COMPREHENSIVE ASSESSMENT OF SEDIMENT REPLENISHMENT IN NAKA RIVER: HYDROLOGICAL, MORPHOLOGICAL, AND ECOLOGICAL PERSPECTIVES

抄録

 Sediment Replenishment (SR) is a common restoration measures implemented in Japanese rivers, which aims to recover the degraded river’s morphology and aquatic ecosystem caused by sediment deficit. In this paper, we developed an integral assessment approach to evaluate the effectiveness of SR strategy on flow regime, river bed, and ecological changes along the downstream reaches. Several indices for riverine assessment, such as GUS (Geomorphic Units Survey), HMID (Hydro-morphological Index of Diversity), and Fish Diversity Index (H Value) have been quantified for multiple SR. Key factors as the placed sediment volume, transported rate, and flushing flow discharge of the developed approach has also been successfully applied for Naka River, based on collected data of topography, sedimentation, flow regime, morphology, and water quality. The results reveal that the efficiency of SR was fluctuant for single replenishment at Kohama and additional SR sites should be considered in the future measures of sediment management. Furthermore, the numbers of geomorphic units, such as runs, rapids, and pools were increased around 15% annually, and a tendency of equal distribution of each units can be founded as well. While habitat quality for fish spawning was promoted partly due to the alteration of the morphological and hydrological characteristics (riverbed material, riverbed level, water depth, and flow velocity) at different sites. To summarize, this comprehensive study will show the influences of SR on riverine characteristics and provide valuable recommendations for the operation of sediment replenishment works in the Naka River.