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HomeMy WebLinkAboutWPO201200087 Study Stormwater Management Plan 2012-10-20For Albemarle Health and Rehabilitation Center Prepared by SHIMP ENGINEERING, PC October 29, 2012 Executive Summary 1Frinafino of p*nrf IFf—�1' This packet contains calculations and details for the stormwater management design for the proposed Albemarle Health and Rehabilitation Center. The report is divided into sections focusing on channel adequacy, lake capacity, and water quality. Relevant reports and calculations by others are attached to the end of this report. Channel Adequacy Summary The analysis concludes that the existing downstream sewer system is adequate to pass additional water from the project for the 10 -year storm. All downstream pipes flow at less than 80% capacity, using conservative estimates for off-site flow. Take Capacity Summary Timmons Engineering designed Hillcrest Lake in 1996 with the Rational Method, but current standards require the TR -55 Method for large areas. The Pre -Development scenario in this report translates the Timmons parameters into TR -55. The 1996 scenario uses the drainage areas and times of concentration determined by Timmons, but uses land cover conditions measured from GIS and projected development of county -owned land. Flows from AHCC can be routed to Hillcrest Lake only if sufficient capacity remains for full development of county -owned lands. The Post-AHCC scenario assumes 70% future impervious cover at the fire station, on the fields behind the high school, and on the parcel between the high school and the shopping center. Stormwater from the AHCC development is also routed to Hillcrest Lake in this scenario. Water Quality Summary Water quality analysis was performed for the entire basin drainage area. The existing basin qualifies as a Detention Basin II with 50% removal efficiency according to the Virginia Stormwater Management Handbook Table 3.06-1. Simple 4 spreadsheets have been provided showing full build -out of the watershed, including AHCC. Pre -Development 1996 Post-AHCC 2 Year 10 Year 2 Year 10 Year 2 Year 10 Year Timmons 97 135 81 118 TR -55 114 313 29 104 42 129 Percent Increase 45% 24% Water Quality Summary Water quality analysis was performed for the entire basin drainage area. The existing basin qualifies as a Detention Basin II with 50% removal efficiency according to the Virginia Stormwater Management Handbook Table 3.06-1. Simple 4 spreadsheets have been provided showing full build -out of the watershed, including AHCC. Channel Adequacy Analysis Stormwater from the project site is proposed to be routed into an existing sewer system underneath Monticello High School's football field. This system serves most of the surrounding catchment, as indicated in the Post-AHCC Drainage Area 5 Detail. The addition of stormwater from AHCC would raise the 10 -year outflow to 135 cfs and the capacity of the system is 160 cfs. Pipe capacities and velocities for the LD -229 worksheets were computed with Visual Urban. Drainage patterns for the high school sewer system underneath the sewer system were obtained from the site plan for Monticello High School. Contents AHCC Storm Sewer Drainage Areas LD -204: AHCC LD -229: AHCC DA -5 Contributing Areas DA -5 Pipe Detail Mill Creek Drive Pipe Detail LD -229: Mill Creek Drive and Monticello High School J AHCC Storm Sewer Drainage Areas f �J ITT - //z 1// Al Drainage Area Boundary Impervious Area Zl- 80 0 80 160 240 SCALE: 1 "=80' LD -204 Stormwater Inlet Computations Inlets on Grade Only Sag Inlets Only Q •� m Q L a CO 4- 0 � E � z Vi Q 0 Q N p N s_ ++ 7 >� C d N N ❑ C^y. CL O U s o ED U) X � c c E r r a c Nc�a aci U Fes- c c a`� aa) > a� B 1° a) a W m a c Q 2 a U) z U U w U c d t� d d 2 C7 aL. (D f°- co o d d U 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) (cfs) ('/') ('/') ('/') (ft) (ft) (cfs) (cfs) (ft) (ft) (ft) STR-1 DI -36 8 0.33 0.47 0.16 4.0 0.626 0.626 0.016 0.053 0.020 0.080 1.9 0.15 100.0% 0.626 0.000 STR-2 DI -313 6 0.25 0.48 0.12 4.0 0.484 0.484 0.016 0.053 0.020 0.080 1.36 0.11 100.0% 0.484 0.000 STR-3 DI -3C 6 0.22 0.72 0.16 4.0 0.631 0.631 0.016 0.016 0.020 0.26 0.5 0.52 4.67 6.5 1.025 1.025 0.30 0.5 0.59 6.45 STR-4 Dl -3C 10 0.40 0.46 018 4.0 0.736 0.168 0.903 0.016 0.034 0.020 0.26 0.5 0.52 4.70 6.5 1.195 0.168 1.363 0.29 0.5 0.59 6.18 STR-5 DI -313 8 0.36 0.48 0.17 4.0 0.684 0.058 0.742 0.016 0.120 0.020 4.04 0.08 77.4% 0.574 0.168 STR-6A DI -36 8 0.49 0.67 0.33 4.0 1.307 1.307 0.016 0.015 0.044 0.30 0.5 0.60 8.92 6.5 2.124 2.124 0.35 0.5 0.70 12.33 STR-66 DI -3C 6 0.20 0.70 0.14 4.0 0.556 0.556 0.016 0.011 0.016 0.25 0.5 0.50 7.80 6.5 0.903 0.903 0.29 0.5 0.57 10.78 STR-6C DI -3C 6 0.72 0.49 0.35 4.0 1.404 1.404 0.016 0.022 0.029 0.33 0.5 0.65 7.23 6.5 2.281 2.281 0.39 0.5 0.77 10.00 STR-7 DI -313 8 0.30 0.58 0.17 4.0 0.685 0.685 0.016 0.046 0.020 4.70 0.09 91.5% 0.627 0.058 STR-86 DI -3C 6 0.44 0.60 0.26 4.0 1.057 1.057 0.016 0.016 0.020 0.30 0.5 0.60 8.23 6.5 1.718 1.718 0.35 0.5 0.70 11.38 STR-8C DI -313 8 0.42 0.64 0.27 4.0 1.071 1.071 0.016 0.030 0.013 0.28 0.5 0.57 9.01 6.5 1.740 1.740 0.33 0.5 0.66 12.45 STR-8D1 DI -1 1.35 0.80 1.08 4.0 4.317 4.317 0.28 0.7 0.40 -- 6.5 7.015 7.015 0.43 0.7 0.61 -- STR-8E DI -313 10 0.45 0.52 0.24 4.0 0.941 0.941 0.016 0.038 0.010 0.26 0.5 0.53 9.66 6.5 1.530 1.530 0.30 0.5 0.60 13.36 STR-8G Yard Drain 0.06 0.30 0.02 4.0 0.07 0.07 STR-81-1 Yard Drain 0.06 0.30 0.02 4.0 0.07 0.07 STR-9 Yard Drain 0.06 0.30 0.02 4.0 0.07 0.07 STR-10 Yard Drain 0.06 0.30 0.02 4.0 0.07 0.07 cn cn cn rrs cn cn cncn [n CO cn Cn U) cn rl3cnCnm o �' -I I -1 A� � 0 X10 � � � -I 707777 E7 -I -A -I � ]]�7J77o 3 1 w al t53 V oo co o0 co co m do co 6 W O Ju (n D W c7 Cj D co n 0 m m 0 m cnwcnmcn!o CI3CnCp (n U) Cn(DCn CnCJJCAC!a Cd3 21CnUscn(n o -� -I � --I � -� -� —i -a -i -I � -I -I � -� -I -i -i -i m - -1 m 70 77 77 77 rE1 T � 3] 77 70 M M M M 11 77 31 77 N o p • lv CO 4� (A 6, qms 6 6 €O 00 co cop () q a R1 � 2 � p^t D C7 n w 0 0 0 0 0 O O O O 000 0 0 _ O 000 v j co N N •4+ W A N V W O W .p A W A O O 0 W S W th N CD m w O N0 m [3) W 2 -F N (nm G73 a) ca n m O C CD 0 0 0 Cl C7 0 0.7 O O 0 O Cm O 0 C3 G O O CD 0 A A V A A m V A cn W W m m m 00 (P. co co w A V commm VC) 0 CO OGO OA 0 N aCD0 00 OCiOOO OPO O Poo OO _ O 000 . j 11 ft��o1 W — O2 V NN O Na OO V. mNmfb V W A C)'t V N cn m V m A N m 0 n � n (P W A A A A 9O Q W O O O N Nc7}� N N + O O O O N {W N � m m 3 CO A V C) N (D Cn tt'i m (n C.0 W V 0 m N co V(A CC.) 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'� I I ' 90 f C=0.6 I C=0.6 I C=0.4 % ~ �r0.88 Ac. _ 1 C=0.3 94 �t I 0,56 A,. I I t -.4 . C=0_6 � Ole • 92 1.15 kc. ������Iilr•��• ~� �� 200 0 200 400 600 \ SCALE; 1 "=200' a A` r+ 3 Q CQ 0 rr O Cf) O p GaL Cr.', -_ ^� C: CD A` r+ 3 Q CQ 0 W 0 n C14 0 I I CIO 0 o � 0 Q -u o0 0 co 41 m 0 to 0 > (D C,) cl) 0 3 > 0 Co 00 00 00 Co f& — 41, — 0 C-) 0 CDOD00 CD OQ M 4� PO C) C) 000 0 7- > 0 0 4b, 0 0 0 0 0 -4 0) rQ ca lt� il) O'l CD O 0) 0) — ca ca 0 PO C) co 0 m 0 C: 0 CP P O0 0 CP p c:> a :3 .1b, 0 ca Ir. 0) 8 �i .0 *1 0 4 0 CD tn 0 C.4 WM CG:)) > to w Q W UeC) JA6) K) ai 4. NN N) 'ra 0 co ro :N '-4 0 (n m 0) (n co -4 0 ca W 0 tD w C�, FO co 07 CO 0 WCJ1: p 0 0 cn 0 Oo co N) 0) 4, cn o C:) 41, (M 3 N2 OD 0 1 0 1 PO p m W N) w 0 c:, 0 cn N(A 0 NW 0 0 N" 0 0 0 -4 V. 6 0) Cn A (n 41. pl 41 0) A m 4$1 al P.. -A, A 7P. pl (P OD ro m CS m N) CA --4 V O K) K) N m- co 6 --4 P j� P CO Ui m co m to O 0 O 0, W -4 — . 