Minnesota Agricultural Ditch Reach Assessment for Stability (MADRAS): A Tool for Local Inspection & Maintenance

Ditches in Minnesota and throughout the upper Midwest USA are becoming morphologically unstable via channel enlargement and aggradation. Most ditches adjust channel form over time; some remain stable whereas other ditches unravel and require thousands of dollars worth of maintenance. Unstable ditch channels have resulted in loss of biotic habitat, excessive turbidity and sediment transport in downstream Minnesota water bodies. Biotic and sediment impaired waters require a total maximum daily load (TMDL) to delist an impaired waterbody from the Clean Water Act (CWA) Section 303(d) list. There are climatic, geologic and land use reasons why ditch channels become unstable. MADRAS is a relatively rapid assessment tool that considers both channel hydraulics and geotechnical factors associated with channel stability. A ditch reach must be walked by an evaluator to determine processes such as toe slope erosion, bank seepage, bank angle, vegetation, slumping, and the relative in-channel sediment storage and transport. Observations of processes and hydrologic pathways are documented and then ranked based on a weighted scale. Localized ground water seepage induced slumps rank lower than bank slumping induced by systematic channel enlargement. Ditch reach ranking offers the local inspector and drainage authority a means to prioritize the nature of ditch channel instability and a plan for guiding the maintenance response. We provide analysis of the factors that result in ditch channel instability and offer an assessment tool for evaluating processes and pathways occurring within a given ditch system.