Assessing climate change impacts on the stability of small tidal inlets: Part 2 - Data rich environments

Abstract

Climate change (CC) is likely to affect the thousands of bar-built or barrier estuaries (here referred to as Small tidal inlets - STIs) around the world. Any such CC impacts on the stability of STIs, which governs the dynamics of STIs as well as that of the inlet-adjacent coastline, can result in significant socio-economic consequences due to the heavy human utilisation of these systems and their surrounds. This article demonstrates the application of a process based snap-shot modelling approach, using the coastal morphodynamic model , to 3 case study sites representing the 3 main STI types; Permanently open, locationally stable inlets (Type 1), Permanently open, alongshore migrating inlets (Type 2) and Seasonally/Intermittently open, locationally stable inlets (Type 3). The 3 case study sites (Negombo lagoon - Type 1, Kalutara lagoon - Type 2, and Maha Oya river - Type 3) are all located along the southwest coast of Sri Lanka. After successful hydrodynamic and morphodynamic model validation at the 3 case study sites, CC impact assessment are undertaken for a high end greenhouse gas emission scenario. Future CC modified wave and riverflow conditions are derived from a regional scale application of spectral wave models (WaveWatch III and SWAN) and catchment scale applications of a hydrologic model (CLSM) respectively, both of which are forced with IPCC Global Climate Model output dynamically downscaled to ~ 50 km resolution over the study area with the stretched grid Conformal Cubic Atmospheric Model CCAM. Results show that while all 3 case study STIs will experience significant CC driven variations in their level of stability, none of them will change Type by the year 2100. Specifically, the level of stability of the Type 1 inlet will decrease from 'Good' to 'Fair to poor' by 2100, while the level of (locational) stability of the Type 2 inlet will also decrease with a doubling of the annual migration distance. Conversely, the stability of the Type 3 inlet will increase, with the time till inlet closure increasing by ~75%. The main contributor to the overall CC effect on the stability of all 3 STIs is CC driven variations in wave conditions and resulting changes in longshore sediment transport, not Sea level rise as commonly believed.

A Multi-Scale Conceptual Model of Flood-Tide Delta Morphodynamics in Micro-Tidal Estuaries

“…Tidal inlets have been comprehensively studied due to their economic and recreational importance as navigational pathways, dominant features in the coastal sediment budget and their role in biological systems with regard to the transfer of water and biological material into and out of backbarrier/estuarine systems [11][12][13][14][15][16][17]. ETDs have also been relatively well studied for the above reasons in relation with inlet and nearshore stability [18,19].…”

A Computational Investigation of Storm Impacts on Estuary Morphodynamics

“…Simulating bathymetry change using a process-based model for 100 years is unrealistic, unreliable, and not feasible due to uncertainties and accumulation of numerical errors. Therefore, the 'snap-shot' approach we used here, which has been successfully used by other researchers to investigate climate change impacts on estuaries (e.g., [27][28][29]), is only the best way to achieve the aims of this study. Additionally, we limited ourselves to 1 in 100-year storms, with the worst-case scenario of storm peak coinciding with highest tide and peak surge.…”

“…Recently, Yin et al [27] investigated the effects of SLR on the meso-tidal, ebb-dominated Deben Estuary in the UK using a numerical model and concluded that the Deben Estuary inlet would become more dynamic as a result of SLR. Duong et al [28,29] computationally modelled sea level rise and wave impacts on small tidal inlets located in a micro-tidal environment. They concluded that inlet stability and some key behavioral characteristics of inlet would change as a result of SLR.…”

Downscaling Future Longshore Sediment Transport in South Eastern Australia

“…Models that run without the atmospheric downscaling step have the same limitations of the GCM, notably the inability to resolve the intensities of tightly structured storm systems such as tropical and extratropical cyclones. The dynamic downscaling of sediment transport modelling with a regional atmospheric model has been investigated for data poor and data rich locations and provides examples of where changes to wave-driven longshore transport will have a larger impact then changes to mean sea level [39,40]. Dynamical downscaling can produce an internally consistent model recreation/realisation of historic (baseline) and future climate changes at the expense of large computer resources to compute the simulations and store the datasets.…”