0) Ln -4 rn cz < o) -4 -j (0 K) (0 0 00 cn 0) �4 4 < :3 C-04 -4 co d O GcpD NJ m N a roC> :3 CD co 8 4 �O �O C> m CID W 0-0 (J) < 4 -4 P. N oo 03 i'O co m co CD 0 -0 -, w M K)CD O Cc, CD 0 N.) 4 ca C) 0 O C) 0 O O :_ ro C) IL. 3 CD Lake Capacity Analysis Timmons Engineering designed Hillcrest Lake in 1996 with the Rational Method, but current standards require the TR -55 Method for large areas. The Pre -Development scenario translates the Timmons parameters into TR -55. Current calculations retain Timmons' values for times of concentration and overall area. Impervious area was extrapolated using the formula: A, CTAT — CpAT _ C, —Cp Where: A, = Impervious Area AT = Total Area C, = Impervious C -factor Cp = Pervious C -factor CT = Total C -factor Pervious cover was assumed to be on soils of the same hydrologic group as the latest NRCS soil survey. The 1996 scenario uses the drainage areas and times of concentration determined by Timmons. On the map, all drainage areas were measured to match the values provided by Timmons except DA -5, which measured a few acres larger. Current calculations employ the larger, more conservative number. Additionally, the boundary between DA -5 and DA -3 was adjusted to reflect actual as -built conditions as observed in a field inspection. Land cover conditions for this analysis were measured from GIS and satellite imagery. This analysis assumes full development of the same county -owned land that Timmons projected for future build -out. The Post-AHCC scenario routes the AHCC development to Hillcrest Lake and assumes future development of existing fields behind Monticello High School. The "Post-AHCC" scenario quantifies the impact on Hillcrest Lake of the proposed AHCC development. Approximately four additional acres will flow into the lake. Furthermore, this scenario includes full development of the fields behind Monticello High School. Pre -Development 1996 Post-AHCC 2 Year 10 Year 2 Year 10 Year 2 Year 10 Year Timmons 97 135 81 118 TR -55 114 313 29 104 42 129 Percent Increase 45% 24% Timmons Engineering designed Hillcrest Lake in 1996 with the Rational Method, but current standards require the TR -55 Method for large areas. The Pre -Development scenario translates the Timmons parameters into TR -55. Current calculations retain Timmons' values for times of concentration and overall area. Impervious area was extrapolated using the formula: A, CTAT — CpAT _ C, —Cp Where: A, = Impervious Area AT = Total Area C, = Impervious C -factor Cp = Pervious C -factor CT = Total C -factor Pervious cover was assumed to be on soils of the same hydrologic group as the latest NRCS soil survey. The 1996 scenario uses the drainage areas and times of concentration determined by Timmons. On the map, all drainage areas were measured to match the values provided by Timmons except DA -5, which measured a few acres larger. Current calculations employ the larger, more conservative number. Additionally, the boundary between DA -5 and DA -3 was adjusted to reflect actual as -built conditions as observed in a field inspection. Land cover conditions for this analysis were measured from GIS and satellite imagery. This analysis assumes full development of the same county -owned land that Timmons projected for future build -out. The Post-AHCC scenario routes the AHCC development to Hillcrest Lake and assumes future development of existing fields behind Monticello High School. The "Post-AHCC" scenario quantifies the impact on Hillcrest Lake of the proposed AHCC development. Approximately four additional acres will flow into the lake. Furthermore, this scenario includes full development of the fields behind Monticello High School. The DA -5 sub -areas used in the SWM analysis are different than the sub -areas used in the channel adequacy analysis. For the channel adequacy analysis, sub -areas were determined by flow patterns, and the area that drains directly to the lake was omitted. For the SWM analysis, sub -areas were determined by parcel boundaries. Notes A field survey of the dam and concrete spillway was performed by Roger Ray and Associates. Routing calculations are based on as -built conditions. In the Post-AHCC HydroCAD model, DA -5 is modeled separately, and the results are imported to the overall basin model through a "link" in the software. Pre -Development Drainage Map HydroCAD Report Lake Basin 1996 Drainage Details HydroCAD Report Post-AHCC DA -5 Drainage Details DA -5 HydroCAD Report Lake Basin HydroCAD Report Pre—Development Drainage r Timmons C-0.37 i Extrapolated CN=6 ► w ToC_=1 .5 m in. . , k i .. DA 2 +' D�-3 i 47 Ac. ,f,�40 Ac. . 4 nmons' C=0.25. Timmons' C= ".35 Extra of a ted C> J —67, Extrapolated CIS E pTcrC=25.0 min. ToC=30.5 mit) Pre—Development Drainage Boundaries 400 0 400 800 1200 M 0 M 0 0 SCALE: I • 1994 Satellite Image Provided by Google Earth EX -2 \SubcajlReach on ,7 ake Location Link 3 EX -3 Lake Basin Pre-Dev Type 1124 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCADO 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 1: EX -1 Runoff = 79.99 cfs @ 12.09 hrs, Volume= 5.781 af, Depth> 0.89" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 9.330 98 63.000 60 Woods, Fair, HSG B 5.700 74 >75% Grass cover, Good, HSG C 78.030 66 Weighted Average 68.700 88.04% Pervious Area 9.330 11.96% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.5 Direct Entry, Summary for Subcatchment 2: EX -2 Runoff = 33.31 cfs @ 12.30 hrs, Volume= 3.667 af, Depth> 0.94" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 23.500 60 Woods, Fair, HSG B 23.500 73 Woods, Fair, HSG C 47.000 67 Weighted Average 47.000 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 30.5 Direct Entry, Summary for Subcatchment 3: EX -3 Runoff = 17.04 cfs @ 12.25 hrs, Volume= 1.998 af, Depth> 0.60" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 40.000 60 Woods, Fair, HSG B 40.000 100.00% Pervious Area Lake Basin Pre-Dev Type 1124 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCADO 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Paae 3 Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 25.0 Direct Entry, Summary for Pond 7: Lake Location [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 165.030 ac, 5.65% Impervious, Inflow Depth > 0.83" for 2yr event Inflow = 113.40 cfs @ 12.13 hrs, Volume= 11.445 of Primary = 113.40 cfs @ 12.13 hrs, Volume= 11.445 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Lake Basin Pre-Dev Type 1124 -hr 10yr Rainfal1=5.55" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCAD® 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment 1: EX -1 Runoff = 206.26 cfs @ 12.08 hrs, Volume= 13.668 af, Depth> 2.10" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 9.330 98 63.000 60 Woods, Fair, HSG B 5.700 74 >75% Grass cover, Good, HSG C 78.030 66 Weighted Average 68.700 88.04% Pervious Area 9.330 11.96% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 15.5 Direct Entry, Summary for Subcatchment 2: EX -2 Runoff = 85.62 cfs @ 12.26 hrs, Volume= 8.518 af, Depth> 2.17" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 23.500 60 Woods, Fair, HSG B 23.500 73 Woods, Fair, HSG C 47.000 67 Weighted Average 47.000 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 30.5 Direct Entry, Summary for Subcatchment 3: EX -3 Runoff = 58.44 cfs @ 12.20 hrs, Volume= 5.397 af, Depth> 1.62" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) ON Description 40.000 60 Woods, Fair, HSG B 40.000 100.00% Pervious Area Lake Basin Pre-Dev Type 1124 -hr 1Oyr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCADO 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 5 Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 25.0 Direct Entry, Summary for Pond 7: Lake Location [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 165.030 ac, 5.65% Impervious, Inflow Depth > 2.01" for 10yr event Inflow = 312.71 cfs @ 12.11 hrs, Volume= 27.582 of Primary = 312.71 cfs @ 12.11 hrs, Volume= 27.582 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Lake Basin 1996 j DA -1 1 -DA,-2 DA -6 I t DA- 6 f� Mop -j nl E •� it " DA -3 JJ • ' 10007. WON �. f 000woo woo 400 0 400 800 121 40• Drainage Details Drainage Details ID Area (ac.) ToC (min.) Impervious Grass Woods Lake County Land* Building Road 1 22.609 16.8 0.316 13.759 4.305 4.229 2 9.122 12.0 1.679 0.848 4.649 1.946 3 46.607 25.5 1.866 7.524 33.255 3.863 0.099 5.152 4 1.956 11.0 0.194 1.382 0.380 5 58.387 17.0 2.144 11.126 15.335 13.392 16.390 6 36.513 7.37 2.717 9.160 13.739 2.199 6.155 2.543 *Assume Ultimate Build -out with 70% Total Impervious DA -X: Watershed Sub -Areas L --- J County Land to be Developed Outfall annel DA -1 f DA -2 Lake DA -4 DA -5 DA -3 ,,Subca lReach on Linki Drainage Diagram for Lake Basin 1996 Prepared by Shimp Engineering, P.C., Printed 8/24/2012 HydroCADO 9.10 s/n 07054 @ 2011 HydroCAD Software Solutions LLC Lake Basin 1996 Type// 24 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCAD@ 9.10 s/n 07054 @2011 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 1: DA -1 Runoff = 25.57 cfs @ 12.11 hrs, Volume= 1.875 af, Depth> 1.00" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 0.316 98 Paved parking, HSG B 4.229 98 Water Surface, HSG B 13.759 61 >75% Grass cover, Good, HSG B 3.858 55 Woods, Good, HSG B 0.447 70 Woods, Good, HSG C 22.609 68 Weighted Average 18.064 71 79.90% Pervious Area 4.545 20.10% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 16.8 Direct Entry, Summary for Subcatchment 2: DA -2 Runoff = 14.88 cfs @ 12.05 hrs, Volume= 0.888 af, Depth> 1.17" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 1.679 98 Roofs, HSG B 0.848 98 Paved parking, HSG B 4.182 61 >75% Grass cover, Good, HSG B 0.467 74 >75% Grass cover, Good, HSG C 1.691 55 Woods, Good, HSG B 0.255 70 Woods, Good, HSG C 9.122 71 Weighted Average 6.595 72.30% Pervious Area 2.527 27.70% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 12.0 Direct Entry, Summary for Subcatchment 3: DA -3 Runoff = 58.68 cfs @ 12.21 hrs, Volume= 5.233 af, Depth> 1.35" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type 11 24 -hr 2yr Rainfall=3.67" Lake Basin 1996 Type 11 24 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCADO 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Pa ece33 Area (ac) CN Description 1.866 98 Roofs, HSG B 7.524 98 Paved parking, HSG B 0.099 98 Water Surface, HSG B 20.460 61 >75% Grass cover, Good, HSG B 6.199 74 >75% Grass cover, Good, HSG C 1.444 80 >75% Grass cover, Good, HSG D 2.331 55 Woods, Good, HSG B 1.532 70 Woods, Good, HSG C 3.606 98 County Development 1.546 74 County Open Space 46.607 74 Weighted Average 33.512 71.90% Pervious Area 13.095 28.10% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 25.5 Direct Entry, Summary for Subcatchment 4: DA -4 Runoff = 3.51 cfs @ 12.04 hrs, Volume= 0.200 af, Depth> 1.23" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 0.380 98 Water Surface, HSG B 0.194 61 >75% Grass cover, Good, HSG B 0.315 55 Woods, Good, HSG B 1.06_7_ 70 Woods, Good, HSG C 1.956 72 Weighted Average 1.576 80.57% Pervious Area 0.380 19.43% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 11.0 Direct Entry, Summary for Subcatchment 5: DA -5 Runoff = 125.53 cfs @ 12.10 hrs, Volume= 8.582 af, Depth> 1.76" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type 11 24 -hr 2yr Rainfall=3.67" Lake Basin 1996 Type 1124-hr2yr Rainfall=3.67' Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCADO 9.10 s/n 07054 @2011 HydroCAD Software Solutions LLC Page 4 Area (ac) CN Descriotion 2.144 98 Roofs, HSG B 11.126 98 Paved parking, HSG B 8.619 61 >75% Grass cover, Good, HSG B 4.760 74 >75% Grass cover, Good, HSG C 1.956 80 >75% Grass cover, Good, HSG D 7.975 55 Woods, Good, HSG B 4.721 70 Woods, Good, HSG C 0.696 77 Woods, Good, HSG D 11.473 98 County Development 4.917 74 County Open Space 58.387 80 Weighted Average 33.644 57.62% Pervious Area 24.743 42.38% Impervious Area Tc Length Slope Velocity Capacity Description _ (min) (feet) (ft/ft) (ft/sec) (cfs) 17.0 Direct Entry, Summary for Subcatchment 6: DA -6 Runoff = 143.79 cfs Ca) 11.99 hrs, Volume= 7.140 at, Depth> 2.25' Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 2.717 98 Roofs, HSG B 9.192 98 Roofs, HSG B 6.155 98 Water Surface, HSG B 1.584 61 >75% Grass cover, Good, HSG B 12.296 74 >75% Grass cover, Good, HSG C 1.469 80 >75% Grass cover, Good, HSG D 0.851 55 Woods, Good, HSG B 1.349 70 Woods, Good, HSG C 1.780 98 County Development 0.763 74 County Open Space 38.156 86 Weighted Average 18.312 47.99% Pervious Area 19.844 52.01% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.3 Direct Entry, Lake Basin 1996 Type 1124 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 8/29/2012 HydroCAD® 9.10 s/n 07054 @2011 HydroCAD Software Solutions LLC Page 1 Summary for Pond 7: Lake Inflow Area = 176.837 ac, 36.83% Impervious, Inflow Depth > 1.62" for 2yr event Inflow = 304.94 cfs @ 12.03 hrs, Volume= 23.920 of Outflow = 28.89 cfs @ 13.21 hrs, Volume= 15.579 af, Atten= 91 %, Lag= 70.9 min Primary = 28.89 cfs @ 13.21 hrs, Volume= 15.579 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 456.77'9 13.21 hrs Surf.Area= 10.465 ac Storage= 12.826 of Plug -Flow detention time= 269.7 min calculated for 15.579 of (65% of inflow) Center -of -Mass det. time= 157.9 min ( 999.1 - 841.2) Volume Invert Avail.Storage Storage Description #1 455.50' 55.550 of Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (acres) (acre-feet) (acre-feet) 455.50 9.803 0.000 0.000 460.50 12.417 55.550 55.550 Device Routing Invert Outlet Devices #1 Primary 456.05' 17.9' long x 22.0' breadth Broad -Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 rimary OutFlow Max=28.89 cfs @ 13.21 hrs HW=456.77' TW=453.35' (Dynamic Tailwater) 1=13road-Crested Rectangular Weir (Weir Controls 28.89 cfs @ 2.25 fps) Summary for Reach 8: Outfall Channel Inflow Area = 176.837 ac, 36.83% Impervious, Inflow Depth > 1.06" for 2yr event Inflow = 28.89 cfs @ 13.21 hrs, Volume= 15.579 of Outflow = 28.89 cfs @ 13.21 hrs, Volume= 15.573 af, Atten= 0%, Lag= 0.2 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Max. Velocity= 13.30 fps, Min. Travel Time= 0.3 min Avg. Velocity = 10.27 fps, Avg. Travel Time= 0.4 min Peak Storage= 597 cf Co) 13.21 hrs Average Depth at Peak Storage= 0.21' Bank -Full Depth= 2.40', Capacity at Bank -Full= 1,984.58 cfs 10.00' x 2.40' deep channel, n= 0.013 Side Slope Z -value= 2.07' Top Width= 19.60' Length= 275.0' Slope= 0.1165 '/' Inlet Invert= 453.14', Outlet Invert= 421.09' Lake Basin 1996 Type 11 24 -hr 2yr Rainfall=3.67' Prepared by Shimp Engineering, P.C. Printed 8/29/2012 HydroCAD® 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 2 Lake Basin 1996 Type 1124 -hr 10yr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCADOO 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 6 Summary for Subcatchment 1: DA -1 Runoff = 62.27 cfs @ 12.10 hrs, Volume= 4.275 af, Depth> 2.27" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 0.316 98 Paved parking, HSG B 4.229 98 Water Surface, HSG B 13.759 61 >75% Grass cover, Good, HSG B 3.858 55 Woods, Good, HSG B 0.447 70 Woods, Good, HSG C 22.609 68 Weighted Average 18.064 71 79.90% Pervious Area 4.545 20.10% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 16.8 Direct Entry, Summary for Subcatchment 2: DA -2 Runoff = 33.27 cfs @ 12.04 hrs, Volume= 1.925 af, Depth> 2.53" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rai nfall=5.55" Area (ac) CN Descriotion 1.679 98 Roofs, HSG B 0.848 98 Paved parking, HSG B 4.182 61 >75% Grass cover, Good, HSG B 0.467 74 >75% Grass cover, Good, HSG C 1.691 55 Woods, Good, HSG B _ 0.255 70 Woods, Good, HSG C 9.122 71 Weighted Average 6.595 72.30% Pervious Area 2.527 27.70% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 12.0 Direct Entry, Summary for Subcatchment 3: DA -3 Runoff = 125.41 cfs @ 12.19 hrs, Volume= 10.838 af, Depth> 2.79" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type 11 24 -hr 10yr Rainfall=5.55" Lake Basin 1996 Type 1124 -hr 1Oyr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCADOO 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 7 Area (ac) CN Description 1.866 98 Roofs, HSG B 7.524 98 Paved parking, HSG B 0.099 98 Water Surface, HSG B 20.460 61 >75% Grass cover, Good, HSG B 6.199 74 >75% Grass cover, Good, HSG C 1.444 80 >75% Grass cover, Good, HSG D 2.331 55 Woods, Good, HSG B 1.532 70 Woods, Good, HSG C 3.606 98 County Development 1.546 74 County Open Space 46.607 74 Weighted Average 33.512 71.90% Pervious Area 13.095 