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Regime relationships

Method indicator
Bottom-Up Hybrid Top-Down

Summary of key issues:

Issue Description
Description Characterisation of the link between hydrodynamics and estuary morphology in terms of simple empirical formulae to describe both the estuary equilibrium (or quasi-equilibrium) and its subsequent evolution following disturbance to the system
Temporal applicability Typically applied over long-term time periods (10-100 years)
Spatial applicability Generally applied along the length of the estuary.
Links with other tools
  • Often utilises HTA bathymetric analysis as a basis for the method;
  • Can be used on a number of levels ranging from top-down to hybrid  modelling approach
  • Can provide input to deciphering historical behaviour during conceptual model development.
Data sources Bathymetry: maps and charts, aerial photography, topographic and bathymetric surveys, remote sensing imagery
Discharge/Tidal prism: As bathymetry and/or the results of flow modelling
Littoral drift: Wave models and/or observed wave data and littoral drift models
Suspended sediment concentration: field measurements at several places within the estuary
Sediment type: analysed grab samples, water samples, Admiralty Chart sediment information
Necessary software tools / skills Regime theory covers a range of skills depending on the complexity of the application. At its simplest level the skills required are similar to those of HTA, i.e.:
  • Identifying, collating and reviewing relevant data/information sources
  • GIS/image processing software/photogrammetry
  • Cartography/digital ground modelling
  • Basic understanding of estuarine process and sediment transport
  • Geomorphological interpretation of output
At its most complex level Regime Theory becomes a hybrid method with the following necessary skills/tools:
  • Flow model (1D is usually satisfactory but 2D can be used)
  • Programming/IT skills to link flow model results with regime relationships
  • Thorough understanding of estuarine process and sediment transport
  • Experience of predictive modelling in estuarine environments
  • Geomorphological interpretation of output
Typical analyses
  • Prediction of estuary evolution or estuary/inlet entrance evolution following disturbance
  • Assessment of stability of estuary/inlet entrances (using Escoffier theory)
Limitations Estuary/Inlet Entrance Regime Theory
  • No underlying analytical basis except (potentially) for inlet or estuary entrances which can be characterised by a balance between littoral drift and ebb-tide transport.
  • The empiricism of this method results in considerable uncertainty which can limit the applicability of the method.
  • As applied in a predictive sense the method is best suited to tidal inlets. This is because it is often possible to approximate the tidal flows in the inlet by an analytical model, unlike estuary entrances where a flow model will be necessary, and moreover the evolution of estuary entrances will be affected by changes within the estuary as a whole.
Estuary-wide regime theory
  • Not all estuaries can be described by the type of empirical relationships that this method uses
  • The form of regime theory commonly implemented does not necessarily represent estuary evolution adequately
  • Validation data is scarce
  • Method works best where impacts of a disturbance are 1-dimensional in their effect. Where impacts are 2-Dimensional method works less well.
  • To be used effectively in a predictive sense the technique usually requires the use of a flow model and data relating to sediment and/or sediment transport.
Example applications Lune Estuary, Mersey estuary

Regime relationships

Regime theory describes an approach to channel theory that assumes some form of equilibrium relationship between certain morphological parameters, such as width, or depth and hydraulic parameters such as hydraulic slope, discharge, or flow velocity. A summary of the range of relationships available has been drawn together by Spearman (Spearman, 1995). Where sufficient historic data are available, these relationships can be used to explore temporal aspects of the estuary development (ABP Research, 1999; ABPmer, 2003). Increasingly, however they are being used in conjunction with hydrodynamic models to create a form of hybrid model that can iterate to the equilibrium state (see Hybrid methods).

Regime relationships can be used to consider the implications of a change. If an area is to be reclaimed or dredged, then some of the gross properties of the estuary will be altered. Regime relationships can be used to determine whether the changes are likely to move the system towards or away from the particular equilibrium condition and whether or not the change is likely to be significant.

Regime Theory involves the characterisation of the link between hydrodynamics and estuary morphology in terms of a simple empirical formula(e) which can be used to describe both the estuary equilibrium (or quasi-equilibrium) and its subsequent evolution following disturbance to the system. The theory is applied in two distinct forms – application to estuary and tidal inlet entrances and application throughout estuary systems.    Regime methods using flow models enable more detailed flow input to the regime algorithm and can be used as a hybrid model. Either way the flow model will require validation of tidal currents and water levels.

Read the full PDF document for more information on this methodPDF version

Analysis and modelling

Last Modified on: 19 June 2011
Printed from the Estuary Guide on 15/06/2024 05:15:55