Texas
Texas watershed protection plans and TMDLs: flow at every monitoring station
We deliver a SWAT+ model of your watershed, calibrated at a USGS gauge that measures its flow, that simulates daily flow in every stream segment and reports it at each of your stations, so every station has the flow record its flow-duration and load-duration curves need.
Texas models already built
Published SWAT+ models in Texas, each with its own page.
USGS 07312200 · Southern Beaver · 1669.5 km² · 4,450 stream segments
USGS 07315200 · Little Wichita · 502.0 km² · 1,867 stream segments
USGS 08032000 · Upper Neches · 2912.8 km² · 11,079 stream segments
USGS 08063800 · Chambers · 450.5 km² · 1,169 stream segments
USGS 08131400 · South Concho · 207.1 km² · 270 stream segments
USGS 08178800 · Upper San Antonio · 471.0 km² · 617 stream segments
USGS 08185000 · Cibolo · 716.9 km² · 1,385 stream segments
USGS 08195000 · Upper Frio · 1002.4 km² · 2,006 stream segments
Where a Texas model has a gauge to calibrate against
In 122 of the 169 HUC8 subbasins that lie mostly in Texas, at least one USGS stream gauge recorded daily flow on 90 % or more of days from 2014 to 2024, a record a model can be calibrated against.
Calibration fits the simulated streamflow to the observed daily discharge of a USGS gauge.
Where no USGS gauge measures your watershed, we tell you before the project starts which of three it gets: a model built for, and calibrated at, the larger gauged watershed that contains it; parameters carried over from a calibrated neighbouring watershed; or a model delivered uncalibrated and labelled as such.
What your plan gets
The SWAT+ model simulates daily flow in every stream segment of the watershed, from that segment's own drainage area, soils, land cover and climate, and we set it up to report the segment at each of your monitoring stations.
SWAT+ as we build it does not simulate bacteria: the model supplies the flow, and the criterion and the monitoring data are your plan's.
The model also simulates the daily sediment, nitrogen and phosphorus leaving every reach, so a plan can see which subwatersheds carry the most.
Sediment, nitrogen and phosphorus are simulated, not fitted to measurements, unless fitting them to your monitoring data is part of the project.
For a river authority, the same basin model ties the Clean Rivers Program stations you monitor to the subwatersheds upstream of them.
Tidal segments are not modelled.
What TCEQ's support documents say about flow at monitoring stations
“While many WQM stations throughout Texas do not have long term flow data, there are various methods that can be used to estimate flow frequencies at ungaged stations or gaged stations missing flow data.” (Technical Support Document: Bacteria Total Maximum Daily Loads for Rolling Fork Creek, prepared for the Texas Commission on Environmental Quality by the University of Houston, June 2014, p. 49. TCEQ document)
The first step of the load duration curve method, as the same document states it:
“Preparing flow duration curves (FDC) for gaged and ungaged WQM stations”
Two bacteria TMDL support documents published by TCEQ in 2020 made each station's daily flow record by scaling a USGS gauge's record by drainage-area ratio. Walnut Creek (August 2020) · Arenosa Creek (October 2020)
“Develop daily streamflow records at desired stream location using daily gaged streamflow records and drainage area ratios.”
For tidal streams the same TCEQ document uses a different method: “1) the load duration curve method for non-tidal streams and 2) a mass balance method using a tidal prism for tidal streams.” (p. 48).