28.10% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 25.5 Direct Entry, Summary for Subcatchment 4: DA -4 Runoff = 7.65 cfs @ 12.03 hrs, Volume= 0.427 af, Depth> 2.62" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 0.380 98 Water Surface, HSG B 0.194 61 >75% Grass cover, Good, HSG B 0.315 55 Woods, Good, HSG B 1.067 70 Woods, Good, HSG C 1.956 72 Weighted Average 1.576 80.57% Pervious Area 0.380 19.43% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 11.0 Direct Entry, Summary for Subcatchment 5: DA -5 Runoff = 239.11 cfs @ 12.09 hrs, Volume= 16.366 af, Depth> 3.36" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type 11 24 -hr 10yr Rainfall=5.55" Lake Basin 1996 Type 1124 -hr 10yr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 8/24/2012 HydroCAD@ 9.10 s/n 07054 @2011 HydroCAD Software Solutions LLC Page 8 Area (ac) CN Description 2.144 98 Roofs, HSG B 11.126 98 Paved parking, HSG B 8.619 61 >75% Grass cover, Good, HSG B 4.760 74 >75% Grass cover, Good, HSG C 1.956 80 >75% Grass cover, Good, HSG D 7.975 55 Woods, Good, HSG B 4.721 70 Woods, Good, HSG C 0.696 77 Woods, Good, HSG D 11.473 98 County Development 4.917 74 County Open Space 58.387 80 Weighted Average 33.644 57.62% Pervious Area 24.743 42.38% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 17.0 Direct Entry, Summary for Subcatchment 6: DA -6 Runoff = 247.63 cfs @ 11.98 hrs, Volume= 12.646 at, Depth> 3.98" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 2.717 98 Roofs, HSG B 9.192 98 Roofs, HSG B 6.155 98 Water Surface, HSG B 1.584 61 >75% Grass cover, Good, HSG B 12.296 74 >75% Grass cover, Good, HSG C 1.469 80 >75% Grass cover, Good, HSG D 0.851 55 Woods, Good, HSG B 1.349 70 Woods, Good, HSG C 1.780 98 County Development 0.763 74 County Open Space 38.156 86 Weighted Average 18.312 47.99% Pervious Area 19.844 52.01% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.3 Direct Entry, Lake Basin 1996 Type 1124 -hr 10yr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 8/29/2012 HydroCAD® 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 3 Summary for Pond 7: Lake Inflow Area = 176.837 ac, 36.83% Impervious, Inflow Depth > 3.15" for 10yr event Inflow = 596.38 cfs @ 12.03 hrs, Volume= 46.477 of Outflow = 103.77 cfs @ 12.64 hrs, Volume= 37.004 af, Atten= 83%, Lag= 36.3 min Primary = 103.77 cfs @ 12.64 hrs, Volume= 37.004 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 457.74'@ 12.64 hrs Surf.Area= 10.976 ac Storage= 23.311 of Plug -Flow detention time= 204.3 min calculated for 37.004 of (80% of inflow) Center -of -Mass det. time= 122.0 min ( 945.7 - 823.7) Volume Invert Avail.Storage Storage Description #1 455.50' 55.550 of Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (acres) (acre-feet) (acre-feet) 455.50 9.803 0.000 0.000 460.50 12.417 55.550 55.550 Device Routing Invert Outlet Devices #1 Primary 456.05' 17.9' long x 22.0' breadth Broad -Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 rimary OutFlow Max=103.77 cfs @ 12.64 hrs HW=457.74' TW=453.59' (Dynamic Tailwater) 1=13road-Crested Rectangular Weir (Weir Controls 103.77 cfs @ 3.42 fps) Summary for Reach 8: Outfall Channel Inflow Area = 176.837 ac, 36.83% Impervious, Inflow Depth > 2.51" for 10yr event Inflow = 103.77 cfs @ 12.64 hrs, Volume= 37.004 of Outflow = 103.77 cfs @ 12.64 hrs, Volume= 36.996 af, Atten= 0%, Lag= 0.1 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Max. Velocity= 21.37 fps, Min. Travel Time= 0.2 min Avg. Velocity = 13.69 fps, Avg. Travel Time= 0.3 min Peak Storage= 1,336 cf @ 12.64 hrs Average Depth at Peak Storage= 0.45' Bank -Full Depth= 2.40', Capacity at Bank -Full= 1,984.58 cfs 10.00' x 2.40' deep channel, n= 0.013 Side Slope Z -value= 2.07' Top Width= 19.60' Length= 275.0' Slope= 0.1165 '/' Inlet Invert= 453.14', Outlet Invert= 421.09' Lake Basin 1996 Type 1124 -hr 1 Dyr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 8/29/2012 HydroCAD® 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 4 Lake Basin 1996 Type // 24 -hr f 00yr Rainfall=9.13" Prepared by Shimp Engineering, P.C. Printed 8/29/2012 HydroCAD® 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 5 Summary for Pond 7: Lake Inflow Area = 176.837 ac, 36.83% Impervious, Inflow Depth > 6.37" for 1 00y event Inflow = 1,188.53 cfs @ 12.03 hrs, Volume= 93.898 of Outflow = 310.81 cfs @ 12.47 hrs, Volume= 82.698 af, Atten= 74%, Lag= 26.0 min Primary = 310.81 cfs @ 12.47 hrs, Volume= 82.698 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 459.57'@ 12.47 hrs Surf.Area= 11.930 ac Storage= 44.220 of Plug -Flow detention time= 157.3 min calculated for 82.698 of (88% of inflow) Center -of -Mass det. time= 100.2 min ( 905.4 - 805.2) Volume Invert Avail.Storage Storage Description #1 455.50' 55.550 of Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (acres) (acre-feet) (acre-feet) 455.50 9.803 0.000 0.000 460.50 12.417 55.550 55.550 Device Routing Invert Outlet Devices #1 Primary 456.05' 17.9' long x 22.0' breadth Broad -Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 Primary OutFlow Max=310.80 cfs @ 12.47 hrs HW=459.57' TW=453.99' (Dynamic Tailwater) t 1=Broad-Crested Rectangular Weir (Weir Controls 310.80 cfs @ 4.93 fps) Summary for Reach 8: Outfall Channel Inflow Area = 176.837 ac, 36.83% Impervious, Inflow Depth > 5.61" for 1 00y event Inflow = 310.81 cfs @ 12.47 hrs, Volume= 82.698 of Outflow = 310.81 cfs @ 12.47 hrs, Volume= 82.687 af, Atten= 0%, Lag= 0.1 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Max. Velocity= 31.33 fps, Min. Travel Time= 0.1 min Avg. Velocity = 16.76 fps, Avg. Travel Time= 0.3 min Peak Storage= 2,728 cf @ 12.47 hrs Average Depth at Peak Storage= 0.85' Bank -Full Depth= 2.40', Capacity at Bank -Full= 1,984.58 cfs 10.00' x 2.40' deep channel, n= 0.013 Side Slope Z -value= 2.07' Top Width= 19.60' Length= 275.0' Slope= 0.1165 '/' Inlet Invert= 453.14', Outlet Invert= 421.09' Lake Basin 1996 Type 1124 -hr 1 00y Rainfall=9.13" Prepared by Shimp Engineering, P.C. Printed 8/29/2012 HydroCAD® 9.10 s/n 07054 © 2011 HydroCAD Software Solutions LLC Page 6 Post-AHCC Calculations This section begins with a map of DA -5 with the proposed AHCC development. The HydroCAD report for DA -5 follows. The last item in this section is the HydroCAD report for the Hillcrest Lake basin after AHCC is developed. The two HydroCAD reports are linked through the software. Drainage areas 2, 3, 4, and 6 are the same in the Post-AHCC scenario as in the 1996 scenario, so they are not duplicated in this section. Drainage area 1 is modified for projected development of land owned by the School Board. DA5 Drainage Details Drainage Details ID Area (ac.) ToC (min.) Impervious Grass Woods County Land* Building Road High School 12.569 7.0 0.316 3.842 5.971 2.440 Fire Station 16.390 20.0 16.390 AHCC 7.132 9.7 1.749 2.574 2.809 ACSA 9.372 25.0 0.147 1.070 8.155 Remainder 17.272 17.0 1.646 7.248 5.691 2.687 *Assume Ultimate Build—out with 70% Total Impervious —..�..— B r -, c-., L___J County Land to be Developed 00 • 200 400 601 SCALE: 1 00 ACSA �Subcat`%Reach on Link 1 High School AHCC b..4 f Fire Station Remainder -` t spat -J ACSA �Subcat`%Reach on Link 1 High School AHCC b..4 f Fire Station DA -5 Post-AHCC Type// 24 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCAD® 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 1: High School Runoff = 30.81 cfs @ 11.99 hrs, Volume= 1.488 af, Depth> 1.42" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 0.316 98 Roofs, HSG B 3.842 98 Paved parking, HSG B 4.637 61 >75% Grass cover, Good, HSG B 1.334 74 >75% Grass cover, Good, HSG C 0.929 55 Woods, Good, HSG B 1.511 70 Woods, Good, HSG C 12.569 75 Weighted Average 8.411 66.92% Pervious Area 4.158 33.08% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.0 Direct Entry, Summary for Subcatchment 2: Fire Station Runoff = 48.29 cfs @ 12.11 hrs, Volume= 3.675 af, Depth> 2.69" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description * 11.473 98 Ultimate Build -Out * 4.917 74 Future Open Space 16.390 91 Weighted Average 4.917 30.00% Pervious Area 11.473 70.