1944 Lake Okabena Bottom Study
This information came from historic file documents in the Soil Conservation District Office in the form of a city engineers report date 3/14/1944. Since 3/14 is mid-March and the near ice-out time, it is not likely that this was the date that the borings were done, but rather the date the report was written.
Dredging had been temporarily discontinued several years earlier ( the dredge was put up on shore), due to the beginning of WW2, so this study may have been done in preparation for the resumption of the dredging program.
The area of this study was most likely the area on the north side of the lake, mostly in the basin off Centennial Park. This insight comes from one of the documents from the 1952-56 study which mentions that the dredging 1941 to 1951 was focused in that area.
Unfortunately there is no lake map of where each these 1944 core borings were done. But we do have the 1944 core boring data, which I have portrayed graphically below.
There are 20 of the 58 core borings that show more SILT than WATER, at that point in the lake. These high silt core borings are highlighted with a light gray background and a 1 pixel black border. The deepest silt found was 7.6 feet on boring #34. An interesting feature of this is that there was only 2.6 feet of water at that point. So, there was almost three (3) times more silt than water on that particular boring.
Remember the top red line on this graph is the dam overflow level of 1576 feet above sea level. The blue line at 1575.2 feet above sea level, just under the red line, is the water level the day on the borings were done. The light blue water depths are based upon the water level as of the day of the borings, and thus do not continue up to the dam overflow red line. All visual representations and measurements are based upon absolute elevations above sea level.
This may be some help seeing relationships between water depth and other bottom characteristics. Notice that on the areas with the DEEPEST water, there is very LITTLE silt.
This may be some help seeing the relationships between silt and depth or bottom characteristics. Notice the number of places (borings) where there was more silt depth than water depth. Those high silt places are denoted by the 1 pixel black border and light gray background. There are 20 of the 58 core borings where the silt is deeper than the water. #34 has 7.6 feet of silt in only 2.6 feet of water. that is nearly three(3) times more silt than water at that particular point.
Solid bottom is designated as where hard clay begins. This solid bottom has probably been in the same place, undisturbed, since the last glacier, since it is only top soil, sand and gravel that move around.
The lowest solid bottom was at 1552.2 feet above sea level (#20), for a possible maximum water depth of 23.8 feet if there were no silt, sand, etc and the water was up to the runover level of the dam.
Note: there are several core borings that never left sand and gravel and thus never found solid clay bottom ( #44, 56). These may be points where the a spring enters the lake. Unfortunately, we do not know where on the lake these possible springs are because no map of where the core borings were made has been found.
1944 Data Presented in boring # sequence
The 1944 Data in spreadsheet format
The historic data was keyed into an Excel spreadsheet. This is the spreadsheet
1944 Historic Document source of data
The 1944 historic document from which the 1944 core boring data was extracted, was written in 1944 on one very wide piece of graph paper by the City Engineer, whose name is on the document. It was scanned in 2007 in six sections and thus is available in six normal sized documents, rather than the one very wide document which could not be scanned nor printed in one piece. Click on a thumbnail version of the sheet to display the full sized page and allow that particular page of the six to be printed.