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<br />Definition of Erosion and Scour <br /> <br />Stream channel erosion and fill is a natural process that occurs on most <br /> <br />streams most of the time. Erosion is the process whereby the materials of the <br /> <br />earth's crust are loosened, dissolved, or worn away and simultaneously moved <br /> <br />from one place to another. The study of the development of present landforms <br /> <br />produced by erosion or deposition and the history of changes in <br /> <br />characteristics of these landforms is known as geomorphology (Bates and <br /> <br />Jackson, 1980). <br /> <br />General scour occurs is a channel or on a flood plain and is not localized at <br /> <br />a pier, abutment, or other obstruction to flow. In a channel, general scour <br /> <br />affects most or all of the channel width. General scour may occur at a site <br /> <br />without. the presence of bridge piers or abutments. <br /> <br />Local scour in a channel or on a flood plain is localized at a pier, abutment, <br /> <br />tree, or other obstruction to flow. As such, local scour may also occur <br /> <br />without the presence of a bridge structure. In the design of bridge, pier, <br /> <br />and abutment footings, the possible occurrence of both general and local scour <br /> <br />should be considered. <br /> <br />Types of Erosion Control (Countermeasure) Practices <br /> <br />A countermeasure is defined as a measure, either incorporated into the design <br /> <br />of a bridge or installed separately at or near the bridge, that serves to <br /> <br />prevent or control hydraulic problems. Countermeasures are classified <br /> <br />according to the following major categories: <br /> <br />4 <br />