Assessment of Hydrologic Alteration Software
Eric S. Hersh, CRWR
Table of Contents
·
Indicators of
Hydrologic Alteration
·
Hydroecological
Integrity Assessment Process
Introduction
Research currently being conducted at CRWR focuses on assessing the applicability of hydrologic analysis tools such as The Nature Conservancy’s Indicators of Hydrologic Alteration (IHA) and the United States Geological Survey’s National Hydrologic Assessment Tool (NATHAT) for use in the Texas Instream Flow Program (TIFP). These simple, desktop hydrologic tools use flow as an indicator variable for ecological and biological functions and processes.
(TIFP, 2006)
The project has included: (1) application and evaluation of the IHA and NATHAT tools; (2) characterization of the gaged and naturalized flow regimes at 24 gage sites representing the six priority study basins in the State of Texas (Lower Sabine, Middle Trinity, Middle and Lower Brazos, Lower Guadalupe, Lower San Antonio); (3) evaluation of the impact of flow regulation in the priority basins; and (4) comparison of temporal and spatial patterns in hydrology and hydroclimatology within and between the priority basins.
Major results to-date include identification of a strong hydrograph signal, by basin, of the timing and magnitude of streamflow, and of the importance of time scale selection (especially daily versus monthly) in environmental flow analysis. The preferred tool will be employed in the TIFP for characterization and assessment of the four components of the natural flow regime: subsistence flow, base flow, high flow pulses, and overbank flow, via the calculation of low flow, base flow, high flow, and flood frequency statistics and via the description of wet, dry, and normal years.
A key challenge of the sub-basin specific studies to be performed as part of the TIFP is how to identify the four components of the flow regime (subsistence flow, base flow, high flow pulses, and overbank flow) using hydrologic assessment tools such as IHA or HAT and how good such tools would be at this identification. Much work needs to be done to better define ecologically-significant thresholds between the flow components that have clear linkages to the natural biological, chemical, and physical processes of the riverine ecosystem. One example of a way to define these thresholds is by using classical hydrologic tools such as the U.S. Department of the Interior Bureau of Reclamation’s (2004) “BFI: A Computer Program for Determining an Index to Base Flow,” Program, http://www.usbr.gov/pmts/hydraulics_lab/twahl/bfi/ which is based on the British Institute of Hydrology method. BFI seeks to separate the groundwater-driven portion of the hydrograph from the precipitation-driven portion, such as in the example shown below:
Despite the difference in jargon, existing baseflow separation tools may prove quite effective in defining the subsistence flow component of the flow regime for use in the Texas Instream Flow Program.
Indicators of Hydrologic Alteration, The Nature
Conservancy
Overview: http://www.nature.org/initiatives/freshwater/conservationtools/
Documentation: http://www.nature.org/initiatives/freshwater/conservationtools/art17003.html
Download IHA: http://www.nature.org/initiatives/freshwater/conservationtools/art17004.html
Hydroecological
Integrity Assessment Process, USGS
Overview: http://www.fort.usgs.gov/HIP/
Documentation: http://www.fort.usgs.gov/Products/Publications/pub_abstract.asp?PubID=21598
Download the National Hydrologic Assessment Tool (NATHAT): http://www.fort.usgs.gov/Products/Software/NATHAT/
Download the New Jersey Stream Classification Tool (NJSCT) and NJHAT: http://www.fort.usgs.gov/Products/Software/NJHAT/Default.asp
Presented at the
TRRMS is the
Future Work: Development of an Integrated Stream
Classification System for the State of
Senate
Bill 2 passed by the 2001 Texas Legislature established for the first time the
principle that a “sound ecological environment” in
This project takes a synoptic view of the instream flow environment of Texas streams and rivers so that particular classes or regions of streams and rivers can be recognized as having a common identity, and thus conclusions drawn from instream flow studies in particular river reaches can be recognized as having a wider applicability. Such an approach would also help prioritize areas for future studies. A qualitative regionalization of Texas streams and rivers is presented in Mallard et al (2005) and TCEQ proposes to examine this type of regionalization more closely and attempt to draw its boundaries using quantified criteria that will yield a stream classification system for the state.
Data will be managed in a spatially-explicit fashion, using the geo-referenced databases currently available and under development for the Instream Flows Program, and also building upon current research being performed within the Program. Boundaries drawn will be consistent with the prior delineation of river basins for use in TCEQ’s water availability models. Data incorporated into the classification structure may include:
• Hydrology & Hydraulics: USGS discharge and stage data, climate data.
• Biology: Texas Parks and Wildlife Inland Fisheries database, Index of Biologic Integrity metrics.
• Geomorphology & Physical Processes: geology, land use/land cover, soils, channel cross-sectional form and size, channel plan form, bed morphology, and bed slope.
• Water Quality: TCEQ Regulatory Activities and Compliance System (TRACS) database, including: temperature, dissolved oxygen, total suspended solids, and nutrients.
Mallard, G. E.
et al. (2005). The Science of Instream
Flows: A Review of the Texas Instream Flow Program. The National Academies Press,
Eric S. Hersh
Graduate Research Assistant
Center for Research in Water Resources
University of Texas at
E-mail: ehersh@mail.utexas.edu