Evolution And Prediction Of Groundwater Dynamic Field In Plain Area Of Baiyangdian Watershed

Groundwater has the characteristics of large reserves,wide distribution,good water quality,and easy application.It plays an indispensable role in the supply of water resources.At the same time,groundwater circulation is also an extremely important part in the evolution of natural ecology.The current unreasonable development of groundwater resources has caused the regional water level to continue to fall,and the resulting secondary environmental geological problems have occurred frequently,such as land subsidence and ecological vegetation degradation.Reasonable use of groundwater resources,balanced development and the contradiction between ecosystems are urgent problems to be solved.Xiong'an New District is a nationally planned new district.As a template for China's future urban development,groundwater is an important support for its construction and development.Analyzing the evolution of the groundwater dynamic field in this area can provide a scientific basis for the construction of the new district and the rational use of water resources.Based on the national key research and development plan,"Xiongan New Area Groundwater Environmental Risk Prediction,Warning and Prevention Project",and the Baiyangdian River Basin Plain as the research object,comprehensive use of data collection,field supplementary survey,hydrogeological survey and groundwater flow Numerical simulation and other methods are used to study the spatial and temporal evolution characteristics of groundwater dynamic field,construct a three-dimensional groundwater flow numerical model,and predict the evolution law of groundwater dynamic field in the study area in the future.Mainly achieved the following recognition and results:(1)In the past 40 years,the evolution trend of the shallow groundwater system in the study area is that the groundwater level continues to decline,the shallow groundwater forms a water level dropping funnel,and the local flow direction changes.The direction of water flow changed from a single piedmont to Baiyangdian to local water level,the edge of the funnel area flowed to the center,and Baiyangdian groundwater flowed to the surroundings.Spatially,the shallow water level in the southern Anxin County to Gaoyang County decreased by 30-40m,the northern water level in Xiong County decreased by 20?30m,and the Baoding-Xushui-Rongcheng water level decreased by 10?20m.The groundwater level of the deep layer has dropped overall.The drop in water level in the east is greater than that in the west.The drop in water level in the west is 5?10m.The drop in water level in Anxin County and Gaoyang County in the east is 25?35m.(2)By analyzing the dynamic curves of groundwater time series water levels in four locations in Anxin,Rongcheng and Xiong County in the past 30 years,the overall groundwater level in the study area showed a downward trend.Among them,the shallow groundwater level in Rongcheng County was 0.65m/a,the shallow groundwater level in Anxin County was0.52m/a,the shallow groundwater level in Xiong County was 0.50m/a,and the deep groundwater level in Xiong County was 0.79m/a.In descending rate,deep layer>shallow layer,Rongcheng>Xiong County>Anxin.(3)The eco-environmental effects of groundwater level drop in the study area are mainly water level funnel,ground subsidence,ground fissures,etc.The largest water level funnel,HD Lili water level funnel area increases year by year.By 2000,the area of the funnel area increased to 1091km2.By 2015,the water level in the center of the funnel dropped by about 40m.In the entire North China Plain,in 1988,the subsidence area reached 300mm with a surface area of15253km^2.The main factors that cause the groundwater to fall are rainfall and the amount of extraction:the increase in rainfall and the decrease in the amount of extraction cause the groundwater level to rise or fall and the phenomenon of slowing down is slowed down.(4)Comprehensive analysis of regional hydrogeological conditions,the main recharge of groundwater is precipitation recharge,and the main drainage methods:artificial mining and lateral runoff.Through calculation,it is concluded that the recharge of groundwater in the study area is 263737.52×10⁴m³/a,the discharge volume is 297356.8×10⁴m³/a,the equilibrium difference is-33619.28×10⁴m³/a,and the overall balance is negative.The precipitation infiltration amount is 183531.18×10⁴m³/a,which accounts for 69.5%of the total replenishment items,followed by the lateral replenishment amount of 46757.64×10⁴m³/a,which accounts for17.72%of the total replenishment items.The volume of 281693.82×10⁴m³/a is the main excretion volume,accounting for 94.72%of the total excretion volume.(5)On the basis of comprehensive hydrogeological conditions,a three-dimensional geological structure model,a hydrogeological conceptual model and a three-dimensional numerical model of groundwater flow were constructed based on GMS.The conjugate gradient method(PCG)was used to solve the model,and the infiltration system was retrieved by PEST Select appropriate hydrogeological parameters,and after model identification and verification,the constructed model conforms to the actual situation in the study area,meets the prediction accuracy requirements,and is used for model prediction.(6)According to the construction plan of Xiong'an New District and the requirements of water resources development and utilization and ecological environment restoration,three water resources development and utilization and ecological restoration schemes were set up to simulate and predict according to different situations.The results show that under the current annual exploitation,the regional groundwater level continues to decline,and the water level in the observation hole drops to a maximum of 10m and a minimum of 5m;in the case of pressure extraction in the study area,the regional groundwater basically reaches a balance of recharge and discharge,and the groundwater dynamic field Changes have occurred,in which the central water level of the high-definition lili water level funnel area increased by 4?6m,and other areas increased by an average of 0?2m.The downward trend of groundwater in the water level observation hole slowed down;Baiyang Lake was ecologically replenished by external water transfer,which expanded the water area and increased the recharge in the study area.The equilibrium difference was 4058.877×10⁴m³,which made the study area in a positive equilibrium state and changed the local area.The spatial distribution of groundwater increases the groundwater level in the area along the supplementary water and around Baiyangdian.Among them,the water level in the east of Gaoyang County rose the most,being 10-12m.The water level in the center of HD Li Funnel increased by 4-6m,and the water level around Nanjuma River to Baigou River increased by 2?4m.