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Old Man’s Creek – In A Jam

Posted on February 10th, 2013

Similar to last winter, we have been experiencing a fair amount of mixed weather again this year, albeit with slightly colder temperatures for longer durations.  This year, will most likely still end up being warmer than “normal”, but it has been nice to have some seasonable temperatures and recent precipitation.

Given that our property lies along Old Man’s Creek, I often monitor the USGS gage on the Sharon Center Road bridge, just downstream of Old Man’s Timber.  The gage information for this site can be found at the USGS.  In addition, I also keep an eye on Clear Creek and the English River, as they are adjacent watersheds located just north and south of Old Man’s Creek.  I access stream gage information through the Iowa Flood Center’s Iowa Flood Information System portal using the Communities and Places search feature.

As a result of Thursday and Friday’s precipitation on frozen soils, the runoff was high with a short time of concentration resulting in quickly rising rivers and streams.  This can be seen in the hydrograph on Old Man’s Creek.

USGS Gage, Old Man's Creek

USGS Gage, Old Man’s Creek

 

Interestingly this hydrograph shows two peaks.  The first peak indicates a rise in water level of 6′ in an 18 hour period and the second peak a rise in water level of 3.5′ in just a few minutes.  The first is clearly a result of rainfall runoff, although rainfall in the area was relatively light, the runoff percentage was very high as a result of frozen soils.  Similar rises in the Clear Creek (4.5′) and the English River (7.5′) can be seen on the hydrographs on the USGS site for each gage.

The second peak on the Old Man’s Creek hydrograph is most likely a result of local ice jamming near the gage site.  The cold snap during the past couple of weeks resulted in ice thickness of approximately 4 – 6″ on Old Man’s Creek.  The rainfall, and subsequent increase in stage raised and broke the ice sheet into pieces that could be transported downstream.  This can be seen in the photo below.

Overall view of ice jam on Old Man's Creek

Overall view of ice jam on Old Man’s Creek

 

A few points can be made of the close up view of the jam as seen below.  The concentration of suspended sediment resulting from rain on frozen ground was high, most likely a direct result of overland flow across agricultural fields with fall tillage practices in the upstream watershed. The suspended sediments can be seen in the brown waters as wells as deposited on the surface of the ice sheets.  The photo also shows the aggressive nature of the creek and steep cut banks, particularly on the right bank.

Ice jam closeup

 

To get a sense of scale of the ice jam pieces, Miechelle took a photo of me sitting near the upper end of the formation.  As you can see the pieces were 4 – 6″ thick and range in size from a few square feet to larger pieces that exceeded one hundred square feet.  Obviously, ice formations such as this one can be quite unstable, so observe and engage with extreme caution (Miechelle wisely stayed on the upper bank, while I tromped around).

Scale of ice jam pieces

Scale of ice jam pieces

 

Lastly, I wanted to share a photograph of the crystal micro-struture of the ice sheet.  If you look closely, you can see the granular form of the ice that was created during its initial formation, likely during a very cold night.  The ice structure is fine-grained granular (a few mm in diameter) near the surface, and large grained columnar (10-15mm dia.) near the bottom.  As the ice began to grow (thicken), preferably oriented grains grew faster, and out competed non-preferably oriented grains, resulting in larger diameter columnar ice grains near the bottom of the sheet.  Also, given the low flow conditions that existed during the ice sheet formation, the water clarity was high, and the ice sheet shows clear ice near the bottom.

Ice sheet crystal micro-structure

Ice sheet crystal micro-structure

 

Yet again, another great day to be exploring Old Man’s Timber, the ice jam was especially reminiscent for me with a PhD in river mechanics, with a dissertation titled “Fatigue and Fracture Toughness of Freshwater Ice”, sometimes truth is stranger than fiction!

 

 

3 Responses

  1. Maria says:

    Wow, I was amazed at the size of the ice blocks! Cool pictures!

  2. Troy says:

    Those ice sheets are impressive! Looks like it was also a good review of your PhD work. Those types of events are a vivid reminder of the incredible power of nature.

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