Estimation of Discharge:
The estimation of discharge of a stream is necessary for determining the waterway, clearance and foundation details. Discharge is estimated from :
(a) empirical formula, and
(b) rational formula.
There are several empirical formula for estimation of discharge. Dicken's formula, given below is commonly adopted.
Q = CM^{3/4}
where Q = Discharge in cu m/sec,
M = Catchment area in sq. km,
C = A constant with the following values :
C = 11-14 where the annual rainfall is 60-120cm
= 14-19 in Madhya Pradesh
= 22 in Western Ghats.
The rational formula, given below, requires the intensity of rainfall.
Q = 0.028 PAI_{C}
where Q = Discharge in cum per sec.,
P = Coefficient of run-off for the catchment, having values of
0.10-0.90 depending upon porosity of the surface,
A = Catchment area in hectares, and
Ic = Critical intensity of rainfall in cm per hour.