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HomeMy WebLinkAbout_Cliffside Unit 5 CBE - Appendix C1_20200107Duke Energy Coal Combustion Residuals Management Program December 18, 2019 Cliffside Steam Station— Inactive Unit 5 Ash Basin CAMA Closure Plan (Closure by Excavation) Revision 0 Wood E&IS Project No. 7812190194 APPENDIX C: ENGINEERING EVALUATIONS AND ANALYSES wood. Duke Energy Coal Combustion Residuals Management Program December 18, 2019 Cliffside Steam Station— Inactive Unit 5 Ash Basin CAMA Closure Plan (Closure by Excavation) Revision 0 Wood E&IS Project No. 7812190194 APPENDIX Cl: STORMWATER wood. Channel and Dam Breach Calculation Duke Energy — Rogers Energy Complex Inactive Unit 5 Ash Basin Closure Plan Calculation Title: Channel and Dam Breach Calculation Summary: The channels for the Inactive Unit 5 Ash Basin final closure were designed to have adequate capacity and stability for the 25-year, 24-hour design storm event. The breach of the Main Dam (RUTHE-070) was designed to have adequate capacity and stability for the 100-year, 24-hour design storm event. All channels were evaluated for the 100-year, 24-hour design storm event. Notes: Revision Log: No. Description Originator Verifier .•� a y�caI Reviewer 0 Permit Submittal 67 f L:I(s�Za�4 Kevin Ferry Jos6iv& BeJI 0a Bell 4Qs :v0' . GINS !L": .,� " 0, Wood E&IS Project No. 7812-19-0194 1 of 7 wood. 10/1 /2019 Channel and Dam Breach Calculation Duke Energy — Rogers Energy Complex OBJECTIVE: Inactive Unit 5 Ash Basin Closure Plan The objective of this calculation is to support the design of stormwater conveyance measures for the Inactive Ash Basin based on long-term conditions following closure by removal of the basin and decommissioning of the Main Dam (RUTHE-070) METHOD Stormwater flow rates were calculated using the SCS method. The hydraulic capacity and stability of proposed channels was evaluated using Manning's equation and HydroCAD software [Ref. 1]. DEFINITION OF VARIABLES: T = shear; A = area; b = bottom width; CN = curve number; d = flow depth; D = channel depth; 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 Channel Design 1.1 Estimate Drainage Areas Drainage area delineation was based on the proposed final conditions after closure of the Inactive Ash Basin. Outside of the basin footprint, existing topography was used for delineation. Within the basin footprint, a combination of estimated bottom of ash and proposed channel grades was used for delineation. Wood E&IS Project No. 7812-19-0194 2 of 7 wood. 10/1 /2019 Channel and Dam Breach Calculation Inactive Unit 5 Ash Basin Closure Plan Duke Energy — Rogers Energy Complex Table 1: Drainage Area Summary Drainage Curve Drainage Area Soil Class Number Area ID (A) (CN) (ac) DA-1 33.17 B/C 70 DA-2 9.73 B/C 70 DA-3 97.80 B/C 82 DA-4 28.11 B/C 76 1.2 Describe Land Use Conditions Land use conditions were determined based on the proposed final conditions after closure of the Inactive Ash Basin. Areas within the basin footprint are anticipated to be grass in fair condition (50- 75% cover) and areas outside of the basin footprint consist of wooded and grassed areas. Site soils information shows that the drainage areas are comprised of hydrologic soil group B and C soils [Ref. 3]. Based on the following land use conditions and soils data, composite CN values were assigned to the drainage areas as shown in Table 1. 1.3 Calculate Time -of -Concentration The time -of -concentration (Tc) is the amount of time needed for water to travel from the hydrologically most distant point in a drainage area to the drainage area outlet. The estimated time of concentration for each drainage area is shown in Figure 1. The total time -of -concentration for a catchment generally consists of the following three components: sheet flow, shallow concentrated flow, and channel flow. Sheet flow was assumed to be no longer than the first 100 feet of the flow path, followed by shallow concentrated flow and channel flow. Table 2: Time of Concentration from Sheet Flow Time of Flow Length Concentration Manning No. Land Slope Drainage Area ID {L} Surface Description {T } c,sheet {n} (ft/ft) (ft.) (min) [Ref. 2] Woods: Light DA-1 100 0.400 0.0255 17.9 Underbrush DA-2 100 Range 0.130 0.0870 4.5 DA-3 100 Range 0.130 0.0160 8.8 DA-4 100 Range 0.130 0.0530 5.4 Table 3: Time of Concentration from Shallow Concentrated Flow Time of Flow Length Concentration Land Slope Drainage Area ID {L} Surface Description (T (ft.) (min) [Ref. 2] DA-1 1,239 Unpaved 0.0958 5.1 DA-2 673 Unpaved 0.1734 1.7 DA-3 2,295 Unpaved 0.0403 11.5 DA-4 1,416 Unpaved 0.0450 6.9 Wood E&IS Project No. 7812-19-0194 3 of 7 wood. 10/1 /2019 Channel and Dam Breach Calculation Duke Energy - Rogers Energy Complex Inactive Unit 5 Ash Basin Closure Plan Table 4: Time of Concentration from Channel Flow Time of Flow Length Concentration Drainage Area ID (L) {Tc,channel} (ft.) (min) [Ref. 2] DA-1 512 1.1 DA-2 433 1.9 DA-3 1,295 3.8 DA-4 329 1.2 Table 5: Total Time of Concentration Shallow Total Time of Selected Time of Sheet Flow Concentrated Channel Flow Concentration Concentration {Tcshee[ ) Flow {Tc,channel} Drainage Area ID {TC,totai} {TJ (min) {Tqs.f} (min) (min) (min) [Ref.2] min (min) [Ref.2] [Ref.2] [Ref.2] [Ref. 21 DA-1 17.9 5.1 1.1 24.1 24.1 DA-2 4.5 1.7 1.9 8.1 8.1 DA-3 8.8 11.5 3.8 24.1 24.1 DA-4 5.4 6.9 1.2 13.5 13.5 1.4 Peak Flows HydroCAD software was used to estimate stormwater flows from each drainage area for the 25- year, 24-hour and 100-year, 24-hour storm events based on the SCS method. The 25-year storm depth is 6.52 inches, and the 100-year storm depth is 8.21 inches. A type II 24-hr rainfall storm distribution was selected [Ref. 4]. Table 6 summarizes the peak flow for each drainage area: Table 6: Peak Flow Peak Peak Flow Flow Drainage Area ID {Q25) (Qloa) (cfs) (cfs) [Ref.1] [Ref.1] DA-1 105.57 153.16 DA-2 51.16 73.24 DA-3 430.85 587.52 DA-4 145.06 200.72 1.5 Channel Capacity and Stability The proposed trapezoidal channels were designed to tie into the bottom of ash of the Inactive Ash Basin. In areas where channels will be constructed on fill material, the channel side slopes are 10H:1V. In areas where the channel will be constructed by cut below estimated bottom of ash, the channel side slopes are 3H:1 V. A total of four (4) channels were designed and analyzed for capacity and stability. Channel dimensions are summarized in the following table: Wood E&IS Project No. 7812-19-0194 4 of 7 wood. 10/1 /2019 Channel and Dam Breach Calculation Inactive Unit 5 Ash Basin Closure Plan Duke Energy — Rogers Energy Complex Table 7: Channel Dimensions Min. Max. Bottom Min. Left Side Right Side Length Longitudinal Longitudinal Width Depth Channel ID Slope Slope (L) Slope Slope (b) (D) {Z,H:V) {ZZH:V) (ft) (S) (S) (ft) (ft) (ft/ft) (ft/ft) 1R 20 3.0 3 3 512 0.0625 0.0625 2R 20 3.0 3 3 562 0.0107 0.0122 311 20 4.0 3 3 1363 0.0308 0.0308 411 10 3.0 3 3 314 0.0700 0.0700 For the purpose of this analysis, the channel reaches were modeled with the corresponding cut side slopes of 3:1 as this is more conservative and results in a smaller cross -sectional flow area. Due to the irregular cross -sectional geometry of the channel, channels were first modeled as trapezoidal channels using Manning's equation to iteratively determine an approximate Manning's n value. This Manning's n value was then input into HydroCAD and the channels were modeled for capacity and stability using the determined Manning's n. The capacity of the proposed stormwater channel was evaluated using Manning's equation presented as: V _ 1.49 R2/3S1/2 [Ref. 5] n and Q = AV [Ref. 5] For the Manning's equation spreadsheet analysis, the flow area "A" and wetted perimeter "P" were calculated using the following relationships based on the geometry of a trapezoidal channel with a flow depth "d", bottom width "b", left side slope "21", and right side slope "72": A = bd + 0.5Z1d2 + 0.5Z2d2 P = b + [(Z1d) 22 + d2] + [(Z2d) 22 + d2] For the capacity and stability analysis in HydroCAD, the flow area "A" and wetted perimeter "P" were calculated based on coordinate inputs into HydroCAD that represent the actual channel cross- section. The stormwater channel capacities were evaluated using HydroCAD. The minimum longitudinal slope of each diversion was used for the capacity analysis. All channels will be stabilized by grouted riprap for permanent conditions due to the high velocity anticipated as result of their longitudinal slopes. Results from the channel capacity analysis are summarized in the following table: Wood E&IS Project No. 7812-19-0194 5 of 7 wood. 10/1 /2019 Channel and Dam Breach Calculation Duke Energy - Rogers Energy Complex Inactive Unit 5 Ash Basin Closure Plan Table 8: Channel Capacity Peak Min. Storm Manning's n Normal Runoff Logitudinal Freeboard Channel ID Recurrence Channel Lining {n} Depth (Q) Slope (in) Interval (ft) (cfs) (ft/ft) 1R 25 250.63 Grouted Riprap 0.0625 0.036 1.05 23 2R 1 25 1482.01, Grouted Riprap 0.0107 0.028 2.25 9 3R 1 25 1430.851 Grouted Riprap 0.0308 0.031 1.66 28 4R 1 25 1 145.061 Grouted Riprap 0.0700 0.035 1.09 23 Stability of the proposed channel reaches