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Home My WebLink AboutCT 00-02; CALAVERA HILLS; HYDROLOGY STUDY ADDENDUM #3; 2003-09-12HYDROLOGY STUDY ADDENDUM #3 FOR CALAVERA HILLS II Job No. 98-1020 September 12, 2003 Revised: October 24, 2003 Revised: November 21, 2003 Prepared by: O'DAY CONSULTANTS, INC. 2710 Loker Avenue West, Suite 100 Carlsbad, Califomia 92008-6603 Tel: (760)931-7700 Fax: (760) 931-8680 Keith W. Hansen RCE 60223 Exp. 6/30/04 ^3 Date CT W'6l^ Table of Contents Introduction 3 Analysis 3 Conclusion 6 Appendices Appendix A - Conveyance System Exhibits Appendix B - Pipe and Modified Curb Outlet Analysis W:\MSOFFICE\WINWORD\981020\Hydrology Addendum 3.doc Introduction This report is an addendum to Hydrology Study for Calavera Hills Phase II dated May 3, 2002. This report addresses the stormwater runoff discharge rates out of the two pipes leaving Node 126 and two pipes leaving Node 130 and pipe characteristics (see Appendix A). One pipe (E-2) leaving Node 126 slopes southeasterly and into a depoUutant flow- through basin that acts as a vegetated swale located at the southerly comer ofthe site. The second pipe (E-l) leaving Node 126 slopes southerly into a storm drainage conveyance system located along College Boulevard. One pipe (N) leaving Node 130 slopes easterly and into a depollutant flow-through basin that acts as a vegetated swale located at the southerly comer of the site. The second pipe (Ml) leaving Node 130 slopes southeasterly and continues through the storm drainage conveyance system along College Boulevard. E-2 and N convey flows that require BMP treatment, and larger flows are conveyed via E-l and Ml. Flows discharged through E-2 and N flow through the depollutant flow- through basin that acts as a vegetated swale and then discharged into the storm drainage conveyance system along College Boulevard. Analysis E-2 and N are sized to convey the peak flows generated by a rainfall intensity (Iavg) of 0.2 inches per hour. This is the rainfall intensity recommended on Table 3. Numeric Sizing Treatment Standards ofthe Standard Urban Storm Water Mitigation Plan Storm Water Standards for City of Carlsbad Public Work Department. E-l and Ml are sized to convey the 1 OO-year peak flows generated by the upstream areas. These flow analysis were addressed on the Hydrology Study for Calavera Hills Phase II and Drainage Study for Calavera Hills - Village W reports. The peak flows entering E-l and Ml are approximately 36.19 and 109.12 cfs respectively. The total area (A) leaving Node 126 is approximately 22.64 acres. The runoff coefficient (C) used for this site is 0.55. The C and A values are taken from the Drainage Study for Calavera Hills - Village W report. The required average peak flow to be treated is determined as follows: Qave = C*Iave*A Qave = 0.55*0.2*22.64 = 2.49 cfs E-2 is an eight-inch diameter pipe with a 7.31 percent slope and is sized to adequately convey the required peak flow for treatment (see Appendix B). The pipe will be under pressure flow and the Manning's equation was used to approximate the pipe size required to convey approximately 2.49 cfs. The Manning's equation is shown below Q = (1.49/n)*A*(R^0.67)*(S^0.5) Where, A = Pipe Area (sqft) R = Hydraulic Radius (ft) S = Longitudinal Slope of Pipe (ft/ft) so D = ((Q*n)/(0.464*S^0.5))^(l/2.67) and S = ((Q*n)/(0.464*D^2.67))^2 A slope (S) approximated to determine the required pipe diameter for the low flow was calculated by subtracting the high flow discharge elevation, 167.70 (inlet elevation for E- 1) and low flow outiet elevation, 159.60 (outiet elevation for E-2) and dividing it by the length ofthe low flow pipe, 99.36. The slope in this case is 8.15 percent and using the Manning's equation with a peak flow of 2.49 cfs and Manning's "n" of 0.011 yields an approximate pipe diameter of 6.6 inches. An eight-inch diameter pipe will be used since a six-inch diameter would yield approximately 173 feet water surface elevation at Node 126. This water surface elevation is greater than the water surface elevation