Hydrological Change Characteristics And Risk Assessment In The Xiaoqing River Estuary

The estuary is a special area affected by the combined effects of runoff and tide,and the hydrodynamic characteristics often change.Under the joint influence of climate change and human activities,hydrological cycle processes undergo changes.In recent years,extreme hydrological events have occurred frequently in the estuary area,posing a serious threat to the local socio-economic situation.Therefore,studying the characteristics of hydrological changes in the estuary and comprehensively assessing the hydrological risks at the estuary have certain scientific value and practical significance.This article takes the Xiaoqing River estuary as the research area.Firstly,methods such as linear regression,5a moving average,Mann Kendall test,cumulative anomaly,sliding rank sum test,ordered clustering,and wavelet analysis are used to analyze the trend,mutation,periodicity,and annual variation characteristics of the hydrological and meteorological elements at the Xiaoqing River estuary,revealing the characteristics of changes in hydrological and meteorological elements in the past 60 years.Secondly,establish a two-dimensional hydrodynamic numerical model for the Xiaoqing River estuary,simulate the flow characteristics of the Xiaoqing River estuary under storm surge and different flood tide combinations,and analyze the hazards of the Xiaoqing River estuary under different scenarios based on the simulation results.Finally,the index evaluation method is used to establish the hydrological risk assessment system of Xiaoqing River estuary,and the comprehensive assessment value of hydrological risk of Xiaoqing River estuary in 2011-2021 is calculated after determining the weight of each index with the improved analytic hierarchy process and entropy weight method,so as to comprehensively assess the hydrological risk of Xiaoqing River estuary.The main research results of this article are as follows:(1)By analyzing the trend,mutation,and periodicity of the changes in hydrological and meteorological elements at the mouth of the Xiaoqing River in the past 60 years,it can be concluded that the annual precipitation in Shicun showed a slow upward trend from 1959 to2021,with a sustained characteristic.The mutation years were 1964 and 2017.The annual precipitation in Yangjiaogou shows a slow downward trend with a weak anti sustainability feature,with abrupt changes occurring in 1974 and 2017.The annual precipitation in Shicun and Yangjiaogou both fluctuates periodically with the first main period of 22 years.The annual average flow rate in Shicun showed a significant upward trend from 1956 to 2021,with a persistent characteristic.The year of mutation was 2003,and the first main cycle was 22 years,with periodic changes.The annual average high tide level,annual average low tide level,and annual average half tide level in Yangjiaogou showed a significant upward trend between 1957 and 2019.Among them,the annual average low tide level has a persistent feature,while the annual average high tide level and annual average half tide level have a counter persistent feature.The mutation years of the annual average high tide level,annual average low tide level,and annual average semi tidal surface in Yangjiaogou are 1989,1998,and 1997,respectively,with 27 years,17 years,and 21 years as the first main periods for periodic changes.By analyzing the annual variation characteristics of various hydrological and meteorological elements,it can be concluded that the annual variation of precipitation in Shicun and Yangjiaogou has obvious seasonal characteristics,mainly distributed from June to August.The flow rate in Shicun and the annual variation of the average high tide level,average low tide level,and average half tide level in Yangjiaogou also have seasonal characteristics,with higher values from July to September.(2)Establish a two-dimensional hydrodynamic numerical model for the Xiaoqing River estuary and calibrate and verify the model parameters.By simulating the characteristics of water flow changes under different combinations of storm surges and flood surges,it can be concluded that the amplitude of water level changes along the way during the highest tide period is smaller than that during the peak flood period.The closer the tide level reaches the highest,the more significant the fluctuation amplitude of downstream flow velocity is.There is a lateral slope of water surface at the bend of the river.Comparing the simulation results under different flood tide combinations,it can be seen that the greater the runoff effect or the lower the downstream tide level,the greater the decrease in water level along the way and the faster the flow velocity.According to the analysis of simulation results,it can be concluded that under the scenarios of storm surge and different flood tide combinations,there is relatively high risk within the range from the Wangdao Gate to the Laolou River mouth and at the bend of the river.Therefore,when dealing with hydrological disasters such as floods and storm surges,it is necessary to monitor the local rainwater situation at the entrance of the sea in real-time,with a focus on the flood trend of the main stream and the inlet of various tributaries within the range from the Wangdao Gate to the Laolou River mouth,as well as the changes in the water level of the concave bank at the bend of the river,Strengthen the inspection of embankments at the entrances of the main stream,various tributaries,and various bends of the river within this scope.(3)Using the indicator evaluation method to establish a hydrological risk assessment system for the Xiaoqing River estuary,a comprehensive evaluation of the hydrological risk at the Xiaoqing River estuary from 2011 to 2021 was conducted.The results showed that the overall hydrological risk assessment value at the Xiaoqing River estuary showed an upward trend from 2011 to 2021,with medium to high risk in 2018 and 2019,and medium risk in the remaining years.In the criterion layer,hydrological and meteorological factors are the main influencing factors of hydrological risk at the Xiaoqing River estuary.The evaluation value of hydrological and meteorological risks and its proportion to the comprehensive evaluation value of hydrological risks are relatively large between 2011 and 2021.The relatively small proportion of river structure and socio-economic risk assessment values to the comprehensive hydrological risk assessment value indicates that the impact of river structure and socioeconomic factors on the hydrological risk of the Xiaoqing River estuary is relatively small.