Critical Review of Sediment Plug Formation Hypotheses

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Sediment plugs have occurred several times on the Rio Grande in the past 20 years, primarily near the Tiffany Basin where plugs were observed in 1991, 1995 and 2005. In 2008, however, a plug formed farther upstream in the reach of the Rio Grande within the Bosque del Apache National Wildlife Refuge. Sediment plugs present significant challenges for river maintenance on the MRG as they diminish effective water delivery and increase the risk of spoil levee failure. Spoil levees are the current primary flood control protection for the Rio Grande Valley south of Socorro, New Mexico. Conversely, the formation of sediment plugs tends to be a boon for avian species (specifically the southwestern willow flycatcher) due to the abundance of overbanking flows. Understanding the mechanics behind plug formation is crucial to balance these diverse needs. At this time, numerous hypotheses have been proposed in an attempt to explain how and why these sediment plugs form. Given the fact that sediment plugs have formed at different locations and at different times, some of these hypotheses may be viable while others may be pure speculation. The objective of the proposed work would be to critically review the numerous hypotheses that have been proposed to describe the causes of the formation of sediment plugs and identify those that are most viable. This will help provide a better understanding of the mechanics behind sediment plug formation. This may lead to better management of the conditions that affect sediment plug formation, maximizing the environmental benefits, while minimizing the risks for river maintenance on the Middle Rio Grande.

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