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Home My WebLink AboutSUB202000098 Calculations 2020-05-14SHIMP ENGINEERING, P.C. Design Focused Engineering May 14, 2020 Engineering Review Albemarle County Department of Community Development 401 McIntire Road Charlottesville, VA 22902 Regarding: WPO 2020xxxxx Galaxie Farm Subdivision — Road Plan SWM Calculation Packet Dear Reviewer, Enclosed is the stormwater calculation packet for the Galaxie Farm Subdivision Road Plan. The project is a private redevelopment of a site to create a subdivision served by public roads. The main purpose of stormwater design for this site is to route offsite runoff safely through the site into the perennial stream, Cow Branch, which flows through the site. The culverts which lie under Road A, which serves as the only subdivision entrance, were designed for the 25-yr storm. To size the culverts, the VDOT Inlet Control Headwater Depth nomograph was used. The flows used in this nomographs resulted from the Southern Peidmont Rural Regression Equation, which is a VDOT- accepted runoff calculation for road design. If you have any questions about this calculation packet please do not hesitate to contact me at: keane(cr�,shimp-en ing eering com or by phone at 434-299-9843. Regards, Keane Rucker, EIT Shimp Engineering, PC 912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com Contents: Post-Dev Road Drainage Calculations: Drainage Area Spreadsheet Post-Dev Culvert Drainage Map Post-Dev Inlet Drainage Map TOC Calculations — NEH Lag Method TOC Calcs — Seelye, Fig. 15-4, & Kirpitch Rural Regression Equations VDOT Appendix 8C-2 Inlet Control Nomograph VDOT LD-204 Inlet Capacity VDOT LD-229 Storm Drain Capacity VDOT Outlet Protection Nomograph Independent Reports: Excerpt from NRCS Soils Report NOAA Precipitation Report Post-Dev Road Drainage Calculations: Drainage Area Spreadsheet Post-Dev Culvert Drainage Map Post-Dev Inlet Drainage Map TOC Calculations — NEH Lag Method TOC Calcs — Seelye, Fig. 15-4, & Kirpitch Rural Regression Equations VDOT Appendix 8C-2 Inlet Control Nomograph VDOT LD-204 Inlet Capacity VDOT LD-229 Storm Drain Capacity VDOT Outlet Protection Nomograph Galaxie Farm Inlet Drainage Area Summary Impervious C 0.9 Pervious C 0.3 Woods C 0.2 To Inlet Area Impervious Turf C A G2 10,943,095 2,188,619 8,754,476 0.42 251.22 F4 18,600 11,440 7,160 0.67 0.43 F3 27,270 13,700 13,570 0.60 0.63 F2 1,248,870 90,432 1,158,439 0.34 28.67 F1 00 0 0 0.71 0.00 E9 468,399 132,173 336,226 0.47 10.75 E8A 20,483 14,310 6,173 0.72 0.47 E8 39,982 19,230 20,752 0.59 0.92 EX 1,702,368 510,710 1,191,657 0.22 39.08 E7A 10,746 7,344 3,402 0.71 0.25 E7 19,955 9,973 9,982 0.60 0.46 E6Z 00 0 0 0.30 0.00 E6A 17,762 12,437 5,325 0.72 0.41 E6 29,652 12,140 17,512 0.55 0.68 E5 55,189 26,235 28,954 0.59 1.27 E4 6,430 5,100 1,330 0.78 0.15 E3 17,780 12,446 5,334 0.72 0.41 E2 26,021 16,731 9,290 0.69 0.60 D3 51,625 18,486 33,139 0.51 1.19 D2 22,451 8,890 13,561 0.54 0.52 C3 12,692 10,935 1,757 0.82 0.29 C2 6,038 5,570 468 0.85 0.14 B2 14,726,791 3,092,626 11,634,165 0.43 338.08 A2 5,802,223 1,160,445 4,641,778 0.42 133.20 Ditch 1 159,704 38,751 120,953 0.45 3.67 \._aQo ��s e� GALAXIE FARM ,�,gg "J o� °o= / I _ ;,��r,,,,, POSTDEVINLET 49 �10i —, DRAINAGE MAP j Lr-3 U ��'�a�Q�a 3, 0 loll <9 ADD 0 a C;3 a, r- r 01, _4> C3 T,OQ (?