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Home My WebLink AboutWPO201900060 Calculations 2020-08-20UVA Foundation — Discovery Drive Development COUNTY OF ALBEMARLE, VIRGINIA VSMP WP02019-00060 DESIGN CALCULATIONS & NARRATIVE AUGUST 19, 2020 . •' "s ••• TIMMONS GROUP YOUR VISION ACHIEVED THROUGH OURS. Prepared by: Craig Kotarski, PE Timmons Group 608 Preston Ave, Suite 200 Charlottesville, VA 22903 434.327.1688 L� U CRAIGG W�. 7. KarARSKI Lic. No. 0402048507 811912020 Table of Contents Section Title Project Narrative 2 Pipe and Inlet Computations LD204, LD229, LD347 Pipe Calculations For existing pipe under Lewis & Clark Drive LD229 for 10 year and 100 year storm 4 Drainage Subbasin Map — Developed Condition, Flat Branch — Tributary to North Fork Rivanna River, UVA Research Park at North Fork 5 Lewis and Clark Drive — Stormwater Management Exhibit for Pond 6 USGS Geological Survey — Earlysville Quadrangle 7 Ultimate Buildout Conditions Exhibit Final Site Plan — Sheet C6.1— Stormwater Management Quantity Project Narrative: This project will be constructed in two phases. Phase 1 includes the construction of a building addition and associated drainage, utilities, and landscaping at 1725 Discovery Drive. The limits of disturbance totals 0.47 acres for this phase. Phase 2 includes the construction of a new metal building, additional parking, as well as associated drainage, utilities, and landscaping between 1725 and 1670 Discovery Drive. The limits of disturbance of Phase 2 of this proposed project totals 2.94 acres. The total limits of disturbance for this project totals 3.41 acres. Overall, the site drains through a pipe system to Analysis Point 1 and ultimately outfalls to a large wet pond (Pond 1) southeast of the site. Stormwater Management Summar: Per the document titled "Stormwater Management / BMP Analysis and Floodplain Study for the UVA Research Park at Northfork" by Dewberry & Davis, October 1997, the research park ponds have been master planned to handle both stormwater quantity and quality requirements for the future build -out of the research park. The applicability of the pond is conditioned on the pond being built as designed, and the CN value remaining within the plan approved CN value. This Dewberry & Davis document lists approved curve numbers and drainage areas based on the estimated future developed condition of the UVA Research Park. Per the sheet "Drainage Subbasin Map — Developed Condition, Flat Branch — Tributary to North Fork Rivanna River, UVA Research Park at North Fork," dated July 23, 1997 (Section 4), the proposed development falls within Subbasin C2. Subbasin C2 consists of 85.84 ac with a CN value of 82 (see Table 1). "UVA Research Park — Pond 1 Analysis" dated August 18, 2020 demonstrates that Pond 1 was built to satisfy water quantity and quality requirements. Additionally, the proposed CN value remains within the plan approved CN value. This development drains to the wet pond designated as Pond 1 in