Paper No. 12
Presentation Time: 11:20 AM

ANTHROPOGENIC INFLUENCES ON RATES OF COASTAL CHANGE


ABSTRACT WITHDRAWN

, chapke@usgs.gov

There is an increasing need for regional shoreline change assessments to aid management and planning decisions within growing coastal communities. Due to the complex nature of assessing anthropogenic influences, it is rare for coastal vulnerability and hazard assessments to include this component, especially in regional-scale studies. The U.S. Geological Survey recently completed a shoreline change assessment of the New England and Mid-Atlantic coast, as part of a national effort to assess change along the nation’s coastlines. In addition to natural influences on the rates of change, we examine the effects that development and human modifications to the coastline have on the regional shoreline change measurements.

In general, rates of shoreline change are greater in the Mid-Atlantic states than New England. The coast was additionally classified into geomorphic landform types and the rates of change were analyzed in the context of the landform characterization. Results indicate that geomorphology has some influence on rates of change, with barrier islands eroding more quickly than mainland beaches or beaches along rocky coastlines. The anthropogenic impacts on the shoreline change rates are found to be greater along the more densely developed and modified Mid-Atlantic coast than in New England. Jetties at engineered inlets impound large volumes of sediment, resulting in extreme but discrete areas of progradation. This produces a positive shift (averaging 0.12 m/yr) in averaged rate values that if not accounted for, could lead to misinterpretation of the stability of a given section of coast. In addition, we also identify a strong correlation (r2 = 0.88) between rates of shoreline change and relative level of human development. Using the geomorphic characterization as a guide for the expected relative rates of change, we found that the shoreline appears to be changing naturally only along sparsely developed coasts. Even a modest amount of development significantly influences the rates of change and overrides the geomorphic signal. The analysis demonstrates that human activities alter the natural long-term behavior of the coast on a regional scale, and implies that assessments of vulnerability based largely on rates of change along developed coastlines need to take the role of human modification into account.