Scale and Time Dependent Hydrologic Response of Sites with Expansive Soils

粘土膨胀是一个与时间有关的过程，对于一些土壤来说，即使在充足的水供应下，也需要长达一个月的时间才能完成。我们对？旱地吗?智利中部沿海地区的土壤在实验室和野外入渗试验中证明了这种行为。这种依赖时间的水化作用的重要性尚未在实地进行研究，也未包括在水文模型中，但预计在径流产生和含水层补给方面具有深远的应用。本研究的目的是观察随时间变化的溶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至100,000公顷尺度上溶胀土壤的水文响应。作者将在小区和集水区尺度上研究慢膨胀粘土中优先流道对水流的影响。在地块尺度上，将在一系列模拟暴雨期间测量地表水径流量和土壤上部2 m的含水量。在整整两年的时间里，将以5分钟或更短的时间分辨率记录1000公顷流域内9个集水区的水流。集水区的面积如下：700公顷、100公顷、45公顷、15公顷、5公顷（x2）、1公顷（x3）。在此期间，将监测上述径流地块以及其他地点的土壤湿度剖面，并记录连续降雨和其他大气数据。在夏、秋、冬、春4个季节分别对9个样地相邻区域进行入渗试验，观察田间饱和导水率随季节变化的程度。土壤样品在实验室进行分析，以测量：1)膨胀/收缩特性，2)饱和水力电导率随时间的变化，3)保水特性，4)粒径分布。一个空间分布的水文模型，考虑土壤在入渗过程中的缓慢膨胀和收缩，将模拟9个集水区的水流。除了科学活动外，还将资助12名大学生在智利进行为期三周的野外水文实践营，最多可有6名学生自费。野外营地将包括介绍水文测量的科学原理，以及6项基本测量的小组实践。这些测量将成为解决提案的科学假设所需的表征工作的一部分，让学生参与实际研究。该项目的科学成果适用于世界各地发现的膨胀土，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.