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The Evolution of Infilling Incised Valleys

The evolution of infilling incised valleys is initiated by the eroding effect of rivers due to sea level decline. Incised valleys are then filled with sediment such as mineral deposits, forming sand-bodies or barrier islands. This occurs as sea levels rise again. As a result of mineral deposits over time, incised valleys are a potential fossil fuel reservoir. Incised valleys are found on the eastern coast of the United States.

  1. Sea Levels

    • Sea level fluctuation is the principal driver of incised valley evolution. Sea levels rose dramatically after the last glacial period. It is estimated that 18,000 years ago, sea levels were lower by 300 feet. Around 12,000 years later sea levels rose by 285 feet, forming barrier islands and sandy shoals as incised valleys became filled with river sediment. This sediment traveled back and forth between sea and shore as sea levels fell and rose.

    Coastal Prism

    • The coastal prism is defined as a curved shoreline created during high sea levels. Incised valleys are predominantly found at coastal prisms, owing to the fact that sea levels do not fall enough for significant river erosion to occur elsewhere. During small drops in sea level, the shape of coastal prisms determines both the location and depth of incised valleys. Some are as deep as 70 meters.

    Monitoring Evolution

    • Monitoring the evolution of infilling incised valleys provides information on changes in sea level over periods of a few thousand years. Also, incised valleys are characterized by the type and origin of deposited sediments. For example, it is understood incised valleys in the Mississippi-Alabama shelf province contain deposits from the Mississippi delta. Such data gives insight into the effectiveness of current human efforts to reduce shoreline erosion.

    Environmental Impact

    • With predicted sea level increases and levee construction, barrier islands and other wetland areas are under threat of being lost. Levees divert river sediment and sea waves wash sediment away. This causes habitat destruction of several aquatic species including shellfish. There are also significant economic and recreational losses as these areas disappear.

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