Astronomical tides

October is the month that brings us the astronomical tides, or locally to the coasts, the annual high, high tide.  The position of the moon relative the Earth creates a slight alteration in the gravitational pull of the moon on the oceans so high tide, is, well high!  If you lived in a coastal areas, what did you see?  Or experience?  Southeast Florida was rife with email chatter and photographs of flooded streets, yards, and canals.  The City of Fort Lauderdale sent notices to residents warning them about the tides.  We had no rain, just the tide coming in.  These are low lying areas that 20 years ago did not flood except during storms.  This is just a phenomenon that has been monitored in coastal areas over the past 5-10 years, depending on the complaints that have come into local officials.

One of the more interesting complaints I received in my career was in Hollywood Florida where a resident complained about the “fish in the street.”  Sure enough, the storm drain in front of his house was connected directly to the Intracoastal waterway and the October tides had pushed the saltwater up through the catch basin into the street.  Now these weren’t snook or redfish, they were little fish escaping the snook and redfish, about 3-5 inches long.  Pretty funny stuff if you think about it.  Realizing the problem, I called him 3 hours later and asked if the problem had been solved.  He said told me I was a genius to fix that so fast.  My boss told me to take advantage of luck and drop the explanation, but to design a solution (which we did).  My boss was right, but the call made me more cognizant of the issue.

15 years later, I have a student developing models of what happens during the annual high and average tides, especially with respect to the potential for flooding in low lying areas where groundwater is just below the surface.  His work is impressive.  A lot more land, especially inland, may flood as a result of the annual tides, which are a precursor to the long term trend of rising seas.  See the groundwater has a slight upward gradient as you move inland.  As a result, you cannot use the tide levels to predict inland flooding, you need to add the tides on top of historical groundwater levels.  Of course the wet season is the summer in Florida, so the October tides come just at the time groundwater levels are highest.  But at least we can determine where the stormwater pumping improvements need to go.

Determining where stormwater pumping is needed is only part of the problem.  As sea levels rise, more stormwater management will be needed and a place to put the water will become a problem.  Discharging nutrient laden stormwater to tide is not a good answer when you have fragile reefs offshore.  NOAA’s Florida Area Coastal Environment  (FACE) Initiative outline this (see intensives study –  Instead, perhaps at some point we may develop infiltration systems to capture this high water table “problem” and convert it to water supplies, solving two issues for southeast Florida.  Might be 2030, but we probably should be doing some planning….


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