NRCS Practices: Log Cribs for Streambank Erosion
Bank erosion, or the removal of soil, rocks, and vegetation by the force of moving water, is a natural part of river dynamics. Over the course of its life, rivers meander across the landscape, removing soil in some places and depositing it further downstream. The intensity and direction of this change is dictated not only by precipitation but by the surrounding landscape, geology, soils, and vegetation.
A streambank covered by trees and shrubs has a slower erosion rate than a bank with little or no woody plants, as the roots protect and anchor the soil. This means that streambanks without trees and shrubs are at a greater risk of erosion. Excessive erosion may be result of human interference with the natural river course and/or the use of the land next to the river. Structures or rubble deposited in the stream or on the bank can cause eddy currents, sending the water in a circular pattern that can cause severe erosion if the bank is not protected.
NRCS installed several streambank stabilization systems across New Hampshire in efforts to reduce bank erosion. The chosen log crib-style system is constructed with boulders, large logs, and tree root wads. The logs are anchored into the bank and the wood is laid in alternating patterns, creating a cabin or crib-like structure. This method uses natural materials to slow the flow along the bank, reduces erosion and provides habitat for fish and other wildlife in the stream. The cribs and plants trap sediment and allow new trees and shrubs to establish on the bank. Live shrubs and trees are planted near the top of the bank to further anchor soil.