American Scientist

To the Editors:

In “Runaway Devils Lake” (January–February), Douglas Larson says that, in response to climate change, the lake has expanded to 815 square kilometers “with devastating environmental impacts.” But it is not only the climate that has changed in the Devils Lake Basin.

Soil characteristics suggest that 152,975 hectares of the original 238,365 hectares of wetlands in the Devils Lake Basin had been drained by 1997. Those drained wetlands had a storage capacity of 612,800 acre-feet and now contribute more than 400,000 acre-feet of water to the lake in 100-year frequency runoff events. That is the equivalent of nearly 70 percent of the inflows in years like 2009 and 2011.

Larson says that, if the lake rises two more meters, it will overflow into the Sheyenne River. However, at that elevation, the lake would have a surface area of 97,800 hectares and evaporation would remove more than 604,000 acre-feet of water annually. That is more than the record inflows in 2009 and 2011.

Larson raises the “ominous picture” of “great torrents” eroding the lake’s natural outlet, resulting in an uncontrolled release of two million acre-feet of water into the Sheyenne River and “drowning towns and farms.” But geologic evidence shows that, instead of eroding, the elevation of the natural outlet actually rose from 428.7 meters to 444.8 meters as a result of sediment deposition in the seven to nine overflow events that have occurred over the past 10,000 years.

The real catastrophe is North Dakota’s irresponsible mismanagement of water resources in the Devils Lake Basin.

Gary Pearson
Jamestown, ND

Dr. Larson responds:

Undoubtedly, the long-term, agrarian removal of vast wetlands in the Devils Lake Basin has contributed significantly to the destructive expansion of Devils Lake. This, I presume, is what Gary Pearson regards as North Dakota’s “real catastrophe.” But a wetter climate over the past 20 years has been the driving force behind the rising lake levels. Indeed, roughly a quarter of all inflow to Devils Lake during a 45-year period (1950–1995) occurred between 1993 and 1995. How much of this water could have been retained by the basin’s original wetlands is debatable. But in a state where agriculture is a leading economic activity, allowing wetlands to exist in place of productive farmland has long been unrealistic.

I would remind Pearson that the dire projections of continued lake growth and flooding are not solely my own; they appear in U.S. Geological Survey peer-reviewed reports. Pearson’s claim that evaporation will eventually counterbalance inflow is incorrect. The lake has continued to rise despite an average evaporation rate of 0.78 meters per year. In 2011, the lake covered 83,000 hectares, nearly as much as the overflow coverage of 97,800 hectares. Yet, with inflows totaling 595,000 acre-feet, lake volume increased 434,000 acre-feet and lake level rose 0.70 meters.

Pearson cites “geologic evidence” for sediment aggregation, rather than erosion, of the lake’s natural outlet during lake overflow. This is a high-risk proposition that Devils Lake flood-control scientists and engineers are unwilling to bet on. A worst-case scenario can happen. It’s better to be prepared than defenseless.