The surface of the earth we live on is covered with a lot of water, which is generally called the "hydrosphere", which accounts for about 71% of the surface of the earth. In fact, in addition to the extensive oceans, the hydrosphere also includes lakes, rivers, glaciers, and groundwater on land.

In recent years, due to the rapid expansion of the global population and the increase in food demand, the goal has to be turned to the ocean to seek more marine resources; in addition, there are more abundant energy minerals in the ocean, so the current exploration and research of the hydrosphere have been Becoming an advanced country and an equally important issue for space development. Taiwan’s main island is located in a low latitude area in the northern hemisphere, between subtropical and tropical, surrounded by sea, and the coastline of Taiwan is more than 1,000 kilometers long. The main tributary of the Kuroshio and the North Equatorial Current The tributaries pass through the east and west coasts of Taiwan, making Taiwan have high temperature and humidity throughout the year; coupled with the differences in climatic factors, topographical environment and geological structure, when the sea water hits the coast over the years, it is affected by external forces such as waves, currents and tides. After the continuous erosion, transportation and accumulation of the coast, the coast has different shapes and changes. In some places, the coasts are straight and shallows suddenly appear, in some places the coasts are close to deep water, and in some areas there are many bays and islands. There are sandy shores, mud shores, rocky shores and coral reef shores, forming different topographical landscapes and ecological environments.

Although the average annual rainfall in Taiwan exceeds 2,500 millimeters and the average annual temperature is high, there are no obvious glacier relics on the mountains, and only a few mountain lakes and streams are distributed. After the Penglai orogenic movement, the earth's crust rose sharply and the slope increased. Although there are many inland rivers, the mountains are high and the water is rapid, and the use of surface water and groundwater is difficult. Taiwan, which has the second highest population density in the world, has to build a reservoir to solve the problem. The crisis of increasing water consumption has also brought many negative effects.

Although there are no glaciers in Taiwan, there are twelve slices of glaciers on the mountain every year until April of the following year. In some areas, the temperature is often around zero degrees Celsius, and there are short snow periods, and "ice erosion" is strong. For example, the Muteleb Peak (3620 meters above sea level) in the Snow Mountains is mainly composed of slate from the Jiachangchang layer. The slabs are thick and the water easily penetrates into the rocks along the cracks in the slab surface. The temperature often drops to about zero at night. Water becomes ice and the volume can expand by about 8%. The ice melts into water after sunrise, and more water is filled in the cracks. This happens repeatedly, and the slate is peeled off to form a gravel slope.

In the event of heavy rain, gravel is often transported and piled down with flowing water, even damaging roads or destroying trees or buildings on the ground. If “man-made illegal logging and indiscriminate construction are added, more disasters will occur. Although Taiwan’s annual rainfall It is abundant, but due to the uneven distribution of rainfall time, the location of rainfall is often uneven, and the surface slope is large, so although there are more than a hundred rivers in Taiwan, most of them are short and rushing into the sea, and the available water resources are quite limited.

In recent years, due to the excessive concentration of population in cities, the growing economy and the increasing development of public buildings, water source development projects have become necessary measures. Of course, the construction of reservoirs can most directly solve these major projects and people's living needs. In addition, reservoirs have functions such as flood prevention, water conservation, agricultural irrigation, supply of hydroelectric power, and people's recreation. However, from the perspective of long-term goals, the construction of the reservoir is huge. If detailed planning and environmental assessment are not carried out in advance, the constructed reservoir will inevitably cause many problems and reduce the life and function of the reservoir.

After the construction of the reservoir, the sediment originally carried by the rainwater runoff in the catchment area can no longer be transported from the upstream to the downstream, and enters the ocean through the river. When the water with silt enters the reservoir, the depth of the water in the reservoir increases and the flow rate decreases, resulting in a decrease in water transport capacity, and a part of the silt gradually precipitates and siltates, which takes up the space available for water storage, and finally makes the reservoir lost The effect of storing water to relieve dryness greatly reduces the life of the reservoir.

In the water catchment area of ​​Taiwan’s reservoirs, the frequency of people’s activities is high, the land is used at a high density, which accelerates soil erosion, and Taiwan’s high temperature and humidity, rapid weathering of rocks, a large amount of sand and gravel due to water erosion, and violent crust rise, make the river slope steep The water is urgent, and the siltation problem of the reservoir is particularly serious. It greatly reduces the life of the reservoir, strengthens water and soil conservation measures in the catchment area, prevents a large number of man-made activities and fortifications, builds sand storage ponds and sand dams in a planned way, and pumps sand in a timely manner. It is the work that should be done to protect the reservoir.