Pretty Much All Karst

Well, gosh, he must not be talking about Monroe County:

“ We’ve had geotechnical companies review. We’re not gonna go to your sinkholes. We’re not gonna go on top of caves, where the little shrimp lives, the whatever. That’s the purpose of doing all the environmental, to determine all the areas to stay away from, so we don’t cause negative impacts. The area we’re looking at is all (in) corn or beans.”

Joe Koppeis, public meeting hosted by Monroe County Board of Commissioners, 20 August 2018.

Most of our upland areas are classed as the “hill prairie / sinkhole plain” and are within the Northern sector of the Illinois Ozarks Natural Division. The hill prairie corridor and sinkhole plain comprise about 130,000 acres, stretching from Dupo to Modoc, with the largest part of that acreage in western Monroe County. The area ranks as one of our state’s richest for natural resources and largely intact wildlife habitats.

The bluffs – 300 foot tall escarpments looming over the Mississippi River floodplain – are geologically and geographically interconnected with the sinkhole plain. The ravines that twist their way through the upland forests behind the bluff edge prairies send rain and spring water coursing down to the hilly, folding, pond- and sinkhole-dotted acres of fields. The terrain is karst: fairly thin, highly erosive soils overlaid on porous limestone bedrock. Because it’s all karst we also know our bluffs and sinkhole plain as the “holiest” land in the state, with more caves, springs, and surface openings, more voids, drops, and just plain holes than any other area.

Recent analysis shows that our lands are even holier than prior mapped inventories made just a few years ago. Using new technology, along with a re-look at some 60-year old technology, and then ground-truthing their work on long hikes over portions of Monroe County’s sinkhole plain, Sam Panno and Donald Luman of the Illinois State Geological Survey found that the U.S. Geological Survey’s topographic maps underestimate sinkhole numbers by as much as 35% (Panno and Luman, 2018).

Unsurprisingly, foliage density defies accurate measurements and inventory of sinkholes in wooded areas. New technology, specifically use of light detection and ranging (lidar) imagery enabled the researchers to view and characterize sinkholes contained within wooded areas. Lidar imagery strips off above ground features, allowing extremely accurate measurements of elevation and changes in depth and surface contours. Our map of the project area overlaid on Lidar imagery illustrates of extent of karstified terrain; downloading the file allows you to easily zoom in to see the features.

But miss-estimation is even more serious on open field expanses. Farming practices, such as filling in sinkholes, installing drainage tiles, and simple decades of cultivation over the nearly 87% of the sinkhole plain in agricultural land use, has dramatically effected the accuracy of past inventory efforts. By comparing 1940 aerial photography done by the U.S. Department of Agriculture with aerial photographs taken in 2005, Panno and Luman estimate that current USGS topographic maps either completely miss or inaccurately show actual sinkholes (ibid). The authors note that these “palimpsest” (a reference to the rubbing off for re-use of a canvas or manuscript) sinkholes, though hardly visible, remain and are – like the readily apparent sinkhole ponds or agriculturally-defiant steep-sloped ravines and circles of trees that dot the landscape – part of the surface and subsurface of our karst terrain (Panno and Luman, 2012). Researchers with Minnesota’s Ecological and Water Resources Division said it well: “A field-verified karst feature, such as a sinkhole, is direct evidence that karst processes are active both on the surface and in a karst aquifer in the subsurface. However, the absence of karst features on the land surface does not imply the absence of karst processes on the land surface or karst hydrology in the subsurface” (Adams, R., et. al., 2012; emphasis added).

Monroe County residents well know that sinkholes can form without warning, ponds can drain overnight, and that our landscape can’t be taken for granted. Only a bit more than five years ago a golfer at a local course walked a short distance from his golf cart to investigate a slight depression in the ground. He felt the ground collapse under his feet as the final inches of soil gave way into a new cover collapse sinkhole with a 14-foot depth. Emergency crews and heavy equipment were needed to rescue the unsuspecting golfer, as the images at right show.(Starkey, R., 2013).

Photo of people looking in sinkhole collapse courtesy Monroe County Independent.

Photo of equipment at sinkhole collapse courtesy Fox2News.

It’s pretty much all karst, even if it’s in corn or beans.

Not going into sinkholes, as Mr. Koppeis says of his project’s turbine locations, does not mean that he plans to avoid karst, because, quite simply, he can’t, given the section, township, and range areas of his proposal. If Mr. Koppeis is truthful about “doing all the environmental (studies) to determine all the areas to stay away from, so we don’t cause negative impacts,” he – and his geotechnical advisors -- should agree with the Illinois Department of Natural Resources very first recommendation to Monroe County decision-makers:

“Recommendation #1: The Department recommends the County consider an alternate location for this proposed action which will avoid construction over karst geology. Many of the potential adverse effects of this proposal are related to the character of the underlying ground” (IDNR Consultation and EcoCAT, emphasis added).

The adverse effects, or “negative impacts,” to use Mr. Koppeis’ words, are multiple, even if we consider only geologic forces.

Wind turbines vibrate. They vibrate in similar frequency ranges as earthquakes; research in Germany disclosed that wind turbine operations have degraded the earthquake-detection ability of seismic sensor systems (Bauer and Panno, 2018; Stammier and Ceranna, 2016). Wind turbine vibrations, especially during operations at higher wind speeds, have been detected by seismic monitoring equipment to depths of 300 feet and as far away as nine miles from the turbine’s location.

Wind turbines are heavy. Weight, of each machine and concrete foundation, is concentrated on a relatively small footprint area which will receive tremendous downward pressure. The proposed 600-foot high turbines and foundations also will have to bear the varied horizontal pressure of changing wind speeds and direction. The engineering risks associated with karst areas are high.

Among the negative impacts are possible changes in the surrounding landscape, including collapse of sinkholes, creation of new drainage areas (field rills) between sinkholes, and undermining and erosion of soils, even at considerable distances from any given turbine location.

It’s essentially all karst and the damages a wind turbine factory could cause have a significant probability of occurrence due to the nature of karst.

References:

Adams, Roberta, John Barry, and Jeff Green, 2016 Minnesota Regions Prone to Surface Karst Feature Development. Minnesota Department of Natural Resources, Ecological and Water Resources Division, Series GW-01.

Bauer, Robert A., and Samuel V. Panno, 2018 Illinois Caverns Area – Earth Shaking and Underground Facilities Interactive Frequencies. Illinois Geological Survey, unpublished paper.

Panno, Samuel V., and Luman, Donald E., 2012, Sinkhole Distribution and Associated Karst Features of Monroe County, Illinois. Illinois County Geologic Map, ICGM Monroe-SD, Illinois State Geological Survey.

Panno, Samuel V., and Luman, Donald E., 2018, Characterization of Cover-Collapse Sinkhole Morphology On a Groundwater Basin-Wide Scale Using Lidar Elevation Date: A New Conceptual Model for Sinkhole Evolution. Geomorphology 318, pp. 1-17.

Stammler, K. and Ceranna, L., 2016. Influence of Wind Turbines on Seismic Records of the Grafenberg array. Seismological Research Letters, 87(5), pp. 1075-1081.


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