Evaluation of Gage Based Cross Section Data to Represent Habitat Conditions for Riverine Resources at the Reach Level Page: 1
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At-a-station hydraulic properties from multiple gages in all eleven major river drainages across
several Ecoregions in Texas were evaluated in light of similarities and differences both over time
and from gages on the same longitudinal river segment. The relationship between cross sectional
area and discharge was the most consistent in terms of both temporal and spatial scales. Both
width and to a larger degree, velocity relationships with changes in discharge was greater
spatially and temporally. Previous work that was reviewed clearly indicate that reach average at-
a-station exponents of the continuity equations do not reflect the values from specific locations
within a river reach. An examination of variability in channel morphology and the relationship
in the velocity magnitudes and characteristics between runs (i.e., gage locations) and run versus
riffle habitat showed a large difference. Given that velocity profiles are the most sensitive
parameter in estimating fisheries habitat in instream flow assessments it is unlikely that use of at-
a-station hydraulic parameters from gage locations can be utilized to assess reach level fisheries
The principal research question of this project was to explore if available data at gage locations
allow for inference of hydraulic habitat characteristics at the reach scale that could inform the
evaluation of instream flow regimes. Reviews of instream flow programs in Texas, including the
National Research Council (2005) and Science Advisory Committee (2009), recognized the
potential benefit of desk-top methods (i.e. those that can be applied using generally readily-
available data and information without conducting site-specific field studies). The majority of
such methods are based exclusively on statistical relationships derived from hydrologic data.
There have been only limited attempts to validate these methods for use in Texas. The Lyons
Method, often relied on by Texas Commission on Environmental Quality to evaluate small water
rights permits or amendments across the state, was developed based on cross-section data
collected from only two locations on the Guadalupe River in Central Texas. To date, attempts to
find improved desktop methods for use in Texas have focused on methods that employ only
hydrologic data. One such attempt, the Technical Review Group that reported to Texas
Commission on Environmental Quality (2008), was unsuccessful in finding a method
significantly better than the Lyons Method. Through collaborative discussions with the Texas
Water Development Board, the project focused on investigating the potential use of information
collected at gage stations to inform relationships between available habitat and discharge at the
reach level for use in evaluating ecological flow regimes. The rationale behind this approach in
part is that from a regulatory perspective, water rights are associated with specific locations (i.e.,
gages) that determine flow levels at the corresponding downstream reaches. If it were possible
to make inferences of the relationship between habitat characteristics at the reach level based on
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Hardy, Thomas B., Dr. Evaluation of Gage Based Cross Section Data to Represent Habitat Conditions for Riverine Resources at the Reach Level, report, May 10, 2015; San Marcos, Texas. (texashistory.unt.edu/ark:/67531/metapth838905/m1/3/: accessed November 18, 2018), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting UNT Libraries Government Documents Department.