Response Of Shallow Groundwater System To Dryland Changed Into Paddy Field Project In Western Of Jilin Province

Water is essential to all of living things relying for existence and vital resource to humanproduction and life. As one of the most important form of fresh water on land, groundwater isthe main participant in the hydrologic cycle and an important part of the water resources.With the increase of population and an unprecedented economic prosperity today, strong andsustained human activities has also brought serious influence on the surrounding waterresource and water cycle.Western Jilin is located in the southwest of Songnen plain, with climate belongs to thetypical arid and semi-arid area. Average rainfall is only400-500mm, and is unevenlydistributed. Ecological environment is fragile in the study area. The productions of industrialand agricultural make more use of groundwater as a water source in the region. Water levelsfell significantly because of plentiful groundwater mining in some areas. In addition, becausethe industrial and domestic sewage discharge and excessive use pesticides and fertilizers,groundwater quality changed deterioration. In order to increase ten billion axes of commoditygrain production, Jilin province plans to implement Dryland Changed into Paddy Field projectand diverse surface water (Nen River、Second Songhua River) for development of irrigationpaddy field (including upland changed irrigated) in the western. A lot of introduction ofsurface water, the change of land type, the increase of chemical fertilizers and pesticides, willinevitably lead to the change of recharge, runoff, discharge conditions of groundwater. It islikely to aggravate the regional groundwater pollution and continuously deteriorate to ecologyenvironment. Therefore, it is necessary to carry out the research of response of shallowgroundwater system to Dryland Changed into Paddy Field project in western of Jilin province.This thesis is sponsored by the “Jilin Province drought water improvement projects thatfocus on the salinization controlling technology”. Based on the detail, investigation andanalysis of drought water in western Jilin province, the groundwater simulation technology was occupied to build hydrogeological conceptual model of groundwater system and thecorresponding mathematical model of flow and solute transport. The characteristics ofdynamic change of groundwater level and water quality after10years in the study area undertwo solutions: with irrigation district construction and without irrigation district constructionwere predicted by using identified numerical simulation model on the basis of theprecipitation forecasts. Combined with the use of geographic information system ArcGISspatial analysis functions, the impact of the drought water improvement projects on shallowgroundwater flow and solute of the study area was assessed. Furthermore, the globalparameters LH-OAT sensitivity analysis method was employed to calculate permeabilitycoefficient, specific yield, precipitation infiltration coefficient and vertical dispersion of thedegree of influence on the level of ground water and solute distribution by numericalsimulation model.According to the systematic study of both site investigation and modeling work, wemade the following main results:（1）On the basis of in situ investigation and data collection, the projects summary anddisplacement were analyzed. According to the principle of water and salt balance, changingamount of reservoir salt in irrigation area (Dryland Changed into Paddy Field project: leadingNen river into Bai-cheng city, Hada mountain water diversion project and Da-an newconstruction of irrigation) were calculated.The analysis results show that the total quantity water diversion is3.1696billion m~3onwater diversion project in western Jilin, including agricultural irrigation water diversion2.2785billion m~3and irrigation return water810.5million m~3. The upland project planningirrigation area of416.32hectares, of which296.82hectares of paddy field,119.5hectares ofirrigated land. Three irrigation area water diversion project in the cumulative of salt storagevariation are negative, and that from the point of view throughout the year, irrigation area in astate of desalination. Among them, Hada mountain diversion project in salt row led thebiggest difference, is-730.01kg/hm~2, Dan-an irrigation is-674.78kg/hm~2secondly, leadingNen river into Bai-cheng city is the smallest of-482.84kg/hm~2. But the performance of themain ions in the soil is not exactly the same, Na+and HCO3-in three irrigation area is in a state of desalination, Cl–is in a state of salt deposition.（2）Groundwater numerical simulation method coupled with the detail hydrogeologicalconditions were used to generalize aquifer characteristics in terms of, boundary conditions,initial conditions, source sink term and establish conceptual model, mathematical model ofgroundwater flow system. All those results are identified and validated with the measureddata of63observation wells.The average and absolute residual error between the calculating water level and theobserving water level during identification time is0.405m and1.064m respectively; Whilethe error altered during the validation, which are-0.018m, and0.649m respectively; Thefitting error under these two conditions are both less than0.5m and relative observation wellaccounted for85%and more, which demonstrated that the recognition of test results isacceptable and that the groundwater flow model is reasonable.（3）The precipitations were predicted through establishing precipitation forecast modelby using wavelet neural network method over the next10years in western Jilin Province.（4）The groundwater simulation model based on identification test, predicted thecharacteristics of dynamic change of groundwater level after10years in the study area undertwo solutions: with irrigation district construction and without irrigation district construction.The results showed that groundwater flow field in the study area will be roughlyconsistent with initial flow field after five years, the water level in a small local area willdecrease slightly, and the descend range will be less than0.8meters without considering theeffects of Dryland Changed into Paddy Field project. Groundwater level decline is oppositebigger in the region of the southeast of Qian-guo and the high platform region in the east ofChang-ling, reaching to1.2meters. Groundwater flow field will be changed a little after tenyears, there are still parts of regions underground water level slightly decreased, the descendrange will be less than1.5meters. The descend range in the region of the southeast ofQian-guo and the high platform region in the east of Chang-ling will reach to2.2meters.Considering the effects of Dryland Changed into Paddy Field project, compared with theinitial flow field with5years later, the entirety change of flow field of groundwater level isnot obvious, and the water levels rise in a certain scope in local regional, which affected by Dryland Changed into Paddy Field project. The range of the water level will increase in thearea which influenced byDryland Changed into Paddy Field project after ten years, and themaximum increasingrange is1.63meters.