Environmental Engineering Reference
In-Depth Information
The data on water use indicate that humans require and use enormous quantities of
water every day to provide energy, food, and to sustain their lives. But the geography of
water often dictates specific usage patterns. Many regions of the United States lack abun-
dant freshwater supplies and are required to use water more wisely because of its relative
scarcity compared to other areas. The arid southwest and the humid region of the Great
Lakes demonstrate this contrast (Meyer 1989). Because of this geo-climatic factor and other
considerations (one being the water law doctrines existing in eastern and western states),
water is not equally protected throughout the United States, and the methods of conserva-
tion and recycling of water vary widely depending on location.
We now turn our attention to watersheds—the organizers of freshwater supplies. The
focus here will be on urban watersheds and the specific implications their surface waters
and groundwater have for regional geology, contaminant sources and sinks, and the long-
term sustainability of the landscape.
3.3 Surface Water in Watersheds
The importance of surface water to urban centers cannot be overstated. This water acts as a
source of potable water and supports agriculture, commerce, and transportation. From an
environmental perspective, surface water is responsible for the erosion and deposition of
a significant portion of the sediments lying beneath urban areas, and when surface water
is in the form of a stream, it carries suspended and dissolved materials into other bodies
of water.
Nature organizes streamflow by adopting the most energy efficient method of trans-
port within a physical framework consisting largely of the local geology and climate. In
areas of fractured rock, the streams follow the fractures; whereas in sedimentary envi-
ronments consisting of surficial unconsolidated sediments, a dendritic or treelike pattern
of drainage may develop. If it rains more, then a denser stream network evolves. The
primary objective of a stream is to transport the water it receives and the materials it
carries without delay, so the next time a precipitation event occurs, the transport can con-
tinue. The organizational structure nature came up with to perform these tasks is called
a watershed.
3.3.1 Watersheds
A more modern definition of a watershed sees them as an extent of land where water as
rain or snowmelt drains downhill into a body of water such as a river, lake, swamp, estu-
ary, reservoir, wetland, bay, sea, or ocean (Winter et al. 1998). In some cases, the drainage
areas for water at the surface and below within a watershed may differ. When the areas
are different, the groundwater watershed is usually larger than the surface watershed
(DeBarry 2004). Watersheds act as a conduit for the transport of water and materials at the
surface and below the surface (groundwater). Figure 3.8 shows the functional regions of a
surface watershed and their geofluvial characteristics; i.e., their flow volumes and erosion/
deposition balance.
The basic moniker used for watersheds varies. Other terms describing a watershed
include catchment, catchment area, catchment basin, drainage area, drainage basin, river
 
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