Sabine Pass is a 6-mile long tidal channel connecting Sabine Lake, an estuarine coastal bay, with the Gulf of Mexico at the Louisiana-Texas border. Sabine Lake formed when an ancient river valley flooded during rising seas over the past 8,000 to 9,000 years, whereas Sabine Pass formed in response to rapid deposition along the Gulf shoreline fronting Sabine Lake over the past 2,000 years (longshore sediment transport and accretion along the Chenier Plain coasts of TX and LA), creating an elongate inlet between the mouth of Sabine Lake and the present entrance to the Gulf of Mexico. Although constriction of tidal flow through Sabine Pass created relatively deep channels prior to navigation channel construction, dredging has been required since the early 1900s to maintain a channel in support of commerce adjacent to Sabine Lake. Our project purpose was to evaluate sediment transport processes and dredged sediment disposal patterns relative to marsh shoreline changes within Sabine Pass. A vast quantity of historical maps, aerial imagery, channel dredging information, and existing literature for Sabine Pass and adjacent marshes was used to document the formation and evolution of the dredged sediment disposal island created in the navigable waters of Sabine Pass since the 1930s.

Based on observations from analyses, it was determined that dredged sediment disposal associated with navigation channel dredging in Sabine Pass in the early 1930s, east of the channel, was first observed as subaerial sediment mounds in August 1933. Sediment disposal islands grew substantially in size and number after significant channel dimension changes were implemented in 1937. By 1938, two large subaerial sediment disposal islands, and numerous smaller disposal islands, were present east of the dredged channel. Maintenance and new work dredging in the navigation channel continued to supply sediment to these disposal sites through the early 1950s, creating one large disposal island by 1953, resulting from large quantities of sediment placed on existing unconfined disposal mounds and transport from elevated portions of disposal areas to adjacent subaqueous shallow-water areas between the islands and east to the marsh shoreline during hydraulic placement of dredged sediment. This process of hydraulic placement first created low-lying subaerial mudflats and marshes between the original disposal islands that eventually expanded eastward toward the marsh shoreline. By 1955, partially exposed mudflats between the primary disposal island and marshes east were apparent due to hydraulic placement of dredged sediment from the channel. Drainage features from direct disposal locations on the disposal island illustrated the mechanism by which sediment infilling between the island and marshes to the east was creating wetlands where shallow water bottoms once existed. Placement of dredged sediment on the disposal island between 1955 and 1957 promoted rapid eastward growth of the dredged sediment placement island. Progradation of the eastern side of the disposal island was so rapid that by November 1957, mudflat and marsh deposits along the eastern margin of the disposal island had merged with the existing marsh shoreline. As Sabine Pass navigation channel expanded, water areas between the existing disposal island and stationary marsh shoreline filled with dredged sediment until land was continuous from the island shoreline to the original marsh shoreline.

Coastal Structure Impacts and Environmental Response

Applied Coastal