What Are Environmental Flows?

Environmental Flows are the quantity, quality and timing of water that are necessary to sustain a river, wetland or coastal zone and associated fish and wildlife.

Ash Creek at Woodward Ranch, South of Alpine Photo courtesy of Charles Kruvand

Ash Creek at Woodward Ranch, South of Alpine
Photo courtesy of Charles Kruvand

Environmental flows are made up of both “instream flows”— flows in a river or stream—and “freshwater inflows”—the flows of fresh water that make it down the river or stream and into an estuary system. An environmental flow “regime” is a prescription of different amounts of flows that varies by both the time of the year and by hydrologic conditions. A flow regime for a river or stream includes:

  • “subsistence flows”—those very low flows seen only during times of drought;
  • “pulse flows”—short-term events brought on by heavy rainfall producing a surge of water in the river and/or into the bay system; and
  • “base flows”—those flow volumes that fall between subsistence flows and pulse flows and that occur most of the time; generally there are several different levels of base flows.

Rivers and estuaries are naturally dynamic ecosystems that rely on periodic changes in flow to maintain their health and productivity. Keeping our rivers, streams, estuaries and wetlands healthy is important for many species of wildlife and for the state’s economy. Texas has seven major coastal estuary systems, formed where fresh water from rivers mixes with the saltier water of the Gulf of Mexico. This mixture of salt and fresh water is vital for many marine species-including fish, shrimp, oysters and crabs-and fuels a $2 billion+ coastal recreational and commercial fishing economy.

Healthy rivers, wetlands, and estuaries are also important for many of the 600+ species of birds found in the state. Bird species that migrate through Texas and the numerous year-round residents rely on these habitats, and the fish, shellfish and plant life that they sustain, for their food source.

Birding on the Texas Coast Photo courtesy of TPWD

Birding on the Texas Coast
Photo courtesy of TPWD

Freshwater fish in Texas’ rivers need sufficient amounts of clean water to survive. Many species of fish also need higher flows at certain times of year so they can move to their spawning grounds and reproduce. Coastal estuaries and bays are considered “nurseries of the sea” because they provide just the right balance of salinity, nutrients, and temperatures that allow for young fish and shellfish to mature.

In addition to animal species, many plant species also depend on adequate environmental flows for their life cycles. Many wetland habitats, such as bottomland hardwood forests, depend on periodic flow out of the banks of the rivers and streams for seed dispersal and a natural culling of invasive species.

Get Involved

Learn how you can help at home, in your community and at the state level to keep water flowing in Texas streams and rivers and into our estuaries.

Senate Bill 3 Environmental Flows Process

Learn about Texas’ process to determine the water needed to maintain healthy rivers and estuaries and how we can protect or restore these flows.

Brazos River and Associated Bay & Estuary Area

The Brazos River basin is the third largest river in Texas; its watershed stretches from the New Mexico–Texas border west of Lubbock, to the Gulf of Mexico, south of Houston. TCEQ is currently considering what levels of environmental flow protection standards to adopt for this river system and associated estuary, with a final decision expected by March 2014.

Colorado & Lavaca Rivers/Matagorda & Lavaca Bays Area

In September 2012, TCEQ adopted environmental flow standards for the Colorado and Lavaca rivers and Matagorda and Lavaca bays.

Guadalupe, San Antonio, Mission, & Aransas Rivers/Mission, Copano, Aransas & San Antonio Bays Area

Despite receiving a majority recommendation from regional stakeholders, TCEQ adopted flow protection standards in September 2012 that were significantly weaker than those recommended by stakeholders. TCEQ will now apply these standards to any new water right permit they give out in the basin.

Nueces River/Corpus Christi & Baffin Bays Area

TCEQ is currently considering what levels of environmental flow protection standards to adopt for this river system and associated estuary, with a final decision expected by March 2014.

Rio Grande/Rio Grande Estuary & the Lower Laguna Madre Area

TCEQ is currently considering what levels of environmental flow protection standards to adopt for this river system and associated estuary, with a final decision expected by March 2014.

Sabine & Neches Rivers/Sabine Lake Bay Area

TCEQ adopted environmental flow standards for the Sabine and Neches river systems and Sabine Lake that are not adequate to protect a sound ecological environment. TCEQ should be considering revised standards in the near future.

Trinity & San Jacinto Rivers/Galveston Bay Area

TCEQ adopted environmental flow standards for the Trinity and San Jacinto river systems and Galveston Bay that are not adequate to protect a sound ecological environment. TCEQ should be considering revised standards in the near future.

Strategies to Keep Rivers Flowing and Bays Healthy

Threats to Environmental Flows

Projections indicate that many of the state’s estuaries could end up deprived of adequate freshwater on a frequent basis, particularly in drier years, if we do not take aggressive action to implement sufficient environmental flow protections.

Useful Links and Resources

Useful links to additional information on protecting water in rivers and flowing into bays.

Water Rights and Flows Protection in Texas

Since 1985, the Texas Commission on Environmental Quality and its predecessor agencies have included some level of environmental flow protections on new water rights. However, the level of protection varies widely from permit to permit, and unfortunately, over 90% of the water rights currently authorized were issued before 1985 and have no environmental conditions.