Lake Morphology

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Lake Morphology

• How do we describe the physical characteristics
  of a lake?

Make a list
Slide of lake
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1. Bathymetric Map

• Lines represent points of equal depth -- like
  contour lines on a topographic map

Bathymetric map of Mountain Lake
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2. Depth

• Maximum depth
• Lake Baikal 1,741 m
• Lake Tanganyika 1,476 m
• Average depth
• How calculate?

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3. Surface area

• Some very big
• Caspian Sea 436,400 km2
• Lake Superior 83,300 km2
• Most are small
• Only 250 lakes in US gt 10 mi diameter

Slide of areas
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4. Length

• Distance between furthest points
• Length of fetch

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5. Volume -- how much water

• From bathymetric map

hheight of layer A1area of top of layer A2area
of bottom of layer
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Calculating lake volume
Bathymetric map
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Mean Depth
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6. Shoreline lengthlength of the lake perimeter
Shoreline length depends on the size of the
lake. What we want to knows is the length of the
shoreline relative to the size of the lake.
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Shoreline development indexLength of the
shoreline relative to the perimeter of a circle
For a circle DL 1
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Shoreline development index

• Crater Lake, OR (caldera lake) 1.27
• Without Wizard Island 1.10
• Meteor Crater, AZ 1.02
• Montazumas Well, AZ (solution basin) 1.04
• Finger lakes, NY (morainic dams) 3.3
• Lake Baikal (Russia) (graben) 3.4
• Reservoirs 4

Crator Lake Meteor Crater Montazumas
Well Reservoir
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7. Hypsographic curves

• Show the shape of a lake basin
• Area-depth
• Volume-depth

slide
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Hypsographic curvesarea-depth
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Hypsographic curvesvolume-depth
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What use are hypsographic curves?
Example
Two summer stratified lakes. If these lakes were
to turnover (mix) what would be the resulting
dissolved oxygen concentration?
Epilimnion 8 ppm DO
Hypolimnion 1 ppm DO
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8 ppm
Lake A 40 of volume in epilimnion and 60 in
hypolimnion (80.4) (10.6) 3.8 ppm
Thermocline at 8 m
1 ppm
Lake C 90 of volume in epilimnion and 10 in
hypolimnion (80.9) (10.1) 7.3 ppm
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8. Hydraulic Retention Time
Time for water in a lake to be completely replaced
HRT volume / inflow
Lake Tahoe -- 700 y Lake Superior -- 184 y Lake
Pippin a few days The HRT of reservoirs is
generally shorter than HRT of natural lakes.
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9. Lake Zonation
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Littoral zoneThe region affected by the shore.
Generally from the shore out to the depth of
rooted vegetation.
littoral zone (2)
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Pelagic or limnetic zoneopen water, beyond the
influence of the shore
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Benthic zoneThe bottom
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Photic zoneSurface down to where there is lt 1
of surface light -- sufficient light for
photosynthesis
Photic zone
Aphotic zone
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Profundal zoneDeep benthic area part of
benthic zone that is aphotic
Photic zone
Aphotic zone
Profundal