was also analyzed using HydroCAD. Stability analysis was based on the maximum effective longitudinal slope of each channel. Although permissible values for shear and velocity are not provided for Grouted Riprap linings, the shear force for each channel was calculated using the following equation: T = Ywater dS Results from the channel stability analysis are summarized in the following table: [Ref. 5] Table 9: Channel Stability Max. Permissible Calculated Permissible Calculated Storm Peak Runoff Longitudinal Manning's n Velocity Velocity Shear Shear Stress Channel ID Recurrence {Q} Slope Channel Lining {n} Safe {V} {V} {'sperm} {'r} Interval (cfs) {S} (ft/s) (ft/s) (psf) (psf) (ft/ft) 1R 25 250.63 0.0625 Grouted Riprap 0.036 N/A 10.26 N/A 4.44 Yes 2R 25 482.01 0.0122 Grouted Riprap 0.028 N/A 8.02 N/A 1.50 Yes 3R 25 430.85 0.0308 Grouted Riprap 0.031 N/A 10.42 N/A 3.18 Yes 4R 25 145.06 0.0700 Grouted Riprap 0.035 N/A 10.06 N/A 4.75 Yes 1.6 Dam Breach Capacity and Stability Channel 1 R and 2R passes through the Main Dam (RUTHE-070) proposed breach opening and discharges into the Broad river. As a result, the capacity and stability of the channels were re- analyzed for the 100-year, 24-hour storm event. The results of the analysis are summarized in the tables below: Table 10: Channel Capacity Peak Min. Storm Manning's n Normal Runoff Logitudinal Freeboard Channel ID Recurrence Channel Lining {n} Depth {Q} Slope (in) Interval (ft) (cfs) (ft/ft) 1R 100 353.88 Grouted Riprap 0.0625 0.034 1.28 20.7 2R 100 651.76 Grouted Riprap 0.0107 0.028 2.65 4.2 3R 100 578.52 Grouted Riprap 0.0308 0.029 1.89 25.4 4R 100 200.72 Grouted Riprap 0.0700 0.034 1.27 20.8 Table 11: Channel Stability Max. Permissible Calculated Permissible Calculated Storm Peak Runoff Longitudinal Manning's n Velocity Velocity Shear Shear Stress Channel ID Recurrence {Q} Slope Channel Lining {n} {V}(VI { {'Cperm} {T} Interval (cfs) {$} (ft/s) (ft/s) (psf) (psf) (ft/ft) 1R 100 353.88 0.0625 Grouted Riprap 0.034 N/A 11.63 N/A 4.98 2R 100 651.76 0.0107 Grouted Riprap 0.028 N/A 8.79 N/A 1.77 3R 100 578.52 0.0308 Grouted Riprap 0.029 N/A 11.94 N/A 3.63 4R 100 200.72 0.0700 Grouted Riprap 0.034 N/A 11.44 N/A 5.55 Wood E&IS Project No. 7812-19-0194 6 of 7 wood. 10/1 /2019 Channel and Dam Breach Calculation Duke Energy — Rogers Energy Complex DISCUSSION: Inactive Unit 5 Ash Basin Closure Plan The results from the analyses above show that the proposed channels for the Inactive Basin final closure have storage capacity and stability to convey runoff from the 25-year, 24-hour storm event. The flow velocities were all above the permissible velocity of 4.5 feet per second for grass lined open channels; therefore, all channels will be stabilized with grouted riprap. The Main Dam (RUTHE-070) breach opening was designed to have storage capacity and lining stability for the 100-year, 24-hour storm event. In the final condition, Channel 1 R and 2R conveys stormwater runoff through the Dam breach opening. Therefore, the channels were re-evaluated for the 100-year, 24-hour storm. The results of that analysis show that the channels both have adequate storage capacity and maintain stability with the proposed grouted riprap lining. FIGURES: Figure 1 — Drainage Area Map REFERENCES: 1. HydroCAD 10.00 (build 24), HydroCAD Software Solutions LLC, 2018. 2. United States Department of Agriculture, "Urban Hydrology for Small Watersheds", Technical Release 55, June 1986. 3. United States Department of Agriculture, "Web Soil Survey", obtained June 20, 2019. 4. Bonnin, G.M. et. al., "NOAA Atlas 14, Volume 2, Version 3, Point Precipitation Frequency Estimates", NOAA National Weather Service, obtained May 16, 2019. 5. North Carolina Department of Environment and Natural Resources, "Erosion and Sediment Control Planning and Design Manual", Revised May 2013. 6. Manning's Equation Calculation Results, prepared June 20, 2019. 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REVISION ANSI 22"x34" FIGURE 1 0 0 M V J CC N M "K7 < U F INCHES 1 2 3 (TENTHS 10 20 30 REV I DATE I JOB NO. I PROJECT TYPE I DES I DFTR I CHKD I ENGR Plotted By: Ojaruega, Vona Sheet Set: New Sheet Set (3) Layout: FIGURE 1 October 01, 2019 12: 10: 50pm P:\7812 Duke EEOC\Projects\2019\7812-19-0194 Cliffside Closure Plan\Calculations\Inactive Basin Storm water\References\Unit 5 Inactive Drainage Map FG.dwg DESCRIPTION 10 6/3/2019 Precipitation Frequency Data Server NOAA Atlas 14, Volume 2, Version 3" ' Location name: Mooresboro, North Latitude: 3 2147 , Longitude: 81rUSA* 7666° Elevation: 767.52 ft** source: ESRI Maps "ky " source: USGS 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)1 Average recurrence interval (years) Duration ���������� 1 2 5 10 25 50 100 200 500 1000 5-min 0.399 0.474 (0.363-0.439) (0.432-0.521) 0.560 (0.509-0.616) 0.626 (0.568-0.687) 0.711 (0.642-0.779) 0.773 (0.694-0.848) 0.837 (0.748-0.918) 0.900 (0.798-0.989) 0.981 (0.861-1.08) 1.05 (0.910-1.16) 10-min 0.637 0.758 (0.580-0.701) (0.691-0.833) 0.898 (0.816-0.986) 1.00 1 (0.909-1.10) 1.13 1 (1.02-1.24) 1.33 1 (1.19-1.46) 1.43 (1.26-1.57) 1.55 (1.36-1.71 1.65 1 (1.43-1.83) 1.14 1 (1.03-1.25) 1.27 1 (1.15-1.39) 1.44 1 (1.30-1.57) 1.56 (1.40-1.71) 1.68 1.80 1 (1.50-1.84) 1 (1.60-1.98) 1.95 (1.72-2.16) F 2.07 (1.80-2.29) 15-min 0.797 0.953 (0.725-0.876) (0.869-1.05) (1.4751177 1.67--2401 1.92 2333) (2.91 3572 30-min 0.994-11.20) (1. 0--31245) (2.121 2558 2. 0 2783 2. 8--3008) F�273 3 43) 2.07 (1.88-2.27) 2.39 (2.17-2.62) 2.83 (2.56-3.11) 3.18 (2.86-3.49) 4.46 ) (3.92-4.92 4.89 ( 4.25-5.42) 60-min 1.36 1.65 (1.24-1.50) 5.51-1.81) 3.55 3.93 (3.17-3.89) (3.48-4.32) 2.43 1 (2.22-2.67) 11 2.83 (2.57-3.10) 3.39 1 (3.06-3.72) 3.85 (3.46-4.22) 4.35 4.89 5.67 1 (3.88-4.77) 1 (4.33-5.37) (4.96-6.25) 4.79 .44 6.40 (4.24-5.29) [(4:77-6.02) (5.54-7.11) 6.33 (5.48-7.00) 2-hr 1.59 1.93 (1.45-1.75) 1 (1.77-2.13) 3-hr 1.71 2.06 (1.55-1.89) (1.88-2.29) 2.59 (2.36-2.87) 3.03 (2.74-3.35) 3.67 (3.29-4.05) 4.21 (3.76-4.64) 7.23 (6.18-8.05) 6-hr 2.13 2.57 (1.96-2.34) F(2.35-2.82) 2.62 =(2.83.46) (2.40-2.87) 3.13 3.78 (2.91-3.39) (3.51-4.09) 3.20 1 (2.92-3.51) 3.93 (3.59-4.31) 3.73 1 (3.40-4.09) 4.51 (4.08-4.94) 5.50 (4.97-6.02) 5.18 (4.65-5.68) 11 6.29 (5.66-6.89) 5.92 6.74 7.97 (5.26-6.49 1 (5.93-7.40) (6.90-8.77) 7.15 8.09 9.50 (6.37-7.82) (7.14-8.87) (8.26-10.4) 8.23 9.11 10.3 1 (7.54-8.86) 1 (8.32-9.82) (9.39-11.1) F 9.54 F 10.5 11.9 1 (8.77-10.3) 1 (9.67-11.4) (10.9-12.9) 9.04 (7.72-9.98) 12-hr 4.57 (4.16-5.01) 10.7 (9.21-11.8) 24-hr 4.74 1 (4.40-5.12) 5.49 1 (5.09-5.93) 6.44 5.98-6.93 6.54 i (6.03-7.05) 7.62 7.06-8.20) 7.37 1 (6.78-7.94 11.3 (10.2-12.2) 13.0 (11.8-14.0 2-day 3.72 3.46-4.01 4.48 4.17-4.83 5.57 5.18-6.01 F 8.57 1 (7.91-9.22) 3-day 3.95 (3.68-4.25) 4.75 5.87 1 (5.47-6.31) 6.76 (6.29-7.26) 7.97 8.94 1 (8.27-9.59) 9.92 I 10.9 12.4 1 (9.15-10.7) 1 (10.1-11.8) (11.3-13.3) 13.5 (12.3-14.5) 4-day 4.18 (3.91-4.49) 5.01 (4.69-5.38) 6.17 (5.76-6.61) 7.08 1 (6.59-7.58) 8.32 1 (7.73-8.90) F 9.30 (8.62-9.96) 10.3 11.3 12.8 1 (9.54-11.0) (10.5-12.2) (11.7-13.7) 13.9 (12.7-14.9) 7-day 4.88 (4 .57-5.21) 5.82 (5.45-6.21) 7.07 (6.62-7.54) 8.08 (7.56-8.61) 9.45 (8.81-10.1) 10.5 (9.80-11.2) 11.7 12.8 ) 14.4 ( 10.8-12.4) (11.8-13.6 ( 13.2-15.3) 15.6 ( 14.3-16.7) 10-day 5.235591 6.2257002 (7.45 8?42 8.42 9552 9.7 0131.0 10.7- 2.2 11 �13.3 E121:74.6) (14 15 6.2 15 2- 7.5 20-day 10.3 (9.76-10.9) 11.5 1 (10.9-12.2) 13.2 1 (12.4-13.9) 14.5 15.8 F 18.8 1 (14.8-16.7) (16.0-18.0) (17.5-19.9) 20.2 (18.7-21.4) 7.42 (7.03-7.83) 8.76 (8.29-9.24) 30-day 9.07 (8.63-9.54) 10.7 (10.1-11.2) 12.4 1 (11.8-13.0) 13.7 1 (13.0-14.4) 15.5 1 (14.6-16.2) 11 16.8 (15.9-17.6) 11 18.1 19.4 21.2 (17.1-19.0) (18.3-20.4 11 (19.8-22.3 11 22.5 (21.0-23.7) 45-day 11.5 (11.0-12.0) 13.7 (13.1-14.3) 13.4 (12.8-14.0) 15.3 (14.6-16.0) 16.7 (15.9-17.5) 18.6 (17.7-19.4) 20.0 (19.0-20.9) 21.3 22.7 24.4 (20.2-22.3) (21.5-23.7) (23.0-25.6) 24.5 25.8 27� (23.3-25.6) (24.6-27.0) (26.2-29.0) 25.7 (24.2-26.9) 60-day 15.9 (15.2-16.6) 18.0 (17.2-18.8) 19.5 (18.7-20.4) 21.5 (20.6-22.5) 23.0 (22.0-24.0) 29.0 (27.5-30.4) 1 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 https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_Printpage.htmI?Iat=35.2147&Ion=-81.7666&data=depth&units=engIish&series=pds 1/4 6/3/2019 Precipitation Frequency Data Server PD5-based depth -duration -frequency {DDT} curves Latitude: 35.2147a, Longitude:-31.7666' 30 / 25 ........... J.. ...... _._ _I --_ .__. L_ ....................... !" C r 20 4J a. ai C 15 T CL � 10 P, a ti L L L L L r6 rp N rq t6 rq rp N tp O O O N A 4b CV � In 1A rl N r6 4 O O O 6d O -Irl r7 WD r-I N n �T 40 Dlir�tl4n 30 25 C r 20 4� a m � 15 CL � 10 FU a 5 0 — — 1 2 5 10 25 50 100 200 Soo 1000 Average recurrence interval (years) NOAA Atlas 14, Volume 2, Version 3 Created {GMT}: Man jun 3 21:20-46 2019 Back to Top Maps & aerials Small scale terrain Average recurrent$ InleFval {years} —t 2 — 6 — 10 — 26 — 60 — 1aa 200 — 500 1000 Duration — 5-min — 2-day — 1d-min — 3-day 15-min — 4-day — 30-min — 7-day — 64-min — 1O-day — 2fir — 20-day — 3-hr — 30-day — "r — 45-day — 12-hr — 60-day — 24�hr https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.2147&Ion=-81.7666&data=depth&units=english&series=pds 2/4 6/3/2019 Precipitation Frequency Data Server Cliftside'. 