Freezing of Lakes - Freezing of Lakes and the Evolution of their Ice Cover - page 16

extent. The following system corresponds to the present terminology as well as to the
common language (Table 2.2 ).

Table 2.2 Classification of lakes for their lateral and vertical size

Lateral Very large Large Medium Small Very small

1,000 km 100 km 10 km 1 km 100 m

Vertical Very deep Deep Shallow Very shallow

1,000 m 100 m 10 m 1 m

Note ' medium deep ' concept is not used for lakes in general

' max , and the
vertical dimension is taken as the maximum depth H max . Lakes with horizontal extent
much smaller than 100 m are ponds or pools. The minor axis

The lateral dimension is taken as the length of the major axis of the lake,

' min is de ned as the

minimum width of the through which the lake could penetrate. These two axes

together with the area and depth de

' opening '

ne the elongation γ , the shape factor ʺ , and the aspect

ratio ʴ :

c ¼ ' max

A
' max ' min ;

d ¼ H max
' max ' min ;

j ¼ ð 2 : 1 Þ

where A is the surface area of the lake. For a square lake, γ = 1, and for a rectangular lake

10 − 3 . Example medium-size lakes have depth of
10 m and lateral extent of 10 km. Lakes are de

ʺ = 1. The aspect ratio is normally ʴ *

ned open or closed whether there is

out ow or not, respectively.

The horizontal size of a lake in

fl

uences the mixing conditions, since long wind fetches
create more turbulence and higher waves. Freshwater lakes are vertically mixed at the
temperature of maximum density, and therefore the depth of a lake is one of the principal
characteristics to in

fl

uence the timing of the freezing. The deeper or larger the lake, the
later will the freezing be and, consequently, the shorter the ice season. In brackish and
saline lakes, the temperature of maximum density depends on the salinity and mixing by
cooling reaches halocline. In the freeze-up of a lake, the distribution of depth in

fl

uences
the lateral growth of the ice cover. The whole depth distribution is given by the hypso-
graphic curve

fl

Z 1

pð H 0 Þ dH 0

Pð H Þ ¼ ð 2 : 2 Þ

H

where ʠ (H) is the relative are of the lake deeper than H, and ˀ is the spatial density of

depth.
A single lake is connected so that liquid water particles can circulate throughout. There
may be sub-basins with straits between, and sometimes such basins are taken as separate
lakes. The geometry of lakes has fractal characteristics (Korvin 1992). The length of the