Science/Ecology

Effective Discharge and the Design of Channel Maintenance Flows for Gravel-Bed Rivers

Volume: 
Vol. 89( ) 151-164
Year: 
1995
Abstract: 

Water resource developments which deplete the quantity or reduce the range of streamflows usually have a number of unintended effects on the channel downstream, including loss of channel capacity, loss of aquatic and riparian habitat, and channel instabilities. A method for identifying a flow regime sufficient to maintain desired stream characteristics, while permitting significant development, would have great practical value. over the past decade, important advances have been made in our understanding of fluvial processes in gravel-bed streams. Using these advances as a basis, one can outline a method for determining channel maintenance flows for gravel-bed streams typical to the western United States. A common characteristic of gravel-bed streams is that bed particles are transported only about 5-10 percent of the time during the highest flows, and, even then, at a very low rate. Although occasional motion of bed particles begins at a discharge as small as 60 percent of the bankfull value, general motion of the bed surface is exceedingly rare. The proposed method relies on an appropriate bedload transport function and specific reach of discharge in the pre- and post-regulation regimes. Evaluation of possible flow regimes indicates that bankfull channel capacity can be maintained in its pre-regulation condition where as much as 60 percent of the natural flows are diverted.

Author(s): 

Andrews, E.D., Nankervis, J.M.

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Instream flow needs in streams and rivers: the importance of understanding ecological dynamics

Volume: 
Vol. 4, pp. 309-318
Year: 
2006
Abstract: 

Resource managers have traditionally had to rely on simple hudrological and habitat-association methods to predict how changes in river flow regimes will affect the viability of instream populations and communities. Yet these systems are characterized by dynamic feedbacks among system components, a high degree of spatial and temporal variability and connectivity between habitats, none of which can be adequately captured in the commonly employed management methods. We argue that process-oriented ecological models, which consider dynamics across scales and levels of biological organizaion, are better suited to guide flow regime management. We review how ecological dynamics in streams and rivers are shaped by a combination of the flow regime and internal feedbacks, and proceed to describe ecological modeling tools that have the potential to characterize such dynamics. We conclude with a suggested research agenda to facilitate the inclusion of ecological dynamics into instream flow needs assessments.

Author(s): 

Anderson, K.E., Paul, A.J., McCauley, E,L. J. Jackson, J. R. Post, and R. M. Nisbet

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Prioritizing Pacific Salmon Stocks for Conservation

Volume: 
Vol. 11, No. 1, pp. 140-152
Year: 
1997
Abstract: 

Over 300 native stocks of Pacific salmon, steelhead, and coastal cutthroat trout (Oncorhynchus spp.) are at risk of extinction in the Pacific Northwest. With only limited resources available for conservation and recovery, prioritization of these stocks may become necessary of meaningful measures are to be implemented. We propose criteria by which prioritization may be guided. First, we rank stocks for risk of extinction, either by population viability analysis or by a set of surrogate measures. Then we rank stocks for biological consequences of extinction, using sets of questions designed to establish the genetic and evolutionary consequences and the ecological consequences if a stock were to become extinct. Together, these rankings allow stocks to be prioritized for a range of possible actions, with those stocks at highest risk and bearing the greatest biological consequences of extinction receiving attention first. Application of the prioritization process to 20 Pacific anadromous salmonid stocks worked as intended, although data limitations are considerable. The process is most likely to work successfully when applied to many stocks on which data exist, when several experts carry out the prioritization and then the results are peer reviewed.

Author(s): 

Allendorf, F.W., Leary, R.F., Spruell, P,J. K. Wenburg

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The problems with hybrids: setting conservation guidelines

Volume: 
Vol. 16, pp. 613-622
Year: 
2001
Abstract: 

Rates of hybridization and introgression are increasing dramatically worldwide because of translocations of organisms and habitat modifications by humans. Hybridization has contributed to the extinction of many species through direct and indirect means. However, recent studies have found that natural hybridization has played an important role in the evolution of many plant and animal taxa. Determining whether hybridization is natural or anthropogenic is crucial for conservation, but is often difficult to achieve. Controversy has surrounded the setting of appropriate conservation policies to deal with hybridization and introgression. Any policy that deals with hybrids must be flexible and must recognize that nearly every situation involving hybridization is different enough that general rules are not likely to be effective.We provide a categorization of hybridization to help guide Rates of hybridization and introgression are increasing dramatically worldwide because of translocations of organisms and habitat modifications by humans. Hybridization has contributed to the extinction of many species through direct and indirect means. However, recent studies have found that natural hybridization has played an important role in the evolution of many plant and animal taxa. Determining whether hybridization is natural or anthropogenic is crucial for conservation, but is often difficult to achieve. Controversy has surrounded the setting of appropriate conservation policies to deal with hybridization and introgression. Any policy that deals with hybrids must be flexible and must recognize that nearly every situation involving hybridization is different enough that general rules are not likely to be effective.We provide a categorization of hybridization to help guide management decisions.

Author(s): 

Allendorf, F.W., Bayles, D., Bottom, D.L.,K.P. Currens, C.A. Frissell, D. Hankin, J.A. Lichatowich, W. Nehlsen, P.C. Trotter, T.H. Williams

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