Environmental Engineering Reference
In-Depth Information
TABLE 6.2
Rouge River Geologic Vulnerability Scoring
Parameters and Vulnerability Scoring
Geologic Unit
1
2
3
4
5
6
7
8
Total Score
Rank
Outwash unit
10
9
9
10
10
10
10
10
79
1
Recent fluvial
10
6
6
8
10
10
10
10
70
2
Main sand unit
10
9
9
10
10
10
6
1
65
3
Other sand units
10
8
8
10
10
10
6
1
63
4
Moraine unit 1
5
7
7
8
8
10
5
10
60
5
Moraine unit 2
5
6
6
7
7
10
5
10
56
6
Moraine unit 3
5
5
5
7
7
10
5
10
54
7
Moraine unit 4
5
4
4
6
6
10
5
10
50
8
Sandy clay unit
4
3
3
4
1
1
3
1
20
9
Sandy and silty clay
unit
4
2
2
4
1
1
3
1
18
10
Upper clay unit
3
1
1
3
1
1
2
1
13
11
Lower clay unit
(ground moraine unit)
1
1
1
1
1
1
1
1
8
12
Using this geologic, hydrogeologic, and anthropogenic-impact information, a vulner-
ability matrix was developed and is presented in Table 6.2 (modified from Murray and
Rogers 1999b; Rogers and Murray 2002). The geologic units with the highest geological
vulnerability (represented by the total score column) were the outwash unit, recent fluvial
deposits associated with the Rouge River, and the sand unit of glacial lacustrine beach ori-
gin. The next group of units with moderate risk were the four surface moraine units. The
geological units with the lowest risk were a sandy clay unit, silty clay unit, and an upper
clay unit, all associated with the glacial lacustrine deposits.
The outwash, recent fluvial, and sand units were evaluated to be the most geologically
vulnerable geologic units in the watershed because they are generally composed of coarse-
grained sediments, have an abundance of groundwater, and account for the majority of
the base flow of surface water to the Rouge River. The four moraine units were of mod-
erate risk because they are composed of finer-grained deposits, have less abundance of
groundwater, and do not serve to recharge groundwater or discharge to surface water as
significantly as the outwash, recent fluvial, or sand units. The low vulnerability units are
the sandy clay unit, sandy and silty clay unit, upper clay unit, and the lower clay unit.
These geological units generally do not have an abundance of groundwater, are very fine-
grained units, and generally impede the migration of groundwater.
Using the surface geological map of the Rouge River watershed (Rogers 1997b) as a base
map, and the information contributing to the construction of Table 6.2, Figure 6.3 was
developed as the geologic vulnerability map for the Rouge River watershed (Rogers 1997c).
6.5 Demonstrating the Significance of Vulnerability Mapping
As noted by Foster et al. (1993) and Loague et al. (1998), the significance of geologic vul-
nerability is not appreciated until it can be put into environmental, economic, or political
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