（5）In order to analysis the influence of groundwater level by Dryland Changed intoPaddy Field project, groundwater level changes under two programs (considering DrylandChanged into Paddy Field project or not) are compared using the spatial analysis function ofArcgis based on the simulation results of the two kinds of solutions in over the next10years.The results showed that: under the influence of Dryland Changed into Paddy Field project,the groundwater level will rise obviously in the internal of irrigation district due to directseepage of irrigation water, most of the increasing ranges are more than1.0meters, especiallythe Da-an and Zhen-lai irrigation district, the maximum increasing range are more than1.5meters. The groundwater level in surrounding irrigation areas also has the varying degreerises, the nearer to the border irrigation is the more obvious. According to the comparisonresults, under the influence of Dryland Changed into Paddy Field project, the area increasingrange of groundwater level more than1meters is2158.11km~2, among them, in the outside ofirrigation area is1125.16km~2, the inside of irrigation area is1032.95km~2. In connection withstatus of groundwater level rise caused by Dryland Changed into Paddy Field project, themeasure of preventing secondary salinization should be strengthened. Especially the highestrisk of secondary salinization is in outside of irrigated district which area is1032.95km~2. Forthe purpose of controlling groundwater reason ably exploitation and preventing theoccurrence of secondary salinization，it is suggested that the exploitation of groundwatershould increase in the area that water level rise obviously.（6）Based on the groundwater flow simulation model, the groundwater solute transportsimulation model was built. Then, the total nitrogen (NH4+N、N03--N and N02--N) ingroundwater was used as simulated factor in transport simulation model. The model wasidentified through the measured data. The identified results showed that the determination ofsource and sink terms, the generalization of the boundary conditions and the selection ofinterrelated parameter in model were reasonable, and the effect of identified is good. Themodel can be used to predict the groundwater solute transport. （7）We predict total nitrogen distribution of shallow groundwater in the next10yearsbased on the identification of groundwater transport model under the projects of both buildingirrigation and without building irrigation.Simulation results showed that the nitrogen concentration in the next10years ofprograms1, which take no consideration of Dryland changed into paddy field project is higherthan that in2007.The highest concentration locates in the junction of Qian-an and Da-an city.Its concentration is80mg/L. In addition, the concentration near Tong-yu county and Da-ancity is also high. The nitrogen concentration in the next10years of program2, which takesconsideration of Dryland changed into paddy field project, is more significant than that in2007. The heaviest place also locates in the junction of Qian-an and Da-an city, whichexceeded the scope obviously.（8）We do comparative analysis of groundwater total nitrogen concentration distributionon two programs (considering Dryland Changed into Paddy Field project or not) on the basisof the simulation results using ArcGIS and the spatial analysis. Furthermore, we illustrate theimpact of the drought water improvement projects shallow groundwater in the study areaenvironment.The comparison results showed that: after running of dry land changed into paddy fieldproject in the new irrigation area, groundwater total nitrogen concentration increased veryobvious, especially in the area of new Da-an Irrigation District and Wujiazi irrigation. What’smore, the largest increase in value reached15mg/L. Moreover, it is9mg/L in Fu-yu andSong-yuan irrigation. The lowest concentration is3mg/L in Tao’er River Irrigation. Nosignificant concentration changes in other regions. After the completion of the irrigation area,it is encouraged to carry out reasonable scientific fertilization, which can improve foodproduction with less fertilizer leaching. Thus, it can improve the efficiency of fertilizer useand ease the pollution of groundwater.（9）In order to determine the uncertainty of the parameters in the groundwater numericalmodel that had been established, the sensitivity of four parameters: permeability coefficient,specific yield, precipitation infiltration coefficient and longitudinal dispersion coefficient ofthe model were analyzed using the LH-OAT global analysis method, the impact of different parameters zones on the groundwater flow and water quality were also calculated.Results show that: in the13parameters partition zones of the study area, in2,6,7,8,9zones, the rank of the four parameters sorted by influence degree on the groundwater level is:precipitation infiltration coefficient (α)> permeability coefficient (K)> specific yield (u)>longitudinal dispersion degree (DL); in1,3,4,5,10,11,12,13partition zones, the rank of thefour parameters is precipitation infiltration coefficient (α)> specific yield (u)> permeabilitycoefficient (K)> longitudinal dispersion degree (DL).The influence degree of differentparameters partitions on groundwater solute transport were different. The sensitivity of thelongitudinal dispersion are large in common, but the sensitivity of precipitation infiltrationcoefficient is larger than that of longitudinal dispersion in2,9,10parameters partition zones;the sensitivity of specific yield and permeability coefficient in every partition zones aresimilar, but in different parameters partition zones, the sensitivity have different orders sortedby their value. According to simulation results, in the research of the shallow groundwatersystem in the studied area, the exploration and test job of the precipitation infiltrationcoefficient should be added to improve the accuracy of the parameters, which could make theresults of numerical simulation of the model more realistic.