The Kotmale dam is one of the five main head-work projects done under the Mahaweli Ganga Scheme. this is the most upstream of all.
Kotmale dam is the first with an upstream concrete membrane. The power station is the first Sri Lankan underground station. The dam was ceremoniously declared open in 1985.
There are three spillways and the type of it is called Radial gated, chute type spillway. Catchment area is 544 sq Km. The type of the dam is known as Rock fill with concrete membrane.