Environmental Engineering Reference
In-Depth Information
EXAMPLE 6.1.
Compare Morphology of Two Lakes—Crater Lake and Milford Reservoir
Crater Lake, Oregon, and Milford Reservoir, Kansas, are lakes of con-
trasting properties, despite the fact that they are similar in surface area.
Crater Lake (Fig. 1.1) is a deep oligotrophic lake in the crater of a large
volcano; its scenic grandeur has earned it national park status. Milford
Reservoir is a typical Midwest U.S. lake; it is eutrophic but widely used
for recreation, including a vibrant fishery. Much of the difference in lev-
els of productivity in these two systems can be related to their contrast-
ing morphometric properties, but the level of agricultural activity in the
watershed of Milford Reservoir is also much greater. The following are
vital characteristics of the two lakes:
Crater Lake
Milford Reservoir
Area (km 2 )
55
65
Mean depth (m)
364
7.4
Watershed area (km 2 )
81
64,465
Shoreline length (km)
42
122
Inflow (m 3 /s)
4.3
27.2
Calculate volume, water replacement time, and shoreline develop-
ment. Also calculate the ratio of the area of the watershed to the lake
volume and speculate how these features may alter trophic state.
20.3 km 3
Volume for Crater Lake
area
mean depth
55
0.364
0.48 km 3
Volume for Milford Reservoir
65
0.0074
Water replacement for Crater Lake
volume/discharge
203/ 0.136
1500 years
0.48 km 3 /(0.858 km 3 /y 1 )
0 .56 years
Water replacement for Milford Reservoir
)
Shoreline development for Crater Lake
D L
42/(2
55
1.6
)
Shoreline development for Milford Reservoir
D L
122/(2
65
4.3
Watershed area/ lake volume for Crater Lake
4.0
Watershed area/ lake volume for Milford Reservoir
134,000
All these parameters but one suggest that the watershed will have a
much greater influence on the water in Milford Reservoir and that nutri-
ents and light should be greater in Milford Reservoir. The only caveat is
that the water replacement is so slow in Crater Lake that once a nutrient
enters the system, it could be recycled for some time. The high shoreline
development index, watershed area to volume, and low mean depth
suggest that Milford Reservoir should indeed be more eutrophic than
Crater Lake.
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