Sources of Sediment in the Root River Watershed

Sediment is a natural part of river ecosystems. Yet, too much of it can be harmful to the quality and health of the river. It is important to understand the sources of river sediment when making land and water management decisions. Predicting where the sediment is coming from is a difficult task. The Root River Watershed in Southeastern Minnesota is large, nearly the size of Delaware, and the process relies on current science and technology. Scientists from multiple Universities just completed a five-year study to help understand the movement of sediment in the Root River Watershed. The project was funded by the Minnesota Department of Agriculture’s Research program (Clean Water Fund).

 

Study Highlights

• An estimated, 56% of the sediment in the Root River is from non-field sources (i.e. stream banks and bluffland slopes).
  • 43% of this non-field sediment, found at the watershed outlet, is from near-channel stream bank sources. This soil “appears to have been initially derived from agricultural fields, presumably within the past 150 years, but has been temporarily stored in, and reworked from, floodplains and alluvial terraces.” Near channel sediment sources are highly sensitive to flow in the mid to lower reaches of the Root River watershed.
  • Other non-farm field sources of soil include bluffland hillslopes and contributes an estimate 13% of the annual sediment exported from the watershed.
• About 44% of the annual sediment load is derived from agricultural fields within the past 2-4 decades.
• A very significant amount of sediment moves through the system but does not make it out.
  500,000 tons of sediment is exchanged annually due to channel widening and migration processes within the floodplain channel system, but is not directly delivered to the outlet. About 10,000 tons of soil is stored in historical river cutoff areas (ox-bow lakes).
• Each sub-watershed within the Root River Watershed has its own sediment transport story. The full report can be found here.