| Xixian New Area,as the core area of the Guanzhong-Tianshui Economic Belt,occupies an important position in the future economic development pattern.As the main water supply source of the new area,groundwater has caused a series of environmental geological problems in recent years due to unreasonable exploitation,which has seriously affected the construction of urban ecological civilization or the sustainability of urban development.At the same time,with the change of urbanization process,the influence factors of groundwater,such as precipitation,runoff,evaporation,etc.,also showed new characteristics,and the response of groundwater to them also changed accordingly.Therefore,this paper focuses on the groundwater depth of Xixian New Area,studies the dynamic characteristics of groundwater level under the influence of climate change and human activities,and predicts future trends,which can be used for the future development,utilization,management and protection of groundwater resources in Xixian New Area Provide a certain scientific basis.The main research results are as follows:(1)The temporal variation characteristics of groundwater depth in the study area are analyzed.According to the intra-year variation characteristics,the dynamic types of groundwater in the study area can be divided into two types.The fluctuation type is more obviously affected by the seasons;according to the characteristics of the interannual changes,the overall depth of the groundwater table in the Xixian New Area showed an increasing trend from 1990 to 2016.From 1990 to 2002,the water level dropped significantly,with a rate of0.68m/a,The rate of water level decline slowed from 2003 to 2016,and the rate was 0.27m/a;the MK mutation test was used to analyze the buried depth of the groundwater level in the study area.The mutation years of the buried depth are 1995,2004,and 2003,respectively.The mutations are mainly affected by human factors.(2)The contour maps of groundwater depth in the early stage of the planning of the Xixian New Area in 2010 and the current year 2016 were drawn.The results showed that the spatial distribution of the groundwater depth in the Xianxian New Area was basically consistent with the change in terrain elevation.The groundwater in the Loess Plateau in the North The buried depth is large and the contour lines are dense;in the southern and northeastern river terrace areas,the groundwater level is small and the contour lines are relatively sparse.Compared with 2010,the contour lines in the southern river terrace area of the Wei River changed smoothly in 2016 and 2010.The burial depth of the groundwater table decreases,and the water level rises significantly.The contour lines of the Loess Plateau area in the north are denser,the burial depth increases,and the water level drops significantly.(3)Analyze the impact of precipitation,runoff,evaporation and exploitation on groundwater using correlation analysis method.The results show that various factors have varying degrees of impact on the buried depth of groundwater level,and the recharge effect of precipitation on groundwater exists for 1 to 2 months During the lag period,the ratio of precipitation and production increases by 0.01 unit,the average depth of water level will decrease by 0.2m;the correlation coefficients of runoff and water level during the two periods of 1990-2002 and 2003-2016 are 0.88 respectively,037,indicating that the impact of runoff on groundwater is gradually weakening,evaporation has a weaker effect on groundwater burial depth,the correlation coefficient is 0.33,and mining has a significant impact on groundwater level burial depth,the correlation coefficient is 0.77,and the amount of groundwater exploitation increases by every 10~7m~3,the groundwater level in Xixian New Area will drop by 0.5 m.(4)The principal components analysis method and grey correlation method were used to determine the leading factors for the change of groundwater depth in the study area.The results showed that the mining and precipitation from 2001 to 2016 were the leading factors for the dynamics of groundwater depth in the area,and the correlation coefficient 0.86,0.82.(5)For the annual average groundwater depth of the Xixian New Area,the gray model GM(1,1),the multivariate time series CAR model and the gray-BP neural network combination model were established,and the results showed that the gray-BP neural network combination The model has the best effect,and the model is used to carry out burial depth prediction under different mining scenarios in the study area.The results show that under the current mining conditions and the control indicators of groundwater extraction in 2020,the groundwater level will show an increasing trend.The velocities are 0.22m/a and 0.55m/a,respectively,and the extraction volume is reduced by 10%on the basis of the current year,which can approximately maintain the dynamic balance of the groundwater level,indicating that the reduction in extraction volume can make the groundwater level recover well. |
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