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Home My WebLink AboutWPO201400044 Calculations 2014-05-12 STORMWATER MANAGEMENT AND BEST MANAGEMENT PRACTICES AT&T SITE NUMBER CV404A ALBEMARLE COUNTY, VIRGINIA April 28, 2014 Prepared for: a r c h i t e c t s C e n g i n e e r s BC Architects Christopher D. Morin, PE 5661 Columbia Pike, Suite 200 Falls Church, VA 22041 Tel: 703-671-6000 Prepared by: Painter-Lewis, P.L.C. Consulting Engineers 817 Cedar Creek Grade, Suite 120 U.—FA-- Winchester, VA 22601 Tel: 540-662-5792 Fax: 540-662-5793 Email:office cr painterlewis.com "7p�l'r may;" Li-ZA- % gJOHN LENS Mi, �rQAiA�C.. ��. 4 ,a ALBEMARLE COUNTY CV404A SWM/BMP Table of Contents SITE AND PROJECT DESCRIPTION Page 3 SITE SOILS Page 3 FLOOD PLAIN INFORMATION Page 3 STORMWATER MANAGEMENT Page 3 CONSTRUCTION ENTRANCE SEDIMENT TRAP Page 4 WATER QUALITY Page 4 EXHIBITS Page 5 page 2 ALBEMARLE COUNTY CV404A SWM/BMP SITE AND PROJECT DESCRIPTION The proposed development for this site includes the construction of a 30 foot by 30 foot cell tower pad site and a 45' gravel access drive to the pad site for a 119' mono- pole. The site is located on a 15.38 acre parcel under the ownership of Jay Y. & Shirley B. Gillenwater. The parcel is mostly wooded with a 0.90 acre pond. A portion of the parcel is designated by the county as "Water Protection Ordinance Buffer". Ac- cess to the site will come from Dry Bridge Road. The site of the access road and tower pad slopes from south to north. The site is within an area that the county desig- nates as "Managed Steep Slopes". Refer to Exhibit 1. Drainage from the site flows by sheet flow down a slope to the pond. The pond discharges to an unnamed tributary of Mechums River which is a tributary of the South Fork Rivanna River and as such the site lays within the Water Supply Protection Area. The limits of disturbance required for this construction consist of an area of approxi- mately 2,446 sf (0.05 acres) with 1,600 sf (0.038 acres) of proposed gravel surfaces. Effort will be made to conduct the construction using low impact methods, including limiting the amount of disturbed area, preserving existing trees, and locating the ac- cess road to disrupt the existing runoff character of the site as little as practicable, that is, to maintain the existing runoff flow patterns. SITE SOILS The predominant soil types within the work site and adjacent watershed are: o 4E, Ashe loam, 25 to 45 percent slopes o 36C, Hayesville loam, 7 to 15 percent slopes o 36D, Hayesville loam, 15 to 25 percent slopes These soils are in Hydrologic Soils Group B in accordance with the USDA soil textural classification. The soils map and information is contained in Exhibit 2. FLOOD PLAIN INFORMATION The FEMA Flood Insurance Rate Map #51003CO245D shows that the site is located in Flood Zone X. A facsimile of the FIRM is contained in Exhibit 3. STORMWATER MANAGEMENT The tower site is located adjacent to Dry Bridge Road at the top of a local high point. Approximately 0.05 acres of land will be disturbed during the