Long-term morphological modelling of the mouth of the Columbia River

Abstract

With the construction of a process-based long-term morphological model (Delft3D) for the Mouth of the Columbia River (MCR), a first approach is made in trying to simulating the long-term morphodynamics of the MCR. Focus is on simulating the observed morphological changes for the post-jetty period of 1926-1958. The model is supplied with a high-resolution schematisation of river discharge and wave conditions in combination with a representative tide. Seasonal variations of the forcing conditions and their joint probability of occurrence are accounted for. Morphological acceleration techniques allow the simulations to stay with acceptable computation times. General patterns of erosion and sedimentation as a result of jetty construction as well as general bed level developments are represented by the model. Both the model and the observations show that jetty construction pre-dominantly pushed sediments from the inlet and the inner delta onto the outer delta. Differences in quantity and orientation are however present between the observations and the model. Despite the application of lower limit sediment transport calibration factors, a general overestimation of the morphological change is computed. Also, a wider and shallower inlet channel develops in the model. The interaction of the MCR with the adjacent coast is modelled to a limited extent only. Certain morphologically important physical processes may therefore still be missing in the model. The representation of forcing conditions responsible for morphological change at the MCR allows for optimization. Even though model results in this study do not fully simulate the observed morphological changes of the MCR yet, an important first step has been taken in the goal of simulating the long-term morphological change of the complex coastal area of the MCR. The products of this study provide a valuable base for continuing research.