Sediment Budget Analysis for Laguna Madre, Texas: An Examination of Sediment Characteristics, History and Recent Transport

This study aimed to enhance the understanding of sediment fluxes in Laguna Madre and the primary processes responsible for the introduction and redistribution of sediments within and around the lagoon. Additional objectives included quantifying the long-term average annual sediment budget of the lagoon and comparing natural sediment fluxes from various sources (such as eolian transport, storm washover, upland runoff, tidal exchange, shore erosion, and authigenic mineral production) with fluxes related to dredging and disposal activities associated with the Gulf Intracoastal Waterway (GIWW) for channel maintenance.

Long-term analysis of sediment transport mechanisms and associated fluxes provided insights into the potential impact of reworked dredged material on the distribution of seagrasses in the lagoon. The study revealed that, on average, the volume of new sediment introduced into Laguna Madre is significantly less than the volume dredged from the GIWW. Moreover, the average sedimentation rate within the lagoon is lower than the rate of relative sea-level rise. This suggests that instead of filling up, the lagoon is slowly migrating westward, as evidenced by erosion along its western shore.

Comparison of cumulative volumes of dredged sediment from different segments of the GIWW in both northern and southern Laguna Madre with sediment volumes remaining in placement areas indicates that shoaling of the GIWW is primarily caused by the reworking of dredged material. This reworking process is influenced by water depth and location relative to predominant wind-driven currents. Areas with infrequent flooding or extremely shallow water experience minimal reworking, while dredged material in deeper-water placement areas is often reworked and redistributed back into the GIWW or surrounding areas of the lagoon.