ASSESSING THE ROLE OF FRAMEWORK GEOLOGY ON BARRIER ISLAND GEOMORPHOLOGY

Barrier island development and patterns of resiliency can exhibit both free and forced behavior. The influence of framework geology on barrier island geomorphology and geomorphic change has previously been examined in areas where the framework geology is relatively simple or rhythmic. The purpose of this paper is to examine the influence of framework geology on beach and dune geomorphology at Padre Island National Seashore (PAIS), where the framework geology is highly variable. Beach and dune morphometrics were extracted from a topobathy digital elevation model (DEM) using an automated approach. Offshore bathymetric profiles were also extracted from the topobathy DEM. An electromagnetic induction (EMI) survey of PAIS was used to map the subsurface framework geology. Wavelet decomposition, peak spectral density (PSD), bicoherence, auto-regressive fractionally-integrated moving average (ARFIMA) analyses were used to test for spatial relationships between and within the extracted alongshore metrics. Results demonstrate that the island morphometrics are structurally controlled at scales up to 3.5 km. Statistical relationships between surface, subsurface, and offshore metrics suggests that the framework geology has influenced PAIS development, and that its influence is variable along the island. ARFIMA results suggest that the influence of relict infilled paleochannels on the modern barrier island geomorphology is asymmetric, with greater long-range dependence to the north of channels. We propose that the accepted theory of development for PAIS should be revised to reflect this new understanding of the framework geology, and that management explicitly recognizes the importance of framework geology on barrier island morphology and resiliency as anthropogenic and natural forces change in the future.