Missouri River Basin Hydrology, Connectivity, and Geomorphology Assessment Report

The Missouri River basin in Minnesota drains 1783 mi2 of predominantly row cropped and pastured land in the southwestern part of the state. The four Hydrologic Unit Code (HUC) 8 watersheds (Upper Big Sioux, Lower Big Sioux, Rock, and Little Sioux) that comprise the Missouri River basin in Minnesota became subject to the Minnesota Pollution Control Agency's (MPCA) Intensive Watershed Monitoring (IWM) process in 2011 to assess the overall health of the watershed and identify areas of interest that need to be protected or restored. The "healthy watersheds" approach the MPCA and Minnesota Department of Natural Resources (MNDNR) have adopted assesses a five component framework. These five components of a healthy watershed consist of: hydrology, geomorphology, connectivity, water quality, and biology. All of these components are interrelated, and the disruption of any of them can result in undesirable consequences deeming the stream impaired for one or more condition. The MPCA is tasked with the responsibility to monitor and assess the biology and water quality in watersheds active in the IWM process while the MNDNR provides supplementary data and conclusions for the geomorphology, hydrology, and connectivity components. Once all of these components have been evaluated, the MPCA creates a stressor identification (SID) document to show what stressors are causing current impairments within Assessment Unit ID's (AUID) in the study watershed. The SID document helps guide the Watershed Restoration and Protection Strategies (WRAPS); a guidance document for local units to implement clean water projects that will provide the most benefit to local resources. This report analyzes the hydrology, connectivity, and geomorphology components of the Missouri River basin in Minnesota. Historical gage data on the Rock River, stream crossing data, and applied fluvial geomorphology assessments were analyzed in order to find relationships that would help understand water quality and biological impairments throughout the basin. Poor riparian vegetation communities and improper stream crossing sizing were found to have an effect on geomorphic response throughout the assessed parts of the Missouri basin. Altered hydrology, though very well documented in other watersheds as a driver of geomorphic response in rivers, was inconclusive in the Missouri basin likely due to lack of long-term (>30 years) hydrological data. At geomorphology field sites with relatively undisturbed riparian vegetation, it appeared that geomorphic stability was much better than overgrazed reaches. Aerial photo analyses showed improper sizing of culverts and bridges also resulted in increased sediment supply and channel succession downstream. In order to attain a healthy watershed status, the WRAPS process will have to address issues within the watershed. As important as restoration of disturbed sites is, focus must also be set out to protect undisturbed areas that appear to be near "reference" condition. The overall objective is to have a healthy watershed that sustains agriculture, groundwater, fish and wildlife habitat, biodiversity, recreation, and water quality in our landscape.
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Minnesota Water Research Digital Library
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Public Domain