The barrier river reach identification and classification in the Middle Yangtze River

• Published in: Frontiers of earth science 2019-09, Vol.13 (3), p.596-613
• Main Authors: TANG, Jinwu, HU, Chunyan, YOU, Xingying, YANG, Yunping, ZHANG, Xiaofeng, DENG, Jinyun, CHEN, Meng
• Format: Article
• Language: English
• Subjects: Average flow; channel adjustment; Channel morphology; Correlation analysis; Discharge; Downstream; Duration; Earth and Environmental Science; Earth Sciences; Floodplains; Flow rates; Flow velocity; identification and classification; Propagation; Research Article; River beds; River management; River regimes; River regulations; Riverbeds; Rivers; Sediment; Sediment transport; Stability; Thalweg; thalweg migration; the barrier river reach; Upstream; Water depth; Width; Yangtze River
• ISSN: 2095-0195; 2095-0209
• DOI: 10.1007/s11707-018-0689-9

Adjustments of upstream river regimes are one of the main factors affecting downstream fluvial processes. However, not all adjustments of river regimes will propagate downstream. There are some distinctive river reaches where upstream and downstream adjustments have no relevance. However, the irrelevance is neither caused by different river types nor by the different conditions of water and sediment; but rather, the channel boundaries and riverbed morphologies block the propagation effect. These are referred to here as the barrier river reach phenomena. The migration of the thalweg line is the essential reason for causing the propagation effect. Numerous influencing factors for thalweg migration exist, including 1) the average flow rate above the critical bankfull discharge, the average flow rate below the critical bankfull discharge, and their ratio, 2) the ratio of the duration of the aforementioned two periods, 3) the thalweg displacement at the entrance of the river reach, 4) the deflecting flow intensity of the node, 5) the ratio of the river width to water depth, 6) the relative width of the floodplain, and 7) the Shields number. In this study, the correlativity between the measured distances and the restricting indicators of thalweg migration in the Middle Yangtze River over the years was established. The barrier degree of 27 single-thread river reaches was subsequently assessed. These reaches included 4 barrier river reaches; 5 transitional reaches transforming from barrier to non-barrier; 10 transitional reaches transforming from non-barrier to barrier; and 8 non-barrier river reaches. Barrier river reaches were found to be important for maintaining the stability of the river regime and the transverse equilibrium of sediment transport in the downstream reaches. To some extent, the barrier river reaches may protect the natural dynamical properties from being destroyed by artificial river regulation works. Thus, they are of great significance for river management.