Laserfiche WebLink
Determination of Watershed Parameters <br />Nomenclature - Watersheds are denoted by Watershed (X,Y,Z) where "Watershed" is <br />the name of the total watershed, X is the junction, Y is the <br />branch, and Z is the structure, e.g. Johnson (2,1,3) is the <br />watershed above structure 3, branch 1, junction 2 of the Johnson <br />watershed. <br />Area - The area covered by each stage of mining or reclamation in each subwater- <br />shed was determined by planimetering on a 1"=1000' scale map. <br />Curve Number - Each subarea was assigned a Curve Number as shown in the Curve <br />Number determinations. <br />Runoff - The amount of runoff was determined by: <br />Q = (P-0.2S)2/CP+0.85) (SCS, 1972, p. 10.5) <br />~ where Q = runoff (inches) <br />P = rainfall amount (1.7 inches) <br />S = 01000/CN) - 10 <br />Runoff Volume - The total volume of runoff was calculated as runoff times area. <br />Average Curve Number - The average curve number for the watershed was calculated <br />using the runoff weighted average method (SCS, 1972, p. <br />10.10). <br />Horizontal Distance - The hydraulic length was measured as the horizontal dis- <br />tance (shown on Map TR-486-1) from the hydraulically most <br />remote point on the watershed to the base of the <br />watershed. <br />Vertical Distance - The vertical distance is the difference between the eleva- <br />lion of the highest point and the elevation of the lowest <br />point in the watershed. <br />Slope - The slope is the vertical distance divided by [he horizontal distance <br />I times 100 percent. <br />Time of Concentration - The time of concentration was calculated by the curve <br />number method (SCS, 1972, p. 15.7). <br />Tc = ((L)0.8(S+1)0.7)/(1900(Y)0.5) <br />where Tc = time of concentration (hours) <br />L = hydraulic length (Et) <br />' S = (1000/CN) - 10 <br />i Y = slope (Y>>) <br />I <br />cont. next page <br />Revised 8/86 <br />