1977 Lake Okabena Bottom Study

There were two types of bottom studies done in 1977 of the lake.

Simple Study of 180 places on lake

There were 180 places that were tested through the winter ice to determine water depth and where hard bottom began. The method used was to press a pole against the bottom of the lake and determine where water ended and soil began ( soft stop) and then where solid bottom was found ( hard stop). This simple process was used to determine the depth of the silt.

This process produced depth readings that were rounded off to the foot, probably because testing process is less precise than the core boring method.

It appears from the results of this study, as shown on the graphic below, that there was three (3) feet of silt or more on the average as of 1977.

Complex Study of six selected sites

There were six (6) sites on the lake chosen for a complex study using core borings. This process was done in the winter to provide a stable platform to do this manual task and to provide a constant level start point. This process yielded results that were more precise than the simple method and were precise to the tenths of the foot.

The water level at the time of this study was1573.41 feet above sea level.  This is approximately 2.6 feet below the dam runover level of 1576 ( 1576-1573.25=2.6 est). Note: there is a note on this document stating that the dam level is 1576.25, which to my understanding is not accurate. Also, note that there is an attempt to be precise beyond the tenths of a foot to the hundreths of a foot ( as in 1576.25 and 1573.41).

Lake Map shown locations of core borings. This is from the original study : click on a numbered black dot on the map above to go to the document for that boring

Inconsistencies between the Simple and Complex studies

The complex study show nearly twice the silt at 4 out of the 6 sites that the complex method was used.

Simple Study	Complex Study	Difference between the studies at this point
#1 There is between 2 feet and five feet of silt shown in this version at this spot	#1   Silt starts at 5.5 and goes to 14 feet for a total of 8.5 feet of silt at this spot	There is approximately TWICE the silt depth found using the complex method
#2 There is between 3 and 4 feet of silt shown in this version at that spot	#2 Silt starts at 4.5 feet and continues to 14 feet for a total of 9.5 feet of silt at this spot	There is approximately TWICE the silt depth found using the complex method
#3 There is between 3 to 4 feet of silt shown here	#3 Silt starts at 4.5 feet and continues to 14 feet for a total of 9.5 feet of silt at this spot	The complex method shows approximately THREE times more silt depth at this point
#4 There is between 3 to 4 feet of silt shown here	#4 Silt starts at 4.8 feet and continues to 9 feet for a total of 4.2 feet of silt depth	The complex method shows about the same depth of silt
#5 There is between 2 and four feet of silt shown here	#5 Silt starts at 4.8 feet and goes to at least 18 feet for a total of 13.5 feet of silt	The complex method shows approximately THREE times more silt depth.
#6 There is between 3 and four feet of silt shown here	#6 Silt starts at 4.8 feet and goes to 9 feet for a total of 4.2 feet of silt	The complex method shows about the same depth of silt