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Home My WebLink AboutCT 01-05; CALAVERA HILLS VILLAGE W; 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 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 Date RCE 60223 Exp. 6/30/04 Table of Contents Introduction 3 Analysis 3 Conclusion 6 Appendices Appendix A - Conveyance System Exhibits Appendix B - Pipe Analysis W:\MSOFFICE\WINWORD\981020\HydiDlogy 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 (PI) leaving Node 126 slopes southeasterly and into a pollution prevention basin located at the southerly comer of the site. The second pipe (P2) leaving Node 126 slopes southerly into a storm drainage conveyance system located along College Boulevard. One pipe (P3) leaving Node 130 slopes easterly and into a pollution prevention basin located at the southerly comer of the site. The second pipe (P4) leaving Node 130 slopes southeasterly and continues through the storm drainage conveyance system along College Boulevard. Pl and P3 convey flows that require BMP treatment, and larger flows are conveyed via P2 and P4. Flows discharged through PI and P3 flow through the pollution prevention basin and then discharged into the storm drainage conveyance system along College Boulevard. Analysis PI and P3 are sized to convey the peak flows generated by a rainfall intensity (Iavg) of 0.2 inches per hoxar. This is the rainfall intensity recommended on Table 3. Numeric Sizing Treatment Standards of the Standard Urban Storm Water Mitigation Plan Storm Water Standards for City of Carlsbad Public Work Department. P2 and P4 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 P2 and P4 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 Pl 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 Marming'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))^(I/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 P2) and low flow outiet elevation, 159.60 (outlet elevation for PI) and dividing it by the length of the 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 Marming's "n" of O.OI I will yield approximately 3.86 cfs. The 100-year peak flow out of the low flow pipe (Pl) 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 I OO-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 PI during the 100-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 upstream 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 treated is detennined as follows: Qave = Cavg*Iave* A Qave = 0.74*0.2*45.54 = 6.74 cfs P3 is a ten-inch diameter pipe with a 9.70 percent slope and is sized to adequately convey the required peak flow for freatment (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 P4) and low flow outlet elevation, 159.60 (outlet elevation for P3) and dividing it by the length of the 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 O.OI 1 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 1 OO-year peak flow out of the low flow pipe (P3) 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 outlet elevation (159.60) and dividing it by the length of the low flow pipe (171.71). The slope during the I OO-year storm is approximately 12.35 percent. The peak flow out of P3 during the 1 OO-year storm using the above Manning's equation is approximately 9.11 cfs. The permanent pollution prevention basin discharge pipe is designed to convey the peak flows entering the permanent pollution basin. The peak flow that will enter the permanent pollution prevention basin 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 runoff peak flows for BMP freatment will be conveyed to the permanent pollution prevention basin located at the southerly comer of Village W. Pl and P3 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 discharge pipe out of the permanent pollution prevention basin is sized to adequately convey 13.71 cfs. APPENDIX A APPENDIX B Low Flow Pipe (P1) Durinq 85th Percentile Storm Qwq: 2.49 cfs Manning's "n": 0.011 High Flow Inlet Elevation (E1): 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 (lOO-yr): 4.60 cfs Qactual (100-yr) = (4.64/n)*(Da''2.67)*(Sc100''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: Manning's "n": High Flow Inlet Elevation (El): Low Flow Outlet Elevation (E2): Length of Low Flow Pipe (L): Calculated Slope (Sc): 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): QLFactual: Q LFactual = (4.64/n) *(D a "2.67) *(S''0.5) Pipe Area, Pipe Flowing Full (A): A = (3.14*D''2)/4 Velocity (VLF): VLF = QLFactual/A 6.75 cfs 0.011 177.87 ft 159.60 ft 171.71 ft 0.1064 ft/ft 0.77 ft 10 in 0.097 ft/ft 8.07 cfs 0.55 ft'^2 14.80 fps During 100-vear Storm High Flow Inlet Elevation (E1): 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 VU= = QLFactual/A G:\jobs\2002\981020\Calcs\9820CHVilHLowFIPipe.xls 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.) AAAAAAAAA,/\AAAAAAAAAAA Water ^ 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 %