The URL can be used to link to this page

Home My WebLink AboutNC0000396_SARP_Rev 0_ Appendix D_20161219Amec Foster Wheeler Environment & Infrastructure, Inc. December 2016 Duke Energy Coal Combustion Residuals Management Program Asheville Steam Electric Generating Plant Site Analysis and Removal Plan Revision 0 Appendix D – Engineering Evaluations and Analyses of Closure Design Grading Plans for the 1982 Ash Basin Decommissioning Plan Calculations PMP Containment Calculations nuke Energy — Asheville Steam Electric Generating Plant nam necommissioning Plan Calculation Title: PMP Containment Calculations Summary: This calculation determines the minimum crest elevation required for the existing 1982 Ash Basin Dam to contain the design PMP storm event. Stage -storage curves were developed during the decommissioning design for the ash basin dam and the storage volumes within the existing ash basin. Those stage -storage curves were compared with the PMP stormwater volume, and an elevation of 2126' was determined as the minimum required crest elevation for the dam to contain the storm. Once this elevation is reached the dam will be breached along the left abutment to the active fill area (or lower to facilitate underdrain construction) so that the dam will no longer impound significant volumes of water. Notes: Revision Log: No. Description Amec Foster Wheeler Pmipr.t pin. 7R10-15-0950 1 of a n1/j419n1R (Permit Suhmittal) amec fn,tar �nihcolor PMP Containment Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 2 of 4 01/14/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation is to determine the minimum crest elevation of the 1982 Ash Basin dam that is required to store the PMP design storm event without overtopping. The results of this calculation will be used in the construction sequencing design to determine the point in which the dam should be breached. METHOD: Calculations for the PMP storm event are based on stage-storage information associated with the balanced breach design presented in the drawings. Two stage-storage curves were developed for the balanced breach: 1. Volume of dam material generated during excavation, and 2. Impoundment volume present within the existing ash basin after ash removal. The design storm volume was compared to the stage-storage curves to determine the minimum crest elevation required. CALCULATIONS: 1.0 Volume of Dam Material Generated During Excavation A stage-volume curve was developed for the material in the current 1982 Ash Basin Dam that will be used as fill material. The volumes were determined using the computer program AutoCAD Civil 3D. AutoCAD calculates these volumes based on triangulation methods. The volumes were calculated between the crest elevation of approximately 2166’ to an elevation of 2090’. As shown on Figure 1, the cumulative volume present within the 1982 Ash Basin Dam between these elevations is approximately 208 acre-feet. The AutoCAD output of these volumes is included with this calculation as Attachment 1. 2.0 Impoundment Volume within the Existing Ash Basin Storage volumes that will be present within the existing 1982 Ash Basin were also calculated. As part of the decommissioning process, ash that is currently present within the basin will be removed and transported offsite. Therefore, post ash excavation grades were developed for the 1982 Ash Basin, which will represent the configuration of the basin before dam decommissioning activities commence. Using the post ash excavation grades, a stage-storage curve was developed for the storage volume available. The stage-storage curve was calculated using AutoCAD Civil 3D’s triangulation methods. The storage volumes were calculated between the basin elevations of 2074’ and 2130’. As shown on Figure 1, the cumulative storage volume present within the 1982 Ash Basin between these elevations is approximately 492 acre-feet. The AutoCAD output of these volumes is included with this calculation as Attachment 2. PMP Containment Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 3 of 4 01/14/2016 (Permit Submittal) Figure 1: Stage-Storage Curves for the 1982 Ash Basin 3.0 PMP Storage Volume Calculations The design storm volumes for the 1982 Ash Basin was modeled using a Full PMP storm event. These calculations were performed as part of the Phase 2 Reconstitution for the site. As determined from the “Asheville 1964 and 1982 Ash Ponds – Hydrologic and Hydraulic (H&H) Analysis,” the design storm volume under a Full PMP storm event is 258 acre-feet. To calculate the minimum required crest elevation to contain the design storm event, the design storm volume of 258 acre-feet was also plotted with the stage-storage curves presented on Figure 1. As part of the balanced breach activities, excavated materials from the dam will be used as fill materials within the basin. The intersection of the two curves is at 2110’ and 138 acre- feet, thus representing the idealized balanced breach elevation and volume, respectively. It should be noted that the design drawings [Ref. 4] show a balanced breach at elevation 2106’. The final design reflects a lower breach elevation, as more material is necessary to slope the proposed backfill to allow for stormwater drainage. However, the calculation herein presents the idealized balanced breach, which is applicable for interim construction conditions. 2060 2070 2080 2090 2100 2110 2120 2130 2140 2150 2160 2170 2180 0 50 100 150 200 250 300 350 400 450 500 El e v a t i o n (f t ) Volume (acre‐ft) Stage‐Storage Curves PMP 1982 Basin Storage 1982 Dam Breach 258 acre‐ft 2126 PMP Containment Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 4 of 4 01/14/2016 (Permit Submittal) The design storm volume of 258 acre-feet was drawn at the idealized intersection at elevation 2110’, and new line intersects were drawn to determine the required dam crest elevation to contain the storm volume. As shown on Figure 1, a minimum dam elevation of 2126’ is required during balanced breach activities to contain the design storm event. DISCUSSION: During the decommissioning activities, the PMP design storm volume will initially be contained within the existing 1982 Ash Basin at the site. However, as construction of the dam breach progresses, storage volume within the existing basin will be decreased as the dam is lowered and backfill is placed within the basin. Once the basin is no longer able to contain the PMP storm event, a breach through the dam is necessary to safely convey the stormwater runoff away from the basin and prevent overtopping of the dam. Using stage-storage curves for both the dam excavation and the storage volume within the basin, it was determined that the PMP storm event could be contained with a minimum dam elevation of 2126’. REFERENCES: 1. “Asheville 1964 and 1982 Ash Ponds – Hydrologic and Hydraulic (H&H) Analysis,” Phase 2 Reconstitution of Design, December 30, 2014. 2. Microsoft Excel 2013, Microsoft Corporation. 3. AutoCAD Civil 3D 2015, AutoDesk Inc. 4. Amec Foster Wheeler, “Decommissioning and Ash Removal Plan, 1982 Ash Basin,” January 14, 2016. ATTACHMENTS: Attachment 1 – 1982 Ash Basin Dam Breach Volumes AutoCAD Output Attachment 2 – 1982 Ash Basin Storage Volumes AutoCAD Output PMP Containment Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 01/14/2016 (Permit Submittal) Attachment 1 1982 Ash Basin Dam Breach Volumes AutoCAD Output 1982 Dam Breech-Volumes by Triangulation (Prisms).txt Volumes by Triangulation (Prisms) Wed Jan 06 12:03:24 2016 Existing Surface: P:\CADD\Projects\7810\7810150250 Asheville Pond\100% Design Package Pond 1982 & 1964 Closure\Work\APT\1982 Dam Breech Base.tin Final Surface: P:\CADD\Projects\7810\7810150250 Asheville Pond\100% Design Package Pond 1982 & 1964 Closure\Work\APT\1982 Dam Breech.tin Cut volume: 9,042,998.3 C.F., 334,925.86 C.Y. Fill volume: 565.7 C.F., 20.95 C.Y. Area in Cut : 285,518.5 S.F., 6.55 Acres Area in Fill: 477.4 S.F., 0.01 Acres Total inclusion area: 286,004.9 S.F., 6.57 Acres Average Cut Depth: 31.67 feet Cut to Fill ratio: 15984.50 Export Volume: 334,904.9 C.Y. Elevation Change To Reach Balance: 31.616 Volume Change Per .1 ft: 1,059.3 C.Y. Cut (C.Y.) / Area (acres): 51010.91 Fill (C.Y.) / Area (acres): 3.19 Max Cut: 76.000 at 944892.414,642851.901 Max Fill: 2.915 at 944500.922,643111.262 Elevation Zone Volumes Zone: 2166.000 to 2168.000 Cut Volume : 314.49 C.F., 11.65 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Zone: 2164.000 to 2166.000 Cut Volume : 35,794.31 C.F., 1,325.72 C.Y. Fill Volume : 1.47 C.F., 0.05 C.Y. Running Totals: Cut Volume : 36,108.80 C.F., 1,337.36 C.Y. Fill Volume : 1.47 C.F., 0.05 C.Y. Zone: 2162.000 to 2164.000 Cut Volume : 64,747.36 C.F., 2,398.05 C.Y. Fill Volume : 0.32 C.F., 0.01 C.Y. Running Totals: Cut Volume : 100,856.16 C.F., 3,735.41 C.Y. Fill Volume : 1.79 C.F., 0.07 C.Y. Zone: 2160.000 to 2162.000 Cut Volume : 83,739.29 C.F., 3,101.46 C.Y. Fill Volume : 0.07 C.F., 0.00 C.Y. Running Totals: Cut Volume : 184,595.45 C.F., 6,836.87 C.Y. Fill Volume : 1.86 C.F., 0.07 C.Y. Zone: 2158.000 to 2160.000 Cut Volume : 102,073.34 C.F., 3,780.49 C.Y. Fill Volume : 0.10 C.F., 0.00 C.Y. Running Totals: Cut Volume : 286,668.79 C.F., 10,617.36 C.Y. Fill Volume : 1.95 C.F., 0.07 C.Y. Zone: 2156.000 to 2158.000 Cut Volume : 119,667.30 C.F., 4,432.12 C.Y. Fill Volume : 0.02 C.F., 0.00 C.Y. Running Totals: Page 1 1982 Dam Breech-Volumes by Triangulation (Prisms).txt Cut Volume : 406,336.10 C.F., 15,049.49 C.Y. Fill Volume : 1.97 C.F., 0.07 C.Y. Zone: 2154.000 to 2156.000 Cut Volume : 136,460.10 C.F., 5,054.08 C.Y. Fill Volume : 0.01 C.F., 0.00 C.Y. Running Totals: Cut Volume : 542,796.20 C.F., 20,103.56 C.Y. Fill Volume : 1.98 C.F., 0.07 C.Y. Zone: 2152.000 to 2154.000 Cut Volume : 152,439.02 C.F., 5,645.89 C.Y. Fill Volume : 0.07 C.F., 0.00 C.Y. Running Totals: Cut Volume : 695,235.23 C.F., 25,749.45 C.Y. Fill Volume : 2.05 C.F., 0.08 C.Y. Zone: 2150.000 to 2152.000 Cut Volume : 167,634.39 C.F., 6,208.68 C.Y. Fill Volume : 7.53 C.F., 0.28 C.Y. Running Totals: Cut Volume : 862,869.61 C.F., 31,958.13 C.Y. Fill Volume : 9.58 C.F., 0.35 C.Y. Zone: 2148.000 to 2150.000 Cut Volume : 181,338.47 C.F., 6,716.24 C.Y. Fill Volume : 366.78 C.F., 13.58 C.Y. Running Totals: Cut Volume : 1,044,208.08 C.F., 38,674.37 C.Y. Fill Volume : 376.36 C.F., 13.94 C.Y. Zone: 2146.000 to 2148.000 Cut Volume : 193,633.69 C.F., 7,171.62 C.Y. Fill Volume : 187.75 C.F., 6.95 C.Y. Running Totals: Cut Volume : 1,237,841.77 C.F., 45,845.99 C.Y. Fill Volume : 564.11 C.F., 20.89 C.Y. Zone: 2144.000 to 2146.000 Cut Volume : 205,482.72 C.F., 7,610.47 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 1,443,324.49 C.F., 53,456.46 C.Y. Fill Volume : 564.11 C.F., 20.89 C.Y. Zone: 2142.000 to 2144.000 Cut Volume : 216,571.67 C.F., 8,021.17 C.Y. Fill Volume : 0.10 C.F., 0.00 C.Y. Running Totals: Cut Volume : 1,659,896.16 C.F., 61,477.64 C.Y. Fill Volume : 564.21 C.F., 20.90 C.Y. Zone: 2140.000 to 2142.000 Cut Volume : 227,265.20 C.F., 8,417.23 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 1,887,161.36 C.F., 69,894.87 C.Y. Fill Volume : 564.21 C.F., 20.90 C.Y. Zone: 2138.000 to 2140.000 Cut Volume : 237,438.41 C.F., 8,794.02 C.Y. Fill Volume : 0.22 C.F., 0.01 C.Y. Running Totals: Page 2 1982 Dam Breech-Volumes by Triangulation (Prisms).txt Cut Volume : 2,124,599.77 C.F., 78,688.88 C.Y. Fill Volume : 564.43 C.F., 20.90 C.Y. Zone: 2136.000 to 2138.000 Cut Volume : 246,970.04 C.F., 9,147.04 C.Y. Fill Volume : 0.08 C.F., 0.00 C.Y. Running Totals: Cut Volume : 2,371,569.82 C.F., 87,835.92 C.Y. Fill Volume : 564.51 C.F., 20.91 C.Y. Zone: 2134.000 to 2136.000 Cut Volume : 255,418.40 C.F., 9,459.94 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 2,626,988.22 C.F., 97,295.86 C.Y. Fill Volume : 564.51 C.F., 20.91 C.Y. Zone: 2132.000 to 2134.000 Cut Volume : 262,753.18 C.F., 9,731.60 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 2,889,741.40 C.F., 107,027.46 C.Y. Fill Volume : 564.51 C.F., 20.91 C.Y. Zone: 2130.000 to 2132.000 Cut Volume : 267,889.22 C.F., 9,921.82 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 3,157,630.62 C.F., 116,949.28 C.Y. Fill Volume : 564.51 C.F., 20.91 C.Y. Zone: 2128.000 to 2130.000 Cut Volume : 271,568.38 C.F., 10,058.09 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 3,429,199.00 C.F., 127,007.37 C.Y. Fill Volume : 564.51 C.F., 20.91 C.Y. Zone: 2126.000 to 2128.000 Cut Volume : 275,646.87 C.F., 10,209.14 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 3,704,845.87 C.F., 137,216.51 C.Y. Fill Volume : 564.51 C.F., 20.91 C.Y. Zone: 2124.000 to 2126.000 Cut Volume : 279,366.71 C.F., 10,346.92 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 3,984,212.58 C.F., 147,563.43 C.Y. Fill Volume : 564.51 C.F., 20.91 C.Y. Zone: 2122.000 to 2124.000 Cut Volume : 282,625.92 C.F., 10,467.63 C.Y. Fill Volume : 0.09 C.F., 0.00 C.Y. Running Totals: Cut Volume : 4,266,838.50 C.F., 158,031.06 C.Y. Fill Volume : 564.60 C.F., 20.91 C.Y. Zone: 2120.000 to 2122.000 Cut Volume : 285,514.94 C.F., 10,574.63 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Page 3 1982 Dam Breech-Volumes by Triangulation (Prisms).txt Cut Volume : 4,552,353.43 C.F., 168,605.68 C.Y. Fill Volume : 564.60 C.F., 20.91 C.Y. Zone: 2118.000 to 2120.000 Cut Volume : 289,722.86 C.F., 10,730.48 C.Y. Fill Volume : 0.06 C.F., 0.00 C.Y. Running Totals: Cut Volume : 4,842,076.30 C.F., 179,336.16 C.Y. Fill Volume : 564.66 C.F., 20.91 C.Y. Zone: 2116.000 to 2118.000 Cut Volume : 294,265.15 C.F., 10,898.71 C.Y. Fill Volume : 0.21 C.F., 0.01 C.Y. Running Totals: Cut Volume : 5,136,341.44 C.F., 190,234.87 C.Y. Fill Volume : 564.87 C.F., 20.92 C.Y. Zone: 2114.000 to 2116.000 Cut Volume : 297,227.92 C.F., 11,008.44 C.Y. Fill Volume : 0.23 C.F., 0.01 C.Y. Running Totals: Cut Volume : 5,433,569.36 C.F., 201,243.31 C.Y. Fill Volume : 565.10 C.F., 20.93 C.Y. Zone: 2112.000 to 2114.000 Cut Volume : 298,522.04 C.F., 11,056.37 C.Y. Fill Volume : 0.13 C.F., 0.00 C.Y. Running Totals: Cut Volume : 5,732,091.41 C.F., 212,299.68 C.Y. Fill Volume : 565.23 C.F., 20.93 C.Y. Zone: 2110.000 to 2112.000 Cut Volume : 298,002.05 C.F., 11,037.11 C.Y. Fill Volume : 0.04 C.F., 0.00 C.Y. Running Totals: Cut Volume : 6,030,093.46 C.F., 223,336.79 C.Y. Fill Volume : 565.27 C.F., 20.94 C.Y. Zone: 2108.000 to 2110.000 Cut Volume : 297,974.54 C.F., 11,036.09 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 6,328,068.00 C.F., 234,372.89 C.Y. Fill Volume : 565.27 C.F., 20.94 C.Y. Zone: 2106.000 to 2108.000 Cut Volume : 299,642.95 C.F., 11,097.89 C.Y. Fill Volume : 0.17 C.F., 0.01 C.Y. Running Totals: Cut Volume : 6,627,710.95 C.F., 245,470.78 C.Y. Fill Volume : 565.44 C.F., 20.94 C.Y. Zone: 2104.000 to 2106.000 Cut Volume : 301,147.46 C.F., 11,153.61 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 6,928,858.41 C.F., 256,624.39 C.Y. Fill Volume : 565.44 C.F., 20.94 C.Y. Zone: 2102.000 to 2104.000 Cut Volume : 302,469.88 C.F., 11,202.59 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Page 4 1982 Dam Breech-Volumes by Triangulation (Prisms).txt Cut Volume : 7,231,328.28 C.F., 267,826.97 C.Y. Fill Volume : 565.44 C.F., 20.94 C.Y. Zone: 2100.000 to 2102.000 Cut Volume : 303,159.42 C.F., 11,228.13 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 7,534,487.70 C.F., 279,055.10 C.Y. Fill Volume : 565.44 C.F., 20.94 C.Y. Zone: 2098.000 to 2100.000 Cut Volume : 302,756.31 C.F., 11,213.20 C.Y. Fill Volume : 0.31 C.F., 0.01 C.Y. Running