Environmental Change and Water Level Variability

Project Description

Predictions of the impact of environmental change include increased storm intensity and frequency. To date, most research has focused on studying storm surge. Researchers have typically relied on models to represent idealized scenarios of storm surge behavior. Without observations to capture how storm surge behaves inside an estuary, the actual effects remain a mystery. To explore this question, this project aims to develop an improved understanding of storm surge behavior in Maine estuaries with varying physical properties.

Pressure and temperature sensors were deployed at varying spatial locations in the Damariscotta River. These data were converted to water level values and statistical analyses will be used to quantify storm surge patterns considering varying channel geometries, geomorphology, river discharge, and estuary alignments. Follow-on grant funding was secured to include three additional systems, in which the sensors will be maintained by volunteer citizen scientists (including aquaculture stakeholders). Storm surge maps that depict where surge levels are largest will be generated. This information will be useful for future aquaculture site selection and potential placement of kelp curtains used as surge attenuators.

Tidal variability is being studied. Tidal flows can undergo distortion as they propagate into an estuary. Interaction with sharp changes in bathymetry or channel geometry can result in dampening, amplification, reflection, and deformation. The physical nature of these water level variations is important to understand, as they are directly connected to aquaculture relevant material (plankton, sediment, and pollutants) transport. These water level and temperature data will be provided to Theme 1 for validation of the FVCOM hydrodynamic model.

Results and Accomplishments

The main findings of this work during 2017-2018 for the Damariscotta River were:

1. The dominant tidal constituent is the semidiurnal tides, while overtides are also important.
2. Neap tidal heights are 2.2 m, while spring tidal heights are around 3.6 m. The tidal amplitudes marginally decay upstream but are relatively insignificant.
3. Storm surge events observed during Fall 2016 were as high as 44 cm, primarily pressure driven, and did not appear to propagate into the estuary.

The main findings of this work during 2017-2018 for the Bagaduce River were:

1. The tidal height attenuates as much as 50% from the mouth of the river at Castine to near Green Island. Spring tidal ranges near the mouth are 2 to 3 m during neap tide and 4 to 5 m during spring tide. Near Green Island, they range from 1.2 m to 3 m during neap tide and 3 m to 4 m during spring tide. Upstream of the route 175 bridge (referred to as a reversing waterfall), the tidal height decays to 0.3 m during neap and 0.4 m during spring. This drastic reduction is due to the constriction at the bridge limiting the volume of water that can pass through upstream.
2. The dominant tidal constituent is the semi diurnal tide, however overtide constituents are prominent.
3. The highest storm surge observed over the 2017-2018 fall/winter season was at Castine during the October 30th wind storm, where storm surge levels reached nearly 1 m and appeared to be linked to both wind and pressure driven surge. Near Green Island, the observed surge values were 0.8 m, which indicates 20% of the surge attenuated as it propagated upstream. Upstream of the route 175 bridge, the observed surge values was only 0.3 m, and was attributed primarily to the inverse barometer effect. During this event, barometric pressure dropped to 990 millibars and the max sustained winds were 22 m/s.
4. A secondary surge event was observed during the January 4^th, 2018 bomb cyclone, where surge values reached 0.8 m in Castine.

Summary of Data Being Collected

Data	Type	Quantity	Location
Absolute pressure	Field	16 locations, July 2016	Damariscotta River
Absolute pressure	Field	TBD	Bagaduce River
Absolute pressure	Field	TBD	Penobscot Bay / River
Absolute pressure	Field	TBD	Bass Harbor