This command calculates the time of concentration (Tc) by the SCS
method from A Method of
Estimating Volume and Rate of Runoff in Small Watersheds.
The Tc is the time required for water to flow from the most distant
point in the watershed to the measurement point.
The SCS method calculation based on the curve number, length of
flow, and average slope. The curve number defaults to the weighted
curve number from the Curve Numbers & Runoff routine. When the
three inputs are entered, click on Calculate to compute the Tc.
Select CN from Table button opens the CN dialog and allows you to
select the CN based on the drainage area type and the soil type.
Click on Select Flow Line from Screen button to use a 3D polyline
in the drawing. This sets the length of flow and average land
slope. A 3D polyline that models the flow can be created with the
Watershed Above Point or Run Off Tracking commands. While reading
in the 3D polyline, the Tc is calculated by adding the Tc's for
each segment of the polyline. This yields a different and more
accurate Tc than using the average slope with the Calculate
button.
Time of Concentration
Dialog
Pulldown Menu Location: Watershed -> Time of Concentration
> SCS Method
Keyboard Command: flowtc2
Prerequisite: None
