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HomeMy WebLinkAboutSUB202000098 Calculations 2020-08-03SHIMP ENGINEERING, P.C. Design Focused Engineering July 31, 2020 John Anderson, PE Albemarle County Department of Community Development 401 McIntire Road Charlottesville, VA 22902 Regarding: SUB 202000098 Gale Farm Subdivision — Road Plan SWM Calculation Packet Dear John, 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@shimp-en ing eering com or by phone at 434-299-9843. Regards, Keane Rucker, EIT Shimp Engineering, PC 912 E. High Sr. 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 1,249,396 142,244 1,107,152 0.37 28.68 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 0.29 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 M A2 5,802,223 1,160,445 4,641,778 0.42 133.20 Ditch 1/G3 159,704 38,751 120,953 0.45 3.67 Road E CG-7 13,163 8,728 4,435 0.70 0.30 i k� GALAXIE FARM POSTDEV CULVERT DRAINAGE MAP 2100 Scale: 1 "=7 GALAXIE FARM i POSTDEVINLET i DRAINAGE MAP I ' \ 43 / � I\ \V i // // / � I I I A6.6 ACT F3 I I �/ 79 //��'�°"�///EAR � •� �i% � j I I \ \ \ \ \ 26.4 AC TOTAL TO\F2 I \ -- / C T0C2_ ,olay"<FErvLL.cEOFneaic / �� / ) (� _ �`� / SHEETEL�W - - / m / / ) RUNOFF / / / �72.62 ACV . ;cos / / ,/ AREAAOF:�[ft I .27IACT I 39.08J1C71VINITY ______-_ � \�• \ 1 = / �/ /// / \ \ \ \\ 1 ! /VTREATED TO EX -' -\ \ III '-_'�/ 3.67 AC TO DITCH? _ �__�'1 \ — /----_---__- ----_- \ _ .00 / \ '--- - — `-`' may\ \ \ i00,/ 0 / 'Zoo/ 2 / 3/00/ S�aie;_1 "=1001' I\�� 11 1111 1 / `✓ i �``.� i \ `I 1`, \ - ` \ --- / GALAXIE FARM .\ \ \ \ —_ -- '� /i 11 1 \\.�1 1 i 1 "` 1 POSTDEV INLET .\ \ �\ \ ' i I . \ . 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I�' ��v =ea_` I, �I V 11 A\ v` __ - -- I I � I A A I _-_-_ f — r' 200 /' \ I�' I I i I � / ``� ` r_—_____ _ I a IIII' _ \ (\ I 11 \.. ilii \ _________ ____ ___.I� \\\� `\--_---_---_—_' ' —__- ___, \ I I 11 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_Paa(S+1)o' a 1,900y06 (q 15-4a) Applying equation 15-3, L=0.6Tr, yields: Q8.8 `S+1)o.v 1 1,140Y05 (eq 15 4b) where: L = lag, h Tr = time of concentration, h f =flow lengUi, ft Y = average watershed land slope, % S = maximum potential retention, in 1,000 _ 10 cri where: en' = the retardance factor Flow length ( t )—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: P = 209A06 (eq. 15-5) where: f =flow length, it 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): 100(CI) y = (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, ffz (1 acre = 43,5601t ) Retardance factor —The retardance factor, en', is a measure of surface conditions relating to the rate at which runoff concentrates at some point of interest. The term "retardance factor" expresses aninverse 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 A0.8 * (S + 1)0.7 Offsite Time of Concentration Calculations To = 1140 * Yo.s TOC III: POSTDEV TO E7C / POST OFFSITE TO POA 1 (6S) a= 2138 flow length elevations: highest= 624 lowest= 486 Y= 6.5% Avg Watershed Slope cn= 72 curve number S= 3.889 Max Retention Tc= 0.484 hrs NEH 630.1502 (a) TOC - Watershed Lag Method TOC= 29.0 min. TOC V: POSTDEV TO El / POST OFFSITE TO POA 1 (8S) a= 4926 flow length elevations: highest= 692 lowest- 467.5 Y= 4.6% Avg Watershed Slope cn= 72 curve number S= 3.889 Max Retention Tc= 1.122 hrs TOC= 67.3 min. TOC VI: POSTDEV TO B2 / POST OFFSITE TO POA 1 (9S) X= 6920 flow length elevations: highest= 1588 lowest= 467.5 Y= 16.2% Avg Watershed Slope cn= 58 curve number S= 7.241 Max Retention Tc= 1.126 hrs TOC= 67.6 min. TOC VII: POSTDEV TO A2 / POST OFFSITE TO POA 2 (12S) a= 5098 flow length elevations: highest= 1581 lowest= 465 Y= 21.9% Avg Watershed Slope cn= 58 curve number S= 7.241 Max Retention Tc= 0.759 hrs TOC= 45.5 min. GALAXIE FARM PostDev Time of Concentration Calculations TOC I: POSTDEV TO F2 / POST OFFSITE TO BMP 1 (2S) 100 ft overland flow 2.0% slope 0.35 C-value 13.2 min Seelye Chart 390 ft s. c. flow -woods 6.4% slope 1.3 fps velocity 5.0 min. NEH Figure 15-4 849 ft channel 30.0 ft height 5.3 min. Kirpich Chart TOC= 23.5 min. TOC II: POSTDEV TO E9 / POST OFFSITE TO POA 1 (5S) 100 ft overland flow 4.0% slope 0.35 C-value 12.9 min Seelye Chart 476 ft s. c. flow -woods 6.3% slope 1.3 fps velocity 6.3 min. NEH Figure 15-4 810ft channel 56.Oft height 4.0 min. Kirpich Chart TOC= 23.2 min. TOC IV: POSTDEV Tu _ FSITE TO POA 1 (7S) 100 ft overland flow 5.0% slope 0.35 C-value 12.2 min Seelye Chart 298 ft s. c. flow -woods 15.6% slope 1.9 fps velocity 2.6 min. NEH Figure 15-4 121 ft ditch 1 ft height 1.7 min. Kirpich Chart TOC= 16.5 min. GALAXIE FARM POSTDEV TOC NOMOGRAPHS T = 0.225 0.42 5-0.19 L. -1.0 C C,b,ter 15 71.1 fOaneeatrd. ➢art 690 Naeo-]Engmeei gHmd k Ti, =osenar d Flow Time, cr tp L =ler4h of ably. Ma 35 - TRAVEL TIME FOR CHANNEL FLOW (Kirpich Chart) Figora16-4 Velocity vrnsas sloes ]br sbWlow coucevrnvud Oow S+Slope. fmw%et C = Ralipnel'C' Value For G..0 Ch.CM, 600 30 'o.m x (feed o.e0 Soo Paved 0.9 0.70 0so 500 Tt (min.) 400 0.8 25 a n 0M 200 300 0.7 "3 W LL a Ix t� p J (9 Ui 0.8 Bare 0.5 20 \ 200 5011 \ Poor 0.4 Z Qrasa -1 Suliace ~O 0.5 > Averaoe 0.3 w \ a 1.0 i ce 8Q DeII:� OIdSS �` 70 0.2 \ \ + U 80 \\ �i� io - W a 50 20 40 10 F Z Z W ~ 0 a H W 2 0 r w ? pzp o.o�a am 0'm o.oa 0.03 002 o.ot $ 100 100 L (feet) E 10000 50 « 0 5000 to (1) For us! hemels; a rn• 10 (b It .2 chame(s, mu 1000 10 E N x >E 5 a 500 5 a� a F