Urban streams with green walls

ResearchBlogging.orgWill Dalen Rice and a friendNote: This post is a collaborative effort by Anne and guest blogger Will Dalen Rice, a graduate student in the Department of Geography and Earth Sciences at UNC Charlotte. He had the misfortune of taking a couple of courses from Anne this semester and has become a certified stream junkie, going out on rainy nights to see how high Charlotte’s urban streams are running.
Most cities were started around the idea of available surface water resources. Development and misuse of our streams (ex: “dilution is the solution to pollution”) has resulted in the modern urban stream. These streams are straight and good at carrying storm water, full of sediment and pollutants, and they lack good habitat for plants and animals. Now that we are beginning to notice how degraded and trashed these city waterways are though, scientists and engineers are beginning to attempt to address the form and function of these waterways to hopefully return them to a more “natural” (or at least aesthetically pleasing) state. While there are many stream restoration techniques, they often involve mechanical manipulation of the stream channel and banks and the planting of riparian plants along the stream corridor. As the streamside ecosystem redevelops, the idea is that health of the stream will also improve (leave it to nature to clean up our messes, given the chance).
For large urban streams, the standard practices in stream and habitat restoration are sometimes not possible, often because decades of infrastructure development have pinned the stream into a narrow corridor. So other approaches need to be considered, and Robert Francis and Simon Hoggart of King’s College London discuss ways that existing artificial structures can be put to work to mitigate some of the ecological impacts of urbanization. In the specific case of the River Thames in England, habitat development has been observed on man-made structures, and furthermore, certain types of man-made structures grow life better than others. Francis and Hoggart show that indeed plants (and therefore animals) can develop in a riparian zone better when brick and wood and rougher materials are used over concrete and steel. If concrete and steel already exist, adding brick and wood can further trap sediment for habitat growth (like gluing a cup of dirt to a steel wall). They suggest that this should become standard practice when thinking of restoration efforts in large, urban waterways.
The NOAA’s Northwest Fisheries Science Center says Thornton Creek in downtown Seattle exemplifies “the challenges facing rehabilitating urban streams.” But a look at the NOAA picture below shows that this stream is also emblematic of a riparian ecosystem that has developed within the constraints of the existing structures and maybe even a spontaneous model for the sort of restoration that Francis and Hoggart envision.
Seattle urban stream from NOAA website
Francis, R., & Hoggart, S. (2008). Waste Not, Want Not: The Need to Utilize Existing Artificial Structures for Habitat Improvement Along Urban Rivers Restoration Ecology, 16 (3), 373-381 DOI: 10.1111/j.1526-100X.2008.00434.x

Categories: by Anne, environment, hydrology, paper reviews

Comments (5)

  1. Lassi Hippel?┬žinen says:

    “If concrete and steel already exist, adding brick and wood can further trap sediment for habitat growth…”
    Steel is often used to protect fragile materials against the grinding teeth of ice. If you add something soft on top of it, it will be gone by next spring. Ice can dislodge even large blocks of stone.

  2. Darlingtonia says:

    There’s a great passage in the book The River Why, by David James Duncan, where the main character follows an urban stream in Portland to its source at the top of a building.

  3. coconino says:

    Though I’m not a big fan of fish disneylands for wealthy ranchers with lots of river that they want in one same place, I’m a pretty strong believer in use of stone structures such as vanes, cross-vanes and spurs in urban/suburban settings to promote thalweg and bank stabilization while providing some semblance of habitat and “naturalistic” setting. Maybe in Vermont one can get away with condemnation and floodplain purchase to bring urban/suburban stream systems into a more natural floodplain setting, but that’s not going to happen here in the “you can’t tell me what to do with my land” interior west. In the absence of a wide enough floodplain and appropriate upland land management for a river to “behave” naturally, non-manmade material structures are about the next best thing. Disclosure: I have this argument regularly at home regarding some communities I work in or at least know about, in which almost continuous floodplain encroachment occurs up to bankfull, literally. What do you do? The alternative is an disastrous flood, and then placement of gabions over most of “offending” stream course under “emergency” free passes, pretty much wrecking any work any other entities are doing to promote restoration and improvements in water quality. I’ve seen it happen, over the most stringent objections of my colleagues.

  4. Gaythia says:

    There is an excellent website describing the extensive history of development and degredation as well as recent efforts at stream rehabilitation along Seattle’s Thornton Creek here: http://www.homewatersproject.org/pages/Resources/thornton_creek.html.

  5. Russ says:

    Adding brick and wood that traps sediment also reduces the cross-sectional area and increases the roughness, leading to a significant reduction in capacity and causing more frequent flooding. Not exactly desirable in an urban setting.