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Home My WebLink AboutWPO200500074 Calculations 2006-08-08 i `/ 1\/ j ■ ■ � THE COX COMPANY Planners • Landscape Architects Civil Engineers • Urban Designers August 8, 2006 MEMORANDUM To: Mr. David Pennock, Principal Planner County of Albemarle, Virginia From: Mr. Eric Woolley, PE The Cox Company Regarding: SDP 05-094- University Village: Phase Ill, Final Site Plan Responses to comments from County Staff With this memo, I am responding to the comments that were directed to our office following the review of our final site plan for the University Village: Phase III. The comments were received in written format with various dates, the latest being dated May 10, 2006. Per your request, I have attached this memorandum to revised sets of our site plan. Current Development Planning— David Pennock 1. The specific trees that are to be protected during construction are delineated with "Tree Protection" on the erosion and sediment control plan. 2. Kirk Hughes, the surveyor that provided the plat, has discussed the building restriction with you since the issuance of this comment, and believes the comment has been sufficiently addressed. The building restriction line will address the setback issue. Engineering Department—Glenn Brooks &Allan Schuck 1. No response, the comment was previously addressed. 2. No response, the comment was previously addressed. 3. No response, the comment was previously addressed. 4. No response, the comment was previously addressed. 5. No response, the comment was previously addressed. 6. As discussed in our review meeting following the issuance of these comments, a previous typo to the sheet numbers necessitated the revision to reflect the correct sheet number"C- 3.0." The comment was addressed, however, the sheet number changed and created the oversight. 7. The pipe inverts were amended with the previous submission to allow for a lower design velocity that is less than 10 ft/sec. The riprap was shown, but not labeled, the revised storm profile on sheet C-6.1 describes the outlet protection stone. 8. The tyopographical mistake on the plan sheets was amended to reflect the correct drainage area. The calculation booklet reflected the appropriate drainage area. 434°295.7131 220 East High Street Charlottesville,Virginia 22902 �' V' UAL. Slur/ �e UA ■ ■ ■8 Ar Memorandum Re: University Village: Phase III (SDP 05-094) To: Mr. David Pennock August 8, 2006 Page: 2 9. The drainage areas have been added to the stormwater management plan. The calculations relate to the areas shown. 10. The structure description was amended to eliminate confusion. The throat size of the inlet was upsized to (8' DI-3B) to provide 100% intercept capability. 11. No response, the comment was previously addressed. 12. No response, the comment was previously addressed. 13. No response, the comment was previously addressed. 14. No response, the comment was previously addressed. 15. A copy of the requested tables has been attached to this memorandum. Stormwater Management— Glenn Brooks &Allan Schuck 1. No response, the comment was previously addressed. 2. No response, the comment was previously addressed. 3. Due to the fact that the overall development is phased and previously graded, the drainage area prior to the proposed development is essentially the same as post- development. 