g A A 3 a a C a�S - - - A 4 F L _ 1411441111 m 30 ¢ i 9 O a 9 20 Ra+f or.p� "C" Velue ter Seleote0 C�oc*er v Otmee Graes O. tIS F7 Velari[y(me) 100 1 TIME OF CONCENTRATION OF SMALL DRAINAGE BASINS Tahle l641 Equations and assumptions developedflom figure lS-0 Flow typ! Gopth MaaahWg m Velodty equetlaa AVWo s Grose Svtace 0.79 (n) (ma) t pen 0 30 Poer OresO Svr±oee 0.36 Pavement and smafl upland guRies 0.2 0.025 V=20.32g(s)n" Ppeture 0.40 E 10 Bore Soli 0.40 Pares G.90 Grassed waterw$vs 0.9 0.050 V=16.135(s)°' Nowly bare and untilled(ovetimid flow); and alluvial fans in westem moms i 0.2 0.051 V=9.966(s)°6 regions Culmmted straight raw crops 0.2 0.Om V=8.762(s)6° OVERLAND FLOW TIME short-gasapasmre 0.2 D0l3 V=6.962(s)°6 blmimum tillage cuIthatiou,couwur or stdpcmpped, mrd woodlands 0.2 0.101 V=5.032(s)6° Forest i i; hemT ground liner and W meadows 0.2 oao2 V=2.516(srs Source: VDOT Plate 5-3 TOC NOMO LINE COLORS MATCH WITH NOTES IN TOC CALCS Culvert A A E L 133.2 Ac 0.208 sq mi 927.5 ft 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) 45.0 cfs Q10 38.8Ao.848E0.379L-0.430 147.1 cfs 335(A)o... 131.5 cfs Q25 54.8A0.852E0.392L 0.463 227.0 cfs 504(A)0.58i 202.5 cfs Qso 74.3A0.860E0.390L 0.495 301.5 cfs 661(A)0.570 270.2 cfs Q100 101A0.869E0.382L-0.529 384.8 cfs 849(A)u.ssy 353.1 cfs Culvert l3 A E L 338.1 Ac 927.5 ft 6411 ft 0.528 sq mi 1.21 mi Southern Piedmont Regression Equations Storm Multiple -Parameter Drainage -Area -Only Q2 21.6Ao.881E0.310L- 0.423 94.3 cfs 122(A) 81.4 cfs Q10 38.8Ao.848E0.379L- 0.430 276.8 cfs 335(A)0.596 229.0 cfs Q25 54.8A0.852E0.392L 0.463 423.5 cfs 5O4(A)o.sa1 347.9 cfs Q50 74.3A0.860E0.390L 0.495 560.0 cfs 661(A)0.570 459.4 cfs Q10o 101A0.869E0.382L-0.529 711.9 cfs 849(A)u."9 594.3 cfs HALF: 101.24 HALF: 173.93 Chapter 8 - Culverts Appendix 8C-2 Inlet Control, Circular Corrugated Metal OCHART 2 eo w,000 16e 8,000 EXAMPLE (I) 136 6,000 Be la 1 nt No l3.0 feet 6 (2) - 3,000 4.44 Lre 3) 144 4,000 .he + h• 132 i 3.000 D leeetl 6. 120 � 10 I,a 5.4 M 2.000 121 9.1 a.] 4. e. 08 a 171 t.i 6.4 0 In tot 3. 4. 86 a � 1,000 ]. BOOhe 3. 64 w 600 2 CULVERT B 500 --~ O 2s=347.9 2 / W TZ 400 / 1.sD p- 2. =173.9 CFS m SOO _ CULVERT A 1.30 s 1s Q2s=202.5/2 s+ o W W =101.2 CFS IX > e0 O u 42 �u 30 = I.o 1.0 o 40 1.0 .�- 36 30 HW ENTRANCENO Q u N . STR. E7C i SCALE ° TYPE B (FROM LD-204, 0 33 20 1 N.....tl o e e I=6.5) 0=55.9 s0 (2) qll vee to senttrn z I..LLe e 27 10 (]) hLHtlin4 s c B .7 .7 i 29 .7 � 6 B 21 Te eee .sole 121 4 ee11eeM41111. 1041,(1), then 6 Yee et rtl1ht 1LL ne4 line IhroY4h •B 3 0 04 o moue, LL reuru Le .6 IB Ill Yel re M14. 