1- . . 3km R71i CAROLINA 2.i Large scale terrain icdlils011 City', Winston-Salem Alle 6reensl�orc r-11 Mil. 11--11 tam •Ash ewillc TH CAROLI N 0 r' Charlotte F 4P Greenville SOLITH CAI OLIM 100km 60mi Pnipa Large scale map Gre, i!A Le arl otte Gr le fj 100krn tMi V rnb.- Large scale aerial https:llhdsc.nws.noaa.gov/hdsc/pfds/pfds-Printpage.html?lat=35.2147&lon=-81.7666&data=depth&units=english&series=pds 3/4 6/3/2019 Precipitation Frequency Data Server Back to Top US Department of Commerce National Oceanic and Atmospheric Administration National Weather Service National Water Center 1325 East West Highway Silver Spring, MD 20910 Questions?: HDSC.Questions@noaa.gov Disclaimer https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.2147&Ion=-81.7666&data=depth&units=english&series=pds 4/4 Chapter 3 Time of Concentration and 'Navel Time Travel time ( Tt ) is the time it takes water to travel from one location to another in a watershed. Tt is a component of time of concentration ( T, ), which is the time for runoff to travel from the hydraulically most distant point of the watershed to a point of interest within the watershed. T, is computed by summing all the travel times for consecutive compo- nents of the drainage conveyance system. T, influences the shape and peak of the runoff hydrograph. Urbanization usually decreases T,, thereby increasing the peak discharge. But T, can be increased as a result of (a) ponding behind small or inadequate drainage systems, including storm drain inlets and road culverts, or (b) reduction of land slope through grading. Factors affecting time of concen- tration and travel time Surface roughness One of the most significant effects of urban develop- ment on flow velocity is less retardance to flow. That is, undeveloped areas with very slow and shallow overland flow through vegetation become modified by urban development: the flow is then delivered to streets, gutters, and storm sewers that transport runoff downstream more rapidly. Travel time through the watershed is generally decreased. Channel shape and flow patterns In small non -urban watersheds, much of the travel time results from overland flow in upstream areas. Typically, urbanization reduces overland flow lengths by conveying storm runoff into a channel as soon as possible. Since channel designs have efficient hydrau- lic characteristics, runoff flow velocity increases and travel time decreases. Slope Slopes may be increased or decreased by urbanization, depending on the extent of site grading or the extent to which storm sewers and street ditches are used in the design of the water management system. Slope will tend to increase when channels are straightened and decrease when overland flow is directed through storm sewers, street gutters, and diversions. Computation of travel time and time of concentration Water moves through a watershed as sheet flow, shallow concentrated flow, open channel flow, or some combination of these. The type that occurs is a function of the conveyance system and is best deter- mined by field inspection. Travel time ( Tt ) is the ratio of flow length to flow velocity: Tt ❑ L [eq. 3-1] 3600V where: Tt = travel time (hr) L = flow length (ft) V = average velocity (ft/s) 3600 = conversion factor from seconds to hours. Time of concentration ( T, ) is the sum of Tt values for the various consecutive flow segments: Tc ❑Tt1 ❑Tt2 ❑... Ttm where: T, = time of concentration (hr) in = number of flow segments [eq. 3-2] (210-VI-TR-55, Second Ed., June 1986) 3-1 Chapter 3 Time of Concentration and Travel Time Technical Release 55 Urban Hydrology for Small Watersheds Figure 3-1 Average velocities for estimating travel time for shallow concentrated flow .50 .20 10 .02 01 005 �■ �■ �■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■■ ■ ■■ ■ ■ ■ ■ ■ I,I �I �,� ����� ��iii iiiii iiiii �� ����� ����■ IIIII ■■■■� �� ����� ����■ IIIII ■■■■� �� ����...■■■ IIIII ■■■■�.. IIIII ■■■■�.. C���...■■■ ■■■■ ■■■■■ ■■■■■ ■■MI ■MEMO ■■.. IIIII IIIII IIIII ■■ ■■■■ IIIII ■■■1111111 ■■ ■■■■ ■■■■� ��III11111 ■■ 111■■■■■ 1�■■■■ IIIII■ ■■■■■■■■1111111111In ■■■■■■■IIIIIIIIIIII■ 1001111111111111111 ■■■■■■■■1111111111 InIon■■1 .....����. CMEMMMM■■■■■■■■■■■■ ��M...■■■..■■■■.�, ■■■■■■���mm ���..■■■■ IIIII ■■■►.�...■ ■■ ■■ ■■ ����. ���..■■■■ IIIII ■■I ��.., ■■ ■■ ■■ ■■ ����. mm I....■■■■■■����� 1111111■■■■■■■■11■■■■■ 1111111■■■■■■■■IIIII■■ 1111111■■■■���III■■■■■ 111111IMIMIIIIII■■■■■ 111111111■■■1111111■■■■■ 111111IIIIII1111111■■■■■ ■■■■ ■■■■ ■■■■ ■■■ ■■■ ■■■� ■■II■I 11111111111111111111111■■■■■ ■■►►11/ IIII IIIII IIIII II II II II II IIIII ■�/�� �■■■� ��I1IIIIII ■■ ■■ �� �111 IIIII ■��■�� ■■■■11111� ����� ■■ ■� 11111� IIIII ��� � ■■III IIIII IIIII ■■ 11111111 IIIII II.�■ ■■■■11111I IIIII ■■ ■1111111IIIII r�■■ IIIII iiiimiii ■■■ �i ii ii IIIII 1 2 4 6 10 20 Average velocity (ft/sec) 3-2 (210-VI-TR-55, Second Ed., June 1986) Chapter 3 Sheet flow Time of Concentration and Travel Time Technical Release 55 Urban Hydrology for Small Watersheds Sheet flow is flow over plane surfaces. It usually occurs in the headwater of streams. With sheet flow, the friction value (Manning's n) is an effective rough- ness coefficient that includes the effect of raindrop impact; drag over the plane surface; obstacles such as litter, crop ridges, and rocks; and erosion and trans- portation of sediment. These n values are for very shallow flow depths of about 0.1 foot or so. Table 3-1 gives Manning's n values for sheet flow for various surface conditions. Table 3-1 Roughness coefficients (Manning's n) for sheet flow Surface description n 1/ Smooth surfaces (concrete, asphalt, gravel, or bare soil) .......................................... 0.011 Fallow (no residue) .................................................. 0.05 Cultivated soils: Residue cover E200/o ......................................... 0.06 Residue cover >20%......................................... 0.17 Grass: Short grass prairie ............................................ 0.15 Dense grasses 2/................................................ 0.24 Bermudagrass.................................................. 0.41 Range (natural)......................................................... 0.13 Woods:3/ Light underbrush .............................................. 0.40 Dense underbrush ............................................ 0.80 1 The n values are a composite of information compiled by Engman (1986). 2 Includes species such as weeping lvegrass, bluegrass, buffalo grass, blue grama grass, and native grass mixtures. 3 When selecting n , consider cover to a height of about 0.1 ft. This is the only part of the plant cover that will obstruct sheet flow. For sheet flow of less than 300 feet, use Manning's kinematic solution (Overtop and Meadows 1976) to compute Tt: 0.0071k f.s Tt ❑ � �-5S0.4 [eq. 3-3] 2 where: Tt = travel time (hr), n = Manning's roughness coefficient (table 3-1) L = flow length (ft) P2 = 2-year, 24-hour rainfall (in) s = slope of hydraulic grade line (land slope, ft/ft) This simplified form of the Manning's kinematic solu- tion is based on the following: (1) shallow steady uniform flow, (2) constant intensity of rainfall excess (that part of a rain available for runoff), (3) rainfall duration of 24 hours, and (4) minor effect of infiltra- tion on travel time. Rainfall depth can be obtained from appendix B. Shallow concentrated flow After a maximum of 300 feet, sheet flow usually be- comes shallow concentrated flow. The average veloc- ity for this flow can be determined from figure 3-1, in which average velocity is a function of watercourse slope and type of channel. For slopes less than 0.005 ft/ft, use equations given in appendix F for figure 3-1. Tillage can affect the direction of shallow concen- trated flow. Flow may not always be directly down the watershed slope if tillage runs across the slope. After determining average velocity in figure 3-1, use equation 3-1 to estimate travel time for the shallow concentrated flow segment. Open channels Open channels are assumed to begin where surveyed cross section information has been obtained, where channels are visible on aerial photographs, or where blue lines (indicating streams) appear on United States Geological Survey (USGS) quadrangle sheets. Manning's equation or water surface profile informa- tion can be used to estimate average flow velocity. Average flow velocity is usually determined for bank - full elevation. (210-VI-TR-55, Second Ed., June 1986) 3-3 Chapter 3 Manning's equation is: 2 1 V ❑1.49r3s2 n where: Time of Concentration and Travel Time Technical Release 55 Urban Hydrology for Small Watersheds • A culvert or bridge can act as a reservoir outlet if there is significant storage behind it. The proce- dures in TR-55 can be used to determine the peak [eq. 3-4] flow upstream of the culvert. Detailed storage routing procedures should be used to determine the outflow through the culvert. V = average velocity (ft/s) r = hydraulic radius (ft) and is equal to a/pw a = cross sectional flow area (ft2) pW = wetted