【作者】 王晓巍；

【导师】 付强；

【作者基本信息】 东北农业大学 ， 农业水土工程， 2010， 博士

【摘要】 我国作为世界第三冻土大国,季节性冻土的面积约占全国国土面积的一半以上,而这些地区大多为气候寒冷干燥、水资源贫乏、水环境日益恶化、生态环境脆弱的地区,严重的制约着农业经济的飞速发展。季节性冻土的不透水作用,蓄水调节作用和抑制蒸发作用,使冻融期间的土壤蓄水容量、降水入渗能力、土壤含水量的变化状态、产流与径流等水文特性具有不同于无冻土条件下的动态规律和特点,而寒区的大多数水文工作者对于季节性冻土的水文特点与理论一直处于盲区和误区,在水文水利计算、水文预报、与农业有关的旱涝指标计算及耗水定额的确定等领域,都忽视了冻土的水文效应,采用国内外已有的无冻土地区的理论与模型,致使计算结果和模拟方案与实际误差过大,不能反映实际水文过程。目前北方季节性冻土地区的冻融规律和水文特性机理研究还处于初步探索阶段,对冻土作用下的土壤水循环规律的揭示很不完善。现有成果中的水文特性分析及模型大多建立在高山冰川多年冻土区的研究基础上,不符合北方季节性冻土水文的区域性和季节性规律特点;国内应用的水文模型多为经验模型,缺乏对影响寒区水文特性的关键要素的机理研究,模型的建立缺乏必需的野外大田实测数据的支持,其推广应用受到极大的限制。本文选取季节性冻土现象普遍存在的哈尔滨高寒地区为试验基地,以冬季冻融土壤野外大田试验为基础,深入研究了本地区冻土条件下水分动态运移规律、揭示季节性冻融规律及水文特性,在此基础上建立冻土水文特性模拟模型,主要研究内容和成果如下:⑴季节性冻土的冻融过程强烈依赖于土壤温度,通过对地表和地中土壤温度场日变化和季节变化分析,结果显示:土壤温度具有以日和年为周期的波动特点,其变化随深度增加呈现指数规律衰减的现象,即离土壤表层越近,外界气温对土壤温度的影响越明显;土壤温度的变化相对于气温变化存在滞后现象。土壤的冻融深度与地表负积温存在非常显著的相关关系。土壤季节性冻融特点表现为:单向冻结、双向融化。试验年份的最大冻结深度为160.1cm,最大融深是140cm。⑵冻融层的土壤未冻水含水率经历了含量逐渐减少——最低点——含量逐渐增加的过程,曲线呈现“凹”形状,土壤总含水率经历了突然增多——含量基本保持不变——含量陡然减少的变化过程,曲线呈现“凸”形状,其间的差值即为土壤含冰量;土壤水势经历了冰点时突然大幅度降低——变化比较平缓——融化后期达冰点时突然增大的变化过程,曲线呈现“凹”形状,很好地解释了其与土壤总含水量变化的一致性,冰点是导致土壤水势突变的重要原因,而根据冻结土壤总含水量的突变点或土壤水势值的突变点可以判断出不同时间的冻深发展程度。土壤含有少量盐分使相变温度点(冰点)低于0℃。土壤水势与土壤未冻水含量、土壤温度的变化呈现出很好的一致性。土壤水势与土壤液态水含量表现出二次多项式的关系。⑶土壤水分冻融特性曲线中,80cm深度之上的融化特性曲线数值比冻结特性曲线大,源于此期间出现降雨;100cm、140cm深度的冻融特性曲线表现出很好的一致性或略有滞后,说明由于冻结层具有阻渗特性,外界降雨对土壤深层处仍然冻结的土层影响很小。未冻水含量与负温始终保持动态平衡关系,用二次多项式表达的相关程度强于幂函数表达;试验区土壤为非均质土壤,其冻融特性曲线是不重合的。⑷季节性冻土的水文特性包括:土壤垂线含水量分布改变,在20cm～50cm左右出现极大值;土壤含水率变化规律引入特征值含水率概念,其在垂向的空间分布规律并没有随着土壤深度的增加而增大,表现为40cm深度处的特征值最大;冻土的存在使土壤蓄水容量增加显著;冻结条件下的土壤水分入渗过程与非冻结土壤很类似,但入渗时间明显少于非冻结土壤,于60分钟左右均达到稳定;冻结土壤具有明显的减渗特性,其入渗能力远远小于非冻结土壤;冻土作为不透水层,抑制蒸发的作用非常显著;季节性冻土在冻结期间基本不产流,融化期间产流方式兼有饱和产流、蓄满产流等方式;稳定冻结期间由于土壤冻结河流干涸,径流较小,融化期形成春季径流高峰。径流的变化情况与冻土的厚度基本成反比关系。⑸建立基于偏最小二乘回归的冻融深度预测模型,预测结果显示该回归模型的综合效果是令人满意的,可以在季节性冻土冻融深度的建模预测中应用;采取基于MATLAB的BP神经网络设计,建立1.6m土层蓄水容量模型、冻层上水蓄水容量模型和冻层蓄水容量模型,预测结果显示:模型可靠性和预测精度较高,可用于预测哈尔滨地区未来的土壤蓄水容量,;采用最小二乘法拟合多元回归模型进行土壤蒸发量的模拟预测,结果显示回归效果显著,模型精度较好,能够应用在哈尔滨季节性冻土地区的冻融土壤蒸发模拟和预报中。综上所述,研究季节性冻融土壤的冻融规律和水文特性,并建立水文特性预测模型,为北方季节性冻土区研究冻土水文过程机理、水资源循环过程和提高水文特性模拟预报精度提供了理论依据,为丰富冻土水文学科的基础理论体系和完善北方季节性冻土区水文特性模拟的理论体系提供参考。更多还原

【Abstract】 Being the third frozen soil country in the word, the areas of Chinese seasonly frozen soil covers over a half of the whole country, however, most of these areas have the cold and dry climate, lacking for the water resource, and make the water circumstance get more and more bad .Also the zones which have got weak ecological environment have limited the development of the agriculture economic seriously. The functions of seasonly frozen soil, such as the watertight function, the regulation of the soil-water storage function, the inhibition of the water function make those in the freeze-thaw times get dynamic variation regular and character which are different from the condition of un-frozen soil. Those are the capacity of the soil to store water, the ability of the waterfall infiltration, the variable state of the soil moisture, and the hydrological characteristics of the runoff and passoff and so on. But most of the hydrologist in the cold regions have been trapping into the unknown and misunderstanding state about hydrological characteristics and theories of seasonly frozen soil. On the field of the hydrologic and water conservancy calculating, the hydrologic forecasting, the drought quota calculating on the agriculture, the water consumption quota firming and so on..All above have ignored the hydrological effect of the frozen soil, they have adopted the theories and models of the un-frozen soil countries which has already existed overseas. What they have done has a big error between the calculating result and simulated plan and the reality, that can’t react to the real hydrological process.For now , we are standing