Formation and Propagation of Large-scale Sediment Waves in Periodically Disturbed Mountain WatershedsEPA Grant Number: R824779
Title: Formation and Propagation of Large-scale Sediment Waves in Periodically Disturbed Mountain Watersheds
Investigators: Parker, Gary
Institution: University of Minnesota
Current Institution: University of Minnesota , St. Anthony Falls Laboratory
EPA Project Officer: Hiscock, Michael
Project Period: January 1, 1996 through December 1, 1998
Project Amount: $280,000
RFA: Water and Watersheds (1995) Recipients Lists
Research Category: Water and Watersheds , Water
Human-induced disturbances in mountain watersheds, such as timber harvesting, road building, or mining, often result in the delivery of large amounts of sediment to mountain rivers as discrete inputs. The mechanism of input is often landsliding or debris flows. Large, discrete inputs can cause serious bed aggradation, resulting in deleterious effects on aquatic and riparian habitat. In addition, under the right circumstances the sediment lump can devolve into a downstream-propagating wave, resulting in failure of bridges, pipeline crossings, etc., and the loss of roadways. The present project is devoted to a description of the fate of large sediment inputs to mountain rivers. It is being conducted with the informal cooperation of the Redwood Sciences Laboratory, US Forest Service, Arcata, California. The major applied goal of the project is a general, flexible numerical tool that can be applied to forested mountain basins in order to determine the effect of large sediment inputs on the river downstream. The major goal in terms of basic research is a better understanding of the mechanics of sediment transport and grain sorting under conditions of severe aggradation.
Two basins are being used as the basis for study: Redwood Creek and the Navarro River, both draining coastal northern California. Large amounts of field data already collected at the sites are being used to develop a numerical model of the fate of lumped sediment inputs on river morphology and sediment transport. It is expected that two types of behavior might result from large, discrete sediment inputs. In some cases the sediment pile may diffuse in place. In other cases, a discrete sediment wave that translates in the downstream direction may form. The delineation of these two regimes will be of practical importance in determining the applicability of the work to other forested mountain basins. To date, the research team has made two field trips to the sites. A general formulation for the transport of sand over an aggrading gravel bed has been achieved, and has been applied to river bed aggradation for the case of a simplified stream morphology that is nevertheless very similar to Redwood Creek. In addition, progress has been made in defining how a sediment wave might cause the formation of central bars and incipient braiding. Future work calls for including more of the specifics of Redwood Creek and the Navarro River. In addition, a series of experiments on the fate of discrete sediment input are planned.
The experiments will allow for a detailed check of the numerical model.