SB3 - Environmental Flow Standards
There are times when people may wonder why the streamflow increases on the river, especially during times when it hasn’t rained, or reservoirs are not full.
One reason could be that water supply stored in a reservoir is being released for use downstream.
By making water releases for downstream use, these releases also have the additional benefit of contributing to flows that benefit the environment between the point of release and the point of use.
But what is an environmental flow?
The Texas Water Development Board defines environmental flows as “the flow of water (both quantity and timing of the flow) needed to maintain ecologically healthy streams and rivers, as well as the bays and estuaries that they feed.”
In 2007, the 80th Texas Legislature passed House Bill 3 and Senate Bill 3,
which created a process to protect the water needed by aquatic organisms to survive and reproduce, and maintain a healthy ecosystem.
These protected flows, or water released from reservoirs, are called environmental flows.
An environmental flow is the amount of water required in the stream to maintain a sound ecological environment while balancing human needs. They are a highly diverse range of flows that may occur over seasons, years, or decades.
Environmental flows are broken into three categories: subsistence flows, base flows and high flows pulses.
Subsistence flow is the minimum streamflow needed during drought periods to maintain water quality and environmental habitat for the survival of aquatic organisms.
Base flows are the “normal” channel conditions between storm events. These flows provide habitat for the support of native aquatic communities and maintain groundwater levels to support riparian vegetation.
High flow pulses shape the physical habitat in streams, contribute to sediment transport and flushing of slit and fine particulate matter,
and provide other geomorphic and water quality functions. High flow pulses offer environmental cues to reproduction, floodplain connectivity,
allowing movement of organisms between the main channel and off-channel aquatic habitats, like oxbow lakes, and provide foraging opportunities in flooded riparian habitat.
Environmental flow standards were adopted in February 2014 for the
Brazos basin by the
Texas Commission on Environmental Quality. These standards were adopted with the intent that they would be reviewed periodically to provide
continuing validation, refinement of standards, and prescribe monitoring and studies. This is referred to as adaptive management.
The Brazos River Authority, in cooperation with Texas Parks and Wildlife Department, has a
program to collect data on in-stream biology,
riparian composition, and channel morphology. This effort is to provide information to support the adaptive management process.
Flow Standards apply to water rights permits issued since September 1, 2007. For more information on how instream flow standards are applied to water rights
permits and what water rights holders must do to comply with the standards,
The U.S. Geological Survey monitors flows in many streams and rivers throughout the nation and has detailed information about the latest streamflow
readings in Texas, including the Brazos River basin. Links to water levels and the USGS streamflow measurements can be found