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FORWARD LANDFILL <br /> HYDROLOGY STUDY <br /> INTRODUCTION <br /> The Forward Landfill is located at 9999 South Austin Road in the city of Manteca, <br /> San Joaquin County, California. The hydrology study for the site was performed for <br /> the Joint Technical Document (BAS et al 2001) based upon a 1,000-year, 24-hour <br /> storm event. A unit hydrograph was then developed to calculate the peak flow rate <br /> for that event. <br /> METHODOLOGY <br /> The Rational Method was used to develop the hydrology study. Tributary drainage <br /> areas were identified within the Forward Landfill watershed area, based on the <br /> developed condition, and a 1,000-year, 24-hour storm event was used as the design <br /> frequency. Through this methodology Q,000 values for the tributary areas were <br /> developed. <br /> Hydrology modeling software by Advanced Engineering Software (AES) was used to <br /> calculate run-off and the time of concentration of flows based on site specific data. <br /> The time of concentration at the down gradient node of the tributary areas was then <br /> used, along with site specific data sets input into AES, to develop the unit <br /> hydrograph for the detention basin. The unit hydrograph study was used to <br /> calculate the peak runoff from the 156 tributary acres in a 24-hour period. <br /> DEVELOPED CONDITION <br /> There are three identified tributary areas of runoff for this landfill. The tributary area <br /> for the first area at node 1.09 is 210.10 acres with a Q,000 of 377.18 cfs. The second <br /> tributary area at node 2.05 is 156.30 acres with a Q,000 of 278.34 cfs. For the third <br /> area, at node 3.05, the tributary area is 11.52 acres with a Q,000 of 26.97 cfs. (see <br /> Attached hydrology Map) <br /> The developed condition of the site was used for the unit hydrograph study. The <br /> tributary area for the detention basin is 156.30 acres with a Q,000 of 278.34 cfs. The <br /> time of concentration is 25.32 minutes. This corresponds with a lag time of 0.42. <br /> The precipitation depth area factors for this study are as follow: <br /> • 5 - minutes = 0.46 inches of rainfall <br /> • 30 - minutes = 0.95 inches of rainfall <br /> • 1 - hour = 1.24 inches of rainfall <br /> • 3 - hour = 1.95 inches of rainfall <br /> • 6 - hour = 2.63 inches of rainfall <br /> • 24 - hour = 4.53 inches of rainfall <br /> 1 BRYAN A.STIRRAT AND ASSOCIATES <br /> L:\Allied\Forward Landfill\FU-03 Basin\Design Rpt-LE\Forward Hyd Report 06-12-03.Doc <br />