4. No response, the comment was previously addressed. 5. The biofilter berm and protection fabric have been amended on sheet C-5.0. 6. The notes were added to the plan sheet C-5.0. 7. The rock specifics are now noted on the plan sheet C-3.0. 8. The detail sheet that includes the Filterra units has been added to plan set (sheet C-7.0.) The units sizes are labeled on sheet C-3.0. 9. As discussed in our review meeting following the issuance of these comments, several notes and a plan inset were added to the upper right hand corner of plan sheet C-5.0 to address the comment. 10. The Stormwater Maintenance agreement has been submitted and recorded. 11. No response, the comment was previously addressed. 12. No response, the comment was previously addressed. 13. The error was corrected with this submission. 14. See previous comment response. 15. The support documentation from the routing has been attached to this memorandum. 16. The requested hydrographs have been added to this memorandum. 17. The 10-year post-development peak flow rate does not exceed the anticipated pre- developed condition with the implementation of the storm water management facility. The 2-year storm will be drastically less than the pre-developed flow rate. The proposed post- developed outfall condition will utilize an existing ditch line that carries water away from the site. The pre-developed condition will be enhanced with scour protection in the form of rip- rap. The same ditch section with a reduced flow rate provides a lower rate of velocity for the 2-year frequency storm. *444100 'taro? ik Memorandum Re: University Village: Phase Ill (SDP 05-094) To: Mr. David Pennock August 8, 2006 Page: 3 Erosion and Sediment Control — Glenn Brooks &Allan Schuck 1. No response, the comment was previously addressed. 2. No response, the comment was previously addressed. 3. No response, the comment was previously addressed. 4. No response, the comment was previously addressed. 5. No response, the comment was previously addressed. 6. A sediment trap has been adjusted and silt fence was added. Calculation sheets are included within this memorandum. 7. No response, the comment was previously addressed. 8. No response, the comment was previously addressed. 9. No response, the comment was previously addressed. 10. No response, the comment was previously addressed. 11. No response, the comment was previously addressed. 12. No response, the comment was previously addressed. 13. No response, the comment was previously addressed. 14. No response, the comment was previously addressed. 15. No response. 16. The safety fence and silt fence were added to the plan. Albemarle County Service Authority— Pete Gorham & Gary Whelan • Service Authority has completed their review of the plans and has forwarded approval to the County. I hope that these responses, in combination with the revised plan have satisfied the deficiencies as noted in your previous comment memorandum. Please do not hesitate to call with any questions or concerns. Thank you for your time and consideration. AA /9' Eric W. Woolley, P/ Project Engineer Cc: David Turner, MD Development, Developer File Attached: Referenced support documentation Revised Preliminary Site Plan (2 full-sized) `ru+1 Y Ws CC Q co N CO d' U) CD N- CO 0) O c a) Q) a) C) N C) a) a) N a) m LU a a a a a a a a 0. a 2 a n a a E._ 6.