Applying Measurements of Cohesive Soil Erodibility
Through Dam Safety Office research funding ($188,000 in fiscal years (FY) 2007 and 2008), Reclamation has recently developed the capability to quantitatively evaluate the erodibilty of cohesive soils using two methods, the submerged jet erosion test (JET), and the hole erosion test (HET). This Science and Technology (S&T) Program research project will attempt to identify applications for these test methods beyond the dam safety arena. Likely candidates are efforts to model streambank erosion and the erosion of deposited sediments from reservoir areas following dam removal or during periods of significant reservoir drawdown.
Need and Benefit
Erosion of cohesive sediments is a fundamental physical process that is important in a variety of application areas, including dam overtopping, erosion of earthen spillway channels, and stream channel evolution and geomorphology. A multitude of factors affect the erodibility of cohesive materials, which can vary over several orders of magnitude. The relative influence of most factors is poorly understood making it difficult to analytically predict the erodibility of any given material. For this reason, tests that can measure erodibility in a quantitative way (relating erosion rate to applied hydraulic stress) are very important to those attempting to model cohesive sediment erosion.
Until recently, Reclamation had very limited ability to measure the erodibility of cohesive soils. Flume-type tests developed in the 1980s were difficult to perform and not standardized, and the unique equipment that was developed by Reclamation had been surplused. During the last decade, other groups have developed simpler tests that have been standardized to varying degrees and are now seeing widespread use. Two in particular are the JET (ASTM-D5852) developed by the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) and the HET, developed in Australia. The jet test has been used extensively in the study of spillway headcut erosion and dam overtopping erosion, and there has also been some investigation (outside of Reclamation) of its use for streambank erosion modeling. An ASTM standard does not yet exist for the HET, but the HET has been used extensively in the study of piping and internal erosion, and it is a key component of Reclamation's internal erosion risk toolbox. Both tests can be performed in the laboratory using remolded or undisturbed tube samples, and the jet test can also be performed in situ.
Through Dam Safety Office research funding ($188,000 in FY 2007 and FY 2008), Reclamation has recently made significant improvements to our hole erosion test facilities and has studied the correlation between jet and hole erosion test results. This work has brought us to a point where both tests could now be valuably applied to a variety of cohesive sediment erosion modeling problems in Reclamation, but their utility has only been demonstrated thus far in applications related to dam safety.
The primary benefit of applying these tests would be an improved accuracy and reduced uncertainty of results obtained from erosion and sediment transport modeling efforts. The availability of these tests would allow analysts to measure erodibility instead of predicting it by correlation with other variables.
Contact the Principal Investigator for information about these documents.