Tankerton beach experiment 2002

Canterbury City Council, on behalf of the SECG, was awarded funding from the national flood and coastal defence research budget to study the behaviour of newly recharged beaches at Tankerton. The aim of the project is to provide physical data on how the new beach evolves towards the naturally stable condition for the site. Not all of the material which is placed as part of a recharge will remain on the beach and calculating how much will be lost is important in determining the whole life cost of a scheme.

Economically viable sources for such large quantities of recharge material are almost exclusively located offshore. Dredged marine aggregates composed of the ideal material/grading specification are prohibitively expensive and used by the construction industry. As such, a balance has to be struck between the costs of preferably coarser material, distance to source and anticipated scheme life.   

Recycled material from the adjacent coast costs 10 to 20 times less than offshore sources.  There are a number of problems associated with using recharge material finer than that found on the native beach. These include high initial loss rates and cliffing (above) of the beach face.

As part of the Tankerton scheme five bays were filled with significantly different material, both in terms of cost and physical composition:

Bay 1 – Recycled Material from Long Rock Spit

Bay 2 – Dredged Material from Hasting’s Bank

Bay 3 – Dredged Material from Ower’s Bank

Bay 4 – Standard Mix with Coarse Cap

Bay 5 – Standard Mix for Rest of Scheme

Control Bay – Native Beach on Adjacent Coast

Both the new and the mature beach will be subject to the same physical processes (tides, waves, groyne arrangement and coastal orientation) and hence a direct comparison of the behaviour of the performance of the different bays will be possible. The conclusions reached should provide guidance for future schemes and allow for more realistic estimates of beach maintenance costs in coastal strategies.

Monitoring methods will include a combination of sediment sampling, water level analysis, surveying and modelling.