-. a cn C) u) o -c 0 w ,_ � 0 CL ODw5 n I- a) ,- El I-- Z L 3 v0 0) g c 0 «) o 8 > Z Q N- Ln ti CD Ln N. N- CO C . Ln �' > d O Lf) CO CO Ln Ln Ln CC) CO c-- u O cd 4 ti CA o) Ln Ld o) O) a)> N- M O) N- Ln 1-- D W d I- IL 'n °� coOc ti O o) co 't U Ln W U V 0 O CO CO 4 N ocNi ) 6 CD I (1) O O O O O O O O O O _Q z v O OCD 000 O O 00 O - .� L[) Ln Ln Ln Ln Ln in LU N N I- 0 o c E a ,!z. 0 0 0 0 0 0 0 0 M M M •- N Zr Zr M co O O F- CO N N N- O CO .- N L�0 d u) LL N Ln O) 4 N6 Ln O) 3'. Q N CO r-- 0) h •- N CO a0 co O O CO `- L.f) V. M oo Oz u v N _ Ln tri o J LNC) o) N V 0) _ NN- LO N- C 0) W O O C) CO CO C) O 0 O O •y LU p .-. O N. N CO CO CO N CD CO 0 z Z Z--- M N .- N M6 6 M o) M N O O w CD in CO CO CD LO Ln CD Ln CD C E W - J CD CO CD CD CO CO CO CO CO CD •Cp CD Z > ft O O CO CO O O 0 0 0 N - w W a Ln 0 N ti 0 Ln O CO O cl- f=1 Q W CL W O U CO CD CO CO LO CD CO CO CO 0 E Z D CO CO CO CD CO CD CD CO CO CO 0 `o 0 ''- Z LL u) CO N N 0) N- .- O ,- N ,. co P. � tL 0 u rn o) V O Lf) V V M M V O 0) J- 0_ CC 0 0 Ln CO N N- 4 O N ,- H Z O N dj a O O W Q Q = O N N O N O C) 0 O N N-. N- N- ti N- ti 1`.. N- ti ti N 0 U W LL Z O CO CD CD CO CD CO CO CO CD 03 C) LU C) O O O 0 O Co C) O OW ZWv O000000 O OOJZ R D Ln Ln Ln co in to co to co co LO Q W _ OO CO N M ti CO CO 0) d to Lo Q U ~ O N N CO ON O CO a Z Q a O CD 0 Ln CO N U) w ~ N- CO N- CD N-M in 4 O 0 co co to to W ce 0 W 0 to 00 O N ' 1- O N N-- 0 co --0 (n Z 2 O O O O O O O O O O cr Z W O Z LI- U: Ln CO '� Ln O O O O O Ln — 0 u w U v ti CO CO ti CO 0) rt' LO Ln � < C0 00 O O O O O O O O O O w N. N- CO WWQ mD O O CO c- d (NO < 0 - Q O O O O O O O O O O co O C6 CO CO O Z v N CO d Ln j O Q ~ � O 0 o 0 0 0 X W w W W O O O CO 0) N Z N CO d In O CT d CO N >, CrO •-- 0 0 0 CI CI X 0 0 W W 0 W J -� (SAO).land e0 'Q0 N o 0 0 0 0 i rn ti rn ti (Sd0) paldezJalul "0 co CO N 0 LO LO • 0 0 0 0 0 O N (el.-06 'ddt�) v oo - r T Cr) o 11/-I r. cc?) rn p Cu) y16ua l pal�loadS '� v v` co c W (L1- co O N O ( -06 •'ddt/) (l j) 'll 'Lll6ue-1 pelndwo0 -(.1-' M N 0 v (li/ld) '(°9)M.S + "S = °S N 0 cD CD o CO O 0 0 0 0 __ l cc) CO CO CO CO (MZ6)/e = '".S v v v v v v O 0 0 0 0 uolssaJdaa leoo1 + (xs-MS)MZ L = e N "' ") M M M M M w (9-06 'ddy) 'op N C — o .<0 xS/,v,S °' v v v v v v o _ M M M M M E "O 0 0 0 0 0 V N N O) I'D 1/M - o ,- o N d a) (±J) AA N N N N N 4-. as Q. ad) ped 'l U3 m °r° CND C co `, - .- In r 0 r 8 C) _ O ca O °o O O Co cc 0 0 0 0 0 0 N (ld/ld)edolS sssoa0 'xS v o 0 0 0 0 0 Nr o �' 0 0 0 0 0 0 N ` _ O Cl) N CO N N CD U) J >_ (1d/1j)adolS aallno 's T o P o 0 0 0 D -- 000000 0) Fi O in N S � � X (SAO)Mold Ja11nJ ''0 c`? o N O LO co •C 0 0 c4 0 0 0 0 C - _ _ a a (SAO)Janp �(JJ80 '40 v o 0 0 0 0 0 Q 0 _ _ (SA0)Joula O N O c!)c M r� r8 v CO - 0 N 0 0 0 0 (2JH/NI) I Cr) v v v v '4' — N- CO I- CO CO CO v0 wns a S COf) O O ' O O 0 0 0 0 0 N- CO N- CO CO CO VO o 0O O CO T O O O O O O U) co U) O O 0 cD N- CO CO O o O O o O - - F- (0d) eoN 06euieaa v - 0 o o (X 60 0 0 0 0 0 0 0 0 1r .) o s-1-- + cc-3 + + + uogels N- CO O O O N ,- ,- ,,- r r r ad) 416u9-1 v v CO - CO CD COCO CC) CO 03 CO 03 CO w O J ad�(l v M M M M M M N • Z 0 0 0 0 0 D a a) JagwnN N M - U) C° C) Hydrogr- h Peak Inflow CB,3/4,,t'tion 2yr sir, • 51 4 31 r �+ Plotted Curves i MOD.RATIONAL IN 2yr LL 21 ;' i ON-SITE BASIN OUT 2yr t - 1 0 i I , 1 1 I I 1 1 I 0 5 10 15 20 25 30 35 40 45 50 Time (min) Hydrogr- h Peak Inflow Coon 10yr i 6 '‘ 5r r ! 