Totals: Cut Volume : 7,837,244.01 C.F., 290,268.30 C.Y. Fill Volume : 565.74 C.F., 20.95 C.Y. Zone: 2096.000 to 2098.000 Cut Volume : 301,936.72 C.F., 11,182.84 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 8,139,180.72 C.F., 301,451.14 C.Y. Fill Volume : 565.75 C.F., 20.95 C.Y. Zone: 2094.000 to 2096.000 Cut Volume : 301,296.97 C.F., 11,159.15 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 8,440,477.70 C.F., 312,610.29 C.Y. Fill Volume : 565.75 C.F., 20.95 C.Y. Zone: 2092.000 to 2094.000 Cut Volume : 301,078.88 C.F., 11,151.07 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 8,741,556.58 C.F., 323,761.35 C.Y. Fill Volume : 565.75 C.F., 20.95 C.Y. Zone: 2090.000 to 2092.000 Cut Volume : 301,433.49 C.F., 11,164.20 C.Y. Fill Volume : 0.00 C.F., 0.00 C.Y. Running Totals: Cut Volume : 9,042,990.07 C.F., 334,925.56 C.Y. Fill Volume : 565.75 C.F., 20.95 C.Y. Page 5 PMP Containment Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 01/14/2016 (Permit Submittal) Attachment 2 1982 Ash Basin Storage Volumes AutoCAD Output 1982 Ash Removal-Pond Storage Volumes.txt Pond Storage Volumes Wed Jan 06 10:05:48 2016 Water Elev Storage(AcreFt) (C.Y.) (C.F.) Area(Acre) 2074.00 0.00122 2.0 53.0 0.005 2076.00 0.09708 156.6 4228.7 0.108 2078.00 0.43280 698.3 18852.9 0.203 2080.00 0.96722 1560.4 42131.9 0.319 2082.00 1.78284 2876.3 77660.3 0.463 2084.00 2.93112 4728.9 127679.4 0.662 2086.00 4.57653 7383.5 199353.6 0.960 2088.00 6.82646 11013.4 297360.6 1.270 2090.00 9.78460 15785.8 426217.2 1.664 2092.00 13.63750 22001.8 594049.5 2.140 2094.00 18.41436 29708.5 802129.5 2.632 2096.00 24.23012 39091.3 1055464.1 3.167 2098.00 31.25953 50432.0 1361665.0 3.797 2100.00 39.79823 64207.8 1733611.1 4.741 2102.00 52.63097 84911.3 2292605.0 7.809 2104.00 69.45406 112052.5 3025418.8 8.982 2106.00 88.42905 142665.5 3851969.6 9.956 2108.00 109.27234 176292.7 4759902.9 10.880 2110.00 132.05249 213044.7 5752206.3 11.872 2112.00 156.86645 253077.9 6833102.5 12.925 2114.00 183.69336 296358.6 8001682.7 13.918 2116.00 212.95642 343569.7 9276381.6 15.183 2118.00 244.59829 394618.6 10654701.7 16.421 2120.00 278.85199 449881.2 12146792.5 17.770 2122.00 315.93646 509710.8 13762192.0 19.286 2124.00 355.91596 574211.1 15503699.3 20.646 2126.00 398.63035 643123.6 17364338.2 22.027 2128.00 444.17086 716595.7 19348082.7 23.446 2130.00 492.47209 794521.6 21452084.1 24.826 Page 1 slnpe Stahility of nam Rrearh (alculatinns Duke Energy — Asheville Steam Electric Generating Plant I)am Dernmmissinnjng Plan Calr_ulation Iitle: Slope Stability of Dam Breach Calculations Summary: This calculation determines the stability of the existing 1982 Ash Basin Dam after dam decommissioning and final grading activities are completed. In this analysis, seepage modeling was performed using SEEP/W, and slope stability modeling was performed using SLOPE/W. Both steady- state and pseudo -static scenarios were analyzed using both circular and block failure surfaces. The slope stability modeling resulted in factors of safety greater than the minimum required values accepted under current geotechnical engineering standards of practice. Notes: Revision Log: No. Description Originator / D ...ua��nrrnr.,._ Technical Reviewer / Date Luke V #O .Es ARO ��'y Carl Tockstein, PE O Initial Suhmjttal P41 f— /`f ' ��E' _/•ram` �n a` Amec Foster Wheeler Project No. 7810-15-0250 1 of 4 01 /14/2016 (Permit Submittal) amec foster whaalar Slope Stability of Dam Breach Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 2 of 4 01/14/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation is to evaluate the stability of the existing 1982 Ash Basin Dam after dam decommissioning and final grading activities are completed. Seepage and slope stability modeling were performed through the section of the embankment with the highest existing embankment height using the proposed final grading as shown on the project drawings. METHOD: Seepage and slope stability modeling were performed using GeoStudio 2012 computer software. The seepage analysis was performed using SEEP/W to calculate the pore water pressures through the profile under possible upstream water level scenarios. The stability analysis was performed using 2-dimensional limit equilibrium analysis based on the method of slices according to the Spencer Method using SLOPE/W. This method satisfies both force and moment equilibrium and incorporates the effects of interslice forces. Search methods built into the software were used to determine the minimum (critical) factors of safety for circular and block failure geometries. The analyses performed consider the impoundment under conditions that will exist a sufficient length of time after construction to reach equilibrium both within and underneath the impoundment. In this scenario, the embankment is no longer acting as a dam that is impounding water, steady-state seepage and/or hydrostatic conditions have developed, and drained (effective stress) shear strengths were used for all materials. In addition, a pseudo-static analysis was performed to model the effects of earthquake loading on the cross-section. In this scenario, undrained (total stress) parameters were also used for materials with low permeability. CALCULATIONS: 1.0 Geometry and Material Properties The geometry of the modeled section was first developed based upon the final grading configuration as shown on the design drawings. Profile 1 from Sheet C-1.5 was used to develop the final grades in the SLOPE/W and SEEP/W models. After the final grades were established, the subsurface geometries were also incorporated into the model. These geometries were developed based upon previous sections from the Phase 2 Reconstitution of Design report (Reference 1). Section 17+50 for the 1982 Ash Basin Dam was used to determine the subsurface geometries, as it closely matched the intersection of Profile 1 through the embankment. Material properties for this analysis were established from the previously developed values from the Phase 2 Reconstitution of Design report. The materials previously used in the Phase 2 Reconstitution of Design report consist of “Embankment Fill”, “Sand Drain”, “Foundation Soil (Residuum)”, and “Weathered Rock”. As part of this analysis, an additional material named “Backfill” was also developed to represent the backfill soils used in the final grading design. Since the backfill will consist of embankment soils as part of the balanced breach design, the material Slope Stability of Dam Breach Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 3 of 4 01/14/2016 (Permit Submittal) properties of these two materials were modeled as the same. See Table 1 for a summary of material properties used in the analysis. Table 1 – Material Properties used in the Analysis Unit Material Description Unit Weight (psf) Shear Strength Coefficient of Permeability Effective Total c' (psf) Φ’ (degrees) c (psf) Φ (degrees) k (ft/sec) Embankment Fill 120 400 33.9 0 32.8 3.77 x 10‐8 Sand Drain 120 0 36 0 36 3.28 x 10‐5 Foundation Soil (Residuum) 130 400 32 650 30 4.63 x 10‐7 Weathered Rock 135 10000 45 10000 45 4.63 x 10‐7 Backfill 120 400 33.9 0 32.8 3.77 x 10‐8 2.0 Seepage Modeling The seepage modeling was performed with SEEP/W using the permeability values and functions previously developed as part of the Phase 2 Reconstitution of Design report. For the current model, the upstream boundary conditions was modeled using a total head of 2110’. This elevation corresponds with the emergence of Wet Area 1 as shown on the design drawings. Thus, the phreatic surface for this model was analyzed by using the observed wet area as the primary source of flow upstream of the balanced breach. SEEP/W was used to predict the phreatic surface through the remainder of the cross-section, with the results showing a consistent drop down to the “Sand Drain” layer shown in the model at the exit of the existing embankment. The results from the seepage modeling are included as Attachment 1. 3.0 Slope Stability Modeling As mentioned previously, slope stability results were generated for two scenarios: steady-state conditions and pseudo-static conditions. In both scenarios, the phreatic surface generated from the seepage modeling was used, and both circular and block failures were considered. In the steady-state models, the effective stresses of the materials were used for each region as shown in Table 1. These models result in a circular failure factor of safety of 2.54 and a block failure factor of safety of 5.02. In the pseudo-static models, the total stresses of the materials were used for each region as shown in Table 1. In addition, a horizontal seismic coefficient of 0.20g was also applied to the model, as was performed previously in the Phase 2 Reconstitution of Design report. This horizontal seismic coefficient represents the anticipated earthquake accelerations predicted for the Asheville site under the design earthquake. These models result in a circular failure factor of safety of 1.08 and a block failure factor of safety of 1.85. Slope Stability of Dam Breach Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 4 of 4 01/14/2016 (Permit Submittal) DISCUSSION: The seepage and slope stability modeling performed for this analysis resulted in slope stability factors of safety above 2.5 for steady-state conditions and above 1.0 for pseudo-static conditions. According to geotechnical engineering standards of practice, minimum acceptable values for each of these scenarios are regarded as 1.5 for steady-state conditions and 1.0 for pseudo-static conditions. Therefore, the slope stability results in these models predict acceptable factors of safety for the final grades proposed for the 1982 Ash Basin Dam. REFERENCES: 1.“Calculation No. G-004: Slope Stability Analysis of Embankments,” Phase 2 Reconstitution of Design, December 31, 2014. 2.SEEP/W, GeoStudio 2012, GEO-SLOPE International Ltd. 3.SLOPE/W, GeoStudio 2012, GEO-SLOPE International Ltd. ATTACHMENTS: Attachment 1 – SEEP/W Output File Attachment 2 – SLOPE/W Output Files Slope Stability of Dam Breach Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 01/14/2016 (Permit Submittal) Attachment 1 SEEP/W Output File Scale Exaggerated 2V per 1H Seepage Analysis Distance (feet) -1,200 -1,150 -1,100 -1,050 -1,000 -950 -900 -850 -800 -750 -700 -650 -600 -550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 El e v a t i o n 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 El e v a t i o n ( f e e t , N A V D - 8 8 ) 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 Slope Stability of Dam Breach Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 01/14/2016 (Permit Submittal) Attachment 2 SLOPE/W Output Files 2.54 Scale Exaggerated 2V per 1H Steady-State Analysis Circular Failure Distance (feet) -1,200 -1,150 -1,100 -1,050 -1,000 -950 -900 -850 -800 -750 -700 -650 -600 -550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 El e v a t i o n 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 El e v a t i o n ( f e e t , N A V D - 8 8 ) 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 5.02 Scale Exaggerated 2V per 1H Steady-State Analysis Block Failure Distance (feet) -1,200 -1,150 -1,100 -1,050 -1,000 -950 -900 -850 -800 -750 -700 -650 -600 -550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 El e v a t i o n 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 El e v a t i o n ( f e e t , N A V D - 8 8 ) 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 1.08 Scale Exaggerated 2V per 1H Pseudo-Static Analysis Circular Failure Horz Seismic Coef.: 0.2 Distance (feet) -1,200 -1,150 -1,100 -1,050 -1,000 -950 -900 -850 -800 -750 -700 -650 -600 -550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 El e v a t i o n 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 El e v a t i o n ( f e e t , N A V D - 8 8 ) 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 1.85 Scale Exaggerated 2V per 1H Pseudo-Static Analysis Block Failure Horz Seismic Coef.: 0.2 Distance (feet) -1,200 -1,150 -1,100 -1,050 -1,000 -950 -900 -850 -800 -750 -700 -650 -600 -550 -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 El e v a t i o n 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 El e v a t i o n ( f e e t , N A V D - 8 8 ) 2,000 2,010 2,020 2,030 2,040 2,050 2,060 2,070 2,080 2,090 2,100 2,110 2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190 2,200 2,210 Final Conditions Stormwater Calculation Duke Energy — Asheville Steam Station Dam Decommissioning Plan Calculation Title: Final Conditions Stormwater Calculation Summary: Stormwater channels and culverts were designed to convey stormwater for the 100 year, 24-hour design storm event (1 % annual) from the 1982 and Ash Basin considering final closure conditions. The Interstate 26 culvert crossing downstream of the 1982 basin was also evaluated for the 100-year 6-hr event. Notes: Revision Log: No. Description Originator / Date Technical Reviewer / Date Luke C a i+r6, Daniel R. Smith 0 '`` O oFEss •• ��''' o4y903 / '01NE a �C Amec Foster Wheeler Prnject No. 7R1 n1 sn9sn 1 of 8 n1 i14ign1 s amarf foster wh..I.r Final Conditions Stormwater Calculation Dam Decommissioning Plan Duke Energy – Asheville Steam Station Amec Foster Wheeler Project No. 7810150250 2 of 8 01/14/2016 OBJECTIVE: The objective of this calculation is to design the stormwater conveyance measures based on proposed conditions after decommissioning of the 1982 Ash Basin. METHOD: Stormwater flow rates were calculated using the SCS runoff method. The hydraulic capacity of proposed stormwater channels was evaluated using Manning’s equation. Channel lining was determined using the permissible shear stress approach specified in FHWA HEC-15. The Interstate 26 culvert was evaluated using standard procedures specified in FHWA HDS-5. CALCULATIONS: 1.0 Hydrology Drainage areas were developed from the final grading plan drawings and represent final condition after closure of the 1982 Ash Basin. The drainage areas are shown in Figure 1. Runoff coefficients (SCS curve number) and flow travel times (time concentration) were determined using standard methods documented in the National Engineering Hand Book Part 630 Hydrology for each of the drainage areas. The runoff coefficients for the 1982 basin considered the ground surface to be vegetated and have a minimum of 75 percent grass cover. The soils for the ash basin and existing plant footprints were considered to have moderately high runoff potential (HSG C classification) because of the disturbed nature of these soils. Area outside the 1982 ash basin and existing plant footprints were considered to have moderately low runoff potential (HSG B classification) as determined from NRCS soil mapping data. The hydrologic input parameters for the 1982 basin are summarized in the Table 1. Table 1: Summary of Drainage Areas 1982 Basin Drainage Area Area (acres)Area (mi 2 )Curve Number CN Tc (hr)Lag Time (min) 1982 East1 31.3 0.0489 68 0.44 16 1982 East2 28.5 0.0445 71 0.468 17 1982 East Lower 5.9 0.0092 74 0.186 7 1982 West 40.9 0.0638 79 0.564 20 1982 Lower 15.5 0.0242 58 0.329 12 Proposed stormwater channels were designed for the 100-year 24-hour storm event. Temporary sediment control structures were designed for the 10-year 24-hour storm event. Table 2 below shows the precipitation depth for these three storm events. Precipitation depths were retrieved from NOAA Precipitation Frequency Data Server (Atlas 