UNDERSTANDING SHORT- AND LONG-TERM COASTAL EVOLUTION VIA QUANTITATIVE SEDIMENT BUDGETS

A one-dimensional, geomorphic model is being used along the glaciated coast of Cape Cod, Massachusetts to develop quantitative sediment budgets. The model output quantifies the directions and volume rates of net longshore sediment transport and delineates sediment sources and sinks. The mapping of littoral cells in this manner can improve our understanding of sediment transport pathways, coastal evolution along many spatial and temporal scales and the impact of anthropogenic alterations. Along glaciated coasts in particular, due to the absence of rivers and river-supplied sediment, the amount of sediment available to create or maintain active coastal landforms is limited to that provided by erosion of the coast itself. The understanding of coastal sediment sources and sinks has significant socio-economic value for densely-populated and heavily touristed coastal areas. These data can better inform coastal managers and other stakeholders and could provide the basis for regional sediment management based on littoral cells rather than arbitrary political boundaries.

Sediment budgets for the individual cells were calculated from cross-shore coastal volumetric change rates determined at 150 m intervals alongshore from contemporary and historical topo-bathymetric data and adjusted to account for on- and offshore sediment losses. Null points in net longshore transport were estimated from geologic indicators, longshore transport gradients and existing literature. Longshore transport diagrams, delineating source and sink zones, were produced through integration of the cross-shore volumetric change rates alongshore from the source to the sink null points. In addition, three-dimensional datasets from the 1930s to the present have been developed throughout the study area. The comparison of historical and contemporary surface models of the region have provided insights into recent and ongoing coastal evolution as well as potential future coastal configurations.