An assessment of spatial variability in water level observations and susceptibility to inundation from coastal storms in a developed estuary, Raritan Bay, New Jersey.

摘要

Coastal flooding is an integral part of the development of natural estuarine ecosystems but also threatens human populations living along estuarine shores. A study was conducted on the Raritan Bay, New Jersey shore to determine the spatial variability of elevated water levels from coastal storms and the physical controls on susceptibility to inundation. Raritan Bay is used as a study site because it is a developed estuary with a high population density and a variety of flood mitigation strategies in place. Water levels are identified from wrack (debris) lines on field profiles 200 m apart over 10 km of shoreline for five storms. Elevations on the field profile are referenced to a standard datum for comparison throughout the study area. The greatest spatial variability of water levels between sites from the observed storms was 1.7 m. Variability in water levels at the same site for different storms is used to evaluate site-specific relationships between shoreline characteristics and storm conditions. Fourteen onshore variables are determined from the field profiles and include natural and human-altered geomorphic features. Thirty-three offshore variables, including bathymetry and fetch, are determined or calculated from data derived from digital nautical charts. Fifteen of the variables are significantly correlated to water levels, with only one variable, the maximum elevation of the profile, correlated to all five storms. Correlated variables were categorized into five susceptibility classes and combined to produce two susceptibility indices using a Geographic Information System (GIS). The first index uses onshore and offshore variables to determine susceptibility to actual inundation. The second index uses only offshore variables to determine susceptibility to potential inundation. Water levels are highest where hard, vertical shore protection projects exist, suggesting that these structures increase water levels and susceptibility to actual inundation of human structures landward of them. Marshes and nourished beaches reduce water levels and susceptibility to actual inundation of human structures landward of them. Site-specific coastal data analysis and the use of GIS are consistent with modern research objectives to develop and enhance digital coastal databases and advance current flood mitigation based on single flood elevations for entire shorelines.