【作者】 李云龙；

【导师】 付强；

【作者基本信息】 东北农业大学 ， 农业水土工程， 2021， 硕士

【摘要】 在季节性冻土区,由于冬季时间较长,导致积雪大量囤积,在融化期大量积雪融化并伴随着频繁的风吹,形成大量的融水,并且在昼夜温差的作用下,融雪反复冻融,严重影响着春耕计划。融雪过程中的质能变化以及融水量估算方法相关的研究还需要进一步完善。融雪水不仅仅补充地下水,产生地表径流,为作物根系提供所需水分,同时大量融水极易造成土地渍涝,融雪洪水等灾害。融化初期积雪厚度与融水产流情况的定量关系尚不明确,明晰上述关系对预判融雪灾害,灌溉计划制定和开耕计划安排等有着积极意义,同时对积雪消融过程和融雪水入渗的研究对于了解融雪质能过程、探究春季土壤墒情变化、评估春季土壤耕作环境和有效利用农田水资源有着重要意义。本研究研制了一种积雪消融实时监测装置（Real-time snow melt detector-RSMD）,用于在风速为3.2m/s和0m/s的情况下,同时监测积雪融水量和水汽量（雪的升华量和融水蒸发量之和—SVS）,并在监测结果的基础上,定义了风消雪能量系数（EC）和质量系数（MC）。融化期不同积雪厚度覆盖下对大田土壤含水率和温度进行监测,根据质量守恒定律估算融雪水入渗量,根据理论分析假设出入渗率曲线,利用限定条件得出假设曲线的参数。同时,提出了大田最大融水囤积量的概念,通过结合融雪初期不同积雪厚度与融水入渗时长关系曲线和实际观测得出融化初期导致大田积雪产流的最小积雪厚度的取值范围既大田最大融水囤积量时对应的积雪厚度,主要内容和结论如下:（1）2019年融化期,选取代表日（融化前期,中期和后期）,采用（RSMD）在风速为3.2m/s和0m/s的情况下对积雪消融过程进行监测,发现在3.2m/s风速作用下,极大的增强了积雪转化为汽态过程,其中包括积雪的升华和融水的蒸发（SVS）。为了丰富恒定风速对积雪消融影响程度的描述指标,本研究依据能量守恒定律定义了风消雪能量系数EC,并给出了相应的计算公式。同时定义了风消雪质量系数用以描述积雪消融过程中融水所占积雪消融总量的比例。根据上述风消雪质量系数,计算代表日日末风消雪质量系数的平均值作为融化期的风消雪质量系数,采用所有代表日融水产生时段瞬时风消雪质量系数平均值作为融水估算的参数(η₄4)))。在潜热（EC）层面3.2m/s风速对积雪消融起到促进作用,这种促进程度大约为50～150%。对日最高温度和日SVS进行相关性分析,结果为中等程度负相关。得出较高温度对积雪SVS起到抑制作用。采用RSMD进行室内实验,监测不同的恒定温度下积雪消融过程,得出当温度大于0℃时,温度越高,积雪SVS现象越弱。当温度小于0℃时,温度越低积雪SVS现象越明显。并且在温度恒定的情况下,积雪融水和SVS速度基本不变。（2）根据质量守恒定律并结合环境特征建立了融水量估算公式,并定义了融水系数,通过实验结果计算得出融水系数为0.726,此系数可以为季节性冻土区积雪消融产水量估算提供参考。（3）2019年10月11日～2020年5月30日,对融化初期不同雪厚下的大田土壤含水率和温度进行监测。通过对融化期土壤水热变化特征得出不同积雪厚度下融水入渗时长,同时根据质量守恒定律计算出了15cm雪厚度下融水入渗总量为2.14cm,30cm雪厚度下融水入渗总量为3.07cm。（4）通过对融水入渗过程的观测和理论分析,假设出每日融水入渗率曲线。基于融化期日环境变化的周期性和每日环境条件的相似性,假设每日融化期入渗率曲线相同,发现假设曲线趋势符合玻尔兹曼分布函数。通过日平均融水入渗量和融水明显入渗时长作为两个限定条件,对假设曲线参数进行计算。得出融化期平均每日融水入渗率曲线,通过曲线可估测融水日平均最大入渗率为0.06 cm/hour。并且得出,每日平均融水入渗率从开始增加到达到最大需要约两个小时。（5）提出大田最大融水囤积量的概念,为分析大田融水过程提供新的分析结构。本研究实验观测到15 cm和30 cm积雪覆盖下无明显径流,因此本实验设置积雪厚度均小于使大田达到最大融水囤积量的积雪厚度。因此,基于融化期环境的变化特征,结合0cm、15 cm和30 cm积雪厚度和融水入渗时长绘制了积雪厚度和融水入渗时长趋势线。通过趋势特征判断最大融水入渗时长及其对应的积雪厚度的范围,并认为在多年融化期环境条件无剧烈波动的情况下,积雪厚度达到某一定值,融水入渗时长达到最大值后不再明显增加。本研究结果发现当融化初期积雪厚度大于30 cm小于60 cm,达到大田融水最大囤积量,最大融水囤积量对应的融水入渗时长D取值大于21天小于35天。（6）本研究利用张力入渗仪监测融化期冻土潜在最大饱和入渗率。根据入渗液的密度、融冰性和冰点,本研究选用45%的乙二醇溶液。入渗液入渗过程中充分填充非密闭性孔隙,并减少对原有冻土结构的改变,从而达到最大的入渗效果。本次研究得出融化期冻土潜在最大饱和入渗率为9.47 cm/hour。综上所述,对东北寒区融化期积雪融化质能过程和融水入渗机理进行了研究和分析,能够了解东北地区融化期积雪的消融和融水的入渗情况,有助于挖掘东北地区冬季覆雪的利用潜力,对落实保障东北地区春耕计划顺利实施,促进实现春汛期融雪水的合理利用具有重要的参考价值。更多还原

【Abstract】 In seasonal frozen soil areas,a large amount of snow accumulates.During the melting period,a large amount of meltwater is accompanied with frequent wind blowing and under the action of the temperature difference between day and night,the snow melting is repeated freezing and thawing.Those have seriously affected the spring plowing plan.Research on the changes in mass and energy in the process of snow melting and the methods for estimating the amount of meltwater still need to be further improved.Snowmelt water not only replenishes groundwater,but also generates surface runoff to provide needed water for crop roots.At the same time,a large amount of meltwater can easily cause land waterlogging,snowmelt floods and other disasters,as shown in Figure 0-1.The quantitative relationship between different snow thicknesses and meltwater flow in the early stage of melting is still unclear.The clarification of the above relationship has positive significance for predicting snowmelt disasters,formulating irrigation plans,and arranging farming plans.It also has a positive effect on the process of snow melting and the influx of snowmelt water.The study of snow melting process and meltwater infiltration is of great significance for understanding snow melting mass and energy process,exploring changes in soil moisture,evaluating the soil cultivation environment in spring and effectively using farmland water resources.This research has developed a real-time