Signals of sea-level rise in Delaware and Chesapeake Bay tides Andrew C. Ross and Raymond G. Najjar Pennsylvania State University Also thanks to Ming Li, Serena Lee, Fan Zhang, Wei Liu
Observations show tides are changing Flick et al. (2003): 2 / 23
Observations show tides are changing Flick et al. (2003): Redman (1877) Doodson (1924) Ray (2006) Jay (2009) Woodworth (2010) Müller et al. (2011) Feng et al. (2015) 2 / 23
Tides control many estuarine processes Mixing and distribution of salinity, nutrients, and pollutants (e.g., Simpson et al., 1990; Prandle, 2004; Li and Zhong, 2009; Wei et al., 2016) Suspension, transportation, and deposition of sediment (e.g., Scully and Friedrichs, 2007) Growth and development of salt marshes (Friedrichs and Perry, 2001; Kirwan and Guntenspergen, 2010) and erosion of shorelines (Rosen, 1977) Flooding in coastal cities (Zhang and Sheng, 2013; Ezer and Atkinson, 2014) 3 / 23
Questions for this talk How are tides changing in Delaware and Chesapeake Bays? What is causing these changes and trends? Sea-level rise? How might tides change in the future? 4 / 23
Components of the tide 1.0 M2 N2 S2 K1 O1 Water level (m) 0.5 0.0 0.5 Water level (m) 1.0 01 Jul 1.5 2015 1.0 0.5 0.0 0.5 02 03 04 05 06 07 08 09 10 11 12 13 14 15 datetime Observations M2 1.0 01 Jul 2015 02 03 04 05 06 07 08 09 10 11 12 13 14 15 5 / 23
Methods overview 1. Calculate trends in observed tidal properties 2. Determine sensitivity of tidal properties to mean sea level Compare observed sensitivity (from statistical model) with predicted sensitivity (from numerical model) 3. Calculate trends after removing effect of mean sea level 6 / 23
Observations: tide gauges 40 N 38 N 36 N 34 N 32 N p l m b a q c n d o e f g h j i k r 76 W 74 W 72 W 70 W 2 8 32 128 512 2048 Model depth (m) Observation site a Tolchester Beach b Baltimore c Annapolis d Cambridge e Solomons Island f Lewisetta g Windmill Point h Yorktown i Sewells Point j Kiptopeke k CBBT l Philadelphia m Reedy Point n Cape May o Lewes p Sandy Hook q Atlantic City r Duck 7 / 23
Observations: data processing Split each tide gauge time series into chunks by year. Use least squares harmonic analysis to calculate amplitudes and phases for each component of tides, for each year, for each site. 8 / 23
Example: M 2 amplitude time series Amplitude (cm) Amplitude (cm) 25 Upper Chesapeake Cambridge 20 Lewisetta Tolchester Beach Windmill Point Baltimore Solomons Island 15 Annapolis 1900 1920 1940 1960 1980 2000 Delaware Bay 80 Reedy Point Philadelphia 70 Cape May 60 Lewes 1900 1920 1940 1960 1980 2000 Amplitude (cm) Amplitude (cm) 40 Lower Chesapeake Kiptopeke 38 Sewells Point CBBT 36 34 Yorktown 32 1900 1920 1940 1960 1980 2000 70 65 Mid Atlantic Bight Sandy Hook 60 55 Atlantic City 50 Duck 45 1900 1920 1940 1960 1980 2000 Type: Raw time series Nodal cycle removed 9 / 23
Observations: statistical model for sensitivity y = β H H + β t t + β 3 sin(ω) + β 4 cos(ω) + β 5 sin(2ω) + β 6 cos(2ω) + β 0 + ɛ y is the time series of amplitude or phase (one value per year) H is the annual mean sea level t is the year β H is the sensitivity to sea level β t is the trend not explained by sea level 10 / 23
Numerical model: domain Finite Volume Coastal Ocean Model (FVCOM) (Chen et al., 2003, 2006) Resolution varies from less than 200 m in the bays to several kilometers in the deep ocean 40 N 38 N 36 N 34 N 32 N l m b a c d e f g h j i k r n o q p 76 W 74 W 72 W 70 W 2 8 32 128 512 2048 Model depth (m) Observation site a Tolchester Beach b Baltimore c Annapolis d Cambridge e Solomons Island f Lewisetta g Windmill Point h Yorktown i Sewells Point j Kiptopeke k CBBT l Philadelphia m Reedy Point n Cape May o Lewes p Sandy Hook q Atlantic City r Duck 11 / 23
Numerical model: configuation Runs in full 3D mode with forcing from atmosphere, ocean boundary, and rivers. Tides specified at the ocean boundary using data from TPXO8. No inundation/wetting and drying of land. Model performance in Chesapeake is good; DE tides are too strong. 12 / 23
Numerical model: experiments Two main experiments, each one year long: Control (present-day sea levels) Historical (sea levels reduced by 25 cm) Sensitivity to sea level: y/ H y is the change in model-simulated amplitude or phase H is the change in mean sea level (imposed and simulated) 13 / 23
M 2 trends Trend (% / century) 10 0 10 20 30 M2 amplitude Chesapeake Delaware Mid Atlantic Trend (min / century) 50 25 0 25 CBBT Kiptopeke Sewells Point Yorktown Windmill Point Lewisetta Solomons Island Cambridge M2 phase Annapolis Baltimore Tolchester Beach Lewes Cape May Reedy Point Philadelphia Duck Atlantic City Sandy Hook 14 / 23
M 2 sensitivity to sea level M2 amplitude 30 Chesapeake Delaware Mid Atlantic A/ h (cm / m) 20 10 0 M2 phase φ/ h (min / m) 0 50 100 150 CBBT Kiptopeke Sewells Point Yorktown Windmill Point Lewisetta Solomons Island Cambridge Source: Model Annapolis Baltimore Tolchester Beach Observed Lewes Cape May Reedy Point Philadelphia Duck Atlantic City Sandy Hook 15 / 23
M 2 trends, removing sea level 10 M2 amplitude Chesapeake Delaware Mid Atlantic Trend (% / century) 0 10 20 30 Trend (min / century) 60 40 20 0 20 CBBT Kiptopeke Sewells Point Yorktown Windmill Point Lewisetta Solomons Island Cambridge M2 phase Annapolis Baltimore Tolchester Beach Lewes Cape May Reedy Point Philadelphia Duck Atlantic City Sandy Hook 16 / 23
Sea-level rise and background trend are the best explanation for most observed tide changes Things that do not sufficiently explain tide changes: Abrupt, large-scale tide trends River discharge Errors and instrument problems in tide gauge data Dredging and channel deepening (known periods excluded from analysis) 17 / 23
Sensitivity to sea level is nearly linear Toffolon and Savenije (2011) analytical model. A/ H (cm/m): 18 / 23
But, future changes might depend on inundation Past inundation of wetlands and low-lying areas is insignificant compared to future predictions. Future inundation increases friction, lowering amplitudes. Hall et al. (2013): 19 / 23
Conclusions How are tides changing in Delaware and Chesapeake Bays? Different M 2 amplitude trends; many negative M 2 phase trends. What is causing these changes and trends? Combination of sea-level rise and large-scale changes. How might tides change in the future? Large increases possible if no new inundation; smaller changes with inundation. 20 / 23
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