Evaluation of spatio-temporal variability of ocean wave power resource around Sri Lanka

The paper presents a detailed analysis of the spatio-temporal variability of wave power resource around Sri Lanka, using computationally simulated 25 years of wave data that represents the prevailing ocean climate in the region. The computational wave model was validated against a measured wave dataset collected over a 44-month period at 70 m water depth off the coast of the south-west of Sri Lanka and compared with ERA-Interim Reanalysis wave data and, good agreement found. The analysis reveals that the ocean around Sri Lanka from the south-west to south-east have a substantial wave power resource. The available offshore wave power resource remains between 10 and 20 kW/s throughout the year although it is significantly modulated by the south-west monsoon which falls between May and September thus increasing the power up to around 30 kW/m. The inter-annual to decadal scale variability of wave power resource remains small. Wave power reduces when waves travel from the margin of the narrow continental shelf around Sri Lanka to shallow water areas closer to the shoreline. A significant longshore variability of wave power is also observed where the south-west coast of Sri Lanka has the highest available power under the prevailing ocean climate

Coastal flood alleviation through management interventions under changing climate conditions

PurposeCoastal flooding has disastrous consequences on people, infrastructure, properties and the environment. Increasing flood risk as a result of global climate change is a significant concern both within the UK and globally. To counter any potential increase in future flooding, a range of potential management options are being considered. This study aims to explore future coastal management practice for flood alleviation, incorporating the influence of climate change.Design/methodology/approachThe Taf estuary in South West Wales, a macro-tidal estuary which has a history of coastal flooding, was chosen as the case study in this paper to investigate the impact of coastal management interventions such as construction of hard defences, managed realignment or altering land use of affiliated ecosystems such as salt marshes on the complex hydrodynamics and hence flooding of the surrounding areas of the estuary. The study was carried out using a numerical hydrodynamic model of the Taf estuary, developed using the process-based Delft3D modelling software.FindingsThe role of the selected management interventions on coastal flooding was investigated using an extreme storm condition, both with and without the impact of future sea level rise. The results highlight the scale of the effect of sea level rise, with the selected management interventions revealing that minimising the increase in flooding in future requires careful consideration of the available options.Originality/valueThis paper explores the highlighted role of coastal management practice in future with the influence of climate change to study how effective alternative methods can be for flood alleviation

Modelling nonlinear responses of a desert rodent species to environmental change with hierarchical dynamic generalized additive models

Modelling abundance fluctuations of species is a crucial first step for understanding and forecasting system dynamics under future conditions. But, especially in multivariate response data, this can be hampered by characteristics of the study system such as unknown complexity, differently formed spatial and temporal dependency, non-linear relationships, and observation characteristics such as zero-inflation. This study aimed to explore how such challenges can be addressed by using hierarchical Dynamic Generalized Additive Models (DGAM) for multivariate count responses in a Bayesian framework while modelling multi-site monthly captures for the Desert Pocket Mouse (Chaetodipus penicillatus) over 23 years from a long-term study in Arizona, USA. By fitting models of increasing complexity and developing bespoke checking functions that captured targeted ecological aspects such as spatio-temporal dependence, we show how nonlinear dynamic models can be built to improve forecasts for multivariate count-valued time series.We found strong evidence that accounting for non-linear and time-lagged effects of as much as 12 months improved model fit and forecasting performance. Evaluation of models for other species in geographically different habits is essential for generalizing model strategies and insights into long-term abundance-environment relationships, while systematic comparisons will only be possible if multivariate modelling workflows account for the complexity of non-linear and lagged effects and potentially also other aspects such as biotic interactions

