Type	Cause	Description
Energy	Freshwater Flow	In the context of morphological change persistent actions on a short or medium time scale provide the boundary conditions for the response model. It is the long term and intermittent changes which are most likely to result in changes in form.
	Tides	Whilst a single tide is the main period of action, there can be significant variations between spring and neap tides, which can have a significant influence on the overall form of the estuary.
	Mean Sea Level	Inter-annual variations may have a small effect but the main variation of interest will be the longer-term isostatic and eustatic changes. (Note: strictly speaking this should be relative sea level change as it is assumed to include any tectonic, settlement or other changes in land elevations).
	External Wind Waves	Short, medium and intermittent time scales are generally used for process-based studies. The long-term time scale makes more use of climatic trends and cycles to evaluate changes.
	Local Wind Waves	Short, medium and intermittent time scales are generally used for process-based studies. The long-term time scale makes more use of climatic trends and cycles to evaluate changes.
	Meteorological Surge	Estuary wide, medium and intermittent time scale effects have been grouped because they would be investigated in the same way.
	Bio-chemical Flux	Short/medium/intermittent events are likely to be treated in a similar way at all three space scales.
Sediment	Terrestrial Sediment Input	Estuary wide, short and medium time scale effects have been grouped because they would be investigated in the same way. In this case, it can again be argued that short and intermittent time scales could be similarly combined.
	Marine Sediment Input	Short and medium time scale effects have been grouped because they would be investigated in the same way. Sediment carried in by the daily tide would be the main short-term event but this may be altered intermittently by additional sediment inputs from the adjacent coast (e.g. due to a cliff fall). Hence intermittent is simply a variant of short.
Management	Barrage	Local effects are likely to give rise to rapid adjustments (e.g. local scouring), whereas estuary wide changes are likely to take significantly longer (see O’Conner et al, 1990)
	Barrier	Local effects will cause rapid adjustments but estuary wide effects are only likely when the barrier is in operation (assuming the structure is not too intrusive when in its non-operational position) and even these may be quite short lived.
	Dredging	Capital, maintenance and extraction dredging generally occur at undefined intervals, although some maintenance dredging operations are almost continuous and might be considered as short-term.
	Fauna	Introduced changes might include oyster or mussel beds, which have a seasonal time scale. In some estuaries such farming might be sufficiently extensive to have an estuary wide effect.
	Flora	Generally, introduced flora will be localised, although wider colonisation is possible as has been the case following the introduction of Spartina in a number of estuaries around the UK.
	Intake or Outfall	Whilst the impacts due to structure are most likely to be localised, the effect of inputs, such as nutrients or heat, could give rise to new bio-chemical fluxes, which induce change over a longer time scale.
	Jetty or Pier	Unlikely to have more than a local effect in most cases.
	Reclamation	The location of the reclamation within the estuary and any change in tidal prism determines the scale of influence. Some may only have a local effect but in most cases it is prudent to check the estuary wide impact.
	Sea Defences	The main implication of defences is the loss of high water storage volume. Some alteration of the flow regime may also occur depending on the structural form of the defences.
	Sea Disposal	Although sea disposal of waste is now prohibited, dredged spoil continues to be dumped at sea and in estuaries. The latter may however benefit the system by redistributing sediment to the intertidal. Consequently whilst the dumping is local, there may be estuary wide effects.
	Training Works	The location of the training works within the estuary and any changes to the channels determines the scale of influence. Some may only have a local effect but in most cases it is prudent to check the estuary wide impact
	Managed Realignment	The location of the realignment within the estuary and any change in tidal prism determines the scale of influence. Some may only have a local effect but in most cases it is prudent to check the estuary wide impact.
	Intertidal recharge	The magnitude of a recharge can vary from large placements of sediment through to so called trickle charging of small amounts of material. They type of material can also vary from sand to fine silt. The location of recharge within the estuary and any change in tidal prism determines any wider influence. Some may only have a local effect but in most cases it is prudent to check the estuary wide impact.