Northern and Central Watersheds Characterization Phase II

Funding provided by the Texas Commission on Environmental Quality through a Clean Water Act § 319(h) grant from the U.S. Environmental Protection Agency.

This funding is to address non-point source (urban runoff, stormwater runoff) pollution problems.

The Lower Laguna Madre (LLM) is designated as an impaired waterway for high concentrations of bacteria and low dissolved oxygen (DO).

North and Central (NC) primary waterways (Raymondville Drain, Hidalgo Willacy Main Drain, and IBWC North Floodway) in the Lower Rio Grande Valley (LRGV) have not been characterized which can potentially be the flow water carriers of these contaminants into the LLM.

• Aquatic Life
• Laguna Atascosa Wildlife Refuge: Protects nearly 100k acres of habitat.
• Recreation activities: Fishing and Swimming

For more Low- Dissolved Oxygen Information visit:  MIT (2014) Dissolved Oxygen 

• Watershed Characterization Phase I (2019-2021) UTRGV: Thesis and  Research Publication. 
• Lower Laguna Madre - Fresh Water Flows (2021-2023) - RATES

• Phase II: Water Quality Data Collection (2024-Present) - RATES

Characterize water quality and flow at three of the primary watersheds that discharge into the Lower Laguna Madre.

• Raymondville Drain
• Hidalgo Willacy Main Drain
• IBWC North Floodway

• Project Duration: 24-36 months.

• Extend Phase I Lower Rio Grande Valley-North and Central Watershed Characterization (UTRGV).
• Real-Time Hydrologic System (RTHS): Leverages three RTHS commissioned by TWDB-FWF.
• Continuous water quality measurements: Dissolved Oxygen, Water Temperature, Specific Conductivity, and Nitrate.
• Quarterly water quality and hydrodynamic measurements: Dissolved Oxygen, Water Temperature, Conductivity, pH, Nitrate/Nitrite, Total Phosphorus, Total Nitrogen (TKN), and E. coli.
• Acoustic Doppler Current Profiler (ADCP) discharge transects and flow measurements to develop discharge rating curves as a function of stage height.

• QAPP Draft
• Water Quality Analysis: Summarize all data collected.
• Load Duration Curves: Characterized watersheds by load reductions.
• Load Characterization: GIS Spatial Analysis Tool: Spatially Explicit Load Enrichment Calculation Tool (SELECT).

• Leveraging Data: LRGVDC Flood Infrastructure Fund Project: Flow measurements taken at the N&C sites can be used.
• Continuous water quality and stream stage heights.
  • Address measurement bias.
  • Can be combined with derived flows to quantify nutrients loads.
  • Ability to characterize episodic events (e.g. spills, extreme weather)
• Watershed Protection Plan:
  • Best Management Practices
  • Nutrient Management
  • Irrigation Management

• Continuous: Real-time water quality data taken over the total length of the project (18 months).
• Instantaneous: Six quarterly sampling campaigns over the length of the project.

Equipment: YSI EXO-2, Acoustic Doppler Current Profiler (ADCP), Sampling Pole.

Data Collection: flow, water quality parameters, bacteria and nutrients concentration.

Frequency: Quarterly based, two out of six completed.

Results: Uploaded to TCEQ through SWQMIS. Data is publicly available through TCEQ's website.

TCEQ's maximum allowable bacteria concentration value for recreational waterways is 126 cfu/mL. From the 58 observations made across the three waterways, 42 exceedances were detected.

 RTHS Datahub 

 EPA-NAD Bank 

 TWDB Fresh Water Flows