the "Lewis and Clark Drive - Stormwater Management Exhibit for Pond 1" updated August 18, 2020 by Timmons Group (Section 5). This document lists curve numbers and drainage areas based on the updated developed condition of the UVA Research Park. The subject property falls within area C2 on this map. Area C2 was analyzed to determine the change in impervious and pervious surface area resulting from this proposed Discovery Drive Development. These values have been incorporated into the previously approved overall CN value for the drainage area. This proposed development results in a net +1.69 acres impervious area which increases the CN value to 68. This remains significantly below the approved full build out development plan CN value of 82. Based on the USGS topographic map (Section 6) for Earlysville, Virginia, the overall watershed draining to Pond 1 is approximately 450 acres. Analysis downstream of Pond is unnecessary since the project limits of disturbance (3.41 acres) is less than 1% of the pond drainage area. Both water quantity and quality requirements for this site will be met by utilizing the existing Pond 1. Existing Channel Adequacy Summar3L The existing natural channel was analyzed according to 9VAC25-870-97.B and 9VAC25-840-40.19. Per the NRCS Web Soil Survey, the soil type along the entire channel is 36C — Hayesville Loam, which assuming the top layer of loam has washed away, is clay. From Table 5-22 (VESCH), the permissible velocity for stiff clay is 5.0 feet per second. The estimated ultimate development conditions of the drainage area utilizing this channel are illustrated in the Exhibit in Section 7. Based on the cross sections presented in the plans on Sheet C6.1 (included as Section 8), and considering ultimate development conditions, the following criteria are met. 1. The 2-year velocity routed through the channel does not exceed 5 FPS at any section. 2. The 10-year water surface elevation does not overtop the channel at any section. Therefore, the channel is adequate to handle the stormwater conditions resulting from the estimated ultimate development conditions, which includes this proposed development. Approved Drainage Areas and CN Values 7/23/1997 Area (Ac.) CN Al 57.25 79 A2 12.61 64 B1 54.48 72 B2 48.56 80 C1 27.38 80 C2 85.84 82 D1 12.33 78 D2 84.03 86 E1 27.8 81 E2 17.28 83 F1 66.44 91 F2 31.64 91 G1 48.9 92 G2 49.05 92 Proposed Drainage Areas and CN Values 8/18/2020 Area (Ac.) CN Al 56.35 60 A2 11.77 55 131 49.59 50 B2 47.79 67 C1 31.15 42 C2 83.90 68 D1 9.55 51 D2 81.90 70 E1 28.71 55 E2 16.91 38 F1 64.97 53 F2 30.75 54 G1 47.53 76 G2 49.25 72 Table 1— Drainage Areas and CN Values FORM LD 20a STORMWATER INLET COMPUTATIONS SHEET OF2 LDZ PROJECT Diswv Dm De lope M DESIGNER: A. MaL DATE SMOGV20 CHECKED: A.Allism UNITS ENGLISH ��■gym■�o��m��m�m�m�� ■moo■oo��■��m ��■moo■oo��■�� ■gym■�o��■�� ■moo■oo��■�� ■moo■�o��■�� ■moo■oo��■�� ■moo■oo��■�� ■moo■oo��■�� ■gym■oo��■�� IN E SOFT BY ENSOFTEC DATE: S I$M2O FORM LD 20a