The aim of the risk analysis is to make statements on the extent of the flood risk through the combined consideration of hazard and damage potential. The risk analysis shows the existing need for action and provides the basis for the development of precautionary measures by identifying high-risk areas and objects. Particular attention is paid to critical infrastructures and objects.
Method
A high flood risk is given at locations where there is a high flood hazard (e.g. in the form of high water levels) and at the same time an object with a high damage potential (e.g. a hospital). The assessment of the risks to human health, the environment, cultural heritage, infrastructure facilities, and other objects is based on a qualitative assessment in four classes according to DWA-M 119: low, moderate, high, very high. If an object or area is not exposed to the hazard, the damage potential does not become damage and the risk is zero. In principle, the greater the water depths and flow velocities are at the object/area, the higher the risk. The risk analysis can be carried out in different ways (simplified, detailed, or object-specific), which can be differentiated according to the level of detail and effort involved as well as their purpose. In the simplified risk analysis, buildings and areas are only characterized and assessed based on how close they are located to a flooded area, taking water levels into account. The damage potential is not considered. The detailed risk analysis determines the risk with a combination matrix in which the flood hazard and damage potential are combined, see table below.
Tab.1: Flash flood risk matrix (combinatation of hazard and damage potential).
Challenges
Creating flash flood risk maps can present various challenges. The accuracy of the risk analysis depends on the accuracy of the hydraulic modelling results and the quality of the damage potential analysis. So, it is mostly dependent on the data availability and quality of input data like digital elevation model (DEM), building polygons, building use etc.
Flash flood risk map
The results of the risk analysis are visualized in a map, which shows the risks identified for infrastructure, critical objects, buildings, areas and additionally the extent of flooding and the water depth in the study area. Depending on the size of the study area, it may be advisable to produce detailed maps in addition to overview maps for the entire area. This will ensure that both the overall events and small-scale results are clearly visible in the finalised maps.
Fig.1: Flash flood risk map for Downtown Amman.
Flash flood risk maps Amman
Risk map Amman (complete) Baseline rainfall scenario
Risk map Amman (complete) Moderate rainfall scenario
Risk map Amman (complete) Intense rainfall scenario
Risk map Amman (complete) Catastrophic rainfall scenario
Risk map Amman (Downtown) Baseline rainfall scenario
Risk map Amman (Downtown) Moderate rainfall scenario
Risk map Amman (Downtown) Intense rainfall scenario
Risk map Amman (Downtown) Catastrophic rainfall scenario
Flash flood risk maps Wadi Musa
Risk map Wadi Musa Baseline rainfall scenario
Risk map Wadi Musa Moderate rainfall scenario
Risk map Wadi Musa Intense rainfall scenario
Risk map Wadi Musa Catastrophic rainfall scenario
References
- DWA, 2016: German Guideline, DWA-Merkblatt 119. Risikomanagement in der kommunalen Überflutungsvorsorge für Entwässerungssysteme bei Starkregen (Risk management in municipal flood prevention for drainage systems during heavy rain), DWA German Association for Water, Wastewater and Waste, e.V., Hennef, ISBN: 978-3-88721-393-0.