The Depths of Crystal Lake’s West End

As part of the Crystal Lake Park District’s lake study, the Illinois State Geological Survey was paid $5,000 to take a look at the bottom of the lake.

McHenry County Blog got photos of the survey boat last year [2006] during one of the four May through September surveys and has been waiting with interest for the captured images and analysis.T

Today and tomorrow the [ones I can retrieve] will appear on McHenry County Blog.

We’ll start with the West End.

Earlier articles have covered [the links won’t work, but they at least give me an idea what I’m looking for; unfortunately, many of the images have not yet been retrieved]:

Timothy H. Larsen of the University of Minnesota at Duluth and the Illinois State Geological Survey’s B. Brandon Curry wrote a paper that was completed over a year ago. This article is based upon it.

It says the lake is about 6,800 feet long and 1,500 feet wide.

The spillway elevation is 890.81 feet above sea level.

During the survey, the water level was 889.35 feet above sea level, so the findings have to be adjusted upward by a foot and a half to reflect how deep a “full” lake is.

A 1957 study by Illinois State Water Survey scientist Robert Sasman found the lake had gotten 4 feet below the spillway.

The park district reported the same four-foot below-the-dam situation in 2006. (That’s the year before this Skinner family moved to Crystal Lake.)

Depths found in Crystal Lake in 1957 by the Illinois Geologic Survey.

The measurements then were made in ten foot intervals.

This time, they are shown in five foot gradations, except in the West End where the map lines are every foot.

Depths of the West End of Crystal Lake found in 2006 by the Illinois Geologic Survey.

The depths of both the west basin and the much large east basin were measured, but by different techniques.

Last year in the west end, “depth soundings were made with a pole, graduated in feet and recorded in quarter – inch increments.” 252 soundings were recorded electronically.

Curry made supplement soundings by wading in the shallows along the south shore.

The findings follow:

There is a shallow bar less than two feet deep on the west end that “drops steeply into an elongated north-south basin south of the inlet.” The basin is 6-7 feet deep.

“A slight, but continuously rise on its eastern edge separates this basin from the main body of the lake south and east of the peninsula. Maximum depth of the west basin is 21 feet near the center of the channel south of the peninsula.”

A winter study was made in 1990, drilling holes every 50 feet when the lake level was 889.6 feet above sea level, about 3/10 of a foot higher than last summer’s level.

An adjustment for the difference was made and a comparison map was prepared.

The red on the map shows where additional sedimentation has occurred. The blue represents were there has been scouring, that is, where there is less sedimentation.

But, the large area of blue on the “east side of the basin is attributed to inadequate data coverage in 1990. Otherwise, the most prominent feature on the map is the large area of possible scour on the north end of the western bar.”

Otherwise, the report continues, “sediment accumulation of less than 1 foot are inferred over most of the rest of the basin.”

It’s about a foot south and east of the inlet and more than a foot and a half in the “north end of the deeper basin, south of the inlet.“

Over two feet of sedimentation was “inferred in the small area along the southeast slope of the western bar.

The most significant different discovered was “in the northwest corner of the basin. The northeast edge of the shallow bar was encountered much farther east in 1990 than in 2006.”

Tomorrow, what was found in the main basin of Crystal Lake.

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All of the images in the original article could have been enlarged by clicking on them.


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