Along the entire 246 mile length of the Sangamon River there is but one dam. And even it was a bad idea.

Construction was complete on the dam on the Sangamon River that forms Lake Decatur in 1922. And problems with this dam were already apparent as early as 1936. The solution to Lake Decatur’s problems, first proposed by the Army Corps of Engineers in 1947, was to build Oakley Dam, just upstream and still in the headwaters of Lake Decatur.

As regular readers (hi Mom!) are aware, I’ve been writing about the monumental (and ultimately successful) political struggle to stop Oakley Dam. But this week we ask the obvious question: why did we need another dam on the Sangamon River in the first place?

The answer is dirt.

By 1936, the first siltation survey showed that Lake Decatur was already filling in with dirt, in the form of silt, at the alarming rate of 198 acre feet (one acre, one foot deep) per year. Ten years later that rate had increased to 236 acre feet per year.

The Sangamon River drains one of the most productive agricultural areas in North America, if not the world. And the Sangamon is good at its job. One could honestly say that the Sangamon River carries away a ton of dirt. In fact, at peak concentration rates, the Illinois DNR has found that the Sangamon River at Monticello carries away 25,000 tons of Illinois topsoil per day. That’s a lot of dirt.  

In 1949, “The Story of a Lake” outlined Lake Decatur’s siltation problem and urged farmers to save their dirt, which would be good for them and for the river. But alas, by 1956 the problem persisted and Lake Decatur had lost 30 percent of its storage capacity to dirt.  

Oakley Dam was the answer the Army Corps of Engineers provided to the problem of Lake Decatur’s lost storage capacity to dirt. Oakley Dam would impound the dirt and save Lake Decatur.

But a different answer is saving dirt. So to find about saving dirt, I knew I had to go to the source. 

So I took a walk with Lisa Haynes, proprietor of Tomahnous Organic Farm, conveniently located just north of me, so I could get a firsthand look at how at least one farmer was saving her dirt.

First, we looked over some of the untilled fields.  Using “no till” methods is a fairly well accepted (and money saving) method that many farmers use to prevent soil loss.

Then we walked past her cover crops of wheat and clover. These not only serve to save soil over the winter, but they also can be harvested and the clover makes good animal feed for the critters of Tomahnous Farm.

This area was also deep with compost. But not just any compost, Tomahnous Farm is also where your shredded leaves end up, Mahomet, and, as I can attest, so do things such as your shredded yard trash including your shredded lost kid toys.  We picked up some dirt just below your leaves and even in dry weather it was still cool and moist. Proving that composting is also a great way to save dirt.

Further on, we found ourselves walking along their rather attractive “grassed waterway”, a 30 foot wide stretch of grass meandering across their corn and bean fields, shaped in the form of a very shallow curve. Just looking around, the benefits are obvious compared to the non-grassed waterway: there, the rain seeks the low channel and quickly carves out gullies and erodes massive amounts of topsoil. Grassed waterways slow the flow and control erosion, saving dirt.

It was then that her husband Eric, aka “County Outsider”, came by and rained on my little parade (figuratively speaking of course, given the weather) by pointing out what a pain it is to actually plow and plant on odd shaped triangles of land bisected by meandering grassed waterways while also staying perpendicular to the contour of the land, which also saves dirt. He also pointed out that their nifty grassed waterways take about three of their 20 acres out of production. But Eric soldiers on in the interest of doing the right thing: saving dirt (and not incidentally, keeping Lisa happy).

The point is that while there are many ways to save dirt, none of them come without a price tag. And this is the dilemma faced by any farm operation when trying to save dirt. And it’s also why the Sangamon River is so full of it.

I know, I know, this is not a column about farming practices, it’s a column about dirt. Actually, it’s a column about the Sangamon River, and it’s telling the story of Oakley Dam, which would have been unnecessary were it not for so much dirt in the river, which belongs in our farm fields and not in the river in the first place.

How do we keep our riverways clean, make large dams unnecessary and preserve our amazing agricultural productivity?

The answer is, as it has always been: save the dirt!

Appeared as Notes from the River, Mahomet Citizen, June 28, 2012, by Scott Hays