Author(s): Andreas Wurpts; Dennis Oberrecht
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Keywords: No Keywords
Abstract: The Ems estuary is a partially stratified mesoscale estuary in the northwest of Germany. In order to fulfill increasing demands for shipping, several deepenings and straightenings were carried out in the past. In turn, the turbidity zone shifted further upstream and at a given point in time, higher by one to two orders of magnitude concentrations of fine cohesive sediments accumulated, forming stable layers of fluid mud. The sedimentinduced density strongly interacts with the salinity driven estuarine circulation, also the high concentrated fluidsediment suspension exhibits non-newtonian flow behavior. As a result, the fluid mud forms layers of several meters thickness in the lower half of the water column. Those layers undergo cyclic transition during the tidal cycle and also over the annual turn. This strong sediment-induced stratification has major impact on several aspects of the estuary and its management: The ecological state suffers, mainly due to the strong decrease of dissolved oxygen concentration, but also navigational depth determination and related maintenance dredging get more difficult and expensive. The investigation shown here deals with an engineering approach that includes the continuous use of the existing Ems storm surge barrage in order to reduce the tidal asymmetry driven sediment transport behavior to a less flood dominated system. So far extensive model simulations as well as field tests have been carried out which show the strong potential of the approach to influence the estuary at large scale. The investigation is based on a three-dimensional hydro-morphological numerical modeling approach with an extension that transiently considers the complex behavior of the fluid mud-water mixture. The results show a reduction of tidal asymmetry, which provides a weaker formation of fluid mud layers in the turbidity zone of the estuary as well as increased net seaward transport of suspended sediment. The basic approach and annual variability and overall management considerations is shown.
Year: 2018