This paper aims to achieve optimum design of storing water through dams, and also to predict the storage unit cost through dams. The storage unit cost means the cost for storing 1 m3 of water. For these objectives, data are collected for forty dams that were constructed in Al-Baha, Saudi Arabia, for storing water from 1975 till 2012.
For the optimum design of storing water according to the required capacity, it is concluded that considering the type of the required dam gives more accurate results. For earth fill dams, the water capacity does not matter. While for concrete dams, the water capacity of 4 million m3 is significant. An equation is obtained to get the optimum design of storing water through earth fill dams. Two equations are obtained to get the optimum design of storing water less than and more than 4 million m3 through concrete dams.
Concerning the storage unit cost of water through dams, it is concluded that introducing the type of the required dam gives only slightly more accurate results. An equation is obtained to predict the storage unit cost of water through dams regardless the type of the dam. Also, two equations are obtained to predict the storage unit cost of water through earth fill dams. Finally, an equation is obtained to predict the storage unit cost of water through concrete dams.