT DESCRIPTION '4{ Y'�j �:..:�.w.r f£-*'-^¢^lts' Nrr.SS d d d' 'f 1` b.r fiter3` A6 30" NYLO - 471.95 - 469.60 68.53 LF OF 15" HDPE @ 0.50% A5 MH - 472.65 469.26 469.16 104.58 LF OF 15" HDPE @ 0.50% A4 30" NYLO - 471.90 468.64 468.54 181.93 LF OF 18" HDPE @ 0.50% A3 30" NYLO - 472.00 467.63 467.53 29.92 LF OF 24" HDPE @ 0.50% A2 MH - 473.00 467.38 467.28 _ 59.06 LF OF HDPE @ 0.47% Al END - - 467.00 - :1Ar 0.4,g >� & � * dt s > `' ,;*„;„;„,,,,,,i.„✓ s. d ? rY S '�`„cm. t;P' .1-14,0000Ax"fd' 9„�.e. L: 1,„-p Z B1 DI-1 - 475.50 - 470.00 70.26 LF OF 15" HDPE @ 1.42% A2 MH - 473.00 469.00 467.28 Cl DI-1 - 472.65 - 470.39 63.01 LF OF 15" HDPE @ 1.00% A5 MH - 472.65 469.76 469.16 D2 MH - 470.00 467.00 466.75 18.55 LF OF 24" HDPE @ 1.35% D1 END - - 466.50 - «. rvy' ,., ,T P3 MH - 467.75 464.00 463.90 _ 44.83 LF OF 15" HDPE @ 0.89% P2 MH - 468.50 463.50 463.40 _ 31.31 LF OF 15" HDPE @ 1.28% P1 ES - - 463.00 - t .4 t 1 � El DI-2B 4' 467.06 - 460.07 25.77 LF OF 15" HDPE @ 4.15% EX EX MH - 463.00 459.00 EX. RATIONAL METHOD WORKSHEET Project: Albrecht Comrnons Date: 6/19/2012 Designer: AGF Watershed ID: Pre-Development West Drainage Area: 1.85 Acres c-factor: 0.25 (see worksheet) tc: 9.23 mins. (see worksheet) Q(2): 1.97 cfs Q(10): 2.56 cfs Time of Concentration Worksheet Weighted c-factor Worksheet Overland Flow Time Cover Type Area c Source: Seelye Chart as modified in VDOT Drainage Manual(Fig.1.5.1.1 Paving I 0.90 - on Page 1-13E) Woods 1.85 0.25 Notes: 0.40 1)Length of overland flow always<=200 ft 2) Calculate a separate Tc for each ground cover condition along the flow path c-factor= 0.25 45.00 Enter Length of Strip(ft) Sample"C"values: 25.00 Enter Slope(%or ft/100ft) 0.22 Dense grass 0.25 Enter Rational Method"C"value 0.28 Average grass 0.36 Poor grass 5.79JResuit Tc(minutes) 0.48 Bare soil 0.90 Pavement Shallow Concentrated Flow Time Source: SCS Velocity Graph as published in Virginia Erosion and Sediment Control Handbook,Third Edition(Plate 5-2 on Page V-12) Notes: 1)Not intended for well-defined channels-see channel flow calculation 2)Calculate a separate Tc for each ground cover condition along the flow path 468.00 Enter Length of Flow(ft) 2.00 Enter Slope(%or ft/100ft) 3.44 Result Tc(minutes)IF UNPAVED 2.70 Result Tc(minutes)IF PAVED Channel Flow Time Source: Kirpich Chart as modified in VDOT Drainage Manual(Fig.1.5.1.2 on Page 1-14) Notes: 1)For small drainage basins. 2)For concrete channels,use 0.2*Tc 0.00 Enter Length of Flow(ft) 1.00 Enter Height of most remote point along flow path above outlet 0.00IResult Tc(minutes) Pipe Flow Time Assumes 10 ft/s velocity in pipe 0.00 Enter Length of Flow in Pipe(ft) 0.00IResuit Tc(minutes) Rainfall Intensity(Albemarle County,Virginia) Return Duration Intensity Period (mins.) (in/hr) 2 9.2 4.2 5 9.2 4.9 10 9.2 5.5 25 9.2 6.2 50 9.2 6.6 100 9.2 7.2 Intensities derived from NOAA Atlas-14 Rainfall Precipitation Frequency Data Short Version BMP Computations For Worksheets 2 -6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Albrecht Commons Water Resources Area: Development Area Preparer: Alan G.Franklin,PE Date: 4/7/2013 Project Drainage Area Designation East Drainage to 48" L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(1) Pj small storm correction factor,0.9 percent imperviousness P annual precipitation,43"in Albemarle A project area in acres in subject drainage area, ( A= T 0.31 C pollutant concentration,mg/I or ppm target phosphorus f factor applied to RR ✓ required treatment volume in cy,0.5"over imperv.area= A(I)43560(0.5/12)/27 RR required removal, L(post)-f x L(pre) %RR removal efficiency, RR100/L(post) Impervious Cover Computation(values in feet&square feet) _ Item pre-development Area post-development Area Roads Length Width subtotal Length Width subtotal i ( 01 0 0 Oi 0 0 0 0. 0€ 0 0 0 1 0 0 _ ( 0 0 ,Driveways Length Width no. subtotal Length Width no. subtotal and walks 01 0 0 0 0 0' 0l 0 1 0 0 0 0 0 0 0 0 0 _ 0 Parking Lots 1 2 3 4j 1 2 3 4, �4� I 09 0 --r- J 6,4384 6438 Gravel Areas 1 2 subtotal _ .�1_11 2 subtotal 1 L____, x 0.75 0 _.. r, _.. 01 x 0.75; 0 Structures Area no. subtotal Area no. subtotal 0 0 0 61-- OI 0 0 0 0 0 0 0 0 0 0 0' 0 Actively-grazed pasture& Area - Area yards and cultivated turf 0_x 0.08= 0 0{x 0.08= 0 Active crop land Area Area _._._________ _____I x 0.25= 0 0.25= 0 Other Impervious Areas 00 Impervious Cover - 0% _ 48%1 I(pre) l(post) Rv(post)` V 0.489.9 New Development(For Development Areas,existingimpervious cover<=20%) C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type ' ' �� ?; 0.23 0.44 0.91 - 0.47 ' - 52% Development Area , '' 0.05 0.05 0.46 0.41 90%1 Drinking Water Watersheds , 0.06 0.06 0.52 0.46 88%''Other Rural Land *min.values Redevelo.mentiFor Develo.ment Areas,existing impervious cover>20%) f I re * R .re I L .red_L(post) ( RR %RR Area Type ) ", 0.23 0.44 0.91 i 0.52 57% Development Area i 0.05 0.05 0.46 0.42 91% Drinking Water Watersheds A - '; 1 ' � 0.06 0.06 0.52 0.47 90% Other Rural Land Interim Manual,Page 70 rev. 31 March 1998 GEB Short Version BMP Computations For Worksheets 2-6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Albrecht Commons Water Resources Area: Development Area Preparer: Alan G. Franklin,PE Date: 4/7/2013 Project Drainage Area Designation West Drainage to Channel L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(1) Pj small storm correction factor,0.9 I percent imperviousness P annual precipitation,43"in Albemarle A project area in acres in subject drainage area, A= mm 2.84 C pollutant concentration,mg/I or ppm target phosphorus f factor applied to RR ✓ required treatment volume in cy,0.5"over imperv.area= A(1)43560(0.5/12)/27 RR required removal, L(post)-f x L(pre) %RR removal efficiency, RR100/L(post) Im•ervious Cover Computation(values in feet&square feet) _ Item T m , pre-development Area post-development _ _ Area Roads Length Width subtotal Length _ Width subtotal , 0 0` w0 0 0 0 0 _ 0 0 0 0 ,01 i \ 0 0 0 0 _0 0 8,161 8,161 Driveways Len•th Width no. subtotal Len.th Width no. subtotal and walks 0 01 0 " 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0° 1 0 Parking Lots 1 2 3 4 1 2 3 4 mm_ 0 0 r j 38,812 38,812, Gravel Areas _ 1 2 subtotal 1 2 subtotal ---t r.__. ...( j 1. x0.75 0 1 _.i ,01 x0.75 0, Structures Area no. subtotal Area no. subtotal 0 0 001 0 01 0 00 0 0 0 0 0 _ 0 37,745 37,745 Actively-grazed pasture& Area Area ards and cultivated turf 0 x 0.08= 0 0 x 0.08= 0, Active crop land Area Area 1 t 0x0.25= 0x0.25= 0i Other Impervious Areas 0 , 0 Impervious Cover 0% 68% I(pre) l(post) Rv(post) V 1 1„,,,, 0.67 130.7 New Development For Development Areas,existing jm•ervious cover<=20% C f I(pre)-;" Rv(pre) L(pre) f L(post) RR I %RR Area Type ' 1 gf z �� 0.23 4.01 11.62 7.61 65%' Development Area i ; f'.: 0.05 0.44 5.81 5.37 92% Drinking Water Watersheds -1 -, , 0.06 0.59 6.64L 6.05 91%-Other Rural Land *min.values Redevelo•ment(For Development Areas,existinjimpervious cover>20%) C f I re * Rv(pre) L(pre) L(post) RR 1 %RR Area T pe f 0.23 4.01 11.62 8.01 - 69% Development Area 1 < r 0.050.44 5.815.44 94% Drinking Water Watersheds j •., ` ' . ,'E. 0.06 0.59 6.64 6.14 92% Other Rural Land Interim Manual,Page 70 rev.31 March 1998 GEB RATIONAL METHOD WORKSHEET Project: Albrecht Commons Date: 6/19/2012 Designer: AGF Watershed ID: Pre-Development East Drainage Area: 1.39 Acres c-factor: 0.28 (see worksheet) tc: 7.33 mins. (see worksheet) Q(2): 1.79 cfs Q(10): 2.31 cfs Time of Concentration Worksheet Weighted c-factor Worksheet Overland Flow Time Cover Type Area c Source: Seelye Chart as modified in VDOT Drainage Manual(Fig.1.5.1.1 Paving 0.06 0.90 on Page 1-13E) Woods 1.33 0.25 Notes: 0.40 1)Length of overland flow always<=200 ft 2)Calculate a separate Tc for each ground cover condition along the flow path c-factor= 0.28 40.00 Enter Length of Strip(ft) Sample"C"values: 25.00 Enter Slope(%or ft/100ft) 0.22 Dense grass 0.25 Enter Rational Method"C"value 0.28 Average grass 0.36 Poor grass 5.51IResult Tc(minutes) 0.48 Bare soil 0.90 Pavement Shallow Concentrated Flow Time Source: SCS Velocity Graph as published in Virginia Erosion and Sediment Control Handbook,Third Edition(Plate 5-2 on Page V-12) Notes: 1)Not intended for well-defined channels-see channel flow calculation 2)Calculate a separate Tc for each ground cover condition along the flow path 350.00 Enter Length of Flow(ft) 4.00 Enter Slope(%or ft/100ft) 1.81 Result Tc(minutes)IF UNPAVED 1.41 Result Tc(minutes)IF PAVED Channel Flow Time Source: Kirpich Chart as modified in VDOT Drainage Manual(Fig.1.5.1.2 on Page 1-14) Notes: 1)For small drainage basins. 2)For concrete channels,use 0.2*Tc 0.00 Enter Length of Flow(ft) 1.00 Enter Height of most remote point along flow path above outlet 0.00IResult Tc(minutes) Pipe Flow Time Assumes 10 Ws velocity in pipe 0.00jEnter Length of Flow in Pipe(ft) 0.00IResult Tc(minutes) Rainfall Intensity(Albemarle County,Virginia) Return Duration Intensity Period (mins.) (in/hr) 2 7.3 4.6 5 7.3 5.3 10 7.3 6.0 25 7.3 6.7 50 7.3 7.2 2-212 �l r. 100 7.3 7.8 U. t'0 2D13-C 2-9 Intensities derived from NOAH Atlas-14 Rainfall Precipitation Frequency Data RATIONAL METHOD WOI' KSHEEC Project: Albrecht Commons Date: 6/19/2012 Designer: AGF Watershed ID: Pre-Development West Drainage Area: 1.85 Acres c-factor: 0.25 (see worksheet) tc: 9.23 mins. (see worksheet) Q(2): 1.97 cfs Q(10): 2.56 cfs Time of Concentration Worksheet Weighted c-factor Worksheet Overland Flow Time Cover Type Area c_ Source: Seelye Chart as modified in VDOT Drainage Manual(Fig.1.5.1.1 Paving 1 0.90 on Page 1-13E) Woods 1.85 0.25 Notes: 0.40 1)Length of overland flow always<=200 ft 2)Calculate a separate Tc for each ground cover condition along the flow path c-factor= 0.25 45.00 Enter Length of Strip(ft) Sample"C"values: 25.00 Enter Slope(%or ft/100ft) 0.22 Dense grass 0.25 Enter Rational Method"C"value 0.28 Average grass 0.36 Poor grass 5.791Result Tc(minutes) 0.48 Bare soil 0.90 Pavement Shallow Concentrated Flow Time Source: SCS Velocity Graph as published in Virginia Erosion and Sediment Control Handbook,Third Edition(Plate 5-2 on Page V-12) Notes: 1)Not intended for well-defined channels-see channel flow calculation 2)Calculate a separate Tc for each ground cover condition along the flow path 468.00 Enter Length of Flow(ft) 2.00 Enter Slope(%or ft/100ft) 3.44 Result Tc(minutes)IF UNPAVED 2.70 Result Tc(minutes)IF PAVED Channel Flow Time Source: Kirpich Chart as modified in VDOT Drainage Manual(Fig.1.5.1.2 on Page 1-14) Notes: 1)For small drainage basins. 2)For concrete channels,use 0.2*Tc 0.00 Enter Length of Flow(ft) 1.00 Enter Height of most remote point along flow path above outlet 0.00IResult Tc(minutes) Pipe Flow Time Assumes 10 ft/s velocity in pipe 0.001 Enter Length of Flow in Pipe(ft) 0.001Result Tc(minutes) Rainfall Intensity(Albemarle County,Virginia) Return Duration Intensity Period (mins.) (in/hr) 2 9.2 4.2 5 9.2 4.9 10 9.2 5.5 25 9.2 6.2 50 9.2 6.6 100 9.2 7.2 Intensities derived from NOAA Atlas-14 Rainfall Precipitation Frequency Data 3S Post- EastTo Ex . 