Humans have been working on water conservancy projects since ancient times, endeavoring to store and utilize water resources for the needs of life and economy. The annual mean precipitation in Taiwan is approximately 9.507 million tons. 20% of which evaporate due to solar radiation and cannot be utilized; 70% flow into rivers and the rest 5% permeate to the ground and become groundwater. We divert 50% of water resource from rivers, 25% from reservoirs (second only to rivers), 20% from groundwater pumping for national water demand so as to store and utilize these natural water resources. Among approximately 2.1 million tons of mean water consumption in Taiwan every year, 71% are used for irrigation, cultivation and agricultural use for raising poultry; 9% are for industrial use in industrial areas, whereas 20% are for daily life use for everybody.
A dam is a barrier that impounds water. It is an important installation for water resources in Taiwan. The water supply offered is 24% of the total water use, possessing adaptation functions such as floodwater storing and droughts saving. Recently, the silt in dams increases promptly and the effective volume of water reserving decreases significantly, bringing severe influences to the functions of dams. The total sedimentation rate of reservoirs in Taiwan is 28.6%, which is nearly 1/3 of the dam volume; among all of them, the condition in southern areas is the worst as the total sedimentation rate reaches up to 36.8%. From the pictures below, we can see four main dams in Taiwan: Feitsui Dam, Shihmen Dam, Zengwun Dam and Nanhua Dam. The sedimentation rate of these dams is higher than 30%, signifying that 1/3 of the volume in a dam contains silt that cannot be drained. On top of that, the dams cannot store enough water, either. This means that the gap of water resources supply is getting wider and water crisis will emerge frequently.