construction of the tower and approximately 0.04 acres of gravel and/or impervious areas will be created. In- creases in the 2 year-, and 10 year-, 24 hour precipitation events runoff will be slight. As such, no storm water detention is proposed. Exhibit 4 contains a pre-development drainage area map. Exhibit 5 contains a post development drainage area map. The contributing drainage areas and times of concentration are identical in the pre- and post development conditions. There is a slight increase in the impervious area in the post development condition. The peak discharge rates for the pre -and post develop- ment conditions were calculated by the SCS 10 year-24 hour storm method. Rainfall depths for the 2 year (3.68"), 10 year (5.56"), and 100 year (9.1") storms were taken from the NOAA Atlas 14, Volume 2, Version 3 for Charlottesville, VA. Exhibit 6 con- page 3 ALBEMARLE COUNTY CV404A SWM/BMP pre-development conditions. Exhibit 7 contains the results of the SCS Unit Hydro- graph Model and peak discharge rates for the post development conditions. The re- sults are summarized in the following table. PRE- POST STORM EVENT DEVELOPMENT DEVELOPMENT PEAK PEAK DISCHARGE DISCHARGE 2 YR 0.6 cfs 0.7 cfs 10 YR 2.46 cfs 2.66 cfs CONSTRUCTION ENTRANCE SEDIMENT TRAP In accordance with Albemarle requirements, a sediment trap at the Construction En- trance is part of the Erosion and Sediment Control Plan. A small sediment trap will be installed on the east side of the entrance. The contributing drainage area to the trap is about 1,800 square feet. The trap location is shown on Exhibit 8 and a detail of the sediment trap is shown on Exhibit 9. WATER QUALITY In accordance with the Virginia Department of Environmental Quality, Performance- Based Water Quality Computations, there is no requirement for water quality devices for this site. Please refer to the worksheet contained in Exhibit 10. page 4 ALBEMARLE COUNTY CV404A SWM/BMP EXHIBITS: EXHIBIT 1 COUNTY WPO AND SLOPES MAP EXHIBIT 2 SOILS INFORMATION EXHIBIT 3 FEMA FIRMETTE EXHIBIT 4 PRE-DEVELOPMENT DRAINAGE AREA MAP EXHIBIT 5 POST DEVELOPMENT DRAINAGE AREA MAP EXHIBIT 6 PRE-DEVELOPMENT PEAK FLOW DATA EXHIBIT 7 POST DEVELOPMENT PEAK FLOW DATA EXHIBIT 8 CONSTRUCTION ENTRANCE SEDIMENT TRAP PLAN VIEW EXHIBIT 9 CONSTRUCTION ENTRANCE SEDIMENT TRAP EXHIBIT 10 PERFORMANCE-BASED WATER QUALITY COMPUTATIONS page 5 ALBEMARLE COUNTY CV404A SWM/BMP EXHIBIT 1 COUNTY WPO AND SLOPES MAP page 6 1 *..i•i ii_...rillri I II a a ri Z'1•. E tkel& , g .1141% ' •• g 1— II 1 I I 3 3 3 i (f C t 1 i'i tli 2 lir .i %oh _i.j13))1 lidhin I i4I ill I i > 4 ,_ : 7 7 czIT 79, - EL '•", GOSS a ,.. ,;1 Et l' •• t•••- r—r''.., • \ '90-,,----/E,L, \ Int \ 6' / ." .--, 'cle,6■,3 ‘ .., i i I ii , N ."--- . 