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Morphological bed-updating models

Method indicator
Bottom-Up Hybrid Top-Down
YES    

Summary of key issues:

Issue Description
Description Prediction of changes to bed levels based on sediment transport modelling. The bed elevations are updated at regular intervals to provide a feedback to the hydrodynamic and sediment transport models.
Temporal applicability Often applied to the medium-term (single tide up to several months) but can also be applied to consider the long-term.
Spatial applicability Varying from a single point to estuary-wide including the open coast.
Links with other tools Hydrodynamic; sediment transport, and various top-down modelling tools.
Data sources Similar to those for the hydrodynamics and sediment transport modelling.
Model set up:
  • Land boundary (x,y format);
  • Bathymetric data;
  • Wind and atmospheric pressure;
  • Measurements of bed friction or roughness.
Boundary conditions:
  • Seaward tidal boundary conditions;
  • Freshwater discharge information;
  • Salinity boundary conditions;
  • Offshore wave climate.
Calibration data:
  • Water levels along the length of the estuary;
  • Flow speeds and directions (or vector format u, v);
  • Salinity measurements;
  • Wave measurements or statistics.
Necessary software tools / skills Hydrodynamic model (e.g. TELEMAC); top-down hybrid models such e.g. realignment model.
A good understanding of long term estuary processes including hydrodynamics and sediment transport and long-term estuary response to environmental changes is required to interpret the predicted changes in bed elevations.
Typical analyses Sediment transport and hydrodynamic modelling. The hydrodynamic model predicts flows and water levels over the model domain. This information is then used to determine the sediment transport regime.
The accretion or erosion estimates are then used to update the bed levels before the sequence recommences with calculations of water levels and current flows in the next time step of the model.
Morphological models have to deal with a high degree of uncertainty regarding the processes which occur and the manner in which the system reacts to them as morphology is at the end of a chain of the following inter-related processes.
Limitations Calibration and validation of the model predictions against historic bathymetric data is often a limitation. Sediment flux information for boundary conditions is often limited. Long computational time.
Example applications Tollesbury Creek, Humber Estuary

Morphological bed updating models are based on hydrodynamic and sediment transport models that consider feedback between the models. Generally the two components of the model are run in parallel with the results fed from one into the other at each time step. The hydrodynamic model predicts flows and water levels over the model domain. This information is then used to determine the sediment transport regime. The accretion or erosion estimates are then used to update the bed levels before the sequence recommences with calculations of water levels and current flows in the next time step of the model.

Morphological models have to deal with a high degree of uncertainty regarding the processes which occur and the manner in which the system reacts to them as morphology is at the end of a chain of the following inter-related processes (STOWA-RIZA, 1999).

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Analysis and modelling

Last Modified on: 19 June 2011
Printed from the Estuary Guide on 18/06/2019 04:31:27