Climate Change Impacts on the Stability of Small Tidal Inlets: A numerical modelling study using the Realistic Analogue approach (original) (raw)
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Marine Geology, 2018
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 socioeconomic consequences due to the heavy human utilisation of these systems and their surrounds. This article demonstrates the application of a process based snapshot modelling approach, using the coastal morphodynamic model Delft3D, 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.
Assessing climate change impacts on the stability of small tidal inlet systems: Why and how?
Earth-Science Reviews, 2016
Bar-built or barrier estuaries (here referred to as Small tidal inlets, or STIs), which are commonly found along wave-dominated, microtidal mainland coasts, are highly likely to be affected by climate change (CC). Due to their predominance in tropical and subtropical regions of the world, many STIs are located in developing countries, where STI related activities contribute significantly to the national GDPs while community resilience to coastal changes is low, with the corollary that CC impacts on STIs may lead to very serious socioeconomic consequences. While assessing CC impacts on tidal inlets is in general difficult due to inherent limitations of contemporary numerical models where long term morphodynamic simulations are concerned, these difficulties are further exacerbated due to the lack of sufficient model input/verification data in often data poor developing country STI environs. As a solution to this problem, Duong et al. (2016) proposed two different process based snapshot modelling approaches for data poor and data rich environments. This article demonstrates the application of Duong et al.'s (2016) snapshot modelling approach for data poor environments 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). Results show that Type 1 and Type 3 inlets will not change Type even under the most extreme CC driven variations in system forcing considered here. Type 2 inlets may change into Type 1 when CC results in a reduction in annual longshore sediment transport. Apart from Type changes, CC will affect the level of inlet stability and some key behavioural characteristics (e.g. inlet migration distances, inlet closure times). In general, CC driven variations in annual longshore sediment transport rates appear to be more relevant for future changes in inlet stability and behaviour, rather than sea level rise as commonly believed. Based on model results, an inlet classification scheme which, for the first time, links inlet Type with the Bruun inlet stability criteria is presented.
Marine Geology
Bar-built or barrier estuaries (here referred to as Small tidal inlets, or STIs), which are commonly found along wave-dominated, microtidal mainland coasts, are highly likely to be affected by climate change (CC). Due to their predominance in tropical and subtropical regions of the world, many STIs are located in developing countries, where STI related activities contribute significantly to the national GDPs while community resilience to coastal changes is low, with the corollary that CC impacts on STIs may lead to very serious socioeconomic consequences. While assessing CC impacts on tidal inlets is in general difficult due to inherent limitations of contemporary numerical models where long term morphodynamic simulations are concerned, these difficulties are further exacerbated due to the lack of sufficient model input/verification data in often data poor developing country STI environs. As a solution to this problem, Duong et al. (2016) proposed two different process based snapshot modelling approaches for data poor and data rich environments. This article demonstrates the application of Duong et al.'s (2016) snapshot modelling approach for data poor environments 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). Results show that Type 1 and Type 3 inlets will not change Type even under the most extreme CC driven variations in system forcing considered here. Type 2 inlets may change into Type 1 when CC results in a reduction in annual longshore sediment transport. Apart from Type changes, CC will affect the level of inlet stability and some key behavioural characteristics (e.g. inlet migration distances, inlet closure times). In general, CC driven variations in annual longshore sediment transport rates appear to be more relevant for future changes in inlet stability and behaviour, rather than sea level rise as commonly believed. Based on model results, an inlet classification scheme which, for the first time, links inlet Type with the Bruun inlet stability criteria is presented.
Effect of Sea Level Rise in Tidal Inlet Evolution: A Numerical Modelling Approach
Eustatic sea level rise (SLR) is likely to affect shoreline position and coastal processes which may have severe implications on tidal inlet/basin systems around the world. Large inlet/basin systems, such as those found in the Wadden sea are along the Dutch coast, have a very high ecological and socio-economic value and any negative impacts may result in massive losses (both ecologically and socio-economically). This study investigates the potential impact of SLR on the morphological evolution of one such system along the Dutch coast: The Ameland Inlet. A state-of-the art 2DH process-based model, incorporating the MORFAC approach which enables long term morphodynamic simulations, is applied to a schematized representation of this inlet. The model is forced by tide only and three different SLR scenarios are tested. Results indicate that, in the next 50 years, the ebb delta volume will decrease while the flood delta volume will increase. Both, the decrease in ebb delta volume and the increase in flood delta volume increase with increasing rates of SLR. An acceleration of sediment import into the basin is also predicted under SLR conditions. A large portion of the sediment is transported towards the end of the basin resulting more flat areas. The tidal flats appear to be able to keep up with the projected SLR rate (5 mm/year) for the study area during the next 50 years while they appear to drown at an SLR rate of 10 mm/year.
