Can Mobile Phone Data Improve Emergency Response to Natural Disasters?

Peter Gething and Andrew Tatem discuss the potential impact of mobile phone positioning data on disaster response and highlight challenges that must be addressed if use of this technology is to develop

Wave fields in transitional water depth

Hydraulic structures are needed for the development of an oil reservoir in the North Caspian Sea. Witteveen+Bos are engineering these structures and need for this reason more insight in the wave boundary conditions at the locations Kashagan East (KE) and Kashagan West (KW). These wave boundary conditions are very specific since the North Caspian Sea has a small water depth that extends over a large area. The purpose of this study is to obtain more insight in wave spectra and wave height distributions at KE and KW during extreme conditions. Special interest goes to the wave parameters that are needed for input in the presently used design formula for rubble mound breakwaters. A SWAN model for the Caspian Sea has been developed to simulate wave fields under extreme conditions. The performance of the model is shown in the figures below. Remarkable is that the simulated mean wave period in SWAN seems to approximate the measured mean wave period for more extreme conditions. The SWAN model has been used to simulate wave fields for the 96 most extreme wind events in the period 1948 to 2000. Since water level fluctuations are significant in the North Caspian Sea the events were simulated for 5 different still water levels. The simulation results showed a depth-dependent wave height limit. It has been possible to define wave fields for return periods larger than 30 years as function of the water depth only. The most used parameters in design formula have been given as function of the still-water level. Furthermore design spectra have been produced for five different water levels. The shape of these spectra is between a JONSWAP spectrum and a TMA spectrum and varies with the water depth. A comparison of the found conditions with simulated design parameters from fetch-based wave growth models showed good similarity.Civil Engineering and Geoscience

Dune erosion during storm surges

Large parts of The Netherlands are protected from flooding by a narrow strip of sandy beaches and dunes. The aim of this thesis is to extend the existing knowledge of dune erosion during storm surges as it occurs along the Dutch coast. The thesis discusses: \u95 A large scale dune erosion experiment to obtain better insight in near dune hydrodynamics, sediment transport and the interaction between dune face and swash zone; \u95 Detailed models to study dune erosion physics, which are validated against measurements; \u95 A morphodynamic dune erosion model that includes the longshore direction and new physical insights. The model is applied in a variety of dune erosion conditions.Hydraulic EngineeringCivil Engineering and Geoscience

Dune erosion above revetments

In a situation with a narrow dune, the dune base can be protected with a revetment to reduce dune erosion during extreme events. To quantify the effects of a revetment on storm impact, the functionality of the numerical storm impact model XBeach (Roelvink et al., 2009) is extended to account for the complex morphodynamics around revetments. Here the focus is on dune erosion above revetments, which is simulated with a simple avalanching algorithm that is triggered by the combined runup of short waves and long waves. The simulated runup statistics depend on the incident wave groupiness and associated long wave variance.Hydraulic EngineeringCivil Engineering and Geoscience

Modelling aeolian sediment accumulations on a beach

This paper aims to conceptually simulate observed spatial and temporal variability in aeolian sediment transport rates, erosion and deposition on a beach. Traditional strategies of modeling aeolian sediment transport rates do not account for supply limitations that are common on natural beaches. A recently developed 1D linear advection model is used in which supply limitations are taken into account in a highly aggregated manner. It is shown that the model is able to simulate the appearance and disappearance of sediment accumulations. However, sediment accumulations alike observed in the field using ARGUS cameras behave on a different time and spatial scales.Hydraulic EngineeringCivil Engineering and Geoscience

The effect of longshore topographic variation on overwash modelling

This paper describes an application of the XBeach model to investigate the effect of longshore topographic variance on overwash. The model is used to simulate the morphological response of an eight-kilometer section of Santa Rosa Island, Florida, due to Hurricane Ivan (2004). The influence of longshore scales in the bed elevation is investigated by comparing the morphological response of the reference simulation to the morphological response of six sensitivity simulations in which the initial bed elevation was modified to remove longshore topographic variance. It is shown that the morphological response of the foreshore-foredune area to Hurricane Ivan is not influenced strongly by the initial longshore bed variance. The morphological response of the back barrier and the back barrier bay to Hurricane Ivan is influenced by features on the back barrier with longshore length scales of 100–500 meters, which hamper the flow across the island during inundation overwash. It is noted that these results may vary for other overwash regimes.Hydraulic EngineeringCivil Engineering and Geoscience

Dune erosion near sea walls: Model-data comparison

This paper describes the validation of the dune erosion model XBeach with laboratory measurement data of dune erosion in the presence of sea walls and revetments. Simulation results show that the essential dune set back processes are captured by the model and that the measurements at most locations are approximated quite well. Some aspects however need more attention in further research. The alongshore distance from a fixed structure over which the dune erosion is influenced was not well captured by the model. Also the absence of short wave run-up on the revetment still causes an underestimation of the amount of dune erosion above the revetment. Furthermore the influence of the angle of incidence was investigated with a conceptual model approach. This revealed a relatively high influence of the angle of incidence on the governing flow pattern in front of a transition between a dune and a fixed structure.Hydraulic EngineeringCivil Engineering and Geoscience

Morphological modelling of strongly curved islands

Land reclamations and island coasts often involve strongly curved shorelines, which are challenging to be properly modeled by numerical morphological models. Evaluation of the long term development of these types of coasts as well as their response to storm conditions requires proper representation of the governing physical processes. Not all types of numerical models are equipped to represent an entire island and allow waves from any direction. In this paper we demonstrate XBeach’s capabilities of plying a curvilinear grid around a small-scale circular island and exchanging model variables between the lateral boundaries by the recently implemented cyclic boundaries. The small-scale physical model tests by Kamphuis and Nairn (1984) were modeled with XBeach using both the stationary and the nonhydrostatic wave model on a rectangular as well as a curvilinear grid. The wing-bars that typically develop in Kamphuis’ tests are represented in the model, albeit that the angle of the bars is different. In a different XBeach model series, we investigate the behaviour of a larger scale curved coastline model under extreme storm conditions, for varying coastal radius. The results show that maximum erosion occurs at the locations where the incident wave direction is under an angle of 45 degrees with the coastline, and the coastal radius is of secondary importance.Hydraulic EngineeringCivil Engineering and Geoscience