Scott Air Force Base/Mid America Airport St. Clair County, Illinois
Mid America Airport was my first restoration project. The overall project design was already in place when I began my consulting career in 1990: A civilian runway and terminal would be built on farmland east of Scott Air Force Base, with a taxiway connecting the two sides and allowing maintenance facilities and other infrastructure to be shared. The joint-use concept had already been in use in Europe for some time, but this may have been the first application in the U.S.
The taxiway had to cross Silver Creek and it's associated floodplain, easily a quarter mile wide. The northwest end of the 10,000 foot long new runway also projected into the floodplain, requiring the relocation of half a mile of the channelized part of the river. Because the river south of this point remained in a more natural channel, this offered an obvious opportunity to re-meander the straightened part of the river.
There were also impacts to floodplain forest jurisdictional wetlands to mitigate. The floodplain had been logged repeatedly; by examining old air photos going back to the late 1930s, we were able to assign age classes to the remaining forest. Very little of it was more than 40 years old, and it consisted mostly of structurally simple assemblages of pioneer species like green ash, silver maple, cottonwood, and box elder. There were a few oxbows and meander scars, mostly away from the river on the outer floodplain, with mixed open water and buttonbush swamp.
There were also numerous openings fragmenting the forest, marginal farmlands leveed off and cleared but too wet to grow anything about half the time. These were the basis of our restoration design. By breaching the low levees to restore flood hydrology (the river came out of it's banks nearly every year) and returning the openings to forest, we could reduce fragmentation.
Working with staff from the Corps of Engineers Waterways Experiment Station in Vicksburg, Mississippi, we applied a draft bottomland hardwood forest community habitat suitability index model to quantify existing and proposed conditions. This confirmed long-term benefits at the community level. We also did extensive baseline monitoring of plant and animal communities, including Index of Biotic Integrity (IBI) monitoring of fish assemblages in the river and a tributary stream using both boat and wading methods to sample.
Construction began in 1995. Willows were used to stabilize the banks of the re-meandered 50-foot wide river, which proved to be important when a major flood hit not long after. The newly graded banks held.
Post-construction monitoring documented rapid recovery in the restored streams. In Silver Creek proper, fish assemblages rebounded within a few years to slightly better than pre-project levels as the river found equilibrium and regained structural complexity. The biggest improvements came in Crooked Creek, which had been little more than an agricultural ditch before the project. A few years later, with a new floodplain and meandering through a new riparian corridor, IBI scores had climbed by as much as 10 points, and species richness had improved considerably.
Floodplain forest restoration results were more mixed. In a purely functional sense, everything seemed to be working well. However, these were the early days of forest restoration. The planting plan and success criteria imposed by some of the agencies had, by today's standards, been simplistic and homogenous. Survival of planted oaks, intended to jump start succession and increase diversity, had been uneven. They had done well enough on higher terraces, in spite of considerable deer grazing of saplings. But on the lower, wetter places survival had been, not surprisingly, very poor.
With several years of monitoring in hand, we met with the agencies. Although the term "adaptive management" wasn't in wide use until a few years later, that's what happened. Once we had documented that the interspersion caused by micro-topographic variation and difference in hydrology was actually a good thing, success criteria were revised so that they encouraged habitat interspersion. Different targets were applied to different parts of the site. Not long after that the oldest and largest block of mitigation, more than 100 of the total 200 acres of restored habitat, was accepted as successful by the agencies. The design for more remote parts of the site, planted later, was also revised to reflect the more sophisticated criteria.
One of the innovations of the project was the use of trees cut during project construction to add down woody debris and snags to mitigation sites. Normally these habitat components are scarce in young forest, but they are a key habitat component in more mature stands. The new structural features were being used by state listed species within a year of construction.
For me, the project was a key learning experience. I was able to to participate in all phases of a large project, from early environmental review through design, permitting, and construction and post-construction monitoring. Many of the lessons learned would be applied on future projects.