Abstract:

Patterns of freshwater inflow and salinity are presented for the Sabine-Neches, Trinity-San Jacinto, Colorado-Lavaca, Guadalupe, Mission-Aransas, Nueces, and Laguna Madre estuaries of Texas. There is a strong precipitation gradient from west to east, which translates into a strong freshwater inflow gradient where estuary inflows generally increase from west to east. There is a strong correlation between inflows of adjacent estuaries. Another driver of inflow is a cycle of extreme droughts and floods. Inflows to each estuary are highly variable, with the standard deviation of monthly inflows exceeding the mean in all estuaries except the Sabine-Neches. Seasonal patterns of inflows exist, with the easternmost estuaries (Sabine-Neches and Trinity-San Jacinto) exhibiting high inflows during winter and spring, mid-coast estuaries (Colorado-Lavaca and Guadalupe) having high spring and fall inflows, and lower coast estuaries (Mission-Aransas, Nueces, and Laguna Madre) having higher fall inflows, and lower coast estuaries (Mission-Aransas, Nueces, and Laguna Madre) having higher fall inflows. Freshwater inflow patterns create similar patterns in salinity, although salinity is complicated by the estuaries having differing volumes, tidal passes, and tidal prisms. In general, the Sabine-Neches Estuary is often oligohaline, whereas the Nueces Estuary and the Laguna Madre are often euhaline to hyperhaline, and the intervening estuaries are mesohaline and polyhaline. In most cases, salinity variability is highest where the salinity average is moderate in locations that swing between fresh and salt water. Near the Gulf passes, and near freshwater sources, the average salinity is high, and low, respectively, but the standard deviation is relatively low. More salinity monitoring and a more modern approach to salinity modeling is needed. Long-term trends are uncertain because of high spatial and temporal variability of inflow and salinity.

Suggested Citation:

Trungale, Joe, Josef Hoffmann, Paul A. Montagna, Dan Opdyke. 2024. Freshwater inflows to Texas bays and estuaries: hydrology, circulation, and salinity data (1977-2018). Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/8KR3TNDT

Purpose:

To provide information on the long-term dynamics of freshwater inflows, circulation, and salinities in Texas estuaries.

Data Parameters and Units:

salinity (practical salinity units, psu), flow (cubic feet per second, cfs; acre-feet per month, ac-ft/mo; acre-feet per year, ac-ft/yr; cubic meters per month, m3/mo; cubic meters per year, m3/yr), flow velocity (feet per second, ft/s; meters per second, m/s), precipitation (inches per day, in/day), evaporation (inches per month, in/mo), depth (ft; m)

Methods:

Measured flow and salinity data were downloaded from the USGS and TWDB web pages, respectively, in August 2022. Measured water quality data were acquired from TPWD staff (Mark Fisher) in May 2021. For each measurement location, the entire data record was acquired that was available at the time. Model flow and salinity data were acquired from TXBLEND model simulations. Data were spatially and temporally analyzed, using various statistical methods where useful (e.g., frequency analysis; correlation analysis; regression analysis; mean, median, and standard deviation calculations), and visualized using various graphical methods. Original TXBLEND input files for these simulations were acquired from TWDB staff (Mellissa Luper) starting in August, 2021 and completing in September, 2021 for each bay/estuary system. Files from TWDB include: a. The main ‘input’ file which contains model runtime parameters (including time step, period of record, etc.) model mesh and nodes (including initial salinity, bathymetry, Manning’s roughness, dispersion coefficient), paths to time series data (inflows, winds, tides, evaporation, precipitation, and off-shore salinity), and specification of outputs including daily salinity nodes. b. Timeseries data for the period of record (inflows, winds, tides, evaporation, precipitation, and off-shore salinity). TXBLEND inputs files were pre-processed using excel spreadsheets. Several model parameters were adjusted, including start and end dates, number of timesteps, paths to time series data, and interval between restart file. The Nueces model was unique in that it was dependent on results from the GSA model for flow exchange between the two systems; therefore an additional step was required to create the inputs for the flow and salinity exchange files from the GSA to the Nueces system. The TXBLEND simulations were executed on a cloud server for each bay/estuary system. Although a DOS version of the TXBLEND models is available from TWDB for execution on PC desktop computers, these simulations can take several days to run. Therefore a cloud computing site (Digital Ocean - https://cloud.digitalocean.com) was used where droplets were created for each bay/estuary system and all models were run simultaneously. Putty and WinSCP software where used to execute the simulations and transfer files to and from the site. Model simulations times varied based on number of timesteps and number of nodes.

Provenance and Historical References:

Freshwater Inflows to Texas Bays and Estuaries (Paul Montagna and Audrey Douglas, editors), Chapter 4 (Hydrology, Circulation, and Salinity by Dan Opdyke, Josef Hoffmann, Joe Trungale, and Paul A. Montagna)

Individual Files: