Sandy Hook study conclusion

link to previous page

Final Summary

Date ranges selected for analysis had either rainfall greater than 1 in. and/or wind speeds greater than 20 mph and/or significant tidal forcing. The Northeastern heavy Rain and High Wind event (10/26/2017 to 11/13/2017) had the highest precipitation at approximately 2.55 inches and the highest wind speed at 29.35 knots on 10/29/2017. The highest of high diurnal tides occurred during the High Precipitation events (09/01/2018 to 10/25/2018) with a maximum recorded sea level of 2.67 feet abv MHHW on 09/10/2018 at 10:12 AM. The highest groundwater and sea levels were recorded during the High Precipitation and High Wind Event - Low Lunar Tide (10/26/2018 to 11/05/2018) with a maximum sea level of 3.54 ft. on 10/27/2018 at 09:24 AM (table 2):

Well Name	Date	Time	Water Level
GWW30	10/27/2018	1030	2.92
GWW32	10/27/2018	0915	3.12
GWW33	10/27/2018	0945	3.26
GWW34	10/27/2018	0945	2.77

Table 2: Maximum Water Levels During the High Precipitation and High Wind Event - Low Lunar Tide (10/26/2018 to 11/05/2018)

Water level response

There were three types of water level response: 1. Short-term fluctuations coupled to diurnal tides, 2. short-term fluctuations coupled to meteorological events (precipitation and wind) and 3. long-term fluctuations coupled to a combination of meteorological events with lunar tides. Tidal fluctuations complicated the determination of relationship of water level fluctuations to either wind or precipitation. For example, were increased water levels with high tides linked to meteorological events or were they linked to naturally occurring tidal fluctuations?

In general, high winds yielded higher groundwater levels but that was not always the case. For example, during the 10/26/2017 to 11/13/2017 event (Northeastern Heavy Rain and High Wind Event Followed by a High Spring Tide) a high wind event (> 30 knots) late on 10/29/2018 resulted in sea and groundwater level spikes in each of the near-shore wells. However, during a sustained high wind from 10/30/2018 to 11/01/2018 significant increases in either sea or groundwater levels were not observed. Another example is the observed change in water levels in GWW30. During the High Precipitation and High Wind Event at Low Lunar Tide (10/26/2018 to 11/05/2018), the moderate precipitation (~1.1 in.) and high (~26 knot) wind at low tide on 10/27/2018 resulted in sea and groundwater levels spiking above the land surface elevation. However, during a later High Precipitation and High Wind Event at Low Lunar Tide (12/20/2018 to 12/30/2018) the greater precipitation (~1.5 in.) and slightly slower wind speed (~23 knots) resulted in only a mild, longer lasting increase in water levels.

The near shore wells were highly responsive to both tidal (diurnal and lunar) and meteorological forcing. The amplitude of the water level response generally decreased moving inland from the coast. GWW31 was the closest to the shoreline and, therefore, most responsive to any forcing. GWW31 was also constantly inundated by seawater. GWW32 was also frequently inundated during the highest of high tides as well as during high wind and high precipitation events, though not as often as GWW31. GWW33 and GWW34 were the farthest inland from the shore and were only occasionally inundated by seawater.

Inundation of GWW33 and GWW34 (sea and groundwater levels >0.5 ft above land surface elevation) occurred during the High Precipitation Events from 09/01/2018 to 10/25/2018 (~ 1.0 to 1.5 ft above land surface) and High Precipitation and High Wind Event to Low Lunar Tide from 10/26/2018 to 11/05/2018 (~3.0 ft abv land surface). Sea levels did reach the land surface elevations of GWW33 and GWW34 for other high precipitation, high wind and high tide events but only slightly and sporadically during the highest of high tides.

GWW30 experienced only a mild increase in groundwater levels in response to high precipitation and/or wind speeds (High Precipitation Events (09/01/2018 at 10/25/2018); Heavy Rain and High Wind Event (4/12/2018 to 4/30/2018)). However, the High Precipitation and High Wind Event at Low Lunar Tide (10/26/2018 to 11/05/2018) did push water levels above land surface on 12/21/2018.

Specific conductance

Specific conductance levels in the near-shore wells were correlated to the proximity of the well to the shoreline. This was true in both the response to tidal fluctuations and storm events.

GWW31 was nearest to the shoreline and exhibited the highest ambient specific conductance (~30,000 to 40,000 µS/cm), most likely related to constant inundations during high tide and storm events. The effects of specific storm events on the specific conductance in this well was limited. Significant fluctuations were observed during high amplitude tidal cycles where water levels in the well fluctuated significantly. However, fluctuations in specific conductance did not necessarily correlate to water level fluctuations in the well. For example, during the Northeastern Heavy Rain and High Wind Event Followed by a High Spring Tide (10/26/2017 to 11/13/2017) specific conductance levels actually dropped by about 1,000 to 2,000 µS/cm when sea and groundwater levels were highest. In general, the changes in specific conductance to any forcing event was either minimal or not directly correlated in GWW31.

GWW32 was frequently inundated by either storm or high lunar tides. During most of the events, rapid and prolonged increases were observed in the specific conductance. During the Heavy Wind and Rain (4/12/2018 to 4/30/2018) event, for example, the specific conductance increased from ~20,000 µS/cm to ~40,000 µS/cm and remained near or at that level for the duration of the event. The exception was the specific conductance response during the High Precipitation and High Wind Event at Low Lunar Tide (10/26/2018 to 11/05/2018) where the specific conductance level spiked to ~15,000 µS/cm to ~30,000 µS/cm and then rapidly returned to the starting level of ~15,000 µS/cm.

GWW33 was occasionally inundated by either storm surges or high lunar tides. Specific conductance levels increased significantly during the events. However, the time and duration of time of the increases varied between events. For example, during the Heavy Rain and High Wind Event (4/12/2018 to 4/30/2018) the specific conductance increased rapidly from ~2500 µS/cm to ~40,000 µS/cm and then dropped to ~7500 µS/cm in approximately 2 days. Conversely, during the High Precipitation and High Wind Event at Low Lunar Tide (12/20/2018 to 12/30/2018) event, the specific conductance increased gradually from ~7500 µS/cm to ~22,500 µS/cm over 5 days and then gradually declined over 9 days to 10,000 µS/cm.

The specific conductance in GWW33 exhibited an unusual response during The High Precipitation and High Wind Event at Low Lunar Tide (10/26/2018 to 11/05/2018) event. During this period, groundwater levels spiked approximately 1.5 feet above the land surface elevation on 10/27/2018 in response to the high wind, rain, and tide. However, while the water level decreased steadily back to the base level, the specific conductance exhibited a concurrent spike that decreased rapidly, immediately increased again and then remained elevated for the remainder of the event.

Specific conductance levels in GWW34 (the deep well) generally fluctuated with diurnal tides though occasional spikes with storm or tide events were observed (Precipitation and High Wind Event at Low Lunar Tide (10/26/2018 to 11/05/2018); Northeastern Heavy Rain and High Wind Event Followed by a High Spring Tide (10/26/2017 to 11/13/2017)).

Data References:

National Oceanic and Atmospheric Administration, Tides and Currents website, Top Ten Highest Water Levels for long-term stations in meters above MHHW (as of 4/2018) https://tidesandcurrents.noaa.gov/est/Top10_form.pdf, accessed on 11/8/2022.

link to Maritime Forest Study introduction

link to Assateague Island study

link to Fire Island study