Morphological and sedimentary impacts and recovery on a mixed sandy to pebbly seabed exposed to marine aggregate extraction (Eastern English Channel, France)

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• 作者：Sophie Le Bot ; Robert Lafite ; Matthieu Fournier ; Agnè ; s Baltzer ; Michel Desprez
• 关键词：dredging ; Eastern English Channel ; physical impacts ; recovery ; sediment
• 刊名：Estuarine, Coastal and Shelf Science
• 出版年：2010
• 出版时间：10 October 2010
• 年：2010
• 卷：89
• 期：3
• 页码：221-233
• 全文大小：2454 K

文摘

The impacts of marine aggregate dredging and the recovery levels, 1 and 10 years after cessation of dredging, are investigated for a commercial dredging site. The site consists of mixed sandy to pebbly sediments. Dredging intensity is low (generally less than 1 h/ha/year) and heterogeneous in space and time, allowing to distinguish adjacent areas of active extraction, fallow, recovery and overflow deposition. Surveys were conducted using a combination of acoustic (side-scan sonar), video and grab sampling techniques. Multivariate analysis has been utilized to define a seabed morphological and sedimentary zonation that provides a good habitat description and mapping. Sedimentary patchiness characterized by grain-size increased variability is identified as a feature indicative of seabed disturbance due to dredging activities. In the vicinity of the dredging areas, fine-sand content greater than 10 % is indicative of overflow deposition resulting from dredging activities while coarse sand is found to be covering areas previously dredged but now recovered. Furrows created by dredging operations collapse within one year, and generally fully disappear within 10 years. They are usually covered by sands and bedforms, indicative of active sediment transport, are formed. This study confirms that a low dredging intensity strategy is recommended for mixed sediment areas under moderate hydrodynamic energy regimes as this of the study area. This allows natural recovery of the seabed to take place within a period of 10 years.