Programme for national flood defences: Assessment and action perspective for canal dikes

Rijkswaterstaat manages over 500 kilometres of regional flood defences, primarily canal dikes. Between 2018 and 2020, these flood defences were assessed for the first time against their water safety functions, following a specially developed guideline. In collaboration with Tauw, HKV, and WSP, Iv carried out this assessment for Rijkswaterstaat. This involved not only evaluating the dikes themselves but also examining all water-retaining structures and non-water-retaining objects.

For the defences that could not be fully approved for all failure mechanisms, we developed action perspectives. These perspectives outline the necessary works for each canal in the coming years. To achieve this, a more detailed safety analysis was conducted, refining the initial assessment by incorporating additional data and, for example, recalculating reference water levels. In some cases, we moved away from the often conservative assessment rules and provided an evaluation based on a failure pathway analysis.

Since the canal dikes had never been assessed before, limited information was available, and much of it still needed to be investigated. For instance, we conducted research into the presence of clay linings on the dikes and developed various methods to incorporate aspects such as residual width into the macro-stability assessments. Assessing hundreds of kilometres of flood defences required a smart approach, with multiple assessment teams working simultaneously on different canals or sections.

A weekly collaboration day brought together staff from the various firms and Rijkswaterstaat, ensuring clear communication, facilitating knowledge exchange, and enabling significant progress within a relatively short timeframe.

The assessment ultimately showed that approximately 70% of the dikes, 80% of the water-retaining structures, and over 95% of the non-water-retaining objects met the required standards. Using the assessment results and the detailed safety analysis, a scope for improvements was defined in the action perspective for the elements that did not comply. Together with the canal managers, we also interpreted the results and determined whether improvement measures were necessary, and if so, within what timeframe. These outcomes have provided Rijkswaterstaat with a clear understanding of the required improvements.