The one that wasn't

My other major early project at TAMS was the proposed South Suburban Airport near Chicago. Beginning in 1990, we analyzed five alternative search areas ranging up to 18,000 acres in size; full biological inventories of each, over a two and a half year period. While two of the sites were almost entirely agricultural, one included some woodlands of moderate to good quality, and two, the Gary Indiana and Lake Calumet IL sites, included remnants of significant natural communities such as nearshore dune and swale, mesic prairie, and marsh. A lot of experience that would later prove to be valuable came out of this project, not to mention the world-class team I was fortunate enough to work with for those first seven years.

After some political contortions far too complex to describe here, eventually the Peotone site was chosen. It was one of the greenfield, or  agricultural sites and the vast majority of it was in row crops. All of the headwater streams that crossed it were channelized. And therein I found an opportunity.

One of the streams was Exline Slough. Today it's a straight ditch. Where it crosses Beecher-Peotone Road it's as much as 10 feet deep. Each year we sampled fish from within an earthen canyon, unable to see over the sides for the entire 200-meter sampling reach. It had been dredged, probably before 1910, and the rich black dirt sidecast into low irregular levees on either side. it was located just southeast of the proposed airport, well within the noise contours where we'd need to create unpopulated buffer areas.

In spite of the massive alteration we got above average fish assemblages there most years, with IBI scores around 44 if I recall correctly. There was at least one fishkill associated with nutrient over-enrichment, followed by fairly rapid recovery. So it was a reasonably diverse if sometimes unstable assemblage.

The obvious clue came from the name; it had been called a slough for a reason. Standing atop the bank, one could see an elongated basin slowly rising off to either side to the surrounding Valparaiso Moraine.  A glance at a topographic map confirmed it; there was a quarter-mile wide abandoned floodway perched 10 feet above the modern elevation of the streambed. Finally, a look at the 1830's GLO survey notes and map provided additional confirmation. At that time, prior to channelization, Exline Slough had been a quarter-mile wide flowing marsh with a very narrow open channel in the center. It had been like this for miles, from the headwaters all the way to the edge of the higher gradient sloping down to the post-glacial Kankakee Torrent valley.

Exline Slough, we determined, originated from a series of drain tile outlets about a mile and a half north of our sample reach. Here a south facing shallow basin climbed gradually to the divide between the Mississippi River drainage... Exline Slough into the Kankakee River, to the Illinois, and finally to the Mississippi; and the Lake Michigan drainage, via Plum Creek and Thorn Creek and into the Calumet. On the north side of this divide, only a few hundred meters from the Exline Slough drain tiles, we discovered a previously unknown 30-acre prairie set well in from the section roads. It had been heavily grazed by horses, but was restorable.

We quickly developed a concept to grade several miles of Exline Slough back to something like original elevations, re-establishing the wide, shallow and slowly flowing marsh that had once been there. At least two section road crossings would have been removed entirely. The drain tiles would have been removed. The prairie would have anchored the northern end.

Unfortunately, two things got in the way. Most importantly, the FAA issued published guidance restricting wetland mitigation within 10,000 feet of an active runway, for wildlife hazard reasons. The northern part of our site fell within this radius, effectively killing it as potential mitigation. Also, the proposed airport bogged down in Illinois politics. It still hasn't been built almost 20 years later, although land for the first runway (of six originally proposed) and a small terminal has been acquired.

Still, it's worth sharing the concept because there are other places in the Midwestern and Eastern U.S. where it's applicable. Structurally it's obvious enough. What made it so possible though was the existence of a published analog, a reference site a century removed in time. The photo below is from Sherff (1914), based on work done in the Skokie Marsh north of Chicago in 1910-1911 and published by the State of Illinois.

The photo was taken west of Glencoe. Note the relatively narrow open channel, choked with submerged vegetation, and the bordering bands of what appear to be bulrush, dropping into a marsh and wet prairie complex with lower vegetation to either side. Topographically this marsh would have been similar to the one at Exline Slough before both were extensively modified. There's an extensive vegetation list included in the published article and while the two site are perhaps 60 miles apart and they certainly weren't identical, they would have had much in common. It wouldn't have been hard to develop a planting mix from the available information. There's also a surviving area in Barrington Hills, around Spring Lake and Mud Lake, that's similar in appearance and which could serve as a reference site.

This one wasn't to be. However it's an excellent example of how to use historic information and a bit of temporal imagination to re-establish what once was, when the circumstances allow.