STORMWATER INLET COMPUTATIONS SHEET 2 OF2 LD2 PROJECT Diswv Dm De lope M DESIGNER: A. MaL DATE SNOGV20 CHECKED: A.Allism UNITS ENGLISH �m��■gym■om��m■��m�� ■moo■om��■��m �m��■moo■om��m■��m�� m��■gym■om��m■��m�� ■moo■om��■��m �m��■gym■mtm��m■��m�� IN E SOFT BY ENSOFTEC DATE: S I$M2O LD-229 STORM SEWER DESIGN COMPUTATIONS STORM FREQUENCY 10 PROJECT: UVAF DISCOVERY DRIVE LOCATION: ALBEMARLE COUNTY COUNTY: Chi NOAA STATION: Designed by. AM Checked by: UNITS ENGLISH PIPE NO FROMKONT TO PoMT DRAIN. AREA RUNOFF COEFF, 'C" (4) CA TOTAL INLET TNT M.. (]) RAIN FALL INHs (8) RONOFF RTyFRT ELEVATIONS LENGTH of Pipe Ft (12) SLOPE FtTl (13) SIZE (Dia Or SpWRise) ht (14) SHAPE Number of Pipes Capacity CFS (15) Friction Slcpe Ftfft NORMAL FLOW FLOW TIME Sm (17) REMARKS (18) NCRE MENT (5) ACCUA- ULATED (6) L sgl CFS Te Q CFS (9) UPPER ENO (10) LOWER ENO 01) D"p f FIow,M Ft Areaof Flow,An SgFI F; Ft Vn Fb$ (16) En Ft REFERENCE (1) STA. REFERENCE (2) STA. 'A' Au. (3) "1 302 IX300 000 000 2% am 564 0W 1550 53627 5M56 5694 003003 24 Cinw. 1 4247 O00420 0.84 124 044 1246 325 457 303 304 302 041 0.60 033 2.56 909 569 0W 1550 53].17 536.67 66.65 OW750 24 OrcWar 1 2122 O00420 127 2.10 057 738 2.11 904 305 3% 304 007 ON OW 2]A 795 571 0W 13" 540.05 53]2] 101.19 002748 24 OrcWar 1 4063 0W320 0.00 1.17 043 1166 291 868 307 308 306 00C 0.93 003 2.14 7.W 441 0W 13.10 540.63 540 is 64.00 OW750 m OrcWar 1 2122 000300 1_14 184 054 711 192 9W 309 310 308 OW OW 2.11 768 578 0W 12% 541.10 540.73 4995 OW741 24 OrcWar 1 2110 O00290 1.13 184 054 7W 191 708 311 312 310 003 043 001 2.11 752 582 0W 12% 54171 54120 6751 OW755 m OrcWar 1 2130 000296 1.13 182 054 711 191 950 313 314 312 046 075 034 2.10 723 589 0W 12.99 543.19 54181 13792 OOIWI 24 OrcWar 1 2452 O00290 103 163 051 790 2W 1745 315 316 314 1 353 038 134 169 5.12 650 0W 1101 54344 54329 1502 O009W m OrcWar 1 2450 0 00210 094 145 048 759 LM 198 317 318 316 048 O'D 035 035 500 654 0W 229 5"53 5"17 3634 OW991 15 OrcWar 1 697 000110 049 045 020 5W 090 714 321 322 306 001 0Q OW 004 539 642 0W 025 54308 54232 76W 001000 15 OrcWar 1 7W 000000 0.16 OW 010 269 027 2827 323 324 322 008 1 043 1 003 1 003 500 654 0W 022 5"40 543]] Q.51 001008 12 OrcWar 1 398 1000000 0.16 1 006 010 269 1 027 2327 331 332 314 004 050 002 006 671 603 0W 037 54367 54329 7644 OW4W 12 OrcWar 1 272 000010 025 0.15 015 243 0M 3140 333 334 332 003 047 001 004 622 6.17 0W 025 5"09 543]] 079 O00502 12 OrcWar 1 274 O00000 021 0.12 012 2.18 028 2925 335 336 334 002 0W 001 003 597 624 0W 0.17 5"33 5"19 2963 OW489 12 OrcWar 1 270 000000 0.17 OW 010 192 OD 1495 337 338 336 002 070 001 001 500 654 0W 0W 5"93 5"43 "50 OW503 B OrcWar 1 093 O00010 0.14 005 008 1.71 0.19 5922 400 TO EX 4W IX 041 0.88 036 036 500 654 0On 2.)6 SM28 532Q 1 1 00316] 15 OrcWar 1 1150 OW140 036 032 022 ]3] 123 711 501 502 IX500 432 036 156 1.56 15W 33] OW 524 53605 131.62 22.63 0010W 24 C-W- 1 2459 O.W050 00 084 035 622 123 367 EXI-EX300 EXI IX300 5% 049 292 5.A 1523 334 OW 22r 533M 531.99 