48 " Pipe Subcat Pon Drainage Diagram for Anvince f �Reach Prepared by Terra Concepts, PC, Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Post East Anvince Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Pane 2 Area Listing (selected nodes) Area C Description (sq-ft) (subcatchment-numbers) 4,356 0.45 Open Developed Area (3S) 3,049 0.45 Permeable Pavers (3S) 6,098 0.90 Pavement (3S) 13,504 TOTAL AREA Post East Anvince VA-Albemarle-ATLASI4 2-Year Duration=5 min, Inten=5.18 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 3 Time span=0.00-3.00 hrs, dt=0.01 hrs, 301 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment3S: Post-EastTo Ex. 48" Pipe Runoff Area=0.310 ac 0.00% Impervious Runoff Depth=0.42" Tc=5.0 min C=0.65 Runoff=1.03 cfs 473 cf Total Runoff Area = 13,504 sf Runoff Volume = 473 cf Average Runoff Depth = 0.42" 100.00% Pervious = 13,504 sf 0.00% Impervious = 0 sf Post East Anvince VA-Albemarle-ATLAS14 2-Year Duration=5 min, Inten=5.18 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment 3S: Post-EastTo Ex. 48" Pipe Runoff = 1.03 cfs @ 0.08 hrs, Volume= 473 cf, Depth= 0.42" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 2-Year Duration=5 min, Inten=5.18 in/hr Area (ac) C Description 0.140 0.90 Pavement 0.100 0.45 Open Developed Area 0.070 0.45 Permeable Pavers 0.310 0.65 Weighted Average 0.310 Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment 3S: Post-EastTo Ex. 48" Pipe Hydrograph (_ ❑Runoff 1.03 cfs 1 VA-Albemarle-ATLASI4 2-Year Duration=5 min, Inten=5.18 in/hr Runoff Area=0.310 ac Runoff Volume=473 cf Runoff Depth=0.42" Tc=5.0 min LT C=0.65 o '/.//i //////.///////00/////000'/''////////////0 0 1 2 3 Time (hours) Post East Anvince VA-Albemarle-ATLAS14 2-Year Duration=5 min, Inten=5.18 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 5 Hydrograph for Subcatchment 3S: Post-EastTo Ex. 48" Pipe Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 1.04 0.00 2.08 0.00 0.02 0.25 1.06 0.00 2.10 0.00 0.04 0.51 1.08 0.00 2.12 0.00 0.06 0.76 1.10 0.00 2.14 0.00 0.08 1.01 1.12 0.00 2.16 0.00 0.10 0.95 1.14 0.00 2.18 0.00 0.12 0.82 1.16 0.00 2.20 0.00 0.14 0.69 1.18 0.00 2.22 0.00 0.16 0.57 1.20 0.00 2.24 0.00 0.18 0.44 1.22 0.00 2.26 0.00 0.20 0.32 1.24 0.00 2.28 0.00 0.22 0.19 1.26 0.00 2.30 0.00 0.24 0.06 1.28 0.00 2.32 0.00 0.26 0.00 1.30 0.00 2.34 0.00 0.28 0.00 1.32 0.00 2.36 0.00 0.30 0.00 1.34 0.00 2.38 0.00 0.32 0.00 1.36 0.00 2.40 0.00 0.34 0.00 1.38 0.00 2.42 0.00 0.36 0.00 1.40 0.00 2.44 0.00 0.38 0.00 1.42 0.00 2.46 0.00 0.40 0.00 1.44 0.00 2.48 0.00 0.42 0.00 1.46 0.00 2.50 0.00 0.44 0.00 1.48 0.00 2.52 0.00 0.46 0.00 1.50 0.00 2.54 0.00 0.48 0.00 1.52 0.00 2.56 0.00 0.50 0.00 1.54 0.00 2.58 0.00 0.52 0.00 1.56 0.00 2.60 0.00 0.54 0.00 1.58 0.00 2.62 0.00 0.56 0.00 1.60 0.00 2.64 0.00 0.58 0.00 1.62 0.00 2.66 0.00 0.60 0.00 1.64 0.00 2.68 0.00 0.62 0.00 1.66 0.00 2.70 0.00 0.64 0.00 1.68 0.00 2.72 0.00 0.66 0.00 1.70 0.00 2.74 0.00 0.68 0.00 1.72 0.00 2.76 0.00 0.70 0.00 1.74 0.00 2.78 0.00 0.72 0.00 1.76 0.00 2.80 0.00 0.74 0.00 1.78 0.00 2.82 0.00 0.76 0.00 1.80 0.00 2.84 0.00 0.78 0.00 1.82 0.00 2.86 0.00 0.80 0.00 1.84 0.00 2.88 0.00 0.82 0.00 1.86 0.00 2.90 0.00 0.84 0.00 1.88 0.00 2.92 0.00 0.86 0.00 1.90 0.00 2.94 0.00 0.88 0.00 1.92 0.00 2.96 0.00 0.90 0.00 1.94 0.00 2.98 0.00 0.92 0.00 1.96 0.00 3.00 0.00 0.94 0.00 1.98 0.00 0.96 0.00 2.00 0.00 0.98 0.00 2.02 0.00 1.00 0.00 2.04 0.00 1.02 0.00 2.06 0.00 Post East Anvince VA Albemarle-ATLASI4 10-Year Duration=5 min, Inten=6.65 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 6 Time span=0.00-3.00 hrs, dt=0.01 hrs, 301 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment3S: Post-EastTo Ex.48" Pipe Runoff Area=0.310 ac 0.00% Impervious Runoff Depth=0.54" Tc=5.0 min C=0.65 Runoff=1.32 cfs 607 cf Total Runoff Area= 13,504 sf Runoff Volume= 607 cf Average Runoff Depth = 0.54" 100.00% Pervious = 13,504 sf 0.00% Impervious = 0 sf Post East Anvince VA-Albemarle-ATLAS14 10-Year Duration=5 min, Inten=6.65 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 7 Summary for Subcatchment 3S: Post-EastTo Ex. 48" Pipe Runoff = 1.32 cfs @ 0.09 hrs, Volume= 607 cf, Depth= 0.54" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 10-Year Duration=5 min, Inten=6.65 in/hr Area (ac) C Description 0.140 0.90 Pavement 0.100 0.45 Open Developed Area 0.070 0.45 Permeable Pavers 0.310 0.65 Weighted Average 0.310 Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment 3S: Post-EastTo Ex. 48" Pipe Hydrograph 0 Runoff 1.32 cfs VA-Albemarle-ATLASI4 10-Year Duration=5 min, Inten=6.65 in/hr 1 Runoff Area=0.310 ac Runoff Volume=607 cf w '4r0 Runoff Depth=0.54" Tc=5.0 min LL C=0.65 0 IA WA '///.//,///. /• /////(//7r`'////�/////i////////f///orf//////f/// 0 1 2 3 Time (hours) Post East Anvince VA-Albemarle-ATLAS14 10-Year Duration=5 min, Inten=6.65 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 8 Hydrograph for Subcatchment 3S: Post-EastTo Ex. 48" Pipe Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 1.04 0.00 2.08 0.00 0.02 0.32 1.06 0.00 2.10 0.00 0.04 0.65 1.08 0.00 2.12 0.00 0.06 0.97 1.10 0.00 2.14 0.00 0.08 1.30 1.12 0.00 2.16 0.00 0.10 1.22 1.14 0.00 2.18 0.00 0.12 1.05 1.16 0.00 2.20 0.00 0.14 0.89 1.18 0.00 2.22 0.00 0.16 0.73 1.20 0.00 2.24 0.00 0.18 0.57 1.22 0.00 2.26 0.00 0.20 0.41 1.24 0.00 2.28 0.00 0.22 0.24 1.26 0.00 2.30 0.00 0.24 0.08 1.28 0.00 2.32 0.00 0.26 0.00 1.30 0.00 2.34 0.00 0.28 0.00 1.32 0.00 2.36 0.00 0.30 0.00 1.34 0.00 2.38 0.00 0.32 0.00 1.36 0.00 2.40 0.00 0.34 0.00 1.38 0.00 2.42 0.00 0.36 0.00 1.40 0.00 2.44 0.00 0.38 0.00 1.42 0.00 2.46 0.00 0.40 0.00 1.44 0.00 2.48 0.00 0.42 0.00 1.46 0.00 2.50 0.00 0.44 0.00 1.48 0.00 2.52 0.00 0.46 0.00 1.50 0.00 2.54 0.00 0.48 0.00 1.52 0.00 2.56 0.00 0.50 0.00 1.54 0.00 2.58 0.00 0.52 0.00 1.56 0.00 2.60 0.00 0.54 0.00 1.58 0.00 2.62 0.00 0.56 0.00 1.60 0.00 2.64 0.00 0.58 0.00 1.62 0.00 2.66 0.00 0.60 0.00 1.64 0.00 2.68 0.00 0.62 0.00 1.66 0.00 2.70 0.00 0.64 0.00 1.68 0.00 2.72 0.00 0.66 0.00 1.70 0.00 2.74 0.00 0.68 0.00 1.72 0.00 2.76 0.00 0.70 0.00 1.74 0.00 2.78 0.00 0.72 0.00 1.76 0.00 2.80 0.00 0.74 0.00 1.78 0.00 2.82 0.00 0.76 0.00 1.80 0.00 2.84 0.00 0.78 0.00 1.82 0.00 2.86 0.00 0.80 0.00 1.84 0.00 2.88 0.00 0.82 0.00 1.86 0.00 2.90 0.00 0.84 0.00 1.88 0.00 2.92 0.00 0.86 0.00 1.90 0.00 2.94 0.00 0.88 0.00 1.92 0.00 2.96 0.00 0.90 0.00 1.94 0.00 2.98 0.00 0.92 0.00 1.96 0.00 3.00 0.00 0.94 0.00 1.98 0.00 0.96 0.00 2.00 0.00 0.98 0.00 2.02 0.00 1.00 0.00 2.04 0.00 1.02 0.00 2.06 0.00 Post East Anvince VA-Albemarle-ATLAS14 100-Year Duration=5 min, Inten=8.76 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 9 Time span=0.00-3.00 hrs, dt=0.01 hrs, 301 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment3S: Post-EastTo Ex. 48" Pipe Runoff Area=0.310 ac 0.00% Impervious Runoff Depth=0.71" Tc=5.0 min C=0.65 Runoff=1.74 cfs 800 cf Total Runoff Area= 13,504 sf Runoff Volume= 800 cf Average Runoff Depth = 0.71" 100.00% Pervious = 13,504 sf 0.00% Impervious = 0 sf Post East Anvince VA-Albemarle-ATLASI4 100-Year Duration=5 min, Inten=8.76 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Pane 10 Summary for Subcatchment 3S: Post-EastTo Ex. 48" Pipe Runoff = 1.74 cfs @ 0.09 hrs, Volume= 800 cf, Depth= 0.71" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 100-Year Duration=5 min, Inten=8.76 in/hr Area (ac) C Description 0.140 0.90 Pavement 0.100 0.45 Open Developed Area 0.070 0.45 Permeable Pavers 0.310 0.65 Weighted Average 0.310 Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment 3S: Post-EastTo Ex. 48" Pipe Hydrograph I 0 Runoff 1.74 cfs VA-Albemarle-ATLASI4 100-Year Duration=5 min, Inten=8.76 in/hr 10 O Runoff Area=0.310 ac Runoff Volume=800 cf Runoff Depth=0.71" 1- 0 Tc=5.0 min 0 '12 C=0.65 0 0 p 01 ///////////;/////i////!/,//////,'//1i'•//////i'//////////✓1ir/.//llf/ p 1 2 3 Time (hours) Post East Anvince VA-Albemarle-ATLASI4 100-Year Duration=5 min, Inten=8.76 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 11 Hydrograph for Subcatchment 3S: Post-EastTo Ex. 48" Pipe Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 1.04 0.00 2.08 0.00 0.02 0.43 1.06 0.00 2.10 0.00 0.04 0.85 1.08 0.00 2.12 0.00 0.06 1.28 1.10 0.00 2.14 0.00 0.08 1.71 1.12 0.00 2.16 0.00 0.10 1.60 1.14 0.00 2.18 0.00 0.12 1.39 1.16 0.00 2.20 0.00 0.14 1.18 1.18 0.00 2.22 0.00 0.16 0.96 1.20 0.00 2.24 0.00 0.18 0.75 1.22 0.00 2.26 0.00 0.20 0.53 1.24 0.00 2.28 0.00 0.22 0.32 1.26 0.00 2.30 0.00 0.24 0.11 1.28 0.00 2.32 0.00 0.26 0.00 1.30 0.00 2.34 0.00 0.28 0.00 1.32 0.00 2.36 0.00 0.30 0.00 1.34 0.00 2.38 0.00 0.32 0.00 1.36 0.00 2.40 0.00 0.34 0.00 1.38 0.00 2.42 0.00 0.36 0.00 1.40 0.00 2.44 0.00 0.38 0.00 1.42 0.00 2.46 0.00 0.40 0.00 1.44 0.00 2.48 0.00 0.42 0.00 1.46 0.00 2.50 0.00 0.44 0.00 1.48 0.00 2.52 0.00 0.46 0.00 1.50 0.00 2.54 0.00 0.48 0.00 1.52 0.00 2.56 0.00 0.50 0.00 1.54 0.00 2.58 0.00 0.52 0.00 1.56 0.00 2.60 0.00 0.54 0.00 1.58 0.00 2.62 0.00 0.56 0.00 1.60 0.00 2.64 0.00 0.58 0.00 1.62 0.00 2.66 0.00 0.60 0.00 1.64 0.00 2.68 0.00 0.62 0.00 1.66 0.00 2.70 0.00 0.64 0.00 1.68 0.00 2.72 0.00 0.66 0.00 1.70 0.00 2.74 0.00 0.68 0.00 1.72 0.00 2.76 0.00 0.70 0.00 1.74 0.00 2.78 0.00 0.72 0.00 1.76 0.00 2.80 0.00 0.74 0.00 1.78 0.00 2.82 0.00 0.76 0.00 1.80 0.00 2.84 0.00 0.78 0.00 1.82 0.00 2.86 0.00 0.80 0.00 1.84 0.00 2.88 0.00 0.82 0.00 1.86 0.00 2.90 0.00 0.84 0.00 1.88 0.00 2.92 0.00 0.86 0.00 1.90 0.00 2.94 0.00 0.88 0.00 1.92 0.00 2.96 0.00 0.90 0.00 1.94 0.00 2.98 0.00 0.92 0.00 1.96 0.00 3.00 0.00 0.94 0.00 1.98 0.00 0.96 0.00 2.00 0.00 0.98 0.00 2.02 0.00 1.00 0.00 2.04 0.00 1.02 0.00 2.06 0.00 1 s Pos -West to Channel 2P Bio-Basin Subcat Reach Pon MI Drainage Diagram for Anvince Prepared by Terra Concepts, PC, Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Post West to Channel -2 yr Anvince Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 2 Area Listing (selected nodes) Area C Description (sq-ft) (subcatchment-numbers) 27,007 0.45 Open Developed Area (1S) 11,761 0.45 Permeable Pavers (1S) 47,045 0.90 Paved Area (15) 37,897 0.90 Rooftop (15) 123,710 TOTAL AREA Post West to Channel -2 yr Anvince VA-Albemarle-ATLASI4 2-Year Duration=63 min, Inten=1.45 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 3 Time span=0.00-3.00 hrs, dt=0.01 hrs, 301 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: Post-West to Channel Runoff Area=2.840 ac 0.00% Impervious Runoff Depth=1.20" Tc=5.0 min C=0.76 Runoff=3.15 cfs 12,363 cf Pond 2P: Bio-Basin Peak Elev=467.28' Storage=9,457 cf Inflow=3.15 cfs 12,363 cf Outflow=1.87 cfs 6,871 cf Total Runoff Area= 123,710 sf Runoff Volume= 12,363 cf Average Runoff Depth = 1.20" 100.00% Pervious= 123,710 sf 0.00% Impervious = 0 sf Post West to Channel - 2 yr Anvince VA-Albemarle-ATLAS14 2-Year Duration=63 min, Inten=1.45 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment 1S: Post-West to Channel Runoff = 3.15 cfs @ 0.09 hrs, Volume= 12,363 cf, Depth= 1.20" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 2-Year Duration=63 min, Inten=1.45 in/hr Area (ac) C Description 1.080 0.90 Paved Area 0.870 0.90 Rooftop 0.620 0.45 Open Developed Area 0.270 0.45 Permeable Pavers 2.840 0.76 Weighted Average 2.840 Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment 1S: Post-West to Channel Hydrograph 1 0 Runoff` 3.15 cfs /��//'�/�///��/'� VA-Albemarle-ATLAS14 2-Year s d Duration=63 min, VA Inten=1.45 in/hr 4t VA Runoff Area=2.840 ac Runoff Volume=12,363 cf 2 Runoff Depth=1.20" VA Tc=5.0 min ,+! 0, ri C=0.76 0 2 V I VA PA OP WI o ////2;77////,//./// ///�'�///// '/////.