Our weekly feature Chasing Shadows
It is said that a man should not argue with women, shrimp or tropical gales. In this spirit, the storm called Nestor offered a morning of assessment.
It came ashore at sunrise exactly at high tide, and its five-foot rise flowed under businesses at the south end of Water Street in Apalachicola. On St. George Island, it overtopped the boat ramp at the bridge and lapped across Sawyer Street on the bay north of 11th Street West (Figure 1).
There are at least two ways to compare today’s water levels with conditions 20 years ago. One way to evaluate changing tide levels is to look at the shoreline using Google Earth’s timeline feature, which shows satellite views back to 1994 before Hurricane Opal.
Figure 2 shows aerial views of Sawyer Street on St. George Island along the bay between Nedley Street and Bradford Street from 2004 (top) and 2019 (bottom). The arrow in the lower picture is where the photo in Figure 1 was taken during Nestor.
There used to be room to park cars along the bay north of Sawyer Street, and the area had a few pine trees and sandbars with sea grass. Over the years, seawalls were built and rock rip-rap had to be put in place to stabilize the road. Several pines north of Nedley Street died and most of the sea grass disappeared along with the fiddler crabs that once lived there.
The area north of Sawyer Street once had lots for home sites, and there is an exposed water line that the tides have uncovered. Probably, homes were not built there because of Hurricanes Elena and Kate that eroded the area in 1985.
A second way to compare changing tides is to look at water levels measured at the mouth of the Apalachicola River. The information for any period back to 1999 is found on the internet at NOAA Tides and Currents, Apalachicola station 8728690. The tidal patterns are compared with a benchmark that is has not been changed.
Figure 3 shows tidal patterns for the months of June in the years 2000 (top) and 2019 (bottom). In June 2000, the measured tide patterns (green line) almost exactly matched the pattern predicted from a numerical tide model (blue line). Small deviations do occur because of weather conditions, such as low atmospheric pressure during storms and heavy rainfall or drought that changes the river level.
However, in 2019 the measured water level is consistently higher than that predicted from the tide model. As indicated by the arrows, nearly every high and low tide in the month of June was measurably higher than the model based on the old baseline. The patterns of the measurements and the model are similar, but the measured values are higher by about six inches.
If one checks the patterns at five-year intervals, one sees that over the years, more and more measured high tides are higher than the ones predicted. Also, the pattern is true for other months and other tide stations. For example, the tide station at Panama City Beach gives a very clear picture because it is not located on a river mouth and because the tide pattern is simpler.
Everyone in Franklin County faces the question of how to adapt during the next 20 years. The rising tides are caused by physical events, mostly due to melting glaciers far to our north, and expansion of the oceans as the sun warms the seas.
Maybe it is just ducking the question, but a man cannot argue with the mind of women, shrimp and hurricanes. But he can know that changes will come and prepare before the trouble starts.