SOME CHARACTERISTICS OF BOTTOM SEDIMENTS ALONG THE ILLINOIS SHORE LINE OF LAKE MICHIGAN

One phase of this study is devoted to the characteristics of the bottom sediments of the lake based upon samples taken annually along certain selected range lines. These range lines were first established for the 1946 cooperative study with the Beach Erosion Board, Corps of Engineers and were used that year by the Corps and again in 1950, 1951, 1952 and 1953 by the Division of Waterways. The ranges are spaced approximately one mile apart commencing at the Wisconsin-Illinois State line and extending southward through Chicago to the Indiana-Illinois line. At the present time, the sampling program is confined to that reach of the lake from the Wisconsin line to the northern limits of Chicago. (Fig. 1.) Each range line azimuth was established at approximately 90° to the general shore line at that locality.

range down through the No. 325 mesh.

Separation of light and heavy minerals, using broaoform.
3. Magnetic mineral separation, using a weak magnet.4. Carbonate separation, using diluted hydrochloric acid.
The analysis for heavy minerals, magnetic minerals and carbonates was made in the hope that movement of the sediments might be traced.However, no unusual concentrations were found which could be attributed to any one source material.The glaciation whioh occurred over this area with the resultant extremes of water depths during those periods, has evidently so sorted the bluff, beach and bottom material that the presence in various amounts of heavy minerals, magnetic minerals or oarbonates gives no apparent indication of sediment movement or littoral drift.Therefore, in 1952 the magnetic and carbonate analyses were discontinued, although portions of each sample have been prepared and sorted should these analyses ever need to be resumed.
The results of the grain size analysis of each sample are plotted in the form of a cumulative curve from which the median and quartile diameters and other descriptive parameters may be obtained.
With the thought in mind that a definite pattern of sediment size distribution might be present along the Illinois shore line, plan sheets for each year's survey have been prepared upon whioh are plotted the location and median diameter of eaoh offshore sample.There were then drafted thereon lines of equal median diameter, much in the same manner as the drafting of contour lines on a topographio map.It is recognized that this is not a precise method in view of the relatively small number of samples and the wide spaoing of the ranges, but it is felt that such a procedure does serve to present a general pattern of the size distribution of the material on the lake bottom.This reach is a continuation of the Lake Border Moraine Seotion.The inshore area is still characterized by a narrow band of fine sand or under, but the offshore area shows an increasing amount of medium sands and gravels in apparently no explainable pattern.Southward from the northern limits of Glencoe, the drag sampler did not obtain samples of sufficient quantity for analysis in the areas shown as medium sands and gravels.A drop type sampler similar in design to that used by Dr. Hough of the University of Illinois was developed and samples of about 2 inches in depth were obtained in these areas.
The interesting feature of these samples is that this offshore area is shown to be composed of clay overlain with a very thin layer of medium sands and gravels on the surface.Therefore, the pattern of offshore gravels and medium sands is possibly in error and misleading.However, the size distribution as shown seems to be indicative of the characteristics of the surface materials along this reach..ji/l't,,!,'.•ipff-: '•'.;,:' v.Vj, 'liw^'"' • * ' 1'.* "'*'.^y *'•':': • • .yv"^^l?^" ^•'•V^;-';.':'.'.'::- sand further offshore.However, in this reach, the area of very fine sand is relatively narrow and is completely bounded on the east by another strip of fine sand.The sorting coefficients again vary from about 1.1 to 1.5 for the fine sands and from 2.0 to 6.0 for the medium sands and gravels, foreshore bottom slopes in this area are from 1 on 12 to 1 on 20 and are fairly uniform from north to south.