on the primary hunting stage of the hydrological characteristics and freeze-thaw regular in the northern frozen soil areas, it didn’t bring the water recycling regular of the soil to light perfectly which are under the freezing and thawing soil effect. The hydrological characteristic analysis and models in the achievements gained establish themselves on the base of the research on the frozen soil areas for years like the high mountain and the ice stream, it doesn’t match with the regional and seasonal regular features of the northeren seasonly frozen soil. The models which are applied in our country are experienced ones, they are lacking the researches on the hydrological characteristic key factors which influence the cold region, as well, they have shortage of the necessary field data outside to support to accomplish building up the models, there is a big limit to apply and extend them.The study chosd Haerbin the high and frozen area to be the experiment, since the seasonly freezing and thawing soil phenomenon is common seen, It was based on the winter freeze-thaw soil field experiment outside, being made a minute research on the water dynamic movement regular, revealing freeze-thaw seasonly regular, and hydrological characteristics, and having set up the simulating model on the foundation of them, the followings showed the main research and achievement:First, the process of the seasonly freeeing and thawing soil strongly depended on the temperature of the soil, according to the analysis for daily and seasonal change of the soil temperature on the surface and in the middle part of the soil, the results showed that the temperature of the soil changed with day and year, and it regarded them as its cycle, as the depth went up, the phenomenon was that it changed by decreasing regularly with index, in another word, when it got closer to the surface, the outside environment temperature influenced the soil temperature more evidently, the changes of the soil temperature went behind the outside. The freeze-thaw depths of the soil was related to the cumulative negative temperature of the surface evidently. The characteristic of the seasonly freezing and thawing soil manifested that when it went with one direction, it would be frozen, while with the both directions, it could be melt. During the text years, the largest freezing depths was 160.1cm, and the largest thawing depth was 140cm.Second, un-frozen soil moisture content in the freeze-thaw store had suffered to reduce the content more and more—at the lowest—the process of the content being more and more, the curved line displayed a shape of hollow, the difference between them was the soil holing content, when the soil-water potential passed over the ice point, suddenly it would fall very fast.—the change would be very smooth—when the later period of the melt water that it reached the ice point, all of a sudden , it would go up quickly, the curved line had showed the hollow shape. The ice point results in the sudden change of the water potential in the soil, however we could judge the different degree of the freezing development during different time from the sudden changing point of the whole water content in the freezing and thawing soil and soil-water potential value of the soil. The soil included some little salt , and that made the ice point go below zero. The soil-water potential and un-freozen soil moisture content matched with the change of the soil temperature well. Soil-water potential and un-frozen soil moisture content had relationship of quadratic polynomial.Third, in the property curve of freezing and thawing soil water, the curve of melting characteristic over 80cm depths was larger than that in freezing curve, due to