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

项目摘要标题：合作研究：土壤开裂的时空异质性对流域水文的影响地球上有相当一部分富含粘土的土壤在干燥时开裂，在湿润时膨胀。美国陆地表面。本研究的目的是改善在具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，必须提高将降水在空间和时间上划分为入渗和径流的能力。降水在入渗和径流中的分配高度依赖于这些土壤中裂缝的时空分布和大小。当裂缝粘土非常干燥时，降水几乎全部通过裂缝的大物理容量分配给入渗。当开裂的粘土非常潮湿，入渗的水必须穿过粘土基质的细孔时，大量的降水被分割成径流。在这两种极端土壤湿度之间发生的变化，对于预测具有粘性土壤的流域对降雨事件的水文、农艺和环境反应至关重要，但尚未被水文学家或土壤科学家充分表征，这是本研究的重点。电磁感应、收集和管理空间土壤和环境信息技术的最新发展支持在任何给定时刻和位置对开裂土壤状态的量化，并允许改进跟踪裂缝的空间分布和大小的能力。在我们的研究工作中，我们将测量和表征土壤开裂的空间异质性和时间动态，作为地形属性、土壤水动力学和土壤基本化学、机械和物理性质的函数。测量将在德克萨斯州中部一个高度仪器化的试验性流域进行。将我们对裂缝行为的理解集中在基本信息和性质上，我们将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外，还必须确定水文模型中需要处理的这些信息的尺度，以提高其准确性。为了满足这一需求，将使用一个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、土壤特征和先前水分条件的函数；在降水事件中允许降雨在入渗和径流之间进行动态分配。该模型在三维网格上运行，包括处理土壤性质、水分含量和其他因素的空间变化的能力，这些因素可用于预测裂缝的瞬时大小和持水量。从本研究中提取的裂缝分布、尺寸和容量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联系起来，并将其与周围的野外网格单元、子流域和流域联系起来。计算每个单元对入渗和径流的贡献，得出降水命运的空间格局。随着网格单元的增大，将实验流域的实测水文与模型生成的水文进行比较，可以确定土壤开裂信息需要处理的尺度，以产生一定程度的准确性。这项研究是合作的，由一名土壤水文学家、一名环境物理学家和一名景观水文建模师组成；通过连接土壤微环境、野外尺度异质性和流域水文，桥梁的尺度从毫米到公里不等。研究成果将全面纳入研究人员讲授的土壤水文学、土壤形态学、环境物理学和空间统计学等研究生和本科生课程。与当地学区的合作将使农村学生接触到科学和现实世界中基于实地的科学问题。

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.