Abstract:

To investigate the impacts of river-channel erosion and deposition evolution on the ecological sluice gates and water diversion outlets along the middle reaches of the Tarim River mainstream, Xinjiang, China, a fluvial process model of the Yingbazha-Wusiman reach under the 2018 shoreline conditions was established and validated in MIKE21 software. Incorporating the geomorphic acceleration factors, the model simulated the decadal channel evolution under varying water-sediment conditions under five hydrological scenarios (wet, normal, dry, extreme flood, and extreme drought years). The results indicate th following: (1) Significant differences in the river-regime evolution processes under different water and sediment conditions. (2) Diversion-inlet siltation, bend cutoff and bank erosion, channel straightening through meander truncation, and river course realignment in certain river regions during exceptionally heavy flood years and typical high-flow years. In particular, the scour and silting evolution intensifies with increasing incoming water and sediment volumes. The river channel is characterized by meandering paths at low water levels and straighter paths at high water levels. Meanwhile, the morphological changes under high-flow conditions have increased the operational difficulty of diverting the water through the ecological sluice gates, sometimes leading to complete water-diversion failure. For instance, when the siltation elevation at the Kahatuhedi sluice exceeded the maximum flood level by 0.71 m, the water diversion was completely blocked and the ecological water supply to the right bank was compromised. Flow-direction changes in the Yilanlike sluice also threatened the right bank embankments. In dry scenarios, the channel sinuosity increased by 6.8% (to a total length of 212.05 km), albeit with less dramatic morphological changes than in wet years. (3) To maintain the functionality of water diversion, the authors recommend proactive regulatory measures that prevent inlet siltation and bend instability in bend segments containing sluices, particularly in free meanders. These findings enhance our understanding of erosion-deposition trends in meandering reaches of the Tarim River mainstream, providing scientific guidance for future management and sustainable development of the middle reach.

Key words: mainstream of Tarim River, erosion-deposition variation, MIKE21, ecological water diversion, meandering river