the rainfall during this period, the curve in 100cm and 140cm depths shows the same or something that differ each other a little, it illustrated that since the freezing store has the characteristic of preventing the leakage, the rainfall outside had a very small effect on the frozen layer in the deep soil. The un-frozen soil moisture content and the negative temperature kept a relation of dynamic balance all the way. The interrelated degree expressed by quadratic polynomial was better than that expressed by power function. The text soil was the not even material, its lines of the freeze-thaw soil characteristic didn’t coincide.Fourth, the hydrological characteristics of the seasonly freezing and thawing soil as follows: vertical line properties of soil moisture content was changed. at 20cm-50cm around it presented the maximum value, the variable regular of soil moisture content brought in the concept of the feature value of soil moisture content, the regular in the vertical line direction didn’t get change as the soil depth increasing, it showed that the feature value at 40cm was the maximum, the water content of the soil increased evidently results from the frozen soil existence. Under the frozen soil condition, the process of the soil water permeating closely resembled the un-frozen one, but the freezing soil needed a less time to infiltration, about 60 minutes later, both of them would be smooth., the frozen soil had an evident characteristic of reducing the infiltration, the capacity of infiltration in the frozen soil was poorer than the un-frozen one. The frozen soil, as the watertight store, the function of restraining evaporation was very striking. The seasonly frozen soil didn’t produce runoff during the soil freezing period. During the soil melt periods , the run-off methods were the saturation way ,the fulfill way and so on.. For the reason of dry river frozen, the runoff produced a little small during the stable soil freezing time, the melt period came into being the runoff peak. The circumstance of the variable runoff had the inverse proportion with the thickness of the frozen soil.Fifth, the forecasting model of freeze-thaw depths had been established which was based on the partial least-square regression model.The result presented that regression effect was perfec, it could be used to forecast soil frozen depths in the seasonly freezing and thawing time. The forecasting model of 1.6m soil-water storage、up soil-water storage on frozen soil layer and frozen layer soil-water storages had been established which was based on MATLAB BP neural network.The result showed that the model was highly reliable and accurately forecasted, it could be used to forecast soil-water storage in the future such as Haerbin. The forecasting model of soil water evaporation which was based on the multiple linear regression equation was established.The result showed that regression effect was perfect, model precision was high, and it could be used to simulate and forecast soil water evaporation in the seasonly frozen soil of Herbin area. To sum up, the regular of the seasonly freeezing and thawing soil and the hydrological characteristics had been studied, as well, hydrological characteristics model had been set up. It provided the theoretical evidence for the sturdy of hydrologic process and mechanism, for the study of circling process of water resourcese and enhancing forecasting precisionin of hydrologic properties model in seasonally frozen soil regions in the north of China ; It provided reference for enriching the basic theory system of frozen soil hydrology and perfecting the theory system of hydrologic properties model in seasonally frozen soil regions in the north of Chinese.更多还原