12
I
fExercise 1
by means of a tracing wheel whose revolutions are recorded directly on a graduated dial. The
shore line is traced from a starting point through the periphery of the area. This distance is then
converted to real units by a simple proportional comparison to the distance measured on the
scale of the map with the same map measurer.
Shore Line Development (Dd. The ratio of the length of the shore line (SL) to the length
of the circumference of a circle whose area is equal to that of the lake:
SL
DL = - - ==,
2JnA o
As the length of the shore line becomes more irregular, the shoreline development deviates more
and more from the minimum DL -value of one, i.e., that of a circle. Only a few lakes, such as Crater
Lake in Oregon and a few kettle lakes, approach this circular shape. Many subcircular and
elliptical lakes have DL-values of about 2; lakes of flooded river valleys have much larger DLvalues. Shoreline development is of interest because it reflects the potential for development of
littoral communities, which are usually of high biological productivity.
Hypsographic Curves. A hypsographic curve, or depth-area curve, is a graphic representation
of the relationship between the surface area of a lake basin and its depth. This relationship may be
expressed in absolute units of area (m 2 , hectares, or km2), which are at a given depth, or in terms
m 2 )( 10 3
or-------~r_--------1~ 0~ 0 ------==~ 15~0,
--------_ .... -. .. .. -
/
~ ~
/"
6
8
/
/ '
.... ~
"
A
o _
100
----2
6
8
10
B
,5 12
I
fn..
PE RCE NT VOLUME
400
~
25
PERCENT AR EA
o 0 r-----~~------~ 50~----~75~--~~ 100 UJ
0 0
25
50
75
100
---- ---~~~
" , ~
- --- ---. ...... - ---,,"
. .
/
/
4
,/'
6 .... .. /
..-,,'
~~
6
8
10
12
8
A
10
B
Figure 1.6. Hypsographic (depth-area) curve (A) and depth-volume curve (8) of mesotrophic
Lawrence Lake (- - - ) and hypereutrophic Wintergreen Lake (- - - - -), southwestern
Michigan. (From Wetzel, 1983).