Modeling Vadose Zone Moisture Dynamics with the Integrated Hydrologic Model (IHM)

Reproducing moisture retention behavior of the upper and lower vadose zone in shallow water table settings provides unique challenges for the integrated (combined surface and groundwater) hydrological models. The theory and behavior of one model, the Integrated Hydrological Model (IHM) is examined through comparisons with collected data at a study site in West-Central Florida. The objectives of this exploration were to (1) test a model of the vertical processes controlling water table behavior, evapotranspiration, ET distribution flux and infiltration, (2) investigate the sensitivity of model parameters on model vs. observed vertical behavior, and (3) offer recommendations for improvements and parameterization for regional model application. Rigorous testing was done to better understand the robustness and/or limitations of the methodology of the IHM for upper and lower vadose zones. The results are also generally applicable and useful to the upper zone and lower zone conceptualization and parameterization of stand-alone HSPF applications and perhaps other surface water models. Simulation results indicate IHM is capable of providing reasonable predictions of infiltration, depth to water table elevations response, evapotranspiration distributions from the upper soil, lower soil and water table while incorporating field scale variability of soil and land cover properties.