The Science of Instream Flows A Review of the Texas Instream Flow Program (2005) / Chapter Skim
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5 Evaluation of the Texas Instream Flow Technical Overview Document
5 Evaluation of the Texas Instream Flow Technical Overview Document
Pages 75-109
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From page 75... ...
OVERVIEW OF TOD CONTENT The TOD describes the methods to be used to collect, analyze, and integrate technical information among hydrologic, biologic, physical processes, and water quality aspects of instream flow study. The TOD is a fairly detailed document (74 pages)
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From page 76... ...
In the context of the state mandate to maintain a "sound ecological environment," the ecological setting of rivers is described. Biology, hydrology and hydraulics, geomorphology, water quality, and connectivity are defined and introduced as the components of an instream flow study.
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From page 77... ...
Water Quality Water quality is unlike the other technical aspects of instream flow study in Texas because it is regulated at the federal and state levels. There are several well established water quality programs in Texas.
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From page 78... ...
Integration and Interpretation Findings from the technical evaluations (i.e., biology, physical processes, hydrology and hydraulics, and water quality) will be integrated to develop a flow recommendation.
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From page 79... ...
surface water quality monitoring procedures and lists elements deemed important for a comprehensive monitoring program. STRENGTHS OF AND OPPORTUNITIES TO IMPROVE THE TOD The TOD sets out to prescribe the technical aspects, including methodologies, for conducting the detailed technical evaluations in the Texas instream flow program.
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From page 80... ...
Technical areas of hydrology and hydraulics, physical processes, biology, water quality and connectivity are recognized as important elements and described in the TOD. The TOD also includes initial approaches for integrating results into a flow recommendation.
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From page 81... ...
Three other overarching findings come from evaluating the TOD. First, for each technical evaluation (i.e., hydrology/hydraulics, physical processes, biology, and water quality)
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From page 82... ...
It is unclear in the TOD whether the spatial scale of the hydrologic/hydraulic studies coincides with the spatial scales of the biology, physical processes, or water quality empirical studies. A stronger connec
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From page 83... ...
For some distance below a dam, a river's hydrology, water quality, substrate, and biota will be greatly affected by the dam's operation. The TOD also does not discuss how instream flow characteristics may change due to watershed and land use changes, such as increases in urbanization, irrigation, and impervious surface area in the watershed.
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From page 84... ...
Biology, physical processes, and water quality aspects of instream flow work all can be tied to components of the hydrologic regime. Indeed, the TOD and PWP suggest strongly that the intention of the Texas program is to capitalize on these naturally occurring connections to develop a strong, comprehensive instream flow program for the state.
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From page 85... ...
However, the TOD Biology section gives a limited description of the program's rationale and plans for implementing alternative methods for field sampling, data analysis, and derivation of flow recommendations. The connection between the biological surveys and goals of the instream flow program or of individual studies is not discussed in this section.
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From page 86... ...
Before being used to monitor the effectiveness of the Texas instream flow program, the Texas regionalized IBIs should be evaluated for application to instream flow studies and larger rivers. These evaluations should be published in the open, peer-reviewed scientific literature as a means to validate the Texas approach.
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From page 87... ...
For example, the TOD states that microhabitat utilization data will be collected quantitatively, but seining and electrofishing are unlikely to provide information at this fine spatial scale in any systems except the smallest streams. The TOD does not outline how these specific methods can be standardized across different size streams and various geographic regions across the state.
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From page 88... ...
The TOD should be revised to more strongly emphasize riparian habitats as elements of a sound ecological environment, augment the methods presented for riparian surveys, and present ways to relate riparian sampling results to flow needs necessary to maintain a sound ecological environment in Texas rivers. Instream Habitat Models The TOD presents instream habitat models (Section 5.3)
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From page 89... ...
In some cases, the potential severity of ecological risks or the complexity of the ecological setting may demand multiple approaches, some perhaps involving considerable investment of time and resources, to provide sound recommendations. Rather than attempt to apply a diverse set of methodologies to project responses by a diverse set of biological response variables at a diverse set of spatial and temporal scales, the instream flow program should develop consistent study plans using the fewest possible biological response indicators to derive defensible flow recommendations.
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From page 90... ...
After the hydrology component, the channel geometry may be the most important component of an instream flow study, but the TOD gives physical processes very cursory treatment. This section is noticeably shorter and less comprehensive than the hydrology/hydraulics, biology, and water quality technical segments, and it needs
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From page 91... ...
Compilation of data in a geospatial data base structure and use of a GIS to store, display, and analyze data for all parts of the study will improve the quality of the study and also provide documentation for subsequent review, reassessment and adaptive management. A GIS database should be used for data storage and analysis in instream flow studies and the instream flow program at the state level.
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From page 92... ...
or losing (supply water to groundwater sources) water can be critical in determining whether sufficient flows are provided for physical processes as well as aquatic and riparian biological needs.
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From page 93... ...
