Impact of human intervention on channel shrinkage and restoration in the Huanghe Estuary

Human intervention has become a globally dominant factor in the morphological evolution of estuary channels in recent decades. This paper analyzes seasonal morphological changes in the Huanghe estuarine channel for a 37-year period from 1976 to 2012 as a measure of estuarine shrinkage and restoration. The results show that the channel underwent four stages of development: enlargement (1976–1985), a gradual decreased area (1986–1994), shrinkage (1995–2001), and restoration (2002–2012). Generally, changes in the channel transect geometry during the first stage are regulated by natural fluctuations in water and sediment discharges, but the other three stages are impacted mainly by human intervention. The decreased runoff and sediment discharge caused by dam construction and water and soil conservation are the main reasons for the decrease and shrinkage of the channel transect. During the fourth stage, the increased ratio between water and sediment due to new reservoir construction and the water–sediment regulation scheme (WSRS) progressively affects runoff discharge, producing remarkable impacts on channel morphology during restoration. Human intervention has varying influences on different channel transects. The upstream channel section is more stable than the downstream channel, and human intervention in the downstream unstable channel has a 50% greater effect than that in the upstream stable channel. The WSRS has greater effects on the downstream unstable channel than on the upstream stable channel; however, a higher water–sediment ratio during the restoration stage results in greater impacts on the upstream stable channel than on the downstream unstable channel. Seasonal changes in the channel geometry indicate that seasonal adjustment is important for channel self-adjustment and that human intervention enhances variations in seasonal transect areas and impacts channel morphology.