|A new approach for managing the morphology and ecology of a coastal plain estuary|
Ides, S.; Plancke, Y.; Peters, J.J. (2008). A new approach for managing the morphology and ecology of a coastal plain estuary, in: 32nd Congress of IAHR, the International Association of Hydraulic Engineering and Research. Proceedings: Harmonizing the Demands of Art and Nature in Hydraulics. Engineering and Management of Fresh-water Systems. Data Acquisition and Processing for Scientific Knowledge and Public Awareness. Fluid Mechanics and Hydraulics. Maritime and Coastal Research and Engineering, July 1-6, 2007, Venice, Italy. pp. [1-11]
Morphological management; Disposal strategy; Eco-morphology
An expert team appointed by the Port of Antwerp proposed the idea of morphological dredging, aiming at steering the estuarine morphology. A pilot project was implemented, modifying the shape of a sandbar by disposing dredged material on the eroded tip of the Walsoorden sandbar. The new shape would help restoring the degraded ecology and morphology, but it also aims at modifying the flow on a crossing in the navigation channel, reducing the dredging effort if the self-dredging capacity of the flow could be increased on it.
A research programme about the feasibility of the idea was conducted in 2002 and 2003, combining several tools: desk studies on historical changes with maps, field measurements, physical scale model tests and numerical simulations. The expert team concluded in 2003 that none of the results denied the feasibility of the new disposal strategy, although final judgement would only be possible after the execution of an in situ disposal test.
During one month at the end of 2004, 500.000 m³ of sand was disposed with a diffuser in relatively shallow water at the seaward end of the sandbar. The experiment was well monitored with frequent multi-beam bathymetric surveys, LIDAR-flights, marked sediment tracing, in-situ sediment measurements and ecological monitoring. After one year, it was concluded that the test was a success from morphological viewpoint. Also the ecological monitoring did not reveal any significant negative changes in trends due to the disposal test.
In 2006 a new disposal test was executed, using the traditional technique with hopper dredgers. Due to practical limitations, the disposal (again 500.000 m³) was spread over a 3 months period. The new experiment was again thoroughly monitored for morphology as well as for ecology. Up to now, the morphological results of the second test are satisfying. The ecological results will become available during the first half of 2007, with the preliminary results not showing any negative impact.