Environmental Engineering Reference
In-Depth Information
Fig. 1.4
Generalized root
distribution with depth and
respect to the water-table surface
(indicated by the
inverted
triangle
) for hydrophytes,
phreatophytes, mesophytes,
halophytes, and xerophytes.
Facultative phreatophytes include
plants belonging to the willow
family, such as
Populus spp
. and
Salix spp
., and obligate
phreatophytes include plants such
as mesquite (
Prosopis
glandulosa
).
was no consensus on what name to give this topic of study.
For example, the terms hydrogeology and hydric geology
were used as early as 1802 and 1885 by Jean Baptiste
Lamarck and John Wesley Powell, respectively. Lamarck
is perhaps best known for his idea that all species were
descended from other species, including man, and is widely
regarded as the Father of Invertebrate Paleontology. John
Wesley Powell fought in the Civil War, explored the
Colorado River, and was the first Director of the U.S. Geo-
logical Survey (USGS), a federal agency created by an Act
of Congress in 1879 to, in part, systematically study the
water resources of the western United States. However,
these men were describing geologic processes of erosion
and sedimentation controlled by water, not groundwater.
The first use of the term hydrogeology to mean the study
of groundwater was in a report in 1880 by J. Lucas, and was
later used by the USGS (Fuller 1906).
consistent supply of water to succeed. Because precipitation
was neither abundant nor consistent in this area of the United
States, and most surface-water sources were intermittent,
isolated, and unreliable at best, water trapped deep in under-
ground layers of rock and soil, called aquifers, became the
focus of study. The early USGS hydrogeologists who stud-
ied these resources crossed the area on horseback. Conse-
quently, some hydrogeologists noticed that certain plants
persisted in arid areas in spite of inadequate precipitation.
Moreover, plants that grew along often dry river flood plains
were similar to those in more humid eastern areas.
Although these hydrogeologists were not trained in clas-
sical plant physiology, a few of them hypothesized that the
survival of plants in arid areas must be linked to their ability
to use groundwater. Understanding whether or not this was
the case had not only scientific but economic implications.
Such plants could be used as indicators of groundwater that
may provide adequate supplies, when tapped, to support
municipal usage. Others realized, however, that these same
plants also would compete with man for water. Moreover,
this groundwater use by plants was considered to be con-
sumptive because the water left the basin after transpiration.
Today, we realize that even though consumptive use occurs,
these plants support a diverse ecological niche and are nec-
essary to maintain part of the ecological system of riparian
1.2.1 Water Quantity in the Western
United States
During the late 1800s, it was clear that issues of water
quantity
were as important to managers then as water
quality
is today. New settlements needed to have an abundant and
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