Evaluation of Optimum Design Parameters for Saturated Riparian Buffers
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 streambank stability at five sites in central Iowa. Four of the five sites were found to have an adequate factor of safety against failure, and while the fifth site was unstable, the bank failure was not likely to be caused by installation of the SRB. Additionally, our model shows that a reduction in SRB width decreases the factor of safety but does not lead to slope failure.