CALCULATION OF DIRECT RUN-OFF FROM STORM HYDROGRAPH

From storm hydrograph measure ordinates at fixed time intervals.

These ordinates represent discharge or flow (Q).

Also measure the ordinates of base flow, at the same time interval as adopted earlier.

By subtracting ordinates of base flow from corresponding ordinates of total discharge Find out the net ordinates which represent direct run-off in that time interval.

Add up all the ordinates of direct run-off which is nothing but total volume of direct run-off.

By dividing total volume of direct run-off by area of the basin, direct run-off available from the catchment is obtained.

The method can very well be understod from the following illustrative example.

Direct run-off in depth of water = Total

\[= \frac{Total volume of direct .run-off }{Area of the basin}\]