Geologic Effects of Cities: ABSTRACT

Human activities in an industrial society are geologically significant in coastal cities because of the amounts of sediment and wastes moved and resulting topographic changes. Small streams are altered or destroyed, many becoming sewers. Large streams are dredged to accommodate ocean-going vessels and nearby river banks are bulkheaded. Shallow areas (including wetlands) are filled to provide space for city growth. Sewer, industrial, and sediment discharges are deposited in navigation channels which eventually require extensive dredging and waste disposal operations. The volume of wastes, and the sediment yield per unit area of the city, equals or exceeds the discharge of many rivers. Dams and public water-supply systems change river flows and dredging can change tidal reg mes in the estuaries. Sand and gravel production and construction of groins, bulkheads, and other structures change ocean shorelines and disturb beach processes. In the future, human activities will extend to the continental shelf where sand and gravel deposits will be exploited, offshore electrical power plants will be built, and port facilities will be constructed for deep-draft vessels requiring extensive dredging across the shelf. Even offshore airport centers have been proposed. These urban processes and their geologic effects are well documented in the New York metropolitan region. End_of_Article - Last_Page 782------------