Q = A * C * I * kwhere:

Q = discharge in cubic metres per second

A = area in square kilometres

C = coefficient of runoff

I = intensity of rainfall in millimetres per second

k = constant of proportionality

1. Define the
perimeter of the watershed and measure the watershed area.

2. Identify
the appropriate rainfall intensity for the location and rainstorm desired.

3. Subdivide
the watershed according to cover types, soils and slopes. Asssign
a coefficient of runoff to each, and measure each subarea.

4. Determine
the percentage of the watershed represented by each subarea and multiply
this figure by the coefficient of runoff of each. This will give
you a coefficient adjusted according to the size of subarea.

5. Sum the adjusted
coefficients to determine a coefficient of runoff for the watershed as
a whole.

6. Multiply
the watershed area times the coefficient of runoff times the rainfall intensity
value to obtain peak discharge in cubic metres per second.

* Source: adapted from William M. Marsh's