///' 0 1 2 3 Time (hours) Post West to Channel -2 yr Anvince VA-Albemarle-ATLASI4 2-Year Duration=63 min, Inten=1.45 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 5 Hydrograph for Subcatchment 1S: Post-West to Channel Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 1.04 3.15 2.08 0.00 0.02 0.76 1.06 2.96 2.10 0.00 0.04 1.51 1.08 2.58 2.12 0.00 0.06 2.27 1.10 2.20 2.14 0.00 0.08 3.02 1.12 1.82 2.16 0.00 0.10 3.15 1.14 1.45 2.18 0.00 0.12 3.15 1.16 1.07 2.20 0.00 0.14 3.15 1.18 0.69 2.22 0.00 0.16 3.15 1.20 0.31 2.24 0.00 0.18 3.15 1.22 0.00 2.26 0.00 0.20 3.15 1.24 0.00 2.28 0.00 0.22 3.15 1.26 0.00 2.30 0.00 0.24 3.15 1.28 0.00 2.32 0.00 0.26 3.15 1.30 0.00 2.34 0.00 0.28 3.15 1.32 0.00 2.36 0.00 0.30 3.15 1.34 0.00 2.38 0.00 0.32 3.15 1.36 0.00 2.40 0.00 0.34 3.15 1.38 0.00 2.42 0.00 0.36 3.15 1.40 0.00 2.44 0.00 0.38 3.15 1.42 0.00 2.46 0.00 0.40 3.15 1.44 0.00 2.48 0.00 0.42 3.15 1.46 0.00 2.50 0.00 0.44 3.15 1.48 0.00 2.52 0.00 0.46 3.15 1.50 0.00 2.54 0.00 0.48 3.15 1.52 0.00 2.56 0.00 0.50 3.15 1.54 0.00 2.58 0.00 0.52 3.15 1.56 0.00 2.60 0.00 0.54 3.15 1.58 0.00 2.62 0.00 0.56 3.15 1.60 0.00 2.64 0.00 0.58 3.15 1.62 0.00 2.66 0.00 0.60 3.15 1.64 0.00 2.68 0.00 0.62 3.15 1.66 0.00 2.70 0.00 0.64 3.15 1.68 0.00 2.72 0.00 0.66 3.15 1.70 0.00 2.74 0.00 0.68 3.15 1.72 0.00 2.76 0.00 0.70 3.15 1.74 0.00 2.78 0.00 0.72 3.15 1.76 0.00 2.80 0.00 0.74 3.15 1.78 0.00 2.82 0.00 0.76 3.15 1.80 0.00 2.84 0.00 0.78 3.15 1.82 0.00 2.86 0.00 0.80 3.15 1.84 0.00 2.88 0.00 0.82 3.15 1.86 0.00 2.90 0.00 0.84 3.15 1.88 0.00 2.92 0.00 0.86 3.15 1.90 0.00 2.94 0.00 0.88 3.15 1.92 0.00 2.96 0.00 0.90 3.15 1.94 0.00 2.98 0.00 0.92 3.15 1.96 0.00 3.00 0.00 0.94 3.15 1.98 0.00 0.96 3.15 2.00 0.00 0.98 3.15 2.02 0.00 1.00 3.15 2.04 0.00 1.02 3.15 2.06 0.00 Post West to Channel - 2 yr Anvince VA-Albemarle-ATLASI4 2-Year Duration=63 min, Inten=1.45 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 6 Summary for Pond 2P: Bio-Basin Inflow Area = 123,710 sf, 0.00% Impervious, Inflow Depth = 1.20" for 2-Year event Inflow = 3.15 cfs @ 0.09 hrs, Volume= 12,363 cf Outflow = 1.87 cfs @ 1.12 hrs, Volume= 6,871 cf, Atten= 41%, Lag= 61.7 min Primary = 1.87 cfs @ 1.12 hrs, Volume= 6,871 cf Routing by Stor-Ind method, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs Peak Elev= 467.28' © 1.12 hrs Surf.Area= 6,175 sf Storage= 9,457 cf Plug-Flow detention time= 60.6 min calculated for 6,848 cf(55% of inflow) Center-of-Mass det. time= 46.2 min ( 81.5 -35.3 ) Volume Invert Avail.Storage Storage Description #1 465.50' 28,750 cf Custom Stage Data (Irregular)Listed below (Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 465.50 4,411 335.0 0 0 4,411 466.00 4,928 381.0 2,334 2,334 7,038 467.00 5,975 326.0 5,443 7,777 10,153 468.00 6,715 342.0 6,341 14,118 11,066 469.00 7,318 352.0 7,014 21,132 11,719 470.00 7,922 362.0 7,618 28,750 12,390 Device Routing Invert Outlet Devices #1 Primary 463.90' 15.0" x 44.8' long Culvert CPP, square edge headwall, Ke= 0.500 Outlet Invert= 463.50' S= 0.0089 '/' Cc= 0.900 n= 0.012 #2 Device 1 466.50' 1.08'W x 0.50' H Vert. Orifice/Grate C= 0.600 #3 Device 1 467.75' 48.0" Horiz. Orifice/Grate Limited to weir flow C= 0.600 Primary OutFlow Max=1.87 cfs © 1.12 hrs HW=467.28' (Free Discharge) L1=Culvert (Passes 1.87 cfs of 9.80 cfs potential flow) 12=Orifice/Grate (Orifice Controls 1.87 cfs @ 3.46 fps) 3=Orifice/Grate ( Controls 0.00 cfs) Post West to Channel - 2 yr Anvince VA-Albemarle-ATLASI4 2-Year Duration=63 min, Inten=1.45 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 7 Pond 2P: Bio-Basin Hydrograph 0 Inflow 3.15 cfs ❑Primary /X,7/./ `./ 7/747/79:74 ` 7' ` Inflow Area-123,710 sf 3 p 04Peak EIev=467.28' rg VA Storage-9,457 cf 2 1.87 cfs 60 %/ "-A Zdr AV . Are 17404.70,7° 1111 0 //. ////////' 0 1 2 3 Time (hours) Pond 2P: Bio-Basin Stage-Discharge 470 ;^/ ❑Primary, 469 w ��O 468 r/ Orifice/Grate r-- 0 w 467 i Orifice/Grate 466 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Discharge (cfs) Post West to Channel -2 yr Anvince VA-Albemarle-ATLASI4 2-Year Duration=63 min, Inten=1.45 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 8 Pond 2P: Bio-Basin Stage-Area-Storage 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 Surface / / 0 Storage 470. ./// • 469 //' / 468 c ro 467 466 Custom Stage Data 0 5,000 10,000 15,000 20,000 25,000 Storage(cubic-feet) Post West to Channel -2 yr Anvince VA-Albemarle-ATLAS14 2-Year Duration=63 min, Inten=1.45 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 9 Hydrograph for Pond 2P: Bio-Basin Time Inflow Storage Elevation Primary (hours) (cfs) (cubic-feet) (feet) (cfs) ,/ y 0.00 0.00 0 465.50 0.99--------\ hi(k�l 0.10 3.15 659 465.65 .00 0.20 3.15 1,792 465.89 0.00 0.30 3.15 2,924 466.12 0.00 0.40 3.15 4,057 466.34 0.00 0.50 3.15 5,188 466.55 0.04 0.60 3.15 6,247 466.74 0.40 0.70 3.15 7,153 466.89 0.86 0.80 3.15 7,896 467.02 1.29 0.90 3.15 8,513 467.12 1.55 1.00 3.15 9,051 467.21 1.74 1.10 2.20 9,446 467.27 1.86 1.20 0.31 9,234 467.24 1.80 1.30 0.00 8,632 467.14 1.60 1.40 0.00 8,095 467.05 1.38 1.50 0.00 7,639 466.98 1.14 1.60 0.00 7,269 466.91 0.93 1.70 0.00 6,967 466.86 0.76 1.80 0.00 6,719 466.82 0.63 1.90 0.00 6,512 466.78 0.53 2.00 0.00 6,338 466.75 0.44 2.10 0.00 6,190 466.73 0.38 2.20 0.00 6,064 466.71 0.32 2.30 0.00 5,956 466.69 0.28 2.40 0.00 5,862 466.67 0.24 2.50 0.00 5,780 466.66 0.21 2.60 0.00 5,708 466.64 0.19 2.70 0.00 5,645 466.63 0.16 2.80 0.00 5,589 466.62 0.15 2.90 0.00 5,539 466.61 0.13 3.00 0.00 5,494 466.60 0.12 Post West to Channel Anvince Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Pane 1 Area Listing (selected nodes) Area C Description (sq-ft) (subcatchment-numbers) 27,007 0.45 Open Developed Area (1S) 11,761 0.45 Permeable Pavers (1S) 47,045 0.90 Paved Area (1S) 37,897 0.90 Rooftop (1S) 123,710 TOTAL AREA Post West to Channel Anvince VA-Albemarle-ATLASI4 10-Year Duration=66 min, Inten=2.00 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 2 Time span=0.00-3.00 hrs, dt=0.01 hrs, 301 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: Post-West to Channel Runoff Area=2.840 ac 0.00% Impervious Runoff Depth=1.73" Tc=5.0 min C=0.76 Runoff=4.35 cfs 17,868 cf Pond 2P: Bio-Basin Peak Elev=467.75' Storage=12,447 cf Inflow=4.35 cfs 17,868 cf Outflow=2.59 cfs 12,149 cf Total Runoff Area= 123,710 sf Runoff Volume= 17,868 cf Average Runoff Depth = 1.73" 100.00% Pervious = 123,710 sf 0.00% Impervious = 0 sf Post West to Channel Anvince VA-Albemarle-ATLAS14 10-Year Duration=66 min, Inten=2.00 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 sin 002893 ©2007 HydroCAD Software Solutions LLC Pape 3 Summary for Subcatchment 1S: Post-West to Channel Runoff = 4.35 cfs @ 0.09 hrs, Volume= 17,868 cf, Depth= 1.73" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 10-Year Duration=66 min, Inten=2.00 in/hr Area (ac) C Description 1.080 0.90 Paved Area 0.870 0.90 Rooftop 0.620 0.45 Open Developed Area 0.270 0.45 Permeable Pavers 2.840 0.76 Weighted Average 2.840 Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment 1S: Post-West to Channel Hydrograph Runoff 4.35 cfs /////////vZ;;;//// VA-Albemarle-ATLAS14 10-Year 4._. 0PA Duration=66 min, 0 2 Inten=2.00 in/hr Runoff Area=2.840 ac 3- 0 Runoff Volume=17,868 cf w 2 Runoff Depth=1.73" a0 / Tc=5.0 min LL C=0.76 20 - VA0 VAi 0 r VA oi/////l//,I/I///////////////.///// 0 1 2 3 Time (hours) Post West to Channel Anvince VA-Albemarle-ATLAS14 10-Year Duration=66 min, Inten=2.00 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Paqe 4 Hydrograph for Subcatchment 1S: Post-West to Channel Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 1.04 4.35 2.08 0.00 0.02 1.04 1.06 4.35 2.10 0.00 0.04 2.09 1.08 4.35 2.12 0.00 0.06 3.13 1.10 4.35 2.14 0.00 0.08 4.17 1.12 3.83 2.16 0.00 0.10 4.35 1.14 3.30 2.18 0.00 0.12 4.35 1.16 2.78 2.20 0.00 0.14 4.35 1.18 2.26 2.22 0.00 0.16 4.35 1.20 1.74 2.24 0.00 0.18 4.35 1.22 1.22 2.26 0.00 0.20 4.35 1.24 0.70 2.28 0.00 0.22 4.35 1.26 0.17 2.30 0.00 0.24 4.35 1.28 0.00 2.32 0.00 0.26 4.35 1.30 0.00 2.34 0.00 0.28 4.35 1.32 0.00 2.36 0.00 0.30 4.35 1.34 0.00 2.38 0.00 0.32 4.35 1.36 0.00 2.40 0.00 0.34 4.35 1.38 0.00 2.42 0.00 0.36 4.35 1.40 0.00 2.44 0.00 0.38 4.35 1.42 0.00 2.46 0.00 0.40 4.35 1.44 0.00 2.48 0.00 0.42 4.35 1.46 0.00 2.50 0.00 0.44 4.35 1.48 0.00 2.52 0.00 0.46 4.35 1.50 0.00 2.54 0.00 0.48 4.35 1.52 0.00 2.56 0.00 0.50 4.35 1.54 0.00 2.58 0.00 0.52 4.35 1.56 0.00 2.60 0.00 0.54 4.35 1.58 0.00 2.62 0.00 0.56 4.35 1.60 0.00 2.64 0.00 0.58 4.35 1.62 0.00 2.66 0.00 0.60 4.35 1.64 0.00 2.68 0.00 0.62 4.35 1.66 0.00 2.70 0.00 0.64 4.35 1.68 0.00 2.72 0.00 0.66 4.35 1.70 0.00 2.74 0.00 0.68 4.35 1.72 0.00 2.76 0.00 0.70 4.35 1.74 0.00 2.78 0.00 0.72 4.35 1.76 0.00 2.80 0.00 0.74 4.35 1.78 0.00 2.82 0.00 0.76 4.35 1.80 0.00 2.84 0.00 0.78 4.35 1.82 0.00 2.86 0.00 0.80 4.35 1.84 0.00 2.88 0.00 0.82 4.35 1.86 0.00 2.90 0.00 0.84 4.35 1.88 0.00 2.92 0.00 0.86 4.35 1.90 0.00 2.94 0.00 0.88 4.35 1.92 0.00 2.96 0.00 0.90 4.35 1.94 0.00 2.98 0.00 0.92 4.35 1.96 0.00 3.00 0.00 0.94 4.35 1.98 0.00 0.96 4.35 2.00 0.00 0.98 4.35 2.02 0.00 1.00 4.35 2.04 0.00 1.02 4.35 2.06 0.00 Post West to Channel Anvince VA-Albemarle-ATLASI4 10-Year Duration=66 min, Inten=2.00 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Pacie 5 Summary for Pond 2P: Bio-Basin Inflow Area = 123,710 sf, 0.00% Impervious, Inflow Depth = 1.73" for 10-Year event Inflow = 4.35 cfs @ 0.09 hrs, Volume= 17,868 cf Outflow = 2.59 cfs @ 1.17 hrs, Volume= 12,149 cf, Atten= 40%, Lag= 64.6 min Primary = 2.59 cfs @ 1.17 hrs, Volume= 12,149 cf Routing by Stor-Ind method, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs Peak Elev= 467.75' @ 1.17 hrs Surf.Area= 6,524 sf Storage= 12,447 cf Plug-Flow detention time= 56.2 min calculated for 12,149 cf(68% of inflow) Center-of-Mass det. time= 45.2 min ( 82.0 - 36.8 ) Volume Invert Avail.Storage Storage Description #1 465.50' 28,750 cf Custom Stage Data (Irregular)Listed below (Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 465.50 4,411 335.0 0 0 4,411 466.00 4,928 381.0 2,334 2,334 7,038 467.00 5,975 326.0 5,443 7,777 10,153 468.00 6,715 342.0 6,341 14,118 11,066 469.00 7,318 352.0 7,014 21,132 11,719 470.00 7,922 362.0 7,618 28,750 12,390 Device Routing Invert Outlet Devices #1 Primary 463.90' 15.0" x 44.8' long Culvert CPP, square edge headwall, Ke= 0.500 Outlet Invert= 463.50' S= 0.0089 '/' Cc= 0.900 n= 0.012 #2 Device 1 466.50' 1.08'W x 0.50' H Vert. Orifice/Grate C=0.600 #3 Device 1 467.75' 48.0" Horiz. Orifice/Grate Limited to weir flow C= 0.600 Primary OutFlow Max=2.59 cfs @ 1.17 hrs HW=467.75' (Free Discharge) L1=Culvert (Passes 2.59 cfs of 10.61 cfs potential flow) I2=Orifice/Grate (Orifice Controls 2.59 cfs @ 4.80 fps) 3=Orifice/Grate ( Controls 0.00 cfs) Post West to Channel Anvince VA-Albemarle-ATLASI4 10-Year Duration=66 min, Inten=2.00 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 6 Pond 2P: Bio-Basin Hydrograph / 0 Inflow 4.35 cfs 0 Primary ' '' ''''''°''` Inflow Area=123,710 sf 4 Peak Elev=467.75' v, Storage=12,447 cf 310 2.59 cfs dea fes/ LL 2 1r\ 1"/ //////�/ .