IMOO 0014'M 24 C-War 1 297I OWBW 130 2.11 058 1041 299 1289 EX500-IXI EX 500 IXI 2W 051 133 2.88 15W 444 OW 12.M 53]]1 5M08 12200 0M9]5 ]A C-War 1 4227 0W280 076 109 041 IIA 291 1035 OU'TFALL EX 300 FES 0W OW 83] 1545 439 0W 36]I 526.42 5M99 3342 00U2 30 C-War 1 91W OW010 110 209 05] 1]68 595 1.99 LD-347 PROJECT: UVAF DISCOVERY DRIVE DESIGNED BY: AM HYDRAULIC GRADE LINE ANALYSIS C6ecketl: INCIDENCE PROBABILITY 10 Yw INLET OR JUNCTION STA. INVERT EL. OUTFLOW PIPE DEPTH OFFLOW OUTFL PIPE OUTLET WATER SURFACE ELF/. OIA PIPE D. INmm DESIGN DISCH. Go CFSMMS LENGTH PIPE Ln FM FRICTION SLOPE Slo (FT/FT) MRA FRICTION IDSS H! FRV JUNCTION LOSS SURFACE FLOW AJL HI 13 Hl FLM InW S oml YIN RS Hl (FRV) FINAL H (FMI Inlet WaW Suda- El-Uon T, oI MH T, N lnkl E. APPRO%. PilµslmTl] Vo 0- Ho H. Yi mi , 111(Enpn) 03YMAK. SKEW A,Ie K Pap H FM Sun HL FLM (1) (2) (3) (4) (5) (6) (7) (8) 9) (10) (11) 12 (13) 14) 15) 16) 16) (17) (18) (19) FES 527.390 EX 300 524.990 2.50 527.390 30 36.712 33.42 0.00714 0.238 17.675 1.213 IOA06 1.681 0.589 0.0 0.00 0.000 1.801 0.000 1.801 NO 1.801 2.040 529.430 540.640 O.K. EX 1 531.890 2.00 533.490 24 22.570 134.00 0.00887 1.188 10.406 0.420 11.792 2.159 0.756 0.0 0.00 0.000 1.176 9.766 1.529 YES 0.764 1.952 535.442 544.340 O.K. EX 500 534.080 2.00 535.680 24 12.801 122.00 0.00285 0.348 11.792 0.540 6.223 0.601 0.210 0.0 0.00 0.000 0.750 5.900 0.975 YES 0.488 0.836 538.465 542.540 O.K. 502 537.820 2.00 539.420 24 5.239 22.83 0.00048 0.011 6.223 0.150 0.000 0.000 0.000 0.0 0.00 0.000 0.150 5.239 0.195 YES 0.098 OA09 539.529 543.600 O.K. 302 534.560 2.00 536.160 24 15.503 56.9I 0.00418 0.238 12.459 0.603 7.375 0.845 0.296 0.0 0.00 0.000 0.898 0.000 0.898 YES 0."9 OA87 537.106 543.270 O.K. 304 536.670 2.00 538.270 24 15.503 66.65 0.00418 0.279 9.375 0.211 11.656 2.110 0.738 0.0 0.00 0.000 0.950 1.862 0.950 YES 0.475 0]54 539.024 542.590 O.K. 306 531.2]0 2.00 539.024 24 13.641 101.17 0.00324 0.328 11.656 0.527 7.109 0.785 0.275 0.0 0.00 0.000 0.802 0.320 0.802 YES 0.401 0129 540.848 546.700 O.K. 308 540.150 2.00 541]50 24 13.104 64.00 0.00299 OA91 7.109 0.196 ].05] 0]13 0.271 0.0 0.00 0.000 0.467 0.145 0.467 NO 0.467 OA58 542.408 550.060 O.K. 310 540.730 2.00 542.408 24 12.959 49.95 0.00292 0.146 ].05] 0.193 7.108 0.785 0.275 0.0 0.00 0.000 0.468 0.000 0.468 YES 0.234 0.380 542.788 552.500 O.K. 312 541.2DD 2.00 542.800 24 12.959 67.51 0.00292 0.197 7.108 0.196 1.9D2 0.970 0.339 0.0 0.00 0.000 0.535 0.076 0.535 YES 0.268 0.465 543.265 548.500 O.K. 314 541.810 2.00 543.410 24 12.883 137.92 0.00289 0.398 7.902 0.242 1.590 0.895 0.313 0.0 0.00 0.000 0.555 2.027 0.555 YES 0.278 0.676 544.220 548.200 O.K. 316 543.290 2.00 544.890 24 11.013 15.02 0.00211 0.032 7.590 0.224 5.090 0.402 0.141 0.0 0.00 0.000 0.364 8.721 0.474 YES 0.237 0.269 545.159 551.350 O.K. 318 544.170 1.25 545.170 15 2.292 36.34 0.00112 0.041 5.090 0.101 0.000 0.000 0.000 0.0 0.00 0.000 0.101 2.292 0.131 YES 0.065 0.106 545.276 556.000 O.K. 322 542.320 1.25 543.320 15 0.248 