近几十年来珠江三角洲网河水位时空变化及原因初探

Spatial and temporal characteristics of water level change and its causes in the Zhujiang Delta in recent decades

根据珠江三角洲网河区25站的验潮序列,应用功率谱分析和正、反傅氏变换方法对网河区月均水位序列的周期变化和趋势变化进行研究,探讨大规模人类采砂活动对珠江三角洲网河区近几十年来水位变化的影响。结果表明:水位序列中包含0.2～11.7a多尺度的显著周期波动;应用正、反傅氏变换方法消除月均序列中的短周期波动(消除6a以短的周期),由低通序列进行一元线性回归分析确定水位变化率,变化率从-3.8到3.7mm/a不等,珠江三角洲网河区水位总体呈上升趋势。从网河区上段到下段再到口门,水位变化趋势由下降转为上升;变化率由负转正,并逐渐增大。网河区上段部分验潮站水位下降主要与西北江网河上段大规模无序采砂引起的河床大幅人为下切有关;大规模采砂导致局部水位下降,使不同时段的水位变化率发生波动,甚至造成部分验潮站的水位变化由缓慢上升转为大幅下降的"逆变"。

Based on the measured tide gauge records at 25 stations in the Zhujiang Delta,the periodic oscillations and secular trends of water level series were studied with Power spectra analysis and Fourier transformation analysis.The Power spectra analysis of monthly mean time series reveals that there were several predominant periods of water level change,varying from 0.3 a to 11.7 a.Results from Linear regression of low-passed time series which were the outcome of Fourier transform process suggest that the water level of river network of Zhujiang Delta was rising in general,and the rate of water level change generally ascended as shifting from the top of the delta to the outlets of the Zhujiang River.The rates of water level change of 25 tide gauge stations differ from-3.8 mm/a to 3.7 mm/a,and the secular trend of seven stations among them was descending,which was largely due to large-scale disordered sand excavation in the upper reaches of the Xijiang and Beijiang River network.Analysis on the change in the rates of water level change of different periods indicates that large-scale sand excavation in the river network which led to bed scour and deepening resulted in the significant fluctuation of water level,and even reversed the secular trend of water level change.