Growing dikes: Optimization of layer thickness for ripening of dredged sediment on dikes

In the Netherlands, where approximately 1500 km of dikes require raising and strengthening to address climate challenges, a pilot experiment was conducted by the “Growing Dike” consortium. This collaborative effort, involving research institutes and the public sector, focuses on leveraging dredged and locally available sediment to reinforce dikes efficiently and sustainably, particularly along river areas. Two scenarios were tested: 1) 3 cm layer sediment on 4 cm long vegetation and 2) 6 cm layer sediment on 20 cm long vegetation. The freshly dredged sediment from a harbor was diluted with fresh water to a workable density before it was applied to the dike test sections. The sediment was placed on the field experiment dike test sections to the required initial sediment layer thickness on top of the initial vegetation length. The evolution of the water content, organic content, ions dissolved in the water-sediment mixture and sediment layer thickness was measured. By comparing the results, it is seen that for scenario (1), the sediment layer thickness reduces with 70% within 6 days and maintains a constant thickness. For scenario (2), the sediment layer thickness reduces with 60% within 14 days before it reaches a constant thickness. The results of the sediment layer thickness reaching a constant thickness coincides with the water content evolution. The organic matter content results in the sediment layers showed a slight increase in time as the sediment oxidized on the dike. The results also shown that most ions which was measured increased as time advanced. The initial mowed vegetation on the dike for both scenarios recovered rapidly and was able to grow through the sediment layers. Overall, this study represents a significant step towards utilizing dredged sediment for dike reinforcement, contributing to circular economy and flood protection initiatives in the Netherlands and beyond.