Because the cost of energy has risen considerably in recent decades, the addition of a suitable capacity hydropower plant (HPP) to the end of the pressure conduit of an existing irrigation dam may be economically feasible. First, a computer program capable of realistically calculating total losses from the inlet to outlet throughout any pressure conduit for many discharges (Qs)from the minimum to the maximum at small increments is coded, the outcome of which enables the determination of the C coefficient of the Total Head Loss = C.Q2. Next, a computer program is used to determine the hydroelectric energy produced at monthly periods, the present worth (PW) of their monetary gains. The average annual energy produced by a HPP is then coded. Inflows series, irrigation water requirements, evaporation rates, turbine running time ratios, and the C coefficient are the input data of this program. Running the program with a synthetically generated M number of m-year-long inflows series, histograms of both the average annual energies and the PWs of energy incomes are determined to which suitable probability distributions are then fitted. This model has been applied to ten randomly chosen irrigation dams in Turkey, and a regression equation is obtained to estimate the average annual energy as a function of gross head available and the annual volume of irrigation water, which should be useful for reconnaissance studies.