When the situation becomes salty
All water flows downstream, right? Then that might include what’s in the water too, like salt.
Why salt? If you’re not familiar with the uppermost portions of the Brazos River basin, you may also be unaware of the naturally occurring, salt-bearing geologic formations in this section of the state. To put it plainly, there are areas of the Brazos basin where white stuff resembling snow is visible on the ground. But the white stuff is naturally occurring salt.
The most common issue affecting water quality and water use in the mainstem of the Brazos River is excessive levels of chlorides and total dissolved solids. These natural minerals arise from brine springs in the uppermost portion of the basin in Stonewall, Kent and Garza counties, depositing highly mineralized groundwater into the watershed of the Salt Fork and Double Mountain Fork of the Brazos. Rainfall then flushes this residual salt into the river.
Downstream of these salt flats are the water storage reservoirs you’ve come to know and love: Possum Kingdom Lake, Lake Granbury, and further still to Lake Whitney. High chloride levels can affect water quality all the way to the Gulf Coast.
During prolonged droughts, chloride and total dissolved solids or TDS levels in mainstem lakes frequently become even higher than normal as evaporation reduces water levels, leaving chlorides and other minerals in the remaining water.
Why should this matter to you?
During these times, chloride levels can become higher than allowed under state drinking water standards. For example, between 1997 and 2010, the average chloride concentration measured at Possum Kingdom Lake near the dam was 881 milligrams per liter (mg/L). During the same period, the measurement near the Lake Granbury dam was 651 mg/L. While these readings are well below state standards for surface water quality, they are higher than the standards set by the Texas Commission on Environmental Quality for drinking water. As a result, before the water may be sent to your faucets for drinking, cooking and bathing, chloride levels must be lowered through operational changes at potable water treatment plants.
And, those that use untreated water for crop irrigation, livestock or business operations must seek other methods of managing day-to-day operations.
Surface water quality is largely influenced by flow. During extended dry periods, flows are low, and chlorides become concentrated. Conversely, periods of high flow often have a diluting effect on chloride concentrations. With high flow events following periods of drought, there is a decrease in dissolved solids
This was the case in 2005 when a tropical storm stalled over the Lubbock area for an extended period of time, said Tiffany Malzahn, Brazos River Authority environmental and compliance manager.
Malzahn explained that there normally is not enough flow out of the upper basin’s underground salt springs s to push that salty, snow-like flow out of the springs and into the Brazos River.
That is, of course, until a tropical storm floats into the area, she said.
The heavy rain generated by the 2005 tropical storm sent a wave of saltwater into the Brazos River, flowing directly into Possum Kingdom Lake, she said.
As drier West Texas weather moved quickly into drought conditions, the salt that had accumulated in the reservoir concentrated. Fast forward a year, and suddenly the basin went from drought to drenched. There was so much water, Possum Kingdom Lake opened three gates at once, and Lake Granbury filled and refilled 13 times, pushing salt downstream throughout the basin.
The increased levels had an impact on drinking water treatment plants and other industries' production processes, she said.
Suddenly, it seemed everyone was asking the BRA about chloride levels. Malzahn said continuous, real-time monitoring of chloride levels in the Brazos was not available online, and the BRA scrambled to create a way for treatment plants, agriculture and industries to monitor levels round-the-clock.
Surface water with high levels of chlorides does not have a marked effect on the environment, as these fluctuations are common in this area of the state; however, the numbers are critical during these periods, she said. Elevated mineral concentrations can cause a variety of problems for water users ranging from affecting production at industrial and water treatment facilities, causing violations of secondary drinking water regulations at drinking water treatment facilities, and having to stop production at industrial facilities. High chloride levels can also have a profound effect on the health of livestock drinking directly from surface water sources and on crops irrigated with untreated water.
It was not long before the BRA created a chloride and TDS prediction tool available to the cities, industry and agriculture that receive water from BRA reservoirs.
Now the model is available to the public through the upgraded environmental section of the BRA website.
Here, users can view graphs and data showing forecasts at Possum Kingdom Lake, Lake Granbury and Lake Whitney. This site allows basin water users to view the most recent monitoring data at the reservoirs and to be aware of changing chloride and total dissolved solids’ concentrations, allowing them to adjust operations, if necessary. The site also provides the ability to view seven-day forecasts of chloride and total dissolved solids concentrations, allowing water users to anticipate conditions that may be moving their way.
The chloride and total dissolved solids concentration forecasts are estimations based upon historical data, mass balance, flow routing and forecasts of flow and lake levels. The forecast model totals data from web-based sources once per day, executes a model, generates plots, and makes data displays available on the site. Model output is a daily averaged estimation of concentration, presented as upper and lower bounds. These bounds represent a 95 percent confidence that concentrations will occur between the upper and lower bound.
The Brazos River basin has not seen a significant drought followed by flooding and high concentrations of chlorides since 2015. “Will we ever see an event like that again? Probably. Eventually,” Malzahn said. When it does occur, information critical for daily operations is now available to all.