2009 SAC report on water for environmental flows

Senate Bill 3 (SB 3), passed by the Texas Legislature in 2007, directed the development of environmental flow recommendations through a new regulatory approach, using a local stakeholder process and the best available science, and culminating in Texas Commission on Environmental Quality (TCEQ) rulemaking. SB 3 directed the use of an environmental flow regime in developing flow standards from the environmental flow recommendations and defined a regime as a schedule of flow quantities that reflects seasonal and yearly fluctuations that typically would vary geographically and that are shown to be adequate to support a sound ecological environment and to maintain the productivity, extent, and persistence of key aquatic habitats. Initial flow recommendations by the local basin and bay expert science teams (BBEST) are to be made without regard to the need for the water for other uses. Although water availability may be an important consideration, at this stage it is not the primary driver of the analysis. Additionally, SB 3 clearly recognizes that in areas with little or no unappropriated water available to meet environmental flow needs, the Environmental Flows Advisory Group (EFAG), along with the Basin and Bay Area Stakeholder Committees and their respective BBEST, are to try to find innovative ways to provide water for environmental needs. The Science Advisory Committee (SAC) published guidance on using hydrologic data as a method to develop initial instream flow recommendations as part of SB 3 efforts (SAC 2009a). One of the approaches outlined is the Hydrology-Based Environmental Flow Regime (HEFR) methodology which uses hydrologic data to populate an initial flow regime matrix consisting of monthly/seasonal schedules for subsistence flows, base flows, high flow pulses, and overbank flows. The hydrology-based approach constitutes one piece of the multidisciplinary process envisioned by SB 3 for the identification of flows needed to maintain a sound ecological environment in Texas rivers and streams. Completion of the process requires input from other scientific disciplines including biology, geomorphology, and water quality to ensure that environmental flow recommendations are broad-based, use the best available scientific information, and are adequate to support all processes and functions that maintain a sound ecological environment. To facilitate the use of other disciplines to inform, confirm, or modify the hydrology-based initial flow regime matrix, the SAC set out to develop guidance documents related to the overlay of biologic, geomorphologic, and water quality information. SAC 2009b presents information regarding geomorphological, specifically sediment transport, considerations. An additional guidance document addressing water quality overlay issues is in preparation. This Biological Overlay document provides guidance on: 1) Assimilating biological information needed to develop a biological overlay within the context of SB 3 (Section 2), 2) Applying biological information to inform the geographic scope of instream flow recommendations (Section 3), 3) Addressing decision points required before and during hydrology-based modeling, (Section 4), 4) Applying a biological overlay for the purpose of refining and/or confirming preliminary hydrology-based instream flow recommendations (Section 5), and 5) Using the biological overlay document in a hydrology-based environmental flow determination (Section 6). Input from BBEST members through the Instream Biology Workgroup helped to inform the development of this document as a tool that the BBESTs can use to apply biological information in their deliberations. The document offers some background information, but more importantly is meant to be utilitarian and provide the essential steps the BBESTs can use to develop instream flow recommendations in the short time prescribed by SB 3.