Recognition of the escalating hydrological alteration of rivers on a global scale and resultant environmental degradation, has led to the establishment of the science of environmental flow assessment whereby the quantity and quality of water required for ecosystem conservation and resource protection are determined.

A global review of the present status of environmental flow methodologies revealed the existence of some 207 individual methodologies, recorded for 44 countries within six world regions. These could be differentiated into hydrological, hydraulic rating, habitat simulation and holistic methodologies, with a further two categories representing combination-type and other approaches.

Although historically, the United States has been at the forefront of the development and application of methodologies for prescribing environmental flows, using 37% of the global pool of techniques, parallel initiatives in other parts of the world have increasingly provided the impetus for significant advances in the field.

Application of methodologies is typically at two or more levels. (1) Reconnaissance-level initiatives relying on hydrological methodologies are the largest group (30% of the global total), applied in all world regions. Commonly, a modified Tennant method or arbitrary low flow indices is adopted, but efforts to enhance the ecological relevance and transferability of techniques across different regions and river types are underway. (2) At more comprehensive scales of assessment, two avenues of application of methodologies exist. In developed countries of the northern hemisphere, particularly, the instream flow incremental methodology (IFIM) or other similarly structured approaches are used. As a group, these methodologies are the second most widely applied worldwide, with emphasis on complex, hydrodynamic habitat modelling. The establishment of holistic methodologies as 8% of the global total within a decade, marks an alternative route by which environmental flow assessment has advanced. Such methodologies, several of which are scenario-based, address the flow requirements of the entire riverine ecosystem, based on explicit links between changes in flow regime and the consequences for the biophysical environment. Recent advancements include the consideration of ecosystem-dependent livelihoods and a benchmarking process suitable for evaluating alternative water resource developments at basin scale, in relatively poorly known systems. Although centred in Australia and South Africa, holistic methodologies have stimulated considerable interest elsewhere. They may be especially appropriate in developing world regions, where environmental flow research is in its infancy and water allocations for ecosystems must, for the time being at least, be based on scant data, best professional judgement and risk assessment. Copyright © 2003 John Wiley & Sons, Ltd.

http://www.swrcb.ca.gov/waterrights/water_issues/programs/bay_delta/deltaflow/docs/exhibits/swrcb/swrcb_tharme2003.pdf

A global perspective on environmental flow assessment: emerging trends in the development and application of environmental flow methodologies for rivers

The physical component of river channel (instream) habitat is of acknowledged significance, particularly in headwater streams; furthermore, physical habitats have been heavily impacted by human nee...

Geomorphology, ecology and river channel habitat: mesoscale approaches to basin-scale challenges:

Variations in terrestrial water storage affect weather, climate, geophysical phenomena, and life on land, yet observation and understanding of terrestrial water storage are deficient. However, estimates of terrestrial water storage changes soon may be derived from observations of Earth's time-dependent gravity field made by NASA's Gravity Recovery and Climate Experiment (GRACE). Previous studies have evaluated that concept using modeled soil moisture and snow data. This investigation builds upon their results by relying on observations rather than modeled results, by analyzing groundwater and surface water variations as well as snow and soil water variations, and by using a longer time series. Expected uncertainty in GRACE-derived water storage changes are compared to monthly, seasonal, and annual terrestrial water storage changes estimated from observations in Illinois (145,800 km2). Assuming those changes are representative of larger regions, detectability is possible given a 200,000 km2 or larger area. Changes in soil moisture are typically the largest component of terrestrial water storage variations, followed by changes in groundwater plus intermediate zone storage.

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An analysis of terrestrial water storage variations in Illinois with implications for the Gravity Recovery and Climate Experiment (GRACE)

Illinois State Water Survey

Hydraulic geometry of stream reaches

Quantification of the relationship between stream discharge and the availability of suitable aquatic habitat requires detailed information on the values of local depths and velocities as they vary through riffles and pools. Conventional flow models are inadequate to supply the needed information. A basin model is presented which provides a new approach to basinwide flow modeling for stream habitat evaluation. Streams within a basin exhibit similar patterns of development, varying in scale with the drainage area. Average width, depth, and velocity increase in a predictable way with drainage area and discharge. Hydraulic geometry relations define the average values of width, depth, and velocity for any stream in the basin. Local variations of depth and velocity about the average are evaluated from probability distribution models developed from field measurements made throughout riffle and pool sequences. The basin flow model provides the needed hydraulic data to apply the Instream Flow Incremental Methodology (a state-of-the-art methodology for stream habitat evaluation) of the U.S. Fish and Wildlife Service.

Hydraulic Geometry of Streams and Stream Habitat Assessment

/pdf/adequacy-of-illinois-surface-water-supply-systems-to-meet-51t2tvagka.pdf

Adequacy of Illinois Surface Water Supply Systems to Meet Future Demands

Future Water Demands of Public Surface Water Supply Systems in Illinois

Quantification of sufficient or minimum flows needed to sustain the aquatic habitat is necessary for satisfactory resolution of water use conflicts and planning of water allocation strategies. The Instream Flow Group (IFG) of the U.S. Fish and Wildlife Service has developed a methodology to gage the quantity of suitable habitat in a stream. Application of this methodology has been limited because conventional flow models are inadequate to simulate the detailed hydraulic information needed. Currently, evaluation of aquatic habitats requires extensive field work foreach reach studied. There is no methodology for extending results to other reaches with dissimilar drainage areas. A basin flow model was developed which provides the hydraulic information needed to evaluate the aquatic habitat of all streams within a hydrologically homogeneous basin. The model uses hydraulic geometry relations to compute average flow parameter values for unmeasured streams. The variability of reach average conditions with respect to basinwide average conditions for similar drainage area streams was investigated and adjustment factors were developed defining the range of possible parameter values. Information on the local variations of depth and velocity through riffles and pools is needed to evaluate aquatic habitats. This information is obtained from probability distribution models developed from field data collected on the Sangamon and South Fork Sangamon River Basins. Stream habitat suitability calculations using the basin flow model with the IFG methodology are illustrated. Singh, Krishan P., Broeren, Sally McConkey, and King, Robin B. INTERACTIVE BASINWIDE MODEL FOR INSTREAM FLOW AND AQUATIC HABITAT ASSESSMENT--Project Completion Report to the Division of Water Resources, Illinois Department of Transportation, August 1986, Champaign, Illinois, 101 p. KEYWORDS--instream flow/ aquatic habitats/ stream fisheries/ channel morphology/ physical models/ simulation/ habitat suitability/ incremental methodology

Sally McConkey Broeren

Papers

Hydraulic Geometry of Streams and Stream Habitat Assessment

Adequacy of Illinois Surface Water Supply Systems to Meet Future Demands

Future Water Demands of Public Surface Water Supply Systems in Illinois

Interactive Basinwide Model for Instream Flow and Aquatic Habitat Assessment

Mitigative Measures for At-risk Public Surface Water Supply Systems in Illinois