A region's susceptibility to coastal change is defined by the physical, social, economic, and ecological conditions that comprise the area of interest. The Southwest Washington Coastal Erosion Study is actively engaged in quantifying the physical processes and long-term evolution of the Columbia River littoral cell. The resulting scientific data will be integrated with social and economic data of collaborating local communities and counties. It can be argued that physical processes influence short-term coastal change and long-term coastal evolution. However, the management response to these processes is most certainly driven by social and economic priorities established at the community level through a coordinated planning process. The study is integrating multidisciplinary data with results from a suite of modeling applications (e.g., coastal processes, shoreline change, etc.) using a geographic information system (GIS) to develop physical susceptibility parameters as input variables for a decision support system. This tool addresses coastal management issues by presenting coastal research as formalized knowledge that can be incorporated readily into the decision-making process.

An initial attempt at applying a susceptibility framework and developing management products has begun for an 8-kilometer stretch of the southern Long Beach Peninsula. The case scenario examines the seasonal variability of beach-state parameters (beach slope, dune crest elevations, etc.) and the impacts associated with predicted wave runup (impacts on the "toe" of the dune and overwash of the dune crest). Integrated data and model results are plotted on an orthophoto base map to illustrate areas susceptible to wave runup and dune overwash. Beach profiles, spaced at 100-meter intervals, were generated from the LIDAR data. Beach profile parameters, including beach slope, dune toe elevation, and dune crest elevation, were then extracted from each of the profiles as inputs for modelling wave impact.

Figure A displays the alongshore variability of dune toe and dune crest elevations. The mean dune toe and dune crest elevations for this 8-kilometer stretch of coast measure 4.7 meters (NAVD 88) and 7.8 meters (NAVD 88), respectively. Beach slope, as calculated between the 1.0- and 3.0-meter contours averages 0.025 (1:40). An assessment of the frequency of dune toe impact and wave overwash has been performed utilizing a probabilistic total water level model (Ruggiero et al., 1996), and the results are displayed in Figure B. Although dune overwash is an infrequent occurrence, wave impact at the dune toe is problematic along the southern end of the study area, with 9 locations (denoted by asterisks) experiencing more than 75 hours of wave impact per year. Figure C shows a higher potential for dune erosion and coastal flooding along the southern extent of the case example.

While mapped output may be useful over the short term, the static nature of a printed map may limit its utility into the future. Ideally, decision support can be provided as a GIS tool that enables a range of scenarios to be tested. This will allow local communities to determine specific boundary conditions, objective evaluation measures, their associated probabilities, and uncertainties and levels of risk. This will facilitate the adoption of scientifically based, publicly acceptable coastal management plans. LIDAR data can be used to update physical beach parameters rapidly and efficiently as part of a coastal monitoring strategy.

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