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Long-term morphodynamic evolution of the Sillon de Talbert gravel barrier spit, Brittany, France

机译：Sillon de Talbert碎石屏障吐痰的长期形态动力学演变，法国布列塔尼

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摘要

The Sillon de Talbert is the largest gravel barrier spit in Brittany and forms a swash-aligned formation exposed to swell that enters the English Channel from the west. It partially protects the islands of the Brehat Archipelago against coastal erosion and marine flooding of low-lying land. The main morphological changes to the Sillon de Talbert have been studied since the 17th century, and were accurately quantified between 1930 and 2010, based on early marine maps, aerial photographs and topographic surveys recently conducted by DGPS. The examination of early maps shows this barrier was attached to the Olone Islands until the end of the 17th century. Towards the mid-18th century, a breach that had formed in the north of the barrier resulted in its transformation into a trailing spit. A gradual change in its general direction towards a more drift-aligned position promoted longshore sediment drift towards the distal end. A slow cannibalization processes began, dividing the spit into a source area at the proximal section, a transit zone in the median section and an accumulation zone at the distal section of the spit. Long-term analysis of shoreline changes over the past decades highlights the mobility of the Sillon de Talbert, which is characterized by rapid landward retreat by rollover. This trend is mainly due to a sediment supply deficit, which can be explained above all by sediment depletion on the continental shelf and, to a lesser extent, by anthropogenic activities, particularly gravel extraction. The results obtained show that for the entire period (1930-2010), the mean migra- tion rate was 1.1 m/yr. Upon closer investigation, the rate of retreat and the main morphological changes proves to differ between the morphosedimentary units of the spit and illustrates cannibalization processes. Thus, the proximal section shows very high retreat rates (1.35 m/yr) due to a sediment budget deficit, which can be explained by gravel migration towards the north-east section of the spit. For these sections, this evolution results in greater sensitivity to erosion and breaching during severe storms, as was the case in April 1962 and during winter 1989-90. Its median section corresponding to the transit zone shows lower retreat rates than the proximal section (1.05 m/ yr) and a relatively balanced sediment budget, as illustrated by the high resilience of this section of the spit submitted to sluicing overwash. Finally, the distal section has undergone retreat by rollover of its exposed outer face and progradation of its inner face which benefited from sediment supply from proximal section. From the 1970s, several human interventions based on coastal defense strategy attempted to slow the spit's retreat due to rollover. The failure of these interventions led to the definition of a new coastal management policy. Since the 2000s, the national organization in charge of the acquisition of coastal land for its preservation {Conservatoire du Littoral) has been implementing an acquisition policy geared towards urbanized areas sensitive to coastal erosion and marine flooding in the back-barrier area of the Sillon de Talbert. This policy enables the organization of strategic withdrawal and leaves natural processes to gradually take their course.
机译：西永德塔尔伯特（Sillon de Talbert）是布列塔尼（Brittany）最大的碎石屏障吐水，形成一个倾斜的，倾斜的结构，从西面进入英吉利海峡，并出现膨胀。它部分保护了Brehat群岛的岛屿免受海岸侵蚀和低洼土地的海洋洪水的侵袭。自17世纪以来，一直在研究Sillon de Talbert的主要形态变化，并根据DGPS最近进行的早期海洋地图，航拍照片和地形调查，在1930年至2010年之间对其进行了精确定量。早期地图的检查表明，直到17世纪末，该屏障一直与奥隆群岛相连。到18世纪中叶，在屏障北部形成的裂口导致其转变为尾随吐痰。总体方向逐渐向着与漂移方向一致的方向变化，促使沿岸沉积物向远端漂移。开始了缓慢的食人化过程，将唾液分为吐口近端部分的源区域，吐口中段的过渡区域和吐口远端部分的累积区域。过去几十年中对海岸线变化的长期分析突显了西永德塔尔伯特（Sillon de Talbert）的机动性，其特征是翻滚使陆地迅速退缩。这种趋势主要是由于沉积物供应不足，首先可以通过大陆架上的沉积物枯竭来解释，而在较小程度上可以通过人为活动特别是砾石提取来解释。获得的结果表明，在整个时期（1930-2010年），平均迁移率为1.1 m / yr。经过更深入的研究，后退速度和主要形态变化被证明在唾液的形态沉积单元之间有所不同，并说明了食人化的过程。因此，由于沉积物的预算短缺，近端断面的退缩率非常高（1.35 m / yr），这可以用砂砾向着吐口东北部的迁移来解释。对于这些部分，这种演变导致在强风暴期间更容易受到侵蚀和破坏的影响，例如1962年4月和1989-90年冬季。其中段对应于过境区显示出比近端段更低的退缩速率（1.05 m / yr），并且沉积物的预算相对平衡，这表明该段吐出的水具有高回弹力，可以防止过冲。最后，得益于近端部分的沉积物供应，远端部分通过其裸露的外表面的翻转和其内表面的进退而退缩。从1970年代开始，基于海岸防御策略的几种人为干预措施试图减缓由于翻滚而导致的吐水退缩。这些干预措施的失败导致了新的沿海管理政策的定义。自2000年代以来，负责保护沿海土地的国家组织（Conservatoire du Littoral）一直在实施一项针对在西永德（Sillon de）后屏障地区对沿海侵蚀和海洋洪水敏感的城市化地区的收购政策塔尔伯特。这项政策可以组织战略撤军，并让自然过程逐步走上正轨。

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  • 来源
    《Shore and beach》 |2012年第1期|p.19-36|共18页
  • 作者

    Pierre Stephan; Serge Suanez; Bernard Fichaut;

  • 作者单位

    Laboratoire de Geographie Physique - UMR 8591 CNRS, Universites Paris 1 Pantheon Sorbonne et Paris 12 1 Place Aristide Briand, 92195 Meudon cedex, France;

    LETG-Geomer-Brest, UMR 6554 CNRS, Institut Universitaire Europeen de la Mer, Universite de Brest, Technopole Brest-Iroise, Place Nicolas Copernic, 29280 Plouzane, France;

    LETG-Geomer-Brest, UMR 6554 CNRS, Institut Universitaire Europeen de la Mer, Universite de Brest, Technopole Brest-Iroise, Place Nicolas Copernic, 29280 Plouzane, France;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    brittany; france; coastal morphol- ogy; barrier spit evolution;

    机译：布列塔尼法国;沿海形态屏障吐痰演变;

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