monitoring device for snow melting（RSMD）,which is used to simultaneously monitor the amount of meltwater and water vapor（the amount of snow sublimation and meltwater evaporated（SVS）under the conditions of wind speeds of 3.2m/s and 0m/s）,and based on the monitoring results,define the wind-blown snow energy coefficient（EC）and mass coefficient（MC）are defined.During the melting period,the soil moisture content and temperature of the field are monitored under the cover of different snow thicknesses,the snowmelt water infiltration amount is estimated according to the law of mass conservation,the infiltration rate curve is assumed based on the theoretical analysis,and the parameters of the hypothetical curve are obtained by using the limited conditions.At the same time,the concept of the biggest hoarding of meltwater in the field was proposed.Combining the trend line of different snow thicknesses and the duration of melt water infiltration in the early stage of snow melting and actual observations,the value range of the minimum snow thickness that leads to field snow flow in the early stage of melting is obtained.（that is the snow thickness corresponding to the maximum hoarding of meltwater in farmland）.The main contents and conclusions of the corresponding snow thickness during hoarding are as follows:（1）For the thawing period in 2019,select representative days（pre-melting,mid-and late-melting）,and use（RSMD）to monitor the snow melting process under the conditions of wind speeds of 3.2m/s and 0m/s,and it is found that it is 3.2m/s wind speed greatly enhances the transformation of snow into vapor,including the sublimation of snow and the evaporation of melt water（SVS）.In order to enrich the description of the effect of constant wind speed on snow melting,this study defines the wind-blown snow energy coefficient（EC）based on the law of conservation of energy and gives the corresponding calculation formula.At the same time,the wind-blown snow mass coefficient（MC）is defined to describe the proportion of meltwater in the total snow melt in the process of snow melt.According to the MC,the average value of MC at the end of the representative days is calculated as the parameter(η₄4)))for meltwater estimation.At the latent heat（EC）level,the wind speed of 3.2m/s promotes snow melting,and the degree of this promotion is about 50～150%.Correlation analysis of daily maximum temperature and daily SVS showed that the result was a moderately negative correlation.It is concluded that higher temperature has an inhibitory effect on snow SVS.Using RSMD to conduct indoor experiments to monitor the snow melting process at different constant temperatures,it is concluded that when the temperature is greater than 0°C,the higher the temperature,the weaker the snow SVS phenomenon.When the temperature is less than0°C,the lower the temperature,the more obvious the snow-covered SVS phenomenon.And in the case of constant temperature,the snow melt water and SVS speed basically remain unchanged.（2）According to the law of mass conservation combined with environmental characteristics,a formula for estimating the amount of meltwater is established,and the meltwater coefficient is defined.The meltwater coefficient is calculated through experimental results to be 0.726,which can provide reference for water quantity estimation in seasonal frozen soil regions.（3）From October 11,2019 to May 30,2020,monitor the soil moisture content and temperature in fields with different snow thicknesses at the beginning of melting.According to the characteristics of soil water and heat change during the melting period,the infiltration time of meltwater under different snow thicknesses is obtained.At the same time,the total meltwater infiltration under 15cm snow thickness is calculated according to the law of mass conservation to be 2.14cm,and the total meltwater infiltration under 30cm is 3.07 cm.