Changes of river morphology and physical fish habitat following weir removal

Gongneung Weir-2 was built in the 1970s to supply water for irrigation. For a long time, the weir was left untended due to the land-use changes that were made to a nearby area. This weir was removed completely on April 4, 2006. The present study investigated the effect of the resultant flow-regime changes on river morphology and fish habitat. Observed changes in the grain size distribution, bed elevation, and cross-section pre- and post-weir removal are provided and discussed in this paper. Various bed zones such as a sand island and a vegetated marshy zone, which can diversify an aquatic habitat, formed after the removal. In fact, changes in the number of observed fish species post-removal also were investigated. Finally, specific changes to the physical habitat of Zacco platypus were numerically simulated using the River2D model. The results indicated that habitat suitability post-removal was enhanced for all flow discharges. The WUA values increased 32.3-53.4% for all life stages in the flow discharge of 1.5m³s^-1. The numerical results also showed that after the removal of the weir, the distribution of the physical habitat changed to reflect continuity near the weir.