Abstract The Sefidrud, a river flowing into south west Caspian Sea, is prone to avulsion. Previous studies of the river delta support the idea that several major avulsions have occurred during the past few thousand years. During the most recent major avulsion, a 23 km shift occurred along the coast. However, in literature the timing of the event is subject to uncertainty and therefore the causes of the avulsion remain unclear. Lying in the most populated area in Iran explains the importance to investigate the Sefidrud river avulsion. In this study, an 11 m-long sequence was obtained from an area where the river splits off into an old and a new distributary, and where a large pre-avulsion wetland had developed. Palaeo-environmental studies including sedimentology, macro-remain, and palynology were performed to detect changes in environment. Five radiocarbon dates were obtained to determine the avulsion age. In parallel an analysis of historical maps around the timing of the supposed avulsion and for more recent times provided a complementary way of refining the avulsion age. The results from this novel multidisciplinary study show that the last major avulsion occurred at a date after the early1800s and before 1929, during a period of rapid water level fall. Hence this is several centuries more recent than so far suggested. Studying aerial photographs, this research confirms the occurrence of minor avulsion between 1955 and 2014 where the avulsion point is around 2 Km from the coast line, and during a period of sea level fall. The results of this study also suggest that beyond the immediate effects on society and agriculture, avulsion increases the rate of coastal erosion near the abandoned distributary, as sediments are temporarily sequestered on the floodplain and causes intensive erosion. Avulsion has also major impact on coastal lagoons and inland wetlands by river diverting into the lagoons and wetlands.

中文翻译：

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里海西南部 Sefidrud 的近期撕脱史

摘要 Sefidrud 是一条流入西南里海的河流，容易发生撕脱。先前对河流三角洲的研究支持在过去几千年中发生了几次重大撕裂的观点。在最近的一次大撕裂中，沿海发生了 23 公里的偏移。然而，在文献中，事件发生的时间不确定，因此撕脱的原因尚不清楚。位于伊朗人口最稠密的地区，解释了调查 Sefidrud 河撕裂的重要性。在这项研究中，从河流分裂成新旧支流的地区获得了一个 11 m 长的序列，该地区已经形成了一个大的侵蚀前湿地。进行了包括沉积学、宏观遗迹和孢粉学在内的古环境研究，以检测环境的变化。获得五个放射性碳日期以确定撕脱年龄。与此同时，围绕假定撕脱发生时间的历史地图分析以及更近的时间提供了一种完善撕脱年龄的补充方法。这项新的多学科研究的结果表明，上一次大撕裂发生在 20 世纪 00 年代初之后和 1929 年之前，在水位快速下降的时期。因此，这比迄今为止所建议的要晚几个世纪。通过研究航拍照片，这项研究证实了 1955 年至 2014 年间发生的轻微撕脱，其中撕脱点距离海岸线约 2 公里，并且在海平面下降期间发生。这项研究的结果还表明，除了对社会和农业的直接影响之外，撕脱增加了废弃支流附近海岸侵蚀的速度，因为沉积物被暂时隔离在漫滩上并导致强烈侵蚀。河流分流进入泻湖和湿地，撕裂也对沿海泻湖和内陆湿地产生重大影响。