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Table Of Contents
Chapter 5 Working with Hydrology Commands
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To calculate the peak runoff flow by using the TR-55 graphical method
1 From the Hydrology menu, choose Runoff ä TR-55 Graphical Method to
display the TR-55 Graphical Peak Discharge Method dialog box.
TIP
To load a runoff calculation that you previously saved, click Load.
2 In the Description box, type a description for the watershed area.
3 In the Rainfall Distribution list, select the rainfall distribution for the project
location. The available types are: Types I, IA, II, and III.
NOTE
See the map on page B-2 of the TR-55 manual, or contact your local NRCS,
to determine the appropriate rainfall distribution for your project area.
4 In the Drainage Area box, type the watershed area, or click Select to specify the
area by drawing a closed polyline or selecting a closed polyline from the
drawing.
5 In the Runoff Curve Number box, type the curve number for the watershed, or
click Select to select the watersheds curve number from the Runoff Curve
Number Editor. For more information, see Specifying a Runoff Curve Number
in this chapter.
6 In the Time of Concentration box, type the Tc for the watershed, or click Select
to calculate the watersheds Tc.
7 In the Pond and Swamp Areas box, type the total area of ponds and swamps in
the watershed, or click Select to specify the areas by selecting closed polylines
from the drawing. This value is required if the ponds or swamps are scattered
throughout the watershed and are not accounted for in the time of
concentration calculation.