Scale and Time Dependent Hydrologic Response of Sites with Expansive Soils

粘土膨胀是一个时间依赖性的过程，对于某些土壤，即使有充足的水供应，也需要长达一个月的时间才能完成。我们对土壤的初步实验？干地？智利中部海岸线的一个小湖泊在实验室和现场渗透试验中证明了这种行为。这种随时间变化的水化作用的重要性尚未在实地研究，也未列入水文模型，但预计在径流产生和含水层补给方面将有深远的应用。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，并开发一个可扩展的基于过程的模型，以预测水文响应的膨胀土的尺度从0.02到100,000公顷。作者将研究的影响，在缓慢膨胀的粘土优先流路径的水流量在情节和集水尺度。在小区尺度上，将在一系列模拟暴雨期间测量地表水径流和土壤上层2 m的含水量。在整整两年的时间里，将以5分钟或更少的时间分辨率记录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，将监测上述径流区以及其他地点的土壤湿度概况，并记录连续降雨量和其他大气数据。将在夏季、秋季、冬季和春季对9个地块中的每一个地块进行渗透试验，以观察田间饱和导水率随季节变化的程度。在实验室中分析土壤样品以测量：1）膨胀/收缩特性，2）饱和水力传导率随时间的变化，3）持水特性，以及4）颗粒大小分布。一个空间分布的水文模型将模拟来自9个集水区的水流，该模型考虑了土壤在入渗时的缓慢膨胀和收缩。除了科学活动外，还将资助12名大学生在智利举办为期三周的实地水文学夏令营，最多还有6名学生可以自费。野外营将包括介绍水文测量的科学原理，以及6种基本测量方法的小组实践。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，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，美国有突出的例子（例如：德克萨斯州）、加拿大、新西兰和智利。

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.