Longitudinal Connectivity and the Restoration Evaluations in Daejeon Urban Stream by Artificial Weirs-Hydrology-Fish Surveys

This study analyzed the effects of artificial weirs on water quality, fish assemblages, and longitudinal connectivity at 27 weir sites in the urban stream Daejeon Stream, and identified management priorities for restoring aquatic ecological integrity. The analysis integrated weir structural and hydrological characteristics (height, slope, drop, and water depth), sediment accumulation, water quality, fish communities, and the Fish Assessment Index (FAI). Water quality analysis showed a sharp increase in total phosphorus (TP) and organic matter loads at the downstream confluence (WQ4), indicating pollution inputs from domestic wastewater and tributaries. Mean sediment accumulation upstream of the weirs was 73%, with fine sediments and organic matter concentrated in reaches with large drop heights, forming stagnant zones. NMDS analysis based on fish ecological guilds (stress = 0.021) revealed spatial separation among sites, and low FAI values (W1 and W27) were associated with structural impacts and habitat simplification. Connectivity evaluation classified weirs into disconnection (20 sites, 74%), partial connection (2 sites, 7%), and connection (5 sites, 19%), indicating significant constraints on fish movement. A multimetric evaluation model integrating physical (M1), biological (M2–M6), and functional (M7) indicators identified six priority weirs for improvement. Improvement of these weirs was projected to increase longitudinal connectivity from 41.8% to 56.5%.