Response of shallow groundwater to rain-storm flood in Anyang City plain area
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Abstract:
The North China Plain has become the most serious groundwater overexploitation area in China due to development and utilization of groundwater resources.Rainwater resources have gradually attracted people′s attention because of potential water resources.However,most of the current researches focuses on increasing the conversion rate of rain-flood resources and analyzing the fluctuation of groundwater level,lacking the concerns on the characteristics and amount of groundwater recharge under the influence of rain-storm flood events.Based on the systematic analysis of rain and flood events,the response characteristics of groundwater to rain-storm flood events is discussed,a groundwater recharge solution model based on ArcGIS software is proposed to quantitatively analyze the response of groundwater to the events. 7/19 heavy rain-storm flood event in Anyang City is taken as an example.Based on the long-term monitoring data of groundwater level and rainfall,the grey correlation coefficient between the elevation value of groundwater level and the precipitation in the corresponding period is calculated,and the correlation between the variation range of groundwater level and the precipitation is determined.The collected monitoring data of the 7/19 heavy rain from groundwater level monitoring wells and precipitation monitoring stations in the plain area of Anyang City are used to analyze the spatial distribution characteristics of rainfall.Groundwater recharge solution model is established through ArcGIS according to the temporal and spatial distribution characteristics of rainfall and the changing trend of groundwater level.The steps are as follows:the variation of groundwater level is calculated and the point data is filled into the whole study area by Kriging interpolation;use the surface analysis tools of ArcGIS to partition data such as water level variation and hydrogeological parameters to establish corresponding attribute thematic layers;perform overlay analysis on attribute thematic layers,define projection to calculate the recharge of groundwater. The correlation coefficient show that phreatic level and precipitation is greater than 0.85,which reflects the amount of groundwater resources is significantly affected by rainfall intensity.The 7/19 heavy rain formed two rainfall centers:One is located in the western part of Anyang County and the northeastern part of Linzhou,distributed in a north-south direction.Other one is located in the urban area of Anyang and central Anyang County,distributed in a southeast-northwest direction.The total process of flood discharge caused by heavy rain lasted 40 hours.The total amount of discharged floodwater reached 65.6 billion m3 based on estimation of the large cross-section measurement in Anyang Station.The model calculated total amount of groundwater recharged to the study area was 519 million m3,the flood conversion rate was 0.8%.Using the same model to analyze the storm flood events since 1980,the response degree of shallow groundwater to storm floods is directly proportional to the precipitation intensity. Compared with other studies,it is an efficient,intuitive,and feasible method to establish a solution model by using ArcGIS software to determine groundwater recharge which has relatively low data requirements.In addition to the 7/19 event,the analysis and calculation of three torrential rain and flood events in Anyang City exhibited good results.This model is suitable for the calculation of groundwater replenishment and quantitative analysis of rainwater resource utilization in areas with limited data.It also provides a certain reference value for rainwater resource utilization and groundwater response analysis.Under the influence of human activities,there are various correlations between the change of shallow groundwater level and precipitation in different regions.It is necessary to determine the correlation between the change of groundwater level and precipitation to exclude the influence of other factors on the change of groundwater level to ensure the accuracy of the model.
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