Pig. 10 is the median diameter plot from Kenilworth to Foster Avenue at Chicago.The reach from Kenilworth to flilmette Harbor is a continuation of the Lake Border Moraine Seotion and that below V.llmette is in the Southern Lake Plain Seotion.This reach again has the inshore area of fine sands or under and the offshore has more medium sands, fine sands and less gravel than the area immediately north.The drop sampler was also used in this area for the gravel and some of the medium sand areas and these areas were also found to be composed of clay overlain with very thin layers of sand and gravel on the surface.Fig. 11 shows the further classification of the inshore sediments.Below Wilmette Harbor, the inshore area of fine sand is not continuous along the beach as was the case in the areas to the north.The continuation of the fine sands above Wilmette Harbor are now offshore about 2000 ft.Except in isolated locations, the very fine sands are immediately adjacent to the shore.The shore immediately below tsilmette Harbor is not largely protected by bulkheads and rip rap but in the unprotected areas, the foreshore slopes are on the orier of 1 on 10 to 1 on 16.The sorting coefficients of the fine sands and under are still on the order of 1.1 to 1.6 and the medium sands and gravels from 2.0 to 7.0.The above comments and illustrations have been concerned with the general overall characteristics of the bottom surface sediments in Lake Michigan along the Illinois Rhore line.In addition to this study, a detailed sampling program has been in progress for certain selected groin systems.Samples and soundings have been taken at regular intervals on 8 groins in the Lake Bluff area.These groins were constructed by a landowner who was suffering extensive loss of land due to erosion of the high bluff fronting on the lake.The groins were constructed in 1952 and have, as yet, only partially controlled the bluff erosion.Eight sampling ranges and seven additional sounding ranges were established.Ten samples per range were taken out to a depth of 15 feet.Fig. 13 shows the median diameter plot of these samples.
Prior to the groin construction, surveys indioated that only fine and very fine sands were present.It will now be noted that the groins have sorted and held inshore those medium gravels of 1.00 mm or above in median diameter with a narrow band of ooarse and medium sand offshore of the gravel, and fine sand adjacent to the ooarse and medium sand.Very fine sand is still present further offshore outside of the action of the groins.
well sorted, having coefficients of from 1.1 to about 1.6.The foreshore bottom slopes vary in this section from about 1 on 25 at the Wisconsin State line to about 1 on 65 immediately above Waukegan Harbor.From the records of accretion above the harbor, it is evident that the predominant sand movement is in a generally southward direction and is of considerable amount.Fig.6is the plot of the median diameters from Waukegan through Fort Sheridan.This area is in the Lake Border Moraine seotion and is characterized by erosion along the entire reach except immediately above Great Lakes Harbor.As shown by the plot, the inshore area is composed entirely of fine sand or under, with a greater amount of medium sand offshore and the presence of gravel or above showing up off Lake Bluff, Lake Forest and Fort Sheridan.Again the similarity between the 1950 and 1952 survey results are apparent.Fig.7shows the further breakdown of the fine sands in the inshore area.As in the reach from the Wisconsin State Line to Waukegan, there is a narrow band of fine sand present along the immediate shore.However, it can be noted that this sand is apparently not a continuation of that occurring along the shore above Waukegan.rtaukegan Harbor has; seemingly diverted the sand above the harbor offshore with a portion 6f it extending both north and south of the harbor.Very fine sand or under occurs off areat Lakes and this covers a considerable area.Again the fine sands show good sorting with coefficients ranging from 1.1 to 1.7.The medium sands and the gravels' have a coefficient of from 2.0 to about 6.0.The shore line from Waukegan to Great Lakes is largely protected by rip rap but the natural foreshore slopes in this reach were very steep.The foreshore slopes immediately above Great Lakes are about 1 on 55 and these steepen to about 1 on 20 or below near Fort Sheridan.Fig.8is a continuation of the median diameter plot and covers that reach from Fort Sheridan south to Kenilworth.The 1950 Survey, due to unfavorable weather, was discontinued at Highland Park, so for comparison purposes, the 1946 Survey was plotted for the area southward of that point.Sufficient samples were not taken during this survey to adequately define this area, and therefore, the comparison from this point southward will not be in oomplete agreement.

Fig. 12
Fig. 12 shows three typical profiles of the lake bottom with the complete median diameter size classification of the samples taken.This classification is that used by the U.S. Bureau of Soils.The first profile was taken off the Illinois Beach State Park, the second at Fort Sheridan and the third at the southern city limits of Evanston.