Environmental Engineering Reference
In-Depth Information
city models were not replicated in the colonial settlements, except for the earliest
communities (or forts), and then only briefly. In a democratic society based on
collective security, the need for a protective “castle” became irrelevant, although
each citizen hopes for his own simple version, for reasons that are intended to
impress his neighbors rather than defend against them.
As walled fortifications became unimportant, communities grew up around
commercial centers at water, rail, and road confluences, generally on flatter
terrain, but still surrounded by open land kept in cultivation to support the cen-
ter. This city model continued for over two centuries through the agricultural
period, with countless small towns covering the American landscape from coast
to coast. As our modern cities grew, they expanded out from the urban core into
the surrounding farmland, following the rail and primarily the roadway network
extending out from the center, as shown in Figure 3-5. In this Philadelphia model,
the regional growth anticipated in 1930 grew into the surrounding agricultural
counties by 1960, and by 1990 transformed the region into a community with the
same basic population, now diffused over five counties and hundreds of square
miles. This process was repeated in every major city in the United States, as the
economic transformation from a predominantly agrarian society in the nineteenth
century to the sprawling urban regions of the twentieth century began a process
that seemed to know no end, until the energy reality of the twenty-first century
forced a more sustainable model to evolve.
Topography
Of course, since most of the earlier settlements in the United States were intended
to optimize the cultivation of land or graze livestock, they were situated in flat-
ter, fertile locations in any given watershed, with water access to coastal or
down-river centers of commerce. In recent decades, as we have evolved from a
largely agrarian society to an urban industrial culture, the transformation of this
open farmland to residential development has characterized many of the issues
considered here. In many rapidly developing communities, the availability of
open farm fields for conversion to new home communities has been limited, and
development has been forced to move into more steeply sloping portions of the
landscape. This pressure has resulted in massive loss of woodland in many water-
sheds and dramatic soil erosion, the result of trying to turn a steep land surface
into flat terraces for occupation by roads and houses. The long-term harm created
by this alteration of the natural landform is yet to be fully appreciated, although
the water quality impact on local stream systems is painfully obvious.
Building on steeply sloping land is considered standard in some regions of the
country, not only because of the limited availability of flatter land but also to take
advantage of visibility from an elevated site. The southern California model of
a home perched precariously on the side of a mesa may be considered dramatic
by some and foolhardy by others, but it definitely increases the risk of loss by
not fully considering the constraints of topography.
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