DREDGING FOR FLOOD MANAGEMENT AND NAVIGATION IN RIVER SYSTEMS: OPPORTUNITIES AND DILEMMAS

摘要

Human interference has drastically changed fluviatile, deltaic and coastal hydro-morphological regimes. Normalisation of rivers and construction of embankments have reduced the supply of sediments to floodplains and deltas leading to erosion. Drainage, extraction of groundwater and changes in land-use for urbanisation, agriculture and industrialisation for growing populations have caused land subsidence in many coastal and deltaic zones. These increasing pressures make these areas more vulnerable for the consequences of climate change such as sea level rise, increased frequency of storms, and damage to ecosystems. Changes in seasonal precipitation may cause changes in sedimentation and erosion patterns leading to floods and droughts in river basins. Adaptation measures are absolutely necessary to overcome these challenges for which dredging is an important tool. This creates opportunities for the dredging sector. This paper focuses on the relations between flood protection measures and dredging for navigation in river systems. An example of flood management by making space for water is the Dutch programme Room for the River. River discharges are enlarged by a number of measures such as deepening, or widening of river beds, lowering of floodplains, construction of side channels and relocation of dikes. In general increase of flood conveyance capacity will lead to a decrease in flow velocity and increase in sedimentation. Other measures such as for the Water Framework Directive also have effects on the morphology of the river. More frequent dredging will be required to remove restrictions for navigation, which may lead to hindrance for navigation. The Dutch Rhine, an important transport axis from main port Rotterdam to Germany, will be presented as a case study. This case is further complicated by erosion of the river bed in the upstream part caused by measures for regulation and navigation. Erosion of the river bed results in bottlenecks for water management and navigation. In order to maintain the sediment balance it is required that sediments from dredging have to be relocated within the river system, but this does not solve the problem. Understanding of the hydro-morphological system is crucial to solve these dilemmas and find sustainable solutions. Also smart dredging methods are required to reduce hindrance for shipping.