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Custom Soil Resource Report Map Unit Legend Albemarle County,Virginia(VA003) Map Unit Symbol I Map Unit Name Acres in AOI ( Percent of AOI 4C Ashe loam,7 to 15 percent 8.8 1.5% slopes 4D Ashe loam,15 to 25 percent 49.5 8.5% slopes 4E Ashe loam,25 to 45 percent 55.9 9.5% slopes 7B Braddock loam,2 to 7 percent 18.8 3.2% slopes 146 Chester loam,2 to 7 percent 0.7 0.1% slopes 14C Chester loam,7 to 15 percent 9.0 1.5% slopes 14D Chester loam, 15 to 25 percent 59.5 10.2% slopes 34B Glenelg loam,2 to 7 percent 4.5 0.8% slopes 36B Hayesville loam,2 to 7 percent 88.6 15.1% slopes Hayesville loam,7 to 15 percent 68.5 11.7% slopes Hayesville loam,15 to 25 57.5 9.8% percent slopes 3783 Hayesville clay loam,2 to 7 3.6 0.6% percent slopes,severely eroded 37C3 Hayesville clay loam,7 to 15 65.7 11.2% percent slopes,severely eroded 37D3 Hayesville clay loam,15 to 25 50.5 8.6% percent slopes,severely eroded 56B Meadowville loam,2 to 7 percent 6.8 1.2% slopes 56C Meadowville loam,7 to 15 33.4 5.7% percent slopes 77 Riverview-Chewacla complex 3.6 0.6% W Water 0.6 0.1% Totals for Area of Interest 585.5 100.0% Map Unit Description:Ashe loam,25 to 45 percent slopes—Albemarle County.Virginia Albemarle County, Virginia 4E—Ashe loam, 25 to 45 percent slopes Map Unit Setting Mean annual precipitation:25 to 65 inches Mean annual air temperature: 54 to 59 degrees F Frost-free period: 195 to 231 days Map Unit Composition Ashe and similar soils:75 percent Description of Ashe Setting Landform:Mountain slopes Landform position (two-dimensional):Summit Landform position (three-dimensional): Interfluve Down-slope shape: Convex Across-slope shape: Convex Parent material:Residuum weathered from granite and gneiss Properties and qualities Slope:25 to 45 percent Depth to restrictive feature:20 to 40 inches to lithic bedrock Drainage class:Somewhat excessively drained Capacity of the most limiting layer to transmit water(Ksat):Very low to high(0.00 to 5.95 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Low(about 3.2 inches) Interpretive groups Farmland classification:Not prime farmland Land capability(nonirrigated):7e Hydrologic Soil Group: B Typical profile 0 to 10 inches:Loam 10 to 19 inches: Loam 19 to 24 inches: Sandy loam 24 to 79 inches:Bedrock Data Source Information Soil Survey Area: Albemarle County,Virginia Survey Area Data: Version 10, Dec 11,2013 USDA Natural Resources Web Soil Survey 4/29/2014 Conservation Service National Cooperative Soil Survey Page 1 of 1 Custom Soil Resource Report Interpretive groups Farmland classification:All areas are prime farmland Land capability(nonirrigated):2e Hydrologic Soil Group:B Typical profile 0 to 7 inches:Loam 7 to 58 inches:Clay 58 to 67 inches:Sandy clay loam 67 to 83 inches:Fine sandy loam 36C—Hayesville loam, 7 to 15 percent slopes Map Unit Setting Mean annual precipitation:25 to 65 inches Mean annual air temperature:54 to 59 degrees F Frost-free period: 195 to 231 days Map Unit Composition Hayesville and similar soils:80 percent Description of Hayesville Setting Landform:Hillslopes Landform position(two-dimensional):Summit Landform position(three-dimensional):Intertiuve Down-slope shape:Convex Across-slope shape:Convex Parent material:Residuum weathered from granite and gneiss Properties and qualities Slope:7 to 15 percent Depth to restrictive