Experimental manipulation of sandwaves to reduce their navigation hazard potential, Jade shipping channel, N. Germany
Redding, J.H. (2000). Experimental manipulation of sandwaves to reduce their navigation hazard potential, Jade shipping channel, N. Germany, in: Trentesaux, A. et al. Marine Sandwave Dynamics, International Workshop, March 23-24 2000, University of Lille 1, France. Proceedings.
In: Trentesaux, A.; Garlan, T. (Ed.) (2000). Marine Sandwave Dynamics, International Workshop, March 23-24 2000, University of Lille 1, France. Proceedings. Université de Lille 1: Lille. ISBN 2-11-088263-8. 240 pp., more
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Document type: Conference paper
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| Abstract |
In March 1997 the Jade Shipping Channel was the location for a trial, to determine the ability of a water-jetting device (the Wing Excavator) to lower the crests of sandwaves, which pose a navigation hazard. Several methods of operation were tried, including displacement of sand from the crests and deep trenching through the crests. State-of-the-art surveying techniques were used to establish the location and morphology of the sandwaves, and determine the volumes of excavation. Despite encouraging results from each of the trial stages, the final cumulative volume of excavation proved surprisingly low and was insufficient to convince the Waterway Authority of the effectiveness of the technique. Subsequent re-evaluation of the data has shown that, rather than surveying errors being responsible for the anomaly, rapid re-building of the sandwave crests was the cause. Re-building appears to take place in a matter of hours or days, provided that the crests are not lowered by more than 50% of their original height. Crests that were deeply trenched did not re-build in the same way. Symmetrical trochoidal sandwaves of the type present in the trial area are common in the Jade. Oblique imagery of the sandwaves derived from the processed swathe bathymetry, reveals many features that would accord with a Hulscher-type of sandwave building mechanism. Rapid re-building of the crests highlights the inefficiency of any technique that seeks to control the navigation hazard by displacing or removing material from the crests. By considering the dynamics of sandwave/water flow interaction, an alternative method for reducing the up-building tendency is proposed. |
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