/ /i/ l i— 8.0'8 7C 2 f �j` /ZC1 JA_L-T4Xa2�\ 0 33 AC /25 2 G Ap T t9 161 C> 1 GALAXI E FARM POSTDEV INLET DRAINAGE MAP 41 0.52 AC�1/ TO D / % —IRK jJ J / � H ETFLOW 0 43 �o �. , // �A / / /�OFF {j 0.6 AC TO F3 4 1.19 AC i �/� �,,4 / EA R TO D3 / /�/ A,ti� / / / a� / / / ♦, r Iso ��//�/ gt 26.61 AC TO F2 / / ! o Di \Ai _ 0.14 AC TO C2''o- � - _ -- 0.29 AC TO C3 aT �� Q _ �' a — I o/ - ---- \ � I SHEETFLOW 1 In' �RUNOFF j TO E9 12.62 AC — ao o // // / �'j F ,� AREA / � � I 1 0. 0.48 A O E7 .6 A E6 1.27 AC T E5 E6 _ II r51.47 C A o T A o 61 E� 0.60 o A A -' A TO E2 ! I 8r y� D o— 1 ](I �. ow WooIc ss . I max— l — - >o �f - - A _- —496- 488 � 39.08 AC TO VC `-- — ^ 3.67 AC TO DITCH 1 ' 000 1 100 0 100 200 300 / MEMENEEMEN �7 Scale: 1 "=100' 1 Chapter 15 Time of Concentration Part 630 National Engineering Handbook 630.1502 Methods for estimating time of concentration Two primary methods of computing time of concentra- tion were developed by the Natural Resources Conser- vation Service (NRCS) (formerly the Soil Conservation Service (SCS)). (a) Watershed lag method The SCS method for watershed lag was developed by Mockus in 1961. It spans a broad set of conditions ranging from heavily forested watersheds with steep channels and a high percent of runoff resulting from subsurface flow, to meadows providing a high retar- dance to surface runoff, to smooth land surfaces and large paved areas. L _ dos (S+lf , e 1,900Yo.5 (q 15-4a ) Applying equation 15-3, L=0.6T,, yields: fo.s (S+l)o., T� = 1,140Y05 (eq.15-4b) where: L = lag, h T, = time of concentration, h t = flow length, ft Y = average watershed land slope, % S = maximum potential retention, in 1,000 _ 10 cn' where: cn' = the retardance factor Flow length ( e )—In the watershed lag method of computing time of concentration, flow length is de- fined as the longest path along which water flows from the watershed divide to the outlet. In developing the regression equation for the lag method, the longest flow path was used to represent the hydraulically most distant point in the watershed. Flow length can be measured using aerial photographs, quadrangle sheets, or GIS techniques. Mockus (USDA 1973) developed an empirical relationship between flow length and drain- age area using data from Agricultural Research Service (ARS) watersheds. This relationship is: i = 209A0.6 (eq. 15-5) where: i = flow length, ft A = drainage area, acres Land slope (Y), percent —The average land slope of the watershed, as used in the lag method, not to be confused with the slope of the flow path, can be deter- mined in several different ways: • by assuming land slope is equal to a weighted average of soil map unit slopes, determined us- ing the local soil survey • by using a clinometer for field measurement to determine an estimated representative average land slope • by drawing three to four lines on a topographic map perpendicular to the contour lines and de- termining the average weighted slope of these lines • by determining the average of the land slope from grid points using a dot counter • by using the following equation (Chow 1964): Y _ 100(CI) (eq. 15-6) A where: Y = average land slope, % C = summation of the length of the contour lines that pass through the watershed drainage area on the quad sheet, ft I = contour interval used, ft A = drainage area, ft2 (1 acre = 43,560 ft) Retardance factor —The retardance factor, cn', is a measure of