In this case also first of all prepare a mass inflow curve.
Near the same diagram draw various straight lines from a common origin representing various rates of demand.
From the apices points A1, A2, A3 etc., of mass inflow curve, draw tangents in such a way that their maximum vertical intercept from the mass curve does not exceed the given reservoir capacity.
Thus C1D1,C2D2, C3D3 etc., are all equal to the reservoir capacity.
(Say 2500 hectare-metre). Now measure the slopes, of each of these tangents.
The slopes indicate the demand or yield that can be achieved in each year from the reservoir of given capacity.
The slope of the flattest demand line is the safe or firm yield of the reservoir.