calculated (169.89) in the Drainage Study for Calavera Hills - Village W dated November 26, 2002. An eight-inch diameter pipe through the pipe slope of 7.31 percent and a Manning's "n" of 0.011 will yield approximately 3.86 cfs. The modified curb outiet at the discharge end of pipe E-2 will be 3 feet wide and 0.2 feet deep. See Appendix B for modified curb outlet analysis. The 1 OO-year peak flow out of the low flow pipe (E-2) was then approximately using the water surface elevation at Node 126. A slope was calculated by taking the water surface elevation at Node 126 (169.89) during the lOO-year storm and subtracting the low flow outiet elevation (159.60) and dividing it by the length of the low flow pipe (99.36). The slope during the 1 OO-year storm is approximately 10.36 percent. The peak flow out of E- 2 during the 1 OO-year storm using the above Manning's equation is approximately 4.60 cfs. The total area (A) leaving Node 130 is approximately 45.54 acres. The 45.54 acres is a combined upsti-eam portions of Village W, U, Y, X and College Boulevard. An average C value was approximated based on the individual site uses and are indicated as follows: Village Area (ac) C C*Area U 13.50 0.70 9.45 Y(A1) 0.38 0.85 0.32 Y(A2) 0.20 0.98 0.20 X 16.38 0.55 9.01 College Blvd. 15.08 0.98 14.78 Sum 45.54 4.06 33.76 Cavg = 33.76/45.54 = 0.74 The areas are taken from the Hydrology Study for Calavera Hills Phase II report. The required average peak flow to be freated is detennined as follows: Qave = Cavg*Iave*A Qave = 0.74*0.2*45.54 = 6.74 cfs N is a ten-inch diameter pipe with a 9.70 percent slope and is sized to adequately convey the required peak flow for treatment (see Appendix B). The pipe will be under pressure flow and the Manning's equation was used to approximate the pipe size required to convey approximately 6.74 cfs. The Manning's equation is shown below Q = (1.49/n)*A*(R^0.67)*(S^0.5) Where, A = Pipe Area (sqft) R = Hydraulic Radius (ft) S = Longitudinal Slope of Pipe (ft/ft) so D = ((Q*n)/(0.464*S^0.5))^(l/2.67) and S = ((Q*n)/(0.464*D^2.67))^2 A slope (S) approximated to determine the required pipe diameter for the low flow was calculated by subfracting the high flow discharge elevation, 177.87 (inlet elevation for Ml) and low flow outiet elevation, 159.60 (outiet elevation for N) and dividing it by the length ofthe low flow pipe, 171.71. The slope in this case is 10.64 percent and using the Manning's equation with a peak flow of 6.74 cfs and Manning's "n" of 0.011 yields an approximate pipe diameter of 9.2 inches. A ten-inch diameter pipe will be used. A ten- inch diameter pipe through the pipe slope of 9.70 percent and a Manning's "n" of 0.011 will yield approximately 8.07 cfs. The modified curb outiet at the discharge end of pipe N will be 3 feet wide and 0.4 feet deep. See Appendix B for modified curb outiet analysis. The 1 OO-year peak flow out of the low flow pipe (N) was then approximately using the water surface elevation at Node 130. A slope was calculated by taking the water surface elevation at Node 130 (180.80) during the lOO-year storm and subfracting the low flow outiet elevation (159.60) and dividing it by the length of the low flow pipe (171.71). The slope during the 1 OO-year storm is approximately 12.35 percent. The peak flow out of N during the 1 OO-year storm using the above Manning's equation is approximately 9.11 cfs. The permanent depollutant flow-through basin that acts as a vegetated swale discharge pipe is designed to convey the peak flows entering the permanent pollution basin. The peak flow that will enter the pennanent depollutant flow-through basin that acts as a vegetated swale during a 1 OO-year storm is approximately 13.71 cfs. The discharge pipe will be a 36-inch diameter pipe with a 6.62 percent slope and will adequately convey 13.71 cfs of flow. Conclusion The required stormwater mnoff peak flows for BMP freatment will be conveyed to the permanent depollutant flow-through basin that acts as a vegetated swale located at the southerly comer of Village W. E-2 and N