Without a Standard, Low Impact Development Is another Form of High Impact Development

There is a tendency among low impact development designers to think that any project that uses practices and facilities from the low impact development (LID) toolbag qualifies as a low impact project. But, for over three decades, the literature relating urbanization and stream impacts leads us to believe that this may not always be so. The near total destruction of stream habitat often occurs when a watershed reaches effective impervious surface percentages between 10% and 20%. Moreover, studies suggest that the steepest decline in habitat quality begins with the first few percent of forest converted to effective impervious surface. But, before the first square foot of impervious surface is placed, impacts on streams are observed when a watershed is simply cleared or partially cleared. Moreover, streams are particularly sensitive to clearing in the riparian zone. Thus, in order to qualify development as "low impact" it must preserve the characteristics of a healthy watershed. A standard for low impact development must at minimum include limitations on clearing, impervious area, and buffer disturbance. This paper will focus on a standard for development based on the first two limitations. The standards discussed in this paper are aimed at areas which in the pristine state were forested. Although it is a temptation to say that the same principals would apply to prairies and other landscapes, the data is not at present available to say with certainty.