MERCER: Missouri River flooding is likely to last for monthsPIERRE – The U.S. Army Corps of Engineers faces a titanic problem on the Missouri River this year. Homes, farms, businesses, ranches and communities along the river are about to be soaked and battered by the river’s subtly devastating power in ways that people younger than age 60 likely don’t remember or never experienced.
By: Bob Mercer, The Daily Republic
PIERRE – The U.S. Army Corps of Engineers faces a titanic problem on the Missouri River this year. Homes, farms, businesses, ranches and communities along the river are about to be soaked and battered by the river’s subtly devastating power in ways that people younger than age 60 likely don’t remember or never experienced.
Their only knowledge might come from 1950s photographs of the floodwaters before the dams were built. Since then, people have put such confidence in the corps and the dams’ flood-control abilities that they invested many, many millions of dollars in buildings that are too near the water.
In just the past 10 to 20 years, many of the most-expensive homes in the Pierre and Fort Pierre area were built along the river, including entire subdivisions (one developer punched a hole through the river bank to create a system of canals for his home buyers). So were financial institutions, lodging, restaurants, government buildings and business complexes. Pierre’s marketing slogan became “On The River.”
Why not? The dams were there to protect us.
Streets in the lower elevation neighborhoods of Pierre and in much of Fort Pierre clogged Thursday night with pickup trucks and trailers and moving vans, as people hauled sandbags and loaded out their furniture and other belongings. People seemed to be just starting to grasp that the corps had no choice but to start flooding their neighborhoods.
Some houses had white sandbags piled in a barrier around them, rising past the bottoms of the first-floor windows. Others next door had nothing that indicated their residents saw any fear of flooding.
The corps must start releasing a lot more water in the days and weeks ahead from Fort Peck reservoir in Montana, Garrison reservoir in North Dakota and the four reservoirs in South Dakota. Eventually the chain of dams will become one long current into the lower Missouri River from Sioux City down to the Mississippi River near St. Louis. The lower Mississippi has already flooded.
Now the people and cities in many places up and the Missouri throughout the Dakotas face a watery siege of their own that will last for months. The federal government’s dams on the Missouri were built for flood control first. Those dams and the personnel who run them now face the toughest tests in the reservoir system’s more than half-century of existence.
The river’s six enormous dams simply aren’t tall enough, and the reservoirs behind aren’t broad enough, to handle the summer melt that is just starting to rip down from the Rocky Mountains. Month after month the corps has been revising upward its forecast for the snowpack. The accumulations as of early May stood at 136 to 154 percent of normal peak, depending on the location.
Come late spring and summer when the snow melts, the runoff normally has been stored in the reservoirs to prevent flooding. But this year there’s too much to handle and nowhere to put it, other than ship it downriver past New Orleans to the Gulf of Mexico.
As of early May the Corps’ predicted estimate stood at 44 million acre feet of runoff for the Missouri River basin. That is 178 percent of normal. Making matters more difficult was the reservoirs ended 2010 at relatively high levels, after last year’s runoff totaled 38.8 million acre-feet, which was 156 percent of normal.
Both Garrison and Oahe reservoirs are so full of water already that they are in what’s known as their exclusive flood-control zone, a few feet of space left before the water goes spilling over the tops of the emergency flood gates.
The flooding under way at Pierre and Fort Pierre is just the start. The water will get much higher in the next week, and releases from the dams must get much larger. The situation is beyond the point where the corps can confidently predict much of anything, other than the dams will need to keep flowing at very high rates for many months to come.
The corps’ official forecast for dam operations as of Thursday showed releases from Oahe Dam increasing from 75,000 cubic feet per second to 80,000 on Friday, then to 85,000 on Saturday (May 28), then jumping again to 90,000 on June 4; 95,000 on June 5 and 100,000 on June 6. The corps plan called for going to 105,000 on June 21 and 110,000 on July 1. All of that was scrapped Saturday, when a new plan was laid out. It now calls for 100,000 on June 3; 110,000 on June 4; 130,000 on June 5; 140,000 on June 10; and 150,000 on June 15.
July 15 is the last date listed on the corps forecast, and the releases that day now remain at 150,000. There is no indication when Oahe’s releases will be cut back. That means, at least through much of the summer, the river will remain very high and many people will still be flooded out. Emergency levees will be constructed in Pierre and Fort Pierre, but Gov. Dennis Daugaard warned Friday people shouldn’t depend on them working or even being completed by the June 2 deadline.
The best small indicator of how bad the situation could be came Friday morning. The corps’ manager for the Oahe Dam and reservoir, Eric Stasch, said he doesn’t know when the releases will be cut back. Second, he said the stilling basin outlet that was opened at Oahe Dam on May 6 to release more water could remain flowing into December.
The stilling basin outlet has been opened only twice before in the dam’s history. That was on a temporary basis in the mid-1990s. No one has publicly imagined the outlet being necessary to run open for six or seventh months straight, until the winter comes with a new season of snow.
The engineers who designed the Missouri River dam system were geniuses. They did the best they could with the knowledge they had at the time of the climate and the terrain. We became spoiled in the decades since, carefree where we built, angry and demanding when the reservoirs didn’t contain enough water for our pursuits and needs. Now we face what many never expected.