Signals of sea-level rise in Delaware and Chesapeake Bay tides

Transcription

1 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

2 Observations show tides are changing Flick et al. (2003): 2 / 23

3 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

4 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

5 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

6 Components of the tide 1.0 M2 N2 S2 K1 O1 Water level (m) Water level (m) Jul datetime Observations M Jul / 23

7 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

8 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 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

9 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

10 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 Delaware Bay 80 Reedy Point Philadelphia 70 Cape May 60 Lewes Amplitude (cm) Amplitude (cm) 40 Lower Chesapeake Kiptopeke 38 Sewells Point CBBT Yorktown Mid Atlantic Bight Sandy Hook Atlantic City 50 Duck Type: Raw time series Nodal cycle removed 9 / 23

11 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

12 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 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

13 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

14 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

15 M 2 trends Trend (% / century) M2 amplitude Chesapeake Delaware Mid Atlantic Trend (min / century) 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

16 M 2 sensitivity to sea level M2 amplitude 30 Chesapeake Delaware Mid Atlantic A/ h (cm / m) M2 phase φ/ h (min / m) 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

17 M 2 trends, removing sea level 10 M2 amplitude Chesapeake Delaware Mid Atlantic Trend (% / century) Trend (min / century) 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

18 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

19 Sensitivity to sea level is nearly linear Toffolon and Savenije (2011) analytical model. A/ H (cm/m): 18 / 23

20 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

21 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

22 Chen, C., R. C. Beardsley, and G. Cowles, 2006: An unstructured grid, Finite-Volume Coastal Ocean Model (FVCOM) system. Oceanography, 19, Chen, C., H. Liu, and R. C. Beardsley, 2003: An unstructured grid, finite-volume, three-dimensional, primitive equations ocean model: Application to coastal ocean and estuaries. Journal of Atmospheric and Oceanic Technology, 20, Doodson, A. T., 1924: Perturbations of harmonic tidal constants. Proceedings of the Royal Society of London Series A, 106, Ezer, T., and L. P. Atkinson, 2014: Accelerated flooding along the U.S. East Coast: On the impact of sea-level rise, tides, storms, the Gulf Stream, and the North Atlantic Oscillations. Earth s Future, 2, Feng, X., M. N. Tsimplis, and P. L. Woodworth, 2015: Nodal variations and long-term changes in the main tides on the coasts of China. Journal of Geophysical Research: Oceans, 120, Flick, R. E., J. F. Murray, and L. C. Ewing, 2003: Trends in United States tidal datum statistics and tide range. Journal of Waterway, Port, Coastal, and Ocean Engineering, 129, Friedrichs, C. T., and J. E. Perry, 2001: Tidal salt marsh morphodynamics: a synthesis. Journal of Coastal Research, (Special Issue No. 27), Hall, G. F., D. F. Hill, B. Horton, S. E. Engelhart, and W. R. Peltier, 2013: A high-resolution study of tides in the Delaware Bay: Past conditions and future scenarios. Geophysical Research Letters, 40, Jay, D. A., 2009: Evolution of tidal amplitudes in the eastern Pacific Ocean. Geophysical Research Letters, 36, doi: /2008gl Kirwan, M. L., and G. R. Guntenspergen, 2010: Influence of tidal range on the stability of coastal marshland. Journal of Geophysical Research: Earth Surface, 115, doi: /2009jf Li, M., and L. Zhong, 2009: Flood ebb and spring neap variations of mixing, stratification and circulation in Chesapeake Bay. Continental Shelf Research, 29, Müller, M., B. K. Arbic, and J. X. Mitrovica, 2011: Secular trends in ocean tides: Observations and model results. Journal of Geophysical Research, 116, doi: /2010jc Prandle, D., 2004: How tides and river flows determine estuarine bathymetries. Progress in Oceanography, 61, Ray, R. D., 2006: Secular changes of the M2 tide in the Gulf of Maine. Continental Shelf Research, 26, Redman, J. B., 1877: The River Thames. Proceedings of the Institution of Civil Engineers, 49, Rosen, P. S., 1977: Increasing shoreline erosion rates with decreasing tidal range in the Virginia Chesapeake Bay. Chesapeake Science, 18, Scully, M. E., and C. T. Friedrichs, 2007: Sediment pumping by tidal asymmetry in a partially mixed estuary. Journal of Geophysical Research, 112, doi: /2006jc Simpson, J. H., J. Brown, J. Matthews, and G. Allen, 1990: Tidal straining, density currents, and stirring in the control of estuarine stratification. Estuaries, 13, Toffolon, M., and H. H. G. Savenije, 2011: Revisiting linearized one-dimensional tidal propagation. Journal of 21 / 23

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