14) (Attachment 1). Final Conditions Stormwater Calculation Dam Decommissioning Plan Duke Energy – Asheville Steam Station Amec Foster Wheeler Project No. 7810150250 3 of 8 01/14/2016 Table 2: Summary of Precipitation Depths Design Event Precipitation Depth (in) Precipitation Distribution 10‐year (24 ‐hr) 4.28 SCS Type II 100‐year (24 ‐hr) 6.31 SCS Type II Peak runoff rates for the drainage areas were determined using the SCS runoff approach within the USACE HEC-HMS hydrology model. Peak runoff rates for the 1982 basin are shown in Table 3. Table 3: Summary 1982 Basin Peak Flowrates Drainage Area Peak 10‐year Flow (cfs) Peak 100‐year Flow (cfs) Peak 500‐year Flow (cfs) 1982 East1 40 87 126 1982 East2 41 85 120 1982 East Lower 15 29 40 1982 West 76 138 187 1982 Lower 11 33 52 Final Conditions Stormwater Calculation Dam Decommissioning Plan Duke Energy – Asheville Steam Station Amec Foster Wheeler Project No. 7810150250 4 of 8 01/14/2016 2.0 Hydraulics 2.1 Proposed Stormwater Channels Stormwater channels were designed to convey runoff from the 1982 basin for the 100-year flood event in a safe and non-erosive manner. The Manning formula was used to determine the 100- year flow depth in the channels. The shear stress along the channel bottom and sides was calculated to determine appropriate channel lining following the HEC-15 approach for design of riprap lined channels. The stormwater channels located within the basins generally have slopes near 1 percent and were lined with North Carolina Department of Transportation (NCDOT) Class B riprap having a median diameter of 8 inches. The stormwater channels that convey stormwater from the dam breach location to the toe of the abutment, called “outlet” channels on the design drawings, have relatively steep slopes and were lined with NCDOT Class 2 riprap having a median diameter of 14 inches. The proposed stormwater channel dimensions are presented in Table 4. Table 5 shows the riprap sizes for the NCDOT Class B and Class 2 riprap. Table 4: Summary of Stormwater Channels 1982 Basin Channel ID Q100 (cfs) Average Velocity (ft/s) Slope (ft/ft)Channel Type Side Slope (H:V) Bottom Width (ft) Flow Depth (ft)Lining Type 1982 West 138 3.7 0.01 Trapezoidal 2 5 3.2 Class B 1982 West Outlet 138 8.9 0.15 Trapezoidal 3 15 0.9 Class 2 1982 East 2 85 3.1 0.01 Trapezoidal 2 5 2.6 Class B 1982 East 1 87 3.2 0.01 Trapezoidal 2 5 2.7 Class B 1982 East 171 3.9 0.01 Trapezoidal 2 8 3.1 Class B 1982 East Outlet 186 9.5 0.15 Trapezoidal 3 20 0.9 Class 2 1982 Basin Channel Summary Table 5: NCDOT Riprap Sizes Minimum Midrange Maximum A246 B5812 151017 291423 Acceptance Criteria for Rip Rap and Stone for Erosion Control Class Required Stone Sizes (inches) Final Conditions Stormwater Calculation Dam Decommissioning Plan Duke Energy – Asheville Steam Station Amec Foster Wheeler Project No. 7810150250 5 of 8 01/14/2016 3.0 Interstate 26 Culvert Interstate 26 is located below the 1982 basin. Stormwater runoff from the 1982 basin will be directed to existing culvert running underneath I-26. The culvert underneath I-26 is a 66-in diameter RCP culvert with a concrete headwall. A summary of I-26 culvert is shown in Table 6 below. Table 6: Summary of I-26 Culvert I ‐26 Culvert Structure Inlet Invert (ft) Outlet Invert (ft)Length (ft) Slope (ft/ft) Top Road Elevation (ft) Below 1982 Basin 66" RCP 2043.5 2040 273 0.013 2052.6 Table 7 and Figure 1 show the headwater elevations versus culvert discharge for the 66” CMP I- 26 culvert below the 1982 basin. Note the tailwater condition (elevation) for the I-26 culvert was considered to be the water elevation for the 10-year flood elevation of the French Broad or the normal flow depth of the downstream channel whichever was greater. The French Broad River has a 10-year flood elevation near 2039’ (culvert outlet not submerged) at the culvert location which is lower than the normal flow depth of the downstream channel. Therefore, for the I-26 culvert analysis the culvert tailwater condition was set to normal depth of the downstream channel. Headwater elevations for the I-26 culverts were estimated to determine the impact of the proposed 1982 basin closure and stormwater plan. The 100-year headwater elevation was evaluated. Flood storage behind the I-26 road embankment was considered and a storage routing model was developed in HEC-HMS. Topography data from USGS digital elevation model (1 meter) was utilized in estimating available flood storage volumes behind the I-26 embankment. Figure 2 shows the rating curve for the storage area between the toe of the 1982 basin and upstream the I-26 embankment. Table 7: Discharge Curve for I-26 Culvert (1982) Headwater Elevation (ft)Flow (cfs) 2043.5 0 2045.71 36 2046.8 72 2047.74 108 2048.59 144 2049.47 180 2050.45 216 2051.6 252 I ‐26 Culvert (1982) *Top Pavement Elevation = 2052.6' **Inlet Invert Elevation = 2043.5' Final Conditions Stormwater Calculation Dam Decommissioning Plan Duke Energy – Asheville Steam Station Amec Foster Wheeler Project No. 7810150250 6 of 8 01/14/2016 Figure 1: Discharge Curve for I-26 Culvert (1982) Figure 2: Storage Curve for I-26 Culvert (1982) 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 0 50 100 150 200 250 300 350 400 El e v a t i o n (N A V D 88 ) Culvert Discharge (cfs) I‐26 Culvert Performance Curve below 1982 Basin 66‐in RCP Top Pavement = 2052.6' 2042 2044 2046 2048 2050 2052 2054 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 El e v a t i o n (N A V D 88 ) Storage Volume (ac‐ft) Available Storage below 1982 Basin upstream I‐26 Embankment 1982 Outlet Final Conditions Stormwater Calculation Dam Decommissioning Plan Duke Energy – Asheville Steam Station Amec Foster Wheeler Project No. 7810150250 7 of 8 01/14/2016 The headwater elevation behind the I-26 embankment for the 100-year 6-hr flood is shown in Table 8. The headwater elevation below the 1982 basin for the 100-year event is 2050.7’ which is approximately 1.9 feet below the road embankment. Coordination with NCDOT will be required to determine if additional flow capacity is needed below the 1982 basin to lower the headwater depths upstream of I-26. Table 8: Headwater Elevations at I-26 Embankment Headwater Elevation (ft) Freeboard from Top Pavement (ft)HW/D Below 1982 Basin 2043.5 2050.7 1.9 1.3 I ‐26 Culverts Inlet Invert (ft) 100‐year 6 ‐hour Flood Final Conditions Stormwater Calculation Dam Decommissioning Plan Duke Energy – Asheville Steam Station Amec Foster Wheeler Project No. 7810150250 8 of 8 01/14/2016 FIGURES: 1. General Site Drainage Map REFERENCES: 1. NOAA Atlas 14, Point Precipitation Frequency Estimates”, NOAA National Weather Service. 2. HEC-15, Hydraulic Engineering Circular No. 15, Third Edition. “Design of Roadside Channels with Flexible Linings”. September 2005. 3. HDS-5, Hydraulic Design Series Number 5. Hydraulic Design of Highway Culverts, Third Edition. January 2012. 4. North Carolina Department of Environment and Natural Resources, “Erosion and Sediment Control Planning and Design Manual”, Revised May 2013. 5. “Standard Specification for Roads and Structures”, North Carolina Department of Transportation, Raleigh, January 2012. NOTES: Figure No. 1982 WEST 1982 EAST1 1982 EAST2 1982 LOWER 1982 EAST LOWER Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS U serCommunity 0 0.1 0.20.05 Miles¯ CLIENT: Environment & Infrastructure, Inc.3020 Falling Waters, Rd., Suite 300Knoxville, TN 37922 TITLE: PROJECT: DRAWN BY: JMP DATE: 11/04/2015 CHECKED BY: LCW PROJECT: 7810150250 1 DAM DECOMMISSIONING PLANASHEVILLE STEAM STATION Proposed Sto rmwater Cha nnels Proposed Draina ge Basins EXISTING I-26 CULVERT60-INCH DIAMETER CMP 1964 Ash Basin DRAINAGE AREAS AND PROPOSEDSTORMWATER CHANNELS EXISTING I-26 CULVERT66-INCH DIAMETER RCP Temporary Silt Basin Calculations Duke FnPrgy — Asheville Steam Flertric Generating Plant Dam Decommissioninq Plan Calculation Title: Temporary Silt Basin Calculations Summary: The temporary silt basins wPrP rlPsignPri in accordance with the North Carolina Department of Transportation (NCDOT) "Frnsinn and Sediment Control, Field Guide_" Using this guide, appropriatPly- sized silt basins were designed with storage capacities of approximately 84,600 ft3 each, which is greater than the minimum rPguirPd capacities of 82,800 ft' each. Notes: Revision Log: No. Description Originator `,q/ Technical Reviewer / Date 0 Initial Submittal Luke C�� ' _;. /'�� O •�FES$� � ��S AIJ Daniel R. Smith L� _ Amec Foster Wheeler Prnject No. 7R1n-]5-ro5n 1 of 3 n1/14/9n1R (Permit submittal) amen foster -h-1— Temporary Silt Basin Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 2 of 3 01/14/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation is to design the temporary silt basins for the interim closure conditions of the 1982 Ash Basin. METHOD: The temporary silt basins were designed in accordance with the North Carolina Department of Transportation (NCDOT) “Erosion and Sediment Control, Field Guide” [Ref. 1]. Areas used in the calculation were generated from the project drawings using AutoCAD Civil 3D [Ref. 2]. CALCULATIONS: 1.0 Determination of Disturbed Area The limits of disturbance for the dam decommissioning and closure activities at the 1982 Ash Basin are shown on Sheet C-1.3 of the project drawings. The disturbed area is noted as “Limits of Ash Excavation” and represents the area in which ash will be excavated from the basin. Using AutoCAD Civil 3D, this area was calculated as approximately 46 acres. The stormwater flows within this area will be routed through the basin with two separate stormwater channels, noted as “1982 West” and “1982 East” as shown on Sheet C-1.4 of the project drawings. Each channel will convey flows from approximately half of the disturbed areas within the basin. 2.0 Silt Basin Design Silt Basins were designed to intercept flows from the stormwater channels along the excavation limits adjacent to the existing 1982 Ash Basin Dam. The Silt Basins were designed in accordance with the NCDOT “Erosion and Sediment Control, Field Guide” for Silt Basin, Type B recommendations. According to the design guide, each silt basin shall be designed with a storage capacity of 3,600 cubic feet per disturbed acre. Each silt basin will intercept the proposed stormwater channels, and each channel conveys the flows from approximately half of the existing ash basin area. Therefore, each silt basin was designed for half of the total disturbed area (23 acres). As a result, the required storage capacity for each silt basin is 82,800 ft3 (23 acres x 3600 ft3/acre). The silt basin design also incorporated the sizing requirements for Silt Basin, Type B recommendations. The requirements included a minimum of 2’ depth, maximum of 1.5:1 side slopes, and a minimum length of 2 times the width. The silt basin design is shown on Detail 4 of Sheet E-1.2. The design consists of surface dimensions of 100’ x 225’ and a depth of 4’. The calculated volume for this design is approximately 84,600 ft3, which is greater than the minimum required 82,800 ft3 of storage capacity. DISCUSSION: The temporary silt basins were designed in accordance with the North Carolina Department of Transportation (NCDOT) “Erosion and Sediment Control, Field Guide.” Using this guide, Temporary Silt Basin Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 3 of 3 01/14/2016 (Permit Submittal) appropriately-sized silt basins were designed with storage capacities of approximately 84,600 ft3 each, which is greater than the minimum required capacities of 82,800 ft3 each. REFERENCES: 1. North Carolina Department of Transportation, “Erosion and Sediment Control, Field Guide”, 2013. 2. AutoCAD Civil 3D 2015, AutoDesk Inc. Underdrain Sizing Calculations Duke Energy — Asheville Steam Electric Generating Plant Dam Decommissioning Plan Calculation Title: Underdrain Suing Cnlrulntinns Summary: This document provides a summary of the design and rnlrulntinns performed for the proposed underdrain to he installed in the 19ft2 Ash Basin as part of the Dam Dernmmissinning Plan. This underdrain will intercept Wet Area 1 and rnnvey flnws to the dnwnstream fare of the existing dam. Calrulations were performed to determine the flow rnpnrities of the proposed HDPE drainage pipes and No. 57 Stnne that form the underdrain_ Notes: Revision Log: No. Description Originator / Date Technical Reviewer / Date Luke $,. a Daniel R. Smith 10, ' �, a :�� • 0 Initial Submittal %3.�' /j'� AO f�- 0419°3 W I L Ampc Enctar Wheeler Project No. 7910-15-0250 1 of 5 01/14/2016 (Permit Submittal) amec zo fnctar .,h..I., Underdrain Sizing Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 2 of 5 01/14/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation is to design the underdrain for the 1982 Ash Basin based on long- term conditions after decommissioning of the Ash Basin dam and also achieving final grades as shown on the plans. METHOD: Design for the underdrain consists of a combination of geotextile fabric, HDPE drainage pipes and No. 57 Stone backfill. Flow rates through the HDPE drainage pipes were calculated using Manning’s equation and FlowMaster modeling software. Flow rates through the No. 57 Stone backfill were estimated using Darcy’s Law. DEFINITION OF VARIABLES:  = shear; A = area perpendicular to the flow direction; b = bottom width; CN = curve number; d = flow depth; D = channel depth; i = hydraulic gradient; k = hydraulic conductivity; L = length; n = Manning’s n; P = wetted perimeter; Q = flow; R = hydraulic radius; S = longitudinal slope; t = time T = top width; Tc = time of concentration; V = velocity; and Z = channel side slope. CALCULATIONS: 1.0 Design of the Underdrain The underdrain is designed to intercept the existing Wet Area 1 as shown on the Project Drawings. The current flows from this wet area are estimated to be at 15-25 gpm (gallons per minute). The actual ground water exit point feeding the wet areas is covered with fill and actual flow rates to size the drain may be revised as additional flow measurements are obtained. Additionally, if field conditions allow a spring box configuration may be used to capture the flow closer to the source eliminating the need for pipe perforations described below. The underdrain is proposed to begin to the north of Wet Area 1 at approximately Elevation 2116’, and continue southward at an approximately 1.0% grade to intercept the wet area at approximately Elevation 2114’. After intercepting the wet area, the underdrain is proposed to Underdrain Sizing Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 3 of 5 01/14/2016 (Permit Submittal) continue southward through the existing 1982 Ash Basin Dam at a slope of 1.0%. The underdrain will daylight on the downstream face of the dam at approximately Elevation 2102’ and intercept the proposed stormwater ditch to be conveyed to the proposed outfall location. In cross-sectional view, the underdrain is proposed to be constructed to a channel depth (D) of 4’, a bottom width (b) of 12’, and a top width (T) of 20’. A total of two 6” HDPE DR 26 perforated drainage pipes will be placed along the bottom of the underdrain to convey flows. The remainder of the underdrain area will be backfilled with No. 57 Stone to the dimensions referenced above. The underdrain will be wrapped with 12-oz Geotextile filter fabric overlapped a minimum of 2’ across the top of the underdrain. 