珠江三角洲顶点思贤滘分流自适应调节机制

Adaptive regulation mechanism of the Sixianjiao channel at the apex of the Pearl River Delta for flow diversion

近年来珠江三角洲顶点思贤滘区西、北两江分流发生重大调整,并影响三角洲的防洪及供水格局,开展思贤滘分流研究对于三角洲分流调控及治理具有重要意义。本文采用20世纪60年代以来思贤滘区水文地形资料,利用物理模型、数学模型、理论分析等方法,分析思贤滘分流自适应调节规律及其机制。结果表明:思贤滘是一个天然的洪水调节器,具有稳定西、北江洪水分流比的作用,洪水越大,西江马口与北江三水流量之比越稳定,其稳定值约为3∶1,思贤滘下游约7 km河段地形是洪水期间分流自适应调整的主控因素,河道受两岸堤防约束,随着上游流量的增大,西、北江过水断面面积之比趋于定值,驱使两江分流比也趋于定值;当枯水期下游潮汐顶托或闸门启闭等作用引起河段发生变动回水时,思贤滘分流相应调整,且分流比对北江下游水体变化更为敏感。

In recent years,the Sixianjiao channel at the apex of the Pearl River Delta has undergone substantial changes in diverting the flow between the Xijiang River and the Beijiang River,which in turn has dramatically affected the flood prevention and control strategies and the water supply configurations in the delta.Therefore,research into the flow diversion process of the Sixianjiao channel is essential for the effective governance and control of flow diversion throughout the delta.The aim of this study was to elucidate the pattern and mechanism of the adaptive regulation of the flow diversion of the Sixianjiao channel using physical and mathematical models and theoretical analysis of a combination of hydrological and topographical monitoring data for the Sixianjiao region since the 1960s.The results show that the Sixianjiao channel acts as a natural regulator during floods,maintaining a steady distribution ratio of floodwater between the Xijiang and Beijiang rivers.The flow ratio between Makou in the Xijiang River and Sanshui in the Beijiang River becomes increasingly stable as the flood intensity increases,typically with a ratio of approximately 3∶1.The topography of the approximately 7 km long river segment downstream of the Sixianjiao region is the primary factor controlling the adaptive regulation of the water diversion during flood periods.As the upstream flow increases,the ratio of the flow cross-sectional areas of the Xijiang and Beijiang rivers tends to approach a constant value due to the constraint by the embankments on both sides of the two rivers,thereby leading to stabilization of the water diversion between the two rivers.During the low-flow period,the tidal backwater in the downstream region or the operation of sluice gates leads to changes in the hydraulic gradient,which in turn triggers changes in the water diversion in the Sixianjiao channel.The diversion ratio is more responsive to changes in the water body downstream of the Beijiang River compared with the Xijiang River.