perimeter (ft) s = slope of the hydraulic grade line (channel slope, ft/ft) n = Manning's roughness coefficient for open channel flow. Manning's n values for open channel flow can be obtained from standard textbooks such as Chow (1959) or Linsley et al. (1982). After average velocity is computed using equation 3-4, Tt for the channel seg- ment can be estimated using equation 3-1. Reservoirs or lakes Sometimes it is necessary to estimate the velocity of flow through a reservoir or lake at the outlet of a watershed. This travel time is normally very small and can be assumed as zero. Limitations • Manning's kinematic solution should not be used for sheet flow longer than 300 feet. Equation 3-3 was developed for use with the four standard rainfall intensity -duration relationships. In watersheds with storm sewers, carefully identify the appropriate hydraulic flow path to estimate T,. Storm sewers generally handle only a small portion of a large event. The rest of the peak flow travels by streets, lawns, and so on, to the outlet. Consult a standard hydraulics textbook to determine average velocity in pipes for either pressure or nonpressure flow. • The minimum T, used in TR-55 is 0.1 hour. Example 3-1 The sketch below shows a watershed in Dyer County, northwestern Tennessee. The problem is to compute T, at the outlet of the watershed (point D). The 2-year 24-hour rainfall depth is 3.6 inches. All three types of flow occur from the hydraulically most distant point (A) to the point of interest (D). To compute T,, first determine Tt for each segment from the following information: Segment AB: Sheet flow; dense grass; slope (s) = 0.01 ft/ft; and length (L) = 100 ft. Segment BC: Shallow concentrated flow; unpaved; s = 0.01 ft/ft; and L = 1,400 ft. Segment CD: Channel flow; Manning's n = .05; flow area (a) = 27 ft2; wetted perimeter (pw) = 28.2 ft; s = 0.005 ft/ft; and L = 7,300 ft. See figure 3-2 for the computations made on worksheet 3. �100 ft• 1,400 ft 7,300 ft (Not to scale) X 3-4 (210-VI-TR-55, Second Ed., June 1986) 3 m 431000 35' 13' 18" N 35' 12' 4" N 431000 431200 431400 431600 431800 432000 3 m Map Scale: 1:11,100 if printed on A portrait (8.5" x 11") sheet. Meters m N 0 150 300 600 900 Feet 0 500 1000 2000 3000 Map projection: Web Mercator Comer coordinates: WGS84 Edge tics: UTM Zone 17N WGS84 U}DA Natural Resources Web Soil Survey Conservation Service National Cooperative Soil Survey Soil Map —Cleveland County, North Carolina (Active Ash Basin - Soils Map) 431200 431400 431600 431800 432000 43= 432400 432200 4324W N 432600 35° 13' 18" N 35' 12' 4" N 432600 3 N 6/20/2019 Page 1 of 3 MAP LEGEND Area of Interest (AOI) 0 Area of Interest (AOI) Soils 0 Soil Map Unit Polygons rwr Soil Map Unit Lines 0 Soil Map Unit Points Special Point Features Vo Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit .14 Gravelly Spot 0 Landfill Lava Flow Marsh or swamp + Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot 4 Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip oa Sodic Spot Soil Map —Cleveland County, North Carolina (Active Ash Basin - Soils Map) MAP INFORMATION Spoil Area The soil surveys that comprise your AOI were mapped at 1:24,000. Stony Spot Very Stony Spot Warning: Soil Map may not be valid at this scale. Wet Spot Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil Other line placement. The maps do not show the small areas of .- Special Line Features contrasting soils that could have been shown at a more detailed scale. Water Features Streams and Canals Please rely on the bar scale on each map sheet for map measurements. Transportation Rails Source of Map: Natural Resources Conservation Service Web Soil Survey URL: rwr Interstate Highways Coordinate System: Web Mercator (EPSG:3857) US Routes Maps from the Web Soil Survey are based on the Web Mercator L Major Roads projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Local Roads Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. Background . Aerial Photography This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Cleveland County, North Carolina Survey Area Data: Version 21, Sep 10, 2018 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Apr 23, 2014—Oct 18, 2017 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. USDA Natural Resources Web Soil Survey 6/20/2019 Conservation Service National Cooperative Soil Survey Page 2 of 3 Soil Map —Cleveland County, North Carolina Active Ash Basin - Soils Map Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI BuB Buncombe loamy sand, 1 to 5 16.8 2.6% percent slopes, rarely flooded CaB2 Cecil sandy clay loam, 2 to 8 0.7 0.1 % percent slopes, moderately eroded ChA Chewacla loam, 0 to 2 percent 10.3 1.6% slopes, frequently flooded DAM Dam 3.9 0.6% PaD2 Pacolet sandy clay loam, 15 to 3.5 0.5% 25 percent slopes, moderately eroded PbB2 Pacolet-Bethlehem complex, 2 144.6 22.3% to 8 percent slopes, moderately eroded PbC2 Pacolet-Bethlehem complex, 8 196.4 30.3% to 15 percent slopes, moderately eroded PbD2 Pacolet-Bethlehem complex, 58.8 9.1 % 15 to 25 percent slopes, moderately eroded PeD Pacolet-Bethlehem complex, 3.8 0.6% 15 to 25 percent slopes, stony PtD Pacolet-Saw complex, 15 to 25 2.9 0.5% percent slopes, stony RaE Rion -Ashlar complex, 25 to 60 8.7 1.3% percent slopes, rocky RnE Rion-Cliffside complex, 25 to 23.4 3.6% 60 percent slopes, very stony UdC Udorthents, loamy, 0 to 15 119.3 18.4% percent slopes W Water 55.0 8.5% Totals for Area of Interest 648.1 100.0% usDA Natural Resources Web Soil Survey 6/20/2019 Conservation Service National Cooperative Soil Survey Page 3 of 3 5/16/2019 Precipitation Frequency Data Server NOAA Atlas 14, Volume 2, Version 3 Location name: Mooresboro, North Carolina, USA*- Latitude: 35.2146°, Longitude:-81.7479. Elevation: 761.42 ft** * source: ESRI Maps ,, , m y� ** source: USGS 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)1 Average recurrence interval (years) 1 2 5 10 25 50 100 200 500F 1000 0.399 0.474 0.560 0.626 0.711 0.773 0.836 0.898 0.979 1.05 5-mm (0.364-0.439) (0.433-0.521) (0.510-0.616) (0.568-0.687) (0.642-0.779) (0.694-0.847) (0.747-0.917) (0.797-0.988) (0.860-1.08) (0.909-1.16) 0.638 0.758 0.898 1.00 1.13 1.23 1.33 1.42 1.55 1.65 1 0-min (0.581-0.701) (0.692-0.833) (0.816-0.986) (0.909-1.10) 1 (1.02-1.24) 11 (1.11-1.35) 1 (1.19-1.46) 1 (1.26-1.57) (1.36-1.71) (1.43-1.82) 0.797 0.953 1.14 1.27 1.44 1.56 1.68 1.80 1.95 2.07 1 5-min (0.726-0.876) (0.870-1.05) 1 (1.03-1.25) 1 (1.30-1.57) 11 (1.40-1.71) 1 (1.50-1.84) 1 (1.59-1.98) (1.71-2.15) (1.80-2.29) 1.09 1.32 1.61 1.84 2.13 2.35 2.57 2.80 3.10 3.35 30-min (0.995-1.20) (1.20-1.45) (1.47-1.77) (1.67-2.01) (1.92-2.33) (2.11-2.57) (2.30-2.82) (2.48-3.08) (2.73-3.42) (2.91-3.71) 1.65 2.07 2.39 2.83 3.18 3.54 3.92 4.45 4.88 C1.36 60-min (1.24-1.50) (1.51-1.81) (1.88-2.27) (2.17-2.62) (2.56-3.10) (2.86-3.49) (3.17-3.89 (3.48-4.31) (3.91-4.91) ( 4.25-5.41) 1.59 1.94 2.43 2.83 3.39 3.85 4.35 4.887F 5.667F 6.31 2-hr (1.46-1.75) (1.77-2.13) (2.22-2.67) (2.57-3.10) (3.06-3.71) (3.46-4.22) (3.88-4.77) (4.32-5.36) (4.95-6.24) (5.47-6.98) 1.71 2.06 2.60 3.03 3.67 -IF-4-21--ll 4.79 5.44 6.39 7.22 3-hr (1.55-1.89) 1 (1.88-2.29) 1 (2.36-2.87) 1 (2.74-3.35) 1 (3.29-4.05) 11 (3.76-4.64) 1 (4.24-5.29) (4.77-6.01) (5.53-7.09) (6.17-8.03) 2.13 2.56 3.20 3.73 4.51 5.18 5.91 6.73 7.95 9.01 6-hr (1.95-2.34) 1 (2.35-2.82) 1 (2.92-3.51) 1 (4.07-4.94) 1 (4.64-5.67) 1 (5.26-6.48) 1 (5.92-7.39) (6.88-8.75) (7.70-9.94) 2.61 3.14 3.92 4.56 5.49 6.28 7.14 8.08 9.49 10.7 12-hr (2 .39-2.86) (2.88-3.45) (3.58-4.30) (4.15-5.00) (4.97-6.01) (5.65-6.87) (6.36-7.81) 11 (7.13-8.85) (8.25-10.4) (9.19-11.8) 3.13 3.77 4.72 5.48 6.52 7.35 8.21 9.10 10.3 11 .3 24-hr (2.90-3.38) (3.50-4.08) (4.39-5.11) (5.08-5.92) (6.02-7.03) (6.76-7.92) (7.53-8.85) (8.31-9.80) (9.38-11.1) ( 10.2-12.2) 3.71 4.46 5.56 6.42 7.61 8.55 9.52 10.5 11.9 13.0 2-day (3.45-4.00) (4.15-4.82) (5.17-6.00) (5.96-6.92) (7.04-8.19) (7.89-9.21) (8.76-10.2) 1 (9.66-11.3) (10.9-12.8) (11.8-14.0) 3.94 4.73 5.85 6.74 7.95 8.92 9.90 10.9 12.3 13.4 3-day (3.67-4.24) 1 (4.41-5.09) 1 (5.45-6.30) 1 (6.27-7.24) 1 (7.38-8.54) 11 (8.25-9.57) 1 (9.13-10.6) 1 (10.0-11.7) (11.3-13.3) (12.2-14.5) 4.17 5.00 6.15 7.06 8.30 9.28 10.3 11.3 12.7 13.9 4-day (3.90-4.48) 11 (4.68-5.37) 1 (5.74-6.60) 1 (6.58-7.57) (7.71-8.88) (8.60-9.94) (9.51-11.0) 1 (10.4-12.1) (11.7-13.7) (12.7-14.9) 4.86 5.80 7.05 8.06 9.42 F 10.5 F 11.6 12.8 44.3 15.6 7-day (4.56-5.19) (5.44-6.19) (6.61-7.52) (7.53 8.58) (8.78-10.0) (9.77-11.2) (10.8-12.4) (11.8-13.6) ( 13.2-15.3) (14.3-16.6) 5.53 6.58 7.89 8.93 10.3 11.4 12.5 13.6 15.2 16.3 10-day (5.22-5.89) (6.20-7.00) (7.43-8.39) 1 (8.39-9.48) 1 (9.67-11.0) 1 (10.7-12.1) 1 (11.7-13.3) 1 (12.7-14.5) (14.1-16.1) (15.1-17.4) 7.39 10.3 F 13.1 F 14.4 15.7 17.0 F 18.8 8.72 20.1 20-day (7.00-7.80) (8.26-9.20) (9.73-10.8) (10.912.1) (12.4-13.9) 1 (13.6-15.2) 1 (14.7-16.6) (15.9-18.0) (17.5-19.9) (18.7-21.3) 9.03 12.3 F 15.4 16.7 18.0 19.4 21.1 10.6 22.4 30-day (8.60-9.50) (10.1-11.2) 1 (11.7-13.0) (13.014.3) (14.6-16.2) 1 (15.8-17.6) 1 (17.0-19.0) (18.2-20.4) (19.8-22.2) (21.0-23.6) 11.4 15.2 16.7 18.5 19.9 21.3 22.6 24.3 25.6 13.4 45-day 