Year Established: 2013 Start Date: 2013-03-01 End Date: 2016-02-28
Total Federal Funds: $31,181 Total Non-Federal Funds: $69,299
Principal Investigators: Yong Zhang, Li Chen, Donald Reeves
Abstract: Water resources are critical to sustainable development in arid and semi-arid areas. The processes of surface runoff and infiltration govern the fate of precipitation reaching the land surface, and thus control the total amount and timing of precipitation available to generate streamflow and replenish aquifers. This study proposes an investigation into the complex dynamics of surface runoff and infiltration using mathematical methods that are more effective in capturing highly non-linear runoff-infiltration behavior than conventional methods. Runoff-infiltration are the initial processes for many hydrological, biological, and ecological processes. For example, torrential floods and debris flow hazards are all associated with surface runoff generation. Surface runoff also causes water redistribution, and subsequent transport and redistribution of nutrients and contaminants, along land surfaces affecting multiple biological and ecological processes and systems. Efficient and accurate quantification of runoff-infiltration processes, however, has remained a challenge in hydrology, primarily due to the heterogeneity of natural systems. In particular, topography and soil hydraulic properties frequently exhibit multi-scale heterogeneity which can result in anomalous overland flow and transport along discontinuous flow paths. These complex flow patterns and scale dependency in surface runoff cannot be adequately captured by current modeling techniques that ignore the nonlocal connectivity of flow. Conventional models of water infiltration predict monotonically decreasing infiltration rates with Gaussian scaling of wetting fronts, although many laboratory and field measurements show non-monotonic infiltration rates and non-Boltzmann scaling of wetting fronts due to heterogeneity in soil properties that cannot be sufficiently characterized by traditional models. Objectives: The main objective of this research project is to quantify surface runoff and water infiltration in strongly heterogeneous systems across scales, by coupling theoretical development, stochastic analysis, and field applications. Dynamics missed by classical theories and models, including anomalous and scale-dependent surface runoff and non-Boltzmann scaling of wetting fronts, will be captured. The final objective is to build a well-documented software suite that will be released freely to scientists, consultants, regulators, and educators in the hydrologic community to help protect water resources and our environment in Nevada. Methods: We will apply state-of-the-art physical theories and novel mathematical tools to build and solve the physical models for both surface runoff and water infiltration processes. First, random walk theories combined with the subordination technique can account for the nonlocal movement of water packages along a ground surface exhibiting fractal complexity. The local variation of flow behavior can also be captured by conditioning on local soil and topography properties. The resultant model will explain the scale evolution of surface runoff within and across sub-basins through the use of the new mathematical concept of tempered stable laws. Second, we will generalize the Green-Ampt model and the Richards equation using the physical concept of fractal time, which can account for both the sub-diffusive and super-diffusive anomalous motion of moisture observed in heterogeneous, unsaturated soils. Finally, model evaluation and parameterization will be conducted using multiple sets of hydrological data.