Poor land use and construction practices in the catchment area of Shihmen Dam have contributed to a severe sedimentation problem in the reservoir.
 This sediment mainly comes from landslides and other erosion-related issues in the steep, rugged drainage basin, which have been exacerbated by deforestation, land-clearing for agriculture, and the opening of roads into mountainous areas.
The reservoir, which originally had a maximum depth of over 100 metres (330 ft), is estimated to be no more than 40 metres (130 ft) deep today.
The textbook The Hydraulics of Open Channel Flow by Hubert Chanson describes the dam as having "become a vast sediment trap with an inappropriate storage capacity to act as a flood control or water supply reservoir."

In 1981 it was estimated that 2.9 million tonnes of sediment flow into the reservoir each year, or a watershed erosion rate of 3,789 tonnes/km².
According to a 2017 Taipei Times report, the amount of sediment flowing into the reservoir was 3.42 million tonnes per year.
About 1.17 million tonnes were sluiced through the dam's outlets and another 900,000 tonnes were removed by excavation and dredging.
The government has proposed to construct a sediment bypass tunnel,  which would prevent another 640,000 tonnes from entering the reservoir.
This technology has already been employed at reservoirs in Japan and Switzerland, and would essentially allow river water to be diverted around the reservoir instead of flowing into it during periods of high sediment runoff, such as after typhoons.
Poor land use and construction practices in the catchment area of Shihmen Dam have contributed to a severe sedimentation problem in the reservoir.  This sediment mainly comes from landslides and other erosion-related issues in the steep, rugged drainage basin, which have been exacerbated by deforestation, land-clearing for agriculture, and the opening of roads into mountainous areas. The reservoir, which originally had a maximum depth of over 100 metres (330 ft), is estimated to be no more than 40 metres (130 ft) deep today. The textbook The Hydraulics of Open Channel Flow by Hubert Chanson describes the dam as having "become a vast sediment trap with an inappropriate storage capacity to act as a flood control or water supply reservoir."
In 1981 it was estimated that 2.9 million tonnes of sediment flow into the reservoir each year, or a watershed erosion rate of 3,789 tonnes/km². According to a 2017 Taipei Times report, the amount of sediment flowing into the reservoir was 3.42 million tonnes per year. About 1.17 million tonnes were sluiced through the dam's outlets and another 900,000 tonnes were removed by excavation and dredging. The government has proposed to construct a sediment bypass tunnel,  which would prevent another 640,000 tonnes from entering the reservoir. This technology has already been employed at reservoirs in Japan and Switzerland, and would essentially allow river water to be diverted around the reservoir instead of flowing into it during periods of high sediment runoff, such as after typhoons.
Shihmen Dam