Development of a low-cost methodology for data acquisition and flood risk assessment in the floodplain of the river Moustiques in Haiti

Over the past two decades, Haiti was struck by 30 storm events and 40 floods, affecting over 3.5 million people. Being the poorest country in the Northern hemisphere, it is unable to allocate funds to risk assessment and management. Therefore, this research developed a low-cost methodology to analyse flood risk in data-sparse regions. The floodplain of the river Moustiques was chosen as study area. First, a methodology was developed and input data were gathered from existing data, literature, field data, and open source data. Then, a flood risk assessment was performed for the area. The resulting economic risk map and social risk map indicate that the region is at risk for nearly 2 million USD and has potentially 60 casualties per year. Although the assessment was performed as a quantitative analysis, the resulting maps should be interpreted qualitatively, as the values could not be validated. Nonetheless, the results clearly indicate the high-risk areas where measures should be taken. Furthermore, this research shows the potential of citizen science, in the form of a questionnaire survey conducted in the floodplain. This low-cost and fast acquisition method provided many different input data for flood risk assessment, from population data to damage factors and validation information on historic flooding

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

Analyzing the sensitivity of a flood risk assessment model towards its input data

The Small Island Developing States are characterized by an unstable economy and low-lying, densely populated cities, resulting in a high vulnerability to natural hazards. Flooding affects more people than any other hazard. To limit the consequences of these hazards, adequate risk assessments are indispensable. Satisfactory input data for these assessments are hard to acquire, especially in developing countries. Therefore, in this study, a methodology was developed and evaluated to test the sensitivity of a flood model towards its input data in order to determine a minimum set of indispensable data. In a first step, a flood damage assessment model was created for the case study of Annotto Bay, Jamaica. This model generates a damage map for the region based on the flood extent map of the 2001 inundations caused by Tropical Storm Michelle. Three damages were taken into account: building, road and crop damage. Twelve scenarios were generated, each with a different combination of input data, testing one of the three damage calculations for its sensitivity. One main conclusion was that population density, in combination with an average number of people per household, is a good parameter in determining the building damage when exact building locations are unknown. Furthermore, the importance of roads for an accurate visual result was demonstrated

Risk assessment in the Caribbean: modeling a GIS-based Flood risk Tool for Jamaica

The Caribbean is known to be one of the most hazard-prone regions in the world. Although the growing intensity of these disasters increases the concern of decision makers, researchers have not yet succeeded in developing an accurate multi-hazard risk assessment tool to locate the high-risk areas. Many single-hazard risk analyses adequately estimate the risk of one hazard, but the complexity of the relation between the different types of hazards causes difficulties in developing one risk analysis to assess all hazards. This research aims to develop such a model for the Caribbean. In a first step, a flood risk tool was developed for Jamaica. After optimizing this tool, the methods will be used for other hazard types. In a final step, all single-hazard tools will be combined into one multi-hazard risk assessment. To generate the flood risk tool, a new methodology based on minimizing risks rather than building water defences, was used. In the Flemish Region in Belgium, this method is already used in a tool called LATIS, and has proven that using a risk-based methodology helps tremendously in finding the most cost-efficient measures to reduce risk. For Jamaica, the lack of data was and is a big concern. Since there was only minimal rainfall data available, flood hazard maps could not be generated. Therefore, a risk map could not yet be computed, only a vulnerability map and a damage map could. Furthermore, the available damage functions did not cover all elements at risk. Before regenerating the damage map, these functions will have to be reassessed. However, the vulnerability map that was produced shows promising results in indicating the high-risk areas, which are the most important factor in the decision making process. Further research will focus on the flood hazard maps and the damage functions, before applying this method to other natural hazards

Development of a 3D dynamic flood WebGIS 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 public's 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

Flood risk mapping worldwide : a flexible methodology and toolbox

Flood risk assessments predict the potential consequences of flooding, leading to more effective risk management and strengthening resilience. However, adequate assessments rely on large quantities of high-quality input data. Developing regions lack reliable data or funds to acquire them. Therefore, this research has developed a flexible, low-cost methodology for mapping flood hazard, vulnerability and risk. A generic methodology was developed and customized for freely available data with global coverage, enabling risk assessment worldwide. The default workflow can be enriched with region-specific information when available. The practical application is assured by a modular toolbox developed on GDAL and PCRASTER. This toolbox was tested for the catchment of the river Moustiques, Haiti, for which several flood hazard maps were developed. Then, the toolbox was used to create social, economic and physical vulnerability maps. These were combined with the hazard maps to create the three corresponding flood risk maps. After creating these with the default data, more detailed information, gathered during field work, was added to verify the results of the basic workflow. These first tests of the developed toolbox show promising results. The toolbox allows policy makers in developing countries to perform reliable flood risk assessments and generate the necessary maps