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 20.0 Direct Entry, Summary for Subcatchment 3: AHCC Runoff = 27.19 cfs @ 12.01 hrs, Volume= 1.491 af, Depth> 2.51" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type 11 24 -hr 2yr Rainfall=3.67" DA -5 Post-AHCC Type 11 24 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCAD® 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Page 3 Area (ac) CN Description 1.749 98 Roofs, HSG B 2.574 98 Paved parking, HSG B 2.809 74 >75% Grass cover, Good, HSG C 7.132 89 Weighted Average 2.809 60 39.39% Pervious Area 4.323 55 60.61% Impervious Area Tc Length Slope Velocity Capacity Description 9.7 Runoff = Direct Entry, Summary for Subcatchment 4: ACSA 3.99 cfs @ 12.25 hrs, Volume= 0.468 af, Depth> 0.60" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 0.147 98 Roofs, HSG B 1.070 69 50-75% Grass cover, Fair, HSG B 6.286 55 Woods, Good, HSG B 1.869 70 Woods, Good, HSG C 9.372 60 Weighted Average 9.225 55 98.43% Pervious Area 0.147 70 1.57% Impervious Area Tc Length Slope Velocity Capacity Description 25.0 Runoff = Direct Entry, Summary for Subcatchment 5: Remainder 70.58 cfs @ 11.96 hrs, Volume= 3.234 af, Depth> 2.25" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 1.646 98 Roofs, HSG B 7.248 98 Paved parking, HSG B 0.687 61 >75% Grass cover, Good, HSG B 3.048 74 >75% Grass cover, Good, HSG C 1.956 80 >75% Grass cover, Good, HSG D 0.704 55 Woods, Good, HSG B 1.287 70 Woods, Good, HSG C 0.696 77 Woods, Good, HSG D 17.272 86 Weighted Average 8.378 48.51 % Pervious Area 8.894 51.49% Impervious Area DA -5 Post-AHCC Type// 24 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCADO 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Page 4 Tc Length Slope Velocity Capacity Description 5.0 Direct Entry, Summary for Link 6: DA -5 Inflow Area = 62.735 ac, 46.22% Impervious, Inflow Depth > 1.98" for 2yr event Inflow = 155.98 cfs @ 11.98 hrs, Volume= 10.356 of Primary = 155.98 cfs @ 11.98 hrs, Volume= 10.356 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs DA -5 Post-AHCC Type 1124 -hr 10yr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCAD® 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment 1: High School Runoff = 62.66 cfs @ 11.99 hrs, Volume= 3.034 af, Depth> 2.90" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 0.316 98 Roofs, HSG B 3.842 98 Paved parking, HSG B 4.637 61 >75% Grass cover, Good, HSG B 1.334 74 >75% Grass cover, Good, HSG C 0.929 55 Woods, Good, HSG B 1.511 70 Woods, Good, HSG C 12.569 75 Weighted Average 8.411 66.92% Pervious Area 4.158 33.08% Impervious Area Tc Length Slope Velocity Capacity Description _ (min) (feet) (ft/ft) (ft/sec) (cfs) 7.0 Direct Entry, Summary for Subcatchment 2: Fire Station Runoff = 78.82 cfs @ 12.11 hrs, Volume= 6.145 af, Depth> 4.50" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description * 11.473 98 Ultimate Build -Out * 4.917 74 Future Open Space 16.390 91 Weighted Average 4.917 30.00% Pervious Area 11.473 70.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 20.0 Direct Entry, Summary for Subcatchment 3: AHCC Runoff = 45.16 cfs @ 12.01 hrs, Volume= 2.551 af, Depth> 4.29" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type 11 24 -hr 10yr Rainfall=5.55" DA -5 Post-AHCC Type// 24 -hr 10yr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 _HydroCAD® 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Page 6 Area (ac) CN Description 1.749 98 Roofs, HSG B 2.574 98 Paved parking, HSG B 2.809 74 >75% Grass cover, Good, HSG C 7.132 89 Weighted Average 2.809 60 39.39% Pervious Area 4.323 55 60.61 % Impervious Area Tc Length Slope Vel min) (feet) (ft/ft) (ft 9.7 Capacity Description Direct Entry, Summary for Subcatchment 4: ACSA Runoff = 13.69 cfs @ 12.20 hrs, Volume= 1.264 af, Depth> 1.62" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 0.147 98 Roofs, HSG B 1.070 69 50-75% Grass cover, Fair, HSG B 6.286 55 Woods, Good, HSG B 1.869 70 Woods, Good, HSG C 9.372 60 Weighted Average 9.225 55 98.43% Pervious Area 0.147 70 1.57% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 25.0 Direct Entry, Summary for Subcatchment 5: Remainder Runoff = 121,15 cfs @ 11.96 hrs, Volume= 5.727 af, Depth> 3.98" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 1.646 98 Roofs, HSG B 7.248 98 Paved parking, HSG B 0.687 61 >75% Grass cover, Good, HSG B 3.048 74 >75% Grass cover, Good, HSG C 1.956 80 >75% Grass cover, Good, HSG D 0.704 55 Woods, Good, HSG B 1.287 70 Woods, Good, HSG C 0.696 77 Woods, Good, HSG D 17.272 86 Weighted Average 8.378 48.51 % Pervious Area 8.894 51.49% Impervious Area DA -5 Post-AHCC Prepared by Shimp Engineering, P.C. HVdroCADO 9.10 s/n 07054 © 2010 HAro( Tc Length Slope Velocity iin) (feet) (ft/ft) (ft/sec) 5.0 Solutions I Description Direct Entry, Summary for Link 6: DA -5 Type 11 24 -hr 10yr Rainfall=5.55" Printed 10/29/2012 Inflow Area = 62.735 ac, 46.22% Impervious, Inflow Depth > 3.58" for 10yr event Inflow = 278.01 cfs @ 11.98 hrs, Volume= 18.722 of Primary = 278.01 cfs @ 11.98 hrs, Volume= 18.722 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs 4 Outfall annel tore DA -1 e �i �T--ate............., �' Ff *• � , t DA -2 Lake DA -4 I, e DA -5 DA -3 'Isubcat, Reach, oft Link, Drainage Diagram for Lake Basin Post-AHCC __._; yam., Prepared by Shimp Engineering, P.C., Printed 10/29/2012 - - HydroCAD® 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Lake Basin Post-AHCC Type// 24 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCAD® 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Page 2 Summary for Subcatchment 1: Future DA -1 Runoff = 62.02 cfs @ 12.09 hrs, Volume= 4.221 af, Depth> 2.24" Runoff by SCS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 2yr Rainfall=3.67" Area (ac) CN Description 4.229 98 Water Surface, HSG B 0.555 61 >75% Grass cover, Good, HSG B 1.128 55 Woods, Good, HSG B 0.399 70 Woods, Good, HSG C * 11.408 98 Future Development * 4.889 61 Future Open Space 22.608 86 Weighted Average 6.971 30.83% Pervious Area 15.637 69.17% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 16.8 Direct Entry, Summary for Pond 7: Lake Inflow Area = 181.184 ac, 44.42% Impervious, Inflow Depth > 1.86" for 2yr event Inflow = 387.12 cfs @ 12.00 hrs, Volume= 28.039 of Outflow = 41.76 cfs @ 12.88 hrs, Volume= 19.542 af, Atten= 89%, Lag= 52.9 min Primary = 41.76 cfs @ 12.88 hrs, Volume= 19.542 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 456.97'@ 12.88 hrs Surf.Area= 10.573 ac Storage= 14.999 of Plug -Flow detention time= 252.4 min calculated for 19.534 of (70% of inflow) Center -of -Mass det. time= 149.7 min ( 977.3 - 827.6) Volume Invert Avail.Storage Storage Description #1 455.50' 55.550 of Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (acres) (acre-feet) (acre-feet) 455.50 9.803 0.000 0.000 460.50 12.417 55.550 55.550 Device Routing Invert Outlet Devices #1 Primary 456.05' 17.9' long x 22.0' breadth Broad -Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 rimary OutFlow Max=41.76 cfs @ 12.88 hrs HW=456.97' TW=453.40' (Dynamic Tailwater) 1=Broad-Crested Rectangular Weir (Weir Controls 41.76 cfs @ 2.53 fps) Lake Basin Post-AHCC Type // 24 -hr 2yr Rainfall=3.67" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCADO 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Paae 3 Summary for Reach 8: Outfall Channel Inflow Area = 181.184 ac, 44.42% Impervious, Inflow Depth > 1.29" for 2yr event Inflow = 41.76 cfs @ 12.88 hrs, Volume= 19.542 of Outflow = 41.76 cfs @ 12.88 hrs, Volume= 19.536 af, Atten= 0%, Lag= 0.2 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Max. Velocity= 15.28 fps, Min. Travel Time= 0.3 min Avg. Velocity = 11.06 fps, Avg. Travel Time= 0.4 min Peak Storage= 751 cf @ 12.88 hrs Average Depth at Peak Storage= 0.26' Bank -Full Depth= 2.40', Capacity at Bank -Full= 1,984.58 cfs 10.00' x 2.40' deep channel, n=0.013 Side Slope Z -value= 2.0'/' Top Width= 19.60' Length= 275.0' Slope= 0.1165 '/' Inlet Invert= 453.14', Outlet Invert= 421.09' Lake Basin Post-AHCC Type 1124 -hr 10yr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCAD® 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Page 4 Summary for Subcatchment 1: Future DA -1 Runoff = 108.05 cfs @ 12.08 hrs, Volume= 7.477 af, Depth> 3.97" Runoff by SGS TR -20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Type II 24 -hr 10yr Rainfall=5.55" Area (ac) CN Description 4.229 98 Water Surface, HSG B 0.555 61 >75% Grass cover, Good, HSG B 1.128 55 Woods, Good, HSG B 0.399 70 Woods, Good, HSG C * 11.408 98 Future Development * 4.889 61 Future Open Space 22.608 86 Weighted Average 6.971 30.83% Pervious Area 15.637 69.17% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 16.8 Direct Entry, Summary for Pond 7: Lake Inflow Area = 181.184 ac, 44.42% Impervious, Inflow Depth > 3.45" for 10yr event Inflow = 705.10 cfs @ 12.00 hrs, Volume= 52.034 of Outflow - 128.72 cfs @ 12.56 hrs, Volume= 42.429 af, Atten= 82%, Lag= 33.6 min Primary = 128.72 cfs @ 12.56 hrs, Volume= 42.429 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 458.01' @ 12.56 hrs Surf.Area= 11.113 ac Storage= 26.200 of Plug -Flow detention time= 198.1 min calculated for 42.429 of (82% of inflow) Center -of -Mass det. time= 120.8 min ( 933.0 - 812.2) Volum_ a Invert Avail.Storage Storage Description #1 455.50' 55.550 of Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (acres) (acre-feet) (acre-feet) 455.50 9.803 0.000 0.000 460.50 12.417 55.550 55.550 Device Routing Invert Outlet Devices #1 Primary 456.05' 17.9' long x 22.0' breadth Broad -Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 triOutFlow Max=128.71 cfs @ 12.56 hrs HW=458.01' TW=453.65' (Dynamic Tailwater) 1=Broad-Crested Rectangular Weir (Weir Controls 128.71 cfs 9 3.68 fps) Lake Basin Post-AHCC Type 1124 -hr 10yr Rainfall=5.55" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCAD® 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Pape 5 Summary for Reach 8: Outfall Channel Inflow Area = 181.184 ac, 44.42% Impervious, Inflow Depth > 2.81" for 10yr event Inflow = 128.72 cfs @ 12.56 hrs, Volume= 42.429 of Outflow = 128.72 cfs @ 12.56 hrs, Volume= 42.421 af, Atten= 0%, Lag= 0.1 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Max. Velocity= 23.08 fps, Min. Travel Time= 0.2 min Avg. Velocity = 14.14 fps, Avg. Travel Time= 0.3 min Peak Storage= 1,534 cf @ 12.56 hrs Average Depth at Peak Storage= 0.51' Bank -Full Depth= 2.40', Capacity at Bank -Full= 1,984.58 cfs 10.00' x 2.40' deep channel, n=0.013 Side Slope Z -value= 2.07' Top Width= 19.60' Length= 275.0' Slope= 0.1165 '/' Inlet Invert= 453.14', Outlet Invert= 421.09' Lake Basin Post-AHCC Type 1124 -hr 100yr Rainfall=9.13" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCAD® 9.10 s/n 07054 © 2010 HVdroCAD Software Solutions LLC Paas e 6 Summary for Pond 7: Lake Inflow Area = 181.184 ac, 44.42% Impervious, Inflow Depth > 6.72" for 1 00y event Inflow = 1,333.00 cfs @ 12.00 hrs, Volume= 101.517 of Outflow = 344.67 cfs @ 12.43 hrs, Volume= 90.187 af, Atten= 74%, Lag= 26.2 min Primary = 344.67 cfs @ 12.43 hrs, Volume= 90.187 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Peak Elev= 459.82' @ 12.43 hrs Surf.Area= 12.062 ac Storage= 47.233 of Plug -Flow detention time= 155.9 min calculated for 90.187 of (89% of inflow) Center -of -Mass det. time= 101.2 min ( 896.7 - 795.6) Volume Invert Avail.Storage Storage Description #1 455.50' 55.550 of Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (acres) (acre-feet) (acre-feet) 455.50 9.803 0.000 0.000 460.50 12.417 55.550 55.550 Device Routing Invert Outlet Devices #1 Primary 456.05' 17.9' long x 22.0' breadth Broad -Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.68 2.70 2.70 2.64 2.63 2.64 2.64 2.63 rimary OutFlow Max=344.66 cfs @ 12.43 hrs HW=459.82' TW=454.04' (Dynamic Tailwater) 1=Broad-Crested Rectangular Weir (Weir Controls 344.66 cfs @ 5.11 fps) Summary for Reach 8: Outfall Channel Inflow Area = 181.184 ac, 44.42% Impervious, Inflow Depth > 5.97" for 1 00y event Inflow = 344.67 cfs @ 12.43 hrs, Volume= 90.187 of Outflow = 344.67 cfs @ 12.43 hrs, Volume= 90.176 af, Atten= 0%, Lag= 0.1 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.01 hrs Max. Velocity= 32.43 fps, Min. Travel Time= 0.1 min Avg. Velocity = 16.76 fps, Avg. Travel Time= 0.3 min Peak Storage= 2,922 cf @ 12.43 hrs Average Depth at Peak Storage= 0.90' Bank -Full Depth= 2.40', Capacity at Bank -Full= 1,984.58 cfs 10.00' x 2.40' deep channel, n= 0.013 Side Slope Z -value= 2.0'/' Top Width= 19.60' Length= 275.0' Slope= 0.1165 '/' Inlet Invert= 453.14', Outlet Invert= 421.09' Lake Basin Post-AHCC Type 1124 -hr 1 00y Rainfall=9.13" Prepared by Shimp Engineering, P.C. Printed 10/29/2012 HydroCADO 9.10 s/n 07054 © 2010 HydroCAD Software Solutions LLC Page 7 Water Quality Analysis Water quality analysis was performed for the entire basin drainage area. The existing basin qualifies as a Detention Basin II with 50% removal efficiency according to the Virginia Stormwater Management Handbook Table 3.06-1. Simple 4 spreadsheets have been provided showing full build -out of the watershed, including AHCC. Short Version BMP Computations Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Albemarle Health Center Water Resources Area: Development Area Preparer: Lauren Gilroy Date: 29 -Oct -12 Project Drainage Area Designation Lake Basin without AHCC Development (1996 Report Conditions) 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 = 176.84 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(1)43560(0.5/12)/27 RR required removal , L(post) - f x L(pre) %aRR 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 0 0 0 0 863098 0 0 0 0 0 514065 0 0 0 0 0 0 0 1,377,163 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 0 0 Parking Lots 1 2 3 4 1 2 3 4 0 0 0 0 0 0 Gravel areas Area Area x0.70= 0 x0.70 - 0 Structures Area no. subtotal Area no. subtotal 0 0 0 0 0 766569 0 0 0 0 0 220313 0 0 0 0 0 986,882 Actively -grazed pasture & Area Area ;yards and cultivated turf x 0.08 = 0 0 x 0.08 = 0 Active crop land Area Area x0.25= 0 x0.25= 0 Other Impervious Areas 0 Impervious Cover 0% 31% I(pre) I(post) Rv(post) V 0.33 3648.2 New Development (For Development Areas, existing impervious cover e= 200/0 C f I (pre) * Rv(pre) L(pre) L(post) RR % RR Area Type 070 1.00 20°x6 0.23 249.69 354.13 104.44 29% Development Area 0,35 1.00 0% 0.05 27.14 177.07 149.93 85% Drinking Water Watersheds 0.40 1-00 1% 0.06 36.60 202.36 165.76 82% 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 0.73 0.90 20% 0.23 249.69 354.13 129.41 37% Development Area 0.35 0.85 0% 0.05 27.14 177.07 154.00 87% Drinking Water Watersheds 0.40 086 1% 0.06 36.60 202.36 171.25 85% Other Rural Land Short Version BMP Computations Albemarle County Water Protection Ordinance: Modified Simple Method Plan: Albemarle Health Center Water Resources Area Preparer: Lauren Gilroy Date: 29 -Oct -12 Development Area Project Drainage Area Designation Lake Basin with AHCC Development and full build -out of fields behind MHS 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 = 181 19 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(1)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 Len th Width subtotal Driveways and walks Parking Lots Gravel areas Structures 0 0 0 0 0 0 0 0 Length Width no. subtotal 0 0 0 0 0 0 0 0 0 1 2 3 4 0 Area Actively -grazed pasture & yards and cultivated turf Active crop land Other Impervious Areas Impervious Cover x 0.70 = Area no. subtotal 0 0 0 0 0 0 0 0 0 Area x 0.08 = Area x 0.25 = 0 Length 0. 