The Proceedings of the Coastal Sediments 2011, 2011
Over the last decades, efforts have been undertaken to identify the equilibrium and stability state of tidal inlets and to model different morphological time scales and spatial scales of tidal inlet systems using data based models and behaviour based models . These include empirical relationships, such as the tidal prism cross-sectional area relationship ), closure criteria and semi-empirical long-term models such as ASMITA . But better understanding of the underlying processes of tidal inlet evolution toward equilibrium requires detailed information of the hydrodynamics and sedimentary processes at the tidal inlet and in the vicinity of the inlet on short-term and long-term time scales. For this purpose in this study, a processbased model (Delft3D) is used to simulate the morphological evolution of tidal inlets, including basin, ebb and flood delta, forced by various hydraulic conditions.
Scientific Reports
Climate change is widely expected to affect the thousands of small tidal inlets (STIs) dotting the global coastline. To properly inform effective adaptation strategies for the coastal areas in the vicinity of these inlets, it is necessary to know the temporal evolution of inlet stability over climate change time scales (50–100 years). As available numerical models are unable to perform continuous morphodynamic simulations at such time scales, here we develop and pilot a fast, probabilistic, reduced complexity model (RAPSTA – RAPid assessment tool of inlet STAbility) that can also quantify forcing uncertainties. RAPSTA accounts for the key physical processes governing STI stability and for climate change driven variations in system forcing. The model is very fast, providing a 100 year projection in less than 3 seconds. RAPSTA is demonstrated here at 3 STIs, representing the 3 main Types of STIs; Permanently open, locationally stable inlet (Type 1); Permanently open, alongshore migrat...
A morphodynamic model to simulate the seasonal closure of tidal inlets
Coastal Engineering, 1999
Seasonally open tidal inlets usually occur in microtidal, wave-dominated coastal environments where strong seasonal variations of streamflow and wave climate are experienced. These inlets are closed to the ocean for a number of months every year due to the formation of sand bars across their entrances. The annual closure of these inlets inhibits ocean access for boats and could also cause deterioration of water quality in the estuaryrlagoon connected to the inlet. As these estuariesrlagoons are commonly used as harbours or recreational facilities there is increased interest in keeping the inlets permanently open. A process-based numerical model capable of simulating inlet closure is invaluable in terms of identifying the natural processes governing inlet closure. As a further step, this type of model could also be used to determine the effect of any proposed engineering solutions to keep the inlet open on the adjacent beaches. A morphodynamic Ž . model capable of simulating the seasonal closure of inlets, which includes both longshore LST Ž . and cross-shore transport CST processes, was developed in this study. Application of the model to two idealised scenarios indicated that cross-shore processes govern inlet behaviour when LST w rates were low. The Dean's criterion Dean, R.G., 1973. Heuristic models of sand transport in the x surf zone. Proc. Conf. on Eng. Dynamics in the Surf Zone, Sydney, pp. 208-214. for on-offshore transport was employed to show that, for small offshore wave incidence angles, onshore transport Ž . aided inlet closure when the offshore wave steepness H rL was less than the critical wave ) Corresponding author. 0378-3839r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
The morphological response of large tidal inlet/basin systems to relative sea level rise
Climatic Change, 2012
The morphodynamic response of large tidal inlet/basin systems to future relative sea level rise (RSLR), incorporating both Eustatic sea level rise and local land subsidence effects, is qualitatively investigated using the state-of-the-art Delft3D numerical model and the Realistic analogue modelling philosophy. The modelling approach is implemented on a highly schematised morphology representing a typical large inlet/basin system located on the Dutch Wadden Sea (Ameland Inlet) over a 110-year study period. Three different RSLR Scenarios are considered: (a) No RSLR, (b) IPCC lower sea level rise (SLR) projection (0.2 m SLR by 2100 compared to 1990) and land subsidence, and (c) IPCC higher SLR projection (0.7 m SLR by 2100 compared to 1990) and land subsidence. Model results indicate that, for the 110-year study duration, the existing flood dominance of the system will increase with increasing rates of RSLR causing the ebb-tidal delta to erode and the basin to accrete. The rates of erosion/accretion are positively correlated with the rate of RSLR. Under the No RSLR condition, the tidal flats continue to develop while under the high RSLR scenario tidal flats eventually drown, implying that under this condition the system may degenerate into a tidal lagoon within the next 110 years. The tidal flats are stable under the low RSLR scenario implying that, at least for the next 100 years, this may be the critical RSLR condition for the maintenance of the system. Essentially the results of this study indicate that, as the Eustatic SLR is likely to be greater than the apparently critical rise of 0.2 m (by 2100 compared to 1990), the tidal flats in these systems will at least diminish. In the worst, but not unlikely, scenario that the Eustatic SLR is as high as the IPCC higher projections (0.7 m by 2100), the tidal flats may completely disappear. In either case, the associated environmental and socio-economic impacts will be massive. Therefore, more research focusing on the quantification of the physical and socio-economic impacts of RSLR on these systems is urgently needed to enable the development of effective and timely adaptation strategies.