The Science of Instream Flows A Review of the Texas Instream Flow Program (2005) / Chapter Skim
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3 An Introduction to Instream Flow Science and Programs
3 An Introduction to Instream Flow Science and Programs
Pages 32-57
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From page 32... ...
" Instream flow programs help water managers meet management goals of biology, municipal water supply, or water quality considerations. The Instream Flow Council (IFC)
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From page 33... ...
Subsistence flow is the minimum streamflow needed during critical drought periods to maintain tolerable water quality conditions and to pro vide minimal aquatic habitat space for the survival of aquatic organisms. Base flow is the "normal" flow conditions found in a river in between storms, and base flows provide adequate habitat for the support of diverse, native aquatic communities and maintain ground water levels to support riparian vegetation.
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Oct. FIGURE 3-1 Daily streamflow hydrograph for Guadalupe River at Victoria, TX, with base flows, subsistence flows, high flow pulses, and overbank flows identified.
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Principles of Instream Flow Science There are several principles of effective instream flow programs included in the IFC's Instream Flows for Riverine Resource Stewardship (2002) and Postel and Richter (2003)
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Both technical and nontechnical components are important in a state-of-the-art-instream flow program; otherwise, untenable situations can occur. For example, the most scientifically valid instream flow recommendation will not be implemented if it violates a permitting process, is out of compliance with water quality regulation, or lacks public support in the river basin.
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Stakeholder input can occur at several stages in an instream flow program. The public can participate in authorizing legislation, setting goals, and approving or commenting on instream flow recommendations.
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Hydrology and Hydraulics Hydrology is potentially the most critical element of instream flow studies and has been considered the "master variable" because the biology, physical processes, and water quality components directly relate to it (Poff et al., 1997)
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Other subjects of physical processes technical evaluations are listed in Table 3-1. Water Quality The primary assays of water quality in most instream flow studies are sediment and total suspended solids (TSS)
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Flow regime Are the available streamflow data sufficient to character ize annual and seasonal flow variability including the probability of floods or droughts? What is known about the magnitude, frequency, timing, and duration of base flows, subsistence flows, high flow pulses, and overbank flows?
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Flow regime What are the important connections to reservoirs or floodplains? Species of concern What species (fish, birds, mammals, invertebrates, aquatic plants or riparian vegetation)
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Species of concern What water quality components are of greatest concern to the target organisms, life stages, or riverine proc esses (DO, suspended sediment, temperature, chemical elements, nutrients)
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Conceptual Models Often, technical evaluations are conducted independently of each other and the results subsequently combined into a single flow recommendation. A more efficient approach is to design the technical evaluations such that each sampling or modeling effort is tied directly to program goals; and the results of these evaluations are connected to aspects of the flow regime (Postel and Richter, 2003)
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From page 44... ...
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From page 45... ...
Many types of models can be and are applied to instream flow science. Hydrologic and hydraulic models, water quality models, sediment dynamics models, and biological habitat and life stages models are often presented as reliable approaches to derive flow recommendations (see IFC, 2002 for an exhaustive list of models)
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From page 46... ...
Figure 3-2 represents an example of an integrated hydrograph based upon the building blocks of subsistence flows, base flows, high flow pulses, and overbank flows. The building block approach is particularly useful in river basins that have experienced considerable water development like dam construction.
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From page 47... ...
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From page 48... ...
This approach is particularly useful in river basins in which much of the natural flow volume and seasonal patterning remains and instream flow goals aim to mimic the natural ecosystem character. Although integration of the technical pieces leads to the quantitative flow recommendation, the integration phase should also account for legal, institutional and/or socioeconomic issues that may influence the implementation of the instream flow recommendation.
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From page 49... ...
Therefore, a commitment to long- term monitoring, and anticipation that methods and flow recommendations may need revision over several years, are hallmarks of an adaptable instream flow program. INSTREAM FLOW EXAMPLES Many state instream flow programs have been in place for years.
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From page 50... ...
illustrates the utility of "critical flows" in determining instream flow recommendations. Existing Methods for Defining Instream Flow Requirements in Texas Texas currently has two hydrologic methods for defining instream flow requirements; one for water permitting (Lyons method)
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. Flow Recommendations for the Savannah River The instream flow work in the Savannah River in Georgia and South Carolina began in 2002 and continues today.
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The Savannah River project is on-going, and it is too soon to determine the degree to which the flow recommendations have achieved the goals of the project. Still, the process of developing goals and deriving flow recommendations used in the Savannah River project shows how stakeholders and scientists can collaborate successfully on instream flow studies.
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From page 53... ...
drawn together to provide instream flow recommendations for the Colorado River below Austin, TX. The instream flow study was undertaken in response to a condition mandated in the 1988 adjudication of the Lower Colorado River Authority's (LCRA)
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From page 54... ...
is a valuable guide as to how similar studies could be undertaken in those rivers. RESEARCH NEEDS FOR INSTREAM FLOW SCIENCE Instream flow science continues to evolve in its philosophy and application.
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In instream flow science, integration combines the different technical components into one recommendation or a set of flow recommendations. Integration is an important, complicated step in the instream flow process.
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Indicators are measurable quantities or variables that can be used to determine the degree that flow recommendations achieve the goals of the instream flow study or program. Indicators are important role in long-term instream flow monitoring and adaptive management.
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From page 57... ...
Instream flow programs will encompass technical evaluations in biology, hydrology and hydraulics, physical processes, water quality, connectivity, and non-technical aspects of stakeholder involvement and goal setting. Integrating technical evaluations into a flow recommendation is an important, challenging task with few well documented methods.
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