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Table Of Contents
Calculating the Runoff from Watershed Areas
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To calculate a composite (or weighted) curve number for a watershed or
subarea
1 From the Hydrology menu, choose Runoff รค Composite CN Editor to display
the Composite Runoff Curve Number Calculator dialog box.
2 In the Description column, type the descriptions for the subareas for which you
are calculating the composite curve number, one subarea per row.
3 In the Area column, enter the area values for the watershed subareas.
You can either type the area values into the column, or click Select to specify
the areas by drawing or selecting closed polylines from the drawing. For
example, if you used the Terrain Model Explorer to calculate the watershed
values for a TIN surface, then closed polylines may already exist in the drawing
that you can select.
4 In the Curve Number column, enter the curve numbers for the watershed
subareas.
You can either type the curve number values into the column, or click Select to
display the Runoff Coefficients dialog box, where you can select the CN value
to use for the cover and soil type. Double-click the CN value you want to use,
and then click OK to return to the Composite Runoff Curve Number Calculator
dialog box.
As you enter the information for the subareas, the program calculates the total
area of the watershed subareas and the weighted curve number, and displays
this information at the bottom of the dialog box.