Impacts of Channel Morphodynamics on Fish Habitat Utilization

Impact evaluation of instream bar management using morphodynamic modelling

The Bow River's 2013 flood was the costliest natural disaster in the City of Calgary's history. Flood-induced bar growth and subsequent riparian vegetation colonization at many locations has constricted the river channel, which increases flood risk. Although bar removal has been widely employed as a flood mitigation strategy, its effectiveness and associated impacts are still uncertain. This study employs Delft3D to develop a two-dimensional (2D) morphodynamic model in order to evaluate the impacts of a conventional plan of bar removal and a novel plan of bar realignment in terms of flood mitigation, aquatic habitat protection and river recreation realization. A hydrodynamic model was firstly developed and calibrated using post-flood spatially distributed velocimetry data. A morphodynamic model was then developed and validated using post-flood bed elevation survey data. Then, the future channel response and flood peak levels using different bar management plans were modelled and compared. Results show that appropriate bar realignment can protect aquatic habitat and provide river recreation opportunities while bar removal performs the better in terms of lowering the future flood peak level. The findings indicate that manipulation on instream bars has little morphological impact to downstream reach and creating a less obstructed channel is the fundamental strategy in flood mitigation.

Site Fidelity, Habitat Use, and Movement Patterns of the Common Carp during Its Breeding Season in the Pearl River as Determined by Acoustic Telemetry

Understanding fish migration patterns and habitat use is essential for fisheries management. We conducted an acoustic fine-scale tracking experiment from March to June 2017 to determine the common carp movement pattern and habitat use in the downstream area of the Pearl River. The eight tagged common carp were detected for 39.38 ± 29.57 d, on average, with a total average detection period of 42.12 ± 28.02 d. A general linear mixed model suggested they were detected more during the night than during the day. Common carp preferred habitats near the sandbar and riparian shallow habitats, as revealed by their movement tracks and habitat selection indexes. The general additive mixed model (GAMM) analysis of their shortest distances to riverbanks and depth indicated that they migrated to shallower riparian habitat more frequently during the night than during the day. The continuous wavelet spectrum further confirmed the significant diel pattern of their vertical movement. Their habitat use was also influenced by the water temperature, water level, and river discharge, as suggested by the GAMM. Our results provide novel information on common carp spatiotemporal movement and habitat use patterns, and have important implications for its native population restoration and the invasive population control/exclusion.