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Sedimentary education

Letters

A vast majority of the sediment available today in our coastal systems was derived from the present day sea bed during the Holocene period (the most recent period of geological time since the last major glaciation 10,000 years ago).

Available material was combed up and migrated onshore with rising sea levels.

By comparison, there is generally very little contemporary sediment input to most coastal systems, particularly since many potentially erodible and sediment-yielding cliffs have been protected by coastal defence works or are controlled by management activities.

This means that present day coastal processes, and indeed management practices, are largely storing or re-working relict stocks of sediment, with little contemporary input. It is, therefore, not surprising that it is becoming increasingly possible for breaches in natural features to occur, as exemplified by Greg Haigh in his description of the Porlock gravel barrier (NCE 17 May).

Furthermore, management intervention in attempting to hold the existing line of the coast in the face of a recessional tendency is, in many locations, increasing the potential for more catastrophic consequences to occur following eventual breaching or breakdown of the feature.

NJ Cooper (G) CooperNJ@halcrow. com

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