（4）Through the observation and theoretical analysis of the meltwater infiltration process,the daily meltwater infiltration rate curve is assumed.Based on the periodicity of daily environmental changes during the melting period and the similarity of daily environmental conditions,assuming that the daily melting period infiltration rate curve is the same,it is found that the trend of the hypothetical curve conforms to the Boltzmann distribution function.Using the average daily meltwater infiltration volume and the apparent meltwater infiltration time as two limiting conditions,the hypothetical curve parameters are calculated.The daily meltwater infiltration rate curve during the melting period is obtained,and the maximum daily meltwater infiltration rate can be estimated by the curve to be 0.06 cm/hour.And it is concluded that the daily increase in meltwater infiltration rate reaches its maximum after about two hours.（5）Put forward the concept of the maximum hoarding of meltwater in the field and provide a new analysis structure for analyzing the process of meltwater in the field.The experiment in this study observed no significant runoff under the snow cover of 15 cm and 30cm,so the snow thickness in this experiment was set to be less than the snow thickness that enables the field to reach the maximum meltwater accumulation.Therefore,based on the change characteristics of the environment during the melting period,combined with the snow thickness of 0 cm,15 cm and 30 cm and the duration of meltwater infiltration,the trend line of snow thickness and meltwater infiltration duration was drawn.Judge the maximum meltwater infiltration time and the range of corresponding snow thickness by trend characteristics and believe that under the condition of no drastic fluctuations in environmental conditions during the melting period for many years,the snow thickness reaches a certain value and the meltwater infiltration time reaches the maximum,the value no longer increases significantly.The results of this study found that when the snow thickness is greater than 30cm and less than 60 cm at the beginning of melting,the maximum hoarding of meltwater in the field is reached,The meltwater infiltration duration D corresponding to the maximum hoarding of meltwater is greater than 21 days and less than 35 days（6）This study uses a tension infiltration meter to monitor the potential maximum saturated infiltration rate of frozen soil during the thawing period.According to the density,ice melting and freezing point of the infiltration fluid,45%ethylene glycol solution was used in this study.The infiltration liquid fully fills the non-closed pores during the infiltration process and reduces the changes to the original frozen soil structure,so as to achieve the maximum infiltration effect.In this study,the potential maximum saturated infiltration rate of frozen soil during the thawing period was 9.47 cm/hour.In summary,the study and analysis of the snow-melt mass-energy process and the mechanism of meltwater infiltration during the melting period in the northeast cold region can help to understand the melting of snow and meltwater infiltration in the northeast region.Exploiting the utilization potential of winter snow cover in Northeast China has important reference value for ensuring the smooth implementation of the spring plowing plan in Northeast China and promoting the rational use of snowmelt water during the spring flood season.更多还原