Towards a consistent suite of models for flood risk management.

Robert Slomp, Ferdinand Diermanse, Hans de Waal, Jan Stijnen, Jan Noort, ludolph wentholt

Monday 29 june 2015

15:20 - 15:35h at Asia (level 0)

Themes: (T) Special session, (ST) Flood defences and flood risk: hydraulic engineering aspects

Parallel session: 2E. Special session: Flood Risk and Flood defences

Consistent national flood-risk management is only possible if the tools to analyse and implement policy are consistent. However, policy tools, flood defence assessment tools, design tools, flood forecasting tools have different requirements for computation times, accuracy, and spatial and temporal scale. Another challenge is that the instruments commissioned by the national water authority (Rijkswaterstaat), or the regional water authorities (water boards) have been developed by different (sub)contractors. The responsibility for the national waters is with the national government, while the STOWA (the training and research organisation for the regional water authorities) and provincial governments are responsible for the regional water systems. Facing this problem, the national and regional water authorities greatly reduced the number of separate instruments and achieved a fairly well-organized set of instruments and data for some main types of analyses during the past years: • The same hydrodynamic models for water levels, and wave propagation are used. • In the last 5 years probabilistic instruments have been used to calculate hydraulic loads for both the national water systems (Hydra-model suite), and the regional water systems (PROMOTOR). • The instrument to assess the strength regional flood defences (DAM) has been used for policy analysis of the national flood defences (3600 km) as well. • Indicators for policy tools have been provided using these tools. The national and regional water authorities have to be flexible, and should be able to use, adapt, and expand the instruments to cope with new policy questions. However, there is a major drawback to keep developing new tools for every policy question: the danger of inconsistencies. Therefore the national water authorities aims at the development of reusable, common software components. Consistent models are important for long term and short term policy choices and the evaluation of measures, and for explaining the level of a flood alert. Inconsistency definitely costs money and may cost lives.