SCS Triangular Response
From the MIDUSS Version 2
Reference Manual - Chapter 7
(c) Copyright Alan A. Smith Inc.
Figure 7-19 -
Representation of the triangular response function.
A very common and
popular technique proposed by the Soil Conservation Service uses a
triangular response function as shown in the upper part of Figure 7-19
above. The time to peak
of the triangular IUH and the time base
are given by equations [7-42] and [7-43] respectively.
The ‘Triangular SCS’
option in MIDUSS represents a modification of this method in that the
is obtained by [7-41] and is assumed to vary in a nonlinear fashion in
much the same way as for the rectangular response function. For each
time step the effective rainfall intensity is known and the triangular
response function for the corresponding time of concentration
is discretized and multiplied by the
effective rainfall. The resulting contributions to the overland flow
hydrograph are lagged and accumulated. The computation is made more
efficient by representing the triangular response as the difference
between two right‑ angled triangles as indicated in the lower part of
It will be found that
with both the “Rectangular’ and ‘Triangular SCS’ methods the time of
concentration of the impervious fraction is much shorter than that for
the pervious area due to smaller values of Manning's 'n' and higher
effective rainfall intensities. In cases where the contribution from
each fraction is of the same order of magnitude the total runoff
hydrograph exhibits a double peak because of this feature.