HomeMy WebLinkAboutNC0000396_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)
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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
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Initial Suhmjttal
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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0419°3
W I L
Ampc Enctar Wheeler Project No. 7910-15-0250 1 of 5
01/14/2016 (Permit Submittal)
amec
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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
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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.
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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.
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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-
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Figure 9: West Stormwater Basin Discharge Hydrograph
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Figure 10: Project Outfall Hydrograph
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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