This Thursday marked the five-year anniversary of the 2010 Cannon River Flood. On September 23rd of 2010, Carleton received over six inches of rain over the course of 29 hours, causing the Cannon River to rise from its base flow depth of five feet to a staggering 14 feet at the Welch, Minnesota gauge station. Northfield experienced extensive flood damage, and Carleton’s track and field facilities had to be completely replaced. Although the damage caused by the flood was terrible, it is important to remember that flooding is a natural and inevitable part of any riparian (river-based) landscape.
The eastern edge of the Lower Arboretum lies within the Cannon River floodplain, a low-lying area that lies just beyond the banks of the Cannon, and the ecosystem of this area is largely controlled by the actions of the river. Due to the intermittent presence of standing water caused by flooding, any plants that live in the floodplain must be able to cope with high waters or be able to revive themselves quickly after a flood event.
The oaks that are so iconic of the Arb’s prairies do not survive well in these conditions and are accordingly rare in the lowland floodplains. Boxelder, willow, green ash and silver maple, on the other hand, are very adept at surviving in high waters and are consequently the dominant trees within the floodplain. Flooding also has a large effect on the geo-morphology of the Arb. Floods have high erosive power and can change the shape of the river by enlarging riverbanks and widening sandbars.
In addition, the flooding river often deposits large amounts new sediment within the floodplain. This process helps to reinvigorate the soil with nutrients and is also responsible for the large amount of sand present on the trails north of the West Gym parking lot.
The historical navigational and industrial importance of floodplains has insured that they are some of the most heavily settled areas of the country and within this context flooding is usually seen as a purely destructive force, but it is important to remember that flooding is a natural and beneficial part of the floodplain ecosystem.