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HomeMy WebLinkAboutWPO201800028 Calculations WPO VSMP 2018-06-21 PROJECT MANAGEMENT SHIMP CIVIL ENGINEERING LAND PLANNING ENGINEERING June 21, 2018 41 ® 4cA-',, l Mr. Frank Pohl j ' N Department of Community Development 401 McIntire Road - M SHIMP Charlottesville, VA 22902 Li•7 I.q`A / 11 % s, Regarding: Seven Oaks Runoff Calculations Dear Frank, Enclosed is the runoff calculation packet for the Seven Oaks VSMP Plan. Since the existing downstream conditions are the same as the pre-development, and the post-development improvement will not alter the runoff conditions, we have analyzed the site for impacts from increased sheetflow runoff. Our calculations have determined that the increase in impervious area will not cause downstream impact from increased volume of sheetflow. We have concluded this after calculating the increase in runoff for the 1- year, 2-year, and 10-year storms. The 10-year post-development runoff is 9.46 cfs and would only warrant a 10' level spreader per Green Book design specifications. The point of analysis is a heavily-grassed plain with slopes less than 2%, so a level spreader would be an unnecessary addition as the site conditions already drive sheetflow from the development area. If you have any questions please do not hesitate to contact me at: JustinAshimp-enqineerinq.com or by phone at 434-299-9842. Contents: Pre-Development Drainage Map Post-Development Drainage Map HydroCAD Runoff Calculations NOAA Precipitation Report NRCS Soil Report O II I I CO 0_ ' 117 _ 1 O — I� 17 ;--- I 1 I z 0QQ •- � L__ J --- � ++� W � � Nc� I� I� ; 1` `J " II � cvin � i N o \ 1 1 1 " I o i� I ■ o Q �� / ■ II CL m : - ) ( : •.04,;:.... x "*. * _ I �- o N. (no .,.., r„,... . / i , Ii ...) ( O kV I / 1 / -- --1 / /i r \ I / /1 1 ' o = f ' 1 /\ hl � -. ' I 1 I \ 1\ 1 " r- L_.1 I I \\c 1(,:3 t}' —F1t-31_--'i *i _,// 1 r} Lt1 if I lame. I I �/ -J I I / .$: 11 j-1----- -----'-J t r. II I F % 1 I I i' 1 / I L J °2�� _ _ — — \ IL__ �_ ----� ti I �ozc— " \ / N I I - -r - - �`\ ! 1 t' 1 j 1 —' �� 1 / \ ,. i _j- \ \ 1 _��_\_ , \ \ \ �Fo g vv \v \\ 'A ✓tS' 1 \�� I I 1 1 1 4} \ 1. t 1 �\ \` \ \ \ ` / t 0 In Q © w II DZ CD W < 1 7 0 z Q ,I > —1 V ) r---J tj`1 I W --1 I m ---- I 0 � 7--- 1 I ill = cn (n 1L.---II \ L—•-r I r W = � cnmd--- i0 • 0 /, CL 00 1-0 ` ■■ U c` - • ' Y:. .. 