Leaky Levees

Our regular bloggers are out gathering data so today we have a guest blogger, Stephanie Long from the Department of Earth and Environment

Despite all of the extreme weather reporting and constant television coverage, Hurricane Isaac was just another storm for most of South Floridians. The only trouble the storm brought us was copious amounts of rain. So when I got a chance to go take samples along the L30 Levee just three days after the storm had passed, I was given a very fundamental lesson in South Florida hydrogeology.

Fast moving water coming through 
the L30 Levee and into the L30 Canal.
Water Conservation Area 3B is FIU's nearest WCA neighbor. It is bordered by the Tamiami Canal to the south and the L30 Canal to the east. Three days after Isaac, the water in WCA 3B was pretty high; it even seemed to swamp the invasive cattail. We drove northeast along the L30 levee and got out south of control structure S-335 to collect a grab sample. The sound of trickling water was odd. There is close to zero elevation gradient everywhere in South Florida, we don't get a lot of trickling streams. What is this sound?

Water trickling from the L30 Levee onto the embankment and into the L30 Canal on August 30, 2012.

Water was seeping right through L30 levee at an amazing rate. The limestone levee was more like a cheesecloth at this point. Water was actually rushing through a few conduits in the rock, allowing the stormwater built up in WCA 3B to escape to the L30 Canal.

 Here I'm on top of the Levee and you can see the Miccosukee Casino in the background.

The L30 Levee typically holds water back into the conservation area, allowing it to seep into the groundwater and recharge the aquifer, or else seep into the canal and provide water for the agricultural areas to the south. Understanding the flux of water through and under the levee is important for water budget estimates and managing flows. These images show just how porous the levee really is and, as a researcher from the Park pointed out that day, it may serve as a confirmation that the number we see on our spreadsheets and in our models might be right. Next time you calculate a transmissivity that looks way too high to be real, maybe it is.
 No seepage through this levee, 
 but what's happening underground?

Just south of the Tamiami Canal, a slurry wall was put in along the L31N Canal. The intention here was to stop some of the eastward seepage to maintain water levels and flows within the park. Only time and more investigation will tell if and how well this plan works.

- Stephanie Long
Ph.D. Student, FIU


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