feature:More than 80 inches Drainage class:Well drained Capacity of the most limiting layer to transmit water(Ksat):Moderately high to high (0.57 to 1.98 in/hr) Depth to water table:More than 80 inches Frequency of flooding:None Frequency of ponding:None Available water capacity:High (about 10.6 inches) Interpretive groups Farmland classification: Farmland of statewide importance Land capability(nonimgated):4e Hydrologic Soil Group:B Typical profile 0 to 7 inches:Loam 7 to 58 inches:Clay 58 to 67 inches:Sandy clay loam 67 to 83 inches:Fine sandy loam Custom Soil Resource Report 36D—Hayesville loam, 15 to 25 percent slopes Map Unit Setting Mean annual precipitation:25 to 65 inches Mean annual air temperature:54 to 59 degrees F Frost-free period: 195 to 231 days Map Unit Composition Hayesville and similar soils:80 percent Description of Hayesville Setting Landform:Hillslopes Landfonn position (two-dimensional):Summit Landform position (three-dimensional):Interfluve Down-slope shape:Convex Across-slope shape:Convex Parent material:Residuum weathered from granite and gneiss Properties and qualities Slope: 15 to 25 percent Depth to restrictive feature:More than 80 inches Drainage class:Well drained Capacity of the most limiting layer to transmit water(Ksat):Moderately high to high (0.57 to 1.98 in/hr) Depth to water table:More than 80 inches Frequency of flooding: None Frequency of ponding:None Available water capacity:High(about 10.6 inches) Interpretive groups Farmland classification: Farmland of statewide importance Land capability(nonirrigated):6e Hydrologic Soil Group:B Typical profile 0 to 7 inches:Loam 7 to 58 inches:Clay 58 to 67 inches:Sandy clay loam 67 to 83 inches:Fine sandy loam 37B3—Hayesville clay loam, 2 to 7 percent slopes, severely eroded Map Unit Setting Mean annual precipitation:25 to 65 inches Mean annual air temperature:54 to 59 degrees F ALBEMARLE COUNTY CV404A SWM/BMP EXHIBIT 3 FEMA FIRMETTE E•E • e Y Ind W V C� TI 2` � ▪ � O W : a ea goi R3 ! 1 i if al gi i IN5; ii 4. - a o`EW I E�ifl . vi , a 8 rs li. n1 z- •5. , 16 tp. 0 Xp x,6gas . < % �C" •') a� $4E:2 og n" �E Mil v Q 11111YW 0,9 Pp iiii-i 4iiS6 o il : NI G N W '19, =D y" °� x S W o z N 9 s • i; >.6 1G 4100''' co g u 15 1 _ 03 ... vZ A 3 g o ti.d S Slg VD x11 page 8 ALBEMARLE COUNTY CV404A SWM/BMP EXHIBIT 4 PRE-DEVELOPMENT DRAINAGE AREA MAP page 9 ,,„$ „,` r _ t ■, ,+ �y5.' 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's 1 .40. f. _Wit'_ �r,M'► /P ,fit y� t1+y ,4I ,p,�z.+J ,,rr — ti,',. ,: < /}d' t f' c I _A C'It 4_� ° M : r` ,el - t 1 „e' _-''-----_1 4r ill ,1 ray 4 - if- t�4 � � a'+ r'+, -_ •""`,".—_-"` '�`'�'�'J�(� �P' T� a�"'` ' 1 Il '1,,,,,,,,..:',,,-I� ,,,,,,,,,,,........_-2..„'. ��- i,a,'--_ 'f „. ,_ y ` *'`-' Jrr ! t!', / 0Pt rat° tr -----% 1 * v.- i f opt(' ..-))..,. ed) r-------, ,.. \ .,::\z,,,,-\;,\_:',.-_.+1--_ ,..,_- . - - A E .---- ...----...- ---z.:;;;:"-.:----„;;;Yir-7 :-:;q::;,--- -- - // ! (ii/0,:if.,:-„,:,/,..----- "';'17,,,\,,,,,,,,.:,:.:,...;, ......„,;.--1.