Importance of the Geologic Framework Along the Texas Coast

Importance of the Geologic Framework along the Texas Coast

C. Houser Department of Geography Department of Geology & Geophysics Texas A&M University

Island transgression is accomplished during storms capable of overwashing the foredunes Overwash depends on the elevation of the surge relative to the dune, and the duration of the storm

Resiliency of a barrier island depends on the ability of the dunes to recover in height and extent “..essential to understand this geologic framework Foredune Recovery before attempting to model the large-scale behavior of these types of coastal system..” Beach Recovery -Riggs et al. (1995) Nearshore Recovery Vegetation Vegetation Geologic Framework Does the Framework Geology have a control on the behavior of the Texas coast? Houser, C., and Mathew, S. (2011) Variability in foredune height depends on the alongshore correspondence of transport potential and sediment supply. Geomorphology, 125, 62-72.

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Ridge More sediment in the backshore and intertidal bars upwind of the largest dunes South Padre Island exhibits a similar framework geology as Gulf Islands

Gulf Islands National Seashore South Padre Island Reflective to Intermediate profile Intermediate to Dissipative profile

•! Largest dunes where the beachface is •! Largest dunes where the beachface is more gently sloped at ridges intermediate at swales

•! Smallest dunes where beachface is •! Smallest dunes where beachface is relatively at swales dissipative at ridges

•! Depends on gentle slope to permit •! Depends on intertidal bar migration and transport from beach to dune backshore accretion

Transport limited environment Supply limited environment

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-./9& North Padre Increased washover enhances the alongshore transport gradient

-:/.& Gulf Islands

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5*+1())6#'()-*7(&"(8")"$3*".*9:.-*;".-* Variable Dune Height

Pre- Storm

Dune Scarping Washover and Erosion

Storm Impact

Erosion Deposition Deposition

Slow but Limited Recovery

Post-storm Vegetation Recovery Recovery

Alongshore redistribution (dissipation) Foredune Recovery “..essential to understand this geologic framework before attempting to model the large-scale Beach Recovery behavior of these types of coastal system..” Nearshore Recovery

-Riggs et al. (1995) Vegetation Geologic Framework

Summary

•! Barrier island morphology is dependent on the framework geology –! South Padre Island- Transverse ridge and swale topography –! North Padre Island- Ridge and swale, Pleistocene channels and ?

•! Variability in dune height as a result of framework geology controls the rate of island transgression

•! Human activity can remove strength provided by the framework geology by making the dune more variable or enhance the variation

•! Different management strategies are required based on different framework geology

Importance of the Geologic Framework along the Texas Coast

C. Houser Department of Geography Department of Geology & Geophysics Texas A&M University

Dune Crest Elevation

Dune Base Elevation

Dune Height (Crest-Base)

Beach-Dune Volume

•! Blowout development is accelerated in the main driving section of Padre Island National Seashore

Variable Dune Height