近60年来极端天气影响下南流江入海水沙变化

Variations in water and sediments of the Nanliu River flowing into the sea under the influence of extreme weather in the past 60 years

河流入海水沙变化是河口三角洲演变研究的重要内容。在全球气候变暖引起的极端天气频率和强度增加的背景下,研究极端天气影响下的河流入海水沙通量变化对于理解河口三角洲海岸环境演变具有重要的科学意义。本文以山溪型中小入海河流--南流江为例,基于1966—2020年的水沙、洪水实测数据,采用变差系数和数理统计等方法分析极端天气影响下的南流江入海水沙变化规律。研究结果表明:(1)热带气旋过境期间多年日平均流量为7.72×10^(2) m^(3)·s^(-1),是正常天气下(1.63×10^(2) m^(3)·s^(-1))的4.73倍;热带气旋过境日均输沙量的多年平均值为2.55×10^(4) t,是正常天气下(0.19×10^(4) t)的13.42倍。热带气旋期间,入海水沙量大,具有“丰水多沙”的特点。(2)洪水期间的多年日平均流量和输沙量分别为8.53×10^(2) m^(3)·s^(-1)和3.07×10^(4) t,分别是正常天气下日平均流量(1.56×10^(2) m^(3)·s^(-1))和输沙量(0.17×10^(4) t)的5.46倍和18.18倍。洪水期间,来沙量越大,入海泥沙通量越大,呈现“多来多输送”的典型特征。(3)极端天气对南流江入海水沙通量具有重要的贡献作用,热带气旋对径流量和输沙量的多年平均贡献率分别为6.78%和19.31%,而洪水对径流量和输沙量的多年平均贡献率分别为14.33%和36.21%。

The change of river inflow sediment is an important content in the study of estuarine delta evolution.Against the backdrop of increased frequency and intensity of extreme weather caused by global warming,it is of great practical significance to study the variability of sediment fluxes in rivers entering the sea under the influence of extreme weather for understanding the environmental evolution of estuarine deltas.This paper takes the Nanliu River,a small and medium-sized river flowing into the sea,as an example.Based on the measured data of water,sediment and floods from 1966 to 2020,the variation coefficient of variation and mathematical statistics are used to analyze the variation law of water and sediment under the influence of extreme weather.The research results show that:(1)the multi-year average daily flow during the transit of tropical cyclones is 7.72×10^(2) m^(3)·s^(-1),which is 4.73 times that of normal weather of 1.63×10^(2) m^(3)·s^(-1).The multi-year average of the average daily sediment transport of tropical cyclones was 2.55×10^(4) t,which is 13.42 times that of 0.19×10^(4) t in normal weather.During the tropical cyclone,the amount of sediment entering the sea is large,and it has the characteristics of"rich water and sand";(2)the multi-year average daily flow and sediment load during the flood period were 8.53×10^(2) m^(3)·s^(-1) and 3.07×10^(4) t,respectively,which were the average daily flow(1.56×10^(2) m^(3)·s^(-1))and sediment load(0.17×10^(4) t)5.46 times and 18.18 times.During floods,the greater the amount of incoming sediment,the greater the flux of sediment into the sea,showing the typical feature of“more incoming and more transportation”;(3)extreme weather has an important contribution to the sediment flux of the Nanliu River into the sea.The multi-year average contribution rates of tropical cyclones to runoff and sediment transport were 6.78%and 19.31%,respectively,while the multi-year average contribution rates of floods to runoff and sediment transport were 14.33%and 36.21%,respectively.