All online resource as well as schools talk briefly about dams and it's working but everything is taught about the END part of the dam...that great tall wall, no one cares about what happens at the back...and that's exactly what I wanna know. I assert this might be happening - A river comes form up to down, while it's at it's early stages (or when it's at a higher altitude), it has a high potential energy relative to it's mid phase (which's at a lower altitude); at it's mid phases this potential energy is converted to kinetic which gives a usual river maximum swiftness at this phase; most of this energy gets lost in the form of collisions of water with rocks and stuff, as a consequence the lower phases of the river is slow. We can harvest this potential energy through the height difference - The arrows in the above diagram show the direction of flow of fluids of a typical river on the ground by virtue of height difference...the gray block acts as a barrier such that it results in accumulation of water. The accumulation of water along the barrier will increase the potential energy of water to such a level as if the river was at an earlier stage; if this water is made to release towards the lower part of the block, it will contain lot's of kinetic energy cause of the high height of the water accumulation; this energy is harvested for various purposes and this arrangement is called a dam. Of course, we will need another 2 set of walls to confine the fluid and make it attain such a height - This 3-d image above is the same as the 2-d image; the gray block is the wall of the dam, the brown plane is the ground, and it has water (blue) flowing which's getting accumulated along the block...the other 2 walls which have been referred previously are a part of the valley which have been shown as green; thus the preferred place to grow a dam is between walls of a valley...also notice that the height drop of the river is within the valley, if there's no height drop at any place in the valley, the whole valley is unsuitable for dam construction. Am I right about whatever I've written here?