Evaluation and causes analysis of changes in morphological diversity in Yichang-Chenglingji reach downstream of the Three Gorges Dam
The diversity of river channel morphology largely determines the diversity of physical habitats for riverine organisms,playing an important role in shaping the abundance and diversity of aquatic biological species.After the impoundment of the Three Gorges Dam,downstream riverbed underwent severe erosion and deposition adjustments,leading to changes in river channel diversity.Using field-measured fixed cross section morphology data from Yichang to Chenglingji in the downstream reach of the Three Gorges Dam during the years 2003 and 2018,the composite diversity index of the river channel was constructed based on indexes of longitudinal diversity,lateral di-versity and bathymetric habitat integrity.These indexes were employed to analyze the differences in diversity be-tween different river patterns and reaches after the impoundment of the Three Gorges Dam,and the causes of the changes.The results revealed that,morphological diversity varied across different river patterns,with correspond-ing differences in morphological diversity among different reaches.Meandering river patterns exhibited a lower kur-tosis coefficient and a higher proportion of low bars,resulting in higher diversity compared to other river patterns.Consequently,the Lower Jingjiang River,primarily characterized by meandering river pattern,exhibited greater diversity than other reaches.Following reservoir impoundment,overall morphological diversity in the downstream reaches generally decreased.However,changes in morphological diversity varied among different river patterns and reaches.Kurtosis coefficients increased significantly in straight river patterns under both low and bankful water lev-els,and was increasing in bifurcated river patterns under low water level,but decreased for meandering patterns under bankful water level.Accordingly,the kurtosis coefficient of the Lower Jingjiang Reach,dominated by mean-dering patterns,decreased.The difference in post-dam erosion and deposition adjustment patterns between different river patterns was the intrinsic mechanism that led to different trends in diversity change.The research findings can support to understand the changes in riverine habitats under the influence of human activities.
river habitatdiversityThree Gorges Damriver channel erosion
万方数据
维普