are sized to convey approximately 3.86 and 8.07 cfs respectively and will convey approximately 4.60 and 9.11 cfs respectively during the 1 OO-year storm. The modified curb outiets are sized to adequately convey the upstream 85* percentile stonnwater peak flow. The discharge pipe out of the permanent depollutant flow-through basin that acts as a vegetated swale is sized to adequately convey 13.71 cfs. Low Flow Pipe (PI) During 85th Percentile Storm Qwq: 2.49 cfs Manning's "n": 0.011 High Flow inlet Elevation (El): 167.70 ft Low Flow Outlet Elevation (E2): 159.60 ft Length of Low Flow Pipe (L): 99.36 ft Calculated Slope (Sc): 0.0815 ft/ft S = (E1-E2)/L Required Pipe Diameter (D): 0.55 ft = 6.6 in D = ((Qwq*n)/(0.464*Sc''0.5))''(1/2.67) Actual Pipe Diameter (Da): 8 in = 0.67 ft Low Flow Pipe Longitudinal Slope (S): 0.0731 ft/ft QLFactual: 3.86 cfs QLFactual = (4.64/n)*(Da^2.67)*(S''0.5) Pipe Area, Pipe Flowing Full (A): 0.35 ft'^2 A = (3.14*D''2)/4 Velocity (VLF): 11.07 fps VLF = QLFactual/A During 100-vear Storm High Flow Inlet Elevation (El): 169.89 ft Low Flow Outlet Elevation (E2): 159.60 ft Length of Low Flow Pipe (L): 99.36 ft Calculated Slope (Scioo): 0.1036 ft/ft S = (E1-E2)/L Qactual (100-yr): 4.60 cfs Q actual (100-yr) = (4.64/n) *(D a "2.67) *(S c100 '^0.5; Velocity (VLF): 13.17 fps VLF = QLFactual/A G:\jobs\2002\981020\Calcs\9820CHVilHLowFIPipe.xls Low Flow Pipe (P3) During 85th Percentile Storm Qwq: 6.75 cfs Manning's "n": 0.011 High Flow Inlet Elevation (El): 177.87 ft Low Flow Outlet Elevation (E2): 159.60 ft Length of Low Flow Pipe (L): 171.71 ft Calculated Slope (Sc): 0.1064 ft/ft S = (E1-E2)/L Required Pipe Diameter (D): 0.77 ft = 9.2 in D = ((Qwq*n)/(0.464*Sc^0.5))^(1/2.67) Actual Pipe Diameter (Da): 10 in = 0.83 ft Low Flow Pipe Longitudinal Slope (S): 0.097 ft/ft QLFactual: 8.07 cfs QLFactual = (4.64/n)*(Da^2.67)*(S^0.5) Pipe Area, Pipe Flowing Full (A): 0.55 ft'^2 A = (3.14*D''2)/4 Velocity (VLF): 14.80 fps VLF = QLFactual/A During 100-vear Storm High Flow Inlet Elevation (El): 180.80 ft Low Flow Outlet Elevation (E2): 159.60 ft Length of Low Flow Pipe (L): 171.71 ft Calculated Slope (Scioo): 0.1235 ft/ft S = (E1-E2)/L Qactual (100-yr): 9.11 cfs Qactual (100-yr) = (4.64/n)*(Da''2.67)*(Sc100''0.5) Velocity (VLF): 16.70 fps VLF = QLFactual/A G:\jobs\2002\981020\Calcs\9820CHVilHLowFIPipe.xls O'Day Consultants Inc. 2710 Loker Avenue West, Suite 100 Carlsbaci, CA 92008 Tel: (760) 931-7700 Fax: (760) 931-8680 l<-( 3.00' ->l * * ^Water Surface ( 0.18')^'""* * * * * + •* * * * Rectangular Open Channel Modified Curb Outlet Opening Downstream of Pipe E-2 Flowrate 2.4 90 CFS Velocity 4.714 fps Depth of Flow 0.176 feet Critical Depth 0.278 feet Total Depth 0.17 6 feet Base Width 3.000 feet Slope of Channel 2.000 % X-Sectional Area 0.528 sq. ft. Wetted Perimeter 3.352 feet AR^{2/3) 0.154 Mannings 'n' 0.013 O'Day Consultants Inc. 2710 Loker Avenue West, Suite 100 Carlsbad, CA 92008 Tel: (760) 931-7700 Fax: (760) 931-8680 l<-3.00" )• •>l ^•^'^'"Water Surface ( 0.33')^'^'^* * * * * * * * * * ****** ****** Rectangular Open Channel Modified Curb Outlet Opening Downstream of Pipe N Flowrate 6.740 CFS Velocity 6.778 fps Depth of Flow 0.332 feet Critical Depth 0.539 feet Total Depth 0.332 feet Base Width 3.000 feet Slope of Channel 2.000 % X-Sectional Area 0.995 sq. ft. Wetted Perimeter 3.663 feet AR^(2/3) 0.417 Mannings 'n' 0.013 O'Day Consultants Inc. 2710 Loker Avenue West, Suite 100 Carlsbad, CA 92008 Tel: (760) 931-7700 Fax: (760) 931-8680 Inside Diameter ( 36.00 in.) * * S^AAAAAAAAA/\AAA/^AAA/\A A Water * I * + I * I I * ( 6.88 in.) { 0.574 ft.) I I V Circular Channel Section Permanent Pollution Prevention Basin Discharge Pipe Depth of Flow During 100-yr Storm Flowrate 13.720 CFS Velocity 14.539 fps Pipe Diameter 36.000 inches Depth of Flow 6.885 inches Depth of Flow 0.574 feet Critical Depth 1.183 feet Depth/Diameter (D/d) 0.191 Slope of Pipe 6.620 % X-Sectional Area 0.944 sq. ft. Wetted Perimeter 2.716 feet AR^(2/3) 0-467 Mannings 'n' 0.013 Min. Fric. Slope, 36 inch Pipe Flowing Full 0.042 %