IOWA STUDIES IN NATURAL HISTORY 



By shore development is meant the ratio of the periphery of the 

 water to the circumference of a circle of equal area. 

 The mean slope is computed from the formula 



S=J ^/^Io+Ii+l2+l3 • •'•• +In-1 +^21, 



H 

 A~ 



In this foiTnula S=mean slope; I^^, I^, etc.=length of contour lines 

 from surface to bottom; n=number of such contours; H=maximum 

 depth; A=area of the lake. (See Juday '14, p. 123). 



TABLE 3— DETAILS OF OKOBOJI LAKE 



The volume development is the ratio of the volume of a 

 lake to that of a cone of equal base and height. If the lake 

 were a tank with vertical sides the volume development 

 would be three. Since in this case the volume development 

 is less than 1.00, the volume of the lake is smaller than that 

 of a cone of equal base and altitude. 



This condition is rarely found in lakes, especially in lakes 

 of considerable depth, and it constitutes the main peculiar- 

 ity of the basin of lake Okoboji. In most lakes there is a 

 steep slope on the sides below the level to which the work 

 of the waves extends and a nearly flat bottom. In such a 

 lake the volume exceeds that of the cone with which it may 

 be compared. In order that this condition may be better 

 appreciated a comparison is made between Okoboji lake and 

 lake Geneva, Wisconsin — a lake of somewhat larger area 

 but not much exceeding Okoboji in depth. The area of 

 lake Geneva is 2210 ha. ; its maximum depth is 43.3 meters ; 

 its mean depth is 19.7 m ; and its volume development 1.41. 

 The instructive comparisons are those of percentage of 

 volume and area at certain depths. 



