Lower Laguna Madre - Fresh Water Flows (FWF)

The Lower Laguna Madre (LLM) located at South Texas is the home of a large diversity of aquatic animals and a big source of recreational activities that take place on it. The LLM has its impact in flood planning as it receives the discharge of the four major drainage ditches in the Lower Rio Grande Valley (LRGV). These four waterways are: Raymondville Drain (RVD), Hidalgo Willacy Main Drain (HWMD), US International Boundary Water Commission (US-IBWC) North Floodway, and the Arroyo Colorado (AC).

The LLM was declared as an impaired waterway due to screening levels of bacteria from 2010 until 2020 (TCEQ, 2011, 2013, 2015, 2018, 2019, 2020), reason that motivates the implementation of a water characterization project that allow to address the real problem and potential solutions. Since 2020, the bacteria concentrations decreased enough to no longer classify the LLM as impaired (TCEQ, 2020, 2022), however, the LLM still has a warning as low levels of Dissolved Oxygen (D.O.) had been observed.

The LLM is one of the most important environmental and economic assets in South Texas, therefore, the necessity of implementing monitoring actions that allow to characterize water flows, water quality, and bacteria along with nutrients concentration. The study in this Story Map describes the efforts conducted by RATES, Inc aiming to produce reliable data that will help stakeholders to take informed decisions that led to the successful development and implementation of effective remediation and preventive strategies to improve water quality of the Lower Laguna Madre.

During the length of this study (July 2021 - June 2023), the following actions were implemented at the four major waterways that drain into the LLM:

1. Monitor in Real-Time water depths and water surface elevation for two years (Continuous data).
2. Conduct quarterly monitoring campaigns that allow to characterize water flows, water quality, as well as bacteria and nutrients concentration (Instantaneous data).

The following slides provide an overview of the four waterways analyzed:

RATES installed one Real-Time monitoring station at each of the main waterways that drain into the LLM in order to fulfill objective no. 1: Continuous Data. Each monitoring station takes a reading every 5 minutes of the following variables: 1) water depths, 2) water surface elevation, 3) water temperature, 4) wind speed, 5) wind direction, 6) wind temperature, and 7) barometric pressure. Real-time readings from each station are open access (free to visualize and to download), the link to retrieve these datasets is available:  here . Monitoring stations details are discussed in the following slides:

A total of six monitoring campaigns were conducted on a quarterly basis (December 2021 - May 2023). Equipment, procedures, and objectives behind instantaneous data collection are described in the following section.

• Equipment: EXO 2 Multiparameter Sonde with handheld.
• Goal: Measure levels of: pH, Specific Conductance, Dissolved Oxygen, and Water Temperature.
• Sonde Calibration: A pre-calibration, valid for 24-hours, was conducted before each monitoring campaign using proper calibration standards for pH (three-point calibration: pH 4, pH 7, and pH 10), Specific Conductance (one point calibration: 10,000 us/cm), and Dissolved Oxygen (one point calibration: 100%). A post-deployment analysis was conducted for each of the previously mentioned sensor after sampling activities, the procedure consisted of recording readings from the EXO2 Sonde after being used in the field.
• Field Procedure: The EXO2 Sonde was placed in the water for a minimum of 20 minutes, the sonde took readings every 30 seconds that were locally stored in its handheld and later retrieved in a spreadsheet format.
• Software Utilized: KorEXO to calibrate the sonde and review or format field data.

• Equipment: Stream Pro Acoustic Doppler Current Profiler (ADCP).
• Goal: Measure water flow in m ³ /s.
• Software Utilized: WinRiverII to calibrate, operate, and post-process data collected with the Stream Pro ADCP. A computer was required during field activities as the equipment was controlled with WinRiverII wirelessly through Bluetooth.
• Calibration: A software-guided compass calibration was performed in the field before using the Stream Pro to collect data.
• Procedure Description: The Stream Pro had a mounted transducer responsible to draw the profile of the ditch (cross-section) and characterize water flow and speed. The data collection procedure was quite simple, it required of three personnel, one on each edge of the ditch and one more operating the WinRiverII software. The goal was to move the Stream Pro, as steady and straight as possible, from edge to edge to complete a transect, the process was repeated until the difference between observations was less than 5% which was usually achieved after 6 transects. Once completed, the Stream Pro could be taken out of the water and no post-calibration was required.

• Holding Times: 24 hours.
• Goal: Address concentrations of bacteria (E. Coli) and nutrients (Total Kjeldahl Nitrogen (TKN), Nitrate-Nitrite Nitrogen [NO ₂ -NO ₃ ], and Total Phosphorous [TP].
• Containers: Provided by the Lab, sterilized plastic containers of 250 mL for Bacteria, and 150 mL for Nutrients. Therefore, 2 containers were filled per monitoring site.
• Procedure: Containers were filled with water samples using a sampling pole that was previously rinsed three times with water from each waterway. After this, using a marker, container labels were marked with information such as: sample ID, date and time of collection, sampler initials, and waterway name.
• Laboratory: All samples collected for this project were analyzed by SPL-LAB, formerly known as ANA-LAB, located in Brownsville, TX. This lab has the NELAP Accreditation.
• Results: Results were sent electronically to RATES typically within the next 2 weeks after receiving the samples.

The real-time observations from monitoring stations help to identify trends in water, i.e., TWDB 3 and TWDB 4 monitoring the US-IBWCNF and the AC respectively, had clearly shown a tidal influence which makes the waterways flow to the upstream during certain periods of time. Addressing trends across the 4 waterways its crucial for characterization purposes and modeling efforts. Real-Time and historic data from all 4 stations is available using the following link:

Findings from the six monitoring campaigns (instantaneous data) are shown in the next tables. Values in red mean concentration exceedances, according to TCEQ's surface water screening levels (TCEQ, 2020a). The focus of this study is non-regulatory; therefore, the environmental status of the analyzed waterways is not impacted.

The Fresh Water Flows Lower Laguna Project was concluded in July 2023 however, instantaneous and continuous data collection for characterization purposes will continue at stations TWDB 1, TWDB 2, and TWDB 3 starting in Fall 2023 under the 319 Non-Point Sources (NPS) Program, grant awarded to RATES by the Texas Commission on Environmental Quality (TCEQ). For more information details visit:

Station TWDB-4 will continue reporting continuous data as it will be incorporated to an extensive network of 44 monitoring stations across the LRGV willing to feed real-time computer cloud based hydrologic models aiming to forecast flood extents using artificial intelligence (AI). This project is being funded through the Flood Infrastructure Fund (FIF) Category 1; grant awarded to RATES by the Texas Water Development Board (TWDB).

This project was funded by the Texas Water Development Board (TWDB) under the Fresh Water Flows Program (FWF).

• TCEQ. (2011). 2010 Texas Integrated Report-Texas 303(d) List (Category 5).
• TCEQ. (2013). 2012 Texas Integrated Report-Texas 303(d) List (Category 5).
• TCEQ. (2015). 2014 Texas Integrated Report-Texas 303(d) List (Category 5).
• TCEQ. (2018). Draft 2016 Texas Integrated Report-Texas 303(d) List (Category 5).
• TCEQ. (2019). 2018 Texas Integrated Report-Texas 303(d) List (Category 5).
• TCEQ. (2020). 2020 Texas Integrated Report-Texas 303(d) List (Category 5).
• TCEQ. (2020a). 2020 Guidance for Assessing and Reporting Surface Water Quality in Texas.
• TCEQ. (2022). 2022 Texas Integrated Report-Texas 303(d) List (Category 5).