Water, Heat and Solute processes in Seasonally frozen Soils: Experimental and Modeling Study
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Soil freezing and thawing is of importance in transport of water, heat and solute, which has coupled effects. Solute type and solute content in frozen soil could influence the osmotic potential of frozen soil and decrease freezing point, resulting in differences in soil freezing characteristic curves under various solute conditions. Prediction model provides an approach for estimating soil freezing characteristic curves under various water and solute conditions based on soil freezing characteristic curve obtained at certain water and solute conditions. Water, heat and solute transport in seasonally frozen soil is a coupled process strongly linked to evaporation and energy balance of soil surface. High solute content and shallow GWTD provide good conditions for water and solute accumulation in surface layer, which would result in more evaporation during thawing. Also, high solute content in upper layer would cause more liquid water to exist in upper layer, which may enhance evaporation during freezing period. Obvious increase in cumulative evaporation amount was detected for frost tube experiments, 51.0, 96.6, to 114.0 mm when initial solute content increased from 0.2%, 0.4%, to 0.6%, and initial GWTD of 1.5 m. Similar trends were observed for other GWTD and solute treatments. Water and heat transport simulated by the CoupModel combined with GLUE calibration showed good performances, when constrained by certain criteria. Uncertainties were investigated using ensemble of modeling results. Simulated energy partitioning showed intensive oscillations in daily courses during soil freezing/thawing periods and strongly influenced the stability of energy system on surface of soil. The study demonstrated the complexity in water, heat and solute transport in seasonally frozen soil, and the necessity of combining experimental data with numerical model for better understanding the processes as well in decision making for irrigation district water resources management.
土壤冻融过程对于水热及溶质的运移具有十分重要的影响，并对于寒旱区水文过程的研究有着深远意义。在冻土中，溶质的种类及溶质含量会对土壤溶质势产生影响，并导致冰点的降低，进而影响土壤冻结曲线的变化。本研究通过建立含盐冻土冻结曲线的预报模型，有效地利用一定水盐试验条件下的冻结曲线对未知条件下的冻结曲线进行预测，进而为数值模型实时根据土壤水盐条件获得准确的液态含水量与温度的关系时提供了可行的方法。冻融土壤中的水热盐运移过程与地表的水热平衡有着密切联系，进而影响冻融土壤蒸发过程。试验研究表明，高溶质含量及浅埋深地下水条件为地表的蒸发提供了便利条件，因为高溶质含量土壤冰点降低，同一负温条件下的液态含水量增大，为蒸发提供了可利用水分；而浅埋深地下水对冻融期水盐的表聚提供的方便，进而有助于融化期地表水分的大量蒸发及下层土层水分的大量向上补给。例如，当地下水初始埋深设置在1.5 m时，对于初始含盐量分别为0.2%，0.4% 和0.6% g/g的冻融试验组，冻融期累积蒸发量分别为51.0，96.6和114.0 mm。同样的增加趋势在其它初始地下水埋深设置试验组里也被验证，且初始地下水埋深越浅，累积蒸发量也越大。CoupModel 与GLUE相结合的方法能够有效地根据实测数据对模型进行率定并经过筛选后得出较好的模拟结果集合。通过对筛选的模拟输出集合的不确定性分析，对模型模拟过程的不确定性有了很好的了解。模拟的地表能量分配过程显示，地表能量的日变化过程较为剧烈，并且对地表能量平衡系统的稳定性产生了显著影响。研究通过试验与模拟相结合的方法，展示了季节性冻融土壤中水热盐耦合运移过程的复杂性，同时也表明利用试验取样与数值模型相结合的方法研究冻融土壤中水热盐运移过程的必要性，并为高效的水资源管理决策的制定提供了有效的手段。
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xiv, 19 p.
TRITA-LWR. LIC, ISSN 1650-8629 ; 2015:01
frozen soil; water-heat-solute transport; coupled effects; water and energy balance; uncertainties
Research subject Land and Water Resources Engineering
IdentifiersURN: urn:nbn:se:kth:diva-166699ISBN: 978-91-7595-602-2OAI: oai:DiVA.org:kth-166699DiVA: diva2:811901
2015-06-09, V3, V3, Teknikringen 72 (05 tr), 10044 Stockholm, Sweden, Stockholm, 13:15 (English)
Jarvis, Nicholas, Prof.
Jansson, Per-Erik, Prof.Huang, Jiesheng, Prof.Hansson, KlasGustafsson, David
QC 201505182015-05-182015-05-132016-04-08Bibliographically approved
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