BY ED FELIEN
As we enjoy the last moments of fall, it’s hard to think ahead to the snowmelt and rains that could flood our basements again next spring.
In September I had the pleasure to meet with Lars Erdahl, the executive administrator for the Minnehaha Creek Watershed District, and hydrology experts from Wenck Associates, to discuss the problems of flooding for homes in the Lake Hiawatha and Lake Nokomis area.
We discussed the problem of flooded basements in South Minneapolis caused by the high water table. My proposition has always been that it’s necessary from time to time (every 50 years or so) to dredge Minnehaha Creek, particularly the stretch from 28th Avenue to the falls, and that would lower the water table, relieve the saturated ground and reduce flooded basements.
Erdahl and the hydrology experts said that as soon as you dredged the creek, water would flow in to fill it back up. I know that’s true for the dredging of Lake Hiawatha. As long as the intake and outtake are at a constant level, the water in Lake Hiawatha would remain at a constant level. No matter how deep you dredge the lake, the water will fill to the exit level. But if you dredged the exit level, then the water level in the lake (and the water table in the surrounding neighborhood) would eventually lower to the level of the outlet.
The hydrology experts point to a topographical decline of 20 feet from the northeast corner of Lake Calhoun to the northwest corner of Lake Hiawatha. The water level of Lake Calhoun is 20 feet higher than the water level of Lake Hiawatha, and, therefore, the assumption is that the water table around Lake Hiawatha would remain constant because water from Lake Calhoun would run in to fill the creek back up to its current level.
But there are at least three objections to that projection.
First, the water table does not always follow a neat and even pattern of decline. Nature moves according to its own laws and not necessarily according to classroom formulae.
Second, man-made obstructions can change the water table. There are two 20-foot concrete walls between Lake Calhoun and Lake Hiawatha—the barriers on 35W—that reach from 31st Street to Minnehaha Creek.
Third, water flowing from Lake Calhoun might eventually re-fill the creek, but it could take 50 years to do that.
Southside Pride found someone who would dredge the creek from 28th Avenue to the Falls for less than $100,000. Surely that would be a worthwhile investment in trying to save the homes around Lake Hiawatha. But the hydrologists pointed out to me that there could be utilities underground passing under the creek, and it might cost much more than that to move the utility pipes.
Of course, before beginning to dredge the creek, people should check with the city engineer to see if there are sewer or utility pipes under the creek bed, but it is unlikely that the pipes would be less than 4 feet below the surface of the creek.
There are answers to those questions and solutions to those problems if the people who are responsible for the present condition had the will to want to change the situation.
However, it seems the Minnehaha Creek Watershed District is quite content to see Lake Hiawatha revert to Mud Lake and the area around it return to mud flats and a swamp.
