Laserfiche WebLink
- State Reg. <br />age to the major incised drainage channels which are essentially cut to the <br />bedrock level as they now exist. <br />4.03.1(4) Curve Number <br />The runoff curve number (CN) is a factor relating the amount of rainfall to <br />the amount of runoff for a given area. It is dependent upon the infiltration <br />characteristics of soil types and the type and amount of vegetation. <br />The curve number was determined as a weighted curve number Coking into <br />account the different soil types encountered throughout the drainage area. <br />These soil types appear on ExhibiT 9-I "Soil Types and Topsoil Salvage <br />Depths." <br />Approximately 400 acres or 50 percent of the drainage area will be mined or <br />is presently disturbed land. After mining, the area will be graded and too- <br />soiled. A conservative curve number of 88 corresponding to cultivated land <br />with no treatment, is estimated for this disturbed area. <br /> <br />The remainder of the drainage area is covered by soils of hydrologic soil <br />groups "B", "C", and "D" and since the drainoge area is predominately range- <br />land in fair-to-poor condition, the curve numbers for these soils would be <br />between 79 and 89. <br />The weighted curve number is calculated to be 86. Table I "Soil Type and <br />Hydrologic Grovp" gives a breakdown of the soil type, number of acres, <br />hydrologic group, and curve number used to calculate the weighted curve <br />number. <br />Consequently, ail culverts and ditches have been redesigned using a runoff <br />curve number of 86. <br />7-169a Revised September 23, 1985 <br />