0 Area 0 0 0 0 0 0% I(pre) 0 0 0 Width no. 0 0 0 0 1 2 0 0 0 973653 0 514065 0 0 0 1,487,718 subtotal 0 0 0 0 0 0 3 4 0 0 x 0.70 = 0 Area no. subtotal 0 0 841231 0 0 220313 0 1,0.61,544 Area 0 x 0.08 = 0 Area x 0.25 = 0 Future development behind MHS 496,932 39% I(post) Rv(post) V 0.40 4700.9 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 1,0C 20% 0.23 255.83 441.99 186.16 42% Development Area 0.35 1.00 0% 0.05 27.81 221.00 193.19 87% Drinking Water Watersheds 0.40 1.00 1% 0.06 37.50 252.57 215.07 85% Other Rural Land * min. values Redevelopment (For Development Areas, existing impervious cover > 20%) C f I (pre);k Rv(pre) L(pre) L(post) RR % RR Area Type 0.70 0.90 20% 0.23 255.83 441.99 211.75 48% Development Area 0.35 0.85 0% 0.05 27.81 221.00 197.36 89% Drinking Water Watersheds 0.40 0.85 1% 0.06 37.50 252.57 220.69 87% Other Rural Land References Lake Design Sheets Soil Reports NOAH Rainfall Report Attached Separately Monticello HS Storm Sewer Design Sheets Original Timmons Drainage Map for Hillcrest Lake COUNTY OF ALBEMARLE lr t, Lakb'Dam' Invento ry R po' e A Inventory Number: VA -#00379 6 July 2000 Contents: Inventory Report For Class M and Class R' Impounding Structures (DS -21R) Emergency Action Plan For Class 1, 11, and III Impounding Structures (DS-2EAP) Operation and Maintenance Application - Class L 9, and III Impounding Structures (DS -21) Flow Calculations To Existing Dam (portion of stormwater report by Timmons) Department of Engineering & Public Works 401 McIntire Road Charlottesville, Virginia 22902-4596 Phone (804) 296-5861 Departmenit.of Engiteenin''g & Public Woiks FLOW CALCULATIONS TO EXISTING DAM The peak flows to the existing lake and impoundment were calculated for two conditions. The first condition is the flow prior to the construction of the dam, and the second condition is after construction of the dam and ultimate build -taut in the watershed. The purpose for calculating the flow prior to the construction of the dam is to ensure that by redesigning the spillway, we will not be increasing the flow to downstream areas and causing potential flooding and/or erosion problems. All hydrology was obtained using the Modified Rational Method (following the VDOT Drainage Manual.) Time of concentrations were calculated using Fig. 1.5.1.1 Overland Flow Time Nomograph and Fig. 1.5 1.2 Time of Concentration of Small Drainage Basins. All rainfall intensities based on Fig. 1.5.1.9 Albemarle Co. Hydrographs were added using the software program Pondpack to develop total peak flaws for both existing and proposed conditions The flow calculation for the first condition includes the lake area within the drainage area, and assumes a cover factor for the lake area of 4.3. The total drainage area for this condition was broken down into three sub -watersheds which are shown on the drainage area provided. A hydrograph was generated for each subwatershed using the modified rational approach within the TR55 software program produced by Haested Methods The hydrographs for each subwatershed were then combined in a time relative manner to provide a peak flow for the entire drainage area. The flow calculations including time of concentrations and cover factors are summarized below. Existing D.A. 1 = 78 Acres Forest: c = 0.3 Apartments: c = 0.7 cA = (0.3)(63.1 Acres) + (0, 7)(14.4 Acres) = 29,0 Tc A. Overland Flow Time = 11.7 rain.: L = 150'; c = 0.3, slope = 10% B. Channel Flow Time = 1.8 min.: L = 4001, H = 44' C. Channel Flow Time = 2.0 min. L = 450', H = 54' Total Tc = 15.5 min. Q = i(cA): Q3 = (3.35 in.)(29) = 97 cfs Qjo = (4.65 in.)(29) = 135 cfs -,. Q1©o = (1.25)(6.65 in)(29) = 241 cfs Existing D.A. 2 = 47 Acres Forest. c = fl -25 cA= (4.25)(47 Acres) = 11:8 Tc: A. overland Flow Time = 15,9 min, : L = 200', c = 0.25. slope = 6.5%0 B. Channel Flow Time = 3.1 min. ; L = 843', H 11' C. Channel Flow Time = 5.0 min.: .L = 1,000', H = 47' D_ Channel Flow Time = 6.5 min.: L = 1,440', H = 28' Total Tc = 30.5 min. QZ = (2.2 in -)(11.8) = 26 efs Q10 = (3.18 in.)(11.8) = 38 cfs Q10o = (1 -25)(4-65 in)(11.8) = 69 cfs Existing D.A. 3 = 40 Acres Forest: c = 035 cA = (0.3 5)(40 Acres) = 14 Tc: A_ Overland Flow Time = 12.4 min.: L = 200', c = 0.35', slope = 8% B. Channel Flaw Time = 6 0 min.: L = 1,156', H = 57' C Channel Flow Time = 6.6 min.: L = 850', H = 15' Total Tc = 25.0 min. Q = (2.5 in.)(14.0) = 35 efs Quo = (3.55 in.)(14.0) = 50 cfs Q100 = (1.25)(5.23 in.)(14 0) = 92 cfs Total Existing Flow to Dam (See combined hydrographs on fallowing pages) Qz = 97 els Qxo =135 cfs QtoU = 243 efs The proposed flow to the dam was broken down into six different drainage areas (see attached Drainage Area Map,) Flow calculations and time of concentration calculations are summarized below, Proposed D„ A. 1 = 22 Acres Pasture: c = 0.4 Lake: c = 0.9 cA= (0.4)(17.6 Acres) + (0. 9)(4.6 Acres) = 11.2 Tc A. Overland Flow Time = 11.4 min, : L = 100', c = 0.4, slope = 2% B_ Channel Flow Time = 2.4 min.: L = 180', H = 2' C. Storm Sewer Flow Time= 1.5 min.: L = 530', v = 6 fft/s D. Channel Flow Time = 1.5 ruin.: L = 320', H = 37' Total Tc = 16.8 min. Q = i(cA): Qz = (3.20 in,)(11.2) = 36 cfs QIo = (4.41 in,)(11.2) = 49 cfs Qioo _ (1 25)(6.40 in)(11.2) = 90 cfs Proposed D.A. 2 = 9 Acres School. c = 0.6 cA.= (0.6)(9) = 5.4 Tc: A. Overland Flow Time = 7.7 min.: L = 100', c = 0,6, slope = 2% B. Channel Flow Time= 1.5 mire.: L = 130', H = 2' C. Storm Sewer Flaw Time = 1.3 min L = 460', v = 6 ft/s D. Channel Flow Time= 1.5 min.: L = 300', H = 27' Total Te = 12.0 min Q = i(cA): Q2 (3.85 in.)(5.4) = 21 cfs Qzo = (5.20 in.)(5.4) = 28 cfs Qum = (1 .25)(7.5 in)(5.4) = 51 cfs Proposed D.A. 3 = 51 Acres Pasture: c = 0,45 School' C = 0,6 Future Commercial: c = 0 65 cA= (0.45)(5.7 Acres) + (0.6)(10.7 Acres) + (0,65)(34 9 Acres) = 31.7 Tc: A. Overland Flow Time = 8.7 min.: L = 200', c = 0 53, slope = 81/o B. Channel Flow Time = 6.0 min,: L=1,156,H=57' C. Storm Sewer Flow Time = 4.4 min, L = 1,600', v = 6 ft/s D. Channel Flow Time = 4.7 min.: L = 500, H = 7' E. Channel Flow Time= 1.7 min.,- L=270',H=15' Total Te = 25.5 min, Q = i(cA): Q2 = (2.45 in.)(31,7) = 78 cfs Qio = (3-52 in.)(31.7) = 112 cfs Qloo = (1.25)(5.15 in)(31.7) = 204 cfs Proposed D.A. 4 = 2 Acres Forest.- c = 0,30 cA = (0- 3 0)(2. 0 Acres) = 0.60 Tc.- A. Overland Flow Time-= 10.1 min.. L=100',C=0.30, slope =10% B. Channel Flow Time= 0.9 min. .- L=100',H=10' Total Tc = 11.0 min. Q = i(cA): Q2 =(4.05 in)(0, 60) = 2 cfs Qio = (5,40 in.)(0,60) = 3 cfs Qioo = (1.25)(7.70 in)(0.60) = 6 cfs Proposed B.A. 5 = 51 Acres School: c = 0.6 Future Commercial: c = 0.55 cA= (0.60)(13.1 Acres) + (0.55)(38 Acres) = 28.8 Tc: A. Overland Flow Time = 11.4 min.: L = 200', c = 0.41. slope - 6.5% B. Channel Flow Time = 3.1 min.: L 843', H = I I U C. Storm Sewer Flow Time = 0,2 rein.: L = 70', v = 6 ft/s D. Storm Sewer Flaw Time = 2.3 ruin.: L = 800', v = 5.7 ft/s Total Tc = 17.0 rain. Q = i(cA): Q2= (3.20 in.)(28.8) = 92 cfs Qio = (4.40 in.)(25.8) = 127 cfs Qio©; (1:25)(6.4 in)(28.8) = 230 cfs Proposed D.A. 6 = 36 Acres Apartments: c = 0.70 School. c = 0,60 Lake: c = 0.90 cA= (0. 70)(14.4 Acres) + (0.60)(1`3.4 Acres) + (0. 90)(7,9 Acres) = 25.2 Tc: A. Overland Flaw Time = 5.5 min. B. Channel Flow Time = 1.8 min. Total Tc = 7.3 min. Q = i(cA): Qz = (4.80 in.)(25.2) = 121 efs Qjo = (6.30 in,)(25.2) = 159 efs Q,on =(I .25)(8,80 in)(25.2) = 277 cfs L = 150', c = 0. 70, slope = 12.0% L =500', H = 72' Total Proposed Flow to ant (See combined hydrographs on the following pages) Q2 = 150 CfS Qio = 208 cfs Qioo = 378 efs POND -2 Version: 5.17 SIN: Page 1 EXECUTED: 09-27-1996 10:46:41 Return Freq: 2 years LAKE MONTICELLO H.S. WSE = 456.8 SUMMARY OF ROUTING COMPUTATIONS Pond File: C:\PONDPACK\MONTIc\bAm-P PND Inflow Hydrograph: C:\PONDPACK\MONTIC\P-T-2 -HYD Outflow Hydrograph: C:\PONDPACK\MONTIC\DP-T-2 =D Starting Pond W.S. Elevation = 456.80 ft Summary of Peak Outflow and Peak Elevation Peak Inflow = 150.30 cfs Peak Outflow = 81.55 cfs Peak Elevation 457.61 ft ***** Summary of Approximate Peak Storage ***** Initial Storage = 4,953,905 cu -ft Peak Storage From Storm = 395,118 cu -ft --------------- Total Storage in Pond 5,349,023 cu -ft POND -2 Version: 5.17 SIN: EXECUTED: 09-27-1996 10:46:42 LAKE MONTICELLO H.S. W8E = 456.8 SUMMARY OF ROUTING COMPUTATIONS Page 1 Return Freq: 10 years Pond File.