Texas Administrative Code
Title 30 - ENVIRONMENTAL QUALITY
Part 1 - TEXAS COMMISSION ON ENVIRONMENTAL QUALITY
Chapter 298 - ENVIRONMENTAL FLOW STANDARDS FOR SURFACE WATER
Subchapter D - COLORADO AND LAVACA RIVERS, AND MATAGORDA AND LAVACA BAYS
Section 298.320 - Calculation of Hydrologic Conditions
Current through Reg. 50, No. 13; March 28, 2025
(a) For new water right authorizations which increase the amount of water authorized to be stored, taken, or diverted as described in § 298.10 of this title (relating to Applicability), the determination of the hydrologic condition for a particular season shall be determined once per season. The conditions present on the last day of the month of the preceding season will determine the hydrologic condition for the following season. For each measurement point specified in this section, either cumulative streamflow for the previous 12 months, combined storage in major reservoirs, or reservoir elevation will determine the hydrologic condition, as described in subsections (b) - (d) of this section.
(b) For measurement points located on the Colorado River above Lake Travis and tributaries of the Colorado River, and in the Colorado-Lavaca and the Lavaca-Guadalupe Coastal Basins, cumulative streamflow for the preceding 12 months and the corresponding hydrologic conditions are:
(c) For measurement points located on the Colorado River below Lake Travis, the combined reservoir storage in Lakes Travis and Buchanan and the corresponding hydrologic conditions are:
(d) For measurement points located in the Lavaca River Basin, the reservoir elevation of Lake Texana and the corresponding hydrologic conditions are:
(e) For purposes of water availability determinations, for measurement points on the Colorado River above Lake Travis and tributaries of the Colorado River, and in the Lavaca River Basin and the Colorado-Lavaca and Lavaca-Guadalupe Coastal Basins, hydrologic conditions used in the commission's water availability models shall be calculated such that severe conditions occur approximately 5% of the time, dry conditions occur approximately 20% of the time, average conditions occur approximately 50% of the time, and wet conditions occur approximately 25% of the time.
(f) For purposes of water availability determinations, for measurement points on the Colorado River below Lake Travis, hydrologic conditions used in the commission's water availability models shall be calculated such that severe conditions occur approximately 5% of the time, dry conditions occur approximately 45% of the time, and average conditions occur approximately 50% of the time.
(g) The hydrologic condition indicators set out in subsections (b) - (d) of this section govern the operations of permits subject to this subchapter during the initial period, of not longer than ten years, until the environmental flow standards in this subchapter are reevaluated. Those indicators were calculated to achieve compliance with the percentages of time stated in subsections (e) and (f) of this section. The hydrologic condition indicators set out in subsections (b) - (d) of this section will be recalculated, no less frequently than once every ten years, in order to achieve, to the greatest extent possible, compliance with the percentages of time stated in subsections (e) and (f) of this section.