--- __ Ir AO' o 0 1 2 3 Time (hours) Pond 2P: Bio-Basin Stage-Discharge 470 Is0 Primary / 469 • 9 468 / Orifice/Grate = 0 > w 467 Orifice/Grate 466 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Discharge (cfs) Post West to Channel Anvince VA-Albemarle-ATLASI4 10-Year Duration=66 min, Inten=2.00 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 7 Pond 2P: Bio-Basin Stage-Area-Storage v-fti 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 Surface ❑Storage 470 ��//% 469 ./// �� 468- w 467 466 Custom Stage Data 0 5,000 10,000 15,000 20,000 25,000 Storage(cubic-feet) Post West to Channel Anvince VA-Albemarle-ATLAS14 10-Year Duration=66 min, Inten=2.00 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 8 Hydrograph for Pond 2P: Bio-Basin Time Inflow Storage Elevation Primary (hours) (cfs) (cubic-feet) (feet) / (cfs) 0.00 0.00 0 465.50 ✓ 0.00 0.10 4.35 911 465.70 0.00 0.20 4.35 2,476 466.03 0.00 0.30 4.35 4,041 466.34 0.00 0.40 4.35 5,597 466.62 0.15 0.50 4.35 7,001 466.87 0.78 0.60 4.35 8,164 467.06 1.41 0.70 4.35 9,151 467.23 1.77 0.80 4.35 10,030 467.37 2.03 0.90 4.35 10,826 467.50 2.23 1.00 4.35 11,556 467.61 2.40 1.10 4.35 12,230 467.71 2.55 1.20 1.74 12,397 467.74 2.58 1.30 0.00 11,700 467.63 2.43 1.40 0.00 10,858 467.50 2.24 1.50 0.00 10,086 467.38 2.05 1.60 0.00 9,386 467.27 1.85 1.70 0.00 8,758 467.16 1.64 1.80 0.00 8,204 467.07 1.43 1.90 0.00 7,730 466.99 1.20 2.00 0.00 7,342 466.93 0.97 2.10 0.00 7,027 466.87 0.79 2.20 0.00 6,768 466.83 0.65 2.30 0.00 6,553 466.79 0.55 2.40 0.00 6,373 466.76 0.46 2.50 0.00 6,220 466.73 0.39 2.60 0.00 6,090 466.71 0.33 2.70 0.00 5,978 466.69 0.29 2.80 0.00 5,881 466.67 0.25 2.90 0.00 5,797 466.66 0.22 3.00 0.00 5,723 466.64 0.19 Post West 100-yr Anvince Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 1 Area Listing (selected nodes) Area C Description (sq-ft) (subcatchment-numbers) 27,007 0.45 Open Developed Area (1S) 11,761 0.45 Permeable Pavers (1S) 47,045 0.90 Paved Area (1S) 37,897 0.90 Rooftop (1S) 123,710 TOTAL AREA Post West 100-yr Anvince VA-Albemarle-ATLASI4 100-Year Duration=40 min, Inten=3.83 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 2 Time span=0.00-3.00 hrs, dt=0.01 hrs, 301 points Runoff by Rational method, Rise/Fall=1.0/2.0 xTc Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: Post-West to Channel Runoff Area=2.840 ac 0.00% Impervious Runoff Depth=2.06" Tc=5.0 min C=0.76 Runoff=8.34 cfs 21,259 cf Pond 2P: Bio-Basin Peak Elev=467.99' Storage=14,037 cf Inflow=8.34 cfs 21,259 cf Outflow=7.66 cfs 15,732 cf Total Runoff Area= 123,710 sf Runoff Volume= 21,259 cf Average Runoff Depth =2.06" 100.00% Pervious= 123,710 sf 0.00% Impervious = 0 sf Post West 100-yr Anvince VA-Albemarle-ATLASI4 100-Year Duration=40 min, Inten=3.83 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 3 Summary for Subcatchment 1S: Post-West to Channel Runoff = 8.34 cfs @ 0.09 hrs, Volume= 21,259 cf, Depth= 2.06" Runoff by Rational method, Rise/Fall=1.0/2.0 xTc, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs VA-Albemarle-ATLAS14 100-Year Duration=40 min, Inten=3.83 in/hr Area (ac) C Description 1.080 0.90 Paved Area 0.870 0.90 Rooftop 0.620 0.45 Open Developed Area 0.270 0.45 Permeable Pavers 2.840 0.76 Weighted Average 2.840 Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment 1S: Post-West to Channel Hydrograph 0 Runoff 8.34 cfs/ J/ 4 VA-Albemarle-ATLAS14 100-Year 8 Duration=40 min, 7 0 Inten=3.83 in/hr Runoff Area=2.840 ac 6 0, Runoff Volume=21,259 cf H / Runoff Depth=2.06" • 5 Tc=5.0 min O LL 4 C=0.76 3 PA 2 PIA 0 1 2 3 Time (hours) Post West 100-yr Anvince VA-Albemarle-ATLAS14 100-Year Duration=40 min, Inten=3.83 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 4 Hydrograph for Subcatchment 1S: Post-West to Channel Time Runoff Time Runoff Time Runoff (hours) (cfs) (hours) (cfs) (hours) (cfs) 0.00 0.00 1.04 0.00 2.08 0.00 0.02 2.00 1.06 0.00 2.10 0.00 0.04 4.00 1.08 0.00 2.12 0.00 0.06 6.00 1.10 0.00 2.14 0.00 0.08 8.00 1.12 0.00 2.16 0.00 0.10 8.34 1.14 0.00 2.18 0.00 0.12 8.34 1.16 0.00 2.20 0.00 0.14 8.34 1.18 0.00 2.22 0.00 0.16 8.34 1.20 0.00 2.24 0.00 0.18 8.34 1.22 0.00 2.26 0.00 0.20 8.34 1.24 0.00 2.28 0.00 0.22 8.34 1.26 0.00 2.30 0.00 0.24 8.34 1.28 0.00 2.32 0.00 0.26 8.34 1.30 0.00 2.34 0.00 0.28 8.34 1.32 0.00 2.36 0.00 0.30 8.34 1.34 0.00 2.38 0.00 0.32 8.34 1.36 0.00 2.40 0.00 0.34 8.34 1.38 0.00 2.42 0.00 0.36 8.34 1.40 0.00 2.44 0.00 0.38 8.34 1.42 0.00 2.46 0.00 0.40 8.34 1.44 0.00 2.48 0.00 0.42 8.34 1.46 0.00 2.50 0.00 0.44 8.34 1.48 0.00 2.52 0.00 0.46 8.34 1.50 0.00 2.54 0.00 0.48 8.34 1.52 0.00 2.56 0.00 0.50 8.34 1.54 0.00 2.58 0.00 0.52 8.34 1.56 0.00 2.60 0.00 0.54 8.34 1.58 0.00 2.62 0.00 0.56 8.34 1.60 0.00 2.64 0.00 0.58 8.34 1.62 0.00 2.66 0.00 0.60 8.34 1.64 0.00 2.68 0.00 0.62 8.34 1.66 0.00 2.70 0.00 0.64 8.34 1.68 0.00 2.72 0.00 0.66 8.34 1.70 0.00 2.74 0.00 0.68 7.67 1.72 0.00 2.76 0.00 0.70 6.67 1.74 0.00 2.78 0.00 0.72 5.67 1.76 0.00 2.80 0.00 0.74 4.67 1.78 0.00 2.82 0.00 0.76 3.67 1.80 0.00 2.84 0.00 0.78 2.67 1.82 0.00 2.86 0.00 0.80 1.67 1.84 0.00 2.88 0.00 0.82 0.67 1.86 0.00 2.90 0.00 0.84 0.00 1.88 0.00 2.92 0.00 0.86 0.00 1.90 0.00 2.94 0.00 0.88 0.00 1.92 0.00 2.96 0.00 0.90 0.00 1.94 0.00 2.98 0.00 0.92 0.00 1.96 0.00 3.00 0.00 0.94 0.00 1.98 0.00 0.96 0.00 2.00 0.00 0.98 0.00 2.02 0.00 1.00 0.00 2.04 0.00 1.02 0.00 2.06 0.00 Post West 100-yr Anvince VA-Albemarle-ATLAS14 100-Year Duration=40 min, Inten=3.83 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 5 Summary for Pond 2P: Bio-Basin Inflow Area = 123,710 sf, 0.00% Impervious, Inflow Depth = 2.06" for 100-Year event Inflow = 8.34 cfs @ 0.09 hrs, Volume= 21,259 cf Outflow = 7.66 cfs @ 0.68 hrs, Volume= 15,732 cf, Atten= 8%, Lag= 35.4 min Primary = 7.66 cfs @ 0.68 hrs, Volume= 15,732 cf Routing by Stor-Ind method, Time Span= 0.00-3.00 hrs, dt= 0.01 hrs Peak Elev= 467.99' © 0.68 hrs Surf.Area= 6,706 sf Storage= 14,037 cf Plug-Flow detention time= 40.9 min calculated for 15,679 cf(74% of inflow) Center-of-Mass det. time= 35.6 min ( 59.5 -23.8 ) Volume Invert Avail.Storage Storage Description #1 465.50' 28,750 cf Custom Stage Data (Irregular)Listed below (Recalc) Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 465.50 4,411 335.0 0 0 4,411 466.00 4,928 381.0 2,334 2,334 7,038 467.00 5,975 326.0 5,443 7,777 10,153 468.00 6,715 342.0 6,341 14,118 11,066 469.00 7,318 352.0 7,014 21,132 11,719 470.00 7,922 362.0 7,618 28,750 12,390 Device Routing Invert Outlet Devices #1 Primary 463.90' 15.0" x 44.8' long Culvert CPP, square edge headwall, Ke= 0.500 Outlet Invert= 463.50' S= 0.0089 '/' Cc= 0.900 n= 0.012 #2 Device 1 466.50' 1.08'W x 0.50' H Vert. Orifice/Grate C= 0.600 #3 Device 1 467.75' 48.0" Horiz. Orifice/Grate Limited to weir flow C= 0.600 Primary OutFlow Max=7.66 cfs @ 0.68 hrs HW=467.99' (Free Discharge) 4-1=Culvert (Passes 7.66 cfs of 11.00 cfs potential flow) 12=Orifice/Grate (Orifice Controls 2.89 cfs @ 5.35 fps) 3=Orifice/Grate (Weir Controls 4.77 cfs @ 1.59 fps) Post West 100-yr Anvince VA-Albemarle-ATLAS14 100-Year Duration=40 min, Inten=3.83 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 6 Pond 2P: Bio-Basin Hydrograph / Cl Inflow 8.34 cfs 0 Primary ' `" Inflow Area=123,710 sf 8_ 7.66 cf° Peak Elev=467.99' 7 % - Storage=14,037 cf 6 }k 5 PAIo ir 4- 3 /2f,./ dr~:Arff.eoferao—feor 4/e004,40) 7 p 1 2 3 Time (hours) Pond 2P: Bio-Basin Stage-Discharge 470-/ z ❑Primary 469- 4111111111011.11r 468- Air Orifice/Grate w 467- /7 Orifice/Grate 0 466 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Discharge (cfs) Post West 100-yr Anvince VA-Albemarle-ATLAS14 100-Year Duration=40 min, Inten=3.83 in/hr Prepared by Terra Concepts, PC Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Page 7 Pond 2P: Bio-Basin Stage-Area-Storage SurfaceJHoozcntai/uetteC A.a ��.;;,.c-ff 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 Surface 0 Storage / 470 7 �/�� f 469 // ./rVV a, — 468 o s, 467 // 466 Custom Stage Data / 0 5,000 10,000 15,000 20,000 25,000 Storage(cubic-feet) 0 Post West 100-yr Anvince VA-Albemarle-ATLASI4 100-Year Duration=40 min, Inten=3.83 in/hr Prepared by Terra Concepts, PC �`` Printed 4/9/2013 HydroCAD®8.50 s/n 002893 ©2007 HydroCAD Software Solutions LLC Pape 8 Hydrograph for Pond 2P: Bio-Basin Time Inflow Storage Elevation Primary (hours) (cfs) (cubic-feet) (feet) (cfs) 0.00 0.00 0 465.50 0.00 0.10 8.34 1,747 465.88 0.00 0.20 8.34 4,749 466.47 0.00 0.30 8.34 7,591 466.97 1.11 0.40 8.34 10,003 467.36 2.02 0.50 8.34 12,179 467.71 2.54 0.60 8.34 13,696 467.94 6.16 0.70 6.67 14,006 467.98 7.52 0.80 1.67 13,274 467.87 4.55 0.90 0.00 12,228 467.71 2.55 1.00 0.00 11,346 467.58 2.36 ' 1.10 0.00 10,533 467.45 2.16 1.20 0.00 9,790 467.33 1.96 1.30 0.00 9,119 467.22 1.76 1.40 0.00 8,521 467.12 1.56 1.50 0.00 8,000 467.04 1.34 1.60 0.00 7,561 466.96 1.10 1.70 0.00 7,205 466.90 0.89 1.80 0.00 6,915 466.85 0.73 1.90 0.00 6,675 466.81 0.61 2.00 0.00 6,475 466.78 0.51 2.10 0.00 6,307 466.75 0.43 2.20 0.00 6,164 466.72 0.37 2.30 0.00 6,042 466.70 0.31 2.40 0.00 5,936 466.68 0.27 2.50 0.00 5,845 466.67 0.24 2.60 0.00 5,765 466.65 0.21 2.70 0.00 5,695 466.64 0.18 2.80 0.00 5,633 466.63 0.16 2.90 0.00 5,579 466.62 0.14 3.00 0.00 5,530 466.61 0.13 Short Version BMP Computations For Worksheets 2-6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Albrecht Commons Water Resources Area: Development Area Preparer: Alan G. Franklin,PE Date: 4/7/2013 Project Drainage Area Designation East Drainage to 48" L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(1) Pj small storm correction factor,0.9 I percent imperviousness P annual precipitation,43"in Albemarle A project area in acres in subject drainage area, A= 0.31 C pollutant concentration,mg/I or ppm target phosphorus f factor applied to RR V required treatment volume in cy,0.5"over imperv.area= A(I)43560(0.5/12)/27 RR required removal, L(post)-f x L(pre) %RR removal efficiency, RR100/L(post) Impervious Cover Computation(values in feet&square feet) Item pre-development Area post-development Area Roads Length Width subtotal Length Width subtotal 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Parking Lots 1 2 3 4 1 2 3 4 0 0 6,438 6438 Gravel Areas 1 2 subtotal 1 2 subtotal x 0.75 0 0 x 0.75 0 Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Actively-grazed pasture& Area Area yards and cultivated turf 0 x 0.08= 0 0 x 0.08= 0 Active crop land Area Area Ox0.25= 0 x0.25= 0 Other Impervious Areas 0 0 Impervious Cover 0% 48% I(pre) l(post) Rv(post) V 0.48 9.9 New Development(For Development Areas,existing impervious cover<=20% C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 1.00 20% 0.23 0.44 0.91 0.47 52% Development Area 0.35 1.00 0% 0.05 0.05 0.46 0.41 90% Drinking Water Watersheds 0.40 1.00 1% 0.06 0.06 0.52 0.46 88% Other Rural Land *min.values Redevelopment(For Development Areas,existing impervious cover>20% C f I(pre)' Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 0.90 20% 0.23 0.44 0.91 0.52 57% Development Area 0.35 0.85 0% 0.05 0.05 0.46 0.42 91% Drinking Water Watersheds 0.40 0.85 1% 0.06 0.06 0.52 0.47 90% Other Rural Land Interim Manual, Page 70 rev.31 March 1998 GEB Short Version BMP Computations For Worksheets 2-6 Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Albrecht Commons Water Resources Area: Development Area Preparer: Alan G.Franklin,PE Date: 4/7/2013 ,,,_. Project Drainage Area Designation West Drainage to Channel L storm pollutant export in pounds, L=[P(Pj)Rv/12] [C(A)2.72] Rv mean runoff coefficient, Rv=0.05+0.009(1) Pj small storm correction factor,0.9 1 percent imperviousness . P annual precipitation.43"in Albemarle A project area in acres in subject drainage area, A= 2.84 C pollutant concentration,mg/I or ppm target phosphorus f factor applied to RR V required treatment volume in cy,0.5"over imperv.area= A(I)43560(0.5/12)/27 RR required removal, L(post)-f x L(pre) %RR removal efficiency, RR100/L(post) Impervious Cover Computation(values in feet&square feet; - Item pre-development Area post-development Area W._. Roads Length Width subtotal Length Width subtotal 0 0 0 0 0 0 0 0 0 0 0 0' 0 0 0 0 0 0 8,161 8,161 Driveways Length Width no. subtotal Length Width no. subtotal and walks 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Parking Lots 1 2 3 4 1 2 3 4 0 0 38,812 38,812 Gravel Areas 1 2 subtotal 1 2 subtotal x 0.75 0 0 x 0.75 0 Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 37,745 37,745 Actively-grazed pasture& Area Area yards and cultivated turf 0 x 0.08= 0 0 x 0.08= 0 Active crop land Area Area 0 x 0.25= 0 x 0.25= 0 Other Impervious Areas 0 0 Impervious Cover 0% 68% I(pre) ((post) Rv(post) V 0.67 130.7 New Development(For Development Areas,existing impervious cover<=20% C f I(pre)" Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 1.00 20% 0.23 4.01 11.62 7.61 65% Development Area 1 0.35 1.00 0% 0.05 0.44 5.81 5.37 92% Drinking Water Watersheds 0.40 1.00 1% 0.06 0.59 6.64 6.05 91% Other Rural Land i min.values .,.. m .. Redevelopment(For Development Areas,existing impervious cover>20% C f I(pre)" Rv(pre) L(pre) L(post) RR %RR Area Type 0.70 0.90 20% 0.23 4.01 11.62 8.01 69% Development Area 0.35 0.85 0% 0.05 0.44 5.81 5.44 94% Drinking Water Watersheds 1. 