1.ItJIr /° t I 1. �Eo j I I .I. 1 .I.; \ 4.9...) ( .. \ r.,....,7.,4747,,,,;:.f.s,„,:.1 11,,A,.., _ 1 .,...,:,"4,,,,t,....,„41,..w..:4:k„..?,.., v • /V•. . t..xi sg N:‘\.Nis.k.;:l: 1 I / f\, k } M4 f k rJ.? w)I Y�` .45Y :4" tiY71:1�, ; i I; c n �h tyt Pts, /a- 5t�C� lyi \ 4C..i illiv, 01,:i = — 1 o , �I I_---__-- :-.E.1.--- 1."'s,f,,,,,-k . L3 J CI • 04• i- 0 i . , I o l 1 i CI o I I �� 1 / z,.. I L_ ee , 1 —_,,,_ ;0. 11e 1 1 \e \` e ` \ \ \ a \ , // p • PREDEV POSTDEV SubCat Reach 'on• Link Drainage Diagram for RUNOFF CALCS Prepared by Shimp Engineering, P.C., Printed 6/21/2018 HydroCAD®9.10 s/n 07054 ©2011 HydroCAD Software Solutions LLC RUNOFF CALCS Type 1124-hr 1-YR Rainfall=3.07" Prepared by Shimp Engineering, P.C. Printed 6/21/2018 HydroCAD®9.10 sin 07054 ©2011 HydroCAD Software Solutions LLC Page 2 Time span=1.00-24.00 hrs, dt=0.05 hrs, 461 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: PREDEV Runoff Area=2.210 ac 20.81% Impervious Runoff Depth>0.62" Tc=10.0 min CN=67 Runoff=1.83 cfs 0.114 of Subcatchment 2S: POSTDEV Runoff Area=2.210 ac 39.37% Impervious Runoff Depth>0.95" Tc=10.0 min CN=74 Runoff=3.09 cfs 0.175 of RUNOFF CALCS Type 11 24-hr 2-YR Rainfall=3.71" Prepared by Shimp Engineering, P.C. Printed 6/21/2018 HydroCAD®9.10 s/n 07054 ©2011 HydroCAD Software Solutions LLC Page 3 Time span=1.00-24.00 hrs, dt=0.05 hrs, 461 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: PREDEV Runoff Area=2.210 ac 20.81% Impervious Runoff Depth>0.97" Tc=10.0 min CN=67 Runoff=3.06 cfs 0.178 of Subcatchment 2S: POSTDEV Runoff Area=2.210 ac 39.37% Impervious Runoff Depth>1.38" Tc=10.0 min CN=74 Runoff=4.59 cfs 0.255 of RUNOFF CALCS Type I124-hr 10-YR Rainfall=5.57" Prepared by Shimp Engineering, P.C. Printed 6/21/2018 HydroCAD©9.10 sin 07054 ©2011 HydroCAD Software Solutions LLC Page 4 Time span=1.00-24.00 hrs, dt=0.05 hrs, 461 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: PREDEV Runoff Area=2.210 ac 20.81% Impervious Runoff Depth>2.20" Tc=10.0 min CN=67 Runoff=7.35 cfs 0.406 af Subcatchment 2S: POSTDEV Runoff Area=2.210 ac 39.37% Impervious Runoff Depth>2.82" Tc=10.0 min CN=74 Runoff=9.46 cfs 0.519 af NOAA Atlas 14,Volume 2,Version 3 fi x<-,4 Location name:Greenwood,Virginia,USA* r" ''� k Latitude:38.0426°,Longitude:-78.7469° , Elevation:717.76 ft** f �r„ 'source:ESRI Maps '',.., ,,," "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 Macs & aerials PF tabular • • PDS-based point precipitation frequency estimates with 90%confidence intervals(in inches)1 Duration Average recurrence interval(years) 1 2 5 1 10 25 50 100 200 500 1000 5-min ' 0.333 0.397 0.470 0.531 0.600 ' 0.654 0.705 0.753 0.811 0.858 (0.301-0.369) (0.360-0.440) (0.425-0.519) (0.479-0.586) (0.539-0.661)'(0.583-0 720) (0.625-0.777) (0.661-0.832) (0.703-0.901) (0.737-0.958) : 10-min 0.532 0.636 j 0.753 0.849 0.956 1.04 1.12 1.19 1.28 1.35 (0.481-0.589) (0.577-0.703) (0.681-0.832),(0.766-0.936) (0.858-1.05) (0.929-1 15) (0.993-1.24) (1.05-1.32) (1 11-1 43) (1 16-1.51) ' 15-mini 0.665 0.799 0.952 1.07 1.21 1.32 1.42 1.51 1.61 1.70 (0.601-0.736),(0.725-0.884), (0.862-1.05)' (0.969-1 19) (1.09-1.33) : (1 18-1 45) (1.25-1.56) (1.32-1.66) (1 40-1 79) (1 46-1.89) 30-min 0.911 1.10 1.35 1.56 1.80 1.99 2.17 2.34 2.57 2.75 (0.824-1.01) (1.00-1.22) ! (1.23-1 49) (1 41-1 72) (1.61-1.98) (1 77-2.19) . (1.92-2.39) (2.06-2.59) (2.23-2.85) (2.36-3.07) 60-min ; 1.14 ) 1.39 1.73 2.03 2.39 2.69 2.99 (2.89 39s3) 3.69 4.01 (1.03-1.26) ' (1.26-1.53) (1.57-1.92) : (1.83-2.24) (2.15-2.63) . (2.40-2.96) (2.65-3.29) 2_-_ 63 (3.20-4.09) (3.44-4 48) 2-hr , 1.35 1.65 2.07 i 2.44 2.91 3.31 3.71 4.13 4.71 5.20 (1.21-1.52) ! (1 47-1.84) ; (1.86-2.32) ; (2.18-2.73) (2.58-3.25) ; (2.92-3.69) ; (3.25-4 14) (3.59-4.62) , (4.03-5.29) (440-5.86) , 3-hr 1.49 1.81 1 2.27 2.67 3.19 3.63 4.08 4.55 5.20 5.76 (1.33-1.68) (1.61-2.04) (2.02-2.56) (2.37-3.00) ' (2.82-3.58) (3.19-4.07) (3.56-4.58) (3.93-5.13) (443-5.88) (4.84-6.54) ' 6-hr ' 1.93 2.34 2.91 3.43 4.12 4.73 5.36 6.06 7.04 7.91 : (1 73 2 17) ; (2.09-2.63) (2.59-3.27) , (3.04-3.85) (3.63-4.63) (4 13-5.30) ' (4.64-6.02) (5.17-6.82) (5.91-7.97) (6.54-8.98) : 12-hr 2.46 2.98 3.71 4.39 5.34 6.19 7.11 8.13 9.64 11.0 (2.20-2.80) , (2.65-3.38) ; (3.29-4.21) : (3.88-4.98) , (4.68-6.04) (5.36-7.00) (6.07-8.06) . (6.84-9.23) . (7.93-11.0) (8.88-12.6) 24-hr ; 3.07 3.71 4.73 5.57 6.81 7.87 9.04 10.3 12.2 13.9 (2.76-3.43) : (3.34-4 15) s (4.24-5.28) , (4.98-6.21) (6.05-7.58) (6.94.8.75) ; (7.90-10.0) (8.92-11.5) (10.4-13.6) (11.6-15.5) . 2-day ' 3.61 4.38 i 5.55 6.51 7.89 9.05 10.3 11.7 13.7 15.3 (3.26-4.02) (3.95-4.88) ! (4.99-618) ! (5.84-7.24) (7.02-8.76) (8.00-10.0) (9.03-11 4) (10.1-13.0) (11 7-15.3) (13.0-17.2) 3.85 4.66 5.90 6.92 8.38 9.61 10.9 . 12.4 14.5 16.2 3-day (3.49 4 . )_ 27 (4.23-5.17) (5.35-6.54) ._(6.25-7.66) (7.5.„._ (8.57-10.6) (9.67-12.1) (10.8 13.7) l (12.5-16.1) ' (13.9-18.1) 4.08 4.94 6.26 7.33 8.88 10.2 11.6 13.1 15.2 17.1 4-day 73- .51) (4 51-5.45) : (5.70-6 91 (3 4 � ) (6.66-8.08) (8.02-9 78) (9.14-11.2) (10.3-12.7) (11.6-14 4) (13.3-16.9) (14.8-19.0) 7-day ' 4.74 5.71 7.13 8.29 9.93 11.3 12.7 14.3 16.5 18.4 i (4.34-5.18) (5.23-6.24) (6.52-7.80) , (7.56-9.06) (9.01-10.8) ' (10.2-12.3) (11 