Leopold Center for Sustainable Agriculture

Looking for resilience after a year of flooding

Back to Leopold Letter Fall 2010

By LAURA MILLER, Newsletter editor

Faced with massive and frequent flooding throughout much of the state for the second time in three years, Iowans may hear a new term in discussions about long-term solutions: resilience.

Resilience is defined as the capacity of a system to absorb disturbance and still retain its basic function and structure. Recently, resilience has been linked to how people view the capacity of natural resources and ecosystems to manage risk, whether from too much rain or too little, effects of an unstable climate, or changing environmental conditions that lead to new pests and disease.

The Leopold Center queried researchers who have been studying alternative systems to see how their projects fared during last summer’s floods. We checked in with investigators of two Leopold Center projects, one fairly new and another alternative system established nearly 20 years ago.

Neal Smith National Wildlife Refuge, Jasper County

What: Horizontal strips of perennial prairies planted among corn-soybean fields in 12 sub-watersheds (2 to 10 acres). The strips comprise either 10 or 20 percent of the watershed area and vary in size from a tenth of an acre (about 50 X 100 feet) to one acre. Flumes catch runoff after rainfall, and depth of runoff is calculated. Water and sediment are sampled.

When: Plots set up in 2007 (prairie plants still getting established)

Findings: In general, plots with prairie strips reduce overall amounts of runoff, and are most effective after small and medium storms. Heavy rain on already wet soil results in a greater percentage of the rainfall leaving the system as runoff.

2010 flood observations: All cropping systems in the experiment were stressed. By the end of August, more than 40 inches of rain were recorded, including 9.75 inches in two days. Very large rainfall events are difficult to manage in these experimental settings, no matter what system is in place.

Comments from Matt Helmers, ISU ag and biosystems engineer:
Plots with some perennial vegetation have less runoff than those without it, but can farmers afford this option? That’s a big question. This experiment uses 10 percent and 20 percent of the land area for perennials. I think we’d still see positive effects with only 5 percent of the land in perennials but this is important to study in the future.

We’ve been lucky in Iowa to have ideal growing conditions in recent decades for corn and soybeans. But what if we have more seasons with too much or too little moisture? How will corn-soybean rotations function? They may not function as well as in the past.

This project has been done on small watersheds and catchments, and we can see effects on a small scale. I’m interested in how it might work on a larger scale.

Flooding is a natural process and what happens during a flood is very visible. But what we do on the landscape other times of the year when it is not flooding also is very important.

Bear Creek National Demonstration Watershed, Story County

What: Plantings of native trees, shrubs and perennial grasses at least 66 feet wide on both sides of Bear Creek, the first on a half-mile section of stream. In addition to buffers, the project includes stabilizing streambeds and banks with in-stream or bioengineering techniques and other riparian management practices next to crop fields or within pastures.

When: First buffer planted in 1990 on Ron Risdal farm north of Roland and has now expanded to 10 landowners along 7 miles of Bear Creek, with a variety of widths, designs and plant species.

Findings: Depending on design and characteristics, buffers can reduce sediment in runoff by 70 to 95 percent, with dramatic increases in soil organic matter, fine root biomass and infiltration observed after 5-6 years. Stream banks returned to perennial vegetation are much less susceptible to erosion, even during large flood events.

2010 flood observations: After the August 10 storm that caused massive flooding downstream in Ames, the depth of water in Bear Creek was at least four feet over the top of a bridge at the original research site and 3-4 feet over some adjacent crop fields. Normally 10 feet wide during typical August conditions, Bear Creek spanned 300 feet in flat areas where the channel was in contact with the flood plain.

Comments from Dick Schultz, ISU Natural Resource Ecology and Management:
We definitely had significant flooding but as the water receded, almost all parts of the buffered stream bank covered by grass and/or trees had very little evidence of accelerated bank erosion. I saw deposits of sand, woody debris and corn stover caught in the buffer, so the farmer didn’t have to deal with them in a crop field.

The buffers did exactly as we had hoped. We compared what happened at Bear Creek this summer to a similar-sized stream in Boone County, where we have just started working with a private landowner on bank stabilization. The area, which was grazed pasture, was decimated by extensive bank erosion, but that’s exactly how the land along Bear Creek had been used before we planted buffers. Our erosion pins on the Boone County stream showed that more than one to two feet of soil were lost from many areas of the stream bank during the August storm.

Comments from Tom Isenhart, ISU Natural Resource Ecology and Management:
Usually we think of buffers keeping things out of the stream, but during extreme flooding events they also have a reverse effect, keeping water in its place longer before it moves downstream. Buffers are a drag on water flow, which can reduce the severity of flooding. The flooding may last longer, but peaks are not as high or as ruinous.

Comments from Ron Risdal, farmer and landowner along Bear Creek:
While there were a couple of areas with some erosion of the stream bank, it was nothing like it would have been before the buffer was planted. There may not have been anything left the way it was before.

 

Back to Leopold Letter Fall 2010