2015-1113 Special City Commission Meeting

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Summary Minutes:Special City Commission Meeting November 13,2015 City of Sunny Isles Beach,Florida sand settles and doesn't settle, etc. Ms. Cutt said what Jordan did with this slide is he analyzed some historical photos that were readily available and he just traced the shoreline position over the years. If we look at the spacing of the Pier, basically the Pier is acting as a permeable groin,and so we know from the structures that everyone has seen up and down the Jersey shore back in the 1940's, 1950's, and 1960's, that engineers can design anything. They can design a structure that is going to stop all sands from moving down the coast. We have got to recognize that the shoreline is essentially a river of sand, and so that sand is moving with a net movement to the south of about a mile a year. In the winter we do have some sand that moves north but the net volume of sand moves to the south. And so when we have got a non- permeable groin of fixed solid structure that stops the sand from moving, it holds all the sand north of it on the east coast and it causes the area south of it to erode,or no new sand is coming into the system south of it because that sand is still moving south and it is not being sent from the north. With the old Pier, it had a lot more piles, and so if we go to the photograph and the restroom, it is a really good photo to show this. It shows the density of those piles, and so when we have got the majority of our wind driven waves coming in at the angle it is going to hit the beach most of the year, pushing that sand south along our shoreline, it hits those piles and gets knocked out of suspension, and so that sand accumulates. Now being a permeable groin,the Pier with the piles,more sand is being held right in that area then would otherwise move down the beach if that structure wasn't there. And so now the new Pier has fewer piles and so it is letting more wave energy and more sands move through so that may be part of why we are observing the erosion here. But as Jordan also mentioned,we can't look at this as a closed system. We have to realize that there is a lot of other things going on here, and one of the things that knowing what is going on in the region seems most evident is that Broward County nourishment Statement 3 from Port Everglades to Golden Beach in 2005. That sand wave has moved through the system about the same time that we are looking at on these aerial piers, and so we see a wider shoreline in 2009, 2012 but a narrower shoreline in 2006 as that Broward sand had not gotten here yet. But by 2009, 2012 the Statement 3 sands were moving through so we have a nice wide beach. Since the Pier was replaced,we are seeing erosion again. Is that truly erosion or is it the beach returning to previous equilibrium and we just don't have the benefit of a huge project being done north of us to feed our beach. Commissioner Aelion said this system is always going to be in play anyway, because beach renourishment is going to be an ongoing thing in the future. You cannot look at this as a closed system because it is consistently in motion. What is interesting to observe is the differential between 2013 and 2015, 2012 is actually when the Pier was completed. He is sure that the engineers who built the Pier, in the design structure, must have taken beach erosion into account. It is too early to make an informed opinion because so much action has happened in the last 6 to 8 years. Ms. Cutt said we would like to do some research and determine whether they did consider the permeability of the structure in the design. A lot of times they have gone from the wood piles to the concrete piles to improve the longevity of the structure. Commissioner Levin said she thinks Jordan has said that the sand was not moving south from Golden Beach. Is there some structure preventing the sand from moving south from Golden Beach? Ms. Cutt said there is no structure but generally the shoreline configuration in Golden Beach is more concave so that focuses all the wave energy and the sand stays in 4