Bridge Scour Essay

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Bridge scour is the removal of sediment such as sand and rocks from around bridge abutments or piers. Scour, caused by swiftly moving water, can scoop out scour holes, compromising the integrity of a structure.
Bridge scour is one of the three main causes of bridge failure (the others being collision and overloading). It has been estimated that 60% of all bridge failures result from scour and other hydraulic-related causes. Major damage to bridges at river crossings occurs during flood. Damage is caused for various reasons, the main reason being riverbed scour at bridge foundations, namely piers and abutments.

6.2.4.1 Types of scour and scour process

The theoretical basis for the structural design of bridge is well established. In contrast, the mechanics of flow and erosion in mobile-boundary channels has not been well defined and it is
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Short-term general scour develops during a single or several closely-spaced floods. Long-term general scour has a considerably longer time scale, normally of the order of several years or longer, and includes progressive degradation and lateral bank erosion. Progressive degradation is the quasi-permanent general lowering of the riverbed due to hydrometeological changes, geomorphological changes, or human activities. Lateral shifting of channel banks can lead to the bridge being outflanked by the river or to undermining of the abutments. Banks erosion may result from channel widening, meander migration, a change in the river controls or a sudden change in the river course. The long-term general scour may not be significant during the design life of a bridge if the rate of scour development is relatively slow. The effects of long-term general scour can be felt suddenly however, e.g. through the formation of a cut-off near the bridge

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