So the reservoir can store water to build tall buildings?

You can't. The silt at the bottom of the reservoir should be completely replaced, but the foundation cannot be replaced. The foundation is not firm after filling, and the backfill soil should be compacted to meet the requirements, otherwise it will not sink easily. The flood discharge channel of the reservoir is blocked, the flood storage function of the reservoir is lost, and it is impossible to build high-rise buildings on the reservoir. Reservoirs refer to artificial lakes, and smaller ones are called ponds, ponds and reservoirs. The general formation method is to dam the middle and upper reaches of the river, and the river will flood the valley to form a reservoir.