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Hydrodynamic modelling

Method indicator
Bottom-Up Hybrid Top-Down
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Summary of key issues:

Issue Description
Description A hydrodynamic model is used to solve governing equations for oceanic movements. Hydrodynamic models provide the base on which advection-diffusion, sediment transport, particle tracking and morphological bed updating modelling is undertaken.
Temporal applicability Typically applied to the short to medium-term.
Spatial applicability Varying from a single point to estuary-wide, including the open coast.
Links with other tools Outputs from these models will feed into many of the other tools, including accommodation space, historical analysis, sediment transport models and behaviour models, for example.
Data sources
  • Land boundary (xy format)
  • Bathymetric data
  • Wind and atmospheric pressure data
  • Measurements of bed friction or roughness
  • Seaward tidal boundary conditions
  • Freshwater discharge information
  • Salinity boundary conditions
  • Offshore wave climate
  • 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 A range of modelling skills are required depending greatly on the complexity of the hydrodynamic model and area being studied. Typically, expert knowledge of hydrodynamics, water quality and morphology is required along with a good understanding of the estuary processes.
Typical analyses Flow and transport simulated from tidal forcing;
Limitations Computation time, disk space, calibration data (water levels, salinity, flow speeds,
Example applications Blackwater Estuary, Southampton Water

Introduction

Hydrodynamic modelling is the base on which advection-diffusion, sediment transport, particle tracking and morphological bed updating modelling is undertaken. Outputs of hydrodynamic modelling are predictions in water levels, tidal currents and waves that result from tidal, meteorological and density forcing.

All hydrodynamic models solve one form or other of the same governing equations for oceanic motions (Abbott & Basco, 1989). These equations are written in the co-ordinate frame of reference fixed to the rotating earth, and are essentially the Navier-Stokes equations, or more appropriately Reynolds-average equations, since the flow is invariably turbulent. The Navier-Stokes equation, otherwise known as the momentum equation is derived from Newton's second law of motion applied to a fluid particle. The forces due to gravitation buoyancy (Archimedean force due to density stratification) and the Coriolis (accelerations generated due to the non-inertial nature of the rotating co-ordinate frame) are included in the equations. An additional equation, known as the continuity equation, is required to insure that mass is conserved (Clayson & Kantha, 2000).

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Analysis and modelling

Last Modified on: 19 June 2011
Printed from the Estuary Guide on 31/10/2014 10:31:58