Mudflats!

One of the interesting talking points of opponents of the removal of the Estabrook Dam, Grafton Dam, and Limekiln Dam on the Milwaukee River is that, after dam removal, large mudflats will be left behind. These large unsightly stretches of clay and silt will then become homes for weeds, thus spoiling their scenic view of the river.

This is a true statement, but only in the short run. In order to find out why, let us examine what a mudflat is, and how it is formed.

Rivers are great earthmovers and builders. Over vast amounts of time, they erode outside bends and deposit silt and particulates on inside bends. These initially form flats of sediment or rock. In the Midwest, these inside bends are mostly composed of silt, sand, dissolved clay and tiny wood debris. This inherent character of rivers is why they bend and meander in their channels, always eroding earth and depositing it in new places such as inside bends and estuary regions. One look at a map or trip to a river will prove this to be true. As time passes, these inside bends grow larger and larger, beginning as mud flats and ending up as land that people build homes upon. First grasses and hearty plants (weeds to some) grow upon the flats. Then small shrubs and trees take hold. Finally, the former flat becomes part of the shore structure and may be indistinguishable from the surrounding woods.

All these building, moving, and eroding processes are natural, so why the fuss over a natural riparian structure? Here we find the irony. Because, simply put, it is man’s interference with rivers by slowing the water flow with dams and creating impoundments, and channelizing the river with artificial bank structure that impedes the river from its earth moving, its ability to push the silt downstream, form new channels, and build new river banks. Thus, the actual composition of the bottom of the river changes from gravel, boulders, silt, mud, and sand, to primarily long flat bars of silt. When water levels are lowered, these become mudflats. Anyone who lives in a tidal basin on the ocean knows this process well, albeit in a natural way.

Flow rates and gradient also play a part. Faster flow moves the sediment, while slow deep areas of a river (like an impoundment) allow the sediment to fall to the bottom and collect.

So it is ironic in a sense that the very dams and resulting impoundments that they create are primarily responsible for the formation of these mudflats that seem to be the bane of dam proponents.

There is, obviously, one missing factor here, and that is time. We measure time in days, years, and generations. Nature measures time differently. Given a long enough time, all mudflats become banks and islands. Walking in a river will prove this. Where did that island come from? Was it always there? Chances are it started as a small gravel and silt deposit forming what is known as a ‘braid.’ Over time it continued to build as the river, flowing around it, deposited more and more silt, mud, gravel, and particulate at its downstream end. Then birds nested on it and brought undigested seeds. Nuts and seedpods washed down and took root as well. Then trees began to grow.

We can see, in a shortened time, how mudflats become land. The North Avenue Dam removal created an enormous set of flats on both upstream banks. The river, which was formerly slow, deep and very wide here, shrank to less than half its width. Where did the flats go…?

The answer is that you are walking on them. At present, the land reclaimed from the impoundment all the way up to Hubbard Park in Shorewood is a jumble of brush, shrubs, grasses, and small trees, but in another twenty years, if we don’t mess with it, that area will return to nature completely, and provide an aesthetic view. We can and have aided that process by securing the former flats with bank stabilization, and planting native plants.

So, dam removal opponents, in a nutshell, that is what mudflats are. They are natural, and in time, will morph and grow into something beautiful. They are your mudflats: created in this instance by the dams themselves.