Topography and Drainage

 Topographically, Sri Lanka is divided into three morphological areas and  Sinharaja belongs to the middle elevational range or the "uplands" which has a height range of 270 to 1,060 meters and a slope range of 100 to 350. The forest is located on the Rakwana massif which lies detached from the main central massif of the island.

 The Sinharaja area consists a series of parallel strike ridges valleys. In the eastern part of the forest ,the ridges have an east-west trend while in the western part, the ridges have a northwestern to south-eastern trend. From north to south, the decrease in elevation is gradual while form east to west, the decrease is quite marked (1,100 to 300) meters). There are several prominent peaks in the eastern sector of the Reserve which includes the 1,171 meters high Hinipitigala Peak, the height peak in the Reserve. From this height the altitude often drops down to 90 meters in the valleys

A large number of streams arise in the Sinharaja region and drainage occurs in a rectangular "trellis" pattern. The streams on the southern side form the headwaters of the Gin Ganga while those on the Kukulu Ganga, a major tributary of the Kalu Ganga 

Drainage map of Sinharaja (adapted from Merrit and Ranatunga, 1959)

1 Koskulana Ganga
2 Kudawa Ganga
3 Pitakele Ganga
4 Kalukandawa Ela
5 Napala Dola
6 Maha Ganga
7 Maha Dola
8 Gin Ganga
9 Gin Ganga
10 Aranuwa Dola