黄河宁蒙段洪水过程变化特点

Characteristics of Flood Regime in Ningxia-Inner Mongolia Reaches of the Upper Yellow River

采用Pettitt法和里海哈林法(Lee-Heghinian)检验了流量年际变化中的突变现象,所得到的突变点将宁蒙河段年径流过程划分为三个阶段,即:1969年前;1969年-1986年;1986年以后。分析了三个阶段洪水过程的各自特点,结果显示:1969年前洪水峰型相对多尖瘦,常为多峰型;1969年-1986年洪水过程的特点和前一时期相比,洪水峰型变胖,多为单峰型。1986年以后主要为中小洪水,中小洪水矮胖,洪峰低,历时长。从气候变化、支流来水、灌溉引水、水利工程影响等四个方面分析了洪水变化的原因,发现人类活动(水库修建、灌溉引水)是造成宁蒙河段洪水年内、年际变化的主要原因。气候变化在一定程度上减少了宁蒙河段的来水量,支流对宁蒙河段水量变化影响微弱。

The Yellow River is famous for its high sand content,frequent flood,frequent channel change,and unique channel characteristics in the lower reaches.These changes and characteristics have been well studied.However,Ningxia-Inner Mongolia reaches of the upper Yellow River have experienced a series of changes in recent years.Much more common changes resulted mostly from the impacts of dams on fundamental fluvial processes,and the flow as well as sediment transport regimes.Decreased water quantity and flood magnitudes led to adjustments of the size and shape of the river channels.In the meantime,the amount of sand from the Qingshui River and Ten Great Gullies which is carried by flooding during the flood periods into the Yellow River is increasing.This made the Ningxia-Inner Mongolia reaches of the upper Yellow River converted into a suspended river.Based on data of discharge of flood seasons,characteristics of flood regime in the Ningxia-Inner Mongolia reaches of the upper Yellow River were analyzed.The Pettitt and Lee-Heghinian statistical methods were used to test trends of changes in the discharge.Results indicate that the time series of discharge in Ningxia-Inner Mongolia reaches of the upper Yellow River can generally be divided into three periods,i.e.,before the year 1969,1969-1986,and after the year 1986.Analysis of characteristics of flood regime of the three periods leads to the findings as following.Before 1969,the flood peaks were much thinner,and had often multiple peaks within a year.During the second period,the flood peaks became fatter than the previous period,and mostly had a single peak within a year.After 1986,the flood was essentially small and medium-sized,and lasted longer than the last two periods.Reasons for these changes in the flood regime from aspects of climate change,water input from tributaries in flood seasons,irrigation and water diversion,and influence of water conservancy projects were expounded.The statistics show that human activities,especially construction and operation of large reservoirs,were the primary reason for the change in the flood regime.Climate change reduced water quantity to a certain degree.Water input from the tributaries had less influence on the flood regime.