- -- — — SITE LOCATION 200 0 200 PROJECT: SURVEY: C,1,: POST DEVELOPMENT NCO 2' ��w�� DRAINAGE AREA MAP Ste: DATE: SITE NUMBER CV404A SHOWN 4/25/14 Scale in Feet SHEET: ALBEMARLE COUNTY, VIRGINIA POST ALBEMARLE COUNTY CV404A SWM/BMP EXHIBIT 6 PRE-DEVELOPMENT PEAK FLOW DATA page 11 Type. . . . Master Network Summary Page 1.01 Name. . . . Watershed File. . . . C:\John Lewis\CV404A Albemarle County\PEAK RUNOFF RATES DA1 .yREDEV.PPW. MASTER DESIGN STORM SUMMARY Network Storm Collection: Charlottsville V Total Depth Rainfall Return Event in Type RNF ID 2 3.6800 Synthetic Curve Typell 24hr 10 5.5600 Synthetic Curve TypeII 24hr 100 9.1000 Synthetic Curve TypelI 24hr MASTER NETWORK SUMMARY SCS Unit Hydrograph Method (*Node=Outfall; +Node=Diversion;) (Trun= HYG Truncation: Blank=None; L=Left; R=Rt; LR=Left&Rt) Max Return HYG Vol Qpeak Qpeak Max WSEL Pond Storage Node ID Type Event ac-ft Trun hrs cfs ft ac-ft DA 1 PRE DEV AREA 2 .065 12.1000 .60 DA 1 PRE DEV AREA 10 .197 12.1000 2.49 DA 1 PRE DEV AREA 100 .540 12.0500 7.56 *OUT 10 OCT 2 .065 12.1000 .60 OUT 10 JCT 10 .197 12.1000 2.49 OUT 10 JCT 100 .540 12.0500 7.58 S/N: 021701607007 Painter-Lewis PondPack Ver. 09.00.077.00 Time: 11:56 AM Date: 4/29/2014 Type. . . . Tc Calcs Page 2.01 Name. . . . DA 1 PRE DEV File. . . . C:\John Lewis\CV404A Albemarle County\PEAK RUNOFF RATES DA1 PREDEV.PPW TIME OF CONCENTRATION CALCULATOR Segment #1: Tc: TR-55 Sheet Mannings n .4000 Hydraulic Length 300.00 ft 2yr, 24hr P 3.6800 in Slope .350000 ft/ft Avg.Velocity .33 ft/sec Segment #1 Time: .2558 hrs Segment #2: Tc: TR-55 Shallow Hydraulic Length 200.00 ft Slope .360000 ft/ft Unpaved Avg.Velocity 9.68 ft/sec Segment #2 Time: .0057 hrs Total Tc: .2615 hrs S/N: 021701607007 Painter-Lewis PondPack Ver. 09.00.077.00 Time: 11:56 AM Date: 4/29/2014 Type. . . . Tc Calcs Page 2.02 [Jame. . . . DA 1 PRE DEV File. . . . C:\John Lewis\CV404A Albemarle County\PEAK RUNOFF RATES DAI PREDEV.PPW Tc Equations used. . . - SCS TR-55 Sheet Flow Tc = (.007 * ( (n * Lf)**0.8) ) / ( (P**.5) * (Sf**.4) ) Where: Tc = Time of concentration, hrs n = Mannings n Lf = Flow length, ft P = 2yr, 24hr Rain depth, inches Sf = Slope, - SCS TR-55 Shallow Concentrated Flow Unpaved surface: V = 16.1345 * (Sf**0.5) Paved surface: V = 20.3282 * (Sf**0.5) Tc = / V) / (3600sec/hr) Where: V = Velocity, ft/sec Sf = Slope, ft/ft Tc = Time of concentration, hrs Lf = Flow length, ft S/N: 021701607007 Painter-Lewis PondPack Ver. 09.00.077.00 Time: 11:56 AM Date: 4/29/2014 Type. . . . Runoff CN-Area Page 3.01 Name. . . . DA 1 PRE DEV File. . . . C:\John Lewis\CV404A Albemarle County\PEAK RUNOFF RATES DA1 PREDEV.PPN RUNOFF CURVE NUMBER DATA Impervious Area Adjustment Adjusted Soil/Surface Description CM acres =C 3UC CN Woods - good 55 1.730 55.00 Impervious Areas - Paved parking lo 96 .030 98.00 COMPOSITE AREA & WEIGHTED CN ---> 1.760 55.73 (56) S/N: 021701607007 Painter-Lewis PondPack Ver. 09.00.077.00 Time: 11:56 AM Date: 4/29/2014 ALBEMARLE COUNTY CV404A SWM/BMP EXHIBIT 7 POST DEVELOPMENT PEAK FLOW DATA page 12 Type. . . . Master Network Summary Page 1.01 Name. . . . Watershed