Environmentally Compatible Cobble Berm and Artificial Dune for Shore Protection

摘要

Cape Lookout State Park on the northern Oregon coast, has experienced extensive erosion, much of it associated with the strong El Ninos of 1982-83 and 1997-98, culminating in a series of unusually severe storms during the winter of 1998-99 that flooded the campground. A shore protection structure was clearly needed to prevent continued erosion, but it was decided that a conventional quarry-stone revetment or seawall would be incompatible with this natural park setting. Instead, the decision was made to construct a cobble berm that is similar to a natural cobble beach, backed by an artificial dune containing a core of sand-filled geotextile bags. There has been growing interest in the use of environmentally compatible structures for shore protection; this example provided the opportunity to monitor two such structures to determine their degree of success and to learn more about their designs. The monitoring has included a program of periodic surveys, analyses of tides and wave runup compared with structure elevations, and data collection to document the progressive changes such as the development of cobble sorting patterns wherein the structures evolve to become more like their natural counterparts on the coast. To date the structures have survived several major storms when high tides combined with the wave runup to produce some overtopping of both the cobble berm and artificial dune. In spite of the intensity of wave attack on the high-energy Oregon coast, this natural approach for shore protection has thus far successfully prevented significant erosion and flooding of the park grounds.