Relative Role of Overwash and Aeolian Processes on Washover Fans, Assateague Island, Virginia-Maryland

Kochel, R; Wampfler, Laura

Brief Description: Sediment budget data for six fans along Assateague Island are presented for a four-yearperiod that includes an exceptionally stormy year, an exceptionally calm year, and two years having average storm history. Full Description: There has been considerable controversy in recent years about the relative importance ofoverwash vs. aeolian processes in the vertical accretion or erosion of barrier islands, Most studies have used sediment budget data sets of two years or less in length, Analysis of coastal climatic data suggests that there are significant secular variations in storm intensity, frequency,and duration over time scales of 10's of years. Annual variations in climatic variables such asthe magnitude and frequency of precipitation, high winds, and overwash have a considerableeffect on accretion or erosion of wash over fan surfaces along mid-Atlantic barrier islands, Conclusions and predictions based on data sets from very stormy years may be dramatically different than those based on data from relatively calm periods. Sediment budget data for six fans along Assateague Island are presented for a four-year period that includes an exceptionally stormy year, an exceptionally calm year, and two years having average storm history. Accretion due to overwash processes was exceedingly dominant during the stormy year, but still significant in normal years. In contrast, aeolian deflation and deposition dominated during the calm year. Overall, Assateague Island fan surfaces accreted significantly ove r the course of the study, by an island-wide average of 22 em. Individual fansaccreted by as much as 90 em. Observed variations in fan surface changes depended primarilyupon the frequency of precipitation. frequency of over-wash, and topography of the local fan area. The importance of overwash or aeolian processes with regard to fan accretion and erosion appears to depend upon va riabil rt y and cyclicity of climatic factors. The effects of two exceedingly large storms resulted 10 e xt ensrve accretion on fun surfaces thot was greater than the sum of 15 moderate storms during the four years. Longer observations periods may be needed to project future changes on barrier island surfaces

Relative Role of Overwash and Aeolian Processes on Washover Fans, Assateague Island, Virginia-Maryland

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