Research On Groundwater Exploitation Regulation Scheme In The Sanjiang Plain Based On Suitable Groundwater Levels

The sustainable development of groundwater has become an issue in recent years as the amount of groundwater used for irrigation in the Sanjiang Plain has increased.Therefore,how to ensure food security and ecological environment at the same time,scientific groundwater development and utilization has become an urgent problem in the Sanjiang Plain,research and design of groundwater exploitation and regulation scheme has significant practical significance and value to ensure the balanced development of regional social,economic and ecological benefits.This paper is based on the project of "Science and Technology Innovation Project on Blackland Protection and Utilization"(No.XDA28100100)of the Northeast Institute of Geography and Agricultural Ecology,Chinese Academy of Sciences.By collecting and collating a large amount of meteorological data,hydrological data,geological and hydrogeological data,long-term groundwater observation wells,water consumption data,land use data and irrigation area development project data,the project conducted a study on the evaluation of groundwater resources,the analysis of suitable groundwater level threshold and the design of groundwater exploitation control scheme in the Sanjiang Plain.The main results obtained are as follows.(1)The current situation and exploitation of groundwater resources in the Sanjiang Plain were evaluated.Using the water balance method,it was calculated that the multi-year average total groundwater resources was 8.467 billion m~3/a,the multiyear average total extractable groundwater was 6.817 billion m~3/a,and the current actual total groundwater extraction was 7.805 billion m~3/a.The degree of exploitation at county level ranges from 16.91% to 175.89%,with groundwater in negative equilibrium in some areas.(2)The characteristics of groundwater level changes in the Sanjiang Plain and the current environmental geological problems are analysed.By discussing the historical water table depths,multi-year depth changes and current groundwater depths in the Sanjiang Low Plain and the Muling Xingkai Plain,the distribution characteristics of water table depths,shallow water table depths and medium water table depths in the study area were analysed,as well as the distribution of different water table change types,such as inter-year water table rises,inter-year water table falls and inter-year fluctuations with little inter-year changes,and based on the groundwater level changes,various methods were used to identify deep water table burial zones and continuous groundwater level fall zones in the study area,and three continuous groundwater level fall zones in Jianshanjiang,Baoqing County and Hulin City in the study area were identified.(3)The analysis determined the appropriate water level threshold for groundwater in the Sanjiang Plain.The results show that the lower threshold of the suitable groundwater level in the region lies between 3 and 19 m in general,with most areas ranging from 9 to 15 m.Soil flooding,farmland soaking and building submergence were used as conditions to determine the upper limit of the suitable water table using the capillary rise height method and the dynamic water level analysis method,and the results showed that the threshold value for the upper limit of the suitable groundwater table in the area was generally between 0 and 3.7m,with most areas being 1.9 to 3.7m.(4)Using the appropriate depth of groundwater in the Sanjiang Plain as a constraint,two reasonable groundwater exploitation regulation schemes are proposed based on the current exploitation and the exploitable amount of groundwater,and by constructing a numerical model of groundwater flow in the study area,simulations are carried out to predict the situation of maintaining the current exploitation and the two regulation schemes.Scheme 1 is to maintain the status quo groundwater extraction,the total groundwater extraction under this scheme is 7,623 million m~3/a,without increasing surface diversions,getting a continuous drop in groundwater level in most areas,with the water level drop ranging from 6 to 20 m.Scheme 2 is to implement water-saving irrigation projects on a large scale,and at the same time to implement water replacement irrigation in areas where groundwater still needs to be regulated.The total amount of groundwater extracted under this scheme is 4.161 billion m~3/a,and the total amount of surface water diversion is increased by 4.20 billion m~3/a.The continuous decline in water level is partially alleviated,and the water level suitable area covers 93.33% of the total area at the end of 2045,and the original low water level area in the district The water level rises between 1～7m.Scheme 3 is to use surface water to replace groundwater in some areas.Under this scheme,the total amount of groundwater extraction is 4.14 billion m~3/a,increasing the total amount of surface water diversion by 4.98 billion m~3/a.The continuous decline of water level is significantly alleviated,and the water level suitable area at the end of 2045 accounts for 97.40% of the total area,and the water level in the original low water level area in the district rises between 1.5～7.5m.Taking into account the groundwater level dynamics,the scale of the appropriate water level distribution,groundwater storage variables,as well as the practical implementation and implementation costs,Scheme 3was chosen as the optimal groundwater exploitation control scheme.