Geomorphology and Sediment Transport in the Eklutna River, Alaska

Author: Dube, Kathy V., Watershed GeoDynamics

Video Presentation

Abstract

A geomorphology and sediment transport analysis of the Eklutna River was conducted as part of comprehensive studies related to the 1991 Fish and Wildlife Agreement for the Eklutna Hydroelectric Project. Geomorphic and sediment transport processes in the Eklutna River downstream from Eklutna Lake have been altered by several management actions over the past century including water withdrawals, retention of sediment within constructed reservoirs, removal of the lower dam at River Mile (RM) 4, gravel removal from the river and floodplain, construction of the AWWU pipeline and access road, and channel confinement by roads and bridges. Sediment input, transport, and deposition are important processes that help to provide high quality aquatic habitat. An understanding of substrate conditions and sediment input and transport rates in the Eklutna River provides information that can be used to assess the effectiveness of potential future flow releases and aquatic habitat improvement measures under the 1991 Agreement.

The geomorphology and sediment transport study included:
- Remote sensing analyses using historic aerial photographs and sequential LiDAR data to determine sediment input rates from large natural source areas along the river and to delineate channel migration areas;
- Field work to measure substrate grain size, substrate movement and riverbed profile changes at monitoring transects following test flow releases; and
- Development of a 1-D HEC-RAS model sediment transport model to calculate sediment transport rates under potential future flow regimes and assess the magnitude and effectiveness of high flow alternatives to flush accumulated fine-grained sediment from the river without moving the limited supply of spawning-sized gravel/cobble material out of the channel.

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