2 Is • s 1.0 s — ` 12 HEADWATER DEPTH FOR C. M. PIPE CULVERTS sulrcnu or Puauc hwoa AN. na] WITH INLET CONTROL NOTE: FOR CULVERTS A & B, RUNOFF FLOW " Q" Source: HDS-5 RESULTS FROM SOUTHERN PEIDMONT RURAL REGRESSION EQUATION -- DRAINAGE AREA ONLY. SINCE TWO (2) CULVERTS WILL BE USED, TOTAL 1 of 1 VDOT Drainage Manual Galaxie Farm LD-204 Stormwater Inlet Computations Inlets on Grade Only Sag Inlets Only a E Z w ¢ .. m j Z 0 O N U V i1 L] fA m O E U D %i Z a y X X m y m O1 S a u o 1v `m m o `m v = u a d U m r ,� n w ._ mhi o E ¢' U o 0 0 a r$ S o 0 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 (ft) (ac) (in/hr) (cfs) (cfs) (cis) CM V) ('/') M (ft) (cis) (cfs) (ft) (ft) (ft) F4 DI-3B 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-3B 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 28.68 0.37 10.56 4.0 42.26 0.00 42.26 0.025 0.050 0.150 - 1.29 1 1.29 7.09 6.5 68.67 0.00 68.67 1.78 1 1.78 8.51 'Assumes 259 clogging 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 EBA DI-3B 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 0.29 11.14 4.0 44.55 0.00 44.55 0.025 0.150 0.042 0.083 0.61 4 0.15 12.16 Note: Culvert HW/D = 1.5 for 0=55.89. Inlet is satisfactory. 6.5 72.40 72.40 0.85 4 0.21 14.58 EM DI-3B 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-3B 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-3B 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-3B 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-3B 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 DI-3B 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 Road E Curb CG-7 4" Curb 0.30 0.70 0.21 4.0 0.84 0.00 0.84 0.015 0.040 0.020 0.083 2.36 0.17 0.52 D/H" 6.5 1.37 0.00 1.37 3.97 0.21 0.62 D/H" "depth / 4" curb height LD-229 Storm Drain Design Computations Galaxie Farm From To Catch. I Runoff Incrementl Accum. I Total Total 10-yr Total 10-yr 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) (cfs) (fus) (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 28.68 0.37 10.56 11.23 23.50 3.83 42.96 478.30 476.00 114.73 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 0.29 11.14 11.14 29.02 3.38 37.69 486.00 485.90 5.00 2.00% 36 102.2 15.3 0.01 E76 E7A 0.00 0.00 0.00 11.14 29.03 3.38 37.69 485.70 484.70 86.98 1.15% 36 77.5 12.4 0.12 E7A E7 0.25 0.71 0.18 11.31 29.03 3.38 38.28 484.50 484.20 27.52 1.09% 36 75.4 12.1 0.04 E7 E6 0.46 0.60 0.27 17.51 29.16 3.37 59.09 484.00 476.50 256.02 2.93% 36 123.7 19.3 0.22 E6Z E6` *10 yr Flow from HydroCAD model 25.78 476.00 475.20 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 18.18 29.39 3.36 86.83 475.00 471.40 195.55 1.84% 36 98.0 13.9 0.23 E5 E4 1.27 0.59 0.74 18.92 29.62 3.34 89.01 471.20 470.25 59.92 1.59% 36 91.1 10.2 0.10 E4 E3 0.15 0.78 0.11 19.03 29.72 3.34 89.27 470.05 469.60 