Dikes are a primary defence against flooding from the rivers and sea in the Netherlands, but many no longer meet current safety standards. To ensure the dikes keep meeting the safety standards in the future, climate change will need to be taken into account. Increase in river discharge and upstream water levels through rising temperatures, more frequent extreme precipitation, and increasing meltwater run-off, are climate uncertainties that pose additional challenges for dike reinforcement projects. One critical failure mechanism requiring attention is backward erosion piping (BEP), which has historically been underestimated. Over the past decade research has advanced the knowledge on BEP and led to innovative solutions to mitigate this risk, each based on different working principles and associated with distinct performance characteristics and life cycle costs. However, it is currently unclear how the design, performance, and cost-effectiveness of these solutions compare under climate change uncertainties.

This study evaluates the design performance and life cycle of three piping solutions, both innovative and conventional, under climate change uncertainties. Using a numerical model in COMSOL Multiphysics, the performance of each solution is assessed through fragility curves based on the relevant failure criterion for each solution. Due to the different working principles, the fault trees differ between the solutions. The failure criterion for each solution is based on the critical step they tackle in the fault tree that leads to piping failure. Climate impact uncertainties are represented by considering different future climate scenarios. Using Hydra-NL, water levels for different return periods and future scenarios, including both moderate and high-emission pathways, are calculated. The resulting probabilities of the water levels and the conditional failure probabilities from the fragility curves are used to determine and quantify the timespan of the life cycles. The life cycles are evaluated in terms of cost and their sensitivity
to design and climate uncertainties is assessed. This assessment is done with a life cycle cost analysis using the Equivalent Annual Cost (EAC) method.

The results show that while the sheet pile and plastic filter screen exhibit similar performance in preventing hydraulic heave, their sensitivity to rising water levels differs, with the filter screen performing slightly better under extreme conditions. The SoSEAL barrier demonstrates lower sensitivity to high water levels but exhibits higher failure probabilities at lower water levels due to heterogeneity in the barrier’s hydraulic conductivity and contact zone effects. It is emphasised that the plastic filter screen and SoSEAL barrier have inherent uncertainties due to their innovative designs. Reducing these uncertainties in the future can significantly increase the performance and make them competitive alternatives to conventional solutions like the sheet pile. The life cycle cost analysis indicates that the sheet pile is currently the most cost-effective solution and least sensitive to the uncertainties across the different scenarios, followed by the filter screen and SoSEAL barrier. Cost uncertainties, particularly in annual maintenance & monitoring, were found to influence the performance more than climate uncertainties. Constant yearly costs, resulted in lower values of equivalent annual costs for longer lifespans, while annually increasing costs produce higher values for longer lifespans, stressing the importance of accurate cost forecasting. Furthermore, the results highlight the trade-offs between the technical and functional lifespan, suggesting that increasing annual costs can offset the benefits of extended design life. In the future, the uncertainties in the design-related expenses for the innovative solutions will decrease. The amount and range of the yearly costs will then decrease with time, increasing the cost-effectiveness of the SoSEAL barrier and plastic filter and decreasing their sensitivity to future uncertainties.

This study concludes that the performance of the different piping solutions is influenced by both design and climate change uncertainties. Varying lifespans and annual costs significantly affect the performance of the solutions across different scenarios and have a even greater impact than the uncertainties of climate change. Life cycle cost variability underscores the need for considering economic uncertainties alongside the uncertainties in technical performance into current decision-making processes. Decreasing these uncertainties in innovative solutions could improve their performance and make them suitable alternatives in the evaluation and comparison of different solutions. ... Read more

The Vietnamese Mekong Delta, a vital region in the country’s economy, faces the dual challenges of coastal erosion and mangrove degradation, which threaten its long-term sustainability and flood protection capabilities. This research focuses on the coastal area of the Bac Lieu province, characterized by severe erosion and degrading mangrove forests. The study investigates the applicability and potential impacts of hydraulic measures to decrease the net rate of coastal erosion, utilizing numerical modeling with Delft3D and a comprehensive socio-economic analysis. The research hypothesizes that the coastal erosion is partly driven by the placement of a sea-dike to protect aquaculture farms, initiating a positive feedback loop. This loop explains the relation between coastal erosion and mangrove degradation. The proposed hydraulic measures to interfere with this feedback loop are a porous detached breakwater, a shoreface nourishment and the removal of the existing sea-dike. The socio-economic analysis involves questionnaires for local residents, field investigations, and insights from experts in Ho Chi Minh City. While the questionnaires provide inconclusive results, the overall socio-economic impact of the nourishment and breakwater is deemed positive and worth further exploration, particularly in light of the critical role of mangroves in future flood protection. On the other hand it is concluded that the measure of removing the sea-dike will have a negative impact on the coastal area of Bac Lieu due to the intensive land-use and the lack of individual protection of the farms and villages. Therefore, this measure is not modelled. Numerical modeling with Delft3D assesses the hydraulic impact of the breakwater and nourishment on the heavily eroded and partially eroded coasts of Bac Lieu. Results indicate that the nourishment method exhibits a positive effect in reducing net erosion, especially in low energy conditions. Conversely, the porous breakwater shows minimal impact on cumulative erosion and sedimentation. Since this is against all expectations, the validity of the schematization of the porous breakwater is questioned. It is observed that the schematization does not grasp the complex behaviour of the breakwater and therefore it is concluded that Deft3D is not a suitable modelling tool for modelling a porous breakwater. The findings suggest that the nourishment method is a promising approach for reducing erosion in Bac Lieu, benefiting both the heavily and partially eroded coasts. To determine the best course of action for Bac Lieu, further research into the long-term effects and configurations of nourishment is recommended. Additionally, informing local inhabitants on the threats of relative sea-level rise and flood protection, and fostering consensus between the government and engineering agencies on the importance of protecting the Mekong Delta and its mangrove ecosystems are essential steps toward a more resilient future. ... Read more