Land development characteristics in the southeastern United States

As part of this research, data from about 125 neighborhoods (previously surveyed by Jefferson County USDA Earth Team volunteers) in the Little Shades Creek watershed and another 40 neighborhoods from five drainage areas (part of the Jefferson County, AL, Stormwater Permit Monitoring Program), were intensively investigated to determine the surface covers for each land use type. The local MS4 (municipal separate storm sewer system) monitoring data used to verify the WinSLAMM model for these areas are incorporated in the NSQD (National Stormwater Quality Database) database. This verified model was used in a case study to determine the sources of critical pollutants, and to evaluate different combinations of stormwater controls.

The data shows that the watersheds are highly impervious, with three of them having more than 50% of the watershed area composed of impervious cover. However, TR-55 methods still overestimated the impervious cover for all land uses investigated. As an example, for the high density residential land use area, more than half of the land cover is comprised of landscaped areas, and about 25% of the land use is total impervious cover. Those percentages are much less then the values given by TR-55 for the same housing density (52-65% imperviousness). It was also concluded that the variabilities of the surface covers within the different land uses for the investigated areas was small, especially for the impervious covers. The variabilities are much greater for the backyards and frontyards, but that was associated with the location of the home on the building lot.

WinSLAMM estimates that the stream quality in the receiving waters is in poor condition based on the flow distribution, a fact confirmed by in-stream investigations by the Jefferson County Storm Water Management Authority (SWMA) biologists. The residential watersheds are closer to the threshold between fair and poor biological conditions than the industrial and commercial watersheds, as expected.