The main reason that we are all interested in what happens to the breach is its impact on the Great South Bay and Bellport Bay in particular. The issues are to what extent the exchange with the ocean has minimized nutrient loading within the bay as well as any potential vulnerability to storm surges. Eight years of water level data have shown that there has been no appreciable change in either tides or storm surges. Thus, the main focus is on the water exchange, and the salinity measured at the Bellport dock is the best indicator we have of that exchange. Ocean salinity south of Long Island is typically around 32 psu (practical salinity units, which are numerically nearly equivalent to parts per thousand), while salinity in Bellport Bay prior to the breach was usually between 24 and 25 psu. In a previous report published two years ago. it was pointed out that there had been a fairly steady decline over the two year period 2017-2018 in salinity at Bellport from around 30 psu to roughly 27 psu. That was a clear indication that the breach was steadily getting smaller and less efficient. Figure 3 shows the salinity record from Bellport for the two years since then, 2019-2020, and it is clear that the steady decrease we had seen before no longer seems to apply. Instead we are seeing wide variations from lows of ~20 psu to highs of more than 30 psu. For almost any one of the events it is pretty clear what is happening. When we have big rain events. the sensor that is located along the north shore shows a marked but temporary decrease in salinity. And when we have a big nor’easter, when Bellport Bay waters are blown to the west while the ocean rises up against Fire Island, there is fresh injection of saline ocean water. For each event, it takes a while to recover. But compared to the earlier 2017-2018 period, the number and duration of the 30 psu events have decreased while the times and durations of the low salinity events has increased. Figure 3, Temperature and salinity record for 2019 – 2020 from the Bellport SeaCat. So the net result of these observations is that the eight-year old breach continues to exist and continues to inject higher salinity and lower nutrient waters into Bellport Bay, although not at the rate we saw in the first few years. What I find rather surprising is the continued effectiveness of the breach to provide water to the Bay while the channel depths and cross-sectional area of the breach have been reduced to maybe less than half what they were. As we have known from the beginning, the breach will close at some time but it seems to be holding on despite major alterations in its morphology.
The photos below were taken by Dr. Flagg 1-8-2021