Reshaping Horseshoe Lake into a meadow is fantasy

A June 15 presentation by Frank Greenland of the Northeast Ohio Regional Sewer District (NEORSD), “Shaker Lakes: Review and recommendations” (available online at https://bit.ly/3FYmaMb), contains a proposal for re-shaping the bed of Horseshoe Lake (slide 27). The slide suggests replacing the lakebed with two streams meandering between tree-lined banks in a meadow. It’s a very appealing picture. I’ve heard others describe this scene as, “the natural beauty that was here before the Shakers arrived.”

Doubtless, engineers and landscape architects can design such a place, and bulldozers can construct it. But physics will not abide it for long.

I’m no geologist. What I’m saying here isn’t authoritative. But if the questions I raise have any validity, they could remove from the debate the idea that Horseshoe Lake’s bed could ever be a park-like sanctuary.

Problem 1 - Meander Geometry: Meanders are a work of physics. They’re the result of erosion and deposition. The wavelength of a meander ranges between 10 times and 14 times the channel width. A meander’s radius of curvature is approximately 20% of its wavelength, or 2-3 times the channel width. These are universal parameters, applying to all meanders in all streams—even the Gulf Stream.

I’m unaware of any attempt by NEORSD to justify its meander designs as complying with these laws of physics. I don’t know whether the size of the lakebed would permit meanders of the two branches of Doan Brook that meet there. And I’m unaware of any material produced by NEORSD that addresses these issues. An open question is whether the lakebed is large enough for these two streams to meander at all.

Problem 2: Terrain Morphology: Meanders are inherently unstable. They change continuously, including episodes of dramatic change. Although meanders evolve, they remain meanders. To maintain themselves as meanders, terrain morphology must meet two requirements. First, the flood plain must possess a small elevation gradient. Second, the stream must flow slowly enough that it cannot generate turbulence. The usual geometry that limits stream flow is a barrier to exit from the flood plain. Both of these factors create problems for NEORSD’s proposal.

The lakebed’s elevation gradient is significant, if we measure the elevation change from the points at which the streams enter the lake to the point where Doan Brook exits the bottom of the dam.

But, if we limit the joined branches of Doan Brook by imposing a barrier as they exit the “meadow,” we’re essentially creating a dam, which NEORSD opposes. If we don’t limit the flow, the streams, powered by and swollen in severe storm incidents, will eventually cut through the meanders and the meadow and return to the two-ravine geometry that likely underlies the 25 feet of sediment that now forms the lakebed.

What the future holds for the lakebed when the dam is removed: Although engineers and landscape architects are free to sculpt the lakebed as they like, physics will eventually prevail. During large flood events, the two branches of Doan Brook that now converge at the lakebed will first choose their own meanders, and then eventually chew down through the “meadow” to restore the two ravines. A single Hurricane Ida-scale event could be sufficient to erase the engineered meanders and replace them with a pre-Columbian morphology: two deep ravines joining to form one ravine near what is now the site of the dam—not anyone’s idea of a pleasant setting for a park.

We as humans aren’t free to choose whether we want (a) a scenic lake, or (b) two streams meandering through a park. The real choice is between a scenic lake and two deep ravines.