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Lake morphology



Soil & Water Conservation Society of Metro Halifax (SWCSMH)

June 18, 2015      Lake Data Archives


Contents:



Definitions:

Relative Depth, Zr (Hutchinson, 1957; and Wetzel & Likens, 1991):

Relative Depth is the maximum depth as a percentage of mean diameter.

Relative Depth (Zr) in % = 50 * Zmax * sqrt(π) * (sqrt(Ao))-1, where sqrt=square root

For most lakes, Zr < 2%. Deep lakes with small surface areas exhibit greater resistance to mixing and usually have Zr > 4%


Mean depth, Zmean (Wetzel & Likens, 1991):

Volume divided by surface area:

Zmean = V Ao


Development of Volume, Dv (Hutchinson, 1957):

The Development of Volume (Dv) is a measure of departure of the shape of the lake basin from that of a cone.

Development of volume (Dv) = 3 Zmean Zmax

For the majority of lakes, Dv will be greater than 1 (i.e., a conical depression). Dv is greatest in shallow lakes with flat bottoms (eg. Carolina Bay lakes). Among deep lakes, caldera lakes, graben lakes, and fjord lakes, Dv will be much greater than 1.5 (also in many rock basins). Most lakes in easily eroded rock have Dv in the range of 1 to 1.5. Extremely small values are found in only a few lakes with highly localized deep holes (ponors or sinks, sublacustrine kettle holes). Extensive action of shore processes is apt to reduce the ratio.


Shore Line Development, DL (Hutchinson, 1957):

DL is the ratio of the length of the shore line to the length of the circumference of a circle of area equal to that of the lake.

Shore Line Development (DL) = SL 2sqrt(πAo)

Shore Line Development (DL) is important because it reflects the potential for development of littoral communities, which are usually of high biological productivity. Only a few lakes, such as Crater Lake in Oregon and a few kettle lakes approach the circular shape, i.e., DL = 1 (circular). DL 2 in many subcircular and elliptical lakes. DL is large for lakes of flooded river valleys.


Index of Basin Permanence, IBP (Kerekes, 1977)

Index of Basin Permanence (IBP) = V SL, where V is in 106 m and SL in km.

The Index of Basin Permanence (IBP) is a morphometric index that reflects the littoral effect on basin volume.

Lakes within the Atlantic National Parks (IBP < 0.1) are dominated by rooted aquatic plants and indicate senescence (excessive shallowness, high water color and high TP). Lakes with IBP = 0.2 are more permanent.

Lake Baikal has a IBP of 10,000, for Lake Superior IBP = 4,000, for Lake Erie IBP = 450, and for Caspian Sea (largest inland water basin) IBP = 13,000.


SL/Ao (Rawson, 1960):

Of the several measurements dealing with shoreline (eg. shore line development) and islands (eg. insulosity) the value for shore development including islands may be considered the most meaningful single item. Nevertheless as Larkin has pointed out, this value may be misleading when used to compare lakes which differ greatly in area. In such cases a simple ratio of shore length to lake area is preferable.

Maximum Length, Lmax (Wetzel & Likens, 1991):

The maximum length is the maximum distance on the lake surface between any two points on the shore line. This length is potentially the maximum fetch or effective length for wind to act on the surface of the lake without land interruption.

Maximum Width or Breadth, bmax (Wetzel & Likens, 1991):

The maximum distance between the shores perpendicular to the line of maximum length.

Mean Width, bmean (Wetzel & Likens, 1991):

The mean width is equal to the surface area (Ao) divided by the maximum length (L).



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