76.00 0.00001 0.001 2.689 0.028 2.686 0.112 0.039 0.0 0.00 0.000 0.067 0.026 0.067 YES 0.034 0.035 543.355 548.000 O.K. 324 543.nO 1.00 544.510 12 0.222 62.51 0.00003 0.002 2.686 0.028 0.000 0.000 0.000 0.0 0.00 0.000 0.028 0.222 0.036 YES 0.018 0.020 5 1.590 548.500 O.K. 332 543.290 1.00 544.220 12 0.374 16.44 0.00010 0.008 2.434 0.023 2.181 0.074 0.026 0.0 0.00 0.000 0.049 0.121 0.064 YES 0.032 0.039 544.259 548.250 O.K. 334 543.nO 1.00 544.510 12 0.253 63.79 0.00004 0.003 2.181 0.018 1.915 0.057 0.00 0.000 0.038 0.088 0.050 VES 0.025 0.028 544.598336 544.190 1.00 544.990 12 0.16] 28.63 0.00002 0.001 1.915 0.014 1.709 0.045 0.00 0.000 0.030 0.0]5 0.039 VES 0.020 0.020 545.010338 544.430 0.6] 545.010 8 0.092 99.50 0.00005 0.005 1.]09 0.011 0.000 0.000 0.00 0.000 0.011 0.092 0.015 NO 0.015 0.020 545.071EX T020O.0 526.320 40D 532.620 1.25 533.620 15 2.362 52.41 0.00140 0.073 7.371 0.211 0.000 0.000 0.00 0.000 0.211 2.362 0.274 NO 0.2]4 0.34] 534.664 543.880 O.K. LD-229 STORM SEWER DESIGN COMPUTATIONS STORM FREQUENCY 10 PROJECT: Discovery Drive Development LOCATION: UVAF Research Park COUNTY: Albemarle NOAA STATION: Designed by: A Fontaine Checked by: UNITS ENGLISN PIPE NO. FROM POINT TOMINT ORAIN. AREA 'A' Acre 3 RUNOFF COEFF, 'C' 0 CA TOTAL INLET TIME mk, a ] RAIN FALL INW 8 RUNOFF INVERT ELEVATIONS LENGTFY of Npe F1 13 SLOPE Ft Flt 13 SIZE (Du. Or SWa`] Irt IC SHAPE Nrvnb'r of Np Cepsiry CFS IS Friction Slope Ftfft NORMAL FLOW FLOW TIIr1E Sm 17 REMARKS 18 PICR]FACCUM- MENT 5 ULATED 6 Lekrd CFS TAWQ CPS 9 UPPER FNO IR LOWER FNO 11 Deplhof Flow,M Ft Areaof Flow,An SgFr Hm Ft V. FUS c 16 En Ft REFERENCE (I) STA. REFERENCE 2 STA. EX EWI EW2 DW .. RDO 1. Rl1R ---- ----- 58L 1R 22ZW p-0315J ]3 CK'War I 62142 0RW60 L61 5¢ DW 1605 561 1619 LD-229 STORM SEWER DESIGN COMPUTATIONS STORM FREQUENCY 100 PROJECT: 1725 Discovery Drive Development LOCATION: UVAF Research Park COUNTY: Albemarle NOAA STATION: Designetl by: A Fontaine Checked by: UNITS ENGLISN HPE NO. FROM POINT TOPOINT DRAIN. AREA 'A' Mre 3 RUNOFF COEFF, C. 0 CA TOTAL INLET TIME MmNes ] RAIN FALL INW 8 RUNOFF rNVERTELEVATIONS LENGTH mNpe F1 13 SLOPE Ft Flt 13 SIZE (Ow, Or Spavoriz] Irt IC SHAPE of Pipe Nrnnbe162142 Capsm, CFS IS Friction Slope Rot NORMAL FLOW FLOW TIIr1E Sm 17 REMARK$ 18 PICRE-ACCUM- MENT 5 ULATEO 6 Lekrd CFS TAW CPS 9 UPPER FNO IR LOWER FNO 11 Depthof Flow,M Ft Areaof Fvo ,M SqF[ Him Ft V. FUS c 16 En Ft REFERENCE (I) STA. REFERENCE 3 STA. EX EW EW2 Ol1R Ol1R 0-00 5-00 Rl1R 2153U 556AR 58L IR 22ZW 0-03153 73 CK'War I RR0210 2YC 10 ]B 130 1998 863 1139 . \ Mz / a:' \ ,} / § m� ®• 73 47 A0.EA F2 AREA E2 NOTE: DRAINAGE DIVIDES AND AREA NAMES ARE TAKEN FROM "STORMWATER MANAGEMENT/BMP ANALYSIS AND FLOODPLAIN STUDY FOR THE UVA RESEARCH PARK AT NORTHFORK" BY DEWBERRY & DAVIS, DATED OCTOBER 1997. -J �i]11�7i LEWIS AND CLARK DRIVE - STORMWATER MANAGEMENT EXHIBIT FOR POND 1 LEGEND 1-1 HYDROLOGIC SOIL GROUP A, TURF ■ HYDROLOGIC SOIL GROUP A, WOODS 11 HYDROLOGIC SOIL GROUP B, TURF 