“If the greater Bluffton area is developed according to the approvals as they currently exist, impervious surface will exceed 20% in the May River watershed and edible May River oysters will be a thing of the past.”
Recent decades of development have brought an influx of impervious surfaces, such as parking lots and roads. Now that impervious surfaces cover more than 10 percent of our watershed area, it is a widely held scientific fact that the water quality within has declined. Poor water quality leads to medical illness in humans and decimates oysters, fish and other marine life.
With a few exceptions, the settlement pattern south of the Broad River has been comprised of conventional suburban sprawl: single-use, single-family detached subdivisions, strip-commercial, and auto-dominated thoroughfares which brings with it a high percentage of impervious surface. The clearing of land for sprawling suburban development is directly linked to the impaired waterways because without enough natural land-cover left intact to serve its filtering function, stormwater carries sediment and pollutants across impervious surfaces and directly into the rivers. The impacts of impervious surface are exponential: a one-acre parking lot produces 16 times the volume of runoff that comes from a one-acre meadow (Schueller & Holland, 2000). Therefore, developing under a conventional suburban sprawl settlement pattern guarantees enormous stormwater volumes while amplifying its negative impacts on our waterways.
“The clearing of land for sprawling suburban development is directly linked to the impaired waterways because without enough natural land cover left intact to serve its filtering function, stormwater carries sediment and pollutants across impervious surfaces and directly into the rivers.” (Schueller & Holland, 2000).
Moreover, the streams, creeks, marshes and rivers surrounded by filled and impervious watersheds are less diverse, less stable, and less productive than those in natural watersheds. (Schueller & Holland, 2000) Streams in watersheds with more than ten percent hard surfaces become physically unstable, causing erosion and sedimentation, (Booth, 1991; Booth & Reinelt, 1993) and habitat quality falls below the level necessary to sustain a broad diversity of aquatic life. (Booth, Booth &R; Shaver et al., 1995) In sum, a watershed’s diversity, stability and quality become increasingly compromised as percentages of impervious surface increase. As a general rule, a ten-percent [impervious surface] threshold establishes an empirical point beyond which ecosystem function, in general, declines because of individual and cumulative stresses. (Beach, 2002) Studies specifically focusing on coastal estuaries have confirmed that general degradation begins at the ten-percent impervious threshold. (Taylor, 1993) There is an indisputable positive relationship between the traditional development pattern (compact, mixed-use, traditional neighborhood development) and its minimized impervious surface that ultimately results in greater water quality.
Over the past (two) decade(s), various stormwater management techniques have been employed in an attempt to mitigate the impacts of stormwater runoff caused by impervious surface without altering the conventional suburban settlement pattern. These techniques include, but are not limited to: stormwater management ordinances, Best Management Practices, devices at the end of outfalls, and maintenance and repair of stormwater retention ponds. However, the current inventory of on-site safeguards does not allow us to ignore the ten-percent rule. The only aquatic systems that will retain the full range of species and ecological functions will be those where less than ten percent of the watershed is impervious. (Schueller & Holland, 2000)