link to previous page
1. Northeastern Heavy Rain and High Wind Event followed by a High Spring Tide (10/26/2017 to 11/13/2017)
a. Description
The primary forcing condition during this event was 2.55 inches of precipitation on 10/30/2017 followed 27.8 knot winds (Figure 5a). Additional wind speeds up to 20 knots were observed from 11/10/2017 to 11/11/2017. This primary forcing condition occurred during a low lunar tide that was followed later in the event by a high spring tide from 11/2/2017 to 11/12/2017.
b. Water Level Response
During the heavy rain event, all near-shore wells experienced significant increases in groundwater and tide elevations. Water levels in GWW31 and GWW32 frequently peaked above land surface. Water levels in GWW33 and GWW34 did not peak above land surface. However, the highest tide elevations rose slightly above land surface suggesting some overtopping from the sea. GWW30 also exhibited a significant increase in water level during the heavy rain event.
Water levels in GWW31 and GWW32 were highly responsive to tidal forcing during the spring tide. Both groundwater and sea water elevations exceeded land surface elevations suggesting that overtopping had occurred. GWW33 and GWW34 were also responsive but did not peak above the land surface elevation. Water levels in GWW30 experienced a slight increase during this period with some damped oscillations synched to diurnal tides.
c. Specific Conductance Response
During the precipitation event, the Specific conductance increased rapidly in GWW32, GWW33 and GWW34 followed by a rapid decrease. GWW31 exhibited increases and decreases in specific conductance throughout this period though not necessarily in-sync with the weather event or tides. Specific conductance levels for GWW31 were generally high with an average of approximately 36,000 µS/cm.
Specific conductance levels in GWW32 increased by approximately 2500 µS/cm and remained high for the duration of the spring tide before dropping back to its initial concentration. Specific conductance readings in GWW33 increased intermittently during highest of high tides by approximately 1500 µS/cm before dropping. Specific conductance levels in GWW34 were responsive to tidal fluctuations but did not show appreciable increases during highest of high tides (the overall specific conductance actually decreased).
Figure 5c. GWW34 - Zoom View
2. Heavy Rain and High Wind Event (04/12/2018 to 04/30/2018)
a. Description
Event 2 (Heavy Rain and High Wind) occurred during a low lunar tide with two consecutive forcing conditions. The first condition was heavy precipitation (1.96 inches) and high (~25 knot) winds from 04/15/2018 to 04/16/2018. The second event on 4/20/2018 had maximum wind speed of approximately 28 knots on 4/20/2018.
b. Water Level Response
During the first forcing event, all near-shore wells experienced significant increases in water level. Water levels in GWW31 and GWW32 were highly responsive to tidal forcing with peak levels exceeding the land surface elevation suggestion that overtopping had occurred. GWW33 and GWW34 were also responsive though not on the same scale as GWW31 and GWW32; water levels did not peak above the land surface elevation during tidal forcing. Tidal forcing was not observed in GWW30.
c. Specific Conductance Response
Specific conductance in GWW31 and GWW32 increased and remained elevated for approximately 13 days after the primary event. The specific conductance in GWW31 increased by approximately 2500 µS/cm from 34,500 µS/cm to 37,000 µS/cm and the specific conductance in GWW32 increased by approximately 15,000 µS/cm from 20,000 µS/cm to 35,000 µS/cm. Specific conductance in GWW33 rapidly increased by approximately 35,000 µS/cm from 5,000 µS/cm to 40,000 µS/cm and then decreased rapidly (~ 4 days) to the initial level of 5,000. Specific conductance in GWW34 exhibited two approximate 10,000 µS/cm spikes concurrent to tidal fluctuations.
3. High Precipitation Events (9/01/2018 to 10/25/2018)
a. Description
This event was characterized by three significant precipitation events. The first precipitation event occurred on 9/10/2018 with approximately 1.7 inches of rain and 20 knot winds. Less rainfall was observed in the two subsequent events from 9/25/2018 to 9/28/2018 and 10/10/2018 to 10/11/2018 with 0.5 and 0.9 inches of precipitation respectively. High winds were recorded from 10/10/2018 to 10/28/2018 with the highest windspeed exceeding 29 knots on 10/11/2018 and several high winds above 25 knots over the remainder of the period. The three events were bundled into a single event because of the length of the specific conductance response in GWW32 and, to a lesser extent, GWW33 over this period.
Note: There is only a partial record for GWW31 during this period. Data collection was discontinued in this well at the end of water year 2017.
b. Water Level Response
The first rain event may also have coincided with a high lunar tide resulting in overtopping that extended as far inland as GWW33. During this event water levels in all near-shore shallow wells peaked above the land surface elevation. Water levels in the GWW30 inland well were below land surface. However, diurnal tides peaked above land surface in GWW30 on 9/9/2018.
c. Specific Conductance response
Increases in specific conductance in near shore wells coincided with groundwater and seawater levels exceeding land surface elevations. The length of time specific conductance remained at elevated levels depended on the proximity to the shore and, in-turn, the frequency of overtopping. Specific conductance levels in GWW32 exhibited a rapid rise of 6500 µS/cm to 37500 µS/cm when tides began exceeding land surface elevations on 9/5/2018. This was followed by a gradual decline followed by rapid increases related to the precipitation and higher wind events around 9/25/2018 and 10/10/2018 respectively. Specific conductance levels in GWW33 exhibited rapid increases and decreases during this period. The highest increase occurred on 9/10/2018 and may have been associated with the combination of the high lunar tide, high precipitation and high winds. Smaller increases were observed around the precipitation events around 9/25/2018 and 10/10/2018 respectively. Specific conductance levels in GWW34 increased slightly around the first precipitation event and then gradually dropped for the remainder of the period.
Figure 9c. GWW34 - Zoom View
link to next page
Last updated: December 5, 2022