USACE CWMS - Minnesota River Watershed

The Corps Water Management System (CWMS) includes four interrelated models to assist with water management for the basin:

- GeoHMS (Geospatial Hydrologic Modeling Extension)
- ResSIM (Reservoir System Simulation)
- RAS (River Analysis System)
- FIA (Flood Impact Analysis)

The Minnesota River is approximately 332 miles long, and it drains a basin of about 14,751 square miles in size. The Minnesota River flows over a mantle of glacial drift from an elevation of 960 feet in the headwaters near the South Dakota border, to the confluence with the Mississippi River at an elevation of about 690 feet at Minneapolis/St. Paul. The Minnesota River is a remnant from melting glaciers after the last ice age. Originally the valley drained north; however, glacial deposits and refreezing of the area over time formed a southern outlet into what is now the Minnesota and Mississippi Rivers. Several diversion channels exist within the Minnesota River Valley and some of them are utilized in the Lac Qui Parle project as the Chippewa Diversion and Watson Sag (Minnesota NRCS November 2014).

The soil across the basin is rich in nutrients, so that 90% of land use is used for some form of agricultural production. The fertile, black, fine-grained soils and landscape are conducive to agriculture. The principal crops are wheat, barley, soybeans, sunflowers, corn, and hay. Pasture, forest, open water, and wetlands comprise most of the remaining land area.

After a long winter, temperatures typically rise above freezing across the southern basin, resulting in snowmelt and eventual runoff into the river system. As the swollen river flows north, it encounters less slope, greater amounts of snow and ice due to a colder air mass, and delayed seasonal melting. Ice jams commonly result from these factors and in turn, impedes flow and holds back excessive water. Since the river channel itself is shallow and no more than a few hundred yards at its widest point, water quickly spreads out across the surrounding landscape. The severity of spring flooding depends on several hydrometerological factors, including: freeze/melt cycle; early spring rains or late spring snow storms; snow pack depth and liquid water equivalency; frost depth; soil moisture content; river baseflows and ice conditions; and liquid precipitation from the previous year.