Yah I too had the same doubt. I convinced myself with the below.
But polavaram canal full supply level is at 42 metres(75 tmc). once the level goes down water has to be pumped, Instead release the water down(if possible power generation) and use purushottapatnam/polavaram lifts.
considering the scenario, if the water is below active level, and we don't get good flows in may and june like this year.
Hope someone in the DB has the right answer.