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Université du Xinjiang (2017)

Research on Evaporation Rules of Phreatic Water and Data Assimilation of Soil Moisture in Arid Area

宁娟;

Titre : Research on Evaporation Rules of Phreatic Water and Data Assimilation of Soil Moisture in Arid Area

Auteur : 宁娟;

Grade : Master’s Theses 2017

Université : Université du Xinjiang

Résumé
Water resources are an indispensable resource for humans and the whole ecosystem,especially in arid areas,where groundwater becomes the main source of local water supply due to the scarcity of precipitation.Salt will be brought to the soil surface with the process of groundwater supply to soil water content,salt will be accumulated on the soil surface,and formation of soil salinization.Soil salinization directly leads to reduced farmland production,which has an irreversible negative impact on local agricultural development,and has a huge impact on the local ecological environment and ecosystems.The effects of different total dissolved solids(TDS)and soil texture on the law of capillary water rise were studied by using the indoor lysimeter to test the capillary water rising experiment.The phreatic water evaporation experiment was carried out to study the effects of different TDS and different phreatic water depth and different evaporation intensity on the evolution of phreatic water evaporation,and the mechanism of phreatic water evaporation was analyzed.On the basis of this,the four groups of lysimeter with different phreatic water depth and different TDS were used to study the soil moisture data assimilation.The ensemble Kalman filter assimilation algorithm is coupled into the HYDRUS model,and the soil moisture data assimilation is studied.The study has some reference significance for the control of salt and water in saline soil,salted land and utilization of underground brine.The main research results and summarized as follows :(1)When the content of TDS is different,the increase of capillary water in loam sand in order is : 3g/L>30g/L>70g/L>0.6g/L,the rising height of capillary water is logarithmically related to time,the correlation coefficient is 98%.The increase of capillary water in sandy loam in order is : 3g/L>0.6g/L >30g/L>70g/L,capillary water height and time power function relationship,the correlation coefficient is 97%.The increase of TDS content not only changes the capillary water gravity but also affects the soil particle structure.Therefore,the variation of capillary water gravity potential and matrix potential are different in different soils under different TDS water treatment.In the case of TDS content is constant,the capillary water depth of loam in the initial stage of the experiment is relatively fast,and the soil capillary water rising trend is similar to that of the two soils at the end of the experiment,and the soil sand is higher than the silt soil loam.(2)In the case of the influence of phreatic water depth to the evaporation of phreatic water,when the external conditions are constant,the phreatic water evaporation intensity and the cumulative evapotranspiration gradually increase with the phreatic water depth is shallow,and soil moisture content increased gradually with the phreatic water depth is shallow and soil depth is deeply.With the increase of the depth of the phreatic water depth,the salt content of the same depth in the section increased,and with the increase of the soil depth also increase the soil salt content.The different phreatic water depth also influences the law of different soil column.(3)In the case of the influence of TDS content to the evaporation of phreatic water,when the external conditions are constant,the evapotranspiration intensity and the evaporation decreases with the increase of TDS content.With the increase of TDS concentration,the water content of soil profile decreased gradually.When the content of TDS is low,the difference of soil salinity is not obvious.With the increase of TDS content,the soil salinity in soil surface decrease and in the lower soil layer of soil salinity has been rising,and the depth of salt also will continue to deepen.(4)In the case of the influence of light intensity to the evaporation of phreatic water,when the external conditions are constant,the intensity of light is stronger and the soil moisture changes more intense.The closer the heat source is,the greater the change in soil temperature,and the soil moisture content is affected by the temperature gradient.The farther away from the heat source,the temperature potential of the soil moisture content gradually weakened,while the soil water content is controlled by matrix potential suction,so that the soil moisture change range is small.(5)The ensemble Kalman filter assimilation algorithm is coupled into the HYDRUS numerical simulation model to research the single point data assimilation of soil water content.The results show that using assimilating the surface water can improve the prediction accuracy of soil water content in surface layer and shallow layer significantly.For soil depth of 90 cm,soil moisture assimilation effect is not ideal only assimilating the surface water.

Mots clés : arid area; phreatic water evaporation; TDS of phreatic water; HYDRUS model; the ensemble Kalman filter;

Présentation (CNKI)

Page publiée le 23 janvier 2018