Freshwater Inflows | Texas Water Development Board

Freshwater Inflow Needs of Texas Estuaries

There are seven major and five minor bay and estuary systems covering 2.6 million acres along the Texas Gulf Coast.  These estuarine ecosystems include open water bays, intertidal mudflats, and emergent marshes which contain natural and man-made resources that each contribute multi-billion dollar inputs to the state's economy, including but not limited to (1) a navigation network of national importance; (2) a vast resource base for minerals, seafoods, and recreational opportunities; and (3) a natural source of advanced waste treatment for nutritive materials and by-products of our modern society.  Indeed, the total impact on the state's economy just from commercial fishing, sport fishing, and other recreational activities in the bays has been estimated at over ~$3.5 billion/year (1994 dollars) or ~$1,333/acre annually.  However, the real value of the bays and estuaries is many times this amount and may be fully comprehended only by considering how much it would cost to replace all the goods and services provided by these valuable coastal systems.  Therefore, the character and health of the estuaries is dependent upon freshwater inflows to deliver not only fresh water but also nutrients and sediments which provide for the physical condition of the estuary which supports a diversity of estuarine life.

Early Efforts and the State Methodology

Early efforts to determine the effects of and needs for freshwater inflows to the state's bays and estuaries were conducted in response to Senate Bill 137 (1975), House Bill 2 (1985), Senate Bill 683 (1987), Senate Bill 1 (1997), and other legislative directives.  Until recently, when the Senate Bill 3 (2007) process for developing environmental flow recommendations and standards was implemented, freshwater inflow studies within the State were guided by Section 11.147 of the Texas Water Code to answer the question "How much water is needed to provide a beneficial inflow?" where beneficial inflows are defined as:

"a salinity, nutrient, and sediment loading regime adequate to maintain an ecologically sound environment in the receiving bay and estuary system that is necessary for the maintenance and productivity of economically important and ecologically characteristic sport or commercial fish and shellfish species and estuarine life upon which such fish and shellfish are dependent."

In order to do this, a great deal of information was needed; therefore TWDB, the Texas Parks & Wildlife Department (TPWD), and the Texas Commission on Environmental Quality (TCEQ) jointly established and maintained long-term data collection and analytical study programs focused on determining the effects of and needs for freshwater inflows to the state's bays and estuaries.  The study effort focused on two management goals:

  1. Ensuring the maintenance and productivity of economically important and ecologically characteristic sport or commercial fish and shellfish, and
  2. Ensuring the maintenance of estuarine life upon which such fish and shellfish are dependent.

The State Methodology addressed the first goal, "maintenance of ... fish and shellfish", by setting a management goal to achieve more than 70% of the historical average harvest or abundance of important fish and shellfish.  This requirement was set in the TxEMP optimization model as a lower constraint.

The State Methodology addressed the second goal, "maintenance ... of estuarine life upon which such fish and shellfish are dependent", in the final check of needs.  In this step, salinity levels resulting from the inflow solutions provided by TxEMP were examined at important locations within the estuary.  This step ensured that the recommended inflows would provide conditions favorable to maintaining the fish, shellfish, and other estuarine life, i.e., an ecologically healthy system.

While a complete description of the State Methodology is provided in the Longley (1994) report and in Powell et al. (2002), a brief summary of the seven elements of the State Methodology is available along with a list of frequently asked questions.

Recent Efforts and the Senate Bill 3 Environmental Flows Process

The 80th Texas Legislature (2007) established the Senate Bill 3 (SB3) process for environmental flows in order to determine environmental flow standards for all of the major river basins and bay systems in Texas.  Senate Bill 3 was fashioned to be an accelerated, stakeholder-driven, scientific and consensus-based process that utilizes adaptive management into the future.  The intent of the SB3 process was to address two major questions: 1) How much water is needed to sustain a sound ecological environment in the state's rivers and estuaries, and 2) How can this water be protected?

Whereas previous studies of freshwater inflow needs for Texas bay systems used an optimization program to objectively integrate various management decisions (e.g., minimum acceptable fisheries harvest levels) and ecological needs (e.g., salinity or nutrient needs of fisheries species) in order to compute the minimum amount of freshwater inflow needed to best satisfy a set of specified constraints.  Senate Bill 3 efforts focused on determining a “flow regime” that could provide for a range of inflows necessary to maintain bay health.  For more information, read on the Senate Bill 3 process for Environmental Flows.

What are the Estuarine Systems of Texas?

The seven major estuaries include: Sabine Lake (Sabine-Neches Estuary), Galveston Bay (Trinity-San Jacinto Estuary), Matagorda Bay (Lavaca-Colorado Estuary), San Antonio Bay (Guadalupe Estuary), Aransas Bay (Mission-Aransas Estuary), Corpus Christi Bay (Nueces Estuary), and the Laguna Madre Estuary.

The five minor estuaries include Christmas Bay, the Cedar Lakes and San Bernard River Estuary, and East Matagorda Bay along with two river estuaries, the Brazos River Estuary and the Rio Grande Estuary.

Completed Freshwater Inflow Studies and Supporting Work

Coast-wide Studies

Sabine Lake (Sabine-Neches Estuary)

TxEMP results for the 2005 Sabine Lake recommendation

Galveston Bay (Trinity-San Jacinto Estuary)

TxEMP results for the 2001 Galveston Bay recommendation

Matagorda Bay (Lavaca-Colorado Estuary)

TxEMP results for the 1997 Matagorda Bay recommendation
TxEMP results for the 2006 Matagorda Bay recommendation

San Antonio Bay (Guadalupe Estuary)

TxEMP results for the 1998 San Antonio Bay recommendation

Aransas Bay (Mission-Aransas Estuary)

TxEMP results for the Mission-Aransas Estuary recommendation

Corpus Christi Bay (Nueces Estuary)

TxEMP results for the 2002 Corpus Christi Bay recommendation

Laguna Madre Estuary

TxEMP results for the 2004 Upper Laguna Madre Estuary (including Baffin Bay)
TxEMP results for the 2004 Lower Laguna Madre Estuary (including South Bay)

Data Sources for Freshwater Inflow Studies

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