River flooding can be an ecological benefit

The story of floods is one of destruction and of creation. For as long as history has been recorded, floods have been devastating local populations, but have also been a source of new life. That story is still unfolding as rains brought flooding across the state – from the Front Range and to Colorado Springs.

In some areas like Poudre Canyon, Big Thompson and Saint Vrain, water flowed with enough energy to move boulders the size of cars. But according to Dr. Ellen Wohl, a geologist at CSU that studies the physical process and form of rivers, the energy produced was not the most surprising part, it was the size of the storms.

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“We have sedimentary evidence saying this type of flooding goes back to prehistoric periods,” Wohl said.

Wohl admits the phrase is tried, but says that what Colorado experienced was somewhat of a perfect storm. She explains the chance of a rainfall event like the one we experienced happens on average once every 500 years.

“There have been comparable floods on any particular river, but I don’t know if there has been (floods) on all of these areas at once,” Wohl said.

She adds that floods in natural rivers are a good thing, but that we run into problems when there is infrastructure in the surrounding areas.

“Our valley bottoms are built to handle this, our roads aren’t,” Wohl said.

Stephanie Kampf, associate professor of watershed science, says communities will start developing in a rivers’ floodplain – an area where the flooding naturally occurs around a river. According to Kampf, when rivers such as the Poudre experience low flows for an extended period of time, people are surprised when it spills into its floodplain.

Kampf explains that floodplains differ by the terrain around the river. They are narrower in steeper areas and produce a lot of energy, but wider in shallower areas and spill far out across the land.

“Those are areas you can expect to flood regularly,” Kampf said. “The Poudre didn’t flood in a way that wouldn’t be expected from past records.”

Kampf adds that flooding can be good for the soil and vegetation around a river and, according to Wohl, there are many habitats that can be restored by flooding.

Wohl said there are many species of aquatic and plant life that depend on a periodic flood. Additionally, heavy rainfall can restore an area’s groundwater — something that is good for the river and humans living outside of floodplains.

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“(Groundwater) sustains the base flow in the rivers. If you don’t have rainfall, the bigger rivers just keep flowing anyway, and that’s coming from groundwater.”

Ground water also sustains wells for many residents of eastern Colorado. The bigger rivers that are supplied by groundwater can also be used for drinking water, and agricultural uses, according to Wohl.

While there are certainly ecological benefits coming from a flood of this magnitude, they can be balanced by negatives.

Dr. N. LeRoy Poff, professor in the biology department, says having a flood this late in the season could have negative effects for insect populations. Insects are important for energy flow in a stream system.

“They emerge from the streams and are eaten by birds and bats, they’re a real key player in shallow stream systems,” Poff said.

Poff adds that the timing was probably good in terms of river mechanics, and doesn’t underestimate the effects of flooding on habitats.

“Flooding is a really important process in maintaining river ecosystems,” Poff said.

Wohl explains that the cleaning of the riverbeds is important for fish to breed.

“Most of the native fish need high flows to remove sediment from their breeding grounds, otherwise the embryos don’t get enough oxygen and water flowing by,” Wohl said.

Whatever the effects, it is clear that flooding can be devastating and rejuvenating, depending on your perspective.

“From the rivers perspective this was a pretty good event, a good thing. Just for all of us humans it wasn’t so good,” Wohl said.

Collegian Science Reporter Remi Boudreau can be reached at news@collegian.com.