Engineering Geology in the Marine Coastal Zones of the Continental United States Part I-Pacific Coast

Abstract

The coastal portion of the Pacific Northwest of the United States, the states of Washington and Oregon, involves 2,800 mi (4,510 km) fronting on the Pacific Ocean, ocean estuaries, the Straits of Juan de Fuca and Georgia and Puget Sound and its adjacent waters. Ocean coastal areas are characterized by bold, rock headlands and elevated marine terraces with intervening drowned estuaries guarded by bay mouth spits and bars. The Columbia River is the only stream of continental proportions which exits in this segment of coast line. Much of the mainland shorelines fronting on the Juan de Fuca and Georgia straits and Puget Sound are characterized by sea cliff development in glacial deposits with interveaning spits, hooks and bars. Raveling, landsliding, block calving and rock fall are predominant processes in sea cliff development on the ocean coast, depending on materials, structure and ground-water conditions. The resulting detritus maintains nearby down-drift ephemeral landforms. Engineered works for navigation improvement began in the mid 18809s and has continued to the present time. Twentieth century commercial and residential development of coastal areas with attendant transportation networks and ground-water supply have required solutions to land use, erosion and construction problems. Many of these problems have resulted from failure to recognize some basic principles of coastal geomorphology with expensive and sometimes tragic results. There are other examples where success is a result of appropriate recognition of geologic process.