1-1 HYDROLOGIC SOIL GROUP B, WOODS HYDROLOGIC SOIL GROUP C, TURF HYDROLOGIC SOIL GROUP C, WOODS HYDROLOGIC SOIL GROUP D, TURF HYDROLOGIC SOIL GROUP D, WOODS IMPERMEABLE SURFACES AREA, IN ACRES CN VALUE i DRAINAGE DIVIDE i 1 AREA NAME C> a3 a ', m SCALEnp3gp� 0 a00' fi0V August 18, 2020 DISCOVERY DRIVE / Qq- -- ASSUME 80% IMPER C�CD�F"Y LQABLE AR 49 AC I I / \ B ILD LE REA 1. A / AS UM 80 IMP RVI UVA FOUNDATION - DISCOVERY DRIVE DEVELOPMENT ULTIMATE BUILDOUT CONDITIONS FOR CHANNEL EROSION CONSIDERATION C y7 SCALE 1"=150' 0 150' 300' . •' "•0 TIMMONS GROUP YOUR VISION ACHIEVED THROUGH OURS. DRAINAGE AREA: 22.3 AC DRAINAGE AREA: ZD2 AC DRAINAGE AREA 354 AC DIN S] CHI W LN 70 TC AMIN 1C 2]MIN TO. ZS MIN 2YEARO'13]]CFS 2-YEAR D22.01 CFS 2-YEAR 0:'"D CF3 2-YEAR V. 365 FPS 2-YEAR, V. 3.0. FPS 2YEARV'4.5SFPS 10 YEAR 0: 4325 CFS 10-YEAR 0: 55.25 CFS 10NFAR 0. 15.61 CFS 10NEAR ELEV SYIAT 10 YEAR ELEV: 51073' 10YEAR ELEV. 502.07 535 \ \ no\ 50 \ r us / SZE \ 10.YR WSE 52345' / z o W5D 10-W "'J' CROSS SECTION 1 HOWSCALE 1'rt ' VERTSCALE: 1�5 520 J SID 51B 510 510 III EST 515 ED SID 510 / 505 \ 5% 10-vR WSE 50l \ / so 600 12-M 9.50 10W0 11g3 11.M 9150 1DM0 11• CROSS SECTION 2 CROSS SECTION 3 HOW SCALE: 1'rt HOW SCALE: I'%' VERTSCALE: 1�5 YERTSCALE: 1�6 DMINAGEAREA:H.BAC ON:]2 TO. 29 MIN 2-YEAR 0:4 37 CFS 2-YEAR V 3M FPS 10LYEARO:9619CFS 10YEAR ELEV'495.31' SID 510 \ 505 \ 505 \ 503 � 503 \ i / 495 \ YRWSE 4C 31' a 429 9.50 10-W i 1 A \ \ LEWI6 ANOC gKORIVE / SCAUll �� /% CHANNEL CROSS SECTIONS DMIWIGEAREA: SIAAC CN: TO TO 31 MIN 2-YEAR O: SOXQ DES 2-YEAR V. 3.0 FPS 1PYEOR 0: 118.0 CFS 10-YEAR El 43157' % 495 \ ISO \ / 490 AB lo-mwsE=aaLST W 4 ]5 4] 11-OD 12W0 13-M Ill III 11.00 12100 12150 CROSS SECTION 4 CROSS SECTION 5 HORIZ SOME'. 11501 HOW SCALE :1 SO' VERT SCALE: V=5 VERTSCALE: DE WATER QUANTITY ANALYSIS - CHANNEL ADEQUACY THE NATURAL CHANNEL WAS ANALYZED ACCORDING TO QVAC2Su&M .B AND 9VAC25C4040.19, PER THE NRCS WEB SOIL SURVEY, THE SOIL TYPE ALONG THE ENTIRE CHANNEL IS 36C- HAYESVILLE LOAM. WHICH ASSUMING THE TOP LAYER OF LOAM HAS Vill AWAY, IS CNY. FROM TABLE l (VESCH), THE PERMISSIBLE VELOCITY FOR STIFF CLAY 1550 FPS, THE ESTIMATED ULTIMATE DEVELOPMENT CONDITIONS OF THE DRAINAGE AREA UTILIZING THIS CHANNEL ARE ILLUSTRATED ON THIS SHEET. THE SHADED AREAS REPRESENT THE BUILDABLE AREA AND THE ASSUMPTION IS THAT PO%OF THOSE AREAS WILL BE IMPERVIOUS. THE CN VALUE IS SLIGHTLY DIFFERENT AT EACH CROSS SECTION BASED ON THIS ESTIMATED DEVELOPMENT. BASED ON THE CROSS SECTIONS ABOVE, AND CONSIDERING ULTIMATE DEVELOPMENT CONDITIONS: • 2-YEAR VELOCITY ROUTED THROUGH THE CHANNEL DOES NOT EXCEED 5 FEET PER SECOND AT ANY SECTION. • 10-YEARWATERSURFACEELEVAT10N DOESNOTOVERTOPTHE CHANNEL AT ANY SECTION. THEREFORE THE CHANNEL IS ADEQUATE TO HANDLE THE STORMWATER CONDITIONS RESULTING FROM THE ESTIMATED ULTIMATE DEVELOPMENT CONDITIONS, WHICH INCLUDES THIS PROPOSED SIDE PLAN. 11.50 PEFIDNRPI •• A. FONTAINE • .ECI(EU BY • C. KOTAASRSIG • r=so • CL D 0 U) z 0 44493 C6.