Coastal mesoscale changes on Matagorda Island

Abstract

Sediment analysis and elevational profiles were used to evaluate the morphological and sedimentary dynamics of Matagorda Island, Texas. Several geomorphic variables were found to be important for the analysis of the spatial and temporal patterns on the coastal geomorphology of Matagorda Island. Based on the statistical and morphometric analysis of the coastal landforms, the island was divided into three distinct sub-environments: an erosional eastern zone, a transitional mixed zone, and a depositional western zone. Some of the geomorphic changes detected include an overall decrease in beach slope from the east to the west, with the extreme east end showing an increase in beach slope owing to significant erosion in that area only, and a steady increase in beach width from east to west, with typical values ranging from less than 20 meters in the eastern sections, to over 70 meters in the western part. The increase in beach width was accompanied by an increase in the primary and secondary dunes, with the latter exhibiting some of the highest values at the west end of the island. No significant granulometric changes were identified between the primary and secondary dunes, although some grain size variations were detected between the nearshore environment and the dune systems. The data indicates that Matagorda Island is currently experiencing a net aggradational phase, as part of a geomorphic system undergoing dynamic equilibrium.