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GOING WITH THE FLOW

GOING WITH THE FLOW

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Whether you enjoy floating down the Brazos River or fishing, you have probably noticed times when the water in the river moves either too slowly or too quickly for your purposes. Why does the water flow change, what determines the flow, and is there any way you might know in advance?

Sometimes the reason for higher water flows is obvious. Rain upstream has increased flows within the watershed, adding water to both rivers and reservoirs. The three reservoirs maintained by the Brazos River Authority were constructed for water supply rather than flood control. When reservoirs are full, water from upstream must be released downstream, increasing the flow of the river. The reservoirs built and maintained by the US Army Corps of Engineers serve as flood control reservoirs that can receive and temporarily store water well beyond their normal capacity, further controlling the amount of water released downstream. 

Other times, people may wonder why 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.  Another reason water is sometimes released from a reservoir is to for environmental flows. What are environmental flows and why are they important?

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.”

The flows help to maintain healthy water ecosystems, which are important to a variety of endeavors ranging from recreation and tourism to commercial fishing, transportation, and water supply, according to the TWDB.

Other reasons why water flow may sometimes increase or decrease on the river may be during dam maintenance operations or times when environmental studies are being conducted.

“When we are releasing for water supply or passing inflows, we try to time the releases to benefit recreation downstream,” said Brad Brunett, Water Services Manager for the BRA. “There are typically more flows leading up to the weekend than during the first part of the week. In the Granbury area, much of the recreation is in the Glen Rose area, so we keep that in mind when making a release.”

The normal low flow rate from the Morris Sheppard Dam at Possum Kingdom Lake ranges between 50 and 300 cubic feet per second (cfs).  The low flow rate at Lake Granbury is between 2 and 16 cfs.

The U.S. Geological Survey monitors environmental 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.

What about knowing future streamflow amounts?  It’s difficult to predict future streamflow due to unpredictable weather patterns. However, the National Weather Service’s Hydrologic Prediction Service does give estimates about future streamflow. Predictions are most typically posted when heavy rainfall or potential flooding is expected, and meteorologists with the National Weather Service have said the best accuracy of these predictions is within a 48-hour period.

Another valuable resource for planning a float down the river is Southwest Paddler, an internet website that features maps of different sections of the Brazos with recreation in mind. Marc W. McCord, writing for Southwest Paddler, says, “Parts of the Brazos are absolutely beautiful, and paddling is quite enjoyable. Except after heavy local rainfalls, the upper sections tend to run low and slow, though the river picks up a faster current the further you paddle downriver, especially below Waco.”

The website does point out some reasons to visit the sections of the river between Possum Kingdom and Granbury.

“The upper section is more colorful and the vegetation is denser than on lower sections,” Southwest Paddler states. … “It is hard not to be taken in by the serenity and splendor of that part of the river.”

One important part of enjoying recreation on the river is to know what to expect and to be prepared in advance for whatever conditions are present.

Here is some information that can help you be prepared. Links to water levels and the USGS streamflow measurements can be found here.

Links to the National Weather Service’s Hydrologic Prediction Service outlook for portions of the Brazos and its tributaries (the Bosque, San Gabriel, Navasota, Leon and Lampasas rivers) can be found here.

More details on specific sections of the Brazos and what to expect when canoeing or kayaking can be found at http://southwestpaddler.com/docs/brazos.html

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