File. . . . C:\John Lewis\CV404A Albemarle County\PEAK RUNOFF RATES DA1 POSTDEV.PPW MASTER DESIGN STORM SUMMARY Network Storm Collection: Charlottsvrlle V Total Depth Rainfall Return Event in Type RNF ID 2 3.6900 Synthetic Curve TypeII 24hr 10 5.5600 Synthetic Curve TypeII 24hr 100 9.1000 Synthetic Curve TypeII 24hr MASTER NETWORK SUMMARY SCS Unit Hydrograph Method (*Node=Outfall; +Node=Diversion;) (Trun= HYG Truncation: Blank=Nor.e; L=Left; R=Rt; LR=Left&Rt) Max Return HYG Vol Qpeak Qpeak Max WSEL Pond Storage Node ID Type Event ac-ft Trun hrs cfs ft ac-ft DP. 1 POST DEV AREA .071 12.1000 .70 DA 1 POST DEV AREA 10 .208 12.0500 2.66 DA 1 POST DEV AREA 100 .559 12.0500 7.86 *OUT 10 JCT 2 .071 12.1000 .70 OUT 10 JCT 10 .208 12.0500 2.66 OUT 10 JCT 100 .559 12.0500 7.86 SIN: 021701607007 Painter-Lewis PondPack Ver. 09.00.077.00 Time: 12:00 PM Date: 4/29/2014 Type. . . . Tc Calcs Pape 2.01 Name. . . . DA 1 POST DEV File. . . . C:\John Lewis\CV404A Albemarle County\PEAK RUNOFF RATES DA1 POSTDEV.PPW TIME OF CONCENTRATION CALCULATOR Segment #1: Tc: TR-55 Sheet Mannings n .4000 Hydraulic Length 300.00 ft 2yr, 24hr P 3.6800 in Slope .350000 ft/ft Avg.Velocity .33 ft/sec Segment #1 Time: .2558 hrs Segment #2: Tc: TR.-55 Shallow Hydraulic Length 200.00 ft Slope .360000 ft/ft Unpaved Avg.Velocity 9.68 ft/sec Segment #2 Time: .0057 hrs Total Tc: .2615 hrs S/N: 021701607007 Painter-Lewis PondPack Ver. 09.00.077.00 Time: 12:00 PM Date: 4/29/2014 Type. . . . Tc Calcs Page 2.02 Name. . . . DA 1 POST DEV File. . . . C:\John. Lewis\CV404A Albemarle Ccunty\PEAK RUNOFF RATES DA1 POSTDEV.PPW Tc Equations used. . . ___= SCS TR-55 Sheet Flow Tc = (.007 * ( (n * Lf)**0.8) ) / ( (P**.5) * (Sf**.4) ) Where: Tc = Time of concentration, hrs n = Mannings n Lf = Flow length, ft P = 2yr, 24hr Rain depth, inches Sf = Slope, ___= SCS TR-55 Shallow Concentrated Flow Unpaved surface: V = 16.1345 * (Sf**0.5) Paved surface: V = 20.3282 * (Sf**0.5) Tc = (Lf / V) / (3600sec/hr) Where: V = Velocity, ft/sec Sf = Slope, ft/ft Tc = Time of concentration, hrs Lf = Flow length, ft S/N: 021701607007 Painter-Lewis PondPack Ver. 09.00.077.00 Time: 12:00 PM Date: 4/29/2014 Type. . . . Runoff CN-Area Page 3.01 Name. . . . DA 1 POST DEV File. . . . C:\John Lewis\CV404A Albemarle County\PEAK RUNOFF RATES DA1 POSTDEV.PPW RUNOFF CURVE NUMBER DATA Impervious Area Adjustment Adjusted Soil/Surface Description CM acres C 130 CM Woods - good 55 1.680 55.00 Impervious Areas - Gravel (w/ right 85 .040 85.00 Impervious Areas - Paved parking lo 98 .040 98.00 COMPOSITE AREA & WEIGHTED ON ---> 1.760 56.66 (57) S/N: 021701607007 Painter-Lewis PondPack Ver. 09.00.077.00 Time: 12:00 PM Date: 4/29/2014 ALBEMARLE COUNTY CV404A SWM/BMP EXHIBIT 8 CONSTRUCTION ENTRANCE SEDIMENT TRAP PLAN VIEW page 13 --- - _____ - IM�NT T P - j7 r 00 `" 4 S-E-D- - -- DRAINAGE-AR -TP-TRAP ..\ ' _ I , ' r - - ;- -_- ---'A� ' ' ■ -- ii --- , >: J .� (918.9 ,- 110 - - E"P � (918.8) G ,� ,� J ' . i is N AL%: or EDGE /!