Study Of Soil Freezing And Thawing Law And Simulation Of Hydrologic Properties In The Northern Seasonlly Frozen Soil Area

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.