- C:\PONDPACK\MONTIC\DAM-P -PND Inflow Hydrograph: C:\PONDPACK\MONTIC\P-T-10 HYD Outflow Hydrograph: C:\PONDPACK\MONTIC\DP-T-10 .HYD Starting Pond W.S. Elevation = 456.80 ft ***** Summary of Peak Outflow and Peak Elevation ***** Peak Inflow 208.08 cfs Peak Outflow = 118.01 cfs Peak Elevation 457.84 ft Summary of Approximate Peak Storage Initial Storage = 4,953,905 cu -ft Peak Storage From Storm = 511,972 cu -ft Total Storage in Pond --------------- = 5,465,876 cu -ft POND -2 Version: 5.17 SIN: EXECUTED: 09-27-1996 10:46:42 LAKE MONTICELLO H.S. WSE = 456.8 SUMMARY OF ROUTING COMPUTATIONS Page I Return Freq: 100 years Pond File: C:\PONDPACK\MONTIC\DAM-p PND Inflow Hydrograph: C:\PONDPACK\MONTIC\P-T-100 HYD Outflow Hydrograph: C:\P0NDPACK\M0NT1C\DP-T-100.HYD Starting Pond W.S. Elevation = 456.80 ft ***** Summary of Peak Outflow and Peak Elevation ***** Peak Inflow = 377.97 cfs Peak Outflow = 226.02 cfs Peak Elevation = 458.40 ft ***** Summary of Approximate Peak Storage ***** Initial Storage = 4,953,905 cu -ft Peak Storage From Storm = 812,287 cu -ft --------------- Total Storage in Pond = 5,766,192 cu -ft USDA United States Department of Agriculture o N R C S Natural Resources Conservation Service A product of the National Cooperative Soil Survey, a joint effort of the United States Department of Agriculture and other Federal agencies, State agencies including the Agricultural Experiment Stations, and local participants Custom Soil Resource Report for Albemarle County, Virginia August 21, 2012 38" 0'30" 37` 59 26" Custom Soil Resource Report Map—Hydrologic Soil Group o Map Scale: 1.9,480 if printed on As¢e (8.5" x 11") sheet. m N Meters m ^ 0 50 100 200 300 A Feet 0 350 700 1,400 2,100 38° 0' 29" 37'59'2W' '} $ o 1 + d 0 o c � �1 0 m y (a � n L Z °» O 0 0 m m � D 2 m o � m di _ N m' W m CDm' N fp A7 6 O O m 0 0m_ 3 n CL Q W (n N = m 7 0 � � O m v N < m C; Cr co 0-38) 3 m 3m WEDa_o c m 3 CL 0 v-0 o Q o Q o O (D OL O CL C O N O (D O O S Co S Q (D a N N O .< (D 6 N 63 s(D (D�3 (D O mp �DmC) N O 3 w 3 0 C S .r S� Vr (D N O Cr (n 3 m O (D _ 3 f0 7 OO N O C 7 pl O m Cl) 7 to O) N O O W c Cl) ((D in l< c (o D °1 D vCD .+ v v .. mCr (D N O y w� L O) m c N N C O to O 7 m C -)*Un O (D O O Q - a m °� o M cnl c 2 v (n m C 3 c Z r� C � .S. .il N� w 3 2C (D (D 6 n Z o CDm Z _. zcoo coN G W :3N N O 3 cn a N m O (np G 3 � (D U v pi N CD 0 (D m 0 Sr oa 3 m _. w 3 y y 2 c N 3 �� ,m3�3m� (o O. m3(o3 m a `D -1 0 3 N (D Q `< 7 O Q D 7 3 O O O Sr m Q 6 O m = CD 7 O (D m .m. 3 v v CD -0 m 3 v 0 s O O O 3 fl1 mvaa o m ni a m u m O (D 0 (Q O" O @ O N O O (D O' 0 ym N w O fD 3 O (D (D w 0 m C y 3 O 3 a (D 0 D O N fD 3 m a a co 0 - co co A O m a cn 0 N C) O -o m Q O D m N m U1 X u! (D (D ic D r m Q Z v 0 O 0 X 0 O c 0 x 0 0 A- Custom Soil Resource Report Table -Hydrologic Soil Group Hydrologic Soil Group-- Summary by Map Unit -- Albemarle County, Virginia (VA003) Map unit symbol Map unit name Rating Acres In AOI Percent of AOI 12C 12D 13C 32C Catoctin silt loam, 7 to 15 percent slopes C C 12.3 6.9 12.5 27.3 6.0 25.0 15.8 5.5% 3.1% Catoctin silt loam, 15 to 25 percent slopes Catoctin very stony silt loam, 7 to 15 percent slopes Fluvanna silt loam, 7 to 15 percent slopes Myersville silt loam, 2 to 7 percent slopes Myersville silt loam, 7 to 15 percent slopes Orange silt loam, 2 to 7 percent slopes Pits, quarry Rabun clay loam, 2 to 7 percent slopes Rabun clay loam, 7 to 15 percent slopes Rabun clay, 2 to 7 percent slopes, severely eroded Rabun clay, 7 to 15 percent slopes, severely eroded Rabun clay, 15 to 25 percent slopes, severely eroded Riverview-Chewacla complex C 5.6% C B 12.3% 58B 58C 63B 69 2.7% 11.2% B D 7.1% 1.4% 14.5% 2.3% 4.4% 18.4% 0.8% 4.4% 6.2% 100.0% 3.2 32.2 71 B 71 C B B 5.2 9.7 72133 B B B B C 72C3 72D3 40.8 1.8 77 79B Totals for Area of Interest 9.9 Starr silt loam, 2 to 7 percent slopes 13.7 222.2 Rating Options -Hydrologic Soil Group Aggregation Method: Dominant Condition Component Percent Cutoff.- None Specified Tie-break Rule: Higher 30 2/16/12 Precipitation Frequency Data Server �y NOAA Atlas 14, Volume 2, Version 3 'w Location name: Charlottesville, Virginia, US*` , Ifi Coordinates: 37.9994, -78.4940 i4 l Elevation: 465 ft* 0 4 `source: Google Maps ¢NNI; 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)' Average recurrence interval (years) __ _. _.__......__ __ _._. _. Duration-_ �_... ___._L.��_. _. �.25 _ € _ 50 100 _ 200 .....: _ 4500 IF 1000- ; 5 m € n V 0 352 (0 317 0 392)1 ��) 0.479 (0.378 0.465 0.491 0.441-0.544) 0.552 (0.495-0.611); 0.621 _ (0.555-0.685)i 0.675 (0.601-0.744)€ 0.724 (0 641 0.799); 0.771 (0.679 0 850) 0 826 (0 720-0.914) 0 871 (0 752 0 966)1 F10 --M in 0 563 1 (0 507.0 626) 0 670 (0 604 0 744)i(0.707-0.871) 0.786 0 882 (0.792 0 977)' 0.990 (0.885-L09) 07 (09,57-1 19) 1 15 _(1^02 1 27) 11 1.22 (1.08-1.35) 1 31 U1.14-1.45) 1.37 (1.19-1.52) 1 5-m in� 0.703 0.842 0.994 (0 634-0 782)1(0.759 0 935). (0.894-7 10_), 1 12 (1.00-1-24) ; 1.25 IF (1.12-1-39) 1111 -1-.36 1 50) 1.46 IF (1.29-1.60) i -1--54,F-1- (1.36 1 70) .65 (1 43-1.82) 1 72 (1 49 1 91) _.. 30 min 0.964 1 16 1 41 (0.869-1.07) 1.29) U1.27-11.56) 27-1156) 1 62 (1.45 1 79) 11 1.86 (1.66^2.05) l -Li 2 05 (1.82-2.26) 11 2.23 (1.97-2.46) 2.40 (2.11-2.65) ! 2.62 (2.28-2^90) 2.79 (2.41 ^309). F--F-1-2-0-F _(1.05 1.46 ' 1.81 (1.08L1 34) (132-1.62) (1.63-2.01),, 2.10 (1.89 2 33) v 2.47 21 2.73) 2 78 (2.47-3.06) 3.07 (2.72-3.38) ( 3.37 (2^96 3 71) ; 3 76 (3 27 4.15)Y 4.07 (3.52-4 52) i F2 -h, 1.45 1 75 2 88 (1.27-1 65) E (1:53-2_00) I (1.92-2..49) 2 57 (2^25 2 92j l _(2 3 06 (2 67 3.47) 3 47 01 3 93) 389 (3 35-4.40) 432 (3.70 4 88j € 4.92 (4.16-5.56) 5.42 (4.54-6.15) 1.58 ? 7.91 2.39 ',[12-08-2-75) 2 80 (2.443 21j ' 3.34 i (2.90 3.82) -(3 3 79 27 4 33)()(.)(.., 4 25 4.73 5.39 F51.-9(1.67-2.20) 6 -hr 2 02 2.43 IF -3.02 (1 78- 29} (2.15-2.76) € (2.66.3^42) 1[13.12-4.03) 3 56 4.28 (3.73-4.83) I _(3 4 91 (4.24-5.52) 5.56 (4V77 6.26) 6.27 (5.31-7.06) 7.26 (6.07-8.19 8.14 (6.71-9.19) F12 -hr 2.54 3 O6 3 81 (2.24-2.91) (2.70-350) € (3 35 4 36) 4.52 (3 96-5.16) 5.50 (4.78-6.25) -6.37 (5.48 7 23) i 7 31 (6.21-8.29) 8.34 (6,99 944) :_(8 F9.86 11-11„2) - 17 2 (9.08-12,7) 1 724 -hr 3.04 3.68 ' € 4.70 (2.73-3 41) i (1.31-4.13) (4.21-5.27) ' 2�t f.5 56 (4.97 6.21) 6 83 [ (6 06-7.61) 7 93 (6.98 8 81) 9.14 (798-101) 10.5 (9.04-11.6) 12.5 (10.6-13 . 8) 14.2 (11.9-15.7) 2 -da 3.58 ' 4.34 5.53 (3(3.90-4.86) (4^95-6.17) I -6.5 -0 (5_80 725) 1 7.91 (7.01-8^80) € 9 10 (8.00 10.1) _. 10A (9.06-11.5) 11 8 (10.2-131) F1113.8 .8-15.4) 15.6 (13.1-17.4) F3 -d, y 381 F -4 -.6 -21F -5-.88F (3 46 4 22) ; (4.20-5.12) jtj (5.32-6.50) 691 (624 7 63) 840 (7 55 9.27) € 965 (8.62-10.6) 110 (9 75 -12.1) a 125 (11.0-13.8) 14.6 (12.7-16.2) 16.5 (14.118 2) 4 day 4.04 4.90 6.22 (371-444) ; (4.50-5.38) (5.70-6.83) 731 (6.68.8.01) 889 (8089.73) € 102 (923112) 116 (10412.7) ` 132 (117144 15.4 (13.6-17.0) 3 174 (151 191) W 7 -day F7 _ -4.7 -T -1 -5-.6-F 7.07 (4.33-5.12) i (5.21 6.16) (6.50-7.70) 8 24 7.55-8.97) 9.91 (9.04-10.8)'[(10.2-123) F'11.3 12.8 (11 5^13.9) 14.4 (12.9-15.7) j 16.7 (14 7 18 3) 18.7 (16.3-20.4) i . F10 -day 5.33 639 790 (4.925.75) € (5.92-6.91) (730-8.53) 912 (840984) 108 (995117) 122 (1L2132) 13.7 (12.5-14.8) 153 (13.8166) 11 176 (157190) 194 ; (17.1-21.1) ! 20 -da 6.99 834 10.1 (6.56-7.48) (7.83892) (944-108) 174 133 ( [Ila- 148 (13.7158) 16.2 (15.0-17.4) 778 (16_3.190) 198 (181-213) 21.5 09.5-231) 1 30 -day 8.58 102 12.0 (8.09-9 13) 1 (9.59 10.8) i (11.3-12 8) 135 (12.6-14.3) 153 (14.3-16.3) 167 (156 17 8) 18.1 (16.9-19.2) 194 (18.1-20.7) ; 212 (19 6 -22.6) 22.5 (20.7-24.1) a_ 70.7 12 7 14.8 113) (120134) (14.0-15.7) ; 16 4 (15.5173) . 18 4 (17419.5) 20.0 (18u821.1) 21.4 (20.1-22.7) ? 22 9 (214242) 24.7 (23.0-26.3)y 26.0 1 (24.1--27.8) 1 �-7daY .6 (11.9-13.3)12 ' 14.8 ! (14-0-15.6) f 17.1 (16 2_18 0) 18.8 (17.8 19 8) 21.0 (19.8-22.1) 22.6 (2_t3-23.81 24.1 (22 7 25,4) 25.6 (24.0-27 27.4 28.8 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) w it 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 hdsc.nws.noaa.gov/hdse/pfds/pfds_printpage.html?lat=37.9994&Ion=-78.49... 1/4