surface conditions relating to the rate at which runoff concentrates at some point of interest. The term "retardance factor" expresses an inverse relationship to "flow retardance." Low retardance fac- tors are associated with rough surfaces having high de- grees of flow retardance, or surfaces over which flow will be impeded. High retardance factors are associ- ated with smooth surfaces having low degrees of flow retardance, or surfaces over which flow moves rapidly. (210-VI-NEH, May 2010) 15-5 GALAXIE FARM AO.8 * (S + 1)0.7 Time of Concentration Calculations TC _ 1140 * Yo.s POSTDEV TO E7C / POST POA 1 BYPASS III >,= 2138 flow length elevations: highest= Y= 6.5% Avg Watershed Slope cn= 72 curve number S= 3.889 Max Retention Tc= 0.484 hrs POSTDEV TO G2 / POST POA 1 BYPASS IV A= 4926 flow length elevations: highest= Y= 4.6% Avg Watershed Slope cn= 72 curve number S= 3.889 Max Retention Tc= 1.122 hrs POSTDEV TO B2 / POST POA 1 BYPASS V ),= 6920 flow length elevations: highest= Y= 16.2% Avg Watershed Slope cn= 58 curve number S= 7.241 Max Retention Tc= 1.126 hrs POSTDEV TO A2 / POST POA 2 BYPASS VI >,= 5098 flow length elevations: highest= Y= 21.9% Avg Watershed Slope cn= 58 curve number S= 7.241 Max Retention Tc= 0.759 hrs 624 lowest= 486 NEH 630.1502 (a) TOC - Watershed Lag Method TOC= 29.0 min. 692 lowest= 467.5 TOC= 67.3 min. 1588 lowest= 467.5 TOC= 67.6 min. 1581 lowest= 465 TOC= 45.5 min. GALAXIE FARM Time of Concentration Calculations POSTDEV TO F2 / POST TO BMP 1 100 ft overland flow 2.0% slope 390 ft s. c. flow -woods 6.4% slope 849 ft channel POSTDEV TO E9 / POST POA 1 BYPASS II 100 ft overland flow 4.0% slope 476 ft s. c. flow -woods 6.3% slope 810 ft channel POSTDEV TO DITCH 1 100 ft overland flow 5.0% slope 298 ft s. c. flow -woods 15.6% slope 121 ft ditch 0.35 C-value 13.2 min Seelye Chart 1.3 fps velocity 5.0 min. NEH Figure 15-4 30.0 ft height 5.3 min. Kirpich Chart TOC= 23.5 min. 0.35 C-value 12.9 min Seelye Chart 1.3 fps velocity 6.3 min. NEH Figure 15-4 56.0 ft height 4.0 min. Kirpich Chart TOC= 23.2 min. 0.35 C-value 12.2 min Seelye Chart 1.9 fps velocity 2.6 min. NEH Figure 15-4 1 ft height 1.7 min. Kirpich Chart TOC= 16.5 min. Culvert A A E L 133.2 Ac 927.5 ft 0.208 sq mi 4440 ft 0.84 mi Southern Piedmont Regression Equations Storm Multiple -Parameter Drainage -Area -Only Q2 21.6A0.881E0.310L 0.423 48.5 cfs 122(A)0.635 45.0 cfs Q10 38.8A0.848E0.379L- 0.430 147.1 cfs 335(A)0.596 131.5 cfs Q25 54.8A0.852E0.392L 0.463 227.0 cfs 504(A)""' 202.5 cfs Q50 74.3A0.860E0.390L- 0.495 301.5 cfs 661(A)0.170 270.2 cfs Q100 .869E0.382L0.529 1101AO 384.8 cfs 849(A)u'9 353.1 cfs Culvert B A E L 338.1 Ac 927.5 ft 0.528 sq mi 1 6411 ft 1.21 mi Southern Piedmont Regression Equations Storm Multiple -Parameter Drainage -Area -Only Q2 21.6A0.881E0.310L- 0.423 94.3 cfs 122(A)0.635 81.4 cfs Q10 38.8A0.848E0.379L 0.430 276.8 cfs 335(A)0.596 229.0 cfs Q25 54.8A0.852E0.392L 0.463 423.5 cfs 504(A)""' 347.9 cfs Q50 74.3A0.860E0.390L- 0.495 560.0 cfs 661(A)0.170 459.4 cfs Q100 .869E0.382L 0.529 1101AO 711.9 cfs 849(A)".559 594.3 cfs Culvert G A E L 251.2 Ac 927.5 ft 0.393 sq mi 6080 ft 1.15 mi Southern Piedmont Regression Equations Storm Multiple -Parameter Drainage -Area -Only Q2 21.6A0.881E0.310L 0.423 74.2 cfs 122(A)0.635 67.4 cfs Q10 38.8A0.848E0.379L 0.430 220.1 cfs 335(A)o.see 191.9 cfs Q25 54.8A0.852E0.392L 0.463 337.0 cfs 504(A)0.581 292.7 cfs Q50 74.3A0.860E0.390L- 0.495 445.3 cfs 661(A)0.570 387.9 cfs Q100 1101AO.869E0.312L- 0.529 565.6 cfs 849(A)" "y 503.4 cfs Chapter 8 - Culverts Appendix 8C-2 Inlet Control, Circular Corrugated Metal 0 CHART 2 180 10,000 160 8,000 EXAMPLE 156 6,000 Dr 36 i1ches(3.0 feet) --5,000 0•a6 efe 3) 144 4, 000 • 5. 