Understanding Ecological Responses to Hydrologic Alteration in Streams and Rivers I
Presiding: M Gurtz, U.S. Geological Survey; M Freeman, U.S. Geological Survey
NB23C-01 INVITED 13:30h
Global Evolution in Water Management: Moving Toward Ecological Sustainability?
A variety of human activities are having substantial influence on hydrologic systems globally. Conversion of landscapes from natural vegetation cover to developed conditions has changed the nature and scale of hydrologic variability - including river flow regimes - to varying degrees, depending upon the nature of land development in a catchment. Human demands for water have more than doubled during the past half century and continue to increase as the human population swells globally. River flows are regulated using dams and reservoirs to store water supplies, generate power, and control floods. Alteration of natural river flow regimes has become a leading cause of the precipitous decline in freshwater ecosystems. Fortunately, advancements in river science during the past few decades provide the knowledge necessary to support river management that both sustains ecological integrity and meets human needs. Hundreds of tools and methods are now available for defining environmental flow needs and assessing these flow needs as an integral part of decision making in water management. These improvements in scientific knowledge and tools are supporting substantial changes in water policy and water management practices. This presentation will provide examples of change in water policy and management practices from around the world, and will highlight challenges in implementing ecologically sustainable water management.
http://www.freshwaters.org
NB23C-02 INVITED 14:00h
The Clean Water Act, Flow, and the Quest for Integrity of U. S. Waters
The federal Clean Water Act (Public Law 92-500, amended in 1977 and 1987) contains one of the broadest goals for ecological protection found in American environmental legislation: to restore and maintain the chemical, physical and biological integrity of U.S. waters. The act also refers to attaining water quality sufficient to propagate fish and wildlife and provides for a wide array of regulatory and non-regulatory protection tools. Despite the broad ecological connotations of its goals, its diverse toolbox, and its many successes, the Clean Water Act is not uniformly applicable to all forms of aquatic impairment because its most potent regulations are highly oriented toward controlling pollutants. Flow alterations and their biotic impacts are common examples of non-pollutant impairments that fit the Clean Water Act goal, but not its tools. Nevertheless, the lack of authority to regulate flow under the act has stimulated innovative, indirect approaches to the restoration of flow-related impairments. The presentation will address the limits of the Clean Water Act in addressing flow as well as a variety of examples of working within the scope of the act to overcome those limits.
NB23C-03 INVITED 14:15h
A Template for Conducting Ecosystem-Based Instream Flow Studies
Since the development of the first quantitative instream flow techniques in the 1970's and 1980's much has been learned about ecological processes of rivers. Though much remains to be learned, many technical tools or methods have been developed to incorporate that understanding into developing and applying instream flow prescriptions. However, most studies to date have focused on only one or a few of the several elements that affect biological processes and ecosystem needs of rivers. In a recent project by the Instream Flow Council, a template for conducting instream flow studies and improving strategies for riverine management was developed. That construct draws on existing facts and knowledge to emphasize that effective instream flow management should integrate 5 riverine components (hydrology, geomorphology, biology, water quality and connectivity), public education and involvement, and legal/institutional elements. This paper will illustrate the general characteristics of these various components, why it is important to integrate them all, and provide an example of how they might be addressed to improve the quantification of instream flow needs and protection of riverine resources.
http://www.InstreamFlowCouncil.org
NB23C-04 INVITED 14:30h
Process and Prospects for the Designed Hydrograph, Lower Missouri River
The flow regime of the Lower Missouri River (LMOR, Gavins Point, SD to St. Louis, MO) is being redesigned to restore elements of natural variability while maintaining project purposes such as power production, flood control, water supply, and navigation. Presently, an experimental hydrograph alteration is planned for Spring, 2006. Similar to many large, multi-purpose rivers, the ongoing design process involves negotiation among many management and stakeholder groups. The negotiated process has simplified the hydrograph into two key elements -- the spring rise and the summer low - with emphasis on the influence of these elements on three threatened or endangered species. The spring rise has been hypothesized to perform three functions: build sandbars for nesting of the interior least tern and piping plover, provide episodic connectivity with low-lying flood plain, and provide a behavioral spawning cue for the pallid sturgeon. Among these, most emphasis has been placed on the spawning cue because concerns about downstream flood hazards have limited flow magnitudes to those that are thought to be geomorphically ineffective, and channelization and incision provide little opportunity for moderate flows to connect to the flood plain. Our analysis of the natural hydrologic regime provides some insight into possible spring rise design elements, including timing, rate of rise and fall, and length of spring flow pulses. The summer low has been hypothesized to emerge sandbars for nesting and to maximize area of shallow, slow water for rearing of larval and juvenile fish. Re-engineering of the navigation channel to provide greater diversity of habitat during navigation flows has been offered as an alternative to the summer low. Our analysis indicates that re-engineering has potential to increase habitat availability substantially, but the ecological results are so-far unknown. The designed hydrograph that emerges from the multi-objective process will likely represent a compromise of many values and is unlikely to bear close resemblance to the natural hydrograph. Nonetheless, the hydrograph will provide an essential first step in experimentation and adaptive management of the Lower Missouri River.
NB23C-05 INVITED 14:45h
Biotic Responses to Flow Alteration in Streams: Science, Management, and Research Gaps
Stream hydrology has been altered directly via dams and water withdrawals, and indirectly via landscape alteration. Projected increases in freshwater demands will continue to affect stream ecosystem integrity, such as through losses in native species and altered productivity. Regulatory agencies are challenged with maintaining/restoring ecological integrity in streams while meeting water supply needs and accommodating development. The natural flow regime offers an overarching paradigm for maintaining stream ecosystem health. Based on this paradigm, agencies are looking for ways to manage withdrawals and dam releases that restore natural hydrologic variability. Similarly, management of urban growth has focused on mimicking natural precipitation infiltration patterns to maintain baseflows and reduce flashy stormflows. However, little is known about the mechanisms of hydrologic and hydraulic effects on biota in altered systems, and what aspects of the natural flow regime are required for species survival. Further, we do not know how much water can be withdrawn from streams and how much precipitation must be infiltrated in the landscape to maintain ecosystem integrity. We need to address these (and other) shortfalls in ecological knowledge, and assess costs and benefits of alternative management options in order to provide adequate freshwater for stream ecosystems and the growing human population.