Water Resources Research Act Program

Details for Project ID 2010NV167B

Unsaturated Hydraulic Properties of Anisotropic Soils

Institute: Nevada
Year Established: 2010 Start Date: 2010-03-01 End Date: 2011-02-28
Total Federal Funds: $14,415 Total Non-Federal Funds: $29,483

Principal Investigators: Jianting Zhu

Abstract: Groundwater is the main source of water supply in much of Nevada and the Great Basin. The unsaturated zone is critically important as it determines the partitioning of precipitation over surface runoff and infiltration and the partitioning of infiltrated water over evapotranspiration and the recharge to groundwater. In order to quantify water flow in the unsaturated zone, the soil hydraulic properties of the unsaturated zone have to be specified. Large scale soils usually demonstrate different moisture spreading behavior at different water saturation (or tension) levels. This anisotropic behavior has important implications for recharge to groundwater, especially in arid and semi-arid areas when groundwater tables are typically deep and saturation levels vary greatly from ground surface to groundwater tables since it might either facilitate or retard downward water movement of water at different saturation levels. Pedotransfer functions (PTFs) are often used to estimate soil hydraulic properties when direct measurements are too expensive. PTFs transform basic soil properties such as texture, bulk density into water retention and saturated or unsaturated hydraulic conductivity. Artificial neural network based PTFs have become increasingly more popular in the last decade or so. This project will combine the neural network analysis results with the thin layer approach to explore saturation-dependent anisotropy behavior for a wide range of texture and bulk density conditions. The main objective is to develop hydraulic conductivity models that quantify anisotropy of saturated and unsaturated soils composed of many thin layers distinguished by both the texture and the bulk density. We are mainly interested in the anisotropy arising from a combination of both wide range of soil texture variations and within narrow range of texture units due to particle segregation and compaction that typically affect porosity or bulk density. The expected outcomes from this project will be various unsaturated zone anisotropy models for a wide range of developed soil hydraulic parameter, texture and bulk density relationships for individual soil layers. The new models will also encompass a wide range of textural and bulk density variations and probability density distributions of the anisotropic soil formations. In a broader scope, the models developed in this project can be extended to upscaling of anisotropically layered heterogeneous soils in characterizing effective hydraulic properties for large scale applications. Upscaling of soil hydraulic property is a process that incorporates a mesh of hydraulic properties defined at the measurement (support) scale into a coarser mesh with “effective/average hydraulic properties” that can be used in large-scale (e.g., watershed scale, basin scale, regional scale) modeling of unsaturated zone processes.