Grasslands Impact on Flooding
After epic Midwest winter flooding, there’s renewed discussion about reducing the damage next time. But instead of spending valuable resources trying to hold flood waters back, let’s do a better job preventing floods in the first place.
Missouri receives more than 138 million acre feet of rainwater in an average year; eight times more than the flow through the Colorado river basin. We need to absorb and store that water. And nature has provided the answer.
Roughly one third of Missouri was once covered by tall grass prairie, with root systems several feet long capable of absorbing and storing water deep in the soil and underground aquifers. It is well documented that native prairie grasses can soak up an eight-inch rainfall. But it is equally clear from hydrology research on major U.S. rivers, including that by ecologist Steve Apfelbaum, that the absence of native vegetation increases water run-off by several hundred times that experienced prior to the late 1880’s.
We need a strategic re-introduction of native grasses, with their sponge-like ability to absorb precipitation, to restore the water accumulation systems nature provided in the first place. Instead of highly destructive flood waters running off in torrents -- along with soil, nutrients and fertilizer -- the water would replenish underground supplies.
Restoring perennial warm-season grasses to re-create a natural flood-reducing water accumulation system can be accomplished in three principle ways.
First, owners of the nearly 101 million U.S. acres of highly erodible cropland and pastureland should be incentivized to restore perennial native plantings. Many recent studies indicated several million acres of grassland, wetland and fragile land were converted to corn and soybean production between 2006 and 2012; a period of high commodity prices and generous government crop insurance programs. However, with lower commodity prices, owners of highly erodible acres should be open to returning these assets to their natural intended use. New markets for perennial warm-season grasses can provide financial incentives.
We are documenting the benefits of this concept at my Northern Missouri farm. Dr. Ranjith Udawatta and Dr. Shibu Jose at the University of Missouri are comparing soil and water conditions of constructed prairie on highly erodible land with adjacent land planted in row crops. Initial results show far less water run-off from the prairie tract and that the water itself is much cleaner. We are also implementing the innovative Iowa State University STRIPS program which calls for planting native species in strategic locations on cropland to protect soil and water quality.
One private market incentive to accomplish this conversion is to sustainably harvest and sell a portion of the grass feedstock for renewable energy production. Roeslein Alternative Energy is involved in a major project with Smithfield Hog Production that envisions doing just that. Using the natural process of anaerobic digestion, grassland biomass will supplement manure from approximately two million hogs to create 2.2 billion cubic feet of renewable natural gas each year for transportation fuel and electricity generation. A broad cross section of stakeholders at the Midwest Conservation Biomass Alliance (MCBA) is working to determine the optimum mixture of native plantings to sustain energy production, the environment and wildlife habitat.
A second step involves planting cover crops during the “off” season on commodity agriculture land. Corn and soybean production provides food, feed and fiber for a growing world population; although their production systems reduce water infiltration and storage in the soil compared to native vegetation. However, cover crop vegetation can facilitate natural water absorption and soil protection after the crops are harvested, when valuable top soil can be exposed to erosion-inducing winds and precipitation. It is very encouraging that cover crops have already gained popularity, since they also enhance soil health, prevent erosion, reduce soil compaction, and provide habitat for wildlife and essential pollinators.
Finally, riparian corridors (the floodplain closest to waterway channels) need restoration to take strain off both free-flowing streams and rivers modified by dams and levees. Continuous riparian corridors with natural vegetation retain flood water and prevent property damage. However, riparian corridors are too often not continuous; interrupted by development and other disruptions that replace native grasses and forested areas vital to perform their natural functions.
The main point is that catastrophic flooding is avoidable. Restoring riparian grasslands, forests, wetlands and upland native prairie vegetation delivers a natural water accumulation system to reduce the impact of major floods.
None of this is an indictment of the conversion of the vast majority of native prairie over the past two centuries for commercial agricultural production or for urbanization. That happened for reasons commensurate with the goals of the time. But this is a new and different time. We have an obligation to change land management practices going forward in ways that recognize our collective responsibility for sustaining the resources of our planet. There is a vast amount of good that can come about as a result.