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WW-1811-BAl-DF MEMORANDUM November 1, 1992 <br /> To: Mark Ingham <br /> From: Dan Mattson <br /> Subject: CITY OF STOCKTON LANDFILL DITCH SIZING <br /> r <br /> The proposed ditches for the landfill were first laid out on <br /> the proposed finished grade topography. The ditches were then <br /> sized based upon the Q in cubic feet per second (cfs) as <br /> calculated using the rational method and data as required in the <br /> San Joaquin County Design Manual. Therefore the values of Q were <br /> calculated as follows: <br /> C x I x A <br /> Q = peak rate of flow in cfs. <br /> C = coefficient of runoff ---> use 0.95 as a <br /> conservative coefficient for the covered landfill. <br /> I = the average intensity of rainfall in inches/hour <br /> for a duration equal to the time of concentration <br /> (Tc) . <br /> Tc = used the minimum time of 20 minutes as shown <br /> on drawing D - 5 because the parameters for <br /> each case the results to fall with in that <br /> triangle. <br /> The City of Stockton Landfill falls within Zone 2 <br /> as shown on drawing _D - 3 . <br /> Therefore, using a duration time of 20 minutes on <br /> the Zone 2 line of drawing D - 4 yields a rainfall <br /> intensity of 1.75 inches/hour (for a 10yr storm) . <br /> A = area in acres of the basin in question. <br /> Q = 0.95 x 1.75 x A = 1.66 x A. (for a 10yr storm) <br /> 100yr storm intensity factor = 1.4 <br /> Q = 1.4 x 1.66 x A. (for a 100yr storm) <br /> The largest basin area for each type of ditch was used in <br /> the calculations to size the ditches. Please refer to the <br /> included drawing of the ditch locations and basin sizes, along <br /> with the attached calculations. <br /> Dan Mattson <br /> DLM:dlm <br /> DITCHWRK <br />