A LIMNOLOGICAL RECONNAISSANCE 



TABLE 1— AREA OF OKOBOJI LAKE— ACRES 

 (From map, scale 1 m.= 1,000 ft.) 



Area at sui-face 3788 



20 feet 2750 



40 



60 



80 



100 



120 



132 



.1629 

 . 973 

 . 326 

 . 114 

 . 9 

 . 



Note: The surface area is taken from the report of the state high- 

 way commission, 1916, p. 56. 



The contour map and the measurements show that the 

 main slope of the bottom of the lake is fairly uniform to 

 the depth of 80 ft., but that below this depth the slopes are 

 decidedly steeper. In fact, the form of the basin is such 

 as to lead the observer to expect a maximum depth of about 

 90 ft. or 100 ft. Instead of this, however, a small area ex- 

 tends to a depth of 132 ft., or 30 ft. to 40 ft. more than 

 would be expected. 



From the data thus secured a hypsographic curve of the 

 lake was platted and from this were derived the areas cor- 

 responding to 5 m., 10 m., etc. From these data there were 

 computed the area, volumes, etc., of the lake in metric units, 

 as shown in the following table. The same data computed 

 in cubic yards, etc., directly from the areas of the 20-ft. 

 levels give substantially the same results. 



TABLE 2— OKOBOJI LAKE— GENERAL FEATURES 



Length, 8.79 km; 5.46 mi. 



Greatest breadth, 4.57 km; 2.84 mi. 



Direction of main axis, north and south. 



Area, 1535 ha; 3788 a. 



Greatest depth, 40.2 m; 132 ft. 



Mean depth, 12.3 m; 40.4 ft. 



Volume, 188,340,000 cu. m; 246,340,000 cu. yds. 



Length of shore line, 29.3 km; 18.2 mi. 



Shore development, 2.13. 



Volume development, 0.92. 



Mean slope of bottom, 1°34'; 2.74%. 



NOTES: The mean depth is found by dividing the volume by the 

 area of the surface. The volume of the several strata are computed 



from the fonnula (A+B+V~A^)f^ ^" ^^^*^^ ^ ^^ *^® ^^'^^ °^ ^^^ 

 upper surface of the stratum, B is the area of the lower surface and 

 H the vertical distance between the surfaces — in this case 5 meters. 