6, Hit HIN 132 3,000 D (feet) 5. 6. - 120 F 2,000 108 u 131 e.2 a.a 4. '0 in fast 3. 4. 4 — 1,000 3. T96 D or 184 Soo 3. 0 I-- ann CULVERT B Q25= 347.9 /2 =173.9 CFS CULVERT A w U 7z N u 500 400 300 200 + Q25=202.5/2 54 =101.2 CFS " '° _ so, CULVERT G Q10=191.9/2 U 0 42 / � = 50 =96.0 CFS Q i 40 w — s6 30 HW SCALE o STR. E7C a 33 (FROM LD-204, 20 j11 1=6.5) Q=55.9 30 (21 0 ac 27 10 (31 o e < N 24 6 2. 2. 1.34 1.30 L5 1.5 w s Z r 1.o I.o " a w 1.0 ENTRANCE L TYPE 9 Meedeall Rltored to conform Q w to slope = Projecting T .7 .7 5 To use scale (2) or (3) project 21 4 horfrantollf to Scale (1), teen Vet strelghi inolihed line through 3 D and 0 stoles, ar raven• as 1 f3 llluetrand. 2 k5 I i L Iz BUREAU OF PUBLIC ROADS JAN. 1983 Source: HDS-5 W 6 ,6 .6 .5 .5 HEADWATER DEPTH FOR C. M. PIPE CULVERTS WITH INLET CONTROL NOTE: FOR CULVERTS A, B, & G, RUNOFF FLOW IQ., RESULTS FROM SOUTHERN PEIDMONT RURAL REGRESSION EQUATION -- DRAINAGE AREA ONLY. SINCE TWO (2) CULVERTS WILL BE USED, TOTAL FLOW IS DIVIDED IN HALF FOR THIS NOMOGRAPH. 1 of 1 VDOT Drainage Manual Galaxie Farm LD-204 Stormwater Inlet Computations Inlets on Grade Only Sag Inlets Only E d O L N O z N Q O C > N O O O O- N U O- N U Ol U) N a O U .T. E t i _ N N (n N x X 3 d U O = O ~ U O C id 'c .10. .lN. _� t4 N L w N O_ O -2 O E N O R O Q O U U F N O- W .0 m 'O_ 2 'O U U U Ir U o a o 2 U (L 1 2 3 4 5 6 1 8 9 1 10 11 12 13 14 15 16 17 18 19 1 20 21 22 23 24 (ft) (ac) I (in/hr) (cfs) I (cfs) (cfs) ('/') ('/') ('/') (ft) (ft) (cfs) (cfs) (ft) (ft) (ft) F4 DI-313 12 0.43 0.67 0.29 4.0 1.14 1.14 0.015 0.040 0.020 0.083 3.38 0.19 100.0 % 1.14 0.00 6.5 1.86 1.86 5.00 0.23 100.0 % 1.86 0.00 F3 DI-313 10 0.63 0.60 0.38 4.0 1.51 1.51 0.015 0.025 0.020 0.083 5.62 0.24 100.0 % 1.51 0.00 6.5 2.45 2.45 7.42 0.28 100.0 % 2.45 0.00 F2 DI-7` 4x4 28.67 0.34 9.85 4.0 39.39 0.00 39.39 0.025 0.050 0.150 - 1.29 1 1.29 7.09 6.5 64.00 0.00 64.00 1.78 1 1.78 8.51 E9 DI-7' 4x4 10.75 0.47 5.05 4.0 20.19 20.19 0.025 0.100 0.120 - 0.82 1.5 0.55 8.87 6.5 32.80 32.80 1.14 1.5 0.76 11.49 E8A DI-313 12 0.47 0.72 0.34 4.0 1.35 0.00 1.35 0.015 0.065 0.040 0.083 3.12 0.19 100.0 % 1.35 0.00 6.5 2.20 0.00 2.20 4.74 0.23 96.7 % 2.13 0.07 E8 DI-3C 14 0.92 0.59 0.54 4.0 2.16 0.00 2.16 0.015 0.065 0.020 0.083 4.68 0.22 100.0 % 2.16 0.00 6.5 3.51 0.00 3.51 6.39 0.25 92.4 % 3.24 0.27 E7C 36" ES-1 - 39.08 0.22 8.60 4.0 34.39 0.00 34.39 0.025 0.150 0.042 0.083 0.61 4 0.15 12.16 Note: Culvert HW/D = 1.5 for Q=55.89. Inlet is satisfactory. 6.5 55.89 55.89 0.85 4 0.21 14.58 E7A DI-313 10 0.25 0.71 0.18 4.0 0.70 0.00 0.70 0.015 0.092 0.020 0.083 1.67 0.16 100.0 % 0.70 0.00 6.5 1.14 0.07 1.21 2.20 0.17 97.2 % 1.18 0.03 E7 DI-313 12 0.46 0.60 0.27 4.0 1.10 0.00 1.10 0.015 0.092 0.020 0.083 1.98 0.17 100.0 % 1.10 0.00 6.5 1.79 0.27 2.05 5.32 0.20 95.0 % 1.95 0.10 E6A DI-3C 10 0.41 0.72 0.29 4.0 1.17 0.00 1.17 0.015 0.030 0.020 0.083 3.92 0.20 100.0 % 1.17 0.00 6.5 1.91 0.03 1.94 5.65 0.24 98.6 % 1.92 0.03 E6 DI-313 12 0.68 0.55 0.37 4.0 1.49 0.00 1.49 0.015 0.030 0.020 0.083 4.73 0.22 100.0 % 1.49 0.00 6.5 