Resilience of Coastal Lake Barriers in Poland in Light of Geological and Bathymetric Data and Hydrodynamic Simulations

Grzegorz Różyński,Grzegorz R Cerkowniak

doi:10.3389/fmars.2022.815405

Abstract

The paper presents a study on the insufficient resilience of three coastal lake barriers at the central part of the Polish Baltic Sea coast. Environmental qualities of those lakes belonging to the NATURA2000 network dictate efforts aimed at their conservation through the maintenance of the barriers. The use of recently elaborated high resolution geological surveys demonstrated previously underestimated severe sand scarcity and indicated high threats of enhanced erosion, breaching and overtopping of the barriers. Next, the investigation of alongshore variation of nearshore wave energy dissipation, basing on the available bathymetric records and the concept of ordinary and empirical equilibrium profiles, identified potential erosion hot spots along the barriers. Finally, the XBeach model was applied to simulate the effects of rare, heavy storms with the recurrence period of 20 years with and without climate change induced sea level rise. Overall, the results demonstrated high susceptibility of the barriers to frequent fragmentation and allowed for recommendations of protection measures minimizing interference into the natural landscapes. The novelty of the paper consists in the assessment of aftermaths of extreme events by combining recent advances in coastal geology and climate change effects.

Highlights

IntroductionRecent scientific evidence (BACC II, 2015) suggests that there is a widely accepted consensus as to the consequences of climate change for Baltic Sea region:(1) An increase in air temperature in all seasons, observed in recent decades, will persist; cold winter and warm summer extremes are expected to change more than the average conditions, contributing to greater instability of coastal areas;(2) The summer sea-surface temperature is expected to increase by about 2◦C (4◦C) in the southern (northern) sub-basins of the Baltic Sea;(3) A drastic decrease in sea-ice cover is expected, augmenting the exposure to hydrodynamic forces in winter; sea ice is likely to remain in winters in the northern Baltic Sea;(4) Annual mean storm surges are expected to grow by 10 cm without accounting for the large scale sea level rise or land uplift in the Baltic Sea area;(5) The sea level rise will rise by 0.7 m (±0.3 m) until the end of the 21st century.Coastal Lake Barriers in PolandThese consequences will jointly have negative effects on the stability of sandy beaches in the Baltic Sea:(1) Warmer seawater will substantially reduce the extent and duration of ice cover, thereby largely diminishing protection against hydrodynamic forces in late autumns and winters;(2) The imminent sea level rise will move shoreward the wave action, leading to more frequent direct wave attack on dune feet during storms and greater depletion of sediment;(3) Reduction of mean and maximum sea level air pressure (SLP) during the passage of cyclones for last decades (Sepp et al, 2018) will produce multi-faceted and irregular growth of hydrodynamic regimes and further increase sediment fluxes
The risk of breaching is much lower than at the Kopanbarrier, but due to sand scarcity and prevalence of weaker organic deposits the situation will be gradually aggravated under climate change conditions, when direct exposure of those sediments to hydrodynamic forces can occur
Sand scarcity combined with climate change effects can enhance the rate of degradation of the barriers without human interventions

Summary

Introduction

Recent scientific evidence (BACC II, 2015) suggests that there is a widely accepted consensus as to the consequences of climate change for Baltic Sea region:(1) An increase in air temperature in all seasons, observed in recent decades, will persist; cold winter and warm summer extremes are expected to change more than the average conditions, contributing to greater instability of coastal areas;(2) The summer sea-surface temperature is expected to increase by about 2◦C (4◦C) in the southern (northern) sub-basins of the Baltic Sea;(3) A drastic decrease in sea-ice cover is expected, augmenting the exposure to hydrodynamic forces in winter; sea ice is likely to remain in winters in the northern Baltic Sea;(4) Annual mean storm surges are expected to grow by 10 cm without accounting for the large scale sea level rise or land uplift in the Baltic Sea area;(5) The sea level rise will rise by 0.7 m (±0.3 m) until the end of the 21st century.Coastal Lake Barriers in PolandThese consequences will jointly have negative effects on the stability of sandy beaches in the Baltic Sea:(1) Warmer seawater will substantially reduce the extent and duration of ice cover, thereby largely diminishing protection against hydrodynamic forces in late autumns and winters;(2) The imminent sea level rise will move shoreward the wave action, leading to more frequent direct wave attack on dune feet during storms and greater depletion of sediment;(3) Reduction of mean and maximum sea level air pressure (SLP) during the passage of cyclones for last decades (Sepp et al, 2018) will produce multi-faceted and irregular growth of hydrodynamic regimes and further increase sediment fluxes. (1) An increase in air temperature in all seasons, observed in recent decades, will persist; cold winter and warm summer extremes are expected to change more than the average conditions, contributing to greater instability of coastal areas;. (4) Annual mean storm surges are expected to grow by 10 cm without accounting for the large scale sea level rise or land uplift in the Baltic Sea area;. These consequences will jointly have negative effects on the stability of sandy beaches in the Baltic Sea:. (3) Reduction of mean and maximum sea level air pressure (SLP) during the passage of cyclones for last decades (Sepp et al, 2018) will produce multi-faceted and irregular growth of hydrodynamic regimes and further increase sediment fluxes

Objectives

Methods

Results

Conclusion