Slope Stability Analysis of a Saturated Riparian Buffer: A Case Study

A relatively new solution to reduce nitrate export from agricultural drainage is to use existing riparian buffer zones along the field edge as media to provide storage volume by distributing drainage water to saturate the soil, commonly referred to as a "saturated riparian buffer" (SRB). Though previous research has proven the effectiveness of SRBs to reduce nitrate export, uncertainties about long-term impacts prevent widespread adoption of the practice. One significant uncertainty is the stability of the streambank after saturation, raising concerns about slope instability and erosion. Current design standards use conservative guidelines for minimum buffer width and maximum bank height to prevent bank failure from occurring, thereby limiting site eligibility for installation of SRBs. This study investigated the impact of SRB design parameters on the stability of the streambank at a site in Hamilton County, Iowa. Installation of the SRB did not substantially decrease the factor of safety against failure. Additionally, our model shows that a moderate reduction in buffer width decreases the factor of safety but does not lead to slope failure.