2.41 0.10 2.52 6.59 0.23 99.3 % 2.50 0.02 E5 DI-3C 10 1.27 0.59 0.74 4.0 2.97 0.00 2.97 0.015 0.012 0.020 0.083 0.21 0.5 0.42 4.11 6.5 4.82 0.02 4.84 0.29 0.5 0.58 8.11 E4 DI-313 8 0.15 0.78 0.11 4.0 0.46 0.00 0.46 0.015 0.022 0.020 0.083 1.86 0.16 100.0 % 0.46 0.00 6.5 0.74 0.02 0.76 3.01 0.19 100.0 % 0.76 0.00 E3 DI-3C 8 0.41 0.72 0.29 4.0 1.18 0.00 1.18 0.015 0.022 0.020 0.083 4.63 0.22 100.0 % 1.18 0.00 6.5 1.91 0.00 1.91 6.32 0.25 94.6 % 1.81 0.10 E2 DI-313 10 0.60 0.69 0.41 4.0 1.64 0.00 1.64 0.015 0.020 0.020 0.083 0.24 0.5 0.48 5.77 6.5 2.66 0.10 2.77 0.28 0.5 0.56 7.73 D3 DI-3C 8 1.19 0.51 0.61 4.0 2.44 0.00 2.44 0.015 0.010 0.020 0.083 0.30 0.5 0.60 8.63 6.5 3.97 0.00 3.97 0.34 0.5 0.69 10.82 D2 D1-313 12 0.52 0.54 0.28 4.0 1.11 1.11 0.015 0.020 0.020 0.083 2.62 0.18 100.0 % 1.11 0.00 6.5 1.80 1.80 4.20 0.21 100.0 % 1.80 0.00 C3 DI-3C 6 0.29 0.82 0.24 4.0 0.95 0.95 0.015 0.006 0.020 0.083 0.25 0.5 0.49 5.97 6.5 1.55 1.55 0.28 0.5 0.57 7.82 C2 DI-3C 6 0.14 0.85 0.12 4.0 0.47 0.00 0.47 0.015 0.020 0.020 0.083 0.21 0.5 0.42 3.96 6.5 0.77 0.00 0.77 0.24 0.5 0.48 5.66 `Assumes25% clogging LD-229 Storm Drain Design Computations Galaxie Farm From To Catch. Runoff Increment Accum. Total Total Total Up Down Pipe Invert Pipe Pipe Velocity Flow time Structure Structure Area Coef AC AC TOC Intensity Flow Invert Invert Length Slope Diameter Capacity Increment ac min in/hr cfs Elev. Elev. ft % in cfs ft/s min 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 G2 G1 251.22 0.42 105.51 105.51 67.3 1.88 198.08 467.50 466.50 45.00 2.22% (2) 48 146.4 11.6 F4 F3 0.43 0.67 0.29 0.29 5.00 6.81 1.95 480.00 479.00 149.64 0.67% 15 5.7 4.2 0.59 F3 F2 0.63 0.60 0.38 0.66 5.59 6.64 4.40 478.80 478.50 39.07 0.77% 15 6.1 5.4 0.12 F2 F1 28.67 0.34 9.85 10.51 23.50 3.83 40.21 478.30 476.00 114.73 2.00% 24 34.7 11.0 0.17 E9 E8 10.75 0.47 5.05 5.05 23.25 3.85 19.43 516.00 505.70 250.92 4.10% 18 23.0 14.6 0.29 E8A E8 0.47 0.72 0.34 0.34 5.00 6.81 2.30 506.00 505.70 28.02 1.07% 15 7.3 5.2 0.09 E8 E7 0.92 0.59 0.54 5.92 23.53 3.82 22.65 505.50 492.00 161.72 8.35% 18 32.9 20.0 0.13 E7C E713 39.08 0.22 8.60 8.60 29.02 3.38 29.09 486.00 485.90 5.00 2.00% 36 102.2 15.3 0.01 E713 E7A 0.00 0.00 0.00 8.60 29.03 3.38 29.09 485.70 484.70 86.98 1.15% 36 77.5 12.4 0.12 E7A E7 0.25 0.71 0.18 8.77 29.03 3.38 29.68 484.50 484.20 27.52 1.09% 36 75.4 12.1 0.04 E7 E6 0.46 0.60 0.27 14.97 29.16 3.37 50.52 484.00 476.50 256.02 2.93% 36 123.7 19.3 0.22 E6Z E6" "10 yr Flow from HydroCAD model 35.72 476.00 475.20 16.12 4.96% 36 160.9 18.3 0.01 E6A E6 0.41 0.72 0.29 0.29 5.00 6.81 2.00 477.70 477.00 30.08 2.33% 15 10.7 6.7 0.08 E6 E5 0.68 0.55 0.37 15.64 29.39 3.36 88.24 475.00 471.40 195.55 1.84% 36 98.0 13.9 0.23 E5 E4 1.27 0.59 0.74 16.38 29.62 3.34 90.46 471.20 470.60 59.92 1.00% 36 72.3 10.2 0.10 E4 E3 0.15 0.78 0.11 16.49 29.72 3.34 90.74 470.40 470.10 28.87 1.04% 36 73.7 10.4 0.05 E3 E2 0.41 0.72 0.29 16.79 29.76 3.33 91.66 469.90 469.00 74.82 1.20% 36 79.2 11.2 0.11 E2 E1 0.60 0.69 0.41 17.20 29.88 3.32 92.90 468.80 466.80 149.78 1.34% 36 83.6 11.8 0.21 D3 D2 1.19 0.51 0.61 0.61 5.00 6.81 4.16 469.00 468.20 61.01 1.31 % 15 8.0 6.6 0.15 D2 D1 0.52 0.60 0.31 0.92 5.15 6.77 6.22 468.00 465.00 76.40 3.93% 15 13.9 11.0 0.12 C3 C2 0.29 0.82 0.24 0.24 5.00 6.81 1.62 463.00 462.70 31.95 0.94% 15 6.8 4.5 0.12 C2 C1 0.14 0.85 0.12 0.36 5.12 6.78 2.41 462.50 462.00 8.04 6.22% 15 17.5 10.0 0.01 B2 131 338.08 0.43 144.02 144.02 67.6 1.87 269.63 462.70 460.50 64.00 3.44% (2) 60 18.7 330.5 A2 Al 133.20 0.42 55.94 55.94 45.5 2.52 140.70 464.30 460.50 71.30 5.33% (2) 48 19.0 226.3 DESICIN OF WTLET PROTECTIDN FROM A POUND PIPE FLOWING FULL MINIMUM TAfLWATER CONDITION (Tw ---, 0.5 (DIAMETER) �J,-!