Collaborative Research: Impact of Spatial and Temporal Heterogeneity of Soil Cracking on Watershed Hydrology

项目摘要：合作研究：土壤裂隙的时空异质性对流域水文的影响富含粘土的土壤，干燥时裂开，湿润时膨胀，复盖了相当大一部分地球表面？S。这项研究的目的是改善在拥有这种土壤的地区使用的流域模型的水文响应。为了实现这一目标，必须提高在空间和时间上将降水划分为入渗和径流的能力。降雨入渗和径流的分配在很大程度上取决于这些土壤中裂缝的时空分布和大小。当开裂的粘土非常干燥时，降水几乎全部通过裂隙的大物理容量被分配到入渗中。当开裂的粘土土壤非常潮湿，渗入的水必须穿过粘土基质的细小孔隙时，大量的降水被分割成径流。这两个土壤水分极值之间的变化对于预测粘性土壤流域对降雨事件的水文、农艺和环境响应是至关重要的，但水文学家或土壤学家尚未对其进行充分的表征，这也是本研究的重点。在电磁感应、收集和管理空间土壤和环境信息的技术方面的最新进展支持量化任何给定时刻和位置的开裂土壤的状态，并使跟踪裂缝的空间分布和大小的能力得到改善。在我们的研究工作中，我们将测量和表征作为地形属性、土壤水动力学以及土壤基本化学、力学和物理性质的函数的土壤开裂的空间异质性和时间动力学。测量将在德克萨斯州中部一个高度仪表化的实验分水岭进行。我们将把对裂缝行为的理解集中在基本信息和特性上，促进知识向其他流域的转移。除了能够跟踪裂缝的程度和分布之外，还必须确定在水文模型中需要处理这些信息以提高其准确性的规模。为了满足这一需要，将使用由二维扩散波径流模块和一维点柱生物物理模块组成的水文模型来评估裂缝作为景观位置、土壤特性和先前水分条件的函数；允许在降雨事件期间在渗透和径流之间动态分配降雨。该模型在三维网格上运行，能够处理土壤性质、水分含量和其他可用于预测裂缝瞬时大小和持水能力的因素的空间变化。从本研究的观测中提取的裂纹分布、大小和容量的方程将被添加到模型中。该模型将通过径流将每个网格单元内的裂缝行为与流域水文图联系起来，并将其与田间、子流域和分水岭中周围的网格单元联系起来。计算了每个单元格对入渗和径流的贡献，得出了降水命运的空间模式。通过将实验流域的实测水文曲线与模型生成的水文曲线进行比较，当网格单元的大小增加时，将表征土壤破裂信息需要处理的规模，以产生一定程度的准确性。这项研究是协作的，结合了土壤水文专家、环境物理学家和景观水文建模人员；桥梁通过将土壤微环境、田间尺度异质性和流域水文联系起来，从毫米到公里的尺度。研究成果将完全融入研究人员教授的土壤水文学、土壤形态、环境物理和空间统计学的研究生和本科生课程中。与当地学区的合作将提供推广，让农村学生接触科学和现实世界的实地科学问题。

PROJECT ABSTRACTTitle: Collaborative Research: Impact of Spatial and Temporal Heterogeneity of Soil Cracking on Watershed HydrologyClay-rich soils that crack on drying and swell on wetting cover a considerable fraction of the Earth?s land surface. The goal of this research is to improve the hydrological response of watershed models used in regions that have such soils. To accomplish this goal, the ability to spatially and temporally partition precipitation into infiltration and runoff must be improved. Partitioning of precipitation into infiltration and runoff is highly dependent on the spatial and temporal distribution and size of cracks in these soils. When a cracking clay soil is very dry, precipitation is partitioned nearly all to infiltration via the large physical capacity of the cracks. When a cracking clay soil is very wet and infiltrating water must travel through the fine pores of the clay matrix, significant amounts of precipitation are partitioned to runoff. What happens between these two soil moisture extremes is essential in predicting hydrological, agronomic, and environmental responses of watersheds with clayey soil to rainfall events, but has not been adequately characterized by hydrologists or soil scientists, and is the focus of this research. Recent developments in technologies to electromagnetically sense, collect, and manage spatial soil and environmental information support quantification of the state of a cracking soil at any given moment and location, and allow an improvement in the ability to track the spatial distribution and size of cracks. In our research effort, we will measure and characterize the spatial heterogeneity and temporal dynamics of soil cracking as a function of terrain attributes, soil water dynamics, and basic chemical, mechanical, and physical soil properties. Measurements will be made in a highly instrumented experimental watershed in Central Texas. Focusing our understanding of crack behavior on basic information and properties we will promote transfer of knowledge to other watersheds. In addition to being able to track the degree and distribution of cracking, the scale that this information needs to be addressed in hydrological models to improve their accuracy must be determined. To address this need, a hydrological model composed of a two-dimensional, diffusive wave runoff module and a one-dimensional, point-column biophysical module will be used to evaluate cracking as a function of landscape position, soil characteristics, and antecedent moisture conditions; allowing a dynamic partitioning of rainfall between infiltration and runoff during precipitation events. The model operates on a 3-dimensional grid and includes the ability to handle spatial variations in soil properties, moisture content, and other factors that may be used to predict the instantaneous size and water holding capacity of cracks. Equations for crack distribution, size, and capacity distilled from the observations in this study will be added to the model. The model will link the behavior of cracking within each grid cell to watershed hydrographs via runoff to surrounding grids cells in the field, the sub-basin, and the watershed. The contributions of each cell to infiltration and runoff are calculated, yielding spatial patterns of the fate of precipitation. By comparison of measured hydrographs from the experimental watershed with hydrographs generated from the model as the size of the grid cells are increased, the scale that information on soil cracking needs to be addressed to produce a degree of accuracy will be characterized.This research is collaborative, combining a soil hydropedologist, an environmental physicist, and a landscape hydrologic modeler; and bridges scales from millimeter to kilometer by linking soil microenvironments, field scale heterogeneity, and watershed hydrology. The research findings will be fully integrated into graduate and undergraduate courses in soil hydrology, soil morphology, environmental physics, and spatial statistics taught by the investigators. Collaboration with a local school district will provide outreach exposing rural students to the sciences and real-world, field-based science problems.