珠江三角洲网河区水文与地貌特征变异及其成因

采用珠江三角洲网河区数十年来的人类活动和水文特征资料，通过分析人类活动的水文响应特征，发现该地区近10年多来水文情势发生了显著异变。主要表现在河道人工采砂以及大洪水冲刷导致河床下芬，部分断面水位－流量关系异变。部分河段冲淤特征倒转，汊河分水分沙比发生变化。围垦，臾，码头建设以及水闸的不合理调度使得水量集中，蓄滞洪能力减小，河道流量增加。三角洲上部河床剧烈下切，汇流速度加快；而口门多呈淤只状态，加之海平面上升，潮流顶托阻水，三角洲腹地水位抬升，洪涝威胁加剧。剧烈人类活动是珠江三角洲网河区水文与地貌特征变异的直接原因。

Hydrological Change and Its Causes in the River Network of the Pearl River Delta

This paper aims to summarize and illustrate a variety of human-induced hydrologic and geomorphic changes in the Pearl River Delta (PRD) and to analyse the causes and effects.The hydrologic characteristics of the river network have been altered in the following three main aspects. First, stage has become higher or lower over the past decades in an uneven manner in the delta. From the early 1950s to the 1980s, scattered and small embankments were enlarged and combined to expand land mass and reduce flood hazards in the PRD. However, reduction of water surface area and concentration of flow into major channels generally caused stage to go up slightly. Secondly, corresponding to the stage changes, the stage-discharge relationship has been substantially modified, as evidenced by over 2 m drop of stage for the same amount of discharge. Thirdly, the ratio of flow partition into two channels at several river bifurcation points has continuously changed over the past decade. Closely associated with the hydrologic changes are alterations of river channel and estuarine morphologies. Such geomorphic changes primarily include noticeable or even alarmingly severe modification of river channel bed, extension of river mouth and contraction of estuary in the study region. It was found that the hydrologic and geomorphic changes that have occurred within a relatively short period of time are mainly consequences of a wide variety of human activities, coupled with influences of natural events, including (a) channel dredging of sand for construction usage, (b) combination of embankments and construction of dams, (c) channel constriction and reduction or complete loss of floodplain, (d) sea level rise, and (e) channel bed erosion by record floods.