The vadose zone plays an important role in the hydrological cycle and controls exchange processes at the earth’s surface. Quantifying the water content distribution in the vadose zone is important. However, direct measurement of water content or simulation using experimental soil hydraulic properties are time consuming and may not be very accurate. A multi-year study was conducted at a 0.5-ha grass field to assess methods to quantify unsaturated flow. Soil cores were taken to determine water retention, soil hydraulic conductivity, and basic soil properties in the laboratory. Aluminum access tubes were installed for in situ determination of volumetric water content by neutron probe. The retention data were parameterized using a simplified Brooks-Corey equation that was used in the one-dimensional Richards equation for vertical soil water flow. An analytical solution for the Richards equation was obtained with the Cole-Hopf transformation. Mathematical constants in the equation were optimized using experimental time series of water content while model coefficients were computed from the Brooks-Corey parameters. Three strategies to estimate water content at a location A were used that require a decreasing amount of effort: 1) use analytical simulations based upon constants and coefficients for A, 2) use analytical simulations based upon constants for another location B and coefficients for A, and 3) use experimental water content for B. The estimates were compared with the observed water content.
Antonella Sciortino– Professor, California State University, Long Beach, Long Beach, California