Hydroelectricity is a very great source of energy. Because hydroelectric dams are typically built on rivers, the naturally flowing wter flows into the dam. That way, there is no transporting coal and from the mine to the factory. Dams are also good because they help improve irrigation, they help people navigate rivers easier, and they help with soil conservation. Hydroelectricity is a renewable energy source, and it is reliable, and the dam operation is free-exept for upkeep. Dams also generate huge amounts of energy. They can be used for flood control, and it helps create jobs for people.
There are many trade-offs that dam designers have to face. If your dam cracks, then everything is ruined , and people who live in the region's lives are in jeapordy. People can try to prevent cracks, but that would require more expensive materials, more labor, and it would cost more. So all in all, building dams is a very risky tasks, and wrong desicions can be disastrous. The dam's reservoirs stops water flow, so people have to move, and helpful sediments that makes the soil fertile gets caught in the reservoir.