CORPUS CHRISTI, Texas — Integral calculus aims to find the area under a curve — and while we're not going to do any calculus, we are going to get a rough estimate as to how much water could be headed from Tilden down the Frio River into Choke Canyon. Similar to calculus, we're going to add up the volume of water by piecing together the forecast streamflow for the Frio River at Tilden.
<img src="https://water.noaa.gov/resources/hydrographs/tidt2_hg.png" alt="NOAA hydrograph for the Frio River at Tilden">
By converting the stream flow in the hydrograph for the Frio River near Tilden, we can estimate how much water is going to move down the river in its short ride to Choke Canyon Reservoir — but it's risky. Small changes in this river forecast could mean huge changes in the actual amount of water that makes it into the reservoir. A couple days ago, the river was expected to crest around 27 feet— it is now expected to crest close to 30 feet. That adds a huge increase with just a couple of feet added to the crest of the flood wave, or the floodwater moving down the river. Meteorologist Chris Malave was in Tilden on Wednesday to share how things were looking around town.
The preliminary estimate for what we can expect at Choke Canyon Reservoir adds about 225,000 acre-feet, or 34% to Choke Canyon Reservoir alone. That could increase the combined capacity of Choke Canyon Reservoir and Lake Corpus Christi by 21%. Lake Corpus Christi will see additional water moving down the Nueces River later next week. It's took early to estimate how much water could be expected. The stretch of the river that runs from Cotulla to Tilden is notorious for being "loss-y" or reducing the flood wave between the two river gauges. While the river gauge at Cotulla has recorded impressive streamflows, the brush country along the way may cause a loss of 30 to 60 percent! We'll have to wait to make a reasonable estimate. A river Flood Warning is in place for the Nueces River at Tilden. The Nueces River at Three Rivers is expected to reach Action Stage next week.
<img src="https://water.noaa.gov/resources/hydrographs/tilt2_hg.png" alt="NOAA hydrograph for the Nueces River near Tilden">
<img src="https://water.noaa.gov/resources/hydrographs/thet2_hg.png" alt="NOAA hydrograph for the Nueces River at Three Rivers">
The next question in this mathematical equation is how long the Frio River will stay elevated. If it drops off sooner than the forecast period, we could be seeing less water heading to Choke Canyon than expected. But if that river rise continues for a prolonged period — at least like what we're seeing in the forecast, maybe even longer — that would be substantially more water heading into Choke Canyon, making a huge impact and benefit to our water situation.