Modelling compound flooding: a case study from Jakarta, Indonesia

The paper investigates compound fooding from waves, sea surge and river fow in northern Jakarta, Indonesia, which is a global hotspot of fooding, by combining process-basedcoastal and river models. The coastal hydrodynamic modelling of Jakarta Bay in Indonesiashows that coastal storms can lead to a substantial increase in sea water level due to windand wave setup in the nearshore areas, including Muara Angke river inlet. The compoundfood hazard from a range of food scenarios was simulated and analysed. The results revealthat low-lying areas around the river inlet are prone to fooding even during regular, lowintensity storm events, while rarer storms caused extensive foods. Floods were not causedby direct overwashing of sea defences but by overspill of the banks of the river inlet due tohigh sea water level caused by wind set up, wave setup, and sea surge obstructing the drainage of the river and elevating its water level during storms. We also found that the sea levelrise combined with rapid land subsidence will inundate the existing coastal food defencesduring storms in future. The majority of the city will be below mean sea level by 2100. Theoverfow of existing coastal defences will lead to extensive fooding in northern, western,and eastern Jakarta unless the defences are upgraded to keep up with future sea level rise

Gravel Barrier Beach Morphodynamic Response to Extreme Conditions

Gravel beaches and barriers form a valuable natural protection for many shorelines. The paper presents a numerical modelling study of gravel barrier beach response to storm wave condi-tions. The XBeach non-hydrostatic model was set up in 1D mode to investigate barrier volume change and overwash under a wide range of unimodal and bimodal storm conditions and barrier cross sections. The numerical model was validated against conditions at Hurst Castle Spit, UK. The validated model is used to simulate the response of a range of gravel barrier cross sections under a wide selection of statistically significant storm wave and water level scenarios thus simulating an ensemble of barrier volume change and overwash. This ensemble of results was used to develop a simple parametric model for estimating barrier volume change during a given storm and water level condition under unimodal storm conditions. Numerical simulations of barrier response to bimodal storm conditions, which are a common occurrence in many parts of the UK were also investigated. It was found that barrier volume change and overwash from bimodal storms will be higher than that from unimodal storms if the swell percentage in the bimodal spectrum is greater than 40%. The model is demonstrated as providing a useful tool for estimating barrier volume change, a commonly used measure used in gravel barrier beach management

Reflection Analysis of Impermeable Slopes under Bimodal Sea Conditions

Understanding of the reflection characteristics of coastal seawalls is crucial for design. Wave reflection can cause difficulties in small vessel manoeuvring at harbour entrances; this can cause damage to the toe of coastal structures by scouring. Previous studies have examined the reflection characteristics of coastal seawalls under random wind-generated waves without considering the effects of wave bimodality created by the presence of swell waves. This present study focuses on the influence of random wave bimodality on the reflective characteristics of coastal seawalls. 823 experimental tests were conducted to examine the reflection performance of impermeable sloping seawalls under bimodal waves. Reflection coefficients were computed from each test. The analysis of the results suggests that both unimodal and bimodal waves give similar reflection characteristics. However, the reflection coefficient in bimodal sea states seems to be more prolonged than in the unimodal sea states. It was found that the reflection coefficients of coastal seawalls are strongly influenced by the seawall slope, the wave steepness, the relative water depth, and the surf similarity parameters. A new empirical reflection equation to describe the influence of wave bimodality on the reflection characteristics of coastal seawalls has been formulated based on this study

The cumulative impact of tidal stream turbine arrays on sediment transport in the Pentland Firth

This contribution investigates the impact of the deployment of tidal stream turbine arrays on sediment dynamics and seabed morphology in the Pentland Firth, Scotland. The Pentland Firth is arguably the premier tidal stream site in the world and engineering developments are progressing rapidly. Therefore understanding and minimising impacts is vital to ensure the successful development of this nascent industry. Here a 3 dimensional coupled hydrodynamic and sediment transport numerical model is used to investigate the impact on sediment transport and morphodynamics of tidal stream arrays. The aim of the work presented here is twofold: firstly to provide prediction of the changes caused by multiple tidal stream turbine array developments to some of the unique sandy seabed environments in the Pentland Firth and secondly as a case study to determine the relationship between impacts of individual tidal stream farms and cumulative impacts of multiple farms. Due to connectivity in tidal flow it has been hypothesized that the cumulative impact of multiple arrays on sediment dynamics might be non-linear. This work suggests that, for the Pentland Firth, this is not the case: the cumulative impact of the 4 currently proposed arrays in the area is equal to the sum of the impacts of the individual arrays. Additionally, array implementation only has minimal effect on the baseline morphodynamics of the large sandbanks in the region, smaller more local sandbanks were not considered. These two results are extremely positive for tidal stream developers in the region since it removes the burden of assessing cumulative impact from individual developers and suggests that impacts to sub-sea morphodynamics is insignificant and hence is unlikely to be an impediment to development in the Pentland Firth with the currently proposed levels of extraction