-- Outl et W Q Dg +2 min L� I Diameter, I30 OUTLET G1 Q10=192 CFS (REGRESSION) D50=14rx La= 40' DEPTH=21" OUTLET E1 Q10=127 CFS (RATIONAL) D50=9" La= 28' DEPTH=14" 10 E, - 1 ■p Ilr i* aa�.. _ ai Sra . 4q ■ I 0--361 CFS i1milIl i Ilvlllllllllll��l�■■■■�5�1�1 , ..ram+.dl�.a� � �� il¢�gIG+'4k�p1YVia 1��■1I�� Lief*munend-ed Min. 7 I.1I I' •'!II I 4 3 Ijll��'�t■�I�III�� "_ , I ; I I_ I I I . I I I i i I I 1 1 0 to 0 50 10Q 200 500 1000 Di charge. ':O/sac , Independent Reports: Excerpt from NRCS Soils Report NOAA Precipitation Report MAP LEGEND Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons F] A A/D B B/D C 0 C/D 0 D Not rated or not available Soil Rating Lines A A A A/D x, r B ,.�.r B/D r C C/D D r r Not rated or not available Soil Rating Points 0 A ■ A/D ■ B ■ B/D Hydrologic Soil Group —Albemarle County, Virginia (Cow Branch Drainage Area) MAP INFORMATION p C The soil surveys that comprise your AOI were mapped at 1:15,800. 0 C/D ® D Warning: Soil Map may not be valid at this scale. p Not rated or not available Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil Water Features line placement. The maps do not show the small areas of Streams and Canals contrasting soils that could have been shown at a more detailed scale. Transportation §_§_+ Rails Please rely on the bar scale on each map sheet for map Interstate Highways measurements. US Routes Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Major Roads Coordinate System: Web Mercator (EPSG:3857) Local Roads Maps from the Web Soil Survey are based on the Web Mercator Background projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Aerial Photography Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Albemarle County, Virginia Survey Area Data: Version 13, Sep 17, 2019 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: May 20, 2019—Aug 1, 2019 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. USDA Natural Resources Web Soil Survey 5/5/2020 Conservation Service National Cooperative Soil Survey Page 2 of 5 Hydrologic Soil Group -Albemarle County, Virginia Cow Branch Drainage Area Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 13C Catoctin silt loam, 7 to B 4.4 0.5% 15 percent slopes, very stony Catoctin silt loam, 25 to B 8.0% 13E 66.0 45 percent slopes, very stony 25B Dyke silt loam, 2 to 7 B 11.4 1.4% percent slopes 26C3 Dyke clay loam, 7 to 15 B 5.7 0.7%e percent slopes, severely eroded 39C Hazel loam, 7 to 15 B 0.5 0.1% percent slopes 40D Hazel loam, 15 to 25 B 1.0 0.1 % percent slopes, very stony 58B Myersville silt loam, 2 to B 18.8 2.3% 7 percent slopes 58C Myersville silt loam, 7 to B 46.8 5.7% 15 percent slopes 58D Myersville silt loam, 15 B 26.2 3.2% to 25 percent slopes 59C Myersville very stony silt B 29.7 3.6% loam, 7 to 15 percent slopes 59D Myersville very stony silt B 34.7 4.2% loam, 15 to 25 percent slopes 59E Myersville very stony silt B 91.8 11.1 % loam, 25 to 45 percent slopes 63B Orange silt loam, 2 to 7 C/D 11.8 1.4% percent slopes 69 Pits, quarry 3.3 0.4% 71 B Rabun clay loam, 2 to 7 B 66.8 8.1 % percent