2.0 HDPE Flow Rate Calculations Flow rates for the HDPE drainage pipes were calculated using the program FlowMaster. As part of these calculations, the following variables were required to calculate the full flow capacity of each pipe: Manning’s n (n), channel slope (S), and diameter of the pipe. The Manning’s n was estimated as 0.012 from Mays, 2005. The critical channel slope was defined as 1.0% per the Project Drawings, and the diameter of each HDPE pipe is known as 6”. This calculation resulted in a maximum flow through each pipe of 0.61 ft3/sec, or a total flow through both pipes of 1.22 ft3/sec (548 gpm). Thus, the HDPE drainage pipes are able to convey approximately 548 gpm of flow from the wet area. See Figure 1 below for the output from FlowMaster. Figure 1: HDPE drainage pipe calculations from FlowMaster Underdrain Sizing Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 4 of 5 01/14/2016 (Permit Submittal) However, the pipe can only convey flows that enter the pipe through the orifices of the perforations. The orifice calculations are shown below. Orifice Flow Equation Q= 25 x A x k x h0.5 where: 25 is a conversion for square inches and gpm A = area k = constant based on inlet configuration k= 0.82 for thick wall pipe h = head constant diameter area k h h0.5 q (gpm) 25 0.25 0.05 0.82 1 1 1.01 There will be four (4) perforations placed around the pipe circumference on 1 foot intervals. 4 x 1.01 4.03 gpm/foot For a Factor of Safety of 10 for underdrains the capacity should be: 10 x 25 250 gpm The wet area flow will be contained in the pipe within: 250 ÷ 4.03 62.11 feet 3.0 No. 57 Stone Flow Rate Calculations Flow rates for the #57 stone backfill were estimated using Darcy’s Law, shown in the following equation: ܳൌ݇݅ܣ [Ref. 2] Where Q is the flow rate, k is the hydraulic conductivity, i is the hydraulic gradient, and A is the area perpendicular to the flow direction. The equation was solved for the flow rate (Q) of the 4’ by 12’ cross-sectional area of the underdrain. The hydraulic gradient was set as the critical slope of the underdrain of 1.0%. The hydraulic conductivity of the No. 57 Stone was estimated as 0.3 ft/sec based upon values provided in Coduto, 1999. These calculations resulted in a flow rate of approximately 65 gpm. Underdrain Sizing Calculations Dam Decommissioning Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 5 of 5 01/14/2016 (Permit Submittal) Flow through rock to 6" diameter pipe q = kia k = 0.3 I = gradient top of under drain (4 feet)/ orifice spacing (1 foot) a = flow area, use orifice area x 4 k i a q (cfs) gpm/ 1 cfs gpm 0.3 0.50 0.20 0.03 448.83 13.22 > 4.03 gpm DISCUSSION: The underdrain flow rates are controlled by the orifices in the HDPE drainage pipes. As a result, a factor of safety of 10 is achieved through this design. REFERENCES: 1. Mays, L.W., “Water Resources Engineering, 2005 Edition”, John Wiley & Sons, Inc., 2005. 2. Coduto, D.P., “Geotechnical Engineering, Principles and Practice,” Prentice-Hall, Inc. 1999. 3. Bentley FlowMaster, V8i, Bentley Systems, Inc, 2009. Erosion & Sediment Control Plan Calculations lylov 4k 2,/2Z/14 Final Conditions Stormwater Calculation Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810150250 2 of 8 02/23/2016 OBJECTIVE: The objective of this calculation is to design the stormwater conveyance measures based on proposed conditions after decommissioning of the 1982 Ash Basin. METHOD: Stormwater flow rates were calculated using the SCS runoff method. The hydraulic capacity of proposed stormwater channels was evaluated using Manning’s equation. Channel lining was determined using the permissible shear stress approach specified in FHWA HEC-15. The Interstate 26 culvert was evaluated using standard procedures specified in FHWA HDS-5. CALCULATIONS: 1.0 Hydrology Drainage areas were developed from the final grading plan drawings and represent final condition after closure of the 1982 Ash Basin. The drainage areas are shown in Figure 1. Runoff coefficients (SCS curve number) and flow travel times (time concentration) were determined using standard methods documented in the National Engineering Hand Book Part 630 Hydrology for each of the drainage areas. The runoff coefficients for the 1982 basin considered the ground surface to be vegetated and have a minimum of 75 percent grass cover. The soils for the ash basin and existing plant footprints were considered to have moderately high runoff potential (HSG C classification) because of the disturbed nature of these soils. Area outside the 1982 ash basin and existing plant footprints were considered to have moderately low runoff potential (HSG B classification) as determined from NRCS soil mapping data. The hydrologic input parameters for the 1982 basin are summarized in the Table 1. Table 1: Summary of Drainage Areas 1982 Basin Drainage Area Area (acres)Area (mi 2 )Curve Number CN Tc (hr)Lag Time (min) 1982 East1 31.3 0.0489 68 0.44 16 1982 East2 28.5 0.0445 71 0.468 17 1982 East Lower 5.9 0.0092 74 0.186 7 1982 West 40.9 0.0638 79 0.564 20 1982 Lower 15.5 0.0242 58 0.329 12 Proposed stormwater channels were designed for the 100-year 24-hour storm event. Temporary sediment control structures were designed for the 10-year 24-hour storm event. Table 2 below shows the precipitation depth for these three storm events. Precipitation depths were retrieved from NOAA Precipitation Frequency Data Server (Atlas 14) (Attachment 1). Final Conditions Stormwater Calculation Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810150250 3 of 8 02/23/2016 Table 2: Summary of Precipitation Depths Design Event Precipitation Depth (in) Precipitation Distribution 10‐year (24 ‐hr) 4.28 SCS Type II 100‐year (24 ‐hr) 6.31 SCS Type II Peak runoff rates for the drainage areas were determined using the SCS runoff approach within the USACE HEC-HMS hydrology model. Peak runoff rates for the 1982 basin are shown in Table 3. Table 3: Summary 1982 Basin Peak Flowrates Drainage Area Peak 10‐year Flow (cfs) Peak 100‐year Flow (cfs) Peak 500‐year Flow (cfs) 1982 East1 40 87 126 1982 East2 41 85 120 1982 East Lower 15 29 40 1982 West 76 138 187 1982 Lower 11 33 52 Final Conditions Stormwater Calculation Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810150250 4 of 8 02/23/2016 2.0 Hydraulics 2.1 Proposed Stormwater Channels Stormwater channels were designed to convey runoff from the 1982 basin for the 100-year flood event in a safe and non-erosive manner. The Manning formula was used to determine the 100- year flow depth in the channels. The shear stress along the channel bottom and sides was calculated to determine appropriate channel lining following the HEC-15 approach for design of riprap lined channels. The stormwater channels located within the basins generally have slopes near 1 percent and were lined with North Carolina Department of Transportation (NCDOT) Class B riprap having a median diameter of 8 inches. The stormwater channels that convey stormwater from the dam breach location to the toe of the abutment, called “outlet” channels on the design drawings, have relatively steep slopes and were lined with NCDOT Class 2 riprap having a median diameter of 14 inches. The proposed stormwater channel dimensions are presented in Table 4. Table 5 shows the riprap sizes for the NCDOT Class B and Class 2 riprap. Table 4: Summary of Stormwater Channels 1982 Basin Channel ID Q100 (cfs) Average Velocity (ft/s) Slope (ft/ft)Channel Type Side Slope (H:V) Bottom Width (ft) Flow Depth (ft)Lining Type 1982 West 138 3.7 0.01 Trapezoidal 2 5 3.2 Class B 1982 West Outlet 138 8.9 0.15 Trapezoidal 3 15 0.9 Class 2 1982 East 2 85 3.1 0.01 Trapezoidal 2 5 2.6 Class B 1982 East 1 87 3.2 0.01 Trapezoidal 2 5 2.7 Class B 1982 East 171 3.9 0.01 Trapezoidal 2 8 3.1 Class B 1982 East Outlet 186 9.5 0.15 Trapezoidal 3 20 0.9 Class 2 1982 Basin Channel Summary Table 5: NCDOT Riprap Sizes Minimum Midrange Maximum A246 B5812 151017 291423 Acceptance Criteria for Rip Rap and Stone for Erosion Control Class Required Stone Sizes (inches) Final Conditions Stormwater Calculation Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810150250 5 of 8 02/23/2016 3.0 Interstate 26 Culvert Interstate 26 is located below the 1982 basin. Stormwater runoff from the 1982 basin will be directed to existing culvert running underneath I-26. The culvert underneath I-26 is a 66-in diameter RCP culvert with a concrete headwall. A summary of I-26 culvert is shown in Table 6 below. Table 6: Summary of I-26 Culvert I ‐26 Culvert Structure Inlet Invert (ft) Outlet Invert (ft)Length (ft) Slope (ft/ft) Top Road Elevation (ft) Below 1982 Basin 66" RCP 2043.5 2040 273 0.013 2052.6 Table 7 and Figure 1 show the headwater elevations versus culvert discharge for the 66” CMP I- 26 culvert below the 1982 basin. Note the tailwater condition (elevation) for the I-26 culvert was considered to be the water elevation for the 10-year flood elevation of the French Broad or the normal flow depth of the downstream channel whichever was greater. The French Broad River has a 10-year flood elevation near 2039’ (culvert outlet not submerged) at the culvert location which is lower than the normal flow depth of the downstream channel. Therefore, for the I-26 culvert analysis the culvert tailwater condition was set to normal depth of the downstream channel. Headwater elevations for the I-26 culverts were estimated to determine the impact of the proposed 1982 basin closure and stormwater plan. The 100-year headwater elevation was evaluated. Flood storage behind the I-26 road embankment was considered and a storage routing model was developed in HEC-HMS. Topography data from USGS digital elevation model (1 meter) was utilized in estimating available flood storage volumes behind the I-26 embankment. Figure 2 shows the rating curve for the storage area between the toe of the 1982 basin and upstream the I-26 embankment. Table 7: Discharge Curve for I-26 Culvert (1982) Headwater Elevation (ft)Flow (cfs) 2043.5 0 2045.71 36 2046.8 72 2047.74 108 2048.59 144 2049.47 180 2050.45 216 2051.6 252 I ‐26 Culvert (1982) *Top Pavement Elevation = 2052.6' **Inlet Invert Elevation = 2043.5' Final Conditions Stormwater Calculation Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810150250 6 of 8 02/23/2016 Figure 1: Discharge Curve for I-26 Culvert (1982) Figure 2: Storage Curve for I-26 Culvert (1982) 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 0 50 100 150 200 250 300 350 400 El e v a t i o n (N A V D 88 ) Culvert Discharge (cfs) I‐26 Culvert Performance Curve below 1982 Basin 66‐in RCP Top Pavement = 2052.6' 2042 2044 2046 2048 2050 2052 2054 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 El e v a t i o n (N A V D 88 ) Storage Volume (ac‐ft) Available Storage below 1982 Basin upstream I‐26 Embankment 1982 Outlet Final Conditions Stormwater Calculation Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810150250 7 of 8 02/23/2016 The headwater elevation behind the I-26 embankment for the 100-year 6-hr flood is shown in Table 8. The headwater elevation below the 1982 basin for the 100-year event is 2050.7’ which is approximately 1.9 feet below the road embankment. Coordination with NCDOT will be required to determine if additional flow capacity is needed below the 1982 basin to lower the headwater depths upstream of I-26. Table 8: Headwater Elevations at I-26 Embankment Headwater Elevation (ft) Freeboard from Top Pavement (ft)HW/D Below 1982 Basin 2043.5 2050.7 1.9 1.3 I ‐26 Culverts Inlet Invert (ft) 100‐year 6 ‐hour Flood Final Conditions Stormwater Calculation Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810150250 8 of 8 02/23/2016 FIGURES: 1. General Site Drainage Map REFERENCES: 1. NOAA Atlas 14, Point Precipitation Frequency Estimates”, NOAA National Weather Service. 2. HEC-15, Hydraulic Engineering Circular No. 15, Third Edition. “Design of Roadside Channels with Flexible Linings”. September 2005. 3. HDS-5, Hydraulic Design Series Number 5. Hydraulic Design of Highway Culverts, Third Edition. January 2012. 4. North Carolina Department of Environment and Natural Resources, “Erosion and Sediment Control Planning and Design Manual”, Revised May 2013. 5. “Standard Specification for Roads and Structures”, North Carolina Department of Transportation, Raleigh, January 2012. NOTES: Figure No. 1982 WEST 1982 EAST1 1982 EAST2 1982 LOWER 1982 EAST LOWER Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS U serCommunity 0 0.1 0.20.05 Miles¯ CLIENT: Environment & Infrastructure, Inc.3020 Falling Waters, Rd., Suite 300Knoxville, TN 37922 TITLE: PROJECT: DRAWN BY: JMP DATE: 11/04/2015 CHECKED BY: LCW PROJECT: 7810150250 1 DAM DECOMMISSIONING PLANASHEVILLE STEAM STATION Proposed Sto rmwater Cha nnels Proposed Draina ge Basins EXISTING I-26 CULVERT60-INCH DIAMETER CMP 1964 Ash Basin DRAINAGE AREAS AND PROPOSEDSTORMWATER CHANNELS EXISTING I-26 CULVERT66-INCH DIAMETER RCP Final Conditions Stormwater Calculation Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810150250 02/23/2016 Attachment 1 Precipitation depths from NOAA Precipitation Frequency Data Server Precipitation Frequency Data Server Page 1 of 3 NOAA Atlas 14, Volume 2, Version 3 Location name: Asheville, North Carolina, US* Latitude: 35.5321°, Longitude:-82.5545° Elevation: 2023 ft* t 'source: Google Maps "'+.,,, „Ps 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 �� 10 25 50 100 200 500 1000 0.347 0.412 0.495 0.558 0.641 0.704 0.767 0.829 0.911 0.975 5-min (0.315-0.381) (0.376-0.454) (0.450-0.545) (0.506-0.614) (0.578-0.705) (0.630-0.773) (0.683-0.844) (0.733-0.916) (0.796-1.01) (0.844-1.09) 0.554 0.659 0.793 0.893 1.02 1.12 1.22 1.31 1.44 1.54 10-min (0.503-0.609) (0.601-0.726) (0.721-0.873) (0.810-0.982) (0.921-1.12) 1 (1.00-1.23) 1 (1.09-1.34) 1 (1.16-1.45) (1.26-1.60) (1.33-1.72) 15-min 0.692 0.828 1.00 1.13 1.30 1.42 1.54F 1.66 1.81 1.93 (0.629-0.761) (0.755-0.912) (0.912-1.11) 1 (1.02-1.24) 1 (1.17-1.42) 1 (1.27-1.56) (1.37-1.70)1 (1.47-1.83) (1.58-2.02) (1.67-2.16) 0.949 1.14 1.43 1.64 1.92 2.14 2.36 2.58 2.89 3.12 30-min (0.862-1.04) 1 (1.04-1.26) 1 (1.30-1.57) 1 (1.49-1.80) 1 (1.73-2.11) 1 (1.91-2.35) 1 (2.10-2.60) (2.28-2.85) (2.52-3.21) (2.70-3.49) 1.18 1.44 1.83 2.13 2.56 2.90 3.25 3.62 4 4F.56 60-min (1 .08-1.30) (1.31-1.58) (1.66-2.01) (1.93-2.34) (2.30-2.81) (2.59-3.18) (2.89-3.58) (3.20-4.00) .14 (3.62-4.60) (3.94-5.10) 1.37 7F 1.65 7F 2.10 7F 2.45 7F 2.95 7F 3.36 7F 3.78 7F 4.23 71 4.85 11 5.35 2-hr (1.24-1.50) (1.51-1.82) (1.90-2.30) (2.22-2.69) (2.65-3.24) (2.99-3.69) (3.34-4.16) 1 (3.71-4.66) (4.20-5.38) (4.59-5.98) 1.44 1.73 2.18 2.55 3.09 3.54 4.01 4.52 5.25 5.84 3-hir 1 ( .32-1.59) (1.58-1.91) (1.99-2.40) (2.31-2.81) (2.78-3.39) (3.15-3.89) (3.54-4.42) (3.95-4.99) ( 4.52-5.84) ( 4.96-6.54) 1.75 2.07 2.56 2.98 3.59 4.11 4.67 5.26 6.13 6.84 6-hr (1.61-1.91) (1.90-2.26) (2.35-2.79) (2.72-3.24) (3.25-3.91) (3.69-4.47) (4.15-5.09) (4.63-5.76) (5.29-6.75) (5.82-7.56) 2.17 2.57 3.16 3.63 4.29 4.83 5.37 5.93 6.70 7.29 12-hr 11 2 ( .01-2.35) (2.38-2.79) (2.91-3.43) (3.35-3.94) (3.94-4.65) (4.41-5.24) (4.88-5.84) (5.34-6.48) (5.98-7.37) (6.45-8.06) 2.50 3.00 3.71 4.28 5.05 5.67 6.31 6.96 7.85 8.54 24-hr (2.33-2.70) (2.80-3.24) (3.45-4.00) (3.97-4.60) (4.68-5.43) (5.24-6.10) (5.81-6.78) (6.39-7.47) (7.16-8.43) (7.74-9.18) 2.96 3.54 4.34 4.96 5.83 6.51 7.20 7.91 8.87 9.60 2-day (2.77-3.18) (3.31-3.80) (4.05-4.65) (4.63-5.32) (5.42-6.24) (6.04-6.97) (6.66-7.72) (729-8.48) (8.12-9.51) (8.75-10.3) 3.16 3.77 4.58 5.22 6.08 6.76 7.45 8.14 9.06 9.77 3-day 2 ( .96-3.38) (3.53-4.04) (4.28-4.90) (4.87-5.58) (5.66-6.50) (6.28-7.22) (6.90-7.96) (7.51-8.70) (8.32-9.70) (8.94-10.5) 3.36 4.00 4.82 5.47 6.34 7.01 7.69 8.36 9.26 9.94 4-day (3.15-3.58) (3.75-4.27) (4.51-5.15) (5.11-5.83) (5.91-6.75) (6.52-7.48) (7.13-8.20) (7.74-8.93) (8.52-9.89) (9.12-10.6) 3.93 4.67 5.61 6.35 7.35F 8.13 8.92 9.71 10.8 11.6 7-day (3.69-4.20) (4.39-5.00) (5.26-5.99) (5.95-6.78) (6.86-7.83) (7.57-8.67) (8.27-9.51) (8.98-10.4) (9.89-11.5) ( 10.6-12.4) 4.51 5.34 6.34 7.12 8.18 9.00 9.83 10.7 11.7 12.6 10-day (4.25-4.78) (5.03-5.67) (5.98-6.74) (6.72-7.56) (7.69-8.68) (8.44-9.55) 1 (9.19-10.4) 1 (9.92-11.3) (10.9-12.5) (11.6-13.4) 6.16 7.25 8." 