Trends in TABLE 5-1 Morphological Indicators of Geomorphic Equilibrium Status Equilibrium Status Morphological Indicators Aggrading Abundant bars Low bank height to floodplain surface Active sediment deposition on floodplain surface Recently developed side channels May be braided Incising Very low width:depth ratio High bank height Unstable banks, failure through mass movement Bed is erosional on fine sediment, gravel, or bedrock Relatively dry floodplain with low water table Degrading through widening Large width:depth ratio Wide bed with little inundation in low flow season, but few active bars Armored or embedded gravel bed Dynamic equilibrium Intermediate in characteristics listed above
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From page 94... ...
Sediment transport and related hydrogeomorphic processes are discussed in TOD Section 6.4, with some emphasis on valley maintenance, riparian maintenance, channel maintenance and flushing flows. The TOD appropriately underscores the importance of sediment transport and deposition among the physical processes necessary for maintaining a sound ecological environment.
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From page 95... ...
The TOD recognizes three key discharge levels linked to physical processes that should be evaluated in the physical processes evaluations: floodplain maintenance, flushing flows, and channel maintenance. These terms are broad, perhaps too broad to be useful, and a more detailed breakdown of ecological and management objectives may be more helpful in instream flow studies (Kondolf and Wilcock, 1996)
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From page 96... ...
Currently, the TOD sets forth a thin, single set of analytical approaches for physical processes in Texas rivers that are unlikely to address the range or complexity of physical processes that exist. Recommendations for addressing physical process concerns include: Augmenting this section to equal in detail the hydrology and hydraulics and biology sections and to discuss Texas hydrologic regimes, GIS applications, sediment budget methods, and impacts of changes in land use, population, and climate in the watershed over time.
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From page 97... ...
Current water quality models can be used for discrete aspects of instream flow studies, but no current model exists that can model all water quality elements needed in an instream flow evaluation. The TOD section on water quality contains a summary of each of the TCEQ water quality programs, and also of the Texas water availability modeling program.
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From page 98... ...
If "a sound ecological environment" for instream flows differs from "ecological integrity" used in water quality assessment, the TCEQ Commissioners could be faced with two separate sets of requirements for assessing the ecological conditions of Texas streams and rivers. At a minimum, the existing Aquatic Life Use goals should be considered in implementing instream flow recommendations to avoid conflict or even establish support between the water quality and instream flow programs.
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From page 99... ...
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From page 100... ...
TMDLs include point- and non-point sources, such as pollution from watershed runoff, atmospheric deposition, and contaminated sediments. The Texas TMDL program relies on water quality models that estimate nutrient, bacterial, and other pollutants in surface waters.
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From page 101... ...
Although some of the other water quality models are dynamic and offer a greater range of possible bed geometries than QUAL-TX, the other models used in the TMDL program still employ spatial computational units of the same order of size as QUAL-TX. It might be possible through field scale research to quantify the spatial and temporal variations of dissolved oxygen within a reach so that with a daily and reach-averaged dissolved oxygen concentration available, some type of "down scaling" process could be applied to infer the spatial and temporal patterns of dissolved oxygen at the meso- and microhabitat scale.
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From page 102... ...
. Summary: Water Quality While just as important as hydrology and hydraulics, biology, and physical processes in a Texas instream flow program, water quality is treated differently than its sibling components.
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From page 103... ...
The water quality component of the Texas instream flow program reflects the existing strengths of the Texas water quality management program. These strengths include a comprehensive water quality database for Texas streams and rivers, an established set of water quality standards, and procedures for assessing compliance with them, including standards for aquatic life.
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From page 104... ...
A more comprehensive method is needed for storing all the biological and physical data acquired during Aquatic Life Use assessments, and a more complete digital inventory of biological data on the past condition of Texas streams and rivers needs to be compiled. The instream flow program should be integrated with water quality, water permitting and other water-related programs in Texas to avoid conflict or establish support between the water quality and instream flow programs.
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From page 105... ...
are used to derive flow recommendation is not well described; and (4) the integration of biology and hydraulics is given far more attention than the other technical aspects of water quality, physical processes, and hydrology.
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From page 106... ...
The instream habitat models focus exclusively on integrating hydraulics with biology, and leaves unclear whether any models can be used to integrate hydrology, water quality, and physical processes. Quantitative Analysis Aside from a passing reference to statistical and time series analyses, the section on quantitative analyses (Section 8.7)
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From page 107... ...
and quantitative tools can be helpful to derive a flow recommendation, and some of those tools are introduced in this section. The Integration and Interpretation section of the TOD needs significant revision to: correspond more strongly to the methods presented in the biology, hydrology and hydraulics, water quality and physical processes sections of the TOD; revise the Integration Framework to include sequential steps and clearer direction of how to combine results from the technical evaluations with appropriate models to derive flow recommendations; and augment sections on integrating Hydrology (Section 8.3)
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From page 108... ...
design the biological, physical processes water quality, and hydrology and hydraulics instream flow studies at commensurate spatial and temporal scales to improve the ability to integrate findings from the various technical evaluations into a single flow recommendation; 4) strengthen the physical processes section to align more closely with the hydrology and hydraulics and biology sections; 5)
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From page 109... ...
4) The instream flow program should be integrated with water quality, water permitting and other water-related programs in Texas to avoid conflict between the water quality and instream flow programs.
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