Hanne Glas

DEVELOPMENT OF A 3D DYNAMIC FLOOD WEB GIS VISUALISATION TOOL

Low elevation coastal areas are vulnerable to the effects of sea level rise and to an increase in the frequency and severity of storm surge events due to climate change. Coastal urban areas are at risk because coastal flooding causes extensive damage to energy and transportation infrastructure, disruptions to the delivery of services, devastating tolls on the publics health and, occasionally, significant loss of life. Although scientists widely stress the compelling need to mitigate and adapt to climate change, public awareness lags behind. Because WebGIS maps (web-based geographic information systems) quickly convey strong messages, condense complex information, engage people in issues of environmental change, and motivate personal actions, this paper focusses on searching the ideal flood assessment WebGIS method to encourage people to mitigate and adapt to climate change. Surveys demonstrated that 3D visualisations have an enormous added value because they are more vivid and therefore more understandable and make it easier to imagine the consequences of a flood than 2D visualisations. In this research, the WebGIS will be created using Ol3-Cesium and open layers to visualise a flood event by dynamic layers in a 2D/3D environment.

A GIS-based flood risk tool for Jamaica: the first step towards a multi-hazard risk assessment in the Carribean

The Caribbean is known to be one of the most hazard-prone regions in the world. Hurricanes, flooding, storm surges, earthquakes and landslides lead to extensive material, human and economic losses in the region. The growing intensity of these hazards, combined with the consequences of climate change, rapidly increases the concern among decision makers. Although many researchers have succeeded in developing a single-hazard risk assessment that accurately estimates the risk of one type of hazard, the complexity of the relation between the different types of hazards is causing difficulties in the development of a multi-hazard risk analysis. This research aims to develop such a model. In a first step, the consequences of each type of hazard will be assessed individually, starting with riverine flooding. In the next step, the methodology used in this tool will be assessed and modified to fit other types of hazards. Finally, all single-hazard tools will be combined into a generic multi-hazard risk assessment tool for the region. In Jamaica, local governments use a flood risk methodology that is based on building water defence structures to evacuate the water as quickly as possible. This methodology, however, causes bigger damages downstream. Another method, based on minimizing the consequences of the overall flood, is already in use in many countries. In the Flemish region of Belgium, it is implemented in a tool called LATIS and has already proven to decrease losses after a flood event. Therefore, this risk-based methodology is used as the base for developing the Jamaican flood risk tool. The biggest concern during this research is the lack of data in the region. The methodology used, is based on the Flemish flood risk tool and the acquired data is thus very elaborate. During the implementation of the methods for the Caribbean, especially the lack of sufficient rainfall data and adequate damage functions has proven to result in less accurate damage and vulnerability maps.

The use of terrestrial laser scanning for measurements in shallow-water : correction of the 3D coordinates of the point cloud

Although acoustic measurements are a wide-spread technique in the field of bathymetry, most systems require a water depth of at least 2 m. Furthermore, mapping shallow-water depths with acoustic techniques is expensive and complicated. Over the last decades, the use of laser scanning for mapping riverbeds has increased. However, the level of accuracy and the point density which can be obtained by Airborne Laser Scanning (ALS), and Airborne Laser Bathymetry (ALB) in particular, are not as high as those of terrain measurements originating from ALS. Moreover, ALS and ALB are not yet suited for mapping shallow-water beds. Therefore, more recent research focuses on the use of Terrestrial Laser Scanning (TLS) from either a fixed or static position (STLS) or from a mobile platform (MTLS). An obvious advantage of using STLS and MTLS is that both the river beds and the river banks can be modelled by means of the same data acquisition system. This ensures a seamless integration of data sets describing both dry and wet surfaces, and thus of topography and bathymetry. However, although STLS and MTLS have the potential to produce high resolution point clouds of shallow-water riverbeds and - banks, the resulting point clouds have to be corrected for the systematic errors in depth and distance that are caused by the refraction of the laser beam at its transition through the boundary of air and water. In this research a procedure was implemented to adjust the coordinates of every point situated beneath the water surface, based on the refractive index. The refractive index depends on the wavelength of the laser beam and the properties of the media the beam travels through. The refractive index for a laser beam with a wavelength of 532 nm varies by less than 1% for a wide range of temperature and salinity conditions. Nevertheless, during the case studies, it became clear that it is important to use an estimate of the refractive index which approaches the actual value as closely as possible in order to obtain accuracies of less than 1 to 2 cm. Therefore, the refractive index was determined for each specific case by using water samples.