CAREER: Microtopography-Controlled Puddle-filling to Puddle-merging (P2P) Overland Flow Mechanism: Discontinuity, Variability, and Hierarchy

研究的目标是：(1)开发改进的、多尺度的方法来量化微地形控制下的填坑和合并(P2P)陆面流过程，重点描述陆面流的不连续性、变异性和层次性；(2)开发一个在用户友好的Windows界面中集成了新方法和建模技术的P2P陆面流建模系统；(3)通过提供一个互动的、教育增强的P2P教学软件来改进各级水文教育。初步的野外数据和以往的研究强调了微地形在陆流产生和演变中的重要作用，并强调了沟通宏观和微观尺度水文研究的必要性。这里的主要挑战是：(1)土壤表面粗糙度对P2P坡面流过程的影响是尺度相关的；(2)在更大尺度的建模框架中简单地考虑土壤粗糙度的微观尺度效应可能在计算上是困难的。在这个项目中，将开发多尺度方法来应对这些挑战并提高计算效率，这些方法包括动态水坑划定以及在两个尺度水平上的点和面建模。具体地说，将开发一个准三维模型来模拟成层土壤的垂直入渗和“点”处的降雨过量，以及“点”之间在“区”上的质量交换和水力连接(塘填-连接-合并过程)。“点”模拟将在单元/网格尺度上实施，而“面积”模拟将明确考虑单元微起伏对小规模陆上流动过程的影响，例如由淹没因子决定的流动类型(微通道流或薄层流)。还将通过一系列实验室和田间实验来检验P2P覆盖流机制，这些实验反映了土壤的变异性、土壤的空间组合、粗糙度和降雨特征。将使用激光扫描仪测量土壤表面的微起伏。该模型将用于量化土壤表面粗糙度，并分析粗糙度的尺度效应。为加强这些新方法的应用，将开发一个基于Windows的P2P覆盖流模拟系统。将进一步开发交互式P2P教学软件，以改进各级水文教育。该教育软件具有增强的可视化能力，将在用户友好的Windows界面中集成新的建模技术、计算机引导的自学中心以及一套面向教育的工具和数据库。教学软件将被用作研究生和本科水文学课程以及其他外展项目的核心。智慧的优点和更广泛的影响：多尺度P2P陆上流动方法的研究应该是从多尺度角度表征微地形控制的陆上流动的第一次调查。新方法将提高对陆上流动内在本质的理解：间断性、变异性和层次性。这些模型将成为分析地表径流产生和演变的宝贵工具，并量化暴雨径流贡献区的动态变化，而暴雨径流是非点源污染的关键。因此，这项研究还将对环境和生态研究产生重大影响，并具有广阔的跨学科应用潜力。界面友好的Windows P2P建模系统将特别提高整个水文界对新方法的可及性。作为NSF资助的LTER计划的组成部分，这项独特的水文研究也将为其他LTER项目提供宝贵的支持。这一最先进的交互软件将是第一个专门为各级水文教育设计的综合性教学工具。该软件具有增强的可视化能力、计算机引导的自学中心以及水文工具和数据库，不仅将有效地促进学生对水文科学的学习和兴趣，而且通过在课堂上创造一个积极和创新的教与学环境，使教师受益。最重要的是，这项工作将为代表不足的学生提供一个进行尖端水文研究的绝佳机会，并获得对他们的学习和未来职业生涯非常宝贵的技能和经验。

The objectives of the research are to: (1) develop improved, multi-scale methods to quantify the puddle-filling and puddle-merging (P2P) overland flow process under control of microtopography, with focus on characterizing discontinuity, variability, and hierarchy of overland flow; (2) develop a P2P overland flow modeling system that integrates the new methods and modeling techniques in a user-friendly Windows interface; and (3) improve hydrology education at all levels by providing an interactive, education-enhanced P2P teaching-learning software.Preliminary field data and previous studies highlight the important role of microtopography in overland flow generation and evolution, and emphasize the need for bridging the macro- and micro-scale hydrologic studies. Major challenges herein are: (1) effects of soil surface roughness on the P2P overland flow process are scale dependent; and (2) simply incorporating micro-scale effects of soil roughness in a larger-scale modeling framework can be computationally prohibitive. In this project, multi-scale methods, which involve dynamic puddle delineation and "point" and "area" modeling at two scale levels, will be developed to cope with these challenges and improve computational efficiency. Specifically, a quasi-three-dimensional model will be developed to simulate vertical infiltration into layered soils and rainfall excess at "points," and mass exchange and hydraulic connections between "points" over "areas" (puddle filling-connecting-merging process). The "point" modeling will be implemented on the cell/grid scale, while the "area" modeling will explicitly account for the effects of microrelief of cells on small-scale overland flow processes, such as flow types (microchannel flow or sheet flow) determined by an inundated factor. The P2P overland flow mechanism will also be examined by a series of laboratory and field experiments that reflect variability in soils, their spatial combination, roughness, and rainfall characteristics. Microrelief of the soil surfaces will be measured by using the laser scanner. The fractal model will be used to quantify soil surface roughness and scale effects of roughness will also be analyzed.A Windows-based P2P overland flow modeling system will be developed to enhance applications of the new methods. An interactive P2P teaching-learning software will be further developed for improving hydrology education at all levels. The educational software, with enhanced visualization capabilities, will integrate the new modeling techniques, computer-guided self-learning center, and a set of education-oriented tools and databases in a user-friendly Windows interface. The teaching-learning software will be used as the core for graduate and undergraduate hydrology courses, as well as other outreach programs.Intellectual Merit and Broader Impacts: The research on multi-scale P2P overland flow methods should be the first investigation of characterizing microtopography-controlled overland flow from a multi-scale perspective. The new methods will improve the understanding of intrinsic natures of overland flow: discontinuity, variability, and hierarchy. The models will be valuable tools for analyzing overland flow generation and evolution, and quantifying dynamic changes in the contributing areas of storm runoff, which is critical to nonpoint source pollution. Thus, this study will also have substantial impacts on environmental and ecological research and broad interdisciplinary application potentials. The user-friendly Windows P2P modeling system will particularly improve the accessibility to the new methods by the entire hydrology community. As an integral part of the NSF-funded LTER program, this unique hydrologic study will also provide valuable support for other LTER projects.The state-of-the-art, interactive software will be the first comprehensive teaching-learning tool specially designed for hydrology education at all levels. The software, with enhanced visualization capabilities, the computer-guided self-learning center, and hydrologic tools and databases, will not only effectively promote students' learning and interest in hydrologic sciences, but also benefit instructors by creating an active and innovative teaching-learning environment in their classes. Most importantly, the work will give the underrepresented students an excellent opportunity to conduct the cutting-edge hydrologic research and gain skills and experiences that are invaluable to their studies and future career.