Laserfiche WebLink
Assuming the soil types comprising each pit area are equal in quantity, average <br />curve numbers were calculated on an area basis: ~/~ jv>t s~ h~, ~ <br />Pit Premine CN Postmine CN' <br />1 SO 5 ~ 86 ~z.s~ <br />2 75 .4- ¢ 75 ~7. ~ <br />3 75 q 4- 75 ,~ a <br />4 - 86° <br />5 71 n o 71 ~3 S <br />6 71 ~~ 71 <br />' Postmine curve numbers were lowered by a value of 2 in order to account for <br />contour furrows. This adjustment is consistent with curve number reduction for <br />contouring on cultivated agricuRural lands, Table 2-2b, USDA-SCS TR-55, June <br />1986. <br />Pit 4 had been recently backfilled, recontoured and topsoiled prior to <br />preparation of this report. A curve number representing disturbed conditions <br />was used as a conservative estimate. The value (86) was obtained from the <br />Rockcastle Permit Document. <br />Routing Parameters <br />Routing parameters (Muskingum K and Muskingum X) were calculated to <br />express travel time and attenuation in the more complex watersheds. The <br />parameters are used to route hydrographs from a subwatershed outlet to a <br />structure. If the subwatershed is located at the structure, K and X are equal to <br />zero. The methodology outlined in the SEDCAD+ User's Manual is used to <br />calculate these two routing parameters. The specfic equations and values used <br />are detailed as follows: <br />X = 0.5Vw <br />1.7+Vw <br />Where: Vw =weighted average velocity in fps of all the flow <br />segments from the subwatershed outlet to the structure <br />o~'r ~ <br />~~ > <br />J ~- <br />~~~ <br />~«~ <br />~~~i~ <br />o~ <br />6 <br />