Research and Development Office

Ephemeral Tributary Sediment Transport Measurement

Project ID: 9781
Principal Investigator: David Varyu
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2015, 2016 and 2017
Keywords: arroyo, wash, tributary, ephemeral, sediment load, yield, surrogate, bedload

Research Question

Can a set of surrogate measurements be collected coincident with a definitive (physical) measurement of sediment flux in an ephemeral channel that will help establish a relationship between surrogate data and sediment flux? What set of surrogate measurements needs to be collected in order to develop a relationship between surrogate data and definitive sediment flux?

Need and Benefit

One common source of uncertainty in mobile-bed sediment transport modeling of a river is lateral sediment volumes delivered by tributaries. The uncertainty and error associated with tributary sediment loads is much larger for ephemeral non-armored tributaries as compared to perennial armor-bed systems. Many of the rivers in the western United States, especially in the west, southwest, and central plains, have ephemeral tributaries which can be significant sources of sediment for the mainstem river. This is especially true in situations where an upstream dam cuts off mainstem sediment loads. These tributary sediment loads are very important for sediment management and river restoration purposes, and are often poorly estimated and can involve order of magnitude errors in their quantification.

Current methods to estimate sediment transport involve estimating either: (1) the sediment supply or (2) the sediment capacity. Sediment supply estimates are usually of the Universal Soil Loss Equation types (USLE, MUSLE, RUSLE) and are understood to include significant uncertainties. Sediment transport capacity is typically estimated using a transport equation, which can be effective when the appropriate equation is selected to match the specific conditions. However, nearly all transport equations have been developed based on the energy in perennial systems, and bed load flux in an ephemeral channel has been shown to be "several orders of magnitude higher than maxima measured at similar levels of stream power in perennial counterparts" (Reid, Laronne, 1995). It is imperative that stream restoration studies, sediment management actions, and reservoir sedimentation studies conducted by or for Reclamation include tributary sediment estimates that are more accurate than what is currently being used.

Any advancement made in defining the surrogate data necessary to be collected for improved estimates of ephemeral tributary sediment flux will be beneficial to any Reclamation project manager who is responsible for a system which includes ephemeral tributaries with similar hydrology, geology and morphology to the site selected for this project. Ephemeral tributaries (or "washes", "arroyos", etc.) are found throughout the arid west and southwest. All Reclamation regions have numerous ephemeral systems throughout their jurisdiction.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Bureau of Reclamation Review

The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.

Ephemeral Tributary Sediment Transport Measurement (final, PDF, 12.9MB)
By David Varyu
Research Product completed on September 30, 2017

Ephemeral Tributary Sediment Transport Measurement (final, PDF, 12.9MB)
By David Varyu
Research Product completed on September 30, 2017

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