Identifying Indicators and Guides for Sustainability of Pools in Gravel-bed Rivers
Gravel-bed rivers are an important habitat for salmonids, which are at risk throughout the Northwestern United States and are the focus of extensive environmental legislation and litigation. The pool-riffle morphology in gravel-bed rivers is particularly important because the diversity in physical habitat in these reaches is critical for spawning and other life stages.
A hypothesis to explain the persistence of pools has been that of "velocity reversal." The occurrence of velocity reversals has been controversial for over three decades, but a recent study developed a simple criterion that unifies and explains previous disparate findings regarding the occurrence of velocity reversals (CaamaÃ±o, D., P. Goodwin, J.M. Buffington, J.C. Liou, and S. Daley-Laursen, 2009. A unifying criterion for velocity reversal hypothesis in gravel-bed rivers. The Journal of Hydraulic Engineering, American Society of Civil Engineers [ASCE] 135(1). 66-70.) The criterion uses simple measurements that can easily be collected in the field (tape for measuring channel width and survey rod for measuring the thalweg depth). Preliminary results from the Red River Wildlife Management Area monitoring program show that reversal depends critically on the ratio of riffle-to-pool width, residual pool depth (difference between pool and riffle elevations), and on the depth of flow over the riffle.
Verifying these criteria for a broader range of field conditions could develop very useful equations and establish guidelines for designing restoration projects that would supplement effective discharge and hydraulic geometry information to allow rapid assessment of pool habitat vulnerability, particularly under potential changes to annual streamflow characteristics due to climate change. These parameters could also be useful in lieu of, or as a supplement to, a more detailed modeling exercise of restoration alternatives.
Need and Benefit
The Columbia and Snake River Salmon Recovery Office (CSRO) receives Federal monies to improve and restore salmonid habitat impacted by the construction of Federal dams. These mitigation efforts include the design of specific habitat features for various life stages of salmonids in various streams or rivers identified throughout the Northwestern United States.
Criteria and knowledge gained from this project have the potential to provide design guidelines, assess the need for engineered features, and provide a means for determining design success metrics.
As a result, the CSRO supports this proposed research project to establish criteria and guidelines that can be used in the design of sustainable pools in gravel-bed rivers. The results of this investigation have wide-reaching applicability for instream habitat projects in subbasins funded by the CSRO as well as Bureau of Reclamation-wide habitat projects.
Pacific Northwest Regional Office, Pacific Northwest Region
The following documents were not reviewed. Statements made in these documents are those of the authors. The findings have not been verified.
Field Evaluation of a Pool Sustainability Predictor in Gravel Bed Rivers (interim, PDF,
By Sharon Parkinson
Publication completed on July 07, 2011
Flow Structure and Sustainability of Pools in Gravel-bed Rivers (final, PDF,
By Sharon Parkinson
Report completed on May 14, 2014
igating for dam construction. The velocity reversal hypothesis (Gilbert, 1914, Keller 1971, 1972) has been used as a potential mechanism for the sustainability of pools.