Abstract A braided gravel-bed river provides essential habitats for various plants and animals. However, human regulation of rivers, such as dams, channelization, and other engineering works, alter flow and sediment regimes, which generally cause the degradation of river and riparian ecosystems. One of the prominent changes prevailing in Japanese rivers is forest expansion over gravel bars, and many native plants and animals that depend on gravel-bar habitat are now endangered. The Satsunai River is typical of rivers experiencing forest expansion, so the Japanese government launched a restoration project in 2012 to partially restore its riparian ecosystems. This is a large-scale experiment developed jointly by an interdisciplinary science team and river managers, who conduct monitoring and evaluation under an adaptive management scheme. The main measure to restore gravel bed habitat was an artificial flood regime, releasing a maximum water volume of 120 m3/s, which was a 2-year return period flood before dam construction. A unique feature of the project is that we considered the role of high-magnitude floods with recurrence intervals greater than 20 years after dam construction. We hypothesize that the artificial floods can be timed seasonally to create sites for regeneration and nesting of riparian species, and the high-magnitude floods contribute to maintaining a shifting mosaic structure of floodplain forest and unvegetated gravel-bar patches. We also used critical non-dimensional shear stress analysis to define “flood-disturbance areas” that can be disturbed under the artificial flow regime created by a dam. Artificial floods have been initiated once a year since 2012 at the end of June, synchronized with the seed dispersal period of Salix arbutifolia, which is endangered and a high conservation priority in the project. Thus far, the idea of setting floodplain-disturbance areas and the strategy of using both artificial and high-magnitude floods to restore a shifting mosaic of floodplain habitat patches is appropriate, as we found successful regeneration of S. arbutifolia and an exponential decay curve of the age distribution of floodplain forest patches. However, the sediment regime regulated by the dam was not addressed in this research, so future monitoring should track changes in river morphology associated with reduced sediment supply caused by the dam.

中文翻译：

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在大坝改变的水流状态下恢复漫滩森林的移动镶嵌

摘要 辫状砂砾河床为各种动植物提供了重要的栖息地。然而，人类对河流的调节，如大坝、渠道化和其他工程工程，会改变流量和沉积物状况，这通常会导致河流和河岸生态系统的退化。日本河流中普遍存在的显着变化之一是砾石滩上的森林扩张，许多依赖砾石滩栖息地的本地植物和动物现在濒临灭绝。Satsunai 河是森林扩张的典型河流，因此日本政府于 2012 年启动了一项恢复项目，以部分恢复其河岸生态系统。这是一个由跨学科科学团队和河流管理者共同开发的大规模实验，他们在适应性管理计划下进行监测和评估。恢复砾石床栖息地的主要措施是人工洪水制度，最大泄水量为120 m3/s，为建坝前2年重现期洪水。该项目的一个独特之处在于我们考虑了大坝建造后重复间隔超过 20 年的高强度洪水的作用。我们假设人工洪水可以按季节定时，为河岸物种的再生和筑巢创造场所，而高强度洪水有助于维持泛滥平原森林和未植被的砾石斑块的不断变化的镶嵌结构。我们还使用临界无量纲剪应力分析来定义“洪水干扰区”，这些区域在大坝产生的人工流态下可能会受到干扰。自 2012 年 6 月底开始，每年 6 月底启动一次人工洪水，与濒危且项目高度保护的杨柳种子传播期同步。到目前为止，设置洪泛区干扰区的想法以及使用人工和高强度洪水来恢复洪泛区栖息地斑块的移动镶嵌的策略是合适的，因为我们发现 S. arbutifolia 的成功再生和指数衰减曲线漫滩森林斑块的年龄分布。然而，本研究并未涉及大坝调节的沉积物状况，因此未来的监测应跟踪与大坝造成的沉积物供应减少相关的河流形态变化。这是项目中濒临灭绝和高度保护的优先事项。到目前为止，设置洪泛区干扰区的想法以及使用人工和高强度洪水来恢复洪泛区栖息地斑块的移动镶嵌的策略是合适的，因为我们发现 S. arbutifolia 的成功再生和指数衰减曲线漫滩森林斑块的年龄分布。然而，本研究并未涉及大坝调节的沉积物状况，因此未来的监测应跟踪与大坝造成的沉积物供应减少相关的河流形态变化。这是项目中的濒危物种和高度保护优先事项。到目前为止，设置洪泛区干扰区的想法以及使用人工和高强度洪水来恢复洪泛区栖息地斑块的移动镶嵌的策略是合适的，因为我们发现 S. arbutifolia 的成功再生和指数衰减曲线漫滩森林斑块的年龄分布。然而，本研究并未涉及大坝调节的沉积物状况，因此未来的监测应跟踪与大坝造成的沉积物供应减少相关的河流形态变化。设置洪泛区扰动区的想法以及使用人工和高强度洪水来恢复洪泛区栖息地斑块的移动镶嵌的策略是合适的，因为我们发现 S. arbutifolia 的成功再生和年龄分布的指数衰减曲线泛滥平原森林斑块。然而，本研究并未涉及大坝调节的沉积物状况，因此未来的监测应跟踪与大坝造成的沉积物供应减少相关的河流形态变化。设置洪泛区干扰区的想法以及使用人工和高强度洪水来恢复洪泛区栖息地斑块的移动镶嵌的策略是合适的，因为我们发现 S. arbutifolia 的成功再生和年龄分布的指数衰减曲线泛滥平原森林斑块。然而，本研究并未涉及大坝调节的沉积物状况，因此未来的监测应跟踪与大坝造成的沉积物供应减少相关的河流形态变化。