EVALUATING THE POTENTIAL FOR BANK EROSION TO PRIORITIZE CEDAR REVETMENT BANK STABILIZATION

Streams in southeastern Minnesota are commonly entrenched in legacy floodplain sediments that aggraded prior to 1970. Over the past 50 years sediment yield from upland areas has decreased significantly. However, with decreased sediment loads streams have incised into their floodplains and focused energy on the lateral erosion of their banks. As a result steep, actively eroding cutbanks are common in many streams.

High suspended sediment loads are a common water quality impairment in Minnesota streams. The legacy sediments eroding from cut banks are a significant source of the suspended sediment budget of southeastern Minnesota streams. There is an interest among various stakeholders to implement measures that stabilize stream banks and reduce their rate of erosion. Typical stream restoration techniques are costly and often do not succeed at stabilizing bank erosion. Thus, local agencies have proposed testing an innovative and cost effective stream bank stabilization technique called “cedar revetment” in Riceford Creek located in Houston County, Minnesota. Cedar revetment utilizes “weed” cedar trees that are overgrowing steep xeric prairies adjacent to many stream corridors. The cedar trees are cut down and then mechanically anchored to eroding cutbanks to mitigate erosion by reducing near-bank shear stresses.

To ensure that the cedar revetment is effectively targeted to stream banks where it can provide the most benefit, we have utilized the Bank Erosion Hazard Index (BEHI) Method. The BEHI method is designed to be easy to learn and can be performed rapidly in the field through a series of simple observations, including bank angle, bank height, bank surface protection as a function of vegetative cover and root density, bank sediment texture and stratification. These data were compiled into an overall score and an associated adjective rating that was used to inventory stream bank condition over a 3 km long reach. The BEHI metric provided a rapid and simple means of identifying and prioritizing the banks that were stabilized with cedar revetment. We hope that over the long term BEHI can also be used to evaluate the success of the cedar revetment by documenting a change in the BEHI score.