Intertidal form analysis

Method indicator
Bottom-Up	Hybrid	Top-Down
		YES

Summary of key issues:

Issue	Description
Description	The concept of balance between eroding forces and strength of bed material to resist erosion; or The concept of net balance between erosion and deposition of sediment
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.
Data sources	Topographic and bathymetric profile datasets (as HTA); Tidal forcing over the period of interest; Wave forcing over the period of interest; Allowance for sea level rise; Suspended sediment concentration at offshore boundary; Sea bed resistance to erosion. Wave and tide forcing may be determined from measurements or synthesized, e.g. using astronomical prediction of tides.
Necessary software tools / skills	Understanding of intertidal morphology and flow and sediment processes; Access to reports and papers describing the methods used; Access to existing software codes from developers of the methods; Geomorphological interpretation of output.
Typical analyses	As a conceptual model for understanding the sensitivity of intertidal profile form to tidal current and wave forcing; As a method of predicting the short to medium-term future response of the intertidal profile to changes in forcing or sediment supply.
Limitations	Shorelines may be non-uniform alongshore in which case a profile approach is approximate; Applies only to muddy sediment profiles; Data inputs may be sparse; Cannot predict change in channels running through the mudflat.
Example applications	The Humber; The Wash.

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.

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The Estuary Guide

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