In this report, the influence of the location of the weir in the Ems estuary on the water motion and sediment dynamics has been investigated using an idealised analytical model. The water motion is described by the width–averaged shallow water equations, and the sediment dynamics by a width–averaged advection–diffusion equation with sinks and sources. For an extensive discussion of the model equations, see Chernetsky et al. (2010).
If the length of the estuary would be increased to 90 km, using parameter values representative for the Ems estuary in 2005, the model results suggest that
• the character of the tidal wave changes from a standing wave into a travelling wave.
• the lowest low water level will increase with approximately 60 cm and the highest water level will decrease with 70 cm, 60 km from Knock.
• the ebb velocity will increase to approximately 1 ms−1, while the flood velocity will not change significantly ( 95 cm s−1).
• changes in tidal asymmetry can not be inferred from changes in the sea surface elevations, but can only be deduced from an analysis of the velocity components.
• an increase of the length of the estuary by approximately 10 km would result in accumulation of fine sediment near Emden, instead of close to the weir.
We would like to stress that the results of idealised models, state–of–the–art numerical models and observations should be used in an integrated way. The power of state–of–the–art numerical models is that, after calibrating the model to observations, very detailed calculations of water motion and sediment dynamics under those system conditions can be carried out. However, parameter sensitivity studies are difficult to perform both due to limitations of computational time and the absence of observations for those conditions, necessary to calibrate the model. The power of idealised analytical models is that they are specifically developed to describe the changes in general patterns under varying system boundary conditions and parameter settings. This means that the predicted effects by idealised model(s) need to be carefully tested by state–of–the–art numerical models, and numerical models should qualitatively show the behaviour suggested by the idealised model. Therefore, under the given situation with respect to models, a combination of both types of models will lead to a clear synergy and the best possible results.