RAINWATER AS THE RESOURCE - Low Impact Development and Sustainable Stormwater Management - page 17

Figure 1-11 The urban environment in the eighteenth century (1799). The road was
pervious.
A popular tune of the 1970s declared our wish to “ ... pave paradise and put
up a parking lot ... ”—not an exaggeration but an accurate description of this
transformation of the land surface (Figure 1-13). Recent studies of land devel-
opment patterns in developing watersheds have distinguished the different types
of impervious cover that form the current patterns of land cover, and these land
cover analyses generally conclude that about 25% of the impervious cover found
in a watershed is comprised of the building structures serving human activities,
and 75% is comprised of impervious pavements, largely asphalt concrete, but
also portland cement concrete, that serve for the transport and storage of our
automotive vehicles. Other studies [15] have concluded that when a watershed
approaches an impervious cover of 25%, the water resources have been so altered
that water quality and quantity have been severely degraded.
Countless small stream systems, especially in the headwaters of larger river
basins, have been developed, filled, built upon, piped, and paved over during the
past century. A good example is a small (440-acre) stream called Meeting of the
Waters Creek in Chapel Hill, North Carolina, a tributary of the much larger Flint
River basin, which drains to the coastal Atlantic estuary. Present conditions reflect
expansion of the University of North Carolina over the past five decades. The
present land cover is 77% impervious and still increasing (Figure 1-14A), with