The process of land claim means that it is necessary to exclude the sea from part or all of this intertidal area, and also protect this area from reinundation. Land claim for agriculture and industry generally takes in the higher salt marsh because the higher elevation of the intertidal area claimed means, first, that the wave activity will be reduced by the lower marshes and mudflats fronting the area to be reclaimed. (Yates 235-249) In cases where there are not sufficient areas of such deposits fronting the proposed claim, then the area is perhaps not well suited. Second, less material is needed to build up the newly created dry land. Third, the higher the elevation, the lower the sea walls need to be to prevent tidal overtopping. Finally, agriculture needs good-quality farmland, and the upper marshes provide the most 'mature' sediments available in respect of the processes of soil formation. (Archer 103-120; Knecht 183-199)
There are few areas of coastline in the 'developed' world which have not been subject to some form of land claim, defence works, or development. (Louisse 10-15; Fischer 437-447) It has been the tendency for coastal populations to utilise their immediate environment to the full, obtaining as much land as possible in order to increase their agricultural or industrial potential, and to defend low-lying land to increase their security from flooding by the sea.
As far as port development in estuaries is concerned, one of the key requirements is that the port itself should be afforded as much shelter as possible. Traditionally, this meant that estuaries were the most suitable sites and, because of the small size of the earliest vessels, many of the early ports were built some way upstream from the estuary mouth. As ship size has increased, so these earlier ports have become uneconomic, and thus many have been relocated downstream, towards the estuary mouth. (Guy 219-248) This has meant that the majority of the world's major estuaries have some form of port development located within them. In addition, even these areas may not be suitable for the larger vessels of today, and thus many estuaries have been artificially deepened by dredging to allow for the increased draught of modern ships. This process leads to an artificial intertidal profile in which natural processes are in constant competition with the alien environment in which they find themselves. (Beatley 1-22) As a result, especially over the past few centuries, many estuaries have experienced considerable modification to their natural ecosystems, which have brought about changes in floral patterns and bird populations. From a process point of view, the dredging and land claiming which have occurred in estuaries have also produced changes in circulation patterns, tidal regime, and sediment deposition patterns, causing further knock-on effects for natural habitats and wildlife populations. (Barston 93-116)
The need for coastal defences
Because of the need to protect the newly claimed land from reinundation by the sea, it is also a requirement of land claim to install some form of flood defence. (Doody 275-283) This defence is largely to keep the sea out, rather than an anti-erosion structure, and so tends to be more a flood defence measure than a