Intertidal form analysis
Summary of key issues:
|Temporal applicability||Short to medium-term (Tidal to decadal).|
|Spatial applicability||Intertidal profile from HAT to LAT, where profiles are selected in a shore-normal orientation.|
|Links with other tools||Historical Trend Analysis (HTA) provides information on the profile changes that have taken place.|
|Necessary software tools / skills||
Overview of technique
Intertidal zone geomorphology is an important feature within the larger estuarine morphological system, providing the transition between the estuary’s subtidal channel and the shoreline with its natural features or man-made coast protection or flood defence works. Several approaches are reviewed here to predict the evolution of the intertidal profile formed in muddy sediments (mudflats). These methods can be used to determine the equilibrium shape of the mudflat given the prevailing environmental conditions. The inputs that are required are:
- Initial intertidal profile from subtidal, e.g. Lowest Astronomical Tide (LAT) to at least Highest Astronomical Tide (HAT);
- Tidal range and shape of tidal curve;
- Wave parameters offshore of the intertidal: height, period and direction;
- Bed sediment properties: erosion threshold; and,
- Boundary sediment concentration.
The methodology for application of the various modelling approaches is presented to enable (i) assessments of the natural behaviour of mudflats under wave and current forcing; (ii) response of mudflats to sea-level rise; and, (iii) the response to engineering works or encroachment.
For sandy shores there is an extensive body of work to describe the cross-shore form (Dean, 1977; Dean, 1987), however, work on cohesive shores is not as extensive. Early work on the form of the intertidal under currents and under waves was done by Friedrichs (1993) and Friedrichs and Aubrey (1996). Whitehouse and Roberts (1999) extended the work to include sediment properties and a sediment concentration term, allowing investigation of a wider range of parameters. Pethick (2002) derived a method to predict the profile evolution under waves, examining the role of sea level rise.