slopes 71 C Rabun clay loam, 7 to B 35.2 4.3% 15 percent slopes 71 D Rabun clay loam, 15 to B 15.8 1.9% 25 percent slopes 72B3 Rabun clay, 2 to 7 B 9.7 1.2% percent slopes, severely eroded usDA Natural Resources Web Soil Survey 5/5/2020 Conservation Service National Cooperative Soil Survey Page 3 of 5 Hydrologic Soil Group —Albemarle County, Virginia Cow Branch Drainage Area Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 72C3 Rabun clay, 7 to 15 B 108.3 13.1 % percent slopes, severely eroded 72D3 Rabun clay, 15 to 25 B 78.4 9.5% percent slopes, severely eroded 20.0 72E3 Rabun clay, 25 to 45 B 2.4% percent slopes, severely eroded 73D Rabun clay loam, 15 to B 5.0 0.6% 25 percent slopes, very stony 73E Rabun clay loam, 25 to B 58.8 7.1 % 45 percent slopes, very stony 76 Dan River loam, 0 to 2 B 3.4 0.4% percent slopes, occasionally flooded 79B Meadowville silt loam, 2 B 50.6 6.1% to 7 percent slopes 88 Udorthents, loamy, 2 to 16.3 2.0% 25 percent slopes 90C Unison very stony silt B 7.5 0.9% loam, 7 to 15 percent slopes Totals for Area of Interest 827.9 100.0% usDA Natural Resources Web Soil Survey 5/5/2020 Conservation Service National Cooperative Soil Survey Page 4 of 5 Hydrologic Soil Group —Albemarle County, Virginia Cow Branch Drainage Area Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long -duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink -swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff. None Specified Tie -break Rule: Higher USDA Natural Resources Web Soil Survey 5/5/2020 Conservation Service National Cooperative Soil Survey Page 5 of 5 Precipitation Frequency Data Server https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.9931 &... NOAA Atlas 14, Volume 2, Version 3 Location name: Charlottesville, Virginia, USA'��''T Latitude: 37.9931°, Longitude:-78.4956° Elevation: 481.02 ft" source: ESRI Maps wo source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland PF tabular I PF-graphical I Maps_&_aerials PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)l Average recurrence interval (years) Duration 1 000�00 2 5 10 25 50 100 100 1 200 500 1000 0.352 0.620 0.674 0.723 0.770 0.825 0.870 0.418 0.489 0.551 5-min (0.317-0.391) (0.377-0.465) (0.440-0.543) (0.495-0.610) (0.554-0.685) (0.600-0.743) (0.641-0.797) (0.677-0.849) (0.718-0.912) ((l751-0.964) 0.562 0.669 0.784 0.881 0.988 1.07 1.15 1.22 1.31 1.37 10-min (0.506-0.625) (0.603-0.743) (0.705-0.869) (0.791-0.976) (0.884-1.09) (0.956-1.18) (1.02-1.27) (1.07-1.35) ( 1.14-1.44) (1.18-1.52) 0.703 0.841 0.991 1.11 1.25 1.36 1.45 1.54 1. 44 1.72 15-min (0.632-0.781) (0.758-0.934) (0.892-1.10) (1.00 1.23) (1.12-1.38) 11 (1.21-1.50) 1 (1.29-1.60) 1 (1.36-1.70) 1 (1.43-1.82) (1.48-1.91) 0.963 F 1.16 1.41 1.61 1.86 2.05 2.23 2.40 2.61 2.78 30-min (0.867-1.07) 1 (1.05-1.29) 1 (1.27-1.56) 1 (1.66-2.05) 1 (1.82-2.26) 1 (1.97-2.45) 1 (2.11-2.64) 1 (2.28-2.89) (2.40-3.09) 1.20 1.46 1.81 2.10 2.47 2.77 3.07 3.36 3.75 4.06 60-min (1.08-1.34) 1 (1.31-1.62) (1.63-2.00) 1 (1.89-2.33) 1 (2.21-2.73) 1 (2.47-3.06) 1 (2.71-3.38) 1 (2.96-3.71) 1 (3.27-4.14) 1 (3.51-4.51) 1.44 3.06 3.46 3.88 4.31 1.75 2.18 2.57 4.91 5.40 2-hr (1.27-1.65) 11 (1.53-1.99) 1 (1.92-2.49) 11 (2.25-2.91) 1 (2.66-3.46) 1 (3.00-3.92) 1 (3.35-4.39) 1 (3.69-4.87) 1 (4.15-5.55) 1 (4.53-6.13) 1.58 1.91 2.38 2.80 3.34 3.79 4.25 4.72 5.37 5.93 3-hr (1.38-1.82) 1 (1.67-2.19) 1 (2.08-2.74) 