109-12.0) ( (12.8-14.0) (14.5-15.9) (15.917.4) (17.6-19.4) (18.9-20.8) (20.2-22.2) ( 21.4-23.6) (23.0-25.5) (24.1-26.8) 13.6 15 .9 17.9 19.4 21.4 22.9 24.4 25.8 27.6 28.9 60-day 13.0-14.2) ( (15.2-16.6) (17.1-18.7) (18.6-20.3) (20.5-22.4) (21.9-24.0) (23.2-25.5 24.5-27.0 26.2-28.9) ) ( ) ( (27.4-30.3) 1 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 https:Hhdsc.nws. noaa.gov/hdsc/pfds/pfds_printpage.htmI?lat=35.2146&Ion=-81.7479&data=depth&units=engIish&series=pds 1 /4 5/16/2019 Precipitation Frequency Data Server PF graphical PDS-based depth -duration -frequency (DDF) curves Latitude: 35.2146 Longitude:-31.74791 30 25 C t 20 N d di U O 15 49 CL V 10 FU ill 0 -Y -Y -Y -Y OO OO u'i OO ri ri rn LO ri N rn V ID Duration 30 25 e 20 C CL m 15 ,9 CL 10 a 5 O F --t-- TI I I I I I I 1 2 5 10 25 50 100 200 500 1000 Average recurrence interval (years) NDAAAtlas 14, Volume 2, Version 3 Created {GMT}: Thu May 16 18:50:29 2019 Back to Top Maps & aerials Small scale terrain Average recurrence inlenral {years) — t 2 — 5 — 10 25 50 100 200 500 1000 Duration — 5-min — 2-day — 1 d-min — 3-day 15-min — 4-day — 30-min — 7-day — 8D-min — 10-day — 2fir — 20-(Jay — "r — 30-(Jay — 6-1r — 45-day — 12-hr — 6d-eay - 24-hr https:Hhdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.htmI?lat=35.2146&Ion=-81.7479&data=depth&units=engIish&series=pds 2/4 5/16/2019 Precipitation Frequency Data Server nennettia ClifFsGd - I Broad Rrenf. � I Rd- 3km :AROLINA 2mi 5� A Large scale terrain Kingsport Filri`st61 ' ; .= .-_.- ......�..: �S ' Johnson City Winston-Salem Mlle • Greelnsborc y, 4 CAI Mitchell rtiti7 l • Asl7e�ille NORTH C A R O L I Charlotte F iGreenville SOLITH CAROLI 100km 60mi • Columbia -. Large scale map W Jchnson fifty Winston-Salem Gres .KnQacvali •� f �' Ash €1 Iart Otte le 4 _ 4 100km r olutill) 10 60mi ° ti Large scale aerial https:Hhdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.htmI?lat=35.2146&Ion=-81.7479&data=depth&units=engIish&series=pds 3/4 5/16/2019 Precipitation Frequency Data Server Back to Top US Department of Commerce National Oceanic and Atmospheric Administration National Weather Service National Water Center 1325 East West Highway Silver Spring, MD 20910 Questions?: HDSC.Questions@noaa.gov Disclaimer https:Hhdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.htmI?lat=35.2146&Ion=-81.7479&data=depth&units=engIish&series=pds 4/4 Appendices This section addresses the design of stable conveyance channels and diversions using flexible linings. A stable channel is defined as a channel which is nonsilting and nonscouring. To minimize silting in the channel, flow velocities should remain constant or increase slightly throughout the channel length. This is especially important in designing diversion channels and can be accomplished by adjusting channel grade. Procedures presented in this section address the problems of erosion and scour. More advanced procedures for permanent, unlined channels may be found elsewhere. (References: Garde and Ranga Raju, 1980) Diversions are channels usually with a supporting ridge on the lower side. They are generally located to divert flows across a slope and are designed following the same procedures as other channels. Design tables for vegetated diversions and waterways are included at the end of this section. Flexible channel linings are generally preferred to rigid linings from an erosion control standpoint because they conform to changes in channel shape without failure and are less susceptible to damage from frost heaving, soil swelling and shrinking, and excessive soil pore water pressure from lack of drainage. Flexible linings also are generally less expensive to construct, and when vegetated, are more natural in appearance. On the other hand, flexible linings generally have higher roughness and require a larger cross section for the same discharge. EROSION CONTROL CRITERIA The minimum design criteria for conveyance channels require that two primary conditions be satisfied: the channel system must have capacity for the peak flow expected from the 10-year storm and the channel lining must be resistant to erosion for the design velocity. In some cases, out -of -bank flow may be considered a functional part of the channel system. In these cases, flow capacities and design velocities should be considered separately for out - of -bank flows and channel flows. Both the capacity of the channel and the velocity of flow are functions of the channel lining, cross -sectional area and slope. The channel system must carry the design flow, fit site conditions, and be stable. STABLE CHANNEL DESIGN METHODS Two accepted procedures for designing stable channels with flexible linings are: (1) the permissible velocity approach; and (2) the tractive force approach. Under the permissible velocity approach, the channel is considered stable if the design, mean velocity is lower than the maximum permissible velocity. Under the tractive force approach, erosive stress evaluated at the boundary between flowing water and lining materials must be less than the minimum unit tractive force that will cause serious erosion of material from a level channel bed. 8.05.1 0 The permissible velocity procedure is recommended for the design of vegetative channels because of common usage and the availability of reliable design tables. The tractive force approach is recommended for design of channels with temporary synthetic liners or riprap liners. The tractive force procedure is described in full in the U.S. Department of Transportation, Federal Highway Administration Bulletin, Design of Roadside Channels with Flexible Linings. Permissible Velocity The permissible velocity procedure uses two equations to calculate flow: Procedure Manning's equation, V = 1.49 R2/3 S1/2 n where: V = average velocity in the channel in ft/sec. n = Manning's roughness coefficient, based upon the lining of the channel R = hydraulic radius, wetted cross -sectional area/wetted perimeter in ft S = slope of the channel in ft/ft and the continuity equation, Q = AV where: Q = flow in the channel in cfs A = cross -sectional area of flow within the channel in ftz V = average velocity in the channel in ft/sec. Manning's equation and the continuity equation are used together to determine channel capacity and flow velocity. A nomograph for solving Manning's equation is given in Figure 8.05a. Selecting Permanent Channel lining materials include such flexible materials as grass, riprap and Channel Lining gabions, as well as rigid materials such as paving blocks, flag stone, gunite, asphalt, and concrete. The design of concrete and similar rigid linings is generally not restricted by flow velocities. However, flexible channel linings do have maximum permissible flow velocities beyond which they are susceptible to erosion. The designer should select the type of liner that best fits site conditions. Table 8.05a lists maximum permissible velocities for established grass linings and soil conditions. Before grass is established, permissible velocity is determined by the choice of temporary liner. Permissible velocities for riprap linings are higher than for grass and depend on the stone size selected. 8.05.2 0 60 50 40 30 20 10 5 0.0001 4 0.0002 3 0.0005 2 U) 0.001 0 m 0.002 0.005 1.0 D CCD 0.01 �Qp CD 0.02 0 0 10.5 (n 0.05 - 0.4 0.1 - 0.3 0.2 0.3 - 0.2 - 0.1 Figure 8.05a Nomograph for solution of Manning equation. Appendices 50 40 30 20 0 Oh i 0.01A/ m / 5 / m 4 m / 0 Q 3 O/ c < j 0.05 o, n 0.1 0 co cD a r. 0 0.5 4 1.0 0.5 8.05.3 0 Table 8.05a Maximum Allowable Design Velocities' for Vegetated Channels Typical Soil Grass Lining Permissible Velocity' Channel Slope Characteristics' for Established Grass Application Lining (ft/sec) 0-5% Easily Erodible Bermudagrass 5.0 Non -plastic Tall fescue 4.5 (Sands & Silts) Bahiagrass 4.5 Kentucky bluegrass 4.5 Grass -legume mixture 3.5 Erosion Resistant Bermudagrass 6.0 Plastic Tall fescue 5.5 (Clay mixes) Bahiagrass 5.5 Kentucky bluegrass 5.5 Grass -legume mixture 4.5 5-10% Easily Erodible Bermudagrass 4.5 Non -plastic Tall fescue 4.0 (Sands & Silts) Bahiagrass 4.0 Kentucky bluegrass 4.0 Grass -legume mixture 3.0 Erosion Resistant Bermudagrass 5.5 Plastic Tall fescue 5.0 (Clay mixes) Bahiagrass 5.0 Kentucky bluegrass 5.0 Grass -legume mixture 3.5 >10% Easily Erodible Bermudagrass 3.5 Non -plastic Tall fescue 2.5 (Sands & Silts) Bahiagrass 2.5 Kentucky bluegrass 2.5 Erosion Resistant Bermudagrass 4.5 Plastic Tall fescue 3.5 (Clay mixes) Bahiagrass 3.5 Kentucky bluegrass 3.5 Source: USDA-SCS Modified NOTE: 'Permissible Velocity based on 10-year storm peak runoff 2SoiI erodibility based on resistance to soil movement from concentrated flowing water. 'Before grass is established, permissible velocity is determined by the type of temporary liner used. Selecting Channel To calculate the required size of an open channel, assume the design flow is uniform and does not vary with time. Since actual flow conditions change Cross -Section throughout the length of a channel, subdivide the channel into design reaches, Geometry and design each reach to carry the appropriate capacity. The three most commonly used channel cross -sections are "V"-shaped, parabolic, and trapezoidal. Figure 8.05b gives mathematical formulas for the area, hydraulic radius and top width of each of these shapes. 