Laserfiche WebLink
a forested area or an area with numerous obstructions. A fast response corresponds to an unvegetated <br />ox poorly protected area. SCC used a fast hydxograph response fox the Old Wolf Creek area. <br />The internal convolution increment is 0.05 hours, and values are saved at the user specified interval of <br />0.1 hours or greater. A convolution increment of 0.1 was used for this design. It should be noted that <br />a time of concentration less than 0.125 hours bypasses the unit hydxogxaph technique and instantaneous <br />mn-off is assumed. As explained in the SEDCAD4 Design Guide and User's Manual (Warner, et al., <br />1998), the time of concentration restriction of 0.135 hours is somewhat mandated due to a combination <br />of array size restrictions, minimum internal convolution interval, and the user specified tune increment <br />for saving convoluted values. <br />2.5 Drainage Basin Area <br />The drainage basin area was determined by direct measurement from Drawing 1, Old Wolf Creek <br />Remediation Plan Map. <br />2.G Time of Concentration <br />The time of concentration, T~, was calculated using the Soil Conservation Service (SCS) upland method <br />{SCS, 1986). The hydraulic lengths, drainage heights and associated slopes were determined by direct <br />measurement from Drawing 1, Old Wolf Creek Remediation Plan Map. The values calculated for each <br />stmcture axe shown on a subwatexshed basis in the SEDCAD printouts, Overland flow conditions <br />were assumed for a maximum of 400 feet. <br />2.7 Muskingum Routing <br />Muskingum Routing parameters (I{, ~ are also calculated using the SCS upland method. There was no <br />Muskingum Routing since there is only one subwatershed. <br />2.8 Curve Number <br />The xnnoff curve number is a factor relating the amount of rainfall to the amount of runoff for a given <br />area. Curve number values axe based on vegetation and soils information. <br />Approved Seneca II NGne curve number values axe presented in Table 1, Runoff Curve Numberr for the <br />Seneca II Nlrrre. The values are adapted from Soil Conservation Service's Technical Release No. 55 (T'R- <br />55; SCS, 1986). SCC used a curve number value of 86 for this runoff estimation -reclaimed, bare <br />ground that has characteristics of a "B" Hydrologic Soil Group. <br />The inpuc summary fox the Channel PL-1 SEDCAD hydrologic modeling is presented below: <br />• Stocm event: 10-year, 24-hour <br />• Precipitation amount: 1.7 inches <br />• Unit hydrograph: Type II <br />• TimeoFconcentration:calculated <br />• Drainage area: 16.2 acres <br />• Curve nwnbet: 86 <br />Old Wolf Creek Axea Remediation Plan 2 Revised 06/07 <br />