Q: Dear Ask Us Guy: Just south of Mankato between the Red Jacket Trail and Mount Kato is an area used for parking during the ski season and especially during the State Mountain Bike Championships. After every significant rain, Indian Creek overflows its banks and creates a rushing river of water and mud and cuts what is essentially a new stream bed across this area. Then city of Mankato crews show up with dozers, backhoes, dump trucks, etc., and they dig and grade and haul for several days to repair all the damage done by the flooding water.
Then it rains again, as it does in Minnesota, floods again, rushes across the “parking area” and the whole process begins again. I believe it was at least five times in the past summer.
Isn’t this the definition of insanity: doing the same thing over and over again and expecting a different result? As I write this, the area repaired again last fall is again a raging torrent, and I expect soon to see workers and heavy equipment repairing the damage once again. Is this some kind of ongoing project to train city workers in the use of this heavy equipment? If not, it does seem like an expensive waste of time and material.
A: This question was signed by a local couple, and they seemed to make a solid case that the Mankato Public Works Department is batty.
Turns out, though, that what the couple has witnessed repeatedly occurring is exactly what the city is intentionally causing to happen. Here’s the deal, as explained by Public Works Director Jeff Johnson:
Drainage from rural areas south of Mankato traditionally flowed into Indian Creek, through Rasmussen Woods, through the marshy area that eventually was drained to become home to West High School, and on to the Minnesota River. When the U.S. Army Corps of Engineers built the massive and complex flood-control system, an alternative route was created for the water coming from the farmland that drains into Indian Creek.
“There’s a gatewell out there; it’s known as Gatewell X,” Johnson said.
The gatewell is on the eastern edge of that grassy area that’s just north of Mount Kato. When the gatewell is open, the snowmelt or rainwater can follow the traditional route toward Rasmussen Woods. When it’s closed, the water is diverted across the grassy area and through a mammoth drainage structure that carries it below Blue Earth County Road 1 (Old Highway 66) and through a diversion channel to the Blue Earth River.
The eastern portion of that grassy area is city-owned, and the city has a drainage easement for the western side, which is owned by Mount Kato.
“So we have the ability to control the flow,” Johnson said.
But if diverting the water causes damage to the grassy area, why not let the drainage take its natural course to Mankato?
The reason is sediment. Especially with the spring runoff, but also after heavy rains, the water flowing into that area is thick with sediment. Left unchecked, the fast-moving water carries the sediment to the marshy parts of Rasmussen Woods, where it gets deposited by the ton.
“That’s where a lot of that sediment will end up if we don’t keep that gatewell closed,” Johnson said.
After enough sediment accumulates at Rasmussen, it needs to be removed. Getting heavy equipment into a nature park is a challenge, and removing the sediment without doing environmental and aesthetic damage is difficult.
By contrast, the area around Gatewell X is wide open and is designed to capture sediment and allow it to be conveniently removed. A holding bay sits in front of the gatewell, which slows the flow of the water and allows much of the sediment to settle to the bottom before the cleaner water flows through the grassy area and to the Blue Earth River. When the water dries up, the city crews show up with their dozers, loaders and trucks and haul away the sediment, preparing the holding bay to do its job after the next heavy rain.
“Doing that work out in the open is a lot easier than having to remove sediment in the Rasmussen Woods area,” Johnson said.
So, going back to that definition of insanity. City officials are doing the same thing over and over again, but they’re not expecting a different result. Instead, they’re getting the exact result they intended — keeping sediment out of Rasmussen Woods and capturing it in an area where it can be removed fairly effortlessly.
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