Analysis of multi-scale morphodynamic behavior of a high energy beach facing the Sea of Japan

Monthly cross shore beach profiles measured at the Ogata Wave Observation pier located in Joetsu-Ogata Coast, Niigata Prefecture, Japan, was analysed to investigate multi-scale morphodynamic beach behaviour. The Ogata beach, facing the Sea of Japan, is subjected to high energy wave conditions with that has a strong winter/summer seasonal signature. The measured beach profiles at the beach show very significant variability where cross-shore movement of shoreline position and lowering of the beach at the location of measurements exceed 20 m and 4 m respectively. The shoreline position seems to follow the seasonal variability of incident wave climate where a correlation coefficient of 0.77 was found between monthly averaged incident significant wave height and the measured monthly shoreline position. During the summer months, the beach variability mostly concentrated to in the sub-tidal part of the profile, while a significant amount of upper beach change was observed during the winter months. The beach profile shape was found to rotate between three different beach states in time; (i) concave reflective profile; (ii) profile with sub-tidal berm; and (iii) gentle, dissipative profile. Empirical Orthogonal Function (EOF) analysis of the profiles show that the variability of beach profile shape is dominated by (a) upper shoreface steepening; (b) sub tidal berm development and dissipation; and (c) variability of the overall profile slope, which have some longer than seasonal cyclic signatures. Comparison of temporal EOFs with climate indices such as Southern Oscillation Index and Pacific Decadal Oscillation index shows notable some correlations between profile change and climatic variability in the region. The analysis also shows that the morphological variability of Joetsu-Ogata Coast has similarities and some distinct spatial and temporal differences to beaches of similar kind found elsewhere

Numerical modelling of hydrodynamic and morphodynamic response of a meso-tidal estuary inlet to the impacts of global climate variabilities

Tidal inlets, a common feature along coastlines globally, can be significantly affected by the impacts of global climate variabilities. Computational models provide the best opportunity to assess future changes to the dynamics of inlet systems. In this paper, the morphodynamic response of a gravel-dominated meso-tidal estuary inlet to Sea Level Rise (SLR) is discussed based on three future SLR scenarios. It uses a process-based computational coastal area model. The study's test site is the meso-tidal Deben Estuary inlet in the UK; it is very morphodynamically active and has a unique sediment environment, is used as the test site of this study. The modelling results reveal that the morphological response of Deben inlet is sensitive to the SLR scenario. Rising sea levels give rise to increased hydrodynamic and morphodynamic activities at and around the inlet. The ebb delta, which is a prominent morphodynamic feature of this inlet, shows greater instability as a result of increased sea levels. It is possible that the inlet may deviate significantly from its current morphodynamic regime in the future as a result of the changes imposed by higher sea levels

Forecasts of seasonal to inter-annual beach change using a reduced physics beach profile model

Seasonal to inter-annual variability of beach profiles has been investigated using a one dimensional beach profile model developed on the ‘reduced-physics’ modelling approach. The model uses a diffusion formulation as the governing equation and adopts an inverse modelling technique for solving the equation. The model was applied to Hasaki Beach in Japan to investigate medium term beach change. Hasaki beach is longshore uniform and characterised by a highly dynamic longshore bar-trough system. Seasonal to inter-annual scale beach change was then forecasted using the model. The results are compared with beach change determined from measured beach profiles at Hasaki between 2007 and 2011. The simple modelling approach used yields encouraging results of seasonal to inter-annual scale beach change at Hasaki Coast