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Please read instruction file "readme.txt" at first. Instructions for data repositories of paper entitled "Divergence of sediment fluxes triggered by sea-level rise will reshape coastal bays". 1. Field data, 2. Model results,3 .Notes

Please read instruction file "readme.txt" at first. Instructions for data repositories of paper entitled "Divergence of sediment fluxes triggered by sea-level rise will reshape coastal bays ". 1. Field data, 2. Model results,3 .Notes

Infragravity (IG) waves are long period waves with frequencies lower than wind-waves and swell, usually in the frequency band 0.003 to 0.05 Hz. IG waves are known to dominate hydrodynamic and sediment transport processes close to the shoreline on low sloping sandy beaches, especially when the incoming swell and wind-driven waves (incident waves) are large. However, in extreme wave conditions, how their importance varies on coarser grain sized and steeper beaches, and with different mixes of incoming swell and wind-waves, is largely unknown. Here, a new dataset comprising in-situ and remote observations from five contrasting sites (one low-sloping sandy beach, two steep gravel beaches and two compound/mixed sand and gravel beaches), under extreme wave conditions is used to assess infragravity response across a wider range of wave heights & periods, beach slopes and grain sizes than has been previously explored. The beaches studied ranged in slope from tanβ = 0.02 – 0.35 with median grain sizes (D50) of between 0.25 – 60 mm. During the experiments significant wave heights (Hs) of up to 7 m and peak periods (Tp) up to 20 s were observed. During the five storms recorded, waves in excess of the 95th percentile of the long-term record of Hs were observed at all sites, with waves representative of a 1-in-1, 1-in-5, 1-in-10, 1-in-20 and 1-in-40 year event at the five sites respectively. Video observations of a 1-in-40 year storm, ‘Emma’, impacting a steep gravel beach revealed that significant infragravity swash height (Sig) dominated over significant gravity swash height (Sg) at the shoreline when offshore wave height (H0) exceeded 1.5 m, where ‘dominance’ was defined by the ratio of Sig/Sg exceeding 1. Sig increased linearly with offshore wave height (H0), as has been reported in previously published field work on sandy beaches. However, for a given wave height, Sig was between one third and three times larger on the steep gravel beach than values quoted in the literature for sandy beaches. Observations collected on the steep gravel beach during storm ‘Emma’ were compared to data collected at an additional four sites (a low-sloping sandy beach, a second steeper gravel beach and two compound/mixed sand and gravel beaches). Sig at the shoreline in excess of 0.5 m was consistently observed at all five contrasting beaches. The largest infragravity swash heights were observed at the steeper gravel beach (Sig up to 11.4 m), followed by the low-sloping sandy beach (Sig up to 3.2 m), and the less steep gravel beach (Sig up to 2.6 m) and were lowest at the compound/mixed sites. Due to contrasting incident wave breaking and dissipation processes, infragravity frequencies were observed to be most dominant over gravity frequencies on the low-sloping sandy beach (Sig/Sg up to 4.4), occasionally dominant on the gravel beaches (Sig/Sg up to 2.5), and rarely dominant on the compound/mixed beaches (Sig/Sg up to 1.1). An existing equation commonly used to parameterize Sig on sandy beaches was tested on the new dataset, performing well on data from the sandy beach but less well on data from the gravel beach. An existing equation commonly used to parametrize runup on gravel beaches was modified to produce a new gravel specific parametrization of Sig, which performed well on the gravel sites and less well on the sandy site. Both equations performed poorly when applied to the dataset combining sand and gravel beaches. H02T, proportional to deep water wave power, was found to accurately predict Sig on both the sand and gravel beaches, demonstrating that, under extreme storm wave conditions, combined wave height and period are the main drivers of infragravity oscillations at the shoreline, with the beach morphology playing a secondary role. In-situ observations were collected seaward of the incident wave breakpoint by bed-mounted acoustic Doppler current profilers and through the surf zone by intertidal arrays of pressure transducers at two of the five sites (the low-sloping sandy beach and the less steep of the two gravel beaches). Analysis revealed that energy transferred to the IG band seaward of the surf zone at the sandy beach and landward of breakpoint at the gravel beach. The surf beat similarity parameter (ξSurfbeat) indicated that bound long wave release was the dominant IG wave generating mechanism on the low sloping sandy beach (ξSurfbeat < 0.05) whilst breakpoint forcing was the dominant mechanism on the steep gravel beach (ξSurfbeat > 0.1). The findings presented in this thesis highlight the importance of collecting field data over a wide range of conditions. When deep water significant wave height (H0) exceeds 2 m, IG energy dominates the inner surf zone and swash on both sand and gravel beaches. Therefore, in addition to their well-known importance on sandy sites, infragravity waves are also implicated in the inundation and erosion of gravel beaches during storms.

