Assessing the Impact of Climate Change on Extreme Hydraulic Head Levels and Dry-Wet Cycles Of Dutch Canal Dikes

Canal dikes in low-lying polders worldwide are critical earth structures for flood protection. Historically, inner-slope instabilities have been triggered by extreme dry and wet subsurface water conditions. Additionally, cyclic wetting and drying affect the dikes' resistance through mechanisms such as swelling and shrinkage, shear-strength reduction and soil consolidation. To accurately estimate failure probabilities of canal dikes, quantifying extreme hydraulic head levels and the magnitude of dry-wet cycles is crucial. However, there is limited understanding of changes in extreme head levels and the dry-wet cycles under climate change. This study assessed the impact of climate change on extreme hydraulic head levels and dry-wet cycles of canal dikes and how it varies across different dikes. This is done by analyzing dry-wet cycles and extreme head levels at three canal dikes in the Netherlands using both observations and models. Head observations from three monitoring sites provided data for developing time series models. By forcing 30 years of precipitation and evaporation to these models, extreme head levels and dry-wet cycles were derived. This was done under different climate scenarios to quantify the impact of climate change. It was found that the impact of climate change has a more pronounced effect on extreme low head levels than on high ones for the dikes considered. By 2100, extreme low levels could decrease by up to half a meter in drying scenarios, potentially shifting events from a 100-year frequency to every 2 years. Climate change also amplifies dry-wet cycles in canal dikes, with increases of up to several decimeters. In general, dikes with higher peak head responses and longer response times are more affected by climate change, emphasizing the importance of considering site-specific factors when evaluating canal dike stability under future climate conditions.

Keywords: Dike safety, Time series models, Hydraulic heads, Extreme loadings, Droughts and floods, Dry-wet cycles.