Nature and Effects of County Drainage Ditches in South Central Minnesota

The extent of county drainage was determined for four counties in South Central Minnesota followed by a study of the geomorphic nature of man’s drainage in contrast to natural drainage. Selected drainage ditches and low order rivers were sampled for water quality and quantity in order to determine the contributions and timing of nutrient loads from each. Seventy-nine percent of the drainage ditches were found to terminate into rivers and they more than doubled the length of the surface fluvial systems. The closeness of fit of the drainage ditch systems to the low order Strahler classification scheme suggests that man has taken an immature lake-marsh environment and within 100 years created a geomorphically mature fluvial landscape. Nutrient loading by ditches into receiving bodies was found to vary by season, by individual ditch or river, and by stream order indicating that each ditch was unique. Water quality of one ditch during this wet study year was compared to a previous dry year study and the nutrient loading data was consistent and predictable. The most significant loading nutrient chemical parameter to the Minnesota River was found to be nitrate-nitrogen. Flow showed flashy response to storm events in some ditches and some were quite conservative. Sediment load was directly correlated to flow.Water Resources Research Cente