Direct Run-off Hydrograph Calulation
CALCULATION OF DIRECT RUN-OFF FROM STORM HYDROGRAPH

Direct Run-off Hydrograph Calulation

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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.

CALCULATION OF DIRECT RUN-OFF FROM STORM HYDROGRAPH

 

Direct run-off in depth of water = Total

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

\[= \left [ \frac{\Sigma E\times t\times 60\times 60}{A\times ^{}10} \right ]\times 100\]

\[= \frac{0.36 \Sigma R\times t}{A}cm\]

where

  • t = time interval in hours between successive ordinates
  • A = Area of catchment in km2
  • Q = Discharge in cumecs.
  • ΣR = Sum of discharge ordinates in cumecs or direct run-off is cumecs. In above example t = 2 hrs. and let A is 40 km2.

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