0.40 0.85 1% 0.06 0.59 6.64 6.14 92% Other Rural Land Interim Manual, Page 70 rev.31 March 1998 GEB L ill . 1111 1 e //LW s AV a t- Designing Bioretention with an Internal Water Storage (IWS) Layer Design guidance for an innovative bioretention feature Kira int�srr'acal war e inii/Si iayea is:reared it bioretention cells by acdciing a 9i degree elbow to the underdrains to raise the outlet.This design feature provides addition- al storage in the media,and at sites with sandy in situ soil,such as those located in the sandhills and coastal plain of North Carolina,IWS acts as a sump to drastically reduce pAi outflow from bioretention. The hydro- bioretention performance, including its logic impact is so great that sites with ability to enhance groundwater recharge hydrologic soil groups A or B will re- and stream baseflow. Bioretention ceive higher pollutant removal credits if design, construction, and maintenance IWS is properly used. This publication have previously been discussed in AG- discusses the water quality,hydrologic, 588-5 and AG-588-3,both part of the and thermal benefits of using IWS, as Urban Waterways series. well as the constraints and concerns as- sociated with using IWS. Examples of BIORETENTION DEFINITIONS ways to incorporate IWS into bioreten- Terminology for bioretention hydrologic tion designs are also included. terms follows. Please refer to Figure 1. WHAT IS BIORETENTION? Inflow/Runoff—amount of water leaving(or shed from)the surface of Bioretention combines natural and en- the drainage area. In urbanized areas, gineered systems to manage stormwater this water typically enters the storm from developed areas. One design goal sewer network. is treating the"first flush,"or initial, more polluted portions of a runoff event. Bowl—The surface ponding zone. Reducing the volume of runoff leav- This has been typically designed to be ing a bioretention cell is a crucial part 9 to 12 in deep. of pollutant load reduction and is ac- Media—An engineered sandy fill that complished via evapotranspiration(ET) has moderately high permeability and exfiltration. Promoting exfiltration (1-2 in/hr)and is capable of captur- through the bottom layer and sides of ing or removing nitrogen,phosphorus, the bioretention cell will increase pollut- metals, and other pollutants. ant removal capabilities of bioretention. Understanding hydraulic properties of the in situ soil is important to predict NCState University A&T StateniUniversity COOPERATIVE EXTENSION NAM Empowering People•Providing Solutions Evapotranspiration is 41,1 Inflo 1/Runoff 4.4 ..-ts Bowl — Sandy Fill ` ', Drainage Media o w Internal Water Storage • ;- '..' �- . •". •. . . .» :` 4 • 4 q w Underdrains �:� k. \► Upturned Elbow In-situ Soil Exfiltration In-situ Soil Figure 1.Schematic of a bioretention cell with an internal water storage layer. In situ soil—Existing soil surrounding bioretention Underdrain—Typically small,4 to 8 in diameter, cell. perforated PVC or corrugated plastic pipes. These drainage lines are located in the gravel layer below Mulch Layer—A 2-to 3-in mulch layer is added on the surface of the media in tree/shrub/perennial the fill media to collect water and convey it to the bioretention cells to maintain moisture in the soil storm sewer network(including culverts and open for plants,minimize growth of weeds,and to bind channels). Underdrains are most often used when metals and oils/grease from runoff. bioretention cells are located in clay-influenced or otherwise slowly draining soils. Gravel Layer—Located beneath the media and serves as the layer that surrounds the underdrains to Drainage—Treated water that has passed through the media of the bioretention cell and is recollected prevent clogging. Usually consists of washed#57 stone (1/2 to 3/4 in diameter)with a smaller stone on and released through the underdrain pipes. top to act as a choking layer('/4 to Y2 in diameter) Overflow— Untreated water that bypasses or flows to prevent media from migrating to the underdrains over the bioretention cell. and clogging them.A permeable filter fabric is also Outflow—The total water leaving a bioretention typically placed around the gravel layer to minimize cell and entering the storm sewer network. With media migration. bioretention, outflow is the sum of overflow and Exfiltration/Infiltration—Water that leaves the bot- drainage. tom or sides of the bioretention cell and enters the IWS (Internal Water Storage) layer—This is the in situ soil.Water exfiltrates the bioretention gravel subsurface portion of the media that provides ad- layer. It infiltrates the surrounding soil. ditional water storage volume in the bioretention Evaporation/Evapotranspiration—Some water cell. Water stored in this layer is principally re- temporarily stored in the bowl and top portions of leased by exfiltration. The IWS layer is created by the media will eventually evaporate to the atmo- elevating the underdrain, usually with a 90-degree sphere. If plants aid in the release of water to the at- PVC elbow. mosphere,this process is termed evapotranspiration. 2 PARAMETERS AND PROCESSES OF Outflow Reduction BIORETENTION HYDRAULIC DESIGN • Use of internal water storage will increase Delivery rate of water to the cell(runoff rate) storage capacity and lead to less outflow in most cases (larger events needed to generate outflow). • If the delivery rate of water is less than the • Consecutive large events may reduce perform- infiltration rate, overflow will never occur. ance for cells with internal water storage. The Bowl volume water storage layer may remain full from the • What is the minimum volume of water that preceding event and have little storage available would generate overflow, assuming no event to fully capture and treat the following event. infiltration? CREATING AN INTERNAL WATER STORAGE The bowl volume is typically designed to capture the first flush runoff event(typically (IWS) LAYER ranges from 1 to 1.5 inches in North An internal water storage layer is relatively Carolina). inexpensive and simple to create and install. IWS requires a 90-degree PVC upturned elbow attached Infiltration rate into media to the underdrains to force an elevated outlet.Water • Media composition specified in the NC BMP stored in this created sump can also be released Design Manual should have an infiltration rate through exfiltration and ET. The top of the elbow of 1 to 2 in/hr [associated with 85 to 88 percent should be at least 12 in below the surface of the bowl. sand, 8 to 12 percent silt and clay, and 3 to 5 At sites with highly permeable in situ soils, internal percent organic matter] (N.C. DWQ, 2007). water storage layers can significantly reduce the ratio • For low intensity events, if infiltration rate of outflow volume to inflow volume. Incorporating exceeds runoff rate into bowl, overflow will not IWS into bioretention design will be discussed in occur. more detail later, and examples will be provided of • For high intensity events,when infiltration rate how to tie the outlet into the stormwater network. is less than runoff rate,overflow may occur with CONSTRAINTS AND CONCERNS WITH events greater than the design storm depth. INTERNAL WATER STORAGE Media depth • Research has shown that deeper media depths WHAT FACTORS DO YOU CONSIDER promote more exfiltration and eliminate more Underlying Soils.One of the most important factors to runoff than shallower systems(Li et al., 2009; consider when designing IWS is the in situ soil.At a Brown and Hunt, 2009). site with highly permeable underlying soil,the poten- • In designing internal water storage systems, tial for outflow reduction is great. This makes IWS more media in the internal water storage zone a good drainage configuration to reduce outflow and will increase subsurface storage volume. pollutant loads. Underdrains Surrounding Land Use.An IWS design is recom- mended only for runoff from residential and commer- • Is the system conventionally drained, or does it cial development,and should be avoided in manu- incorporate an internal water storage layer? facturing and industrial areas where the potential for • Where will the underdrains outlet? groundwater contamination is higher. Typically in • In cells with internal water storage,if residential areas, stormwater runoff and surrounding exfiltration rate exceeds infiltration rate, underlying soils are relatively uncontaminated, so drainage will not occur. incorporating infiltration measures,such as the IWS layer, is a beneficial practice (Clark and Pitt, 2007; Overflow is dependent on rainfall intensity Pitt et al., 1999;Pitt et al., 2002). • If the bowl can store 1 in of runoff, overflow may occur if rainfall exceeds 1 in and the Available Storage/Effective Porosity.Another fac- delivery rate exceeds infiltration rate. tor to consider is the storage volume available in the media and gravel layers. This volume is dependent on the average depth of the internal water storage layer. 3 Typically,the underdrains are situated in 6 to 8 in of A general bioretention design concern that affects gravel, and gravel has a porosity of 28 to 34 percent. hydrologic performance has been volume of media Overlying the gravel is the sand-based fill media, used in design. If media is not placed under the side which has a porosity ranging from 39 to 43 percent. slopes, storage volume available in the IWS layer can However,not all of the pore spaces are available to be reduced by up to 30 or 40 percent,depending on free water. The amount of water that remains attached the size and shape of the bioretention cell. If this is to the soil particles inter-event and does not drain the case for a design,the storage depth in the media freely is referred to as field capacity. The effective and gravel will not equal the same depth in the bowl porosity is a measure of the field capacity subtracted because the surface areas are different. from the total porosity. The effective porosity for sand Seasonally High Water Table.The separation dis- is 30 to 33 percent and for gravel is 21 to 28 percent tance between the bottom of the IWS layer and the (McWorter and Sunada, 1977). General approxima- seasonally high water table must be considered, and tions for the effective porosities of sand and gravel designers must still abide by the minimum separa- are 30 and 25 percent,respectively. tion distance between the bottom of the cell and the Based on the above approximations of effective seasonally high water table. In North Carolina,this porosity,the storage volumes in the media and gravel is 2 ft(N.C.DWQ,2007).A seasonally high water layer for several IWS layer depths are presented in table greater than the bottom of the bioretention cell Table 1.The predicted typical storm size that is fully reduces the volume of filter media available to store captured is based on the following assumptions: (1) stormwater. Outflow or overflow is more likely, and the side walls are vertical, (2)the media is present the potential to drain pollutants found in groundwater under the entire bowl, and(3)the IWS layer has no also exists. slope. For the following IWS depths: 12 in, 18 in, and 24 in,the available storage depths in the gravel WHAT