Spatiotemporal Variability Of Groundwater Level And Response Of Irrigation Water In Typical Area Of Well Irrigation

North China Plain is the main area of grain and vegetable production,and the groundwater is the main water sources for irrigation.There has caused a series of environmental and geological problems such as the groundwater level continued to decline,the ground subsidence cracks,salt water interface into the invasion of deep fresh water,ecological degradation and groundwater pollution because of long-term disorderly mining,which is the threaten to food security in China.Feng Nan District of Tangshan is a typical groundwater exploitation area in North China.We can provide guidance for managing and scheduling groundwater resources based on exploring the spatiotemporal variability of groundwater level,establishing hydrology system simulation and seeking reasonable groundwater exploitation and utilization scheme under different irrigation modes.Through the study,the main results obtained are as follows:(1)The spatiotemporal variability of groundwater depth in fresh water and salt water area was studied by the usage of the method of geostatistics based on groundwater depth measuring data from 1984 to 2014 with the combination of GIS and GS+.The gap in wet and drought season was 6.28m and 10.78m from 1984 to 2014.The groundwater level is seasonal variability during the year.The amount of groundwater mining should be 252.29mm/a with the average precipitation of 546.96mm/a during 1984 to 2014.The level of groundwater mining in freshwater and salt water area is 151.35%and 141.78%in dry year,as 108.895 and 104.75%in high flow year.(2)The freshwater area of Feng Nan District is the main area of agricultural activities.We have established the non-homogeneous and isotropic two-dimensional flow numerical model by GMS based on the drilling data and related data of freshwater area.The groundwater flow field in the simulation period and the verification period is basically consistent with the dynamic change of the diving in the study area.The model is reliable.(3)The industrial,living and tertiary industry water in 2020 and 2030 are forecasted based on the data from 1984 to 2014 with the gray model GM(1,1)and the gray swing model GM(1,1,sinw)under the comprehensive planning report of Feng Nan area and the "three red lines",the amount of industrial,living and tertiary industry water in 2020 are 33.117 million m3,213380 million m3,66.42 million m3,respecitively with 270.964 million m3,25.784 million m3 and 466.93 million m3 in 2030.Based on the premise of water saving pressure and stable production and high efficiency,the optimal model of planting structure was established in 2020 and 2030.The results are as follows:The proportion of planted area of summer grain,autumn grain,oil,cotton,vegetables and fruits is 16:27:2:2:0:53 in 2020 which is a wet year,the proportion is 25:33:1:2:14:25 in 2020 which is a median flow year,the proportion is 23:32:1:2:15:27 in 2020 which is a dry year,respectively the proportion is 19:27:2:2:18:32 in 2020 which is an extraordinary dry year.The proportion of planted area of summer grain,autumn grain,oil,cotton,vegetables and fruits is 17:26:2:3:1:51 in 2030 which is a wet year,the proportion is 25:35:1:2:13:24 in 2030 which is a median flow year,the proportion is 26:36:1:2:12:23 in 2030 which is a dry year,respectively the proportion is 19:26:2:3:17:33 in 2030 which is an extraordinary dry year.(4)The groundwater model established by GMS is used to simulate the agricultural water demand scenes in 2020 and 2030,which are the wet year,the median water year,the dry year and the extraordinary dry year.The results are analyzed from two dimensions of time and space.The results are as follows:The annual variation of groundwater depth in the study area is seasonal variability with precipitation and irrigation during the year of planning.The annual average groundwater depth in the wet year,the median water year,the dry year and the extraordinary dry year are rose by 2.3m,2.27m,2.07m and 1.81m in 2020,and respectively rose by 2.65m,2.34m,2.15m and 1.92m in 2030.The average burial depth of groundwater in the dry season of 2020 and 2030 showed a trend of recovery in the current year,and the spatial distribution of groundwater depth was stable.Therefore,it is conducive to alleviate the downward trend of groundwater level and conserve water based on the most stringent water resources management system for the limited and scientific and rational planting structure optimization.