| Since the 1980s,well irrigation has been widely used to plant rice in the Sanjiang Plain.The paddy field area has been expanding,and the mining output of groundwater has increased year by year.Whether the groundwater is overexploited has aroused widespread concern,but no unanimous conclusion has been reached yet.Therefore,based on the high dependence of groundwater overdraft evaluation on time,this article analyzes the time-varying effect of groundwater overdraft evaluation results,proposes a time scale recommendation standard for groundwater overdraft evaluation,and provides scientific basis for the delineation of regional groundwater overdraft areas and the evaluation of the control effect of overdraft areas.The article comprehensively analyzed the differences in the temporal distribution of precipitation,evaporation,hydrology,and mining in the study area,determined the evaluation period with different precipitation characteristics,simulated the flow field change process in the study area using a groundwater flow numerical model,and speculated on the groundwater level compensation data.Combining the precipitation time rule,the evaluation and analysis of groundwater overdraft in the Sanjiang Plain were conducted.Specifically,it includes:(1)Based on the hydrological and hydrogeological conditions of the study area,a conceptual model and a numerical model of groundwater in the Sanjiang Plain were established.Using the input data processing method of this model,the flow field in the study area was estimated from January 1,1980 to January 1,2011.Based on a small amount of measured flow field data during this period,it was verified that this method is relatively reliable in supplementing and predicting missing flow field data.(2)Different evaluation starting points and time periods have a significant impact on the evaluation results of groundwater overdraft.This time,three regular periods are selected to evaluate groundwater overdraft in the current level year 2020:2011-2020(10 year span),2001-2020(20 year span),and 1980-220(41 year span).The evaluation results in different periods show that there is no serious overdraft area in the Sanjiang Plain,and the overdraft amount in the Sanjiang Reclamation Area under construction and the downstream area of the wutong River Dulu River accounts for more than 80%of the total overdraft amount in the whole area.However,there are large differences in the total overdraft amount,the area of the overdraft area,and the annual average overdraft amount:the maximum difference in the area of the overdraft area is about 2.5times,and the annual average overdraft amount is 1.7 times.(3)The variation law of the hydrological cycle in the Sanjiang Plain is analyzed,and the periods of partial abundant water,partial dry water,and complete hydrological cycle are divided.The precipitation in Sanjiang Plain has decreased by 2.4mm every10 years from 1956 to 2018,with 1958 and 2019 being the years of abrupt precipitation changes.The first main period of precipitation in Sanjiang Plain is about 30 years,the second main period is about 10 years,and the third main period is about 3-4 years.Determine the dry water section from 1995 to 2008,the wet water section from 2009to 2020,and the two complete hydrological cycles from 1993 to 2017 and from 1990to 2014.(4)The evaluation of groundwater overdraft should comprehensively consider the impact of precipitation cycles,and the evaluation period should select a complete hydrological period.There is no serious overexploitation area in the Sanjiang Plain,but the groundwater overexploitation is evaluated in different hydrological periods.It shows that the annual mining output of cultivated land irrigation has a clear correspondence with the annual precipitation.The average annual overexploitation in the low water section is 3.3 times that in the high water section.The cumulative overexploitation amount from 1990 to 2014 was 4.961 billion m~3,the average annual overexploitation amount was 198 million m~3/a,and the area of the overexploited area was 14888.7 km~2.The cumulative overexploitation amount from 1993 to 2017 was5.587 billion m~3,and the average annual overexploitation amount was 223 million m~3/a,The overdrawn area is 16642.1km~2.Selecting the dry water section for over mining evaluation is prone to overestimate the severe situation of over mining.Choosing a dry water section for over extraction evaluation can easily overestimate the severity of over extraction.Choosing a high water section for over extraction evaluation can easily underestimate the degree of over extraction.The average annual over extraction during the complete hydrological period is between the two,and the degree of over extraction in 2017 was slightly higher than in 2014.(5)A groundwater development model of"supplementing deficiencies with abundant resources and regulating balance"was proposed in the Sanjiang Plain.The allowable mining output of the section with high water content is 1.55 times that of the section with low water content,and the allowable mining output of the complete hydrological cycle is 5.406 billion m~3/a,which shows that the allowable mining output in the low water year is small,the actual mining output is large,and the overexploitation is more,the allowable mining output in the high water year is more,the actual mining output is less,and the overexploitation is less.It is necessary to take various methods such as labor supply and underground reservoir to make up for the shortage in the high water year,so as to alleviate the problem of groundwater overexploitation. |
