Stream restoration and environmental river mechanics

Abstract

The impact of construction of dams and reservoirs on alluvial rivers extends both upstream and downstream of the dam. Downstream of dams, both the water and sediment supplies can be altered leading to adjustments in the river channel geometry and ensuing changes in riparian and aquatic habitats. The wealth of pre and post-regulation data on the Middle Rio Grande, New Mexico, provides an excellent case study of river regulation, channel adjustments, and restoration efforts. Cochiti Dam was constructed on the main stem of the Rio Grande in 1973 for flood control and sediment retention. Prior to dam construction, the Rio Grande was a wide, sandy braided river. Following dam construction, the channel bed degraded and coarsened to gravel size, and the planform shifted to a more meandering pattern. Ecological implications of the geomorphic changes include detachment of the river from the floodplain, reduced recruitment of riparian cottonwoods, encroachment of non-native saltcedar and Russian olive into the floodplain and degraded aquatic habitat for the Rio Grande silvery minnow. Recent restoration strategies include removal of non-native riparian vegetation, mechanical lowering of floodplain areas, and channel widening.

Impact of Ecological Water Transfer Project on Vegetation Recovery in Dried-Up Kongque River, Northwest China

“…Restoration efforts are underway to reestablish the flow of rivers feeding the Aral Sea, encompassing initiatives such as water transfers, wetland and floodplain restoration, and enhanced water management practices. The Rio Grande, traversing the southwestern United States and northern Mexico, has faced adverse impacts arising from water diversions and climate change, resulting in reduced downstream flow [21]. Even in regions characterized by humid climates, reduced or interrupted flow can occur due to human activities such as the construction of dams on rivers.…”

Downstream hydraulic geometry of alluvial rivers

“…Park (2013) recently examined the formation of sediment plugs in the Rio Grande. Three sediment plugs formed in the Tiffany area of the Rio Grande in 1991, 1995and 2005. In 2008 new plug formed at a new location in the Bosque del Apache National Wildlife Refuge.…”

“…Alternative use of changes in the daily operations of the water levels at the barrage can naturally flush most of the sediment while maintaining a state of equilibrium in the fluvial system. Another case of river restoration on the Rio Grande has been discussed by Richard and Julien (2003) and Julien et al (2005) for the opposite situation where the sediment supply of a river downstream of a dam was essentially eliminated after dam construction.…”