flow regime alteration

A Method for Assessing Hydrologic Alteration within Ecosystems

Volume: 
Vol.10(4) 1163-1174
Year: 
1996
Abstract: 

Hydrologic regimes play a major role in determining the biotic composition, structure, and function of aquatic, wetland, and riparian ecosystems. But human land and water uses are substantially altering hydrologic regimes around the world. Improved quantitative evaluations of human-induced hydrologic changes are needed to advance research on the biotic implications of hydrologic alteration and to support ecosystem management and retoration plans. We propose a method for assessing the degree of hydrologic alteration attributable to human influence within an ecosystem. This method, referred to as the "Indacators of Hydrologic Alteration," is based upon an analysis of hydrologic data available either from existing measurment points within an ecosystem (such as at stream gauges or wells) or model-generated data. We use 32 parameters, organized into five groups, to statistically characterize hydrologic variation within each year. These 32 parameters provide information on ecologically significant features of surface and ground water regimes influencing aquatic, wetland, and riparian ecosystems. We then asses the hydrologic pertubations associated with activities such as dam operations, flow diversion, groundwater pumping, or intensive land-use conversion by comparing measures of central tendency and dispersion for each parameter between user-defined "pre-impact" and "post-impact" time frames, generating 64 indacators of Hydrologic Alteration. This method is intended for use with other ecosystem metrics in inventories of ecosystem integrity, in planning ecosystem management activities, and in setting and measuring progress toward conservation or restoration goals.

Author(s): 

Richter , B.D. , Baumgartner , J.V., Powel , J

Contact: 

Richter, Brian, The Nature Conservancy, FWI

Notes: 
Category: 

The natural flow regime: a paradigm for river conservation and restoration

Volume: 
Vol. 47(11) 769-784
Year: 
1997
Abstract: 

The extensive ecological degradation and loss of biological diversity resulting from river exploitation is eliciting widespread concern for conservation and restoration of healthy river ecosystems. Current management approaches often fail to recognize the fundamental scientific principle that the integrity of flowing water systems depends largely on their natural dynamic character, i.e. the natural flow regime. This natural flow regime varies on a wide range of time scales and includes five critical components: magnitude, frequency, duration, timing, and rate of change of hydrologic conditions. Together, these components can characterize the entire range of flows and specific hydrologic phenomena. Human alteration of the natural hydrologic processes disrupts the dynamic equilibrium of a river. Dams are among the most obvious and prevalent disruptions. Effects of this disruption are not only physical, but ecological in nature. Recent management approaches have taken into account the flow needs of only a few specific economically or recreationally important species. Furthermore, these approaches have focused solely on "minimum flow" requirements for a given system. The authors argue that implementation of a more sophisticated assessment of the needs of the river system, in the form of the Instream Flow Incremental Methodology (IFIM), will allow for management plans to move towards a natural flow regime that is beneficial for the entire ecosystem, not simply high profile species. Examples and suggestions as to implementation of these types of management strategies are given.

Author(s): 

Poff , N.L , Allan , D.J. , Bain , M.B.

Contact: 
Notes: 

American Rivers produced abstract

Category: 

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.

Contact: 
Notes: 
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