Event Title

Coupling sediment transport and channel geomorphology

Presenter Information

John Pitlick

Location

ECC 303/305

Event Website

http://water.usu.edu/

Start Date

4-6-2007 10:50 AM

End Date

4-6-2007 11:35 AM

Description

Alluvial rivers transport much more sediment annually through a cross section than might be accounted for by localized scour and fill of the channel bed and banks. In gravel-bed rivers in Colorado, for example, bed load sediment yields are typically on the order of a few tons/km2/yr, thus streams draining areas of ~100 km2 might transport the equivalent of ~100 m3 of bed load each year. These loads are not high in comparison to rivers in some other regions; however, even under these conditions, the processes of flow and bed load transport must be very tightly coupled, otherwise the balance between sediment input and output would quickly shift and the channel would become unstable. Through a series of studies conducted over the last 10-plus years we have tired to take advantage of the fact that channel properties are not nearly as variable in space or time as is the process of bed load transport, and in so doing have developed a clearer understanding of the interactions between sediment transport and the morphology of alluvial channels. We have investigated trends in bed load transport intensity and frequency in relation to flow and channel properties at hundreds of sites on gravel-bed streams and rivers in Colorado and Utah. In addition we have conducted extensive analyses of flow and transport measurements from streams and rivers throughout the West to develop new relations for transport in steep streams with high relative roughness. Our results indicate that the threshold shear stress for bed load transport in gravel- and cobble-bed channels varies systematically with gradient and relative roughness. However, we also find that the shear stress available at bankfull flow varies in proportion to the threshold shear stress, thus streams and rivers of almost any size and slope are capable of transporting appreciable quantities of bed load over a period of years. We also observe that in the transition from high- to low-gradient channels there is a tradeoff in the frequency and intensity of bed load transport, such that the total load carried in small, steep cobble-bedded channels tends to balance the total load carried in large, low-gradient channels. Our results have several implications for water resources management, as well as conceptual theories of ecosystem function and structure, and models of landscape evolution.

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Apr 6th, 10:50 AM Apr 6th, 11:35 AM

Coupling sediment transport and channel geomorphology

ECC 303/305

Alluvial rivers transport much more sediment annually through a cross section than might be accounted for by localized scour and fill of the channel bed and banks. In gravel-bed rivers in Colorado, for example, bed load sediment yields are typically on the order of a few tons/km2/yr, thus streams draining areas of ~100 km2 might transport the equivalent of ~100 m3 of bed load each year. These loads are not high in comparison to rivers in some other regions; however, even under these conditions, the processes of flow and bed load transport must be very tightly coupled, otherwise the balance between sediment input and output would quickly shift and the channel would become unstable. Through a series of studies conducted over the last 10-plus years we have tired to take advantage of the fact that channel properties are not nearly as variable in space or time as is the process of bed load transport, and in so doing have developed a clearer understanding of the interactions between sediment transport and the morphology of alluvial channels. We have investigated trends in bed load transport intensity and frequency in relation to flow and channel properties at hundreds of sites on gravel-bed streams and rivers in Colorado and Utah. In addition we have conducted extensive analyses of flow and transport measurements from streams and rivers throughout the West to develop new relations for transport in steep streams with high relative roughness. Our results indicate that the threshold shear stress for bed load transport in gravel- and cobble-bed channels varies systematically with gradient and relative roughness. However, we also find that the shear stress available at bankfull flow varies in proportion to the threshold shear stress, thus streams and rivers of almost any size and slope are capable of transporting appreciable quantities of bed load over a period of years. We also observe that in the transition from high- to low-gradient channels there is a tradeoff in the frequency and intensity of bed load transport, such that the total load carried in small, steep cobble-bedded channels tends to balance the total load carried in large, low-gradient channels. Our results have several implications for water resources management, as well as conceptual theories of ecosystem function and structure, and models of landscape evolution.

https://digitalcommons.usu.edu/runoff/2007/AllAbstracts/36