See the picture below to see the visibly large variation in the flow rate of our rivers in Western ghats between summers and monsoons. This is largely due to massive deforestation and damming activities upstream. It shows a bird's eye view of how human activities affect these natural wonders.
The waterfalls are the Mighty Jog in Karnataka and Elegant Athirappilly in Kerala... The rivers Sharavathi and Chalakudy, originate from ranges where rainfall is almost perennial. The full throttle happens when the dams are opened to check the huge inflow owing to heavy monsoon.
See what Wiki says about Jog:
"Before the onset of the monsoon, when there is not much water in the Linganmakki dam, theJog Falls are nearly unrecognizable. Instead of the roar and the spray and the massive flow of water, there are only a pair of thin streams of water trickling down the cliff as the water collected in the dam is exclusively for generation of electicity and during monsoons local rain-water is the source of water to the falls. If you happen to ask any of the local people what happened to the falls, they would tell you that the authorities open the dam only during week ends, when there are a lot of tourists to view it.
During the monsoon of 2007, due to heavy rains, the authorities at the falls had to open the dam. Due to this, the water falls was seen at its best. Unfortunately this also resulted in the flooding of many villages down the river, destroying crops and the fishing industry for weeks"