ARE THE BENEFITS OF USING INTERNAL WATER layer and media are 5.6 in, 7.4 in, and 9.2 in,respec- STORAGE? tively. In the North Carolina Department of Environ- New credit for bioretention with IWS.Based on cur- ment and Natural Resources (NCDENR)bioretention rent research,NCDENR has recently increased the design guidance,an average recommended surface pollutant removal credit for bioretention cells designed with internal water Table 1.Storage volume available for varying internal water storage layer depths.Design storage.A few speci- assumptions:(1)the side walls are vertical,(2)the media is present under the entire bowl, fications must be met (3)the IWS has no slope,and(4)drainage area is 100 percent impervious(CN=98). (Figure 2).The cell must be constructed 36 in media depth(30%effective porosity)and 8 in gravel layer(25%effective porosity) with at least 3 ft(90 IWS Depth in Gravel Storage Volume Depth in Typical Storm Size Captured cm)of fill media.The and Media(in) Gravel and Media(in) (average ponding depth=9 in) top of the internal (8+12)=20 5.6 0.62-inch event water storage layer cannot be closer to (8+18)=26 7.4 0.82-inch event the surface than 12 in (8+24)=32 9.2 1.02-inch event (30 cm).At sites with sandier in situ soils, it is recommended to storage depth is 9 in(N.C. DWQ,2007a).This means maximize the IWS zone depth(12 inches from surface a 24-in IWS layer that is fully drained at the start of of the media);however,if underlying soils are less the event is capable of completely storing the entire permeable,the IWS zone depth should be reduced(18 bowl volume or design storm event.Accounting for to 24 inches from surface of the media).The top of exfiltration that occurs during an event,the internal the water storage layer cannot be closer than 12 in(30 water storage layer will actually be able to store a pre- cm) from the bottom of the media. If all the specifica- cipitation event larger than the design storm,but only tions are met,the total nitrogen removal credit will be when the internal water storage layer is completely increased from 35 to 60 percent,and total phosphorus drawn down before precipitation starts. removal credit will be increased from 45 to 60 percent 4 y , _ arm y 2 A ) Outlet Ideally Media (_> 3 ft.)-� • • -> -1 8 in. Below 12 1 r, ' Bowl u ace Internal Water i . . , ° , Storage (? 12 in.) . • • • • ` •. . n ° .:• w . Gravel Layer . � � (e -8 m.) ' � 4. •� _ Figure 2.Design recommendations for bioretention with IWS to receive updated removal credits. Table 2.Old and revised pollutant removal credits for bioretention with IWS. Region Nitrogen Remov- Phosphorus Total Suspended Solids al Credit Removal Credit Removal Credit Old NCDENR Credit (Statewide) 35% 45% 85% Revised NCDENR Credit' (Sandhills and Coastal Plain) 60% 60% 85% Revised NCDENR Credit' (Piedmont and Mountains) 40% 45% 85% *Hydrologic Soil Group A or B 1 Must incorporate IWS to receive revised credit. __� � ° ,. x' 11 Sandhills and Coastal Plain �} .._ ✓ 0 100 200 Miles N Figure 3.Area impacted by increased pollutant removal credit for bioretention with IWS.Image modified with permission from N.C.DWQ,2007b. 5 (Table 2)in the coastal plain and sandhills(Figure 3). (Chesapeake Bay,Albemarle-Pamlico Sounds). Also,if these design specifications are followed in The results from pilot-scale bioretention studies in the piedmont or mountain region of North Carolina Kim et al. (2003)were positive: 70 to 80 percent mass and the site lies in an A or B hydrologic soil group, removal rates of nitrate plus nitrite(NO2 3-N). Despite total nitrogen removal credit will be increased to 40 these positive laboratory results,later field studies percent.The recommended guideline for underlying by Hunt et al. (2006) and Dietz and Clausen(2006) soil permeability to receive the additional credit is a were inconclusive about adding a saturated layer to pre-construction rate exceeding 1 in/hr. create anaerobic conditions required to convert nitrate into nitrogen gas.A field study by Davis (2007)had REMOVAL CREDITS—WHAT ARE THEY? limited data,but it showed high removal rates of NCDENR assigns pollutant removal credits(or per- nitrate. Passeport et al. (2009)also had promising field results. Their study showed significant reduction centages)to a suite of BMPs, including bioretention. in nitrate for one of two cells examined. Passeport et As pollutant loads enter a given BMP,some frac al. (2009)believed this was due to the longer satura- tion or percentage of them is retained or removed tion period maintained in the one cell surrounded by by the BMP.The higher the fraction of pollutant loamy-clay,but recommended that the role of in situ removal,the better the BMP works.Under the new soils be further explored. NCDENR guidelines,if 10 pounds of nitrogen annu- ally enter a coastal plain bioretention cell with an Hydrologic benefit.Another major benefit of inter- IWS, it is assumed that only four pounds of nitrogen nal water storage is the hydrologic impact. If sited in would leave the bioretention cell. regions of sandy in situ soils, such as the sandhills or coastal plain(Figure 3), IWS zones in bioreten- Nitrate removal. Since 2000,research has been con- tion cells act as a storage sump and eliminate most ducted evaluating the performance of bioretention outflow.An upper coastal plain site studied in Rocky cells with IWS.Kim et al. (2003)proposed includ- Mount rarely had outflow due to its sandy in situ ing an overdrain to create a continuously submerged soils. Two cells had 3 ft of media with a 2 ft IWS anoxic zone to promote denitrification. With conven- layer. The cells had varying vegetative covers (grass tionally drained systems,nitrate removal had been and mulch/shrub). From September 2007 to January poor. Previous bioretention research showed good 2009, 78 events were monitored, and outflow was removal rates and low effluent concentrations for total generated only four and five times in the mulch/shrub nitrogen(TN) and total nitrogen(TKN)in cell and grassed cell,respectively(Table 3).A graph g Kjeldahlg ofthe he outflow volume versus runoff volume for the both field studies (Dietz and Clausen, 2006;Davis grassed cell is displayed in Figure 4.This graph in- et al.,2006;Hunt et al., 2006; and Hunt et al., 2008) eludes events in which overflow occurred because the and laboratory studies (Davis et al.,2001;Hsieh and bowl volume was overwhelmed. Davis,2005; and Davis et al.,2006). Outflow reduction is not as pronounced in less Generally, in conventionally drained systems, or- ganic nitrogen transforms into ammonia via mineral- ization/ammonification. Then ammonia would trans- 4000 form into nitrate-nitrite via nitrification. Both of these •Outflow 4 Drainage Only processes occur in an aerobic environment. However, a 3000 with the absence of an anaerobic zone,nitrite-nitrate could never transform into harmless nitrogen gas c 2000 ,,. • (N2). (N2 accounts for 78 percent of the atmosphere.) Because portions of bioretention cells with inter- t 000 • nal water storage zones should remain saturated for o • •• • extended periods of time, anaerobic conditions are 0 expected to develop. Such conditions would be ideal 0 1000 2000 3000 4110 for denitrification to transform nitrite-nitrate into Run off(c t) nitrogen gas,thus reducing nitrite-nitrate and total ni- trogen concentrations. This use for internal water stor- Figure 4.Ouflow volume versus runoff volume for the grassed cell with a 2-ft IWS zone in Rocky Mount,NC.Drain- age was pioneered for nitrogen sensitive watersheds age and overflow volumes are presented,as well as a 1:1 line. 6 Table 3.Performance of bioretention with IWS in the piedmont versus upper coastal plain. Location! Media IWS Layer #of Events #of Events Site Underlying Soil Depth(ft) Thickness(ft) Monitored with Drainage Greensboro-1 (G-1) Piedmont 4 2 63 18 (clay loam) Greensboro-2(G-2) Piedmont 4 No IWS 63 40 (clay loam) Rocky Mount Upper Coastal 3 2 78 5 (Grassed) Plain (sand) Rocky Mount Upper Coastal 3 2 78 4 (Mulch/Shrub) Plain (sand) Graham South Piedmont 3 2 40 22 (sandy loam) Graham North Piedmont 2 1 40 34 (loamy clay) sandy parts of NC. Internal water storage systems This means that the water storage layer would drain produce different results with varying in situ soils faster and thus have more subsurface storage volume because of different exfiltration rates. Two cells in the available.The benefit of deeper IWS layers is cur- piedmont(Greensboro,NC)were constructed with 4 rently being explored when the previously discussed ft of media. One included a 2-ft internal water storage Rocky Mount bioretention cells are monitored for an zone and the other was conventionally drained. Of additional 12 months at a shallower IWS layer depth 63 events monitored,the internal water storage zone (1 ft). Trends from the data presented in Table 3 show cell had outflow on 18 occasions, and the convention- that deeper media depths with deeper IWS layers and ally drained cell had outflow more than twice as often sandier underlying soils will perform best. (40 occasions) (Table 3) (Sharkey,2006). This shows Thermal benefit.Another benefit of bioretention that these systems perform well in clayey soils,but with internal water storage is reduced thermal pollu- outflow is more likely at sites with clayey in situ soils tion. This is of particular concern in the mountains of due to slower inter-event drawdown of the internal North Carolina due to trout populations,where sum- water storage zone. Events in quick succession make mer thunderstorms could raise runoff temperatures these systems prone to more outflow.As underlying above maximum trout temperature thresholds. Soil soils get tighter(more clayey),the likelihood of out- temperatures have been shown to be coolest at the flow frequency becomes greater. bottom of the soil media. The deeper portion of the At a site in Graham,NC, two Bermuda turf biore- soil profile also experienced the smallest temperature tention cells were constructed with equal drainage fluctuations in response to (1) storms, (2)diurnal ef- areas and equal watershed conditions. One (Graham- fects, or(3) seasonal effects (Jones and Hunt,2009). North)had a media depth of 2 ft with a 1 ft IWS zone Since water is coolest at the bottom of the media, and and a loamy-clay underlying soil. The other(Graham- internal water storage draws water from the bottom South)had a media depth of 3 ft with a 2 ft IWS of the profile,the coolest water will be released at zone and a sandy loam underlying soil. Outflow was the outlet. Forcing a layer of water in the bottom of observed at Graham-South less often than in Graham- the cell (an IWS layer)will allow the water to better North(Passeport et al., 2009). In 40 events that were equilibrate to the cooler temperature of the deeper monitored from April 2006 to August 2007, Graham- surrounding soils. Finally,the decrease in outflow South and Graham-North generated outflow in 22 volume from these bioretention cells further reduces and 34 times,respectively. Graham-South performed the thermal load released to streams. For more in- "better"because it had a deeper water storage layer formation on bioretention design in trout sensitive and its underlying soil had a higher permeability. waters,please see AG-588-10. 