Deforestation increases damaging erosion and destroys a river's watershed. Silt is trapped behind dams, reducing fertility downstream as well as the capacity and life-span of the dam. Downstream silt must be replaced by expensive chemical fertilizer.
Dams always carry the danger of collapse due to earthquakes, flooding or sabotage.
Casualties from dam collapse will be much higher than those from normal flooding. Silt is trapped behind dams, reducing fertility downstream as well as the capacity and life-span of the dam. Downstream silt must be replaced by expensive chemical fertilizer. Reservoirs flood the often-fertile land at the bottom of valleys and displace thousands of people to less suitable land or overcrowded urban areas. Large reservoirs, particularly in hot climates, have enormous losses of precious water through evaporation.