“Water on the Street” app
The “Water on the Street” app gives an indication of water depths during extreme peak downpours in built-up environments. The water depths are displayed by reference to a pair of rubber boots that reflect a downpour’s local impact. Furthermore, the app comprises a map indicating local waterlogging, an indication of an area’s risk of being impacted, and an interpretation of the impact. The app presents three different situations, i.e., the impact of extreme downpours that fall once every 10, 100, and 1000 years. The calculations are based on the most recent precipitation statistics derived by HKV Consultants and the Royal Netherlands Meteorological Institute KNMI on behalf of the Foundation for Applied Water Research STOWA. The Current Elevation Model of the Netherlands (AHN2), subsoil water storage, the storage capacity of the sewer system, and superficial run-off have been taken into account in the determination of local water levels.
The underlying data is made available by HKV Consultants for the performance of stress tests and risk dialogues. They constitute a first step in the conceptualisation of the issues and the potential solutions. In addition to the impact on urban areas, the app also provides an indication of the impact on rural areas. Factoring in multiple causes affecting the frequency of waterlogging will improve the estimates regarding (acceptable) risks and costs of measures. The pros and cons can be weighed up in a risk dialogue, in which other criteria are also taken into consideration. Assessment frameworks, such as those developed for multi-layer flood risk management, can be of assistance in this process.