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|Title:||Boat-wave-induced bank erosion on the Kenai River, Alaska|
|Authors:||Environmental Laboratory (U.S.)|
Cold Regions Research and Engineering Laboratory (U.S.)
Kenaitze Indian Tribe.
Maynord, Stephen T.
Biedenharn, David S.
Fischenich, J. Craig, 1962-
Zufelt, Jon E.
|Publisher:||Coastal and Hydraulics Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||ERDC TR ; 08-5.|
Abstract: The Kenaitze Indian Tribe requested that the U.S. Army Engineer Research and Development Center (ERDC) determine the relative contribution of boat-wake-induced bank erosion to total bank erosion along the Kenai River. The approach used in this study consisted of a delineation of boat wave characteristics along the study reach and a geomorphic and bank stability assessment. This analysis showed that, at specific times of the year and at specific locations, boat wave energy may be a dominant factor. However, on an average annual basis, boat wave energy is secondary to river currents in terms of total bankline recession. Reduction of boat wave energy should focus on areas having large boat passage frequency, such as the drift area at river miles 10–12 and areas where bank erosion is most problematic. Techniques to reduce boat waves from a single boat include the use of flat-bottomed boats, use of 50-hp motors to increase boat speed, keeping boats away from shorelines, and reducing boat weight. Decreased boat weight and keeping boats away from shorelines are two options that can result in benefits even when significant traffic is present. This study found that boat wakes are one of several factors contributing to bank recession. However, quantification of the relative magnitude of boat wakes to other factors such as river currents could not be determined. The results indicate that boat wakes may be a dominant factor during certain high boat usage times, discharges, and locations along the study reach. Although wake-induced erosion may be a secondary factor in bankline recession, it may be ecologically significant because of its persistence, distribution, and timing. However, bank recession associated with large flood events will likely overshadow the contribution from boat waves.
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