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Bathymetric, Hydrodynamic, Biological, and Water-Quality Characteristics of a Nearshore Area of the Laguna Madre Near South Padre Island, Texas, 2021–22

Scientific Investigations Report 2023-5111
Prepared in cooperation with the City of South Padre Island
By: , , and 
https://doi.org/10.3133/sir20235111

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Abstract

A variety of data were collected by the U.S. Geological Survey, in cooperation with the City of South Padre Island, to better understand the physical and biological habitat in Tompkins Channel and adjacent seagrass beds in the lower Laguna Madre, Texas, where the construction of berms has been proposed in the City of South Padre Island’s Shoreline Master Plan. These berms would be used to create living shorelines, defined as shorelines that “connect the land and water to stabilize the shoreline, reduce erosion, and provide ecosystem services, like [maintaining] valuable habitat, that enhances coastal resilience.” Bathymetric surveys show variability in the lagoon depth within the study area and clearly delineate the relatively shallow bay from the deeper Tompkins Channel. There were seasonal patterns in daily mean tidal water-surface elevations, with higher mean tides in the fall and spring and lower mean tides in the winter and summer. Seasonal differences in mean tidal water-surface elevations were primarily caused by astronomical forces. Shorter-term (daily and weekly) variations in tidal water-surface elevations were produced by meteorological forcing resulting from high- and low-pressure systems, the passage of fronts, local storms, and tropical storms. The tide driven currents typically were toward the north-northwest during flood tide or toward the south-southeast during ebb tide, roughly parallel to the general South Padre Island shoreline orientation. Prevailing water current velocity (current speed and direction) indicates that there usually is a net inflow into the lower Laguna Madre from the Gulf of Mexico and a net outflow at locations north of the study area. The overall seagrass density was generally lowest in the northeast section of the transect. Areas of low seagrass density were also most commonly observed close to the channel edge of the transect. Overall, Syringodium filiforme was considerably more abundant than Thalassia testudinum and Halodule wrightii. Amphipods from the families Ampithoidae and Melitidae were the most abundant benthic invertebrates, followed by gastropods in the family Calyptraeidae. Higher abundances of benthic invertebrates were recorded at sites farther away from Tompkins Channel than at sites closer to it, perhaps because of the sensitivity of these organisms to disturbances caused by erosional forces in the channel. Changes in water-quality measured during a 2-day survey were consistent with patterns observed in prior studies, indicating biological processes likely play an important role in the physicochemical environment of the study area. Collectively, the data provide baseline information that can be used as reference conditions prior to any shoreline enhancement activities in the lower Laguna Madre.

Suggested Citation

Opsahl, S.P., Beltran, J.I., and Ockerman, D.J., 2023, Bathymetric, hydrodynamic, biological, and water-quality characteristics of a nearshore area of the Laguna Madre near South Padre Island, Texas, 2021–22: U.S. Geological Survey Scientific Investigations Report 2023–5111, 19 p., https://doi.org/10.3133/sir20235111

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction 
  • Methods
  • Bathymetric, Hydrodynamic, Biological, and Water-Quality Characteristics
  • Implications for Shoreline Conservation Activities
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Bathymetric, hydrodynamic, biological, and water-quality characteristics of a nearshore area of the Laguna Madre near South Padre Island, Texas, 2021–22
Series title Scientific Investigations Report
Series number 2023-5111
DOI 10.3133/sir20235111
Year Published 2023
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Oklahoma-Texas Water Science Center
Description Report: viii, 18 p.; 4 Data Releases
Country United States
State Texas
Other Geospatial South Padre Island
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details