4-13.9) (12.7-15.6) (14.5-18.1) (16.0-20.2) 10-day 5.38 6.46 7.96 9.16 10.8 12.2 13.6 15.1 17.1 18.9 (4,96_5.84) (5.95_7.01) (7.32-8.63) , (8.40-9.93) (9.89-11 7) ' (11 1-13.2) (12.3-147) (13.5-16.4) (15.2-18.7) (16.6-20.6) 20-day 7.06 8.42 10.2 11.5 13.3 14.8 16.2 17.7 19.8 21.3 . (6.59-7.60) , (7.86-9.05) I (9 46-10.9) ! (10.7-12.4) (12.4-14 3) ' (13 6-15.9) (14.9-17.5) (16.2-19.1) (18.0-21 4) (19.3-23.2) 30-day : 8.67 ! 10.3 12.1 1 13.6 15.4 16.8 18.2 19.5 21.3 22.6 (8.13-9.26) (9.64-11.0) (11 4-13.0) : (12.7-14.5) (14 4-16.4) (15.6-17.9) ' (16.8-19.4) (18.0-20.9) (19.6-22.9) (20.7-24 4) : 45-day ; 10.8 12.8 ' 14.9 16.5 18.5 20.0 21.5 22.9 : 24.7 26.0 (10.2-11.5) : (12.0-13.6) (14.0-15.8) j (15.5-17.5) (17 4-19.7) (18.7-21.3) (20.0-22.8) (21.3-24.4) (22.8-26.4) (24.0-27.9) 60-day : 12 7 14.9 • 17.2 : 18.8 21.0 22.5 24.0 25.4 27.1 28.4 (12.0 13.4) . (141-15.8) (16.2-18.1) ; (178-19.9) (19.8-22.1) . (21.2-23.8) (22.5-25.3) (23.7-26.9) (25.3-28.8) (26.4-30.2) ' 1 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 PDS-based depth-duration-frequency(DDF)curves Latitude: 38.0426°, Longitude:-78.7469° 30 1 r I 1 1 ' t I 1 T 1 - , Average recurrence 25 ', • l t .. intefval • ) c .c '---- - - •-- , — 1 • 2 °'o ' ' — 6 E, 15 , -- ----- -- - , — it) — 26 i1 — 60 -1/45 — 100 °_ — 200 5 --"" : _ — 600 _-t--- '- • 1000 . O -- ■.sess c c c c c .0 . ,c 6. G rr m 43 ro ,v r o r`3 a o r ti E E E E E N1 T kb 4MI -0't7 'fl -ra '3 Duration p `� ' Tr VD 30 _ 1 11 25 .- c c 20t ! 1 — 2-day O 15 /• — 10-min — 3-day '� 15 mat — 4-day a — 7-day 10 - .r = BOtt — 10 deny •°' 2 to — 20-day 5 r — 34v — '30-day — &hr — 45-day O . . i— a .. t _T. — 24-hr 1 2 5 10 25 50 100 200 500 1000 Average recurrence interval (years) NOAA Atlas 14,Volume 2.Version 3 Created(GMT):Wed Jun 20 21:28:21 2018 Back to Top Maps & aerials Small scale terrain Croze t Greenwood!, 'is ' ''' _i_ <: t i, 0 254 s , .' #00 ,, 3km 2m1 Large scale terrain *h; \ .. ' ` .' as l 'tjtOn`i, P; . e \\ Harii°.onbury• .tvim �. V I R ,I N I A I N I A Ric- , 311C r • Lynchburg S — Kock'' • .r. r 100km 1 60mi Al n Large scale map / °1' vlaryl d est l rginia a / xr /NI 7' ' -"*\- / Harrisonburg r,+ram,x , fdalcnal Fcrest 2 f., Staurlan ice. 3eorge / „-- , pps glint. Virginia``^, �4$itTn dr�si tu: l chi + Lynchburg Blacksburg .Roanoke Id i 100km d ..