USING ARCVIEW 3.2 GIS WITH 3-D ANALYST & LIDAR DATA HANDLER EXTENSIONS TO STUDY THE DYNAMICS OF A NOURISHED BEACH AREA ON PRESQUE ISLE, LAKE ERIE, PENNSYLVANIA

Beach nourishment is required yearly on the Lake Erie shoreline at Presque Isle State Park, Erie, PA. This annual response to coastal erosion commonly involves over 50,000 cubic meters of sand and often costs a million dollars or more. The dynamics of the nourishment sand movement was not easily determined from the US Army Corps of Engineers monitoring data. In our study we periodically mapped a kilometer-long stretch of beach and offshore area documenting several different topographic surfaces using ArcView 3.2 and the 3-D analyst extension. Using the Lidar Data Handler extension we then calculated changes in sand volumes (cut and fill) for 4 separate areas of the beach and offshore areas from season to season. Having the volumetric data as well as shoreline-change data for the study area makes it possible to determine the fate of the nourishment sand to a degree that was previously impossible. The 4 subdivisions of the study area were comprised of, 1) the onshore nourishment beach, 2) the corresponding offshore area, 3) the down-drift onshore beach and 4) down-drift offshore areas. Maps of the surfaces of the surveyed area produced in ArcView 3.2 GIS were overlaid using the Lidar Data Handler extension. This permits the calculation and spatial display of volumetric changes of the entire area. To some extent, one can easily visualize the dynamics of sediment transport during the time elapsed between two maps simply by observing the spatial distribution of the areas of erosion (cut) and areas of deposition (fill). Having quantitative data for the volumetric changes is also very important for interpretation. During the period from June to September 2001 the onshore beach in the nourishment area lost a volume of 3,145 m3 of nourishment sand. During the same period the beaches down-drift received 8,324 m3, an excess of over 5000 m3 than could have come from the nourishment beach. Where did the excess sand come from? The volumetric data from offshore area show the movement of at least 200,000 m3 of sand there and make it the obvious source. The offshore sand came from nourishment placed well up-drift years ago and just now arriving in the area. Thus significant reduction in overall nourishment of Presque Isle since the break-wall construction might ultimately starve these beaches.