Darby Creek Advocate Volume 9, Issue 3  November 2001

During the spring 2001 semester, the Darby Creek Association provided a $500 grant to Professor Steven I. Gordon’s City and Regional Planning Studio at OSU. This grant helped fund a study entitled “Development and Change in the Big Darby Watershed.” The study concluded that worrisome trends are afoot in the Darby watershed, and unless serious planning controls are put in place the watershed will see a deterioration in its condition.
The study focused on population growth and the changes in land use accompanying that growth. Special emphasis was placed on analyzing the percentage of land covered in impervious surfaces (e.g. roofing, pavement, etc.). Using satellite imagery, the study estimated impervious areas represented 8.98% of the Darby watershed in 1997 and 14.9% in 1999 (this does not represent a total level of impervious surface, just the amount of space, such as urban areas, that includes a high percentage of impervious
surface). Researches have correlated increases in impervious surfaces with declines in water quality.
The study analyzed the correlation between land usage and impervious surface area, and the biological and physical quality of the aquatic habitats, in a set of Darby subwatersheds. The most important predictors of aquatic quality turned out to be land use in the areas immediately adjacent to the
stream. Deciduous forest cover on the stream bank had a strong positive effect on aquatic quality, while adjacent agricultural practices had a strong negative effect. This confirms the importance of buffers in Darby preservation efforts.
The quantity of impervious surface had a weak statistical relationship with aquatic quality, possibly, according to Gordon, because Darby does not have a statistically high level of highly degraded stretches.
The study also modeled flooding scenarios in the Hellbranch Run subwatershed based on varying levels of development. The study predicted floods would occur faster and last longer as the amount of impervious surface increases. The study thus supports what residents of the Hellbranch area already know: management of stormwater from new developments is critical.
The study concludes that there are currently no policies in place that would control growth in the Big Darby watershed. Without such mechanisms, trends suggest that changes in land use and impervious
surface can be expected to greatly increase threats to the biological quality of the system.
The nature of recent trends demonstrate that a variety of conditions are causing the continuing deterioration of some tributaries to Big Darby. These include land use in the riparian zone, changes in habitat associated with these land use changes, changes in runoff and flooding, and increasing chemical and sediment pollution loads. A combination of engineering controls on the runoff generated by new development, changes in agricultural practices, and limitations on growth in critical areas will be required to protect the watershed from further harm.
Gordon’s results from this and other studies can be accessed at the Big Darby Creek Watershed Data Sharing Project on the web at facweb.arch.ohio-state.edu/sgordon/research/darby/start. Click on the “themes” link.

by Paul Dumouchelle