Traverse Gap - Topography and Hydrology

Topography and Hydrology

Despite the low elevation and flat topography of its floor, the Traverse Gap marks southernmost point of the Northern Divide between the watersheds of the Arctic and the Atlantic Oceans. On the north, Lake Traverse is the source of the Bois des Sioux River, a source stream of the Red River of the North, which drains via Lake Winnipeg and the Nelson River to Hudson Bay in the Arctic Ocean. To the south, Big Stone Lake is the source of River Warren's remnant, the Minnesota River, tributary to the Mississippi, which drains to the Gulf of Mexico and the Atlantic. Big Stone Lake is now fed by the Little Minnesota River, the headwaters of which are in South Dakota. The Little Minnesota enters the gap from the west and meanders south through the old channel to Big Stone Lake. The Little Minnesota, part of the Mississippi watershed, is less than one mile (1.6 km) from Lake Traverse in the drainage basin of Hudson Bay.

The floor of Browns Valley is flat, which allows the waters of one basin to flood across the continental divide into the other basin in times of high water. The maximum elevation on the floor of the valley is 987 feet (300.8 m) above sea level. The Browns Valley Dike at the south end of Lake Traverse is at the same elevation; this structure was built to reduce the likelihood of flooding south across the continental divide. At 983.9 feet (299.9 m), that divide is lower than the level of the dike, and flooding at Lake Traverse has the potential to drain over the Big Stone Dike into the Minnesota River watershed. At the south end of the gap, the Big Stone Lake reservoir pool is maintained at 967 feet (294.7 m), and it has recently flooded to over 975 feet (297.2 m). The Little Minnesota River upstream and at a higher elevation near the divide has flooded to a level where it drained across that divide into Lake Traverse. While the natural state of the area has been altered by the dike and control structures on the two lakes, interbasin flooding did occur prior to construction of those improvements. The Traverse Gap therefore allows waters which would naturally flow to the Atlantic Ocean to flow to the Arctic instead, and in the past has allowed water from Lake Traverse to flow in the other direction to Big Stone Lake in the Atlantic basin.