•� i r P 60mi Large scale aerial z z \ _a CCOE1217 _a _a _a OSLZa _a c � M »a MO \ \ @ § e \ / $ § § k § 3 § $ 0 � \ / j �° t5 E § j / I /@ oc. ( ( ) ƒ N / a @ z » / / \® ` $ ^ \ § II \( , i y / < ) `cr., \ ` § k ƒ far§ seven � � . @ ® @{ § � P 2 . { § ? \ g. 4) k / 2 0 01 ) § 2 / zQ ) ) 2 _.0aa _a eMz_a ) _e _a _a _e _a _a § z & N / CO v 00 0 0 0 N N N N a) U O N N a) CO a)' o a' 0 OiL a 00ico w w2 „a) a - 0 a) Z 0co as 0 as O C N a . U O E N O a) E co O_ 03 f6 •_� t0 a)- a) O N a- co co _0 0 O a) as E f6 a) O M 0 U O a w a) m` o co m03 U m C� 0 .Cmflm Z .5n w Q tw a) LQZ Z in 0 '6 f 3 .c 0 c - L N C d 0 0 7 N O 0)N 30 U L O O O m 'a3 0 0 w m O o 5 � r 3 m a) Q Co (a O- O C a t (a ..>'. Co a C L- co re O 'a N N a) 0C CO O `I p �a N c 0 U a O Q >+ Oal >' > Y 0 0 2 a a) C .. a) E O U O a 0 a) T O_ E U (A Z Q o fat a) ai 2 D U --a o co p9 c `00 0. m `�° E 'co � N V a) N 0 a) 5 a. o c a) a� a 003 co o a) o O -a a0i aEi `� a) 0 L. a) c Q 0 a) 0 � EU � � O0nc0 m - > n 0) ma 0 `m cn 1-4 E aomm .0 m � � Q0 `mN Q as smc .0 m m E s 0_ • O 0 0 o U) E ± ~ _ w Z �N � � �CI) as � m rn� cd � � a� E `o 'rn� � a) o c , ac) w oc Xi m � � � � �0c') j0 Q � w � '� O 'C E o v m 'w • co a) y a3 E m 3 o � 'm `o n m •0 E 0 o Os 0 a m N m O O C 0 0 v 0 :) E > 2 Q 0 o O N. z a o yM .` me a0 a) N u) oN13 N U C N O- 0 CO a EM O �O p_ a) m f0 a) a) O Co 0 > .❑ 0 O. •O a) a) 7 0 w _ O a) N C L 7 a) c N C O U a) a) 0 --CD 0 a) O y -c U t w '6 j 'p t0 N p L EO co c t H � w E _ U 0 a E co50 QDQ as H o cncn cn o � 1- U .. 0 FT c N o = U U 0 as QT) .o E U .0 O > Q co m 0 0 O. a CO a O 0 o cis m . >• >0 U U' m c m L > 'a ❑- co o c rn 0 rn c U oc = N 0 V O O N co O (a O fa L .O a) O O a z O` �` N 0 w a' O N N ❑ ` C � N M@ UO 'ou 0 U 0 z in o D Q W ■ ■ ■ 0 A ? a 1 I II 3 co W .J a a) 0o SQ O m G Q co @ 0) O O N c C _ C C O p com- O — O Q 001 0) N co) m O m E c m < a < a m m U 0 ❑ Z rn < a o0 00 U U ❑ Z c a a m [0 c c co so os L Hydrologic Soil Group—Albemarle County,Virginia Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in A01 Percent of AOI 25B Dyke silt loam,2 to 7 B 18.0 75 4% percent slopes 25C Dyke silt loam,7 to 15 B 4 8 20.2% percent slopes 53B Masada loam,2 to 7 B 0.8 3.6% percent slopes 53C Masada loam,7 to 15 B 0.1 0.6% percent slopes 95 Wehadkee silt loam B/D 0 0 0.2% Totals for Area of Interest 23.8 100.0% uNatural Resources Web Soil Survey 4/18/2018 Conservation Service National Cooperative Soil Survey Page 3 of 4 Hydrologic Soil Group—Albemarle County,Virginia 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 (ND, 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 (ND, 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 4/18/2018 210 Conservation Service National Cooperative Soil Survey Page 4 of 4