This thesis applies coupled regional models to address coastal flood risk management needs in hyper-tidal estuaries. The project aims to understand how tide-surge-wind-waves combine to increase flood and wave hazard at the coast, using the Severn Estuary, southwest England as an extreme example. Little previous research has considered the impact of tide-surge-wind-wave interaction on total water level in a hyper-tidal estuary. Numerical modelling tools can be used to predict the individual contributions of physical factors to total water levels and forms a key component of flood hazard assessment. However uncertainty can be introduced into model predictions due to inaccurate boundary forcing or representation of the physical processes which control the volume and rate water moves through a model domain. Uncertainties in model predictions lead to a wide spread of results within which exposure or impacts could occur. Similarly, a range of possible values exist for a single parameter which may cause errors in the definition of critical thresholds or presents challenges to emergency response planners. Sources of uncertainty in flood hazard assessments should be identified and quantified as sustainable coastal management requires confidence in the knowledge of any possible future changes to flood and wave hazard. The thesis utilises wave, ocean and meteorological observation and model hindcast data to simulate total water level and significant wave height using the Delft3D-FLOW-WAVE modelling package. The validated Severn Estuary model domain is used to investigate the sensitivity of extreme water levels to changes in event severity, timing of the peak of a storm surge relative to tidal high water and the temporal distribution of the storm surge component, and wave heights to changes in wind-wave direction, model coupling and forcing processes. Model outputs from Delft3D-FLOW-WAVE are viewed in the context of the source-pathway-receptor-consequence model to better understand the influence of coastal hazard uncertainty on flood and wave hazard. Event severity is the most important control on flood hazard, and concurrence of the sources of flood hazard generate greatest water levels along the coastline of the estuary. Estuarine morphology acts as a pathway for flood hazard, as funnelling effects control the spatial variability of flood hazard and amplify surge magnitude up to 255% up-estuary. Surge predictions from forecasting systems at tide gauge locations could under-predict the magnitude and duration of surge contribution to up-estuary water levels. Wave height and wave period controls the response of wave generation and propagation to other factors. Wind speed generates greatest wave hazard, and uncertainty in wind and wave direction generate a large spread of results. Stronger, opposing winds steepen high amplitude, low period waves in the outer estuary and stronger, following winds enhance propagation of low amplitude high period waves up-estuary. The inclusion of locally generated winds is most important in regional models to continue to add momentum to the estuarine system, and model coupling processes (the representation of interaction between wave and currents) improve accuracy of flood and wave hazard predictions. Exclusion of locally generated winds can generate up to 1.45 m error in high water significant wave heights in the outer estuary, and 1.13 m error in the upper estuary. Coastal hazard uncertainty due to model coupling and forcing processes is propagated through the modelling chain to the two-dimensional inundation model LISFLOOD-FP to understand how changes in boundary condition and boundary position influences depth, extent and volume of inundation over a storm event. The exclusion of local atmospheric forcing increases coastal hazard uncertainty in the boundary forcing and under-predicts damage by up to £26.2 M at Oldbury-on-Severn. Once the threshold for flooding is exceeded, a few centimetres increase in coastal hazard conditions increases both the inundation and consequent damage costs for suburbia and arable land. The results of this thesis identify optimum model setups for simulating coastal flood hazard, which includes incorporating local atmospheric forcing and representing two-way interaction between waves and currents. Coastal hazard uncertainty can cause large variability in simulated total water level and wave heights, which has implications for flood damage assessments, shoreline management plans and emergency response plans. The research findings can aid long-term coastal defence and management strategies for improved public safety, and improve the timing and accuracy of early warning systems. Key sources of coastal hazard uncertainty have been identified here, e.g. the importance of storm surge timing relative to tidal high water and sensitivity of wave propagation to winds speeds, and these can be accounted for in future management plans. Utilising optimal model setups when predicting water level and wave height under current and future climate conditions can also help to increase confidence in results. Further to this, if the key sources of uncertainty which contribute to a large spread of results are known, e.g. exclusion of local atmospheric forcing, then this can be resolved in predictions which are used to inform early warning systems. The spread of model results can therefore be minimised to more accurately know who or what is in a flood or wave hazard zone.

The present project is an effort to identify key parameters and controlling factors of salinity variations in deltaic systems. The salinity’s driving mechanisms and response to hydrodynamic changes are under investigation. This is demanded because of the risks that these ecosystems are subject to by increases of salinity due to sea level rise and human activities. Numerical modelling is implemented to study the salinity distribution in idealized deltas configuration under various hydrodynamic conditions. In particular, variations of the river discharge and tidal levels are considered. The results indicate that salinity undergoes significant seasonal changes due to dynamic flow variability. Sustained drought periods could result in critical conditions with salt intrusion in the delta’s trunk (fluvial) channel. On the contrary, high river discharges during wet periods could mix completely the vertical column with freshwater for at least some distance from the river mouth. Tides could contribute further in mixing improving the conditions in the delta by decreasing the salinity in the downstream delta areas. Hence, many tidally influenced deltas could contain higher freshwater volumes than river dominated systems. Nevertheless, tidal level increases could limit significantly the deltas freshwater availability in mesotidal or macrotidal regimes. Results analysis and implementation of simple and innovative techniques uncovered the existence of certain correlations that could be useful as prognostic tools of salinity. Channels classification by their class or number of links provides a correlation that shows the salinity to increase with the decrease of either the channels order or delta’s cross-section width. In addition, radial and depth averages of salinity are negatively and exponentially correlated with the river discharge. The extracted exponential equation summarizes successfully the complex 3D delta dynamics into a 1D analytical solution. The equation resembles theoretical solutions of the 1D advection-diffusion equations under certain theoretical assumptions of which many are satisfied in the present idealized models setup. The above correlations incur modifications when external (e.g. hydrodynamic forcing) or intrinsic (e.g. bathymetry) parameters cause changes to the spatial salinity distribution. Bathymetric effects affect the salinity distribution in both horizontal and vertical directions especially at low flow periods when the bottom friction becomes stronger. Increases of the river discharge and/or tidal level override these effects. This study aspires to provide knowledge that could be useful for the development of technical or non-technical solutions for the aversion of salinization issues in deltas. With the goal of contributing to the efforts for the development of environmentally friendlier solutions, the last part of this work investigates the effect of different shape but equal volume hydrographs on the salinity. The results show that it is possible to alleviate the consequences of increased salinity by better management of existing water resources instead of seeking for additional ones.