7 TYING-IN OUTLET— INCORPORATING cause the relief(elevation change)required to outlet IWS INTO BIORETENTION DESIGN IWS is less than a conventionally drained system.The Another factor for the designer to consider is where excavated trench to daylight the outlet will not have to outlet bioretention effluent. Outflow can either be to be as deep or as long for bioretention with IWS, so released into existing storm sewers or trenched and using the IWS layer could actually save money. Cost daylighted down slope.Whenupoutflow is released intoed elbow can either savings of using IWS in bioretention retrofits will be existing storm sewers,the turndiscussed in more detail later.A cross section show- be incorporated inside or outside of the storm sewer. ing how incorporating IWS into a design allowed the When the invert of the existing storm sewer is designers to meet the elevation requirements is shown the underdrains,the 90-degree elbow and standpipebelow in Figure 9.The elevation requirement(91 ft)was set can be installed inside the storm sewer. The IWS con- by an existing brick storm sewer structure, shown in nection is most easily installed inside a storm sewer Figure 10. drop inlet structure. Examples of creating an IWS WHAT WILL INSTALLING INTERNAL WATER STORAGE COST? layer using this approach are displayed in Figures Little additional cost is associated with including an 5 and 6 for sites in Rocky Mount and Greensboro, internal water storage design for bioretention. This respectively.The simplest application of retrofitting design configuration requires only a few extra feet bioretention with IWS occurs when existing bioreten- of PVC pipe and 90-degree PVC elbows. When used tion cells outlet into one of these structures because of as a retrofit, an internal water storage configura- the ease of access to the underdrain outlet. tion could possibly even save the installer money, is f 6 . c ��r.. �° v *.. , '...4't:'4.4 7 fif. 4111° . . .. 'gam '1'41' A i"0 _... '.° ik, at P 7%,..°,74,;7,..,,, usJ4:4: � g s''' ,, "° r 9 01;,,,, 'X ,41Te00-;*41,4/7„..ifilt 4,6, '..---.... lira,. . , I c4.,-.. 407 , L mos. `"¢ ,... . '',1 4 ,1,....-Pm7:7,4, ,,,,,,:t,,, A;n::„, 4,,,, ,x .(:. ' « «- 1 4;',.' '4: - 4 _ „".. a 'r"' e': �.,.,,ass,r,:. .a .., Figure 5.Upturned elbow installed in storm sewer drop inlet Figure 6.Upturned elbow installed in storm structure in Rocky Mount. sewer drop inlet structure in Greensboro. However, if the invert of the existing storm sewer depending on the design and site configuration.The is above the underdrains,running the pipes with 90- internal water storage design also makes planning degree elbows will take place outside of the storm for retrofits easier. If a typical bioretention cell has a sewer, in order to raise the elevation of the underdrain 9 in ponding zone, 3 ft media layer,plus 1 ft gravel to that of the storm sewer(Figure 7).For this case,us- and washed sand layer for the underdrains,the out- ing conventional drainage would not be an option.An let needs to be 4.75 ft or more below the surface. example of this approach applied at a site in Wilson, The drainage system needs tol connect to an existing NC,is displayed in Figure 8. drainage network. If there is little relief(elevation IWS also eases daylighting of underdrains be- change), a run of hundreds of feet may be needed to 8 Y,,,;,:' � �' Unable to oninect to � �� IWS Existing Storm Sewer Conventional Figure 7.Example showing how IWS can make retrofits for bioretention possible. Parking Lot r iv ,� ' North Cell 93.5 92,�a —91.75 90.;i 91 ` yz' 90=25 Parking Lot 44 . 1 °- i 94 South Cell 93.5 89 i 1, •-•,,,, ".,„j4'` ,e, .•40i.'..,, ' •••• z , m " Figure 9.Cross sections of Graham bioretention cells(all ,0 ', • units in feet), - outlet the drain. In order to keep the outlet pipe on a ` :_ 1 percent slope, an extra foot of elevation drop would• be required for each additional 100-ft section. The Figure 8.Example where an upturned elbow was installed advantage of having an IWS layer is the outlet of outside of a storm.sewer drop inlet box because the underd the drain pipe may only need to be 1.75 ft below the rains were below nvert elevation of the existing storm sewer. surface (instead of 4.75 ft). Thus, the trench to outlet this drain may be less than one-half as long, lowering trenching costs and cost of pipe. For this reason,IWS •, - , ., bioretention may be an easier alternative to use in retrofits, especially in eastern North Carolina with its �• ' • 1 flatter topography. For retrofits, it would be easier to tie under from 'm/s into existing Storni sewers, especially if the base of the storm sewer is above the � gravel layer(see Figure 7). DESIGN CONCERNSy Diminished performance in subsequent storms.Per- � . . A formance of these systems can be reduced when large rt volume consecutive events occur because the water - �._ storage layer does not have enough time to fully drain Figure 10.Graham bioretention outlets highlighted in between storms.An example of this was documented yellow circles(elevation=91.75 ft)and brick storm sewer for the bioretention cells in Greensboro,NC (Sharkey, structure in white rectangle(elevation=91 ft). 2006). There were two large rainfall events (0.89 in 9 and 1.00 in)that were four days apart in June 2004, and there were two large rainfall events(2.49 in and GENERALIZED GEOLOGIC MAP OF NORTH CAROLINA 1.20 in)that were ten days apart in July 2004.With the shorter antecedent dry period(June 2004),the 4 A y_ IWS layer did not have enough time to fully drain, so :' h - the total potential storage volume for the second event C. .,jko : � *" was reduced in the cell(G-1). Outflow was therefore jµ` , " I. E., generated for an event that would have been totally ;> ,„ , -. captured had the IWS layer been fully drawn down. a , With the longer antecedent dry period(July 2004),the „� '' IWS layer had time to fully drain, so the second event Triacsic Soils i .. 0 was completely assimilated by G-1 (no outflow). I• I'� `�ru�,ut, Plots of water levels in each outlet pipe are displayed M Chatham Group ,, in Figure 11. On an annual basis, consecutive events will cause hydrologic performance to be reduced for s" s''" bioretention cells with tight underlying soils. Figure 12.Geologic map of central NC t° o° highlighting Triassic soil groups(white 02 a outline).Image modified with permission S0 from N.C.GS,2009. o c of Anson, Chatham,Davie, Durham, q {, 0 6 a m Granville,Lee,Montgomery,Moore, 1 j° �� -.animal t °s « Orange,Richmond, Rockingham, '° Stokes,Union,Wake,and Yadkin 15,r,04 .I.,05 Juw06 Jun.0, Jas 06 Jun 02 Jon IC .1u.11 Jul 16 JO 18 J..4•20 Ju182 Ju1.24 Jul 26 JJ-28 Jul 30 I— Lw.S — Conventional —Rain I counties. Hydrologic soil group C soils are currently considered borderline Figure 11.Levels of flow at the outlet for the two cells in Greensboro with vary- sites for IWS use, as IWS may or may ing antecedent dry periods(June,shorter-left&July,longer-right).Zero not be preferable with these tighter represents the surface of the outlet. underlying soils.Not enough research Doesn't perform as well hydrologically with clay in has been completed to date to recom- situ soils in the piedmont.Hydrologic performance mend using IWS in hydrologic soil group C. Field is decreased with clay underlying soils because of monitoring has shown that hydrologic soil groups A limited water storage availability in the IWS layer. and B have a significant impact on runoff and pollut- Clay soils have a lower permeability, so drawdown ant load reduction. times are increased when underlying soils are clay,as illustrated in the previous section.Assuming an aver- Table 4.Relating drawdown time(emptying the age effective porosity of 30 percent for sand and 25 excess water content)to exfiltration rate for biore- percent for gravel and a fully drained internal water tention with IWS.' storage zone,drawdown times were calculated for a Soil Type Exfiltration Drawdown bioretention cell with 3 ft media, 8 in gravel layer, and Rate(in/hr) Time(days) an IWS zone thickness of 2 ft(Table 4).The calcula- tion is simplified by assuming a constant drawdown Loamy Sand 2.5 0.53 rate during the entire period. In actuality,drawdown Sandy Loam 1.0 1.3 times will vary due to exfiltration to the sides and the moisture conditions of the underlying soil. Loam 0.5 2.7 Use of internal water storage is not recommended Clay 0.2 6.7 in Triassic soil groups or other regions with hydrolog- ic soil group D because of the very low permeabili- compacted Clay 0.05 26.7 ties.A map of the Triassic soil groups is presented in 1 3 ft media,8 in gravel,and 2 ft IWS. Figure 12.Triassic soil groups are located in portions 10 Don't set the top of the IWS layer too close to the soil What impact does compaction have on IWS perfor- surface.If the outlet is at the top of the media, forcing mance?Construction activity could reduce the perme- longer-term saturated conditions at the surface, the ability of the bottom layer, so water will not drain as plants will struggle to survive. Moreover, pollutants fast from the internal water storage zone. If the bot- trapped in the surface of the media (metals and phos- tom layer has been impaired greatly from construction phorous)will dissolve in saturated conditions and exit (smeared or compacted), the water storage zone might the bioretention system in the outflow. It is important not be able to fully drain in between rain events. For to maintain some portion of the soil column as an construction guidance for bioretention, please consult aerobic system. This is why N.C. State recommends AG-588-1 7. that at least the top 12 inches of media be above the IWS layer outlet. FLOWCHART FOR IWS DESIGN A)Can an Internal Water Storage drainage configuration be used in bioretention design? 1)Is the site new,or does a bioretention cell already exist? New Existing 2) How far is the water table below the Address#3,then assess if an upturned elbow proposed bottom of the bioretention can be added to the existing under-drain out- cell(below underdrain layer)? let.This is most easily done if the underdrain outlets into a stormwater drop inlet structure (See Figures 5&6). >2ft <2ft 3)What is the Hydrologic Soil Bioretention cannot be used Group of the in situ soil? A or B C D Use IWS. No recommendation Use conventional drain- given at this time. age,never use IWS. 4)How will the underdrain be tied into the outlet? Outlet structure Trenched and daylighted 5) Is the outlet structure/de- IWS recommended to save on vice at or below the eleva- trenching and pipe cost. tion of the underdrains? Yes No Conventional can be used, Use IWS,incorporate upturned but IWS is recommended elbow before entering struc- (elbow inside structure). ture(See Figure 8). 11 FLOWCHART FOR IWS DESIGN B)What removal credit will be granted for these bioretention cells if IWS is properly used? 1)What is the pre-construction underlying soil infiltration rate? > 1 in/hr < 1 in/hr 2)What region of NC is the bioretention TN:35% site in? TP:45%. Piedmont or Coastal Plain Mountains or Sandhills 3)Other regulations to meet to be awarded increased removal credit. TN:40% TN:60% • Media depth greater than or equal to 3 ft. TP:45%. TP:60%. • IWS zone includes at least 1 ft of media. • Outlet of IWS is set at least 1 ft below surface of media(1 to 1.5 ft below the surface of the media would ideally be used for maximum hydrologic benefit). C)Steps to size the IWS layer to capture the bowl volume? 1)What is the bowl volume? > Bioretention surface area x average ponding depth. 