Last week’s heavy rain dropped more than a month’s worth of precipitation in only a few days.
But it was well controlled by the area's flood control system created by the Miami Conservancy District just over a century ago, after the Great Flood of 1913.
WYSO’s Mike Frazier spoke with Mike Ekberg, a hydrologist with the district, about how its network of dams, levees, and floodgates protects areas along the Great Miami River.
Mike Ekberg: This flood protection system consists of five earthen dams and about 55 miles of levees. We maintain that system. It was all built and in place by 1922 and it's kept the downtown areas of the communities that we protect free of flooding from the Great Miami River for over 100 years now.
Mike Frazier: Tell us about the recent rainstorm. What was so impactful about what happened over the past couple of days.
Ekberg: From March 31 to April 6, that seven-day period, we got five to seven inches of rainfall. That’s a lot of rain to get over a seven-day period.
Frazier: So how did the district react when all this water started coming down?
Ekberg: These dams are built with openings through them. They're concrete openings that we call conduits. And what they do is they will let normal flow pass right through the dam.
But as the flow begins to get up to a critical level where it could cause flooding downstream, the conduits are sized so that water will begin to back up behind the dam and begin to build up a lake behind the dam, and they're only going to release water at a rate that the levees in Dayton and downstream can handle the amount of flow that's coming out of all of the dams that are upstream of Dayton for example.
They're kind of like regulators in that the more rainfall and the more water comes into the area behind the dam - we call that area a storage basin. The faster that water flows into the storage basin, the more the dam kind of acts as sort of a regulator and is almost like a break on the flow of water coming out. It's only going to release it just enough that we’re not going to get downstream flooding.
Frazier: Now upstream from the dams, though, those areas could be flooded, but it's in a controlled manner?
Ekberg: Yes. So the land upstream of the dams that we call the storage basin, Miami Conservancy District has flood easements on the deeds on all those properties. And most of that land is either forested or it's agricultural land. But we have an easement that gives us the right to inundate it if needed to temporarily store floodwaters there.
Frazier: What can we expect over the next couple of days in terms of the water receding?
Ekberg: It's going to continue to come down. We had a lot of rain, and it's going to take it a while to return back to a normal pool but I would think by Sunday it'll be getting back close to normal.
"We hope it never comes, but our system is designed for a flood of the magnitude of 1913 plus an additional 40%."
When the river returns back to normal flow, you may think, okay things are back to normal. But there's debris and drift that has to be removed off of miles and miles of trails that run up and down along the river, or boat ramps where people put in canoes and kayaks and that sort of thing. We have to clean the silt and the mud and whatever other debris was left on it.
Frazier: What are the conditions of the conservancy infrastructure, the levees and the dams and such? Do they need maintenance?
Ekberg: Yes. They need continuous maintenance. Our crews will be out inspecting the levees. They're out today, and as the river levels come down, they’ll be looking at them to make sure there hasn't been any excessive erosion, and if they see areas where there was erosion, we’re going to repair them. The levees, we need to mow them and keep trees and vegetation from growing on them because the roots — f they penetrate the levee — they can cause water to seep through them and potentially weaken the levee.
We also have to inspect them for groundhog holes and things like that and if we see them, we try to keep up on that and seal them off. They require constant attention.
Frazier: How concerned is the district regarding the potential of a heavier rain event that might be attributed to a warming climate?
Ekberg: We do everything we can to prepare for that. We hope it never comes, but our system is designed for a flood of the magnitude of 1913 plus an additional 40%.
To put that in perspective, this most recent event, 22 billion gallons of water was stored behind our five dams.
But our total storage capacity is 274 billion gallons, so we were only at a fraction of our capacity. We're prepared and we're always preparing for a big one but we hope it never happens.
Frazier: It sounds like the engineers that designed this way back then really were preparing for a biblical-type flood.
Ekberg: They had a lot of foresight. They designed it with a high level of capacity, and that's kind of what it takes. It's kept downtown Dayton from flooding for over a hundred years, so that's quite a feat.
Ekberg said that the Great Miami River peaked at just over 33 feet Sunday evening. Normal water levels are at 27 feet.
