A Method for Restoring the River Environment by Restoring Meanders

从2003年到2005年，研究人员进行了一项研究，目的是开发一种重新连接十字江上被切断的曲流河的方法。试验场以往的调查表明，双航道修复在防洪和环境恢复方面是有希望的，即在保持弯曲航道的同时重新连接曲流河航道。1)在中比例尺沙波发生的河道动床水工模型试验中，最适宜的河床材料是比重和粘度较低的河床。2)通过现场观测，提出了一种根据恢复后的河道和拉直后的河道的形状，研究两种河道分流汇合处最佳河床中心线的方法。当进行河道分叉时，汇合处的河床退化不容忽视。3)在水流急剧转向的河岸位置，放置倒下的树木比不放置倒下的树木时，樱桃鲑鱼的种群密度更高，年龄分解也更多样。4)通过对牛弓湖(截流曲流河)的污染物收支调查和建立水质估算模型，验证了该模型的适用性。通过建立湿地地下水位估算模型，阐明了河流水位变化对河流附近地下水位变化的影响。

Research was performed from 2003 to 2005 toward developing a method of reconnecting a cut-off meander on the Shibetsu River. Previous surveys at the test site showed that two-channel restoration in which the meander channel is reconnected while the straightened channel is maintained has promise with respect to flood control and environmental restoration. The findings are summarized here.1)In movable-bed hydraulic model tests to reproduce bank erosion at river channels where mid-scale sand waves occur, the most suitable bed materials were those low in specific gravity and viscosity.2)From field surveys, a method for studying the optimum channel centerline at the divergence and confluence of the two channels was developed based on the shapes of the restored channel and the straightened channel. When channel bifurcation is conducted, riverbed degradation at the confluence cannot be ignored.3)At riverbank locations of sharply redirected flow, cherry salmon were observed in higher population densities and more diverse age breakdowns when fallen trees were placed than when no fallen trees were placed. Such placing is expected to be effective in fostering a favorable habitat for fishes.4)By surveying the pollutant budget of the oxbow lake (the cut-off meander) and by constructing a model for estimating the water quality, the applicability of the model was confirmed. By developing a model for estimating the ground water level in wetlands, the effect of changes in river water level on changes in ground water level near the rivers were clarified.