The Science of Instream Flows A Review of the Texas Instream Flow Program (2005) / Chapter Skim
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2 Scientific and Program Context for the Texas Instream Flow Program
2 Scientific and Program Context for the Texas Instream Flow Program
Pages 22-31
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From page 22... ...
Texas' wide span of hydrologic and physical riverine conditions impacts how instream flow science is conducted across the state. Hydrologic Setting Precipitation ranges from an average of 8 inches per year in far West Texas to as much as 60 inches per year in coastal east Texas (TPWD, TCEQ, and TWDB, 2003)
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From page 23... ...
For descriptive, instream flow purposes, the state of Texas and its river systems are coarsely categorized into five generalized districts: East, North-Central, SouthCentral, Lower Rio Grande basin, and West. These districts are described briefly below in terms of geology, climate, hydrologic regime, and biota.
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From page 24... ...
This region is drier than east Texas, with rainfall averaging between 15 and 28 inches a year and occasional severe droughts. These rivers have flow characteristics similar to those of East Texas rivers, but they are smaller and tend to experience more frequent drought conditions.
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From page 25... ...
Annual average rainfall in this region varies from 11 to 26 inches. The region's prevalent land uses are irrigated row cropping in the Lower Rio Grande Valley, and livestock grazing across the region.
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From page 26... ...
Thus, for much of the last half of the nineteenth century, land ownership determined the right to use river water in Texas. A series of state laws adopted at the end of the nineteenth century declared that then unappropriated surface waters were to be the property of the public and that future rights to use water would be acquired under a prior appropriations system.
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From page 27... ...
Prompted by a serious drought as well as dramatic projections of population growth, in 1997 the Texas legislature adopted a sweeping reorganization of its water resource management regime. The legislation, known as Senate Bill 1, mandated that the Texas Water Development Board (TWDB)
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From page 28... ...
This legislation established a Water Advisory Council, and made a number of technical changes to the state's water code. Of particular importance for this report, the legislature also directed the three resource agencies-TCEQ, TWDB, and TPWD to: Jointly establish and maintain an instream flow data collection and evaluation system; Conduct studies to determine appropriate methodologies for determining flow conditions in the state's rivers ands streams necessary to support a sound ecological environment; Complete priority studies by December 31, 2010; and Direct the Commission to consider the results of the studies in its review of management plans, water rights, and interbasin transfers Finally, it is important to note that much of the State of Texas's groundwater resources are managed under an allocation regime that is largely separate and distinct from the prior appropriations system used for surface waters.
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From page 29... ...
Water availability is important because the amount of water in streams that remains available for allocation will have important effects on the ability of the Texas agencies to implement any flows recommended as a result of an instream flow study. The water quality programs are specifically mentioned in the Technical Overview Document (TOD)
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From page 30... ...
This water assessment process using QUAL-TX creates conservative estimates of pollutant loads because QUAL-TX accounts directly for point-sources and indirectly for non-point sources. The biological studies needed to support the Texas instream flow program effectively require collection of much the same kind of data as is needed to complete a receiving water assessment of a wastewater discharge.
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From page 31... ...
Scientific and Program Context 31 quate data to reach conclusions on these assessments are available for only a portion of all the water bodies in the state, especially for toxic substances and biological assessments. Aquatic life in Texas streams and rivers is to some degree impacted by toxic chemicals but the main water quality limitation on aquatic life is depressed dissolved oxygen.
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