The Minnesota River drains a basin of 14,840 square miles including all or parts of 37 counties; 1,610 square miles in South Dakota and the remaining area in North Dakota and Iowa. The Minnesota River meanders 335 miles from where it originates on the Minnesota-South Dakota boarder to its confluence with the Mississippi River near Fort Snelling. The Minnesota River falls 274 feet from its headwaters at Big Stone Lake (964 feet) to the confluence with the Mississippi (690 feet). It drops approximately 0.8 feet per mile (river profile). Surface water flow to the river comes from 1,208 minor watersheds. The Minnesota River Basin is divided into 12 hydrologic major watersheds and 13 management watersheds.
Dams on the Minnesota River
There are five major dams on the Minnesota River. Dams have been constructed at the outlets of Big Stone Lake, Marsh Lake, and Lac qui Parle to control lake levels and floodwaters. These dams create extensive lakes which are important wildlife management areas and hunting grounds. The other two dams are located in Granite Falls and a few miles downstream from Granite Falls called Minnesota Falls Dam.
Climate Change & Precipitation
In the 1930s, many parts of the United States including Minnesota suffered through one of the driest periods in recorded history. Beginning around 1936, the average rainfall amount in Minnesota has steadily increased along with some extreme wet and dry years. According to the Minnesota Pollution Control Agency, precipitation in some areas of the state has increased by up to 20 percent, especially in the southern half.
Minnesota’s location in the middle of the continent results in a variable climate due to the variety of air masses that flow across the state. Winters are typically dominated by cold, dry continental polar air and also occasionally replaced by somewhat milder maritime polar air (State Climatology Office, 2004). During the summer, Minnesota usually sees a clash between hot and dry continental tropical air masses from the desert southwest and the moist maritime tropical air coming up from the Gulf of Mexico.
Precipitation is projected to increase by around 15 percent in the winter, summer and fall, with little change during the spring season according to MPCA. This state agency also projects a likely increase in the number of heavy rainfall events during the summer and the frequency of extremely hot days.
The Average Precipitation 1971-2000 map illustrates the west-to-east precipitation and runoff gradient. There is more rainfall as one moves eastwardly across the basin. Yields of key water quality pollutants (TSS, TP, OP and nitrate-N) follow this same general pattern of increasing in an easterly pattern.
The annual runoff 1935-2003 graph illustrates the trend of increasing runoff volume over the past several decades. There is highly variable runoff from one year to another.
More detailed information about surface water quality monitoring can be found in the State of the Minnesota River Reports.
For a broader look at trends in the river basin, see the Minnesota RIver Basin Trends Report.