Impacts of dam construction on river channel evolution: a case of Minjiang River in Southeastern China

Abstract. The Minjiang River is the largest river in Fujian Province. In 1993, the Shuikou Reservoir, which has an effective storage capacity of 700 million m3, was built at about 161 km above the estuary. The completion of the Shuikou Dam trapped most of the upstream sediment in the reservoir area, resulting in a drastic decrease in sediment in the lower reaches of the Minjiang River. The average annual sand load at the Zhuqi Station (about 45 km below the dam) was reduced about 2∕3 after the construction of the reservoir, from 7.42 to 2.55 million t by average, resulting in severe river bed downward cutting. At the same time, the demand for the sand in Minjiang River channel is increasing year by year. The amount of mined river sand is greater than the incoming sediment deposited in the river, which intensified the downcutting of the river bed. The downcutting leads to a continuous upward movement of the tide limit in the river channel especially in the low-flow season. Meanwhile, river embankments and river-related structures are damaged, and the navigation capacity of the Minjiang River is reduced. At present, the river bed of the lower Minjiang River is not yet stable, and the river regime is in a state of constant adjustment.