8.05.4 Appendices Cross -Sectional Area (A) = Zd2 Top Width (T) = 2dZ Hydraulic Radius (R) = Zedd 2 Z� `+ 1 V-Shape T Z _ e is e Parabolic Shape T Cross -Sectional Area (A) = 2 Td Top Width (T) = 1.5 A d Hydraulic Radius = T2d 1 .5T2 + 4d2 I Trapezoidal Shape T �— b 1. e Cross -Sectional Area (A) = bd + Zd2 Top Width (T) = b + 2dZ Hydraulic Radius = bd + Zd2 b + 2d 4Z2+ 1 Figure 8.05b Channel geometries for v-shaped, parabolic and trapezoidal channels. Z_e _d 8.05.5 0 Design Procedure- The following is a step-by-step procedure for designing a runoff conveyance Permissible Velocity channel using Manning's equation and the continuity equation: Table 8.05b Manning's n for Structural Channel Linings Step 1. Determine the required flow capacity, Q, by estimating peak runoff rate for the design storm (Appendix 8.03). Step 2. Determine the slope and select channel geometry and lining. Step 3. Determine the permissible velocity for the lining selected, or the desired velocity, if paved. (see Table 8.05a, page 8.05.4) Step 4. Make an initial estimate of channel size —divide the required Q by the permissible velocity to reach a "first try" estimate of channel flow area. Then select a geometry, depth, and top width to fit site conditions. Step 5. Calculate the hydraulic radius, R, from channel geometry (Figure 8.05b, page 8.05.5). Step 6. Determine roughness coefficient n. Structural Linings —see Table 8.05b, page 8.05.6. Grass Lining: a. Determine retardance class for vegetation from Table 8.05c, page 8.05.8. To meet stability requirement, use retardance for newly mowed condition (generally C or D). To determine channel capacity, use at least one retardance class higher. b. Determine n from Figure 8.05c, page 8.05.7. Step 7. Calculate the actual channel velocity, V, using Manning's equation (Figure 8.05a, pg. 8.05.3), and calculate channel capacity, Q, using the continuity equation. Step 8. Check results against permissible velocity and required design capacity to determine if design is acceptable. Step 9. If design is not acceptable, alter channel dimensions as appropriate. For trapezoidal channels, this adjustment is usually made by changing the bottom width. Recommended Channel Lining n values Asphaltic concrete, machine placed 0.014 Asphalt, exposed prefabricated 0.015 Concrete 0.015 Metal, corrugated 0.024 Plastic 0.013 Shotcrete 0.017 Gabion 0.030 Earth 0.020 Source: American Society of Civil Engineers (modified) 8.05.6 Rev. 12/93 Appendices 5 4 3 2 Z _U) 0) .08 CZ .06 04 .02 Step 10. For grass -lined channels once the appropriate channel dimensions have been selected for low retardance conditions, repeat steps 6 through 8 using a higher retardance class, corresponding to tall grass. Adjust capacity of the channel by varying depth where site conditions permit. NOTE 1: If design velocity is greater than 2.0 ft/sec., a temporary lining may be required to stabilize the channel until vegetation is established. The temporary liner may be designed for peak flow from the 2-year storm. If a channel requires a temporary lining, the designer should analyze shear stresses in the channel to select the liner that provides protection and promotes establishment of vegetation. For the design of temporary liners, use tractive force procedure. NOTE 2: Design Tables —Vegetated Channels and Diversions at the end of this section may be used to design grass -lined channels with parabolic cross -sections. Step 11. Check outlet for carrying capacity and stability. If discharge velocities exceed allowable velocities for the receiving stream, an outlet protection structure will be required (Table 8.05d, page 8.05.9). Sample Problem 8.05a illustrates the design of a grass -lined channel. MIN Longer than 30" Less than 2" IN 2 .4 .6 .8 1.0 2 4 6 8 10 20 VR, Product of Velocity and Hydraulic Radius Figure 8.05c Manning's n related to velocity, hydraulic radius, and vegetal retardance. Note: From Sample Problem 8.05a multiply Vp x Hydralulic Radius (4.5x0.54=2.43), then enter the product of VR and extend a straight line up to Retardance class "D", next project a straight line to the left to determine a trial manning's n. Rev. 12/93 8.05.7 0 Table 8.05c Retardance Classification for Vegetal Covers Retardance Cover Condition A Reed canarygrass Excellent stand, tall (average 36") Weeping lovegrass Excellent stand, tall (average 30") B Tall fescue Good stand, uncut, (average 18") Bermudagrass Good stand, tall (average 12") Grass -legume mixture (tall fescue,red fescue, sericea lespedeza) Good stand, uncut Grass mixture (timothy, smooth bromegrass or orchardgrass) Good stand, uncut (average 20") Sericea lespedeza Good stand, not woody, tall (average 19") Reed canarygrass Good stand, cut, (average 12-15") Alfalfa Good stand, uncut (average 11 ") C Tall fescue Good stand (8-12") Bermudagrass Good stand, cut (average 6") Bahiagrass Good stand, uncut (6-8") Grass -legume mixture -- summer (orchardgrass, redtop and annual Good stand, uncut (6-8") lespedeza) Centipedegrass Very dense cover (average 6") Kentucky bluegrass Good stand, headed (6-12") Redtop Good stand, uncut (15-20") D Tall fescue Good stand, cut (3-4") Bermudagrass Good stand, cut (2.5") Bahiagrass Good stand, cut (3-4") Grass -legume mixture -- fall -spring (orchardgrass, redtop, and annual lespedeza) Good stand, uncut (4-5") Red fescue Good stand, uncut (12-18") Centipedegrass Good stand, cut (3-4") Kentucky bluegrass Good stand, cut (3-4") E Bermudagrass Good stand, cut (1.5") Bermudagrass Burned stubble Modified from: USDA-SCS, 1969. Engineering Field Manual. 8.05.8 Appendices Table 8.05d Maximum Permissible Velocities for Unprotected Soils in Existing Channels. Sample Problem 8.05a Design of a Grass -lined Channel. Materials Fine Sand (noncolloidal) Sand Loam (noncolloidal) Silt Loam (noncolloidal) Ordinary Firm Loam Fine Gravel Stiff Clay (very colloidal) Graded, Loam to Cobbles (noncolloidal) Graded, Silt to Cobbles (colloidal) Alluvial Silts (noncolloidal) Alluvial Silts (colloidal) Coarse Gravel (noncolloidal) Cobbles and Shingles Maximum Permissible Velocities (fps) 2.5 2.5 3.0 3.5 5.0 5.0 5.0 5.5 3.5 5.0 6.0 5.5 Given: Design Q10 = 16.6 cfs Proposed channel grade = 2% Proposed vegetation: Tall fescue Soil: Creedmoor (easily erodible) Permissible velocity, VP = 4.5 ft/s (Table 8.05a) Retardance class: "B" uncut, "D" cut (Table 8.05c). Trapezoidal channel dimensions: designing for low retardance condition (retardance class D) design to meet VP. Find: Channel dimensions Solution: Make an initial estimate of channel size A = Q/V, 16.6 cfs/4.5 ft/sec = 3.69 ftz Try bottom width = 3.0 ft w/side slopes of 3:1 Z=3 A = bd + Zdz P=b+2d Z2+1 R = AP An iterative solution using Figure 8.05a to relate flow depth to Manning's n proceeds as follows: Manning's equation is used to check velocities. *From Fig. 8.05c, pg. 8.05.7, Retardance Class d (VR=4.5x0.54=2.43) d (ft) A (ftz) R (ft) *n Vt (fps) Q (cfs) Comments 0.8 4.32 0.54 0.043 3.25 14.0 V<V OK, Q<dio (too small, try deeper channel) 0.9 5.13 0.59 0.042 3.53 18.10 V<VP, OK, Q>Qto, OK Now design for high retardance (class B): For the ease of construction and maintenance assume and try d = 1.5 ft and trial velocity V, = 3.0 ft/sec d (ft) A (ft2) R (ft) Vt (fps) n V (fps) Q (cfs) Comments 1.5 11.25 0.90 3.0 0.08 2.5 28 reduce V, 2.0 0.11 1.8 20 reduce Vt 1.6 0.12 1.6 18 **1.5 0.13 1.5 17 Q>Qja OK ** These assumptions = actual V (fps.) (chart continued on next page) 8.05.9 0 (continued) Sample Problem 8.05a Design of a Grass -lined Channel. Tractive Force Procedure Table 8.05e Manning's Roughness Coefficients for Temporary Lining Materials Channel summary: Trapezoidal shape, Z = 3, b = 3 ft, d = 1.5 ft, grade = 2% Note: In Sample Problem 8.05a the "n-value" is first chosen based on a permissible velocity and not a design velocity criteria. Therefore, the use of Table 8.05c may not be as accurate as individual retardance class charts when a design velocity is the determining factor. The design of riprap-lined channels and temporary channel linings is based on analysis of tractive force. NOTE: This procedure is for uniform flow in channels and is not to be used for design of deenergizing devices and may not be valid for larger channels. To calculate the required size of an open channel, assume the design flow is uniform and does not vary with time. Since actual flow conditions change through the length of a channel, subdivide the channel into design reaches as appropriate. PERMISSIBLE SHEAR STRESS The permissible shear stress, Td, is the force required to initiate movement of the lining material. Permissible shear stress for the liner is not related to the erodibility of the underlying soil. However, if the lining is eroded or broken, the bed material will be exposed to the erosive force of the flow. COMPUTING NORMAL DEPTH The first step in selecting an appropriate lining is to compute the design flow depth (the normal depth) and determine the shear stress. Normal depths can be