Abstract
The long-term prediction of morphological bed evolution has been of interest to engineers and scientists for many decades. Usually, process-based models are employed to simulate bed-level changes in the scale of years to decades. To compensate for the major computational effort required by these models, various acceleration techniques have been developed, namely input-reduction, model-reduction and behaviour-oriented modelling. The present paper presents a new input-reduction method to obtain representative wave conditions based on the Shields criterion of incipient motion and subsequent calculation of the sediment pick-up rate. Elimination of waves unable to initiate sediment movement leads to additional reduction of model run-times. The proposed method was implemented in the sandy coastline adjusted to the port of Rethymno, Greece, and validated against two datasets consisting of 7 and 20 and 365 days, respectively, using the model MIKE21 Coupled Model FM. The method was compared with a well-established method of wave schematization and evaluation of the model’s skill deemed the simulations based on the pick-up rate schematization method as “excellent”. Additionally, a model run-time reduction of about 50% was observed, rendering this input-reduction method a valuable tool for the medium to long-term modelling of bed evolution.
Highlights
The prediction of morphological bed evolution and the shift of the shoreline position due to the complex sediment transport processes that take place in the nearshore area has been of interest for coastal engineers and scientists for many decades
The present paper presents a new input-reduction method to obtain representative wave conditions based on the Shields criterion of incipient motion and subsequent calculation of the sediment pick-up rate
Considering bed and shoreline evolution, two distinct model types can be considered [1], namely the 2DH area models concentrating on the morphological evolution of a given area and the shoreline evolution models, where the changes in shoreline position are modelled through the calculation of the longshore sediment transport rates
Summary
The prediction of morphological bed evolution and the shift of the shoreline position due to the complex sediment transport processes that take place in the nearshore area has been of interest for coastal engineers and scientists for many decades. The first category of models is used to determine the morphological changes of rather detailed coastal features (such as dunes, or rip channels) based on the simulation of the waves, hydrodynamics and sediment transport rates over a large area (in the scale of many km). That for the medium and long-term prediction of the bed evolution of a rather large area, performing a simulation through hourly changing boundary conditions can be very time consuming [4] For this purpose a number of input-reduction or wave schematization techniques have been developed based on the principle of selecting representative wave conditions able to accurately predict the long-term morphological bed evolution. In order to evaluate the performance of the newly developed method, the results obtained by the pick-up rate method where compared with the ones stemming from implementation of the widely used energy-flux schematization method
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