Karst Identification Field Day in Viroqua--6/18/09

June 28, 2009 by Lynn Chakoian

A major task of the groundwater vulnerability pilot study is to document karst features in the vicinity of the City of Viroqua.  In order to do this in an accurate and verifiable way, we included a training session as part of the proposal in an effort to educate the public interested in this work.  Drs Ken Bradbury and Fred Madison from the Wisconsin Geologic and Natural History Survey traveled to Viroqua to inform us about the scientific dynamics of karst formations.  After their presentation, we ventured out into the field to see sinkholes, springs, a disappearing stream and quarry location that all showed the variety of ways these features are present as surface manifestations of karst topography.

The public turnout was way beyond our initial estimates of interest.  We had over 60 people present for the morning presentations and 56 travelled out into the field.  Ken Bradbury adapted a talk he had given to another group about the science of karst in Wisconsin.  His presentation is in the "Read More" section of this story.  After the presentation and lunch, we had a caravan of cars and a City of Viroqua bus that traveled along a route that is shown in the "Read More" section.  Pictures and explanations of the karst features visited are recounted after the map.

From expert to novice, the feedback given to organizers of the day was very positive.  We are in a unique area of karst and have much to learn over the next few months of study.  Everyone who participated in this field day seemed to learn something new.

Read More by clicking Here

A pdf of the presentation by Ken Bradbury

Karst_Bradbury_6_18_09

The route of the field tour

Karst Study Training Sites Basemap 11x17 LS 300dpi

Stop 1 was a sinkhole in the City of Viroqua.  Some adults present remember playing in this wooded area as children.  This sinkhole  has become more active recently with a hole visible at the base of the sink.. 

Stop 1 Sinkhole in urban woods

There was some discussion of sealing the sinkhole and two geologists present indicated it is often a futile effort.  Even if the surface water is directed away and geotextile fabric is used to line the hole, collapses beneath the fix can change the surface grade and reopen the surface feature, which then leads to more activity and connectivity with the ground water system.

Stop 2 was a series of sinkholes in a private woods to the east of Viroqua.  The series appears to be linear and probably along a fracture.  Sizes of the sinkholes varied along that line with increasing size from the first observed to the last in the line.

Stop 2 Rural forested sinkhole linear complex

Stop 3 was an agricultural sinkhole in an alfalfa field.  The large depression had been filled-in over the years with demolition debris and covered so it could be used for agricultural use.  Over time this sinkhole has become active again and an opening at the low spot of the depression is now visible.

Stop 3 Agricultural Sinkhole

Stop 4 on the map was not on the final tour.  Stop 5 was in the backyard of a rural property, and quite close to the house.  Because there was severe house flooding during the June 2008 storm the landowner was given flood relief assistance to create a diversion for stormwater coming off an adjacent agricultural field.  The designers then determined it best to extend the berm completely around the side of the sinkhole and  to a drainage way along Railroad Avenue.  This sinkhole is situated to the east of an area that DATCP banned the use of Atrazine.

Stop 5 Rural Backyard Sinkhole

Fred Madison and Ken Bradbury at the field stop (left side.)

Stop 5 Wooded sinkhole: Berm around sinkhole

Stop 6, 7, and 8 were all within walking distance of each other.  Stop 6 was Crume Spring that was running clear the day of the field trip, but has a history of brown water after significant rain events.  Stop 7 was a mining operation that exposed dolomite layering and fracturing that happens in this region.  Stop 8 was a dry stream bed that had evidence of streambed fractures and width characteristics that indicate the stream "disappears" (transports water underground) when actively running. 

Crume springhead

The mine profile...

Stop 7 Mine Profile

Stop 9 was the final destination for the field trip.  The picture below is taken from above the dam, and the area near the telephone pole in the distance is where water discharges from a side hill seep that is effectively bypassing the dam structure.  The bypass of water happens when the water level behind the dam reaches a height that creates enough head for the fractured dolomite to provide a path for water outlet.

Stop 9 at Seasbranch Dam

These pictures can be viewed in the gallery of the field trip.