Benefits of building a dam:
1, regulating river runoff and improving the climate in the reservoir area (reducing temperature difference and increasing air humidity);
2. It can be used for flood control, shipping, power generation, irrigation, aquaculture and tourism.
Disadvantages of building a reservoir:
First, the impact on the upstream of the reservoir area:
1, the reservoir impounded water to stop sand, the water quality decreased, and the number of migratory spawning organisms decreased;
2. The farmland was flooded and the residents had to leave their hometown.
Second, the impact on the reservoir area:
1, the water quality in the reservoir area is eutrophic, and the rising water level makes the groundwater rise and evaporation intensify, which leads to the salinization of cultivated land in the reservoir area;
2. The increase of reservoir pressure caused by water storage may induce new geological disasters such as reservoir earthquake;
Third, the impact on the downstream of the reservoir area:
1, the downstream sediment deposition is weakened, the organic matter deposition is reduced, the runoff is reduced, and the industrial and agricultural production and domestic water consumption are tight;
2. Due to the slow deposition and wave erosion in the estuary, the coastal areas are threatened by the retreat of the delta (coastline);
3. The decrease of nutrients in estuaries affects the survival of animals and plants.
Conditions required for building a dam:
1. Pocket-shaped terrain, with wide hinterland and narrow outlet, which is favorable for water collection and narrow outlet for dam construction;
2. The gap of this river is very large;
3, geological conditions, whether in limestone areas, how about underground caves; Whether there is a fault zone.