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Chapter 2 Quantitative description of lake basins
Chapter 2
QUANTITATIVE DESCRIPTION OF LAKE BASINS
Several quantitative parameters and their definitions are used by limnologists for describing a lake. Only the following are useful when working with ancient lake basins. LENGTH A N D WIDTH
The length and width of a lake basin (or lake) are measured from shore to shore at right angles to one another, the length being the greater distance. Units may be in feet or miles. VOLUME A N D AREA
The volume of a lake basin may be determined by evalution of the HUTCHINSON (1957) integral:
v = j
z= Z M z=o
+
Az . dz
+
or by V = h/3(A1 A Z I/A,A,) where A1 and A2 refer to the upper and lower surfaces respectively of some contour stratum, h representing the contour stratum height. The area of the lake basin ( A ) or of any contour stratum Z is best determined by planimetry. MAXIMUM A N D MEAN DEPTH
The maximum depth of a lake depends on depth of the basin, amount of water in the lake, and amount of sedimentation in the basin; thus depth is subject to rapid change. The mean depth is determined by dividing the volume of a lake by its area. LENGTH A N D DEVELOPMENT OF SHORELINE
The length of a lake’s shoreline is easily measured by a chartometer on any topographic map of suitable scale. The shoreline development ( S D ) is merely a quantitative description of the length of the shoreline (SL) to the length of the circum-
24
QUANTITATIVE DESCRIPTION OF LAKE BASINS
Fig.26. Aerial photograph of Buffalo Lake, Texas, view to the southeast. Notice extreme length of shoreline and consequently high shoreline development (SD)resulting from damming of Yellowhouse Canyon to form the spring-fed basin. (Photo by the author.)
ference of a circle whose area is equal to that of the lake. This may be expressed as: SD
=
SL 2 I/nA
The shoreline development for a circular lake, such as Ungava (Fig.lO), is very near unity, but for basins like Buffalo Lake, Texas (Fig.26), formed by damming of a canyon, or for basins formed by grabens or qords, the shoreline development may exceed 4 or 5. ELLIPTICITY
The ellipticity ( E ) of a lake or lake basin is given by the length ( L ) minus the width ( W ) divided by the length, or:
E=-
L- w L
Paleolimnologists seldom use extensive quantitative descriptions for ancient lakes and basins, thus those interested in detailed lake morphometry are referred to HUTCHINSON (1957). Length, width, maximum depth, and length of shoreline may be quoted and, when comparing the origin of one lake basin to the genesis of other lake basins, the shoreline development and ellipticity may be useful (REEVES, 1966).
QUANTITATIVE DESCRIPTION OF LAKE BASINS
Several quantitative parameters and their definitions are used by limnologists for describing a lake. Only the following are useful when working with ancient lake basins. LENGTH A N D WIDTH
The length and width of a lake basin (or lake) are measured from shore to shore at right angles to one another, the length being the greater distance. Units may be in feet or miles. VOLUME A N D AREA
The volume of a lake basin may be determined by evalution of the HUTCHINSON (1957) integral:
v = j
z= Z M z=o
+
Az . dz
+
or by V = h/3(A1 A Z I/A,A,) where A1 and A2 refer to the upper and lower surfaces respectively of some contour stratum, h representing the contour stratum height. The area of the lake basin ( A ) or of any contour stratum Z is best determined by planimetry. MAXIMUM A N D MEAN DEPTH
The maximum depth of a lake depends on depth of the basin, amount of water in the lake, and amount of sedimentation in the basin; thus depth is subject to rapid change. The mean depth is determined by dividing the volume of a lake by its area. LENGTH A N D DEVELOPMENT OF SHORELINE
The length of a lake’s shoreline is easily measured by a chartometer on any topographic map of suitable scale. The shoreline development ( S D ) is merely a quantitative description of the length of the shoreline (SL) to the length of the circum-
24
QUANTITATIVE DESCRIPTION OF LAKE BASINS
Fig.26. Aerial photograph of Buffalo Lake, Texas, view to the southeast. Notice extreme length of shoreline and consequently high shoreline development (SD)resulting from damming of Yellowhouse Canyon to form the spring-fed basin. (Photo by the author.)
ference of a circle whose area is equal to that of the lake. This may be expressed as: SD
=
SL 2 I/nA
The shoreline development for a circular lake, such as Ungava (Fig.lO), is very near unity, but for basins like Buffalo Lake, Texas (Fig.26), formed by damming of a canyon, or for basins formed by grabens or qords, the shoreline development may exceed 4 or 5. ELLIPTICITY
The ellipticity ( E ) of a lake or lake basin is given by the length ( L ) minus the width ( W ) divided by the length, or:
E=-
L- w L
Paleolimnologists seldom use extensive quantitative descriptions for ancient lakes and basins, thus those interested in detailed lake morphometry are referred to HUTCHINSON (1957). Length, width, maximum depth, and length of shoreline may be quoted and, when comparing the origin of one lake basin to the genesis of other lake basins, the shoreline development and ellipticity may be useful (REEVES, 1966).