9.37 10.6 11.5 12.4 13.2 14.3 15.2 20-day (5.84-6.51) (6.87-7.66) (7.99-8.92) (8.86-9.89) (9.98-11.2) (10.8-12.1) 1 (11.6-13.1) 1 (12.4-14.0) (13.4-15.2) (14.1-16.1) 30-day 7.61 8.92 10.2 11.2 12.4 13.3 14.1 14.9 15.9 16.6 (7.25-8.00) (8.49-9.38) (9.72-10.7) (10.6-11.7) (11.8-13.0) 1 (12.6-14.0) 1 (14.1-15.7) (15.0-16.8) (15.6-17.6) 45-day 9.70 11.3 12.8 13.8 15.1 16.0 16.8 17.5 18.4 19.0 (9.25-10.2) (10.8-11.9) (12.2-13.4) (13.2-14.4) (14.4-15.8) (15.2-16.7) 1 (16.0-17.6) 1 (16.7-18.4) (17.5-19.3) (18.0-20.0) 11.6 13.6 15.1 16.3 17.7 18.6 19.5 20.3 21.2 21.8 60-day (11.1-12.2) (13.0-14.2) (14.5-15.9) (15.6-17.1) (16.9-18.5) (17.8-19.5) (18.6-20.5) (19.3-21.3) (20.2-22.3) (20.7-22.9) ' Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5 %. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top PF graphical http://hdse.nws.noaa.gov/hdse/pfds/pfds printpage.html?lat=35.5321&Ion=-82.5545&data... 8/11/2015 Precipitation Frequency Data Server Page 2 of 3 20 c L J-+ y 15 'C7 C Q _13 10 a V a 5 O F— 1 1 I I I I I I I I I I I I I I I I L L t L L E E E � rL rh uS ry v -ma a -`0o v -`00 m -moo -mo m r• 6 6 6 N O rl 'i rn ID rH 04 en V 'D Duration 25 20 c L v 15 0 `6 10 a V P' a 5 0 1 2 5 10 25 50 100 200 500 1000 acN To Average recurrence interval years ae ��aa�� NOAA Atlas 14, Volume 2, Version 3 Mapsc& ted fGFIT}: Tue Aug 11 19:18:34 2015 Small scale terrain Average recurrence interval {yearel — 1 2 — 5 10 25 50 100 200 500 1000 Duration — 5-min — 2-ay — 1"in — 3Aay 15-min — 4-day — 30-min — 7-day — W-min — 1 D-day — 2fir — 20-day — 3fir — 30-day — 6fir — 45-day — 12-hr — 60-day — 24-hr ® Black5burg•� 'RiSanoke. J Damet 8orrne M1da[ionalFores[ ..-�' King5por JohnsonCAK- Cankowille; .j. ° ._Bonne;..:',.. ,r , ''.i r r+'' W4instan Salerno Greensboro Knoxville v f o o Rr gaiiNahonalFgresl - ;born _Gatlinbur'.,t �'��iHick Dry R 't ', 1 wsI �asn�,rue C A R 0 L I r , gi Charlotte I hattaiiraga I"�rk_!" {,ns i-4�_. _ 0 , ' o Greenville -Spartanburg oRock Hill #t. fi}fir i Chattahoochee National Foresr Andeorsan' i R Florence ' �"•Alpharetta ° Athens o SOUTH i t1f� t�: Atlanta`. C A R f e n 50 km 91 Large scale terrain http://hdse.nws.noaa.gov/hdse/pfds/pfds-printpage.html?lat=35.5321 &Ion=-82.5 545 &data... 8/ 11 /2015 Precipitation Frequency Data Server Page 3 of 3 AShOv611€ ... t`' �. � zaox 2409 '+ 1324 TO L 017° 122_� 41, b Q 3i a E eraC11 11 2;i -3121 „can&er -T5 3d12 3 3[ 53 CL I t91 Biltmore a � [ Biltmore —i— Forest` / .LLi �xsa 3117 Bent Creek is i t llelrltlL .._ .., Map d6tpW-0i IajSeo4e Back to Too US Department of Commerce National Oceanic and Atmospheric Administration National Weather Service Office of Hvdroloaic Development 1325 East West Highway Silver Spring, MD 20910 Questions?: HDSC.Questions(a)noaa.aov Disclaimer http://hdse.nws.noaa.gov/hdse/pfds/pfds printpage.html?lat=35.5321&Ion=-82.5545&data... 8/11/2015 Temporary Silt Basin Calculations Erosion and Sedimentation Control Plan Duke Energy — Asheville Steam FlPctrir. Generating Plant Calculation Title: Temporary Silt Basin Calculations Summary: The tmporary silt basins were designed in accordance with the North Carolina Department of Transpnrtatinn (NmOT) "Frosion and Sediment Control, Field Guide." Using this guide, appropriately- si7Pd silt basins were designed with storage capacities of approximately 84,600 ft3 each, which is greater than the minimum reguired capacities of 82,800 ft3 each. Notes: Revision Log: No. Description Originator / Date Iechnical Reviewer / Date 0 Initial Submittal Matt Bishop / 'z�t &�4r Luke C. Williams, PE c Amec Foster Wheeler Project No. 7810-15-0250 1 of 3 02123/2016 (Permit Submittal) amar foster - h-1— Temporary Silt Basin Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 2 of 3 02/23/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation is to design the temporary silt basins for the interim closure conditions of the 1982 Ash Basin. METHOD: The temporary silt basins were designed in accordance with the North Carolina Department of Transportation (NCDOT) “Erosion and Sediment Control, Field Guide” [Ref. 1]. Areas used in the calculation were generated from the project drawings using AutoCAD Civil 3D [Ref. 2]. CALCULATIONS: 1.0 Determination of Disturbed Area The limits of disturbance for the dam decommissioning and closure activities at the 1982 Ash Basin are shown on Sheet C-1.3 of the project drawings. The disturbed areas are noted on the drawings as the following:  Limits of Dam Breach Excavation (5.8 acres),  Approximate Limits of Impoundment Backfill (13.5 acres), and  Limits of Disturbance for Channel Construction (0.9 acres), note that this area is a result of all channels shown on the plan (0.35 + 0.20 + 0.05 + 0.30 acres). Thus, the total estimated disturbed area is approximately 20.2 acres. In addition, current ash excavation operations are underway and encompass a total area of approximately 46 acres (including the proposed 20.2 acres). There will be some overlap between the current ash excavation work and the proposed disturbance included in this submittal. Therefore, the silt basins included in this calculation were sized to be able to handle the total disturbance area within the ash basin of 46 acres, instead of the disturbed area of 20.2 acres as shown on the E&SC Permit Drawings. The stormwater flows within the disturbed areas will be routed through the basin with two separate stormwater channels: one network of channels along the west limits of the fill, and one network of channels along the east limits of the fill. Each channel will convey flows from approximately half of the disturbed area within the basin. Therefore, each silt basin will be designed to handle half of the total disturbance area within the basin of 23 acres (46 acres / 2). 2.0 Silt Basin Design Silt Basins were designed to intercept flows from the stormwater channels along the excavation limits adjacent to the existing 1982 Ash Basin Dam. The Silt Basins were designed in accordance with the NCDOT “Erosion and Sediment Control, Field Guide” for Silt Basin, Type B recommendations. According to the design guide, each silt basin shall be designed with a storage capacity of 3,600 cubic feet per disturbed acre. Temporary Silt Basin Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 3 of 3 02/23/2016 (Permit Submittal) As mentioned previously, each silt basin was designed to handle half of the total disturbance area within the basin of 23 acres. As a result, the required storage capacity for each silt basin is 82,800 ft3 (23 acres x 3600 ft3/acre). The silt basin design also incorporated the sizing requirements for Silt Basin, Type B recommendations. The requirements included a minimum of 2’ depth, maximum of 1.5:1 side slopes, and a minimum length of 2 times the width. The silt basin design is shown on Detail 4 of Sheet E-1.2. The design consists of surface dimensions of 100’ x 225’ and a depth of 4’. The calculated volume for this design is approximately 84,600 ft3, which is greater than the minimum required 82,800 ft3 of storage capacity. DISCUSSION: The temporary silt basins were designed in accordance with the North Carolina Department of Transportation (NCDOT) “Erosion and Sediment Control, Field Guide.” Using this guide, appropriately-sized silt basins were designed with storage capacities of approximately 84,600 ft3 each, which is greater than the minimum required capacities of 82,800 ft3 each. REFERENCES: 1. North Carolina Department of Transportation, “Erosion and Sediment Control, Field Guide”, 2013. 2. AutoCAD Civil 3D 2015, AutoDesk Inc. Temporary Stormwater (:nntainment Berm Calculations Erosion and Sedim_Pntation Contrnl Plan Duke Energy — Asheville Steam FIPctric Generating Plant Calculation Title: Temporary Stormwater Containment Berm Calculations Summary: The objective of this calculation is to design the temporary stormwater containment berms fnr the interim closure conditions of the 1982 Ash Basin. The temporary stormwater containment ha -ins were designed to adequately contain the 25-year stormwater runoff volumes for each of their respPrtive tributary areas. Each Berm has sufficient capacity to contain the rainfall event with adeguate freehnard without overtopping. Notes: Revision Log: No. Description Originator L Date Technical Reviewer / Date 0 Initial Submittal MattBishopLuke 1` t 2-123114 C. Williams, PE tea/ Amec Foster Wheeler Project No. 7R1n-9s-n9sn ] of 3 09/9�/9n9R (Permit Suhmittal) amec foster .,h..Ior Temporary Stormwater Containment Berm Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 2 of 3 02/23/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation is to design the temporary stormwater containment berms for the interim closure conditions of the 1982 Ash Basin. METHOD: The temporary stormwater containment berms were designed to store the 25-year storm event. Stormwater flow rates were calculated using the SCS runoff method. Stage-storage curves were developed for the Upper and Lower Berms using AutoCAD Civil 3D and Microsoft Excel. CALCULATIONS: 1.0 Determination of Stormwater Runoff Volume The stormwater runoff volume for the drainage areas upstream of each berm were calculated according to the SCS runoff method as presented in the “Final Conditions Stormwater Calculation,” included with this submittal. The following runoff volumes and peak pool elevations were determined for each Berm: Drainage Area (ac) 25‐yr Runoff Volume (ac‐ft) Peak Pool (ft) Upper Berm 16.6 2.98 2131.6 Lower Berm 26.6 4.245 2125.4 2.0 Berm Design Each Berm was designed using AutoCAD Civil 3D software with a maximum height of 14 feet. Using the 25-yr Runoff Volume as shown in the table above, stage-storage curves were generated to calculate the peak pool elevations and their associated depths. The figure below shows the stage-storage curves for the Berms. Temporary Stormwater Containment Berm Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 3 of 3 02/23/2016 (Permit Submittal) DISCUSSION: The temporary stormwater containment basins were designed to adequately contain the 25-year stormwater runoff volumes for each of their respective tributary areas. As shown on the previous figure, each Berm has sufficient capacity to contain the rainfall event with adequate freeboard without overtopping. REFERENCES: 1. NOAA Atlas 14, Point Precipitation Frequency Estimates”, NOAA National Weather Service. 2. HEC-15, Hydraulic Engineering Circular No. 15, Third Edition. “Design of Roadside Channels with Flexible Linings”. September 2005. 3. HDS-5, Hydraulic Design Series Number 5. Hydraulic Design of Highway Culverts, Third Edition. January 2012. 4. North Carolina Department of Environment and Natural Resources, “Erosion and Sediment Control Planning and Design Manual”, Revised May 2013. 5. “Standard Specification for Roads and Structures”, North Carolina Department of Transportation, Raleigh, January 2012. 0 2 4 6 8 10 12 14 16 012345 De p t h (f t ) Storage (ac‐ft) Temporary Stormwater Containment Berms Upper Berm Lower Berm Compost Socks Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 2 of 4 07/18/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation is to design the compost socks for the interim closure conditions of the 1982 Ash Basin. METHOD: The compost socks located on the west and east excavated dam abutments were designed to filter the 10-year runoff volume without overtopping. The compost socks located on the main backfill area were not specifically designed to handle the 10-year runoff volume because the runoff from this area drains to the west and east sediment ponds, which were sized to handle sediment washoff from the main backfill area. Stormwater runoff volumes were calculated using the SCS runoff method considering a conservative runoff curve number of 88 (disturbed soil). CALCULATIONS: Composts socks were designed using the recommended criteria documented in the Chapter 6 Section 6.66 “Compost Sock” in the NCDEQ Erosion and Sediment Control Planning and Design Manual (NCDEQ, 2013). The compost socks will be installed on the west and east excavated dam abutments to handle the 10-year runoff volumes. Compost socks will be placed at every 10 foot change in elevation and will have 12-inch diameter as shown in the design drawings. The abutment cut has a slope of approximately 10H:1V or 10 percent. Table 1 shows the recommended design flow rate per length of compost sock. Table 2 shows that the compost sock for the west and east excavated dam abutments have adequate capacity in handling the 10-year runoff volume. Specially, the 10-year runoff volume per length of compost sock is less than the maximum recommend flow rate specified in Table 1. Table 1: Recommended Sock Flow Rate (NCDEQ, 2013) Compost Sock Design Diameter (in) Flow per foot of sock (gpm/ft) 8 7.5 12 11.3 18 15 24 22.5 32 30 Compost Socks Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 3 of 4 07/18/2016 (Permit Submittal) Table 2: Sock Flow Rate Calculations Summary Sock Slope Elevation (ft) Length of sock (ft) Cumulative Drainage Area (ac) Peak runoff (cfs) Flow per foot of sock (gpm/ft) West Abutment 2160 61 0.028 0.14 1.0 2150 113 0.116 0.56 2.2 2140 155 0.35 1.69 4.9 2130 195 0.612 2.95 6.8 2120 237 0.936 4.51 8.5 2110 284 1.149 5.53 8.7 2104 309 1.287 6.2 9.0 East Abutment 2160 52 0.025 0.12 1.0 2150 87 0.12 0.58 3.0 2140 141 0.234 1.13 3.6 2130 203 0.423 2.04 4.5 2120 250 0.642 3.09 5.5 2110 301 0.727 3.5 5.2 2106 326 1.037 5 6.9 Compost Socks Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 4 of 4 07/18/2016 (Permit Submittal) DISCUSSION: The temporary compost socks were designed to adequately filter the 10-year stormwater runoff volumes for each of their drainage areas to allow for proper sediment control. REFERENCES: 1. North Carolina Department of Environment and Natural Resources, (NCDEQ) “Erosion and Sediment Control Planning and Design Manual”, Revised May 2013. Riprap Energy nissipaters Calculatinns Ernsinn and Sedimentation Control Plan Duke Energy — Asheville Steam Flectric Generating Plant Calculation Title: Riprap Energy Dissipaters Calculations Summary: The following calculations are fnr the riprap basin energy dissipaters fnr the interim closure conditions of the 1982 Ash Basin. Riprap ha -,ins will be located at the 0Htlets of the west and east outlet channels. The riprap basins will GPrve as a transition from the outlet channels to the downstream wetland area. The riprap basins were designed for the 100-year stnrmwater runoff volumes for each of their respective tributary areas. Notes: Revision Log: No. Description Originator / Date Technical Reviewer / Date 0 Initial Suhmittal Joe Parker ��/ 2W6 Luke C. Williams, PE - �1 0-7 /1g I ZIL 27. Amec Foster Wheeler Project No. 7810-15-roso 1 of 6 n7/1RL9n16 (Permit Submittal) Amec