> Because the source of the Indus River is glacial meltwater from the Himalayas, the river carries huge amounts of sediment, with an annual suspended sediment load of 200 million tons.[15] Live storage capacity of Tarbela reservoir had declined more than 33.5 per cent to 6.434 million acre feet (MAF) against its original capacity of 9.679 MAF because of sedimentation over the past 38 years.
Dams all over the world capture sediment. This not only reduces their capacity, it deprives downstream areas of sediment needed for natural habitat, to fertilise wetlands and to buffer against oceanic incursion.
The Sanmenxia Dam in China lost 17% of its capacity in the first 18 months of its operation due to sediment accumulation [1]
Countless other dams have already been dismantled due to sediment build up, and many more will follow, considering that around 19000 large dams worldwide are over 50 years old [2]
Honestly this sounds like mostly poor engineering planification and analysis. If you look at the dams with a lot of sediment it's mostly in South-East Asia and Africa while Europe/North America have little of it.
Asia's rivers have by far the highest level of sediment of any continent [1] meanwhile the US has quietly destroyed over 1000 dysfunctional dams in the post war period [2]
Also, think about it: hydro power is not the only use for a dam. They are also typically used for things such as flood control, water supply, and energy storage. All of those usecases rely on the sam's ability to hold water (and it's sediments) and lower discharge, if not totally block it.
https://en.wikipedia.org/wiki/Tarbela_Dam#Lifespan