Record flooding has struck along the Souris River, leading to record-breaking flooding in Minot and threatening multiple other towns. The river has widely ranging annual flow rates, varying from 4,200 acre feet to 2.1M acre feet. Flooding is not uncommon in this part of the country, but what is striking about this case is how events upstream contributed so dramatically to what happened in Minot.
Rivers have always flooded. Snowmelt and spring rains naturally contribute to higher flow rates. Rivers also naturally move, as soil erodes in places and builds up in others. As communities have developed near rivers, a need arose to control the rivers’ boundaries. After all, you didn’t want to have your farm land constantly submerged by water. Civilizations have been using earthen structures – like levees or dikes – for thousands of years to control the flow of water.
It was only within the last century, that extensive man-made levees have been built within the U.S. The levees along the Mississippi River are some of the most elaborate in the world, extending 3,500 miles. Along with levees, dams help to regulate the flow of water. Dams can create artificial lakes used either to prevent flooding downstream or to provide a source of water for the community.
How is all of this relevant to the flooding in Minot? A visual Cause Map can shed light on what led to the intense flooding there. For starters, the levees meant to keep the Souris River contained were both overtopped and breeched. This occurred because there was a high volume of water flowing downstream over an extended period of time. Why is that?
The Souris River actually begins in Saskatchewan, where a further series of levees and dams controls the river. Southern Canada had a significant amount of snowmelt and spring precipitation, saturating the soil and filling up local lakes and man-made reservoirs. The area also had a heavy amount of rainfall the preceding the weekend, 4 to 7 inches. With reservoirs already filled, officials had no choice but to increase dam flow rates to prevent flooding or worse – a burst dam.
While these complex levee and dam systems usually provide stability for riverside communities, they also can work against some of the systems that evolved in nature to keep water flow in check. For instance, natural levees develop as rivers periodically overflow and deposit silt. Also everglades and marshlands act like a sponge absorbing excess water. Human development has affected these natural processes, and unfortunately there are likely to be many further effects from the flooding as the water continues down the Missouri River Basin.