Saturday, November 10, 2012

"When you hear hoofbeats behind you, expect to see a horse, not a zebra.”

In an earlier SWFWMDmatters blog post, I wrote about the dilemma surrounding the status of an ailing, iconic Silver Springs and a water use permit being sought by a proposed 10,000 acre, 30,000 cattle, feeding operation that would take another 13.2 million gallons every day (annual daily average) from the same aquifer “springshed” that feeds the main spring.
The status of the spring system at that time was historic.  In the many years records have been kept of the spring’s flow, there is no record that documents the spring flow as ever to have fallen to the level it was at that time, approximately 50% of its historic long term average.  It seemed sharply plain to most that taking more water from its source, especially an amount that is even greater than that which City of Ocala now takes, would surely have an undesirable impact upon the springs’ already dangerously low flow.
Since then, the St. Johns River Water Management District has scrambled to put together a position that would legally, scientifically and politically justify the issuance or denial of the requested permit.  Wanting to avoid being accused of thinking only inside that proverbial box, the staff came upon a theory that at best can only be described as novel because it flies in the face of what most would consider reasonable thinking. 
Hal Wilkening, P. E.
In a recent report to his governing board, district staff engineer, Hal Wilkening, suggested that the reduced flow was possibly due to plant growth which, acting as a dam, was backing water up over the springs’ vents and slowing their collective discharge.  He also surmised that the accumulating slimy algae that’s killing the natural eel grass in Silver River was not due to the tons of nitrates leeching into the subterranean spring water from a host of manmade sources but due to low rainfall.

Rather than me trying to explain just how bizarre this concept is, you will likely have greater interest reading the thoughts of Charles Lee.  As most of you know Charles is the widely known and a highly respected voice on many issues for Florida Audubon, especially on legislative matters.  He’s the organization’s Director of Advocacy/Regional Director.  With his permission, here’s what he wrote recently in an email:
Interestingly, this (concept) was presented in much more tentative terms to the board, but is trumpeted here in SJRWMD propaganda as the “Ah, Ha” answer to the decrease in flow at Silver Springs.
Wilkening advanced the theory that vegetation growing in Silver Springs Run and the Ocklawaha River have created a backwater effect, raising water levels in the spring run and therefore creating a hydrostatic head that they claim is suppressing the amount of water coming out of the spring. The amount of water level increase they claim is about .9 foot. The amount of decline in springflow claimed because of this is 100 to 120 CFS. (Note, even if a 100 to 120 CFS decline resulted from increased water levels, Silver Springs is still flowing about 300 CFS less than what would be expected after this summer of extraordinary rains. Flow figures from the 1960s and 1970s would have this spring producing over 1000 CFS after the rainfall we have had recently, and it is only flowing around 600 CFS).
The theory is not without some scientific basis. However, to have publically advanced it at the board meeting, and then trumpeting it here without some peer review and more detailed analysis is, frankly, irresponsible. Had some environmental group presented conclusions like this, Ed de la Parte would have been screaming “JUNK SCIENCE”! Instead, he was sitting in the audience smiling.  For example, one of the tests that they could have performed would have been a statistical analysis of variance in flows from historic norms at times when the water levels in the Silver Run and the Ocklawaha have been distinctly BELOW normal during the past 12 years. That data is readily available, but (conveniently) is not provided.
 The observations about aquatic vegetation growth in Silver Run and the Ocklawaha were tied to drought conditions and not attributed to nitrates. The story according to Wilkening is that lower flows from the chain of lakes down the Ocklawaha produced less brown colored water moving downstream and that in turn allowed greater aquatic vegetation growth because of  increased light penetration. The weeds hold water back in his view, raising the water level therefore pressing down on the spring and reducing flow.
Along with that analysis, Wilkening produced a chart with three monitoring wells near Silver Springs. Two of the wells showed about a .5 foot average decline over the last 12 years, and one showed a water level that did not change. From that, Wilkening told the board that there had been no decline in aquifer levels, therefore a decline in aquifer levels could not have caused spring reductions over the past 12 years…HMM  two wells show a distinct decline, one does not, and that means no change…. Interesting way of looking at math.
I was able to take the graph that other members of the SJRWMD staff had used during the morning session to give the aquifer level readings in the monthly hydrological report to show that even with the huge rainfall amounts since June, the aquifer levels throughout the Silver Springs springshed and in N.E. Florida generally remain at distinctly abnormal low levels. I also questioned picking out just three wells and drawing broad conclusions from them rather than looking at a much bigger data set about aquifer levels which was readily available.  Finally, Guy Marwick of the Felburn Foundation pointed out to the board that the high water levels claimed by Wilkening were really not historically high. The gift shop and walkways at Silver Springs flooded on numerous occasions when springflow at its peak produced very high water levels in decades gone by.  
I characterized Wilkening’s presentation, with an old medical adage, as a “zebra diagnosis”.   ("When you hear hoofbeats behind you, expect to see a horse, not a zebra). 

Well said, Charles.  Thanks.
It’ll be interesting to see where the district technical staff go with this.  As mentioned, they have a task that will require them to make the science legally defensible in the face of an ill political wind that is saying, “Issue a permit or you may find your job in jeopardy.” 

Not likely?  Ask Connie Bersok.


1 comment:

  1. That is definitely an interesting idea. Do you think some people will think that means water flow could be increased if we just cut down the vegetation forming this blockage? I am not well versed in these matters but it seems like this wouldnt be enough to keep the permit from being issued.
    Taylor Beardsley