MODEL SENSITIVITY TO MEASURED AND ESTIMATED HYDRAULIC-PROPERTIES OF AZIMMERMAN FINE SAND

Water retention and hydraulic conductivity are necessary for simulatin g solute transport in process-oriented models because of the fundament al role of water flow, Accuracy and extension of soil hydraulic proper ties are crucial for using models to give site-specific predictions, y et these evaluations are infrequent and often lack rigor. The objectiv es of this study were to compare measured and estimated hydraulic prop erties and their effects on simulation of held soil-water regime, Wate r contents (theta) and hydraulic conductivities (K) at specific matric potentials (psi) alternatively measured in the laboratory and field o r estimated from other soil properties were fitted to water retention and hydraulic conductivity functions to obtain parameters according to the van Genuchten formulation. The estimated parameters were inputs f or the Root Zone Water Quality Model to simulate water movement in a Z immerman fine sand (mixed, frigid Argic Udipsamment), Simulated and in situ measured water contents were compared to assess methods used for measuring or estimating hydraulic properties, Simulation using hydrau lic functions generated from field-measured theta(psi) and K(psi) was closest to measured total water depth in the 1.5-m profile as well as water contents at the 0.2-m depth, Arbitrary variations of a and n in the van Genuchten equations had larger effects on theta(psi) and K(psi ) functions compared with variations caused by methods to measure and estimate hydraulic functions, This test demonstrated the crucial role and importance of soil hydraulic properties in simulating water storag e and movement even in a sandy soil.