长江中游田家镇深槽的特征及其泄洪影响

Features of Deep Trough at Tianjiazhen Reach and Its Impacts on Flood Discharge in the Yangtze River

长江中游田家镇附近江面最狭处仅650m,江底最深处低于黄海基准面以下-90m,是长江干流河床突出的最低所在,距离长江口900km。通过实地地质地貌调查揭示田家镇深槽形成及其对洪水的渲泄有何影响。根据地质、水文、地形和直接考察资料,卡口深槽段长8km,系长江自NW-SE斜切过一排强烈褶曲的三叠系厚层石灰岩山地而成,3个临江石灰岩小山所成矶头导致江流方向变化与流速加速,以至形成多处涡流,向江底侵蚀,而褶皱的石灰岩抗拒侵蚀、溶蚀能力很低,因而导致远低于海平面深槽的形成,估计卡口深槽是从中更新世红色风化壳发育的和缓起伏的地面上叠置下来,已有以10万年年计的长远历史。近数十年多次实测资料比较,侵蚀淤积有小量变化,但河床基本稳定。对正常的中、枯水位江流运行没有影响,但对超过50000￣60000m3/s洪水的排泄则有明显的壅阻作用。

The width of the river reach near Tianjiazhen (23o55'N, 115o25'E), the middle Yangtze River, is only 650 m. The depth of this river reach is 90 m belo w the sea level of the Huanghai altitude, being the lowest place of the Yangtze River, which is about 30 km away from the river mouth. This narrowest width and the lowest depth is unique and intriguing. Some problems are put forward: what i s the formation of this river trough and what is the role of this river trough o n flood discharge. Geologic, hydrological and geomorphologic records and field i nvestigation indicate that the horizontal length of this trough is about 8 km, w hich was formed by the NW-SE cut through an intensively folded range of thick Tr iassic limestone by the Yangtze River. Three small limestone hills near the rive r serve as the node, influencing the river flow patterns and causing accelerated river flow and whirlpools, the calcareous rocks are highly susceptible to the c orrosion and intensified downward erosion, so that the deepest trough is formed. The life of this river trough is estimated to be several thousands of years. Re cent repeated instrumental measurement results indicate that the river reach at Tianjiazhen is in minor changes in erosion and sedimentation with relatively sta ble channel shapes. The river trough exerts no influence on flood discharge duri ng the normal water runoff; while it plays a significant role on flood discharge when the runoff exceeds 50 000-60 000 m3/s.