calculated by Manning's equation as shown for trapezoidal channels in Figure 8.05d. Values of the Manning's roughness coefficient for different ranges of depth are provided in Table 8.05e for temporary linings and Table 8.05f for riprap. The coefficient of roughness generally decreases with increasing flow depth. n value for Depth Ranges* 0-0.5 ft 0.5-2.0 ft >2.0 ft Lining Type Woven Paper Net 0.016 0.015 0.015 Jute Net 0.028 0.022 0.019 Fiberglass Roving 0.028 0.021 0.019 Straw with Net 0.065 0.033 0.025 Curled Wood Mat 0.066 0.035 0.028 Synthetic Mat 0.036 0.025 0.021 * Adapted from: FHWA-HEC 15, Pg. 37 - April 1988 8.05.10 Rev.12/93 Appendices S (ft/ft) 0.1 0.08 0.06 0.05 0.04 10.03 0.02 NOTE: Project horizontal frog d 1 to obtain values for Z z B I Qn (Ft3/S) r-20 •10 8.0 6.0 5.0 4.0 We MCI 0.01 0.008 0.006 \\ 1.0 ♦ 0.8 0.005 �\ \ 0.6 0.004 \ 0.5 \\ 0.4 0.003 \ 0.002 0.2 \ 0.1 -0.001 0.08 0.06 0.05 0.04 0.03 0.02 Figure 8.05d Solution of Manning's equation for trape Adapted from: FH WA-HEC. 15, Pg 40 - N c J 0) c .E H r d (ft) CD B (ft) of N N .01 / Example: Given: Find: Solution: S=0.01 ft/ft d Qn = 0.3 Q = 10 ft3/S d/B = 0.14 n = 0.03 d = 0.14(4) = 0.56 ft B=4ft Z = 4 Manning's equation: Q=11.49 A R2/3 Sll 8 V = 11.n 99 R2/3 S112 f zoidal channels of various side slopes. April 1988 .02 .03 .04 .05 .06 .08 .1 IE 1.3 1.4 1.5 1.6 ,.8 .0 Rev.12/93 8.05.11 0 Table 8.05f Manning's Roughness Coefficient Lining Category Lining Type n - value n value for Depth Ranges 0-0.5 ft 0.5-2.0 ft 2.0 ft (0-15 cm) (15-60 cm) (>60 cm) Rigid Concrete 0.015 0.013 0.013 Grouted Riprap 0.040 0.030 0.028 Stone Masonry 0.042 0.032 0.030 Soil Cement 0.025 0.022 0.020 Asphalt 0.018 0.016 0.016 Unlined Bare Soil 0.023 0.020 0.020 Rock Cut 0.045 0.035 0.025 Gravel Riprap 1-inch (2.5-cm) D50 0.044 0.033 0.030 2-inch (5-cm) D50 0.066 0.041 0.034 Rock Riprap 6-inch (15-cm) D50 0.104 0.069 0.035 12-inch (30-cm) D50 -- 0.078 0.040 Note: Values listed are representative values for the respective depth ranges. Manning's roughness coefficients, n, vary with the flow depth. DETERMINING SHEAR STRESS Shear stress, T, at normal depth is computed for the lining by the following equation: T=yds Td = Permissible shear stress where: T = shear stress in lb/ft2 y = unit weight of water, 62.4 lb/ft' d = flow depth in ft s = channel gradient in ft/ft If the permissible shear stress, Td, given in Table 8.05g is greater than the computed shear stress, the riprap or temporary lining is considered acceptable. If a lining is unacceptable, select a lining with a higher permissible shear stress and repeat the calculations for normal depth and shear stress. In some cases it may be necessary to alter channel dimensions to reduce the shear stress. Computing tractive force around a channel bend requires special considerations because the change in flow direction imposes higher shear stress on the channel bottom and banks. The maximum shear stress in a bend, Tb, is given by the following equation: Tb = K b T where: Tb = bend shear stress in lb/ft2 kb = bend factor T = computed stress for straight channel in lb/ft2 The value of kb is related to the radius of curvature of the channel at its center line, Rc, and the bottom width of the channel, B, Figure 8.05e. The length of channel requiring protection downstream from a bend, LP, is a function of the roughness of the lining material and the hydraulic radius as shown in Figure 8.05ff, 8.05.12 Rev.12/93 Appendices Table 8.05g Permissible Shear Stresses for Riprap and Temporary Liners Permissible Unit Shear Stress, Td Lining Category Lining Type (lb/ft2) Temporary Woven Paper Net 0.15 Jute Net 0.45 Fiberglass Roving: Single 0.60 Double 0.85 Straw with Net 1.45 Curled Wood mat 1.55 Synthetic Mat 2.00 d50 Stone Size (inches) Gravel Riprap 1 0.33 2 0.67 Rock Riprap 6 2.00 9 3.00 12 4.00 15 5.00 18 6.00 21 7.80 24 8.00 Adapted From: FHWA, HEC-15, April 1983, pgs. 17 & 37. Design Procedure- The following is a step-by-step procedure for designing a temporary liner for Temporary Liners a channel. Because temporary liners have a short period of service, the design Q may be reduced. For liners that are needed for six months or less, the 2-year frequency storm is recommended. Step 1. Select a liner material suitable for site conditions and application. Determine roughness coefficient from manufacturer's specifications or Table 8.05e, page 8.05.10. Step 2. Calculate the normal flow depth using Manning's equation (Figure 8.05d). Check to see that depth is consistent with that assumed for selection of Manning's n in Figure 8.05d, page 8.05.11. For smaller runoffs Figure 8.05d is not as clearly defined. Recommended solutions can be determined by using the Manning equation. Step 3. Calculate shear stress at normal depth. Step 4. Compare computed shear stress with the permissible shear stress for the liner. Step 5. If computed shear is greater than permissible shear, adjust channel dimensions to reduce shear, or select a more resistant lining and repeat steps 1 through 4. Design of a channel with temporary lining is illustrated in Sample Problem 8.05b, page 8.05.14. Rev.12/93 8.05.13 0 Sample Problem 8.05b Design of a Temporary Liner for a Vegetated Channel Given: Qz = 16.6 cfs Bottom width = 3.0 ft Z=3 n = 0.02 (Use basic n value for channels cut in earth (Table 8.05b) Vp = 2.0 ft/sec maximum allowable velocity for bare soil (pg. 6.30.1) Channel gradient = 2% Find: Suitable temporary liner material Solution: Using Manning's equation: b(ft) d(ft) A(ft2) R(ft) V(fps) Q(cfs) Comments 3.0 0.59 2.82 0.42 5.88 16.60 V>Vp, (needs protection) Q>_Q2, OK Velocity >2.0 fps channel requires temporary liner:* Calculate channel design with straw with net as temporary liner. n = 0.033 (Table 8.05e). Td = 1.45 (Table 8.05g, pg. 8.05.13) b(ft) d(ft) A(ftz) R(ft) V(fps) Q(cfs) Comments 3.0 0.76 4.05 1.94 4.10 16.60 V<Td, OK Calculate shear stress for QZ conditions: T = yds where: y = unit weight of water (62.4 Ib/ft3) d = flow depth in ft s = channel gradient in ft/ft T = (62.4)(0.76)(0.02) = 0.95 T<Td, OK Temporary liner: straw with net. *In some cases the solution is not as clearly defined; the use of a more conservative material is recommended. DESIGN OF RIPRAP LINING -MILD GRADIENT The mild gradient channel procedure is applicable for channel grades less than 10%. The method assumes that the channel cross section has been designed properly, including undercut and that the remaining problem is to provide a stable riprap lining. Side slope stability. As the angle of the side slope approaches the angle of repose of the channel lining, the lining material becomes less stable. The stability of a side slope is given by the tractive force ratio, Kz, a function of the side slope and the angle of repose of the rock lining material. The rock size to be used for the channel lining can be determined by comparing the tractive force ratio, an indicator of side slope stability, to the shear stress on the sides and shear stress on the bottom of the channel. The angle of repose for different rock shapes and sized is shown in Figure 8.05g. The required rock size (mean diameter of the gradation, d50) for the side slopes is determined from the following equation: K1 d50 (sides) — K d50 (bottom) 2 where: Kt = ratio of shear stress on the sides, Ts, and bottom, T, of a trapezoidal channel (Figure 8.05h), Kz = tractive force ratio (Figure 8.05i) 8.05.14 Rev. 12/93 Appendices 2.0 1.9 1.8 1.7 1.6 Kb 1.5 1.4 1.3 1.2 1.1 1.01 1 ' 1 I 1 0 1 2 3 4 5 Rc B Figure 8.05e Kb factor for maximum shear stress on channel bends. Adapted from: FH WA-HEC 15, Pg. 47 - April 1988 Tb = Kb Td g 7 8 9 10 Rev.12/93 8.05.15 nb 0.5 0.1 DR•1-i 0.01 0 Lp/R = 0.604 ((R")/nb) 9 .0°o '0 0 .j i 1.0 5.0 10.0 20.0 30.0 Lp/ R Figure 8.05f Protection length, LP, downstream from a channel bend. nb = Manning Roughness of the lining material in the bend and the depth of flow (see tables 8.05e and f). R = Hydraulic Radius = Area/wetted perimeter Adapted from: FH WA-HEC 15, pg 48 - April 1988 50.0 8.05.16 Rev. 12/93 Appendices 43 41 39 a� Q 37 cc 0 35 m Q 33 31 Mean Stone Size d50, ft ooti Z1313?L2 /()Y (�/ "</. Emil NONNI .000 low 051111EWMIEU@1 Mean Stone Size, d50, mm Figure 8.05g Angle of repose for different rock shapes and sizes. Adapted from: FH WA, HEC-15, pg. 49 - April 1988 Selection of riprap gradation and thickness. Rpprap gradation should have a smooth size distribution curve. The largest stone size in the gradation should not exceed 1.5 times the d50 size. The most important criterion is that interstices formed by larger stones be filled with smaller sizes in an interlocking fashion, preventing the formation of open pockets. These gradation requirements apply regardless of the type of filter design used. In general, riprap constructed with angular stone performs best. Round stones are acceptable as riprap provided they are not placed on side slopes steeper than 3:1. Flat, slab -like stones should be avoided since they are easily dislodged by the flow. An approximate guide to stone shape is that neither the breadth nor the thickness of a single stone be less than one-third its length. The