7 1 4i 46 Plotted Curves 3 3 % - MOD.RATIONAL IN 10yr ON-SITE BASIN OUT 10yr 2 i 1 _+ 01 0 5 10 15 20 25 30 35 40 45 50 Time (min) HydrogrF Peak Inflow Con 100yr 8-7 ; t ' 1 6 ` Plotted Curves 3 4* MOD.RATIONAL in 100yr ++ i ON-SITE BASIN OUT 100yr t 2- r' ` 0 5 10 15 20 25 30 35 40 45 50 Time (min) Type. . . . Outlet Input I 3 Page 11 . 01 Name. . . . CONTROL DEVICE✓ `d File. . . . D: \COXWOOLLEYBU\UNIVERSITY VILLAGE\POND\BASIN.PPW REQUESTED POND WS ELEVATIONS : Min . Elev.= 644.00 ft Increment = . 10 ft Max . Elev.= 646.00 ft Spot Elevations , ft 645 .00 ********************************************** OUTLET CONNECTIVITY ********************************************** ---> Forward Flow Only (UpStream to DnStream) <--- Reverse Flow Only (DnStream to UpStream) <---> Forward and Reverse Both Allowed Structure No. Outfall El , ft E2, ft Weir-Rectangular WE ---> TW 645.000 646.000 TW SETUP, DS Channel S/N: E21401D06A89 PondPack Ver . 7 . 5 (786c) Compute Time: 14: 36: 23 Date: 03/27/2006 • Type. . . . Outlet Input 3 Page 11 . 02 Name. . . , CONTROL DEVIC File. . . , D: \COXWOOLLEYBU\UNIVERSITY VILLAGE\POND\BASIN.PPW OUTLET STRUCTURE INPUT DATA Structure ID = WE Structure Type = Weir-Rectangular # of Openings = 1 Crest Elev. = 645 .00 ft Weir Length = 6.00 ft Weir Coeff . = 3 .000000 Weir TW effects (Use adjustment equation) Structure ID = TW Structure Type = TW SETUP, DS Channel FREE OUTFALL CONDITIONS SPECIFIED CONVERGENCE TOLERANCES . . . Maximum Iterations= 30 Min. TW tolerance = .01 ft Max. TW tolerance = .01 ft Min. HW tolerance = .01 ft Max. HW tolerance = .01 ft Min. Q tolerance = . 10 cfs Max. Q tolerance = . 10 cfs S/N: E21401D06A89 PondPack Ver . 7 . 5 (786c) Compute Time: 14: 36: 23 Date: 03/27/2006 • Type. . . . Pond Routing ary Page 12. 36 Name. . . . ON-SITE BASINODT Tag: 2yr Event : 2 yr File. . . . D: \COXWOOLLEYBU\UNIVERSITY VILLAGE\POND\BASIN .PPW Storm. . . Alb 2yr Tag : 2yr LEVEL POOL ROUTING SUMMARY HYG Dir = D: \COXWOOLLEYBU\UNIVERSITY VILLAGE\POND\ Inflow HYG file = NONE STORED - ON-SITE BASININ 2yr Outflow HYG file = NONE STORED - ON-SITE BASINOUT 2yr Pond Node Data = ON-SITE BASIN Pond Volume Data = ON-SITE BASIN Pond Outlet Data = CONTROL DEVICE Infiltration = .5000 in/hr INITIAL CONDITIONS Starting WS Elev = 644.00 ft Starting Volume = 0 cu.ft Starting Outflow = .00 cfs Starting Infiltr . = .00 cfs Starting Total Qout= .00 cfs Time Increment = 1 .00 min INFLOW/OUTFLOW HYDROGRAPH SUMMARY Peak Inflow = 3 . 53 cfs at 7.00 min Peak Outflow = 2 .07 cfs at 17 .00 min Peak Infiltration = .03 cfs at 17 .00 min Peak Elevation = 645 . 24 ft Peak Storage = 2331 cu.ft MASS BALANCE (cu.ft) + Initial Vol = 0 + HYG Vol IN = 2953 - Infiltration = 1842 - HYG Vol OUT = 1085 - Retained Vol = 25 Unrouted Vol = - cu.ft ( .014% of Inflow Volume) S/N: E21401D06A89 PondPack Ver . 7 . 5 (786c) Compute Time: 15 : 14: 23 Date: 03/27/2006 Type. . . . Pond Routing , mary Page 12 .46 Name. . . . ON-SITE BASITag: l0yr 'NIS Event : 10 yr File. . . . D: \COXWOOLLEYBU\UNIVERSITY VILLAGE\POND\BASIN. PPW Storm. . . Alb l0yr Tag: l0yr LEVEL POOL ROUTING SUMMARY HYG Dir = D : \COXWOOLLEYBU\UNIVERSITY VILLAGE\POND\ Inflow HYG file = NONE STORED - ON-SITE BASININ l0yr Outflow HYG file = NONE STORED - ON-SITE BASINOUT l0yr Pond Node Data = ON-SITE BASIN Pond Volume Data = ON-SITE BASIN Pond Outlet Data = CONTROL DEVICE Infiltration = .5000 in/hr INITIAL CONDITIONS Starting WS Elev = 644.00 ft Starting Volume = 0 cu. ft Starting Outflow = .00 cfs Starting Infiltr . = .00 cfs Starting Total Qout= .00 cfs Time Increment = 1 .00 min INFLOW/OUTFLOW HYDROGRAPH SUMMARY Peak Inflow = 4. 