2)What is the storage volume > Surface area of gravel layer x depth of gravel x 0.25. in the gravel layer? • 0.25=effective porosity estimate for gravel. • Note:bowl surface area might not equal media surface area if media was not placed below side slopes in bowl or if the pit was not dug with vertical walls. v 3) What does the depth in the > (Bowl volume—volume stored in gravel)-(surface IWS layer need to be to store area of media layer x 0.30). the entire bowl volume? • 0.30=effective porosity estimate for sandy media • Note:bowl surface area might not equal media surface area if media was not placed below side slopes in bowl or if the pit was not dug with vertical walls. v 4) Can this depth be achieved ). Is(Media depth—media depth from#3)> 1 ft? without exceeding the maximum allowable IWS Yes No layer depth? Proceed with Set IWS outlet 1 ft from suggested depth. the surface of the media. 12 SAMPLE CALCULATIONS A few sample calculations illustrating IWS layer design features are provided. Tying underdrains into outlets/water courses(Figure 13) Given: Bioretention description:3-ft media depth, 1-ft gravel and washed sand layer,and 1-ft ponding zone. Surrounding landscape description:land slope=20:1 (5 percent) Problem:If underdrain has a 1 percent slope, (a)What is the length of pipe required to outlet a conventionally drained bioretention cell? (b)What is the length required to outlet an IWS bioretention cell with the IWS layer 1 ft from the media surface? K•r. Note:Not P y to Scale ' t,,*.< t Land Slope=5i Temporary „ Storage 12 in. R' ”" IWS Pipe Length=48 ft: [Slope=gQfj Media=36 in. Internal water — Storage=24 in. • .' Convio conal Ptpe Length=120 ft. Gravel — € a.. ., . . Layer=12 in. . .. Figure 13.Description of site for Example#1 in"Sample Calculations:' (A)Conventional:Underdrain outlet depth= 1 ft+3 ft+ 1 ft=5 ft(assuming minimum elevation change) On a 20:1 slope,to get 5 ft elevation change,length=5 ft x 20= 100 ft With pipe on a 1 percent slope,an additional 1-ft of elevation change is required: Length= 100 ft+ 1 x 20= 120 ft Approximate length= 120 ft. (b)IWS:Underdrain outlet depth= 1 ft+ 1 ft=2 ft(minimum elevation change) On a 20:1 slope,to get 2 ft elevation change,length=2 ft x 20=40 ft With pipe on a 1 percent slope,an additional 0.4 ft of elevation change is required: Length=40 ft+0.4 x 20=48 ft; Approximate length=48 ft. With conventional drainage,the length to outlet the underdrain is 2.5 times longer than the length of pipe needed to outlet the IWS bioretention cell (120 ft versus 48 ft).By using IWS in relatively flat landscapes in eastern North Carolina, the length of the ditch is reduced,as is the depth of the ditch.This can mean a substantial savings in construction cost. 13 SAMPLE CALCULATIONS Storage depth for bioretention with IWS(Figure 14) The depth of water storage in the IWS layer can be estimated with Figure 14 for various depths of the IWS layer.In Figure 14,the first 8 inches assume an effective porosity of 25 percent for 6 in of#57 gravel and 2 in of choking stone. The rest of the IWS thickness assumes a 30 percent effective porosity for the 4 in layer of washed sand and sandy bioretention fill media.The water storage depth calculation assumes that the IWS was completely drained before an event occurs.IWS should never be closer to the surface than 12 in,so trapped pollutants in the media surface do not become soluble and exit with the effluent. 14 Figure 14.Calculation of water . 10 E • -- — —_+, ! stored in IWS layer based on depth g .._...... r...- .__.. of IWS layer(depth includes an -. _ 8 inch gravel layer).(Note:maintain I 12-inches of separation between sur- 4 ....._ ! face of media and top of IWS layer) z i 0 — 0 6 12 18 24 30 36 42 48 Average Depth/Thickness of IWS Layer(in) [includes 8 inch gravel layer] For example,a 36-in media depth bioretention cell has 6 in of#57 gravel,2 in of choking stone,and 4 in of washed sand,as recommended by the North Carolina bioretention design guidelines(N.C.DWQ,2007).In order to maximize the water storage depth,the top of the IWS layer will be 12 in below the surface of the media,so 24 in of media will be included in the IWS layer. Average depth/thickness of IWS layer=6 in+2 in+4 in+24 in=36 in Using Figure 74,this equates to 10.4 in of water storage. If the gravel depth does not equal 8 in or if the designer would prefer to use an equation instead of Figure 14, the following equation can be used to calculate internal water storage depth: Internal water storage depth=(depth of gravel x 0.25)+[(depth of sand+depth of media in IWS)x 0.30] (Note:IWS storage depth will correspond to average ponding depth in bowl only if media is placed below side slopes of bioretention cell and if the pit is excavated with vertical sidewalls) Calculation of internal water storage depth using the equation above, Water storage depth=[(6 in+2 in)x 0.25]+[(4 in+24 in)x 0.30]=2 in+8.4 in= 10.4 in Summary of complementary IWS Calculation Spreadsheet On the NC State University Stormwater Team Web site is a link for downloads(http://www.bae.ncsu.edu/stormwater/ downloads.htm).The model and a document containing an example and model explanations are available on this site.The model allows the user to size a bioretention cell based on two land uses.Then the user can specify the design characteristics of the IWS layer,antecedent moisture conditions,surface infiltration rate,and surrounding soil exfiltra- tion rate.Finally,the user can manually enter hourly rainfall data or enter a depth and use one of the SCS Type II or Type III storms to predict the percentage of runoff that results in overflow,drainage,and exfiltration(no flow). 14 REFERENCES Kim,H.,E.A. Seagren,and A.P.Davis. (2003).Engineered Brown,R.A.,and W.F. Hunt(2009).Effects of media bioretention for removal of nitrate from stormwater run- depth on bioretention performance in the upper coastal off. Water Environment Research, 75(4): 355-367. plain of North Carolina and bioretention construction Li,H.,L.J. Sharkey,W.F.Hunt,and A.P.Davis. (2009). impacts study. In Proceedings, 2009 World Environmen- Mitigation of impervious surface hydrology using tal and Water Resources Congress.Kansas City,MO.: bioretention in North Carolina and Maryland.Journal of EWRI and ASCE. Hydrologic Engineering 14(4): 407-415. Clark, S.E.,and R. Pitt. (2007).Influencing factors and McWorter,D.B.,and D.K. Sunada. (1977)Groundwater a proposed evaluation methodology for predicting Hydrology and Hydraulics. Fort Collins, Colo.:Water groundwater contamination potential from stormwater Resources Publications. infiltration activities. Water Environment Research, 79(1):29-36. North Carolina Division of Water Quality(N.C.DWQ). (2007a). Chapter 12: Bioretention.In Stormwater Best Davis,A.P.,W.F.Hunt,R.G.Traver, and M.E. Clar. Management Practices Manual,pp.12-1-31.Raleigh: (2009).Bioretention technology:An overview of cur- N.C.Department of Environment and Natural Resourc- rent practice and future needs.Journal of Environmental es,Division of Water Quality. Engineering 135(3): 109-117. North Carolina Division of Water Quality(N.C.DWQ). Davis,A.P. (2008).Field performance of bioretention: (2007b).Chapter 18:Permeable pavement.In Stormwa- Hydrology impacts.Journal of Hydrologic Engineering, ter Best Management Practices Manual,pp. 18-1-11. 13(2): 90-95. Raleigh:N.C.Department of Environment and Natural Davis,A.P. (2007).Field performance of bioretention: Resources,Division of Water Quality. Water quality.Environmental Engineering Science, North Carolina Geological Survey(N.C.GS). (2009). Geo- 24(8): 1048-1064. logical Survey-Geology of North Carolina: Geology Davis,A.P.,M. Shokouhian,H. Sharma,and C.Minami. maps.Raleigh:N.C.Department of Environment and (2006).Water quality improvement through bioretention Natural Resources,N.C. Geological Survey,Division of media:nitrogen and phosphorus removal. Water Envi- Land Resources.Available at:http://gis.enr.state.nc.us/ ronment Research,78(3): 284-293. sid/bin/index.plx?client=zGeologic_Maps&site=9AM. Accessed on 17 July 2009. Davis,A.P.,M. Shokouhian,H. Sharma,and C. Minami. (2001). Laboratory study of biological retention for Passeport E.,W.F.Hunt,D.E.Line.,R.A. Smith,and R.A. urban stormwater management. Water Environment Brown. (2009).Field study of the ability of two grassed Research,73(1): 5-14. bioretention cells to reduce storm-water runoff pollu- tion.Journal of Irrigation and Drainage Engineering, Dietz,M. E.,and J.C. Clausen.(2006). Saturation to im- 135(4): 505-510. prove pollutant retention in a rain garden.Environmen- tal Science and Technology,40(4): 1335-1340. Pitt,R., S. Chen,and S. Clark. (2002).Compacted urban soils effects on infiltration and bioretention stormwater Hunt,W.F.,A.R.Jarrett,J.T. Smith,and L.J. Sharkey. control designs. In Proceedings,Ninth International (2006).Evaluating bioretention hydrology and nutrient Conference on Urban Drainage. Portland,Oreg.: IAHR, removal at three field sites in North Carolina.Journal of IWA,EWRI,and ASCE. Irrigation and Drainage Engineering, 132(6): 600-608. Pitt,R., S.Clark,and R.Field. (1999).Groundwater Hunt,W.F.,J.T. Smith, S.J.Jadlocki,J.M.Hathaway,and contamination potential from stormwater infiltration P.R. Eubanks. (2008).Pollutant removal and peak flow practices. Urban Water, 1:217-236. mitigation by a bioretention cell in urban Charlotte,NC. Journal of Environmental Engineering, 134(5):403- Sharkey,L.J. (2006).The performance of bioretention 408. areas in North Carolina:A field study of water qual- ity,water quantity,and soil media. M.S.Thesis,North Jones,M.P.,and W.F.Hunt,. (2009).Bioretention impact Carolina State University,Raleigh,N.C. on runoff temperature in trout sensitive waters.Journal of Environmental Engineering, 135(8): 577-585. Shuster,W.D.,R. Gehring,and J. Gerken,. (2007).Pros- pects for enhanced groundwater recharge via infiltration of urban storm water runoff:A case study.Journal of Soil and Water Conservation, 62(3): 129-137. 15 NC STATE UNIVERSITY RESOURCES RELATED WEB SITES Fact sheets in the Urban Waterways Series,North N.C. State University—BAE Bioretention Research Web Carolina Cooperative Extension,N.C. State University, site:http://www.bae.ncsu.edu/topic/bioretention/ Raleigh: N.C. State University—BAE Bioretention Research Sum- Brown,R.A.,and W.F.Hunt. (2009).Improving Exfiltra- mary Web site:http://www.bae.ncsu.edu/topic/bioreten- tion from BMPs:Research and Recommendations(AG- tion/research-Lit_Review.html 588-17). N.C. State University—BAE Stormwater Team Web site: Hunt,W.F.,and W.G.Lord.(2006).Bioretention Perfor- http://www.bae.ncsu.edu/stormwater/ mance,Design, Construction, and Maintenance(AG- 588-5).Online:http://www.bae.ncsu.edu/stormwater/ PublicationFiles/Bioretention2006.pdf Hunt,W.F.,and N.M.White.(2001).Designing Rain Gar- dens(Bio-retention Areas)(AG-588-3). Online:http:// www.bae.ncsu.edu/stormwater/PublicationFiles/Design- ingRainGardens2001.pdf Jones,M.P.,and W.F.Hunt. (2007).Stormwater BMPs for Trout Waters: Coldwater Stream Design Guidance for Stormwater Wetlands, Wet Ponds, and Bioretention (AG-588-10).Online:http://www.bae.ncsu.edu/storm- water/PublicationFilesBMPsColdTemps2007.pdf Prepared p by Robert A.Brown,E.I William F.Hunt, P.E.,Ph.D. Shawn G. Kennedy Department of Biological and Agricultural Engineering Published by NORTH CAROLINA COOPERATIVE EXTENSION AGRICULTURE LIFE SCIENCES ACADEMICS • RESEARCH . EXTENSION Distributed in furtherance of the acts of Congress of May 8 and June 30,1914.North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race,color,creed,national origin,religion,sex,age,veteran status or disability.In addition,the two Universities welcome all persons without regard to sexual orientation.North Carolina State University,North Carolina A&T State University,U.S.Department of Agriculture,and local governments cooperating. E10 51868 AG-588-19W 11/09—VB/KEL