The Watershed Approach - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 15

the urban areas through the character of their corresponding processes: (1) their energy
inputs come from a source that yields pollution (fossil fuels); (2) the production process
produces growth, but it is in the form of infrastructure, which is likely to impact existing
natural ecosystems through their removal; and (3) the energy and material releases differ
in their magnitudes and impacts. Urban areas release tremendous amounts of heat in the
form of reradiated long-wave radiation from darker surfaces such as asphalt. Substantial
heat is also emitted from automobiles and power plant discharges. This excessive heat
often creates an “urban heat island,” which affects the local microclimate, specifically the
magnitude and frequency of summer thunderstorms (Changnon 1978). In terms of the
material released, in natural ecosystems, the dead biomass is part of the carbon cycle
and eventually becomes a part of another living entity. For example, the biomass from
decomposed trees adds organic materials to the soil, which when they decompose will
help resupply the carbon dioxide in the atmosphere to be taken up later by other plants
through photosynthesis. The biomass in this process is therefore recyclable.
In urban areas, the production of infrastructure does not produce recyclable biomass,
and this reality creates the critical challenge for urban sustainability . How can we con-
tinue to produce “things” in concentrated urban areas, and yet not wreck the surround-
ing ecosystems supporting our existence? Part of the answer lies in reducing pollution at
its source—before it enters the environment. Here, the elimination of certain toxic and
persistent chemicals from the manufacturing process can help. Another piece involves
landscape-based urban planning, so our waters are more effectively protected. The plan-
ning process is required because watersheds are ecosystem units encompassing urban
areas, and their surface area is typically composed of 5% water and 95% land. A third
component to a sustainable urban environment must address the reality that large areas
within them are already contaminated, and these contaminated sites need to be brought
back “on line.” Successful remediation of damaged soil and groundwater must make the
land and water recyclable again.
To succeed, all of these efforts must proceed from a scientific foundation, one which
includes environmental geology, geochemistry, risk analysis, hydrology, and science-
based landscape planning. The following chapters follow this route.
1.5 Organization of This Topic
The three parts of this topic, Geology, Contamination, and Sustainable Development
address the five themes just mentioned within the context of a watershed approach. The
Geology part (Chapters 2 through 6) addresses the role of geology in watershed inves-
tigations; water and hydrogeology of watersheds; preparing a geological analysis of a
watershed, including case studies focusing on the surface geology in various terrains;
and developing geological and vulnerability maps of an urban watershed. Historically,
the majority of geologic investigations have either emphasized identification of what was
present within a few inches of the surface of the ground or characterizing deeper bed-
rock. Detailed geologic investigations of the unconsolidated materials between these two
points have only recently become of interest. This topic forms a critical piece of the linkage
between urban geology, contamination, and urban redevelopment, by focusing on the sur-
face and near-surface geologies and their implications for contaminant sources and sinks,
contaminant migration, hydraulic conductivities, and potable water availability.