Why some of the peninsular river are non-perennial?

The rivers of Peninsular India are not suitable for navigation as they flow swiftly over the plateaus and highlands.

The rivers in South India are rain-fed and dry up in the hot and dry season. The peninsular rivers of the south have their source in the Western Ghats and flow across hills making a number of waterfalls, which are not navigable, but provide Hydro-electricity.