Environmental Engineering Reference
In-Depth Information
Modern
Great Lakes
Glacial retreat
Superior
Location of last
ice barrier
Minong
or sub-Minong
stage
Lake
Stanley
Ice margin
approximately
14,500 years
before present
Huron
St.
Lawrence
Sea
Lake
Chippewa
230 ft
Ontario
Early
Lake Erie
Erie
Rouge River
watershed
Rouge River
watershed
(g)
(h)
FIGURE 5.14 (continued)
(g) Approximately 9,000 years before the present. (h) Modern time.
The purpose of these maps is to (1) convey the concept of regional geological signifi-
cance; i.e., the glacial origin of unconsolidated sediments; and (2) provide a reference point
for the next set of more-detailed maps presented as the figure sequence 5.15a through h.
By starting at the general regional scale and then moving to the more detailed watershed
scale, more information of a specific nature can be included. This progression illustrates
the educational capability of this method.
The map succession shown in Figures 5.15a through h provides an example of how the
use of progressive complexity at the smaller scale of an urban watershed can depict the
processes forming the sedimentary deposits. For example, this sequence shows the glacial
retreat and the associated sedimentary deposits in three dimensions. Figure 5.16 repre-
sents the current geology of the watershed in an enlarged format with a complete legend
describing the stratigraphic column.
5.2.8.2 Three-Dimensional Maps
In addition to map sequences showing increasing amounts of information, three-dimen-
sional digital techniques are also available to develop geologic maps (USGS 2005).
Examples of three-dimensional maps are shown in Figures 5.17 and 5.18 (Great Lakes
Mapping Coalition 2009). Figure 5.17 shows an area being mapped in three dimensions
with the data derived from borings drilled within the site. Using this approach assists with
mapping and data gap analysis while developing the final geologic map. Figure 5.18 shows
a completed draft of a three-dimensional map.
5.2.8.3 Maps Using GIS
GIS are useful for displaying and integrating many sources of information, including
geological maps of urban areas (Chang 2007). One advantage of using GIS is its popu-
larity in urban areas, and most major urban areas in the United States have significant
GIS capabilities. Since the systems already exist, integrating geological information with
other types of readily available layers of digital data provides a distinct cost advantage.
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