foster —h..I., Riprap Energy Dissipaters Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 2 of 6 07/18/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation is to design the riprap basin energy dissipaters for the interim closure conditions of the 1982 Ash Basin. METHOD: The riprap basin energy dissipaters were designed using guidelines found in Chapter 10: Riprap Basins and Aprons from HEC-14 “Hydraulic Design of Energy Dissipaters” (FHWA, 2006). Stormwater runoff volumes were calculated using the SCS runoff method. Further calculation on the inflow volumes for the riprap basins can be found in the H&H calculation package for the channels. The riprap basins were sized for the 100-year runoff event. CALCULATIONS: Riprap basin energy dissipaters will be located at the outlet of the both the west and east outlet channel to transition flow from the channel to the wetland areas. The following guidelines from FHWA were used to size the riprap basins:  The basin is pre-shaped and lined with riprap that is a least 2D50 thick;  The riprap floor is constructed at the approximate depth of scour, hs, that would occur in a thick pad of riprap. The hs/D50 of the material should be greater than 2;  The length of the energy dissipating pool, Ls, is 10hs, but no less than 3W o; the length of the apron, LA, is 5hs, but no less than W o. The overall length of the basin (pool plus apron), LB, is 15hs, but no less than 4W o. Tables 1 and 2 show the dimensions of the west and east dissipater basins, respectively. Tables 3 and 4 shows the calculation steps for the west and east dissipater basins, respectively. Table 1: Riprap Basin Energy Dissipater West Basin Summary Riprap Basin Energy Dissipater (West Outlet Channel) Entrance Channel Width, W O (ft) 7.5 Entrance Channel Flow Depth, Ye (ft) 0.9 Pool Depth, hS (ft) 1.5 Exit Channel Tailwater Depth, TW (ft) 0.7 Dissipater Pool Length, LS (ft) 22.5 Apron Length, LA (ft) 7.5 Total Basin Length, LB (ft) 30.0 Apron Width, W B (ft) 27.5 Riprap Energy Dissipaters Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 3 of 6 07/18/2016 (Permit Submittal) Table 2: Riprap Basin Energy Dissipater East Basin Riprap Basin Energy Dissipater (East Outlet Channel) Entrance Channel Width, WO (ft) 10.0 Entrance Channel Flow Depth, Ye (ft) 1.0 Pool Depth, hS (ft) 1.6 Exit Channel Tailwater Depth, TW (ft) 0.7 Dissipater Pool Length, LS (ft) 30.0 Apron Length, LA (ft) 10.0 Total Basin Length, LB (ft) 40.0 Apron Width, WB (ft) 36.7 Riprap Energy Dissipaters Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 4 of 6 07/18/2016 (Permit Submittal) Table 3: Riprap Basin Energy Dissipater West Basin Calculations FHWA HEC-14 Input West Channel Step 1 Parameter Unit Value Comment Design Flow Q (cfs) 138 Flow Width Wo (ft) 7.5 Flow Depth ye (ft) 0.932 Manning (n) 0.03 Outlet velocity Vo (ft) 15.812545 Froude number Fr 2.89 Step 2 Rock median diameter D50 (ft) 0.67 D50/ye 0.72 (>= 0.1 OK) Tailwater TW (ft) 0.71 TW/ye 0.76 Tailwater parameter Co 1.40 Pool Depth hs (ft) 1.47 hs/D50 2.19 (>= 2 recommended) Step 3 Pool Length Ls (ft) 14.69 Pool Length(min) Lsmin (ft) 22.50 Apron length La (ft) 7.35 Apron length(min) Lamin (ft) 7.50 Total Length (pool + apron) Lb 22.04 Min total length Lbmin (ft) 30.00 Apron width Wb (ft) 27.50 Step 4 Flow Q (ft3/s) 138 gravity g (ft2/s) 32.2 Critical depth yc (ft) 0.9 iterate Basin side slope z1 2 Apron width Wb (ft) 27.50 Q^2/g 591.42857 Ac^3/Tc 589.617 Wetted Area Ac (ft2) 26.37 Wetted Perimeter Tc (ft) 31.1 Exit Velocity Vc (ft/s) 5.2332196 (OK) Step 5 TW/yo 0.7639485 (OK) Riprap Energy Dissipaters Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 5 of 6 07/18/2016 (Permit Submittal) Table 4: Riprap Basin Energy Dissipater East Basin Calculations FHWA HEC-14 Input East Channel Step 1 Parameter Unit Value Comment Design Flow Q (cfs) 186 Flow Width Wo (ft) 10 Flow Depth ye (ft) 0.95 Manning (n) 0.03 Outlet velocity Vo (ft) 16.45289695 Froude number Fr 2.97 Step 2 Rock median diameter D50 (ft) 0.67 D50/ye 0.71 (>= 0.1 OK) Tailwater TW (ft) 0.73 TW/ye 0.77 Tailwater parameter Co 1.40 Pool Depth hs (ft) 1.61 hs/D50 2.41 (>= 2 recommended) Step 3 Pool Length Ls (ft) 16.15 Pool Length(min) Lsmin (ft) 30.00 Apron length La (ft) 8.07 Apron length(min) Lamin (ft) 10.00 Total Length (pool + apron) Lb 24.22 Min total length Lbmin (ft) 40.00 Apron width Wb (ft) 36.67 Step 4 Flow Q (ft3/s) 186 gravity g (ft2/s) 32.2 Critical depth yc (ft) 0.9 iterate Basin side slope z1 2 Apron width Wb (ft) 36.67 Q^2/g 1074.409938 Ac^3/Tc 1030.470376 Wetted Area Ac (ft2) 34.62 Wetted Perimeter Tc (ft) 40.26666667 Exit Velocity Vc (ft/s) 5.372616984 (OK) Step 5 TW/yo 0.772631579 (OK) Riprap Energy Dissipaters Calculations Erosion and Sedimentation Control Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-15-0250 6 of 6 07/18/2016 (Permit Submittal) DISCUSSION: Both the east and west riprap basin energy dissipaters are adequately sized to handle the 100- yr peak flow for their respective tributary areas. The design drawings further show the locations and construction details for each of the riprap basin energy dissipaters. REFERENCES: 1. Federal Highway Administration (FHWA). Hydraulic Engineering Circular No. 14, Third Edition, “Hydraulic Design of Energy Dissipaters for Culverts and Channels”, July 2006. 2. North Carolina Department of Environment and Natural Resources, “Erosion and Sediment Control Planning and Design Manual”, Revised May 2013. Stormwater Management Plan Calculations Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 1 of 19 09/28/2016 (Permit Submittal) Calculation Title: Attachment 3a Stormwater Management Plan Summary: This document presents calculations from both Amec Foster Wheeler as well as Burns and McDonnell as preparers of Phase 1 (Tasks 1 and 2) of the 1982 basin construction. Amec Foster Wheeler is the preparer of the Phase 1, Task 1 stormwater management calculations related to the 1982 dam breach and dam decommissioning. Burns and McDonnell is the preparer of the Phase 1, Task 2 stormwater management calculations related to the structural fill placement and grading in preparation for the combined cycle power plant construction. Notes: Revision Log: No. Description Originator / Date Technical Reviewer / Date 0 Initial Submittal Section 1 – 4 Joe Parker (Amec Foster Wheeler) Section 5 Andy Fries (Burns and McDonnell) Section 1 – 4 Luke C. Williams, PE (Amec Foster Wheeler) Section 5 Andy Fries (Burns and McDonnell) Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 2 of 19 09/28/2016 (Permit Submittal) OBJECTIVE: The objective of this calculation package is to present the pre-construction and post- construction runoff calculations and stormwater management practices for Phase 1 (1982 basin decommissioning and structural fill placement). METHOD: Runoff volume calculations were performed using the SCS Curve Number method. Runoff hydrographs were developed using the SCS unit hydrograph method. CALCULATIONS: 1.0 Determination of Pre-Construction Stormwater Runoff The pre-construction condition was considered to be the land condition prior to the building of the 1982 dam at the Asheville Steam Electric Generating Plant. The runoff volumes for the pre- construction condition were determined using historic aerial imagery and topography from the United States Geological Survey (USGS). The outlet of the project drainage area is located at the inlet of the I-26 culvert crossing. The total drainage area was delineated using the 1965 USGS Skyland, NC quad and was determined to be 119.1 acres. Figure 1 shows this drainage area. Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 3 of 19 09/28/2016 (Permit Submittal) Figure 1: Pre-Construction Topography and Drainage Area (USGS Skyland, NC Quad 1965) Figure 2 shows the 1964 aerial imagery for the 1982 basin. Prior to the building of the 1982 dam the majority of the 1982 drainage area was pasture. Table 1 provides a summary of the land cover, hydrologic soil group, and runoff curve for the 1982 basin prior to the construction of the 1982 dam. The hydrologic soil groups were determined from Buncombe County Soil Survey. Please note the currently available Buncombe County Soil Survey was published in 2013 and the soils shown in the survey do not reflect pre-construction (i.e. pre-1982 dam) condition. Therefore to accurately estimate the pre-construction runoff the soils within the 1982 basin were estimated using the soil data for the surrounding undistributed or native soils shown in the survey. The native soils surrounding the site generally are type B soils. Developed areas associated with the plant were considered to be type C soils because of their disturbed nature. The weighted runoff curve number for the pre-construction drainage area is 68. Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 4 of 19 09/28/2016 (Permit Submittal) Figure 2: Pre-Construction Land Cover (USGS 09/24/1964) Table 1: Pre-Construction 1982 Basin Runoff Curve Number Summary Pre 1982 Dam Land Cover Summary Area (acres) Hydro Soil Group CN Industrial (72% Impervious) 8.8 C 91 Residential 5.4 B 70 Pasture 56 B 69 Pasture Tree Combination 16.3 B 65 Forest 32.6 B 60 Total 119.1 Weighted CN 68 Peak runoff flow rates were estimated using the SCS unit hydrograph method. Drainage parameters used to estimate the runoff hydrograph are shown in Table 2 below. The peak runoff rate for the 1-year, 24-hour storm event was calculated to be 30.4 cfs (Table 3). The 1- Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 5 of 19 09/28/2016 (Permit Submittal) year, 24-hour rainfall depth is 2.5 inches as determined from NOAA Atlas 14. A SCS Type II storm distribution was used for the 1-year, 24-hour rainfall event. Attachment 3b “Pre-1982 Dam Runoff Calculations” provides the supporting runoff calculations for the Pre-1982 dam condition. Table 2: Pre-Construction 1982 Basin Drainage Area Summary Drainage Area Area (acres) Area (mi2) Curve Number CN Tc (min) Drainage Area upstream I-26 119.1 0.1861 68 25 Pre-1982 Dam Conditions Table 3: Pre-Construction 1982 Basin Runoff Summary Storm Event Runoff Volume (ac-ft) Peak Runoff (cfs) Pre-1982 Dam Conditions 1-year, 24-hour 3.7 30.4 Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 6 of 19 09/28/2016 (Permit Submittal) 2.0 Determination of Post-Construction Stormwater Runoff The Post-construction condition was considered to be the land condition after the breach and decommissioning of the 1982 dam and placement of Structural Fill as shown on the “Final Grading and Drainage” sheet in the drawing package. The runoff volumes for the post-construction condition were determined considering the interior of the 1982 basin will be vegetated with grass. The soils within the 1982 basin footprint were considered disturbed and the hydrologic soil group was set to C to account for compaction of heavy equipment and general ground disturbance. The total drainage area was delineated using recent survey data of the site and was determined to be 107.5 acres. The drainage area was subdivided into multiple subbasins to allow for analysis of the East and West Stormwater Basins. The reduction in drainage area from the pre-construction conditions is a result of the low volume stormwater system (LVSW) which captures runoff from the plant area and diverts runoff away from the 1982 basin to an NPDES discharge point. Figure 3 shows the drainage area and the area of the LVSW system. Table 4 provides a summary of the land cover, hydrologic soil group, and runoff curve for the 1982 basin post breach of the 1982 dam. The weighted runoff curve number for the post-construction drainage area is 71. Figure 3: Post Construction Drainage Areas Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 7 of 19 09/28/2016 (Permit Submittal) Table 4: Post-Construction 1982 Basin Runoff Curve Number Summary Subbasin Land Cover Type Area (acres) Hydro Soil Group CN Grass developed area 3.1 C 74 Industrial (72% Impervious) 12.0 C 91 West Grass developed area 20.4 C 74 West Lower Grass developed area 5.4 C 74 Grass developed area 11.2 C 74 Grass woods Combination 20.1 B 68 Grass developed area 19.0 C 74 Grass woods Combination 10.1 B 70 East Lower Grass developed area 5.9 C 74 Lower Grass woods Combination 15.5 B 65 107.5 Weigthed CN 71 LVSW East 1 East 2 Total without LVSW Peak runoff flow rates were estimated using the SCS unit hydrograph method. Drainage parameters used to estimate the runoff hydrograph for each of the subbasins are shown in Table 5 below. Attachment 3c “Post-1982 Dam Runoff Calculations” provide the supporting subbasin runoff calculations for the Post-1982 dam condition. Two Stormwater basins will be constructed within the 1982 basin and will reduce peak flows leaving the project area. The Stormwater Basins details are discussed in Section 3.0. Table 6 shows the peak runoff rate for the 1-year, 24-hour from the project site considering the stormwater basins. Table 5: Post-Construction 1982 Basin Runoff Summary Drainage Area Area (acres) Area (mi2) Curve Number CN Tc (min) Post-1982 Dam Breach Conditions West 20.4 0.0318 74 22.8 West Lower 5.4 0.0085 74 7.1 East 1 31.3 0.0489 70 26.4 East 2 29.1 0.0454 73 28.1 East Lower 5.9 0.0092 74 11.2 Lower 15.5 0.0242 65 19.7 Table 6: Post-Construction 1982 Basin Runoff Summary Storm Event Runoff Volume (ac-ft)Peak Runoff (cfs) Post-1982 Dam Conditions 1-year, 24-hour 4.4 12.1 Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 8 of 19 09/28/2016 (Permit Submittal) 3.0 Stormwater Basins During the breaching activities of the 1982 dam two sediment ponds will be constructed at the toe of the interior face of the dam. The sediment ponds will provide erosion and sediment control during construction and were sized using guidelines from Section 6.61 NCDEQ Erosion and Sediment Control Planning Design Manual. These two sediment ponds will be modified once construction is complete to function as permanent stormwater basins to control peak runoff flow from the project site. These modifications to the sediment ponds include: 1) removal of the skimmer, 2) cleanout of deposited sediment, and 3) reduction in the principal spillway riser height to 4 feet. A 4” diameter orifice will also be put in the riser pipe to keep the stormwater basins dry. The two stormwater basins identified as “East” and “West” stormwater basins on the project drawings are located near the dam breach and will be below final grade to allow for runoff to be collected into the basins. Further details on the permanent stormwater basins are provided below. East Stormwater Basin The principal spillway for the East Stormwater Basin is a riser barrel type spillway. The riser pipe is 3 feet in diameter and has a height of 4 feet from the bottom of the pond. The top of the riser is open and serves as the principal spillway for the basin. The basin is dewatered by a 4-in diameter orifice located at the bottom of the riser. The horizontal barrel section of the principal spillway is a corrugated metal pipe 2 feet in diameter. The emergency spillway for the West Stormwater Basin is a trapezoidal channel with a 5’ bottom width and 3H:1V side slopes. The spillway is set 7 feet off the bottom of the pond. The stage storage information for the East Stormwater Basin is provided in Table 7 and Figure 4. Table 8 – 11 and Figure 5 provide the spillway discharge information for the East Stormwater Basin. Table 7: East Stormwater