Urban Stream Restoration

Sometime in the late 1990s we picked up a private sector client in St. Louis. Our first project for him involved a commercial development just southeast of St. Louis airport, and not too far from the then little known but now infamous locale of Ferguson, Missouri.

I’d never worked in anything remotely like this place. Sandwiched between Interstate 170 and a residential subdivision, it was a surreal island of un-natural nature. Perhaps hundreds of thousands of cars went right by it at high speed every day, and yet I’m pretty sure that hardly anyone except the neighborhood kids knew it was there. Covering several acres and elongated in shape, an urban stream meandered through it, 20-foot deep canyons of hard brown silt with scrubby trees on top of the banks. It was badly eroded, and at some point in the past someone had poured concrete over the edge in a few places. Not in an orderly manner, rather they’d backed the truck up to the edge and let the concrete run randomly down the slope. Upstream it was all fed by culverts and ditches. Downstream it ran into large box culverts and large engineered concrete ditches built as part of the interstate highway. Most of the time flow was gentle and water shallow; all evidence suggested that a typical summer thunderstorm could briefly turn it into a raging torrent.

The stream was so entrenched and so badly eroded that we started over. When the entire development site was graded flat, so was the stream, water briefly went through a bypass pipe, and then a wider, shallower, gently meandering channel was constructed away from the future buildings. A wooded buffer was planted on either side. At the lower end a relatively small flat concrete structure was designed to maintain the channel base level and prevent it from once again eroding too deeply.

We had to make the local contractor do the concrete structure over, they tried to modify the design without asking and got the elevations wrong. Once fixed, the system looked deceptively pleasant. There was no hint of the brown scar on the landscape that had once been. The gentle banks were soon lush and green, and the slower flow allowed a thin layer of clean fine gravel to accumulate in the bottom instead of being instantly scoured away downstream where it could clog the highway box culverts.

The goal was limited to reducing peak flows and minimizing erosion, and it accomplished that quite nicely. The regulatory agencies didn’t even ask for anything beyond 1:1 replacement, since it was clear that almost anything we did would be an improvement.

Overall it was a relatively simple and fast paced project. If not for the urban location and the almost otherworldly pre-project appearance, it might not have been nearly as memorable.