| Hetao Irrigation District is one of China’s three major irrigation district,located in the arid and semi-arid climate zone,relied on the Yellow River for irrigating.For the contradiction between supply and demand of water resources along the Yellow River becoming more and more serious,Hetao Irrigation District needs water saving measures to ensure the production.well-canals irrigation pattern combine groundwater and surface water to irrigate,which is an efficient water-saving irrigation system.However,groundwater system would change after adopting this irrigation system,which may adversely affect the local ecological environment.So it needs to forecast the various changes of groundwater system in Hetao Irrigation District after well-canals irrigation pattern comes to work,and analyze it’s impaction to ensure Hetao irrigation district’s healthy and sustainable development.This paper uses Visual MODFLOW software for groundwater simulation,the Hetao Irrigation District as the study area,collected hydrology information,groundwater level,geological data,meteorological data,irrigation data of Hetao through field test,analysis of historical data and related literature,established groundwater numerical model.By utilizing this model,we can forecast and analyze the groundwater characters after combination use of groundwater and surface water,and provide a theoretical reference for the layout of well-canals irrigation pattern in Hetao Irrigation District.The main research contents and conclusions of this paper are as follows:(1)A three-dimensional numerical model of groundwater in Hetao Irrigation District is established based on Visual MODFLOW.Various hydrogeological parameters were calibrated and verified by measured data.the result show that,the comprehensive infiltration coefficient of irrigation water in the growth period is 0.281,the autumn period is 0.344,and annual average is 0.301,the rainfall infiltration coefficient is 0.1.Specific yield is ranged between 0.02～0.06,and elastic storativity is from 0.000005 m-1 to 0.00005m-1.the permeability coefficient from south to north is becoming smaller,the value is between 2.0m/d～13.0m/d.Evaluated from the groundwater flow field,groundwater level and water balance,the model is accurate and reasonable,and can be used to forecast and analyze the characteristics of groundwater in Hetao Irrigation District after combination use of groundwater and surface.(2)The decline of groundwater level in well-canal irrigation area is mainly affected by the amount of well-canal irrigation area,irrigation quota and surrounding recharge conditions Etc.This research get groundwater level of well irrigation area by setting different schemes and using mathematical function to obtain the relationship between the drop of groundwater and the length of the single well irrigation area and the irrigation quota.The results show that both relationships are quadratic function.Larger the area,lower the groundwater level,smaller the groundwater level’s growth rate;larger the irrigation quota,lower the groundwater level,bigger the groundwater level’s growth rate.(3)The characteristics of groundwater flow field in freezing-thawing period,growth period and autumn irrigation period after well-canal irrigation pattern are changed.In freezing-thawing period,the trend of whole flow field changes little.In the summer and autumn irrigation periods,the groundwater level in well irrigation area decreased,lower than that in the canal irrigation area,and formed the drop funnel.Due to the influence of the whole flow field of the groundwater,the drop funnel is slightly north or east offset.(4)By taking water-saving measures,Hetao Irrigation District save about 8.08×108 m3 water every year.The annual phreatic evaporation is 11.60×108 m3,decrease about 3.77×108 m3,evaporation from phreatic water of well irrigation area and canal irrigation area in well-canal combination irrigation area are decreased by 66.5%and 43.2%.The annual groundwater exploitation is about 1.76×108 m3,and the average annual infiltration recharge is about 11.45×108 m3,which is reduced about 2.55×108 m3.(5)By observing the tracer particles at the boundary between the salt grounwater and fresh groundwater,we found that the moving distance of tracer particles is about 0.5m-1.1m after 5 years.And the direction of motion is from fresh water region to salt water area,so fresh groundwater area will not shrink.(6)In the groundwater model,the sensitivity of parameters which influence the average groundwater level from strong to weak is the phreatic evaporation coefficient,the irrigation infiltration coefficient,the land use coefficient,the rainfall infiltration coefficient,specific yield and the permeability coefficient.The sensitivity of parameters which influence the fluctuation range of groundwater from strong to weak is the phreatic evaporation coefficient,the irrigation infiltration coefficient,the land use coefficient,the permeability coefficient,specific yield,the rainfall infiltration coefficient.The groundwater level is sensitive to the parameters of phreatic evaporation coefficient and irrigation infiltration coefficient.While both the phreatic evaporation coefficient and the irrigation infiltration coefficient changed,the groundwater average level changes little,but fluctuates intensively. |
PDF Full Text Request