Basin Stage Storage Stage (ft) Surface (ft2) Surface Area (ac) Cumulative Storage Volume (ac-ft) 2098 0 0.000 0.0000 2099 2063 0.047 0.0237 2100 6464 0.148 0.1216 2101 11227 0.258 0.3246 2102 13886 0.319 0.6129 2103 15230 0.350 0.9471 2104 16599 0.381 1.3124 2105 17994 0.413 1.7095 2106 19424 0.446 2.1390 2107 20772 0.477 2.6004 2108 22119 0.508 3.0927 Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 9 of 19 09/28/2016 (Permit Submittal) Figure 4: East Stormwater Basin Stage Storage Table 8: East Stormwater Basin Outlet Riser Calculations Principal Spillway Riser Equations Riser Weir Q = CLH^1.5 C 3.3 Crest length (ft) 9.4 Riser Orifice Q = CA(2gH)^0.5 C 0.8 Riser orifice diameter (in) 36 Area (ft2) 7.1 Dewatering Orifice Q = CA(2gH)^0.5 C 0.4 Dewatering orifice diameter (in) 4 Area (ft2) 0.1 2096 2098 2100 2102 2104 2106 2108 2110 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Po n d De p t h (f t ) Pond Storage (ac‐ft) East Stormwater Basin Stage Storage Curve East SW Pond Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 10 of 19 09/28/2016 (Permit Submittal) Table 9: East Stormwater Basin Outlet Barrel Calculations Principal Spillway Outlet Pipe Flow Equations Q = A(2gH)^0.5/(1+ke+kb+f(L/D))^0.5 f = 185*n^2/(D)^(1/3) Entrance Loss coefficient (ke) 0.5 Bend Loss coefficient (kb) 0.1 Friction Loss coefficient (f) 0.084576728 z 3 Outlet Pipe length, L (ft) 300 Outlet Pipe diameter, D (ft) 2 Manning's Roughness (n) 0.024 Table 10: East Stormwater Basin Emergency Spillway Calculations Emergency Spillway Equations Q = CLH^1.5 Weir Coefficient 3.1 Trapezoidal (side slope) 3 Bottom Width of Spillway (ft) 5 Elevation H1 Q 2105 0 0 2105.5 0.5 7 2106 1 25 2106.5 1.5 54 2107 2 96 2107.5 2.5 153 2108 3 226 Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 11 of 19 09/28/2016 (Permit Submittal) Table 11: East Stormwater Basin Stage Discharge Information Elevation Riser Weir Flow Riser Orifice Flow Dewatering orifice Flow Outlet pipe Flow Principal Spillway Control** Emergency Spillway Combined East Stormwater Basin Discharge (ft) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) 2098 0 0 0.0 0 0 0 2098.5 0 0 0.2 6.8 0.2 0.2 2099 0 0 0.3 9.6 0.3 0.3 2099.5 0 0 0.3 11.7 0.3 0.3 2100 0 0 0.4 13.5 0.4 0.4 2100.5 0 0 0.4 15.1 0.4 0.4 2101 0 0 0.5 16.6 0.5 0.5 2101.5 0 0 0.5 17.9 0.5 0.5 2102 0 0 0.6 19.1 0.6 0.6 2102.5 11 32.1 0.6 20.3 11.6 11.6 2103 31 45.4 0.6 21.4 21.4 21.4 2103.5 57 55.6 0.7 22.4 22.4 22.4 2104 88 64.2 0.7 23.4 23.4 23.4 2104.5 123 71.8 0.7 24.4 24.4 24.4 2105 162 78.6 0.7 25.3 25.3 0 25.3 2105.5 204 84.9 0.8 26.2 26.2 7 33.3 2106 249 90.8 0.8 27.1 27.1 25 51.9 2106.5 297 96.3 0.8 27.9 27.9 54 82 2107 348 101.5 0.8 28.7 28.7 96 125.1 2107.5 401 106.4 0.9 29.5 29.5 153 182.7 2108 457 111.2 0.9 30.2 30.2 226 255.8 *Top Principal Spillway Riser = 2102'; Invert Emergency Spillway = 2105' **Principal Spillway Control Flow includes flow from the dewatering orifice. Figure 5: East Stormwater Basin Stage Discharge Curve 2098 2100 2102 2104 2106 2108 2110 0.0 50.0 100.0 150.0 200.0 250.0 300.0 El e v a t i o n ( f t ) Discharge (cfs) East Stormwater Basin Stage-Discharge Curve East SW Basin Discharge Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 12 of 19 09/28/2016 (Permit Submittal) West Stormwater Basin The principal spillway for the West Stormwater Basin is a riser barrel type spillway. The riser pipe is 3 feet in diameter and has a height of 4 feet from the bottom of the pond. The top of the riser is open and serves as the principal spillway for the basin. The basin is dewatered by a 4-in diameter orifice located at the bottom of the riser. The horizontal barrel section of the principal is spillway is a corrugated metal pipe 2 feet in diameter. The emergency spillway for the West Stormwater Basin is a trapezoidal channel with a 5’ bottom width and 3H:1V side slopes. The spillway is set 8 feet off the bottom of the pond. The stage storage information for the West Stormwater Basin is provided in Table 12 and Figure 6. Table 13 – 16 and Figure 7 provide the spillway discharge information for the West Stormwater Basin. Table 12: West Stormwater Basin Stage Storage Stage (ft) Surface Area (ft2) Surface Area (ac) Incremental Storage Volume(ac-ft) Cumulative Storage Volume (ac- ft) 2097 0 0.000 0.000 0.000 2098 1773 0.041 0.020 0.020 2099 5229 0.120 0.080 0.101 2100 9396 0.216 0.168 0.269 2101 13330 0.306 0.261 0.529 2102 14691 0.337 0.322 0.851 2103 16068 0.369 0.353 1.204 2104 17469 0.401 0.385 1.589 2105 18897 0.434 0.417 2.007 2106 20352 0.467 0.451 2.457 2107 21992 0.505 0.486 2.943 2108 23631 0.542 0.524 3.467 Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 13 of 19 09/28/2016 (Permit Submittal) Figure 6: West Stormwater Basin Stage Storage Table 13: West Stormwater Basin Outlet Riser Calculations Principal Spillway Riser Equations Riser Weir Q = CLH^1.5 C 3.3 Crest length (ft) 9.4 Riser Orifice Q = CA(2gH)^0.5 C 0.8 Riser orifice diameter (in) 36 Area (ft2) 7.1 Dewatering Orifice Q = CA(2gH)^0.5 C 0.4 Dewatering orifice diameter (in) 4 Area (ft2) 0.1 2096 2098 2100 2102 2104 2106 2108 2110 0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 Po n d De p t h (f t ) Pond Storage (ac‐ft) West Stormwater Basin Stage Storage Curve West SW Pond Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 14 of 19 09/28/2016 (Permit Submittal) Table 14: West Stormwater Basin Outlet Barrel Calculations Principal Spillway Outlet Pipe Flow Equations Q = A(2gH)^0.5/(1+ke+kb+f(L/D))^0.5 f = 185*n^2/(D)^(1/3) Entrance Loss coefficient (ke) 0.5 Bend Loss coefficient (kb) 0.1 Friction Loss coefficient (f) 0.084576728 z 3 Outlet Pipe length, L (ft) 300 Outlet Pipe diameter, D (ft) 2 Manning's Roughness (n) 0.024 Table 15: West Stormwater Basin Emergency Calculations Emergency Spillway Q = CLH^1.5 Weir Coefficient 3.1 Trapezoidal (side slope) 3 Bottom Width of Spillway (ft) 5 Elevation H1 Q 2105 0 0 2105.5 0.5 7 2106 1 25 2106.5 1.5 54 2107 2 96 2107.5 2.5 153 2108 3 226 Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 15 of 19 09/28/2016 (Permit Submittal) Table 16: West Stormwater Basin Stage Discharge Information Elevation Riser Weir Flow Riser Orifice Flow Dewatering orifice Flow Outlet pipe Flow Principal Spillway Control** Emergency Spillway Combined East Stormwater Basin Discharge (ft) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) 2097 0 0.0 0.00 0.0 0.0 0.0 2097.5 0 0.0 0.20 6.8 0.2 0.2 2098 0 0.0 0.28 9.6 0.3 0.3 2098.5 0 0.0 0.34 11.7 0.3 0.3 2099 0 0.0 0.40 13.5 0.4 0.4 2099.5 0 0.0 0.44 15.1 0.4 0.4 2100 0 0.0 0.49 16.6 0.5 0.5 2100.5 0 0.0 0.52 17.9 0.5 0.5 2101 0 0.0 0.56 19.1 0.6 0.6 2101.5 11 32.1 0.59 20.3 11.6 11.6 2102 31 45.4 0.63 21.4 21.4 21.4 2102.5 57 55.6 0.66 22.4 22.4 22.4 2103 88 64.2 0.69 23.4 23.4 23.4 2103.5 123 71.8 0.71 24.4 24.4 24.4 2104 162 78.6 0.74 25.3 25.3 25.3 2104.5 204 84.9 0.77 26.2 26.2 26.2 2105 249 90.8 0.79 27.1 27.1 0 27.1 2105.5 297 96.3 0.82 27.9 27.9 7 35.0 2106 348 101.5 0.84 28.7 28.7 25 53.5 2106.5 401 106.4 0.86 29.5 29.5 54 83.6 2107 457 111.2 0.89 30.2 30.2 96 126.7 *Top Principal Spillway Riser = 2101'; Invert Emergency Spillway = 2105' **Principal Spillway Control Flow includes flow from the dewatering orifice. Figure 7: West Stormwater Basin Stage Discharge Curve 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 El e v a t i o n ( f t ) Discharge (cfs) East Stormwater Basin Stage-Discharge Curve West SW Basin Discharge Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 16 of 19 09/28/2016 (Permit Submittal) 4.0 Outlet Hydrograph The USACE HMS hydrology model was used to model the storage routing within the East and West Stormwater Basins. Figure 8 shows the inflow and outflow hydrographs for the East Stormwater Basin. Figure 9 shows the inflow and outflow hydrographs for the West Stormwater Basin. Figure 10 shows the outflow hydrograph at the outfall of the project site. The peak flow from the project site for post-construction conditions is 12.1 cfs. Figure 8: East Stormwater Basin Discharge Hydrograph Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 17 of 19 09/28/2016 (Permit Submittal) Figure 9: West Stormwater Basin Discharge Hydrograph Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Amec Foster Wheeler Project No. 7810-16-0620 18 of 19 09/28/2016 (Permit Submittal) Figure 10: Project Outfall Hydrograph Stormwater Management Plan Duke Energy – Asheville Steam Electric Generating Plant Burns & McDonnell, Inc. 14 of 19 Registered in North Carolina 9400 Ward Parkway Kansas City, MO. 64114 Engineering License. C-1435 Burnsmcd.com 5.0 Culverts This section was developed by individuals from Burns & McDonnell in conjunction with Amec Foster Wheeler. Burns & McDonnell is the sole responsible party for information provided in this section. Two proposed culverts will be placed within the site to convey drainage across the main site pad, as well as under the proposed access road. These culverts will be maintained by Duke Energy. The first culvert is a 48” HDPE pipe located under the aggregate road between the main site pad at elevation 2138’ and the portion of the site at elevation 2150’. The second culvert is a 60” HDPE pipe located under the proposed asphalt access road and affiliated turnaround area. Table 14: Post-Construction 1982 Basin with New Plant Grading - Culvert Calculation Summary 1982 Basin ‐ Plant Grading Culvert Summary Pipe ID Area (Ac) Q100 (cfs) Inlet HW (ft) Slope (ft/ft) Pipe Type Critical Depth (ft) Outlet Velocity (ft/s) Flow Depth (ft) Outlet Type 48" 12.9 28.38 2.4 0.005 HDPE 1.58 8.37 1.26 Class 1 60" 47.1 103.62 4.5 0.0075 HDPE 2.90 13.64 2.05 Class 2 Attachment 3b Pre-1982 Dam Runoff Calculations Project Description Pre-1982dam.SPF Project Options CFS Elevation SCS TR-55 SCS TR-55 Hydrodynamic YES NO Analysis Options Sep 27, 2016 00:00:00 Sep 29, 2016 00:00:00 Sep 27, 2016 00:00:00 0 days 0 01:00:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 0 00:01:00 days hh:mm:ss 1 seconds Number of Elements Qty 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Rainfall Details SN Rain Gage Data Data Source Rainfall Rain State County Return Rainfall Rainfall ID Source ID Type Units Period Depth Distribution (years)(inches) 1 01-year Time Series 01-year, 24-hour Cumulative inches User Defined Outlets ...................................................... Pollutants .......................................................... Land Uses ......................................................... Links................................................................... Channels .................................................. Pipes ........................................................ Pumps ...................................................... Orifices ..................................................... Weirs ........................................................ Nodes................................................................. Junctions .................................................. Outfalls ..................................................... Flow Diversions ........................................ Inlets ......................................................... Storage Nodes ......................................... Runoff (Dry Weather) Time Step ...................... Runoff (Wet Weather) Time Step ..................... Reporting Time Step ......................................... Routing Time Step ............................................ Rain Gages ....................................................... Subbasins.......................................................... Enable Overflow Ponding at Nodes .................. Skip Steady State Analysis Time Periods ......... Start Analysis On .............................................. End Analysis On ................................................ Start Reporting On ............................................ Antecedent Dry Days ........................................ File Name .......................................................... Flow Units ......................................................... Elevation Type .................................................. Hydrology Method ............................................. Time of Concentration (TOC) Method .............. Link Routing Method ......................................... Subbasin Summary SN Subbasin Area Weighted Total Total Total Peak Time of ID Curve Rainfall Runoff Runoff Runoff Concentration Number Volume (ac)(in)(in)(ac-in)(cfs)(days hh:mm:ss) 1 Pre-1982dam 119.10 67.66 2.50 0.38 44.90 30.40 0 00:25:24 Node Summary SN Element Element Invert Ground/Rim Initial Surcharge Ponded Peak Max HGL Max Min Time of Total Total Time ID Type Elevation (Max)Water Elevation Area Inflow Elevation Surcharge Freeboard Peak Flooded Flooded Elevation Elevation Attained Depth Attained Flooding Volume Attained Occurrence (ft)(ft)(ft)(ft)(ft²)(cfs)(ft)(ft)(ft)(days hh:mm)(ac-in)(min) 1 Pre-outfall Outfall 2043.50 0.00 0.00 Subbasin Hydrology Subbasin : Pre-1982dam Input Data Area (ac) ........................................................................119.10 Weighted Curve Number ...............................................67.66 Rain Gage ID .................................................................01-year Composite Curve Number Area Soil Curve Soil/Surface Description (acres)Group Number Urban industrial, 72% imp 8.80 C 91.00 1/2 acre lots, 25% impervious 5.40 B 70.00 Pasture, grassland, or range, Fair 56.00 B 69.00 Woods & grass combination, Fair 16.30 B 65.00Woods & grass combination, Fair 16.30 B 65.00 Woods, Fair 32.60 B 60.00 Composite Area & Weighted CN 119.10 67.66 Time of Concentration TOC Method : SCS TR-55 Sheet Flow Equation : Tc = (0.007 * ((n * Lf)^0.8)) / ((P^0.5) * (Sf^0.4)) Where : Tc = Time of Concentration (hr) n = Manning's roughness Lf = Flow Length (ft) P = 2 yr, 24 hr Rainfall (inches) Sf = Slope (ft/ft) Shallow Concentrated Flow Equation :Shallow Concentrated Flow Equation : V = 16.1345 * (Sf^0.5) (unpaved surface) V = 20.3282 * (Sf^0.5) (paved surface) V = 15.0 * (Sf^0.5) (grassed waterway surface) V = 10.0 * (Sf^0.5) (nearly bare & untilled surface) V = 9.0 * (Sf^0.5) (cultivated straight rows surface) V = 7.0 * (Sf^0.5) (short grass pasture surface) V = 5.0 * (Sf^0.5) (woodland surface) V = 2.5 * (Sf^0.5) (forest w/heavy litter surface) Tc = (Lf / V) / (3600 sec/hr) Where: Tc = Time of Concentration (hr) Lf = Flow Length (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) Channel Flow Equation :Channel Flow Equation : V = (1.49 * (R^(2/3)) * (Sf^0.5)) / n R = Aq / Wp Tc = (Lf / V) / (3600 sec/hr) Where : Tc = Time of Concentration (hr) Lf = Flow Length (ft) R = Hydraulic Radius (ft) Aq = Flow Area (ft²) Wp = Wetted Perimeter (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) n = Manning's roughness Subarea Subarea Subarea Sheet Flow Computations A B C Manning's Roughness :0.4 0.00 0.00 Flow Length (ft) :100 0.00 0.00 Slope (%) :5.3 0.00 0.00 2 yr, 24 hr Rainfall (in) :3 0.00 0.00 Velocity (ft/sec) :0.11 0.00 0.00 Computed Flow Time (min) :15.02 0.00 0.00 Subarea Subarea Subarea Shallow Concentrated Flow Computations A B C Flow Length (ft) :1200 0.00 0.00 Slope (%) :5.3 0.00 0.00 Surface Type :Unpaved Unpaved Unpaved Velocity (ft/sec) :3.71 0.00 0.00 Computed Flow Time (min) :5.39 0.00 0.00 Subarea Subarea Subarea Channel Flow Computations A B CChannel Flow Computations A B C Manning's Roughness :0.045 0.00 0.00 Flow Length (ft) :1922 0.00 0.00 Channel Slope (%) :5.3 0.00 0.00 Cross Section Area (ft²) :7.506 0.00 0.00 Wetted Perimeter (ft) :9.721 0.00 0.00 Velocity (ft/sec) :6.42 0.00 0.00 Computed Flow Time (min) :4.99 0.00 0.00 Total TOC (min) ..................25.40 Subbasin Runoff Results Total Rainfall (in) ............................................................2.50 Total Runoff (in) .............................................................0.38 Peak Runoff (cfs) ...........................................................30.40 Weighted Curve Number ...............................................67.66 Time of Concentration (days hh:mm:ss) ........................0 00:25:24 Subbasin : Pre-1982dam Attachment 3c Post-1982 Dam Runoff Calculations Project Description Post-1982dam.SPF Project Options CFS Elevation SCS TR-55 SCS TR-55 Hydrodynamic YES NO Analysis Options Sep 27, 2016 00:00:00 Sep 29, 2016 00:00:00 Sep 27, 2016 00:00:00 0 days 0 01:00:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 0 00:05:00 days hh:mm:ss 1 seconds Number of Elements Qty 1 6 4 3 1 0 0 0 0 0 0 0 0 0 0 0 0 Rainfall Details SN Rain Gage Data Data Source Rainfall Rain State County Return Rainfall Rainfall ID Source ID Type Units Period Depth Distribution (years)(inches) 1 01-year Time Series 01-year, 24-hour Cumulative inches 0.00 Outlets ...................................................... Pollutants .......................................................... Land Uses ......................................................... Links................................................................... Channels .................................................. Pipes ........................................................ Pumps ...................................................... Orifices ..................................................... Weirs ........................................................ Nodes................................................................. Junctions .................................................. Outfalls ..................................................... Flow Diversions ........................................ Inlets ......................................................... Storage Nodes ......................................... Runoff (Dry Weather) Time Step ...................... Runoff (Wet Weather) Time Step ..................... Reporting Time Step ......................................... Routing Time Step ............................................ Rain Gages ....................................................... Subbasins.......................................................... Enable Overflow Ponding at Nodes .................. Skip Steady State Analysis Time Periods ......... Start Analysis On .............................................. End Analysis On ................................................ Start Reporting On ............................................ Antecedent Dry Days ........................................ File Name .......................................................... Flow Units ......................................................... Elevation Type .................................................. Hydrology Method ............................................. Time of Concentration (TOC) Method .............. Link Routing Method ......................................... Subbasin Summary SN Subbasin Area Weighted Total Total Total Peak Time of ID Curve Rainfall Runoff Runoff Runoff Concentration Number Volume (ac)(in)(in)(ac-in)(cfs)(days hh:mm:ss) 1 East_1 31.30 70.15 2.50 0.46 14.43 10.64 0 00:26:24 2 East_2 29.10 72.61 2.50 0.55 16.06 12.32 0 00:28:06 3 East_lower 5.90 74.00 2.50 0.61 3.59 4.52 0 00:11:10 4 Lower 15.51 65.00 2.50 0.30 4.61 3.13 0 00:19:43 5 West 20.40 74.00 2.50 0.61 12.40 11.24 0 00:22:48 6 West_lower 5.40 74.00 2.50 0.61 3.28 4.48 0 00:07:06 Node Summary SN Element Element Invert Ground/Rim Initial Surcharge Ponded Peak Max HGL Max Min Time of Total Total Time ID Type Elevation (Max)Water Elevation Area Inflow Elevation Surcharge Freeboard Peak Flooded Flooded Elevation Elevation Attained Depth Attained Flooding Volume Attained Occurrence (ft)(ft)(ft)(ft)(ft²)(cfs)(ft)(ft)(ft)(days hh:mm)(ac-in)(min) 4 I26 Outfall 2043.50 2108.00 0.00 0.00 0.00 0.00 0.00 2 Lower_out Junction 2043.50 2052.60 0.00 0.00 0.00 3 West_SWbasinJunction 2097.00 2108.00 0.00 0.00 0.00 Subbasin Hydrology Subbasin : East_1 Input Data Area (ac) ........................................................................31.30 Weighted Curve Number ...............................................70.15 Rain Gage ID .................................................................01-year Composite Curve Number Area Soil Curve Soil/Surface Description (acres)Group Number > 75% grass cover, Good 11.20 C 74.00 Woods & grass combination, Fair 20.10 B 68.00 Composite Area & Weighted CN 31.30 70.15 Time of Concentration TOC Method : SCS TR-55 Sheet Flow Equation : Tc = (0.007 * ((n * Lf)^0.8)) / ((P^0.5) * (Sf^0.4)) Where : Tc = Time of Concentration (hr) n = Manning's roughness Lf = Flow Length (ft) P = 2 yr, 24 hr Rainfall (inches) Sf = Slope (ft/ft) Shallow Concentrated Flow Equation : V = 16.1345 * (Sf^0.5) (unpaved surface) V = 20.3282 * (Sf^0.5) (paved surface) V = 20.3282 * (Sf^0.5) (paved surface) V = 15.0 * (Sf^0.5) (grassed waterway surface) V = 10.0 * (Sf^0.5) (nearly bare & untilled surface) V = 9.0 * (Sf^0.5) (cultivated straight rows surface) V = 7.0 * (Sf^0.5) (short grass pasture surface) V = 5.0 * (Sf^0.5) (woodland surface) V = 2.5 * (Sf^0.5) (forest w/heavy litter surface) Tc = (Lf / V) / (3600 sec/hr) Where: Tc = Time of Concentration (hr) Lf = Flow Length (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) Channel Flow Equation : V = (1.49 * (R^(2/3)) * (Sf^0.5)) / n R = Aq / Wp R = Aq / Wp Tc = (Lf / V) / (3600 sec/hr) Where : Tc = Time of Concentration (hr) Lf = Flow Length (ft) R = Hydraulic Radius (ft) Aq = Flow Area (ft²) Wp = Wetted Perimeter (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) n = Manning's roughness Subarea Subarea Subarea Sheet Flow Computations A B C Manning's Roughness :.4 0.00 0.00 Flow Length (ft) :100 0.00 0.00 Slope (%) :7 0.00 0.00 2 yr, 24 hr Rainfall (in) :3 0.00 0.00 Velocity (ft/sec) :0.12 0.00 0.00 Computed Flow Time (min) :13.44 0.00 0.00 Subarea Subarea Subarea Shallow Concentrated Flow Computations A B C Flow Length (ft) :1588 548 0.00 Slope (%) :7 0.7 0.00 Surface Type :Unpaved Unpaved Unpaved Velocity (ft/sec) :4.27 1.35 0.00 Computed Flow Time (min) :6.20 6.77 0.00 Total TOC (min) ..................26.40 Subbasin Runoff Results Total Rainfall (in) ............................................................2.50 Total Runoff (in) .............................................................0.46 Peak Runoff (cfs) ...........................................................10.64 Weighted Curve Number ...............................................70.15 Time of Concentration (days hh:mm:ss) ........................0 00:26:24 Subbasin : East_1 Subbasin : East_2 Input Data Area (ac) ........................................................................29.10 Weighted Curve Number ...............................................72.61 Rain Gage ID .................................................................01-year Composite Curve Number Area Soil Curve Soil/Surface Description (acres)Group Number > 75% grass cover, Good 19.00 C 74.00 Woods & grass combination, Fair 10.10 B 70.00 Composite Area & Weighted CN 29.10 72.61 Time of Concentration Subarea Subarea Subarea Sheet Flow Computations A B CSheet Flow Computations A B C Manning's Roughness :.40 0.00 0.00 Flow Length (ft) :100 0.00 0.00 Slope (%) :7.2 0.00 0.00 2 yr, 24 hr Rainfall (in) :3 0.00 0.00 Velocity (ft/sec) :0.13 0.00 0.00 Computed Flow Time (min) :13.29 0.00 0.00 Subarea Subarea Subarea Shallow Concentrated Flow Computations A B C Flow Length (ft) :1018 1158 0.00 Slope (%) :7.2 1.2 0.00 Surface Type :Unpaved Unpaved Unpaved Velocity (ft/sec) :4.33 1.77 0.00 Computed Flow Time (min) :3.92 10.90 0.00 Total TOC (min) ..................28.11 Subbasin Runoff Results Subbasin Runoff Results Total Rainfall (in) ............................................................2.50 Total Runoff (in) .............................................................0.55 Peak Runoff (cfs) ...........................................................12.32 Weighted Curve Number ...............................................72.61 Time of Concentration (days hh:mm:ss) ........................0 00:28:07 Subbasin : East_2 Subbasin : East_lower Input Data Area (ac) ........................................................................5.90 Weighted Curve Number ...............................................74.00 Rain Gage ID .................................................................01-year Composite Curve Number Area Soil Curve Soil/Surface Description (acres)Group Number > 75% grass cover, Good 5.90 C 74.00 Composite Area & Weighted CN 5.90 74.00 Time of Concentration Subarea Subarea Subarea Sheet Flow Computations A B C Manning's Roughness :.4 0.00 0.00 Manning's Roughness :.4 0.00 0.00 Flow Length (ft) :100 0.00 0.00 Slope (%) :14.7 0.00 0.00 2 yr, 24 hr Rainfall (in) :3 0.00 0.00 Velocity (ft/sec) :0.17 0.00 0.00 Computed Flow Time (min) :9.99 0.00 0.00 Subarea Subarea Subarea Shallow Concentrated Flow Computations A B C Flow Length (ft) :444 0.00 0.00 Slope (%) :14.7 0.00 0.00 Surface Type :Unpaved Unpaved Unpaved Velocity (ft/sec) :6.19 0.00 0.00 Computed Flow Time (min) :1.20 0.00 0.00 Total TOC (min) ..................11.18 Subbasin Runoff Results Total Rainfall (in) ............................................................2.50 Total Runoff (in) .............................................................0.61 Peak Runoff (cfs) ...........................................................4.52 Weighted Curve Number ...............................................74.00 Time of Concentration (days hh:mm:ss) ........................0 00:11:11 Subbasin : East_lower Subbasin : Lower Input Data Area (ac) ........................................................................15.51 Weighted Curve Number ...............................................65.00 Rain Gage ID .................................................................01-year Composite Curve Number Area Soil Curve Soil/Surface Description (acres)Group Number Woods & grass combination, Fair 15.51 B 65.00 Composite Area & Weighted CN 15.51 65.00 Time of Concentration Subarea Subarea Subarea Sheet Flow Computations A B C Manning's Roughness :.8 0.00 0.00 Manning's Roughness :.8 0.00 0.00 Flow Length (ft) :100 0.00 0.00 Slope (%) :13.8 0.00 0.00 2 yr, 24 hr Rainfall (in) :3 0.00 0.00 Velocity (ft/sec) :0.09 0.00 0.00 Computed Flow Time (min) :17.83 0.00 0.00 Subarea Subarea Subarea Shallow Concentrated Flow Computations A B C Flow Length (ft) :680 0.00 0.00 Slope (%) :13.8 0.00 0.00 Surface Type :Unpaved Unpaved Unpaved Velocity (ft/sec) :5.99 0.00 0.00 Computed Flow Time (min) :1.89 0.00 0.00 Total TOC (min) ..................19.72 Subbasin Runoff Results Total Rainfall (in) ............................................................2.50 Total Runoff (in) .............................................................0.30 Peak Runoff (cfs) ...........................................................3.13 Weighted Curve Number ...............................................65.00 Time of Concentration (days hh:mm:ss) ........................0 00:19:43 Subbasin : Lower Subbasin : West Input Data Area (ac) ........................................................................20.40 Weighted Curve Number ...............................................74.00 Rain Gage ID .................................................................01-year Composite Curve Number Area Soil Curve Soil/Surface Description (acres)Group Number > 75% grass cover, Good 20.40 C 74.00 Composite Area & Weighted CN 20.40 74.00 Time of Concentration Subarea Subarea Subarea Sheet Flow Computations A B C Manning's Roughness :0.24 0.00 0.00 Manning's Roughness :0.24 0.00 0.00 Flow Length (ft) :100 0.00 0.00 Slope (%) :9.2 0.00 0.00 2 yr, 24 hr Rainfall (in) :3 0.00 0.00 Velocity (ft/sec) :0.21 0.00 0.00 Computed Flow Time (min) :8.00 0.00 0.00 Subarea Subarea Subarea Shallow Concentrated Flow Computations A B C Flow Length (ft) :481 1271 0.00 Slope (%) :9.2 1 0.00 Surface Type :Unpaved Unpaved Unpaved Velocity (ft/sec) :4.89 1.61 0.00 Computed Flow Time (min) :1.64 13.16 0.00 Total TOC (min) ..................22.80 Subbasin Runoff Results Total Rainfall (in) ............................................................2.50 Total Runoff (in) .............................................................0.61 Peak Runoff (cfs) ...........................................................11.24 Weighted Curve Number ...............................................74.00 Time of Concentration (days hh:mm:ss) ........................0 00:22:48 Subbasin : West Subbasin : West_lower Input Data Area (ac) ........................................................................5.40 Weighted Curve Number ...............................................74.00 Rain Gage ID .................................................................01-year Composite Curve Number Area Soil Curve Soil/Surface Description (acres)Group Number > 75% grass cover, Good 5.40 C 74.00 Composite Area & Weighted CN 5.40 74.00 Time of Concentration Subarea Subarea Subarea Sheet Flow Computations A B C Manning's Roughness :.24 0.00 0.00 Manning's Roughness :.24 0.00 0.00 Flow Length (ft) :100 0.00 0.00 Slope (%) :15.8 0.00 0.00 2 yr, 24 hr Rainfall (in) :3 0.00 0.00 Velocity (ft/sec) :0.26 0.00 0.00 Computed Flow Time (min) :6.45 0.00 0.00 Subarea Subarea Subarea Shallow Concentrated Flow Computations A B C Flow Length (ft) :254 0.00 0.00 Slope (%) :15.8 0.00 0.00 Surface Type :Unpaved Unpaved Unpaved Velocity (ft/sec) :6.41 0.00 0.00 Computed Flow Time (min) :0.66 0.00 0.00 Total TOC (min) ..................7.11 Subbasin Runoff Results Total Rainfall (in) ............................................................2.50 Total Runoff (in) .............................................................0.61 Peak Runoff (cfs) ...........................................................4.48 Weighted Curve Number ...............................................74.00 Time of Concentration (days hh:mm:ss) ........................0 00:07:07 Subbasin : West_lower Junction Input SN Element Invert Ground/Rim Ground/Rim Initial Initial Surcharge Surcharge Ponded Minimum ID Elevation (Max)(Max)Water Water Elevation Depth Area Pipe Elevation Offset Elevation Depth Cover (ft)(ft)(ft)(ft)(ft)(ft)(ft)(ft²)(in) 1 East_SWbasin2 2098.00 2108.00 10.00 0.00 -2098.00 0.00 -2108.00 0.00 0.00 2 Lower_out 2043.50 2052.60 9.10 0.00 -2043.50 0.00 -2052.60 0.00 0.00 3 West_SWbasin 2097.00 2108.00 11.00 0.00 -2097.00 0.00 -2108.00 0.00 0.00 Junction Results SN Element Peak Peak Max HGL Max HGL Max Min Average HGL Average HGL Time of Time of Total Total Time ID Inflow Lateral Elevation Depth Surcharge Freeboard Elevation Depth Max HGL Peak Flooded Flooded Inflow Attained Attained Depth Attained Attained Attained Occurrence Flooding Volume Attained Occurrence (cfs)(cfs)(ft)(ft)(ft)(ft)(ft)(ft)(days hh:mm)(days hh:mm)(ac-in)(min) 1 East_SWbasin2 2 Lower_out 3 West_SWbasin