Effect Of Water-Saving Irrigation On Spatial Distribution Of Groundwater In Middle Stream Of The Heihe River Basin

Zhangye located at the middle stream of the Heihe River basin is the first pilot of water-saving society,which is decided by ministry of water resources in March 2002.It is demonstration area that high efficient water-saving of Hexi corridor in 2014 nationally.Following the introduction of new irrigation technology and the implementation of water saving irrigation technology such as canal water using coefficient,the efficiency that using water in agriculture has improved significantly.But it also has changed the recharge and discharge of groundwater,resulting in the change of groundwater level.Research on the influence of water saving irrigation for the depth of groundwater in the middle stream of the Heihe River basin,which could provide a scientific basis about reasonable regulation of groundwater resources and the standard of irrigation canal anti-seepage lining.Study area is the middle stream of the Heihe River basin.In order to provide useful references for the reasonable development and utilization,the distribution charactieristics of groundwater depth and its causes in middle stream of the Heihe River basin was studied.Based on the local groundwater depth data of 33 observation wells from 1985 to 2010,the spatio-temporal distribution characterisitcs of the groundwater depths were analyzed by the Geostatistics.The random forest method was applied to investigate the the six factors that influence the change of groundwater depth and their importance scores,as which could get the main factors.Using FEFLOW software to establish the numerical simulation model of 3d groundwater in the research area,the model parameters were identified and validated.By orthogonal method to set up the nine scenes about water-saving irrigation,simulated the response of the underground water level under different water saving irrigation situation.Based on the conditions of dynamic balance for underground water level,appropriate images of water-saving irrigation scene is proposed.The main conclusions:(1)It reveals the evolution of the time and space of the underground water in the dark river.Before 2001 of Ganzhou and 2004 of Linze County,the groundwater depth had an increase trend,respectively,afterwards both reduced.The groundwater depth of the northern Gaotai County had a continuous decrease trend,but groundwater depth of the eastern Gaotai region increased.Moreover,according to the analysis of Geostatistics,the sample of the groundwater depths had spatial correlations with middle-level,and its spatial anisotropy had a tendency to enhance.(2)Analysis and determine six factors resulting in the change of groundwater that precipitation,surface water reference quantity,exploitation quantity of the groundwater,utilization coefficient of canal system water,evaporation capacity,Inflow from Yingluoxia analyzing;The score and ranking of the importance by random forest law about the six factors affecting groundwater depth change show that utilization coefficient of canal system water,exploitation quantity of the groundwater,surface water reference quantity,evaporation capacity are the four main factors which affected groundwater depth in the middle stream of the Heihe River basin.The prediction error of random forest method simulating groundwater depth is within 7%,the effect is good,the simulation ability is strong and the result is believable.(3)According to map of hydrogeological profile,drilling figure and DEM data to determine aquifer structure,strata and geological structure,ground elevation data,build the 3D groundwater numerical simulation model in the study area.Based on the FEFLOW and the monthly data about rainfall,exploitation quantity of the groundwater,groundwater lever in the middle stream of the Heihe River basin from January 2007 to December 2009,identify and verify the model.73% observation well simulate water level error within 1 m,value of R2 is above 0.5 which shows the fitting effect between simulated values with measured values model is good,and conforming to the simulated rule.And the proposed model can be used to calculate the hydrogeologic spatial distribution in the study area.(4)Considering three levels of the four main factors influencing the groundwater depth,the orthogonal method is used to set up nine kinds of water-saving irrigation(1 status of scene and eight kinds of scenes),which could realize the well effect with less number of simulation.Integrated application of groundwater numerical simulation model.Based on FEFLOW and ArcGIS software to analysis the change of groundwater deep in different water-saving scene,the results show that with the canal water using coefficient increasing by 10% and 20%,the distribution area of the shallow groundwater depth which is lower 10 meters decreased by 38% and 53.16% respectively.Therefore,by raising the canal water using coefficient to get water-saving needs more careful.The influence degree of the four main factors on the groundwater depth is: canal water using coefficient>groundwater exploitation> irrigation area>irrigation quota,which is consistent with the conclusion of random forest law evaluation;Keeping the canal water using coefficient unchanged,the second scene and third scene can both reach the purpose of easing the drawdown of groundwater by reducing groundwater exploitation,irrigation area and irrigation water quota.Though the effect of the third scene is more obvious,considering sustainable development of the economy in middle stream of the Heihe River basin,the second scene is recommended.