During his Earth Day speech in 2019, the chief of the U.S. Army Corps of Engineers, Missouri River Basin, stated openly that “ the flooding during the last two decades has gotten worse, and it is not getting better.” Acknowledging the impact of climate change on flows, he stated: “The longer we study things, the more we don’t know what we don’t know. … The system was designed for 1881 hydrology” but that is changing as the result of the increase in big rain events. (Yankton Press & Dakotan, April 23, 2019).
With his public statement, the Missouri River chief was simply confirming conclusions already supported by ample scientific investigation. As an example, one set of data is from 14 years of satellite records collected in NASA’s “GRACE” project which quantified the rates at which all regions of Earth are gaining or losing water. Clearly established is the fact that the northern half of the United States is getting wetter:
“This pattern of wet getting wetter, dry getting drier, has long been predicted in a series of Intergovernmental Panel on Climate Change (IPCC)-predicted reports. However, IPCC-predicted changes extend through the rest of the 21st century. Our latest study, and an earlier report from our team, show that it is happening now.” — (Jay Famiglietta, “A Map of the Future of Water,” Trend Magazine, p.8, Pew Charitable Trusts, Spring 2019)
The original plan for basin development was a hasty political compromise; when the “flood control” dams were designed in the early 1940s, there was little hydrologic data available, and the project was planned and developed without any systematic knowledge of the basin’s resources. Since then, the volume of water flowing through the dams has increased steadily, and is moving rapidly toward a point at which the dams can no longer manage high waters without also releasing flows that push-out into the river’s historic, natural flood plain.
Increases in the amount of water which the Corps attempts to control began to accumulate in the 1970s when the Oahe and Garrison irrigation projects — integral parts of the original compromise — were cancelled. These projects, when fully developed, were expected to divert more than 12 percent of the annual average flow from the river. Since then, in both the upper and lower basins, farmlands which previously absorbed and held-back surface snow and rainfall have been underlain with drainage pipe systems which accelerate water runoff into the system. The vast natural grasslands that covered the larger parts of the basin in the 1940s have been plowed in order to grow more corn and soy, leading to a steady increase in runoff. From 2015-2016 alone, more than 2.5 million grassland acres were lost to crop production. The present rate of grassland conversion will add about 4 percent to the total flow volume of the River. https://c402277.ssl.cf1.rackcdn.com/publications/1103/files/original/plowprint_AnnualReport_2017_revWEB_FINAL.pdf?1508791901
The continuing process of eliminating hundreds of thousands of acres of natural wetlands also increases and accelerates flows throughout the basin. And, to top things off, in 2016 the U.S. Bureau of Reclamation recognized the impact of climate change on the volume and timing of runoff, predicting that “[m]ean annual basin runoff is projected to increase as much as 9.7 percent …” (https://www.usbr.gov/climate/secure/docs/2016secure/2016SECUREReport-chapter6.pdf) This conclusion is reinforced by the recently released National Climate Assessment which concludes that, overall, most of the basin is seeing an increase in precipitation. (https://science2017.globalchange.gov/chapter/7/) To further complicate the Corps’ management decisions, there is a steady trend of increased variability in flows, often associated with more intense precipitation events. The Northern Plains have seen a 20 to 30 percent increase in amounts falling during routine storms.
The original development plan required that the Corps construct a navigation channel below Sioux City, intended to capture and hold the flows in a narrow strip of navigable water within the flood plain, utilizing a variety of dikes and levees. When the channel was in place, adjacent landowners moved into the natural flood plain with farming and business operations. Cultivated land increased dramatically and huge expanses of forest land were cleared to make way for the plow. (https://www.nap.edu/catalog/10277/the-missouri-river-ecosystem-exploring-the-prospects-for-recovery) Since navigation began, no less than 750,000 acres of flood plain and channel area has been cleared, cropped, paved or covered with buildings. See, John R. Ferrell, “Soundings: 100 Years of the Missouri River Navigation Project 111” (1995), and Robert Kelley Schneiders, “Unruly River: Two Centuries of Change Along the Missouri River” (1999). Today, the owners of these “protected” flood plain lands naturally expect the Corps to keep the river within the bounds of the original navigation channel, but the emerging pattern of increased flows makes this expectation unrealistic, and it is necessary to change basin land uses to allow the river to spread out into the areas where, in nature, it wants to be.
A strategy to reduce and discourage development in the natural flood plain requires balancing the need to make room for the water with a degree of fairness to those who have relied on the Corps to keep water in the main channel. Just such a strategy was laid out after the 1993 flood in the Galloway Report, “Sharing the Challenge,” published in 1994. Elements include:
(1) creating a basin-long National Wildlife Refuge System, modeled after the Big Muddy Refuge in Missouri;
(2) acquiring lands which flood regularly, including structures which have been previously flooded; and
(3) requiring flood insurance of all landowners in the historic, natural flood plain.
Failure to plan for future floods will assure ever greater economic and ecological disasters, all without addressing the underlying prospect of regularly-occurring high waters.
John H. Davidson is a professor of law emeritus at the University of South Dakota.