Scale and Time Dependent Hydrologic Response of Sites with Expansive Soils

粘土膨胀是一个依赖于时间的过程，对于一些土壤来说，即使供水充足，也需要长达一个月的时间才能完成。我们在旱地土壤上的初步实验。在实验室和田间渗入试验中，智利中部海岸范围的大部分地区都表现出了这种行为。这种依赖时间的水化作用的重要性尚未在实地进行研究，也未纳入水文模型，但预计将在径流产生和含水层补给方面产生深远的应用。本研究的目的是观察随时间变化的膨胀动力学对入渗和径流过程的影响，并建立一个可扩展的基于过程的模型来预测0.02~10万公顷尺度上膨胀土的水文响应。在小区尺度上，将在一系列模拟暴雨期间测量地表径流和土壤上部2m的水分含量。在整整两年中，将在1000公顷流域内的9个集水区以5分钟或更短的时间分辨率记录河流流量。集水区将有以下面积：700公顷、100公顷、45公顷、15公顷、5公顷(X2)、1公顷(X3)。在此期间，将监测上述径流小区以及其他地点的土壤水分状况，并记录连续降雨和其他大气数据。在夏季、秋季、冬季和春季，将在9个地块附近进行入渗试验，以观察田间饱和导水率随季节变化的程度。在实验室中对土壤样本进行分析，以测量：1)膨胀/收缩特征，2)饱和导水率随时间的变化，3)水分保持特征，4)颗粒分布。一个空间分布的水文模型，考虑土壤在入渗时的缓慢膨胀和收缩，将模拟来自9个集水区的径流。除了科学活动外，智利还将资助12名大学生参加为期三周的野外水文夏令营，并允许多至6名学生自费。野外训练营将包括介绍水文测量的科学原理，并对6项基本测量进行小组练习。这些测量将是解决提案的科学假设所需的表征工作的一部分，使学生参与实际研究。该项目的科学成果适用于世界各地发现的膨胀土壤，在美国(例如：德克萨斯州)、加拿大、新西兰和智利都有突出的例子。

Clay swelling is a time-dependent process that, for some soils, requires up to a month to complete, even with abundant water supply. Our preliminary experiments on soils from the ?Drylands? of the coast range of central Chile demonstrate this behavior in laboratory and field infiltration tests. The importance of such time-dependent hydration has not been studied in the field nor included in hydrologic models, but is expected to be of profound application with respect to runoff generation and aquifer recharge. The objective of this study is to observe the influence of time-dependent swelling dynamics on infiltration and runoff processes and develop a scalable process-based model to predict hydrologic response of swelling soils at scales from 0.02 to 100,000 ha.The authors will examine the effects of the preferential flow paths in slow-swelling clay soils on water flow at the plot and catchment scales. At the plot scale, surface water runoff and water content in the upper 2 m of soil will be measured during a series of simulated rainstorms. Throughout two full years, stream flow will be recorded at a temporal resolution of 5 min or less from 9 catchments within a 1000 ha basin. The catchments will have the following sizes: 700 ha, 100 ha, 45 ha, 15 ha, 5 ha (x2), 1 ha (x3). Soil moisture profiles in above runoff plots as well as in other locations will be monitored and continuous rainfall and other atmospheric data will be recorded during this period. Infiltration tests adjacent to each of the 9 plots will be carried out during the summer, fall, winter and spring to observe the degree to which field saturated hydraulic conductivity changes by season. Soil samples be analyzed in the laboratory to measure:1) swelling/shrinkage characteristics, 2) time-dependent changes in saturated hydraulic conductivity, 3) water retention characteristic, and 4) particle-size distribution.A spatially-distributed hydrologic model that accounts for slow swelling and shrinking of soils on infiltration will simulate stream flow from each of the 9 catchments. In addition to the scientific activities, a hands-on three-week field hydrology camp in Chile will be funded for 12 university students, with up to 6 more students allowed to pay their own way. The field camp will include presentation of scientific principles of hydrologic measurement, and small-group practice of each of 6 basic measurements. These measurements will be part of the characterization work required to address the scientific hypothesis of the proposal, giving the students involvement in actual research. The scientific outcomes of the project apply to swelling soils found around the world with prominent examples in the USA (Ex.: Texas), Canada, New Zealand, and Chile.