In June 2019, three gates were open for the first time since June 2016 at Possum Kingdom Lake’s Morris Sheppard Dam, sending massive amounts of water down the Brazos River. The gate openings, plus the above normal heavy rains that fell that spring, caused the river to be, well, brown.
That discoloration is called turbidity - the measure of relative clarity of a liquid – and it can include clay, silt, algae, organic matter and other microscopic organisms.
“It is an optical characteristic of water and is a measurement of the amount of light that is scattered by material in the water when a light is shined through the water sample,” according to the U.S. Geological Survey. “The higher the intensity of scattered light, the higher the turbidity.”
During heavy storms, rain pushes particles from the surrounding land into the river, creating a muddy and brown appearance. The increased amount of water in the river also increases the streamflow, and the faster the water moves, the more easily it stirs up material from the streambed and increases turbidity, according to the USGS.
As turbidity increases, the ability for sunlight to penetrate the water decreases, according to the Texas Commission on Environmental Quality.
“Suspended matter remains in the water column as long as there is sufficient current to carry it, according to TCEQ. “The deposition of suspended matter creates problems for aquatic organisms by covering up habitat and filling in lakes and slow-moving areas of streams. By covering up habitat, the amount of invertebrate food for fish is reduced and predators feed less efficiently in turbid water. If the sediment load is too high fish gills can become clogged.”
For those looking to enjoy the Brazos basin and its reservoirs, the question is when will the water be clear again?
It can take months before the cloudiness level of the water begins to lessen following heavy storms.
A certain level of turbidity is expected and is normal for all rivers, including the Brazos. Some rivers are naturally cloudier than others.
An important reminder when venturing out on the water is that there can be dangers lurking below the surface. High streamflows and large amounts of rain that fill the Brazos basin each spring increase the amount of debris in the water, many just lurking below the surface, hidden by the turbidity.
The cloudiness of a reservoir or river can make popular summer activities like jet skiing or tubing even more dangerous as objects below the water can’t be seen.