I don't think missile can be compared with Type 81 assault rifle which even Zimbabwe can gets free in the time of war so i ask you again how many of these mighty missiles are currently in your inventory.
There are around 180000 power plants in India scattered all over the country generating 250000 M.W electricity so you need Atleast 50000 missiles whereas you have only 50 odd decent P.P generating only 20000 M.W most of them located near border it would be a total black out within few hours in case of war.
My point was not to attack the river basins but to block the rivers flowing to Pakistan you know you have large population engaged in agriculture,or it can also be use to create floods.