Pathways of Water and Sediment in the Biesbosch Freshwater Tidal Wetland

Diversion of water and sediment into drowning delta wetlands aims at renewed sediment accumulation for ecosystem regeneration and compensation of sea-level rise and soil subsidence. The success of such measures requires sound understanding of flow pathways and deposition patterns within wetlands and their feeding channels. This study aimed to (1) identify such pathways in a tidal freshwater wetland in the Netherlands, (2) determine the relative contribution of the two feeding rivers (Rhine and Meuse) to the water and sediment budget and (3) explore whether moving boat campaigns can contribute to a comprehensive understanding of the system. Bed level change was highest in newly developed areas, where equilibrium sets in. Sedimentation takes mainly place in channels close to the feeding rivers, where sediment becomes replenished each tidal cycle. Distal tidal channels receive only water poor in sediment during flood tide and experience erosion. Short term changes in suspended sediment load, measured during moving boat campaigns were generally consistent with average long-term changes in bed level. This means that short-term field measurements can not only be used to explain the processes, but also to predict the longer-term development of the major part of the study area.