Typically, pseudomeandering rivers are gravel-bed streams considered unstable and prone to turning into braided or meandering channels under the effect of external forcings. Channel changes of pseudomeandering rivers have not been investigated in detail so far. This paper analyses the response of a pseudomeandering river (the Cecina River in western central Italy) to variations of sediment supply resulting from streambed material mining and land use change throughout the last two centuries. Old maps and 11 sets of aerial images from 1954 to the present of four representative sites were used to measure the variation through time of bankfull width and channel sinuosity. The changes in the number of bends, chute channels, bank erosion, bend extension, migration and retraction were recorded and the main processes which favoured pseudomeandering river channel changes were investigated. The old maps indicate that in the first half of the XIX century, the study river had probably a braided morphology in response to the increase in sediment supply following the liberalization of deforestation. From the beginning of the XX century to the present, the river had a predominantly single thread, pseudomeandering morphology which did not change during about 20 years of intense gravel mining (the 1960s – mid-1980s) when the main response of the river was channel incision and narrowing. A few years after bed material extraction stopped the river started to widen, to increase channel sinuosity and consolidate its pseudomeandering morphology. The study confirms that marked variations in sediment supply are more effective than floods in triggering river channel changes. The study also shows that the pseudomeandering configuration is less unstable than previously highlighted in other scientific works.

中文翻译：

---

低蜿蜒度伪曲流河的人类影响和河道动力学

通常，伪曲流河是砾石床溪流，被认为不稳定，在外力作用下容易变成辫状河道或曲流河道。迄今为止，尚未对拟曲流河的河道变化进行详细研究。本文分析了一条伪曲流河（意大利中西部的切奇纳河）对过去两个世纪河床物质开采和土地利用变化造成的沉积物供应变化的响应。使用旧地图和 1954 年至今的 11 组航拍图像，测量了四个代表性地点的河岸全宽和河道蜿蜒度随时间的变化。记录了河道数量、河道、河岸侵蚀、河道延伸、迁移和收缩的变化，并调查了有利于伪曲流河道变化的主要过程。旧地图表明，在十九世纪上半叶，研究的河流可能具有辫状形态，以应对森林砍伐自由化后沉积物供应的增加。从二十世纪初期到现在，河流主要具有单线、伪曲流形态，在大约 20 年的密集砾石开采（1960 年代 - 1980 年代中期）期间，河流的主要响应是河道，这种形态没有改变切口和缩小。河床物质开采停止几年后，河流开始变宽，增加了河道的蜿蜒度并巩固了其伪蜿蜒的形态。研究证实，沉积物供应的显着变化比洪水更能有效地引发河道变化。该研究还表明，伪曲折结构的稳定性比之前其他科学著作中强调的要小。