Background on the March 13-14, 2007 Flooding in Browns Valley (Traverse County), Minnesota: Report to the Minnesota Governor's Office

Browns Valley is a community of approximately 650 people in the southerly corner of Traverse County, near the South Dakota border (see Figures 1 and 2). The Little Minnesota River flows through town. The city is located on an ancient floodplain, with very flat local topography, facilitating widespread flooding within the municipal limits. A ridge running northwest-southeast along the margin of the floodplain can increase flooding impacts to Browns Valley in two ways, by preventing the spread of flood waters in the ridgeward direction and by contributing surface runoff from the ridge down to the valley. Local hydrologic patterns are further complicated by the fact that Browns Valley is very near the watershed divide between the Minnesota River headwaters to the south and the Bois de Sioux watershed to the north. Climatic conditions this past winter helped create the set of circumstances leading to the March 13-14, 2007 flood. The extraordinarily cold February weather, coupled with the lack of snow, contributed to very thick ice formation. Warming weather and strong sunshine in mid-March, culminating in a high of 55 degrees Fahrenheit on March 12, promoted very fast melting and the movement of large blocks of ice on the Little Minnesota River. These ice blocks flowed downstream to Browns Valley, where they became lodged beneath bridges over the river. This created ice jams that backed up water and caused the flood of March 13 and 14, 2007.