28.87 1.56% 36 90.3 10.4 0.05 E3 E2 0.41 0.72 0.29 19.33 29.76 3.33 90.19 469.40 468.20 74.82 1.60% 36 91.4 11.2 0.11 E2 E7 0.60 0.69 0.41 19.74 29.88 3.32 91.40 468.00 466.80 149.78 0.80% 42 97.5 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 B1 338.08 0.43 144.02 144.02 67.6 1.87 269.63 462.70 460.50 64.00 3.440/. (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 G3 G2" 3.67 0.45 1.63 1.63 16.50 4.59 7.49 varies varies varies 1.30% 15 8.0 226.3 " Calculates the worst -case scenario for the private storm drain "G" Sewer. Min. slope=1.3% Independent Reports: Excerpt from NRCS Soils Report NOAA Precipitation Report Hy ml ak9 11 Gmuu l x oC Uu ,V ,,Is Rnxpsa.,2aonp�mmes�sae V*a���ss R k wa N-1 wbs0., �o,o con..-s.rvlre nalc ,tllve 81,1E , pp.1 Ga H,tooak moll GWlup le F omoto Caumr. om,ma MAP LEGEND MAP INFORMATION read e.m.alammol, ■ c ib¢wn—,s ..I ..I. In, Rol wy¢m¢pp¢aat ow ■ s.aoo. �b ■ M.I�: MIM Pm.r m .¢Im...ml.. Omn H.m..m "namn—talllLl¢ Emagwrem or m¢w m¢Wna N¢¢um a m¢PPM®no¢um mwMmsm nme m. a¢MII M map" ammry M mll o p HAm.. ..=m wn., �M n..�.e �.bown ..o.m..na L"�.m .e P k m. mom dantlad 1. 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M m Wmstil om tol &°2f4 i Lenawmlm SMu relCmlremaw 9ml9irvry Yaae3o,< XydMtgl�SUIGw�NMmarle Conly VIPoINa Hydrologic Soil Group palatle FarmN itiW Xalural onsw ly p eWn 15�30i0 i CariaerwtlanSmka NetlanelUppweWe 5tll5umy Gp3d0 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* ®i Latitude: 37.9931°, Longitude:-78.4956° Elevation: 481.021t- f 'source: ESRI Maps " source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES G.M Bonnin, D. Nianin, B. Lin, T Parzybok, Myekla, and D. Riley NOAq 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)' Average recurrence Interval (years) Duratlon��� 10 0 50 100 ® 500 1000 0.352 0.918 0.489 0.551 0.620 0.674 0.723 0.770 OS25 0.870 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) (0.751-0.964) 0.562 0.669 0.7M 0.861 0.9M 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 (1.02-1.27) 1 (1.07-1.35) 1 (1.14-1.44) 1 (1.18-1.52) 0.703 0.841 0.991 1.11 1.25 1.36 1.45 1.54 1.64 1.72 15-min (0.632-0.781) (0.758-0.934) (0.892-1.10) (1.00-1.23) 1 (1.12-1.38) 1 (121-1.50) 1 (1.29-1.60) (1.36-1.70) (1.43-1.82) (1.48-1.91) 0.963 1.16 1.41 1.61 1.86 2.05 2.23 2.90 2.6 1 F2.78 30-min (0.867-1.07) 1 (1.05-1.29) 1 (1.27-1.56) 1 (1.45-1.79) 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) 1 (2.40-3.09) 1.20 146 1.81 2.10 2.47 2.77 3.07 3.36 3.75 4.06 60-min (1.08-1.34) (1.31-1.62) (1.63-2.00) (1.89-2.33) (2.21-2.73) (2.47-3.06) (2.71-3.38) (2.96-3.71) (3.27-4.14) (3.51-4.51) 1.44 1.75 2.18 2.57 3.06 3.46 3.88 4.31 4.91 5.40 2-hr (127-1.65) (1.53-1.99) (1.92-2.49) (2.25-2.91) (2.66-3.46) (3.00-3.92) (3.35-4.39) (3.69-4.87) (4.15-5.55) (4.53-6.13) 1.58 7191 2.38 7280 3.34 3.79 7425 4.72 5.37 5.93 3-hr (1.38-1.82) 1 (1.67-2.19) (2.08-274) 1 (2.44-3.21) 1 (2.89-3.81) (327-4.32) 1 (3.64-4.84) (4.02-5.39) (4.51-6.14) (4.93-6.77) 2.02 2.93 3.02 3.56 4.27 4.90 5.55 6.26 7.25 8.12 6-hr (1.78-229) 1 (2.15-2.76) 1 (2.65-3A2) 1 (3.12-4.02) 1 (3.72-4.82) 1 (424-5.51) 1 (4.76-6.25) 1 (5.31-7.05) 1 (6.06-8.17) 1 (670-9.16) 2.59 3.06 3.81 4.51 5.49 6.36 7.30 8.33 9.84 11.2 12-hr (224-2.91) (2.70-3.50) (3.35-4.35) (3.95-5.15) (4.77-6.24) (5.47-7.22) (6.20-8.27) (6.98-9.43) (8.09-11.2) (9.07-12.7) 3.04 3 67 4.70 555 6.83 7.92 9 377 0.5-IF12.5 14.2 24 (2.73-3.41) (3.30-4.12) (4.21-527) (4.96-6.21) (6.06-7.60) (6.98-8.80) (7.97-10.1) (9.04-11.6) (10.6-13.8) (11.9-15.7) 3.58 4.34 5.52 6.49 7.90 9.09 10.4 11.8 13.8 15.5 2-day (321-4.00) (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 4S2 5.87 6.90 8.39 9 64 11 A 12S 14.6 16A 3-d8y (3.46-422) 1 (4.19-5.11) 1 (5.32-6.49) (6.23-7.62) 1 (7.53-9.26) (8.60-10.6) (9.74-12.1) 1 (11.0-13.8) 1 (12.7-162) 1 (14.1-18.2) 4.09 4.89 6.22 7.30 8.88 102 11.6 132 15.4 17.3 4-daylj (3.71-4.44) (4.49-5.37) (5.69-6.82) (6.67-8.00) (8.07-9.72) (9.21-11.2) (10.4-12.7) (117-14.4) (13.6-16.9) (15.1-19.1) 4.69 5.65 7.06 8.23 9.89 11.3 12.8 14A 16.7 18.6 achy (4.32-5.11) (5.20-6.15) (6.49-7.69) (7.54-8.95) (9.02-10.8) (10.2-12.3) (11.5-13.9) (12.8-15.7) (14.7-182) (16.2-20.4) 5.32 6.38 7.88 9.10 10.8 122 13.7 15.3 17.5 19.4 10aay (4.92-5.74) (5.91-6.90) (7.28-8.51) (8.39-9.82) (9.93-11.7) (11.2-13.2) (12.5-14.8) (13.8-16.5) (15.6-19.0) (17.1-21.1) 6.98 8.33 10.1 11.4 13.3 14.7 16.2 17.7 19.8 21.4 20aay (6.55 7.47) (7.81-8.91) (9.43-10.8) (10.7-12.2) (12.4-142) (13.7-15.7) (15.0-17.4) (16.3-19.0) (18.1-21.3) (19.4-23.1) 8.57 10.2 12.0 13.4 15.3 16.7 18.1 19A 21.2 22.5 31kki (8.07-9.12) 1 (9.57-10.8) (11.3-12.8) (12.6-14.3) (14.3-162) (15.6-17.7) (16.8-192) 1 (18.0-20.7) 1 (19.6-22.6) 1 (20.7-24.1) 10.7 12.6 14.8 16.4 18.4 19.9 2 4 221 24.7 MO 45-r18y (10.1-11.3) 1 (11.9-13.4) (14.0-15.6) (15.5-17.3) (17.4-19.5) (18.8-21.1) (20.1-22.7) 1 (21.3-24.2) 1 (22.9-262) (24.1-27.7) 126 14.8 17.1 18.8 21.0 22 6 24.1 25S 27.4 28.7 60-day (11.913.3) (14.0-15.6) (162-18.0) (17.8-19.8) (19.6-22.1) (21.3-23.8) (22.7-25.4) (24.0-27.0) (25.6-29.0) (26.8-30.5) t 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 &... 2m! Large scale terrain \ Washington, D.C.* •Ar 4 Harrisonburg . Y 5 Taunton VIRGINIA n IA Richr>7^^� � Lynchburg prg', Roanoke 100krn OOmi N or foi Large scale map An Washington v Harrisonburg ihn' .19. Virginia Lynchburg 100km ~ 0mi Large scale aerial Nortc 3 of 4 5/5/2020, 9:59 AM