38 cfs at 7.00 min Peak Outflow 3 . 79 cfs at 17.00 min Peak Infiltration = .03 cfs at 17.00 min Peak Elevation = 645. 36 ft Peak Storage = 2608 cu.ft MASS BALANCE (cu.ft) + Initial Vol = 0 + HYG Vol IN = 4196 - Infiltration = 1848 - HYG Vol OUT = 2323 - Retained Vol = 25 Unrouted Vol = - cu. ft ( .010% of Inflow Volume) S/N: E21401D06A89 PondPack Ver . 7. 5 (786c) Compute Time: 15 : 15 :01 Date : 03/27/2006 • Type. . . . Pond Routing aryPage 12. 56 Name. . . . ON-SITE BASINOUT Tag: 100yr `"vent : 100 yr File. . . . D: \COXWOOLLEYBU\UNIVERSITY VILLAGE\POND\BASIN. PPW • Storm. . . Alb 100yr Tag : 100yr LEVEL POOL ROUTING SUMMARY HYG Dir = D : \COXWOOLLEYBU\UNIVERSITY VILLAGE\POND\ Inflow HYG file = NONE STORED - ON-SITE BASININ 100yr Outflow HYG file = NONE STORED - ON-SITE BASINOUT 100yr Pond Node Data = ON-SITE BASIN Pond Volume Data = ON-SITE BASIN Pond Outlet Data = CONTROL DEVICE Infiltration = .5000 in/hr INITIAL CONDITIONS Starting WS Elev = 644.00 ft Starting Volume = 0 cu.ft Starting Outflow = .00 cfs Starting Infiltr . = .00 cfs Starting Total Qout= .00 cfs Time Increment = 1 .00 min INFLOW/OUTFLOW HYDROGRAPH SUMMARY Peak Inflow = 5. 70 cfs at 7.00 min Peak Outflow = 5.43 cfs at 17.00 min Peak Infiltration = .03 cfs at 17.00 min Peak Elevation = 645.45 ft Peak Storage = 2841 cu.ft MASS BALANCE (cu.ft) + Initial Vol = 0 + HYG Vol IN = 5796 - Infiltration = 1852 - HYG Vol OUT = 3920 - Retained Vol = 25 Unrouted Vol = - cu. ft ( .008% of Inflow Volume) S/N: E21401D06A89 PondPack Ver . 7 . 5 (786c) Compute Time: 15: 15 : 33 Date: 03/27/2006 University Village Volume Study Engineering Calculations for the Erosion & Sediment Control Plan Sediment Trap Computations for the Trap "East" Disturbed Drainage Area: 0.6 Acre Wet Storage Required: 67 (cy/ac) x 0.6 Acre 40.2 cy Dry Storage Required: 67 (cy/ac) x 0.6 Acre 40.2 cy Bottom of Trap: 663.00 Bottom of Stone Weir: 666.60 Top of Stone Weir: 667.70 Top of Trap: 668.70 Wet Storage Available: 40.2 cy Dry Storage Available: 40.4 cy Elevation Area (ft^2) Vol. (ft^3) Vol. (cy) Area (ac) 663.0 0 0.0000 664.0 79.7 39.9 1.48 0.0018 665.0 306.2 193.0 7.15 0.0070 666.0 598.65 452.4 16.76 0.0137 666.6 783.57 400.8 14.85 0.0180 667.0 923.99 358.6 13.28 0.0212 667.7 1170 732.9 27.14 0.0269 668.0 1237 361.0 13.37 0.0284 0.0000 Sub-Total Wet 1086.1 40.22 Sub-Total Dry 1091.5 40.43 Total: 2177.6 80.65 University Village Volume Study Engineering Calculations for the Erosion & Sediment Control Plan Sediment Trap Computations for the Trap "West" Disturbed Drainage Area: 1.4 Acre Wet Storage Required: 67 (cy/ac) x 1.4 Acre 93.8 cy Dry Storage Required: 67 (cy/ac) x 1.4 Acre 93.8 cy Bottom of Trap: 641 .00 Bottom of Stone Weir: 643.60 Top of Stone Weir: 645.00 Top of Trap: 646.00 Wet Storage Available: 96.0 cy Dry Storage Available: 94.0 cy Elevation Area (ft^2) Vol. (ft^3) Vol. (cy) Area (ac) 640.0 0 0.0000 641.0 0 0.0 0.00 0.0000 641.0 503 0.0 0.00 0.0115 642.0 850 676.5 25.06 0.0195 643.0 1252 1051.0 38.93 0.0287 644.0 1692 1472.0 54.52 0.0388 645.0 2169 1930.5 71.50 0.0498 Total: 5130.0 190.00