Movement and storage of sediment in rivers of the United States and Canada
Sediment in river systems is of interest to earth and water scientists working at problems that span several time scales. On the longest time scale (108 to 109 years), sediment is the major form in which material is transferred from continents to oceans, and the rates at which river sediment has been produced in the geologic past are major concerns of those who study longterm geochemical cycling. At somewhat shorter time scales (106 to 108 years), the properties of the existing sedimentary rocks and deposits are the major clues to past hydrologic and geologic conditions, and, to the extent that the present really is the key to the past, it behooves us to understand how today’s observable conditions influence today’s river sediments. On a more secular time scale, sediment in rivers is of immediate concern as a reflection of soil erosion, as a major design consideration for reservoir sedimentation, river navigation, and other engineering works, as a transporter of various materials (toxic and otherwise) that are adsorbed onto sediment particles in river systems, and as an influence on the habitat of aquatic wildlife.
These secular-scale considerations have prompted research and monitoring activities during the past half century that have provided much of our basic knowledge of sediment in the river systems of North America. Studies of soil erosion and valley sedimentation became especially intensive and extensive during the 1930s; these studies continue today, mostly under the aegis of the national agricultural agencies of the United States and Canada.