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Analysis And Numerical Simulation On The Salt-water Dynamic In Farmland And Saline Wasteland Of Yichang Irrigation Area

Posted on:2020-02-20Degree:MasterType:Thesis
Country:ChinaCandidate:Y W SuFull Text:PDF
GTID:2370330575998612Subject:Agricultural Soil and Water Engineering
Abstract/Summary:PDF Full Text Request
Soil salinization and water shortage are the main constraints to the economic and social development in arid and semi-arid areas of Northwest China.This study was conducted at a typical study area with farmland and saline wasteland in Yichang Irrigation Area of Hetao Irrigation District of Inner Mongolia.The groundwater level,mineralization of groundwater,soil moisture and soil conductivity were observed.Then,salt-water dynamic of groundwateer and soil in the study area and the main influencing factors were analyzed.Based on Visual MODFLOW4.1,the groundwater numerical model was developed.The groundwater flux and the law of salt transport between farmland and saline wasteland was studied with the developed model.The research may provide theoretical basis for reasonable exploitation and utilization of groundwater resources,prevention and control of soil salinization,and the sustainable development of agriculture in the research area.The main conclusions are as follows:(1)The variation trend of groundwater depth was consistent during the observation period.The groundwater level rose sharply in May,decreased from June to September,and rose again in October,showing seasonal variation characteristics.The inter-annual variation of groundwater depth had little difference and generally showed periodic variation characteristics affected by irrigation both in the farmland and saline wasteland.(2)During the observation period of 2018,the change of groundwater salinity in the study area was not obvious.In general,the mineralization of groundwater in farmland was less than that in saline wasteland.The mineralization of groundwater fluctuated greatly in 2013?2018.The fluctuations can be roughly divided into three stages:?In 2013-2015,the mineralization of groundwater in farmland was higher than that in saline wasteland;?In 2015?2017,the mineralization of groundwater in farmland and saline wasteland had little difference and kept relatively stable;?In 2017?2018,the mineralization of groundwater in saline wasteland was gradually higher than that in farmland,and the effect of dry drainage is gradually prominent.(3)The soil moisture in farmland was generally higher than that in saline wasteland at different stages.With the increasing of soil depth,soil moisture increased gradually both in farmland and saline wasteland.0?10cm soil layer was susceptible to evaporation,rainfall and irrigation,thus the soil moisture changed dramatically.The soil moisture of 70?140cm soil layer changed gently with little difference.(4)The soil conductivity in saline wasteland was generally higher than that in farmland at different stages.Soil conductivity decreased gradually with the increasing of soil depth.The change of soil conductivity in 0?1 Ocm soil layer was much larger than that in the subsoil.The phenomenon of soil salt surface accumulation was obvious.Under the combined effect of irrigation and evaporation,the soil constantly underwent desalination and salt accumulation processes.(5)The homogeneous and isotropic two-dimensional numerical model of unsteady groundwater flow basically conformed to the actual hydrogeological conditions of the study area.The model can be used to simulate the dynamic changes of groundwater flow in the study area.Based on the groundwater numerical simulation model,the average unit-width discharge of boundary between farmland and saline wasteland is 0.16m2/d from May 1 to October 31,2018,the total groundwater transported laterally from farmland to saline wasteland is 10700m3,and the total salt is 16.83t.The results indicated that the saline wasteland in the study area had a great"dry drainage" role to control farmland soil salt and maintained the regional salt-water dynamic balance.
Keywords/Search Tags:Yichang irrigation area, Farmland and saline wasteland, Salt-water of groundwater and soil, Dry drainage, Numerical model of groundwater
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