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<br />DATA REQUIRED <br /> <br /> <br />(Ubba.:~n <br /> <br />I <br /> <br />( <br />, <br />I <br />, <br />\\ <br />.... <br />til' <br />J <br />/ <br />~ <br />, <br />, <br /> <br />Boundary <br /> <br />151 <br /> <br />Grid representation of land use <br />(exhaustive for study area). <br /> <br />131 <br /> <br />Grid representation of hydro- <br />logic soil group. <br /> <br />Typical Grid <br />Cell in <br />Subbasin <br /> <br />112 I <br /> <br />Grid representation of subbasin. <br /> <br />/7/ <br /> <br />Grid representation of land <br />surface alope. <br /> <br />DIRECT <br />INPUT <br /> <br />1[subbasin Outlet <br /> <br />Tabulation of <br />curve, 'number. <br />data bank). <br /> <br />1.30 miles Subbasin hydraulic length. (Not <br />part of grid data bank). <br /> <br />land use-soil type <br />(Not par~ of grid <br /> <br />PROCEDURE <br /> <br />COMPUTATION OF SUBBASIN AVERAGE CURVE NUMBER (CN) <br /> <br />a. Determine cell land use from grid data bank. <br />b. Determine cell hydrologic soil group from grid data bank. <br />c. Determine cell curve number (CN) from input relationship. <br />d. Determine cell subbasin assignment. <br />e. Aggregate CN's for all cells within subbasin and compute <br />average value. <br /> <br />COMPUTATION OF SUBBASIN LAG TIME (EQUATION 3-2) <br /> <br />a. Determine cell land surface slope from grid data bank. <br />b. Determine cell subbasin assignment from grid data bank. <br />c. Aggregate land surface slope for all cells within subbasin <br />and compute mean value. <br />d. Retrieve average CN computed above. <br />e. Compute subbasin lag. <br /> <br />Lag - f (curve number, hydraulic length, mean slope) <br /> <br />FIGURE 3-1 <br />HYDROLOGIC PARAMETER COMPUTATION <br /> <br />3-6 <br />