thickness of a riprap lining should equal 1.5 times the diameter of the largest rock size in the gradation. Filter design: When rock riprap is used, an appropriate underlying filter material must be selected. The filter material may be either a granular, gravel or sand filter blanket, or a geotextile fabric. Rev.12/93 8.05.17 0 For a granular filter blanket, the following criteria must be met: d15 filter <5 d85 base d filter 5 < 15 < 40 d15 base d50 filter < 40 d50 base Where "filter" refers to the overlying riprap or gravel and "base" refers to the underlying soil, sand or gravel. The relationship must hold between the filter blanket and base material and between the riprap and filter blanket. The minimum thickness for a filter blanket should not be less than 6 inches. In selecting a filter fabric, the fabric should have a permeability at least equal to the soil and a pore structure that will hold back the base soil. The following properties are essential to assure performance under riprap: • For filter fabric covering a base with granular particles containing 50 percent or less (by weight) of fine particles (less than U.S. Standard Sieve No. 200): a. d85 base (mm)/EOS* filter cloth (mm) > 1. b. Total open area of filter is less than 36%. - Filter fabric covering other soils: a. EOS less than U.S. Standard Sieve No. 70. b. Total open area of filter less than 10%. *EOS - Equivalent Opening Size to a U.S. Standard Sieve Size Design Procedure- The following is a step-by-step procedure for designing a riprap channel lining with mild gradients. This procedure is designed for smaller channels R i p ra p Lining, Mild that are generally used as erosion control measures, and is not intended for Gradient conveyance channels. Additional design information for lined channels may be obtained from the National Technical Information Services (NTIS) by obtaining a copy of the National Cooperative Highway Research Program Report No. 108, titled "Tentative Design Procedure for Riprap - Lined Channels". Step 1. Select a riprap size, and look up the Manning's n value (Table 8.05f) and permissible shear stress, Td (Table 8.05g). Step 2. Calculate the normal flow depth in the channel, using Manning's equation (Figure 8.05d). Check that the n value for the calculated normal depth is consistent with that determined in step 1. Step 3. Calculate shear stress at normal depth. 8.05.18 Rev.12/93 Channel and Dam Breach Calculation Prepared By: Vona Ojaruega Inactive Ash Basin Closure Plan Duke Energy - Rogers Energy Complex Checked By: Josh Bell METHOD This spreadsheet calculates flow characteristics for an open channel based on channel geometry, channel lining, and peak flow parameters provided by the user. The spreadsheet uses an iterative calculation process to determine the flow depth and the corresponding Manning's n value. Additionally, flow velocity and shear stress are computed and compared against allowable values to determine the stability of the channel's lining. DEFINITION OF VARIABLES A - area (ft2) b - bottom width (ft) C, - retardance curve index d - flow depth (ft) d50 - midrange riprap diameter (ft) m, - left side slope (H:V) m2 - right side slope (H:V) n - Manning's roughness coefficient P - wetted perimeter (ft) Q - flow (ft3/s) R - hydraulic radius (ft) S - longitudinal slope (ft/ft) V - flow velocity (ft/s) T - shear stress (ft2/s) Ywater - specific weight of water (62.4 Ibf/ft3) CALCULATIONS Channels are evaluated using Manning's equation presented as: V = 1.49 Rz/3S1/z and Q = VA [Ref. 1 ] n The flow area "A", wetted perimeter "P", and hydraulic radius "R" were calculated using the following relationships based on the geometry of a trapezoidal channel with a flow depth "d", bottom width "b", left side slope "21", and right side slope "Z2": 1 1 A A=bd+2Z1dz+2Z2dz P=b+d�Z12++1d Z2+1 and R=P [Ref. 1] The shear stress "T" was calculated using the following equation where "Ywatw" is the specific weight of water, "d" is the flow depth, and "S" is the longitudinal slope: T = YwaterdS [Ref. 1 ] Permissible shear stress and permissible velocity values for channel linings were taken from the NCDEQ "Erosion and Sediment Control Planning and Design Manual" [Ref. 1] and from the North American Green "RollMax Product Selection Chart" [Ref. 41. The Manning's n value for grass lined channels was calculated using the following equation where "Cl" is the retardance curve index, "V" is the channel velocity, and "R" is the hydraulic radius: n = e[CI(0.0133[(ln(VR)]Z-0.0954[ln(VR)]+0.297)-4.16] [Ref. 2] The retardance curve index "Cl" for each SCS retardance class is presented in the following table: SCS Retardance Class Retardance Curve Index A 10.0 B 7.64 C 5.60 D 4.44 E 2.88 Wood E&IS Project No. 7812-19-0194 wood. 9/30/2019 Page 1 of 5 Channel and Dam Breach Calculation Prepared By: Vona Ojaruega Inactive Ash Basin Closure Plan Duke Energy - Rogers Energy Complex Checked By: Josh Bell The Manning's n value for riprap lined channels was calculated using the following equation where "d" is the flow depth and "d50" is the midrange riprap diameter: n= d1/6 21.6 X 1og10 V-0) + 14.0 [Ref. 3] The Manning's n value for all other channel linings was calculated based on minimum (nm;n) and maximum (nmaX) n values provided for a given lining option. nm;n corresponds to the Manning's n value at a flow depth of 2.0-feet or greater. nmaX corresponds to the Manning's n value at a flow depth of 0.5- feet or less. For flow depths in between 0.5-feet and 2.0-feet, the Manning's n value was linearly interpolated using the following equation: n = nmin — nmax X (d — 0.5) + nmax 2.0 ft — 0.5 ft REFERENCES 1. North Carolina Department of Environmental Quality, "Erosion and Sediment Control Planning and Design Manual", Revised May 2013. 2. Temple, D.M. et. al., "Stability Design of Grass -Lined Open Channels", United States Department of Agriculture: Agriculture Research Service, September 1987. 3. Pennsylvania Department of Environmental Protection, "Erosion and Sediment Pollution Control Program Manual", Revised March 2012. 4. North American Green, "RollMax Product Selection Chart", Obtained February 13, 2019. Wood E&IS Project No. 7812-19-0194 wood. 9/30/2019 Page 2 of 5 Channel and Dam Breach Calculation Prepared By: Vona Ojaruega Duke Energy - Rogers Energy Complex Checked By: Josh Bell Inactive Ash Basin Closure Plan Wood E&IS Project No. 7812-19-0194 9/30/2019 Page 3 of 5 wood. Channel and Dam Breach Calculation Prepared By: Vona Ojaruega Inactive Ash Basin Closure Plan Duke Energy - Rogers Energy Complex Checked By: Amarachi Eze Channel Input Parameters Channel ID Storm Event (yrs) Peak Flow {Q} cfs ( ) Soil Type (Grass and Soil -Lined Channels Only) Grass Type (Grass -Lined Channels Only) Channel Lining Bottom Width {b} ft ( ) Channel Depth {D} ft ( ) Left Side Slope {Z,H:V } Right Side Slope Z H:V { z } Channel Slope {S} ft/ft ( ) 1 R 25 250.63 N/A N/A Grouted Riprap 20.0 3.00 3.0 3.0 0.0674 2R 25 482.01 N/A N/A Grouted Riprap 20.0 3.00 3.0 3.0 0.0107 3R 25 430.85 N/A N/A Grouted Riprap 20.0 4.00 3.0 3.0 0.0308 4R 25 145.06 N/A N/A Grouted Riprap 10.0 3.00 3.0 3.0 0.0700 1 R 50 300.83 N/A N/A Grouted Riprap 20.0 3.00 3.0 3.0 0.0309 2R 50 565.26 N/A N/A Grouted Riprap 20.0 3.00 3.0 3.0 0.0107 3R 50 503.35 N/A N/A Grouted Riprap 20.0 3.00 3.0 3.0 0.0308 4R 50 172.29 N/A N/A Grouted Riprap 10.0 3.00 3.0 3.0 0.0700 1 R 100 353.88 N/A N/A Grouted Riprap 20.0 3.00 3.0 3.0 0.0625 2R 100 651.76 N/A N/A Grouted Riprap 20.0 3.00 3.0 3.0 0.0107 3R 100 578.52 N/A N/A Grouted Riprap 20.0 4.00 3.0 3.0 0.0308 4R 100 200.72 N/A N/A Grouted Riprap 10.0 3.00 3.0 3.0 0.0700 Wood EMS Project No. 7812-19-0194 g wood. 9/30/2019 Pa e 1 of 5 Channel and Dam Breach Calculation Prepared By: Vona Ojaruega Inactive Ash Basin Closure Plan Duke Energy - Rogers Energy Complex Checked By: Amarachi Eze Channel Capacity Analysis Channel Stability Analysis Channel ID Manning's n {n} Area {A} (ftz) Wetted Perimeter {P} (ft) Hydraulic Radius {R} (ft) Normal Depth (ft) Calculated Flow Rate {Qca�c} (cfs) Freeboard (in) Safe? Permissible Velocity {V} (ft/s) Calculated Velocity {V} (ft/s) Permissible Shear Stress {Tperm} (psf) Calculated Shear Stress {T} (psf) Safe? 1 R 0.036 24.43 26.67 0.92 1.05 250.63 23.3 Yes N/A 10.26 N/A 4.44 Yes 2R 0.028 60.13 34.22 1.76 2.25 482.01 9.0 Yes N/A 8.02 N/A 1.50 Yes 3R 0.031 41.34 30.47 1.36 1.66 430.85 28.1 Yes N/A 10.42 N/A 3.18 Yes 4R 0.035 14.42 16.88 0.85 1.09 145.06 22.9 Yes N/A 10.06 N/A 4.75 Yes 1 R 0.033 33.86 28.85 1.17 1.40 300.83 19.2 Yes N/A 8.88 N/A 2.70 Yes 2R 0.028 67.16 35.52 1.89 2.45 565.26 6.5 Yes N/A 8.42 N/A 1.64 Yes 3R 0.030 44.97 31.23 1.44 1.78 503.35 14.7 Yes N/A 11.19 N/A 3.41 Yes 4R 0.035 16.01 17.47 0.92 1.18 172.29 21.8 Yes N/A 10.76 N/A 5.16 Yes 1 R 0.034 30.42 28.07 1.08 1.28 353.88 20.7 Yes N/A 11.63 N/A 4.98 Yes 2R 0.028 74.18 36.78 2.02 2.65 651.76 4.2 Yes N/A 8.79 N/A 1.77 Yes 3R 0.0289003 48.44 31.94 1.52 1.89 578.52 25.350477 Yes N/A 11.94381 N/A 3.6275475 Yes 4R 0.0338365 17.55 18.03 0.97 1.27 200.72 20.754719 Yes N/A 11.4393 N/A 5.5492826 Yes Wood E&IS Project No. 7812-19-0194 g wood. 9/30/2019 Pa e 2 of 5