1 (2.44-3.21) 1 (2.89-3.81) 1 (3.27-4.32) 1 (3.64-4.84) 1 (4.02-5.39) 1 (4.51-6.14) 1 (4.93-6.77) 2.02 2.43 3.02 3.56 4.27 4.90 5.55 6.26 7.25 8.12 6-hr (1.78-2.29) (2.15-2.76) 1 (2.65-3.42) 11 (3.12-4.02) (3.72-4.82) 1 (4.24-5.51) (4.76-6.25) (5.31-7.05) (6.06-8.17)](6.70-9.16) 2.54 3.06 3.81 4.51 5.49 6.36 7.30 8.33 9.84 11.2 12-hr (2.24-2.91) 1 (2.70-3.50) 1 (3.35-4.35) 1 (3.95-5.15) 1 (4.77-6.24) 1 (5.47-7.22) 1 (6.20-8.27) 1 (6.98-9.43) 1 (8.09-11.2) 1 (9.07-12.7) 3.04 3.67 4.70 5.55 6.83 7.92 9.13 10.5 12.5 14.2 24-hr (2.73-3.41) 1 (3.30-4.12) 1 (4.21-5.27) 1 (4.96-6.21) 1 (6.06-7.60) 1 (6.98-8.80) 1 (7.97-10.1) 1 (9.04-11.6) 1 (10.6-13.8) 1 (11.9-15.7) 3.58 7.90 9.09 10.4 11.8 4.34 F 5.52 6-A9 13.8 15.5 2-day (3.21-4.00) (3.89-4.85) (4.94-6.16) (5.79-7.24) (7.00-8.79) (8.00-10.1) (9.06-11.5) (10.2-13.1) (11.8-15.4) (13.1-17.3) 3.81 4.62 5.87 6.90 8.39 9.64 11.0 12.5 14.6 16.4 3-day (3.46-4.22) 1 (4.19-5.11) 1 (5.32-6.49) 1 (6.23-7.62) 1 (7.53-9.26) 1 (8.60-10.6) 1 (9.74-12.1) 1 (11.0-13.8) 1 (12.7-16.2) 1 (14.1-18.2) 4.04 4.89 6.22 7.30 8.88 10.2 11.6 13.2 15.4 17.3 4-day (3.71-4.44 1 (4.49-5.37) 1 (5.69-6.82) 11 (6.67-8.00) (8.07-9.72) (9.21-11.2) (10.4-12.7) (11.7-14.4) (13.6-16.9) (15.1-19.1) 4.69 F 5.65 F 7.06 8.23 9.89 11.3 12.8 14.4 16.7 18.6 7-day (4.32-5.11) (5.20-6.15) (6.49-7.69) 1 (7.54-8.95) (9.02-10.8) (10.2-12.3) (11.5-13.9) (12.8-15.7) (14.7-18.2) (16.2-20.4) 5.32 7 6.38 7.88 9.10 10.8 12.2 13.7 15.3 17.5 19.4 10-day 11 (4.92-5.74) (5.91-6.90) (7.28-8.51) 1 (8.39-9.82) 1 (9.93-11.7) (11.2-13.2) 1 (12.5-14.8) 1 (13.8-16.5) 1 (15.6-19.0) 1 (17.1-21.1) F 13.3 16.2 17.7 6.98 F 8.33 10.1] 14.7 19.8 21.4 20-day (6.55-7.47) (7.81-8.91) (9.43-10.8) (10.712.2) (12.4-14.2) (13.7115.7) (15.0-17.4) (16.3-19.0) (18.1-21.3) (19.4-23.1) 8.57 15.3 18.1 19.4 10.2 12.0 13.4 16.7 21.2 22.5 30-day (8.07-9.12) (9.57-10.8) (11.3-12.8) 1 (12.6-14.3) (14.3-16.2) (15.6-17.7) (16.8-19.2) 1 (18.0-20.7) (19.6-22.6) (20.7-24.1) 10.7 F 12.6 14.8 16.4 18.4 19.9 21.4 22.8 24.7 26.0 45-day (10.1-11.3) (11.9-13.4) (14.0-15.6) 11 (15.5-17.3) (17.4-19.5) (18.8-21.1) (20.1-22.7) 1 (21.3-24.2) (22.9-26.2) (24.1-27.7)J 12.6 F 14.8 r 17.1 18.8 21.0 22.6 24.1 25.5 27.4 28.7 60-day (11.9-13.3) 1 (14.0-15.6) (16.2-18.0) (17.8-19.8) (19.8-22.1) (21.3-23.8) (22.7-25.4) (24.0-27.0) (25.6-29.0) (26.8-30.5) Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90 % confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5 % . Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top PF graphical 1 of 4 5/5/2020, 9:59 AM Precipitation Frequency Data Server https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.9931 &... 30 25 c -, 20 a Oj 15 .2 10 PDS-based depth -duration -frequency (DDF) curves Latitude: 37.99311, Longitude:-73.49561 5 = :..- 0 t L t L L rp n7 'p rp tp r{y rp rp rR u9 C7 IYI O O ^ N N f�i 4 fa r5' €7' O iJ'9 C] ei ri rn LO ri N rn � tD Duration 30 25 r 20 4� a m 15 9 i1 10 CL a 5 :��- — 1 2 5 10 25 50 100 200 500 1000 ,average recurrence interval (years) NOAA Atlas 14, Volume 2, Version 3 Created (GMT): Tue May 5 13:59:29 2020 Back to Top Maps & aerials Small scale terrain Average r2currence interval (years) — 1 2 5 — 10 25 50 100 200 500 1000 Duration 5-min — 2-day — 10-min — 3-day 15-min — 4-day — 30-min — 7-day — 60-min — 10-day — 2-hr — 20-day — 3-hr — 30-day — 6-hr — 45-day — 12-hr — 60-day — 24-hr 2of4 5/5/2020, 9:59 AM