I sit safe and dry behind a computer well removed from the second hundred-year-flood to hit the Big Sioux–Missouri confluence in three years. From my safe perch, the most telling sign that this flood is serious is a single drastic action that Governor Dennis Daugaard is taking to fight it: he is closing Interstate 29 from Exit 26 (the Vermillion exit—sorry, Elk Point) south and turning the overpass at Exit 4 into a levee. That civil engineering project begins at noon Central today.
Let's look at the map:
Now let's zoom in on Exit 4:
I hear from a source on the ground in Union County that the Big Sioux narrows somewhere near North Sioux City. At that narrowing, the approaching flood waters would rise, accelerate, and undermine whatever channel walls exist. The plan is thus to divert the flood waters before they reach that weak point, pour the excess water across I-29 into McCook Lake, and let it wash down to the Missouri.
Now check the satellite view:
You can see all the houses next to McCook Lake. Those houses will get an unexpected front-porch view of the flood waters. My Union County source tells me those folks were instructed at yesterday's big public meeting at Dakota Valley High School, which is that large lot you see in the satellite photo on the northwest side of the lake, that they should be prepared to defend their homes from the flood waters.
Questions Number 1, 2, and 3 for folks around McCook Lake is, where do I get sandbags? (Dakota Valley Elementary School at 1150 Northshore Drive, right by McCook Lake, and 704 E. Rose Street in Elk Point.)
The next question: will this plan work? Take a look at Exit 4:
The Exit 4 levee is penned in by two long ramps. The water will need to move around both ramps to go where the state wants it to go. Plugging the overpass will create a large, skinny holding pond with a lot of water swirling, saturating and eating away at the southbound off-ramp. I invite any civil engineers not on duty to share their perspective on the best way to manage water flow at this site.
The next question is whether any of the state resources sandbagging the bridge will be made available to help McCook Lake residents defend their property. I know, it's an emergency, and we don't have time for lawyers. But the state is essentially taking private property around McCook Lake for a public purpose, saving the rest of North Sioux City from flood damage. I would assume that the state will either help minimize the damage to McCook Lake property or will be opening up the coffers to compensate those folks for their service to the greater good.
And the final economic question: do the numbers add up here? We are sacrificing one residential area to protect a larger, more populous zone that includes a lot of industry. But we are also diverting a river across a federal highway and putting a serious crimp in travel and commerce between South Dakota and Iowa for an indefinite period of time. Vermillion and Ponca will see a big boost in business from the detour (and State Highway 12 in Nebraska is beautiful), but we're adding a good 35 minutes to every trip from Sioux Falls to Sioux City. Multiply 35 minutes worth of labor and fuel by, say, seven days, and by about 11,000 regular vehicles and about 2,500 trucks, and you get a significant economic impact.
But the water's coming, and we can't stand here with our slide rules and backs of envelopes. We need to lay some sandbags and build some levees. Let's hope when the engineers get done, they can take a moment to show us the calculus they did to demonstrate that the plan under execution really is the smartest use of resources.
Update 11:05 CDT: The state provides detour maps and other flood information on its Disaster Recovery website:
Truckers headed from Sioux Falls to Omaha will be detoured to Albert Lea and Des Moines. That adds four hours and about 270 miles to the trip.