- (918.7 ' ROAD SPNALT t �jEE f A '� Rt�� W,p8 EpGE p / Dr' BTATE4 p. R� , / 1 30 0 30 PROJECT: SURVEY: C.I.: • • CONSTRUCTION ENTRANCE SEDIMENT NA NA ' • _ • TRAP PLAN VIEW SCALE: DATE: Scale in Feet SITE NUMBER CV404A SHOWN 4/25/14 SHEET: ALBEMARLE COUNTY, VIRGINIA CES ALBEMARLE COUNTY CV404A SWM/BMP EXHIBIT 9 CONSTRUCTION ENTRANCE SEDIMENT TRAP page 14 6" 1' I ORIGINAL GROUND ELEV—\ DIRECTION OF FLOW . 67 CU. YD. /1 ACRE TOTAL CONTRIBUTING AREA=0.04 ACRES PROVIDE 2.7 CUBIC YDS. OF DRY STORAGE DIRECTION OF FLOW c' - - DIRECTION OF FLOW 67 CU. YD. /1 ACRE ORIGINAL GROUND (EXCAVATED) ZILTER CLOTH ELEVATION PROVIDE 2.7 CUBIC YDS. OF WET STORAGE COARSE AGGREGATE" CLASS AI RIP–RAP •• COARSE AGGREGATE SHALL BE VDOT #3, #357, OR #5 TEMPORARY SEDIMENT TRAP/ ROCK DAM DETAIL LENGTH (IN FT.)=3 —6 X DRAINAGE ARE• (IN AC.) CLASS Al RIP–RAP DIVERSION DIKE -41111111111111191 . FILTER CLOT EXCAVATED AREA COARSE AGGREGATE / OUTLET (PERSPECTIVE VIEW) SEDIMENT TRAP CALCULATIONS TRAP ID TOTAL TOTAL DRAINAGE STORAGE AREA VOLUME REQ'D. Const. Ent.0.04 acres 44 c. (1144 c.f.f. ) WET STORAGE WET WET DRY STORAGE DRY DRY TOP OF WIDTH AVERAGE DEPTH STORAGE AREA STORAGE VOLUME AVERAGE DEPTH STORAGE AREA STORAGE VOLUME EMBANKMENT OF WIDTH OUTLET 1.5 ft. 60 s.f. 80 c.f, 1.0 ft. 75 s.f. 75 c.f. 18" 3 ft. PROJECT: SURVEY: G.I.: CONSTRUCTION ENTRANCE SEDIMENT NA NA TRAP SCALE: DATE: SITE NUMBER CV404A SHOWN 4/25/14 ALBEMARLE COUNTY, VIRGINIA SHEET: CES ALBEMARLE COUNTY CV404A SWM/BMP EXHIBIT 10 PERFORMANCE-BASED WATER QUALITY COMPUTATIONS PERFORMANCE-BASED WATER QUALITY COUNTY/CITY:Albemarle County COMPUTATIONS DESCRIPTION:CV404A Worksheet 1- STEP 1- Determine the applicable area(A)and the post-developed impervious cover(I Applicable area(A)= 15.38 acres (Total property area) Post-development impervious cover: Structures= 0.06 acres Parking Lot= 0.00 acres Roadways= 0.50 acres other: Walkways= 0.00 acres Total Impervious Cover= 0.56 acres Ipost=(total post-developmet impervious cover/A)x 100= STEP 2-Determine the average land cover condition(Iwatershed)or the existing impervious cover(Iexisting) Average land cover condition(Iwatershed): If the locality has determined land cover conditions for individual watersheds within its jurisdiction use the watershed specific value determined by the locality as'wate,shed• Otherwise,use the Chesapeake Bay default value: ',,,rased= 16 % Existing impervious cover(Iexisting): Determine the existing impervious cover of the development site if present. STEP 3-Determine the appropriate development situation The site information determined in Step 1 and Step 2 provide enough information to determine the appropriate development situation under which the performance criteria will apply. X Situation 1: I < 'watershed 3.6 < 16 Situation 2: I > 'watershed 3.6 > 16 Situation 3: Ie=s ne > 'watershed 0.0 > 16 Situation 4: Iexishnd is served by an existing BMP. If the proposed development meets the criteria for the development Situation 1,than the low density development is considered to be the BMP and no pollutant removal is required. The calculation procedure for Situation 1 stops here. page 15