link to previous page
Ground-Water Levels:
During the event, only two of the wells experienced immediate increases in groundwater elevation (fig. 4) – Inland Well 1) and Inland Well 2. Water levels at Inland Well 1 rose 0.08 ft in 30 minutes, from 1.62 to 1.70 ft (NAVD 88). Similarly, water levels at Inland Well 2 rose 0.06 ft in 30 minutes, from 1.96 to 2.02 ft (NAVD 88). Another well experienced a slightly delayed increase in water levels, Marsh Well rose 0.07 ft in 1.25 hours, from 1.06 to 1.13 ft (NAVD 88). The other two wells, Middle Well and Deep Well, experienced no discernable water-level increase until the afternoon high tide.
Figure 4. Precipitation (dashed blue) and tide elevation (dashed magenta) at USGS Great South Bay at Watch Hill on Fire Island, NY tidal gage (USGS station ID 01305575) and water-level elevations at USGS wells 403922073064401 (Marsh Well – solid brown), 403922073064402 (Deep Well – solid teal), 403921073064801 (Middle Well – solid dark red), 403921073070401 (Inland Well 1 – solid pink), and 403919073064801 (Inland Well 2 – solid blue) for the period September 28, 2017 to October 10, 2017 (2 days before and 10 days after the storm). Storm period shaded in grey.
Specific Conductance:
None of the wells experienced a specific conductance increase or decrease from this heavy rain event besides those attributed to background variations (fig. 5).
Event #3 – High Wind and Heavy Rain Event – October 29-30, 2017
Event Discussion:
The storm that affected the study area from October 29-30, 2017, was characterized by heavy rain and strong winds (fig. 6). Storm-total precipitation of 4.02 in. at Long Island-Islip MacArthur Airport occurred as rainfall on a single day (October 29th). Winds were generally from the south to southeast at the beginning of the event, reaching a maximum sustained wind speed of 41 mph at Long Island-Islip MacArthur Airport on October 29th, then shifted to a more westerly direction on the following day. This event occurred during a period of relatively low astronomical tide as determined from NOAA station 8514779. However, the strong winds associated with this event produced coastal flooding that reached a maximum elevation of 3.53 ft (NAVD 88) at USGS station 01305575 on the morning of October 30th. This maximum coincided with a period of strong westerly winds. This maximum tide elevation was also the highest recorded during the study period.
Figure 6. Precipitation (solid blue), tide elevation (solid magenta), and maximum sustained wind speed (dotted grey), at USGS Great South Bay at Watch Hill on Fire Island, NY tidal gage (USGS station ID 01305575) for the period October 27, 2017, to November 10, 2017 (2 days before and 10 days after the storm). Storm period shaded in grey.
Ground-Water Levels:
During the event, all near-shore wells experienced significant increases in groundwater elevations (fig. 7). Water levels in the Marsh Well and Deep Well increased by about 2.5 ft during the event, with peak water levels of 3.07 ft (NAVD 88) and 3.02 ft (NAVD 88), respectively. Both wells reached their peaks about 45 minutes after the recorded peak storm tide at station 01305575. Water levels in the Middle Well, Inland Well 1 and Inland Well 2 showed smaller increases of about 1 ft, with peak water levels of 1.99 ft (NAVD 88), 2.25 ft (NAVD 88), and 2.48 ft (NAVD 88), respectively. Water levels reached their peak at these wells about 4 hours, 5 ½ hours, and 12 hours, respectively, after the recorded storm tide peak at USGS station 01305575. Water levels returned to pre-storm levels for the Marsh Well, Deep Well, and Middle Well by around November 2nd, while Inland Well 1 and Inland Well 2 remained elevated longer and did not return to pre-storm levels until around November 4th.
Parts of the shoreline above higher-high water were inundated during this event. However, none of the wells were believed to be overtopped by storm tide. Water levels did not peak above land-surface elevation during this event for any of the wells in the study area.
Figure 7. Precipitation (dashed blue) and tide elevation (dashed magenta) at USGS Great South Bay at Watch Hill on Fire Island, NY tidal gage (station USGS station ID) and water-level elevations at USGS wells 403922073064401 (Marsh Well – solid brown), 403922073064402 (Deep Well – solid teal), 403921073064801 (Middle Well – solid dark red), 403921073070401 (Inland Well 1 – solid pink), and 403919073064801 (Inland Well 2 – solid blue) for the period October 27, 2017 to November 10, 2017 (2 days before and 10 days after the storm). Storm period shaded in grey.
Specific Conductance:
Specific conductance at the shallow marsh well (Marsh Well) increased from about 1,300 µS/cm to 4,200 µS/cm on October 30th, generally coinciding with the recorded peak storm tide at USGS station 01305575 (fig. 8) presumably from aquifer infiltration of seawater from the storm-tide inundation of the marsh. Specific conductance after the event slowly declined to about 2,500 µS/cm by November 2nd, then began increasing again and peaked at slightly above 6,000 µS/cm on November 5th. Specific conductance at the Marsh Well then slowly declined, returning to near pre-storm levels by November 16th (not shown on hydrograph). Specific conductance at the deeper marsh well (Deep Well) showed a delayed response to the coastal-flooding event. Specific conductance at this well began a gradual increase from about 600 µS/cm on November 4th to a peak of about 5,000 µS/cm on November 14th (not shown on hydrograph). Specific conductance at the Deep Well then slowly declined, returning to near pre-storm levels by the middle of December (not shown on hydrograph).
Two of the wells located further inland were also monitored for specific conductance during this event (Middle Well and Inland Well 1), with both wells showing significantly less response to the event than the two marsh wells. Specific conductance at the Middle Well showed a rapid decline from about 1,750 µS/cm to 1,450 µS/cm on October 30th near the recorded peak storm tide at station 01305575; however, the decrease in specific conductance began right around the time of heavy precipitation for this event and may be related to dilution of the aquifer from the rainfall. Specific conductance at this well then began a gradual rise and peaked on November 5th at about 1,650 µS/cm, then gradually declined to below 1,400 µS/cm by November 24th (not shown on hydrograph). Specific conductance at Inland Well 1 was the least responsive showing only a very gradual increase from about 380 µS/cm at the start of the event to around 550 µS/cm by November 22nd (not show on hydrograph) when the sensor stopped recording.
link to next page
Last updated: December 2, 2022