The geometry and pattern of river channels adjust to significant changes in the water discharge, size, and quantity of sediment supplied to the channel. When the quantity of water and sediment over a period of years remains relatively constant, the channel geometry and pattern vary about a mean of quasi-equilibrium conditions. Major watershed alterations that change the supply of water, sediment, and size of sediment reaching the channel necessitate an adjustment of the channel geometry and pattern. That is, the channel is transformed from one quasi-equilibrium state to another. Between the two quasi-equilibrium states, there is a period of instability and adjustment. The dynamics and rate of river channel adjustment during the period [...]
Summary
The geometry and pattern of river channels adjust to significant changes in the water discharge, size, and quantity of sediment supplied to the channel. When the quantity of water and sediment over a period of years remains relatively constant, the channel geometry and pattern vary about a mean of quasi-equilibrium conditions. Major watershed alterations that change the supply of water, sediment, and size of sediment reaching the channel necessitate an adjustment of the channel geometry and pattern. That is, the channel is transformed from one quasi-equilibrium state to another. Between the two quasi-equilibrium states, there is a period of instability and adjustment. The dynamics and rate of river channel adjustment during the period of instability have rarely been studied, and are rather poorly understood. The primary focus of this research project is to understand the dynamics and rate of river channel change and develop numerical models to make predictions of river channel characteristics given a particular change in flow regime and sediment supply. The greatest deficiencies in our present knowledge of river channel adjustment are (1) the longitudinal sorting of bed material, especially gravel, (2) the formation and stability of bed forms, (3) adjustment of channel width through the erosion and deposition of bank material, and (4) the rates at which the several hydraulic variables adjust. Specific objectives are to develop physically-based numerical models to describe the processes and rate at which a river channel adjusts in response to a change in the water discharge, sediment size, and sediment load supplied to the channel, emphasizing the adjustment of those aspects of river channels that significantly influence the aquatic ecosystem (that is the bed-material size distribution, occurrence of bars, and channel width); describe the hydraulic processes controlling these characteristics of river channel as well as the rate at which they function; formulate mathematical models of the processes as required for longitudinal routing of water and sediment; and develop new analytical tools for describing river-channel adjustment. For additional information on wildfire studies: seeHydrologic and Erosional Responses of Burned Watersheds.
