Water injection dredging in estuaries characterised by sandy sediments - Experiences in the Weser Estuary
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
Torsten Stengel
Abstract: Water Injection Dredging (WID) is known as a successful technique for maintaining harbours and small areas of fairways which are characterised by fine grained sediments (such as silt). Only a few experiences exist concerning the suitability of WID in sandy surroundings..
Within the Weser estuary, one of the greatest river estuaries in Germany with an important fairway for maritime shipping, a long-term and large scale experiment has been started in August 2003 to examine the use of water injection dredging. The examination will last for about 15 months covering a channel length of about 50 kilometres. The classification of the sediments at this part of the estuary varies between silt (only in relative small areas with extensions up to five kilometres) and middle to coarse grained sands. The bathymetry is mainly characterised by dunes showing amplitudes up to 4 metres. They can become shipping barriers causing a major problem with respect to the maintenance of the fairway. This is because the arising dunes (ridges) of shallow depths are rather small in extension and difficult to locate as they are moving. Up to now mainly trailing suction hopper dredgers were used for maintaining the fairway. Due to the described difficulties the costs per dredged cubic metre in this area are the highest within the German tidal estuaries.
First results of the examinations concerning the suitability of the water injection technique in the above described sandy surroundings will be presented. The efficiency of the injection technique in dune areas will be compared with the hopper technique. Furthermore first statements concerning the regeneration time of the dune peaks in relation with the dredging strategy and the hydrological boundary conditions will be given.
Keywords: water injection dredging, hopper dredgers, sand dunes, Weser estuary, regeneration of dune peaks