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Deltares | R&D Highlights 2015 Flood Risk
LiveDijken (‘live dikes’) are dikes equipped with sensor systems
to deliver real-time information about things like water levels inside the dike. The aim is to assess the actual strength of the dike and to provide additional information before and after improvements are made. Forecasting dike strength provides useful information in early warning situations to guide emergency responses: a specific flood warning is converted into specific measures such as dike reinforcements with sand bags, temporary protection of specific structures or evacuation.
In the Noorderzijlvest pilot project in the province of Groningen (NL), continuous monitoring and forecasting have been established for the strength of the dike system. This system consists of a combination of real-time data, information about the dike structure and behaviour, and calculations based on stability models. Water levels inside the dike are obtained with multiple pressure sensors distributed in several cross-sections of the pilot dike, the Ommelanderzeedijk. Dike stability is calculated on the basis of the phreatic line derived from the water levels and on the schematisation of the subsoil profiles. The resulting safety factor is a direct measure for the dike strength. Fragility curves are derived from the geometry and material properties of the dike profiles. The total fragility curve is calculated with a model-based probabilistic analysis for each failure mechanism considered: overflow, wave run-up, waterside erosion by waves, wave impact, piping, micro- and macro-stability. Total fragility represents a compact summary of the reliability of a dike section in relation to the water level outside the dike. In this way, forecasts of water levels make it possible to determine the probability of dike failure over time.
The two work flows of real-time monitoring and the forecasting of dike strength are being integrated in the FEWS-DAM Live software system. FEWS-DAM Live provides modules for managing the data monitoring and forecasting processes. It is therefore possible to visualise, for each dike section, the real-time and historical water levels measured by each sensor and the safety factor resulting from the stability calculations. The water levels forecast for the next 48 hours are transformed, on the basis of the fragility curve for each dike section, into a forecast time series of failure probability. Both the total probability of failure and the probability for individual mechanisms can be visualised for each section in FEWS-DAM Live. The results generated provide precise information for the purposes of the emergency response about the location, timing and probability of failure of defined sections of the flood defence line. On the basis of this information, emergency measures that apply to the flood defence line (such as more frequent inspections or temporary dike reinforcements) can be operationally planned, adapted to the situation and triggered.
Real-time monitoring and
forecasting of dike strength
Further reading: Bachmann et al. (2015): http://www. slideshare.net/Delft_Software_Days/ dsd-int-2015-fewsrisk-a-step- towards-riskbased-flood-forecasting-daniel-bachmann-54944078 daniel.bachmann@deltares.nl T +31(0)88 335 7520 michel.ponziani@deltares.nl T +31(0)88 335 7237
Time series showing the safety factor for dike stability and failure probabilities for an historical event
Fragility curve with total failure probability and partial fragility curves for different failure mechanisms
stability
standby level
measurement
