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Title: NUMERICAL ANALYSIS OF SOIL LIMITING FLOW FROM SUBSURFACE SOURCES

Author
item LAZAROVITCH, N - HEBREW UNIV. ISRAEL
item SIMUNEK, JIRKA - UC RIVERSIDE, CA
item Van Genuchten, Martinus
item SHANI, U - HEBREW UNIV. ISRAEL

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2005
Publication Date: 10/1/2005
Citation: Lazarovitch, N., Simunek, J., Van Genuchten, M.T., Shani, U. 2005. Numerical analysis of soil limiting flow from subsurface sources. In: S. Torkzaban and S. Majid Hassanizadeh (eds.), Proceedings of Workshop on HYDRUS Applications, p. 53-56, October 19, 2005, ISBN 90-39341125, Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.

Interpretive Summary: When a predetermined discharge from a subsurface source (e.g. a subsurface emitter) is larger than the soil infiltration capacity, the pressure head in the source outlet increases and becomes positive. This pressure buildup in the soil reduces the pressure difference across the source and, subsequently, decreases the source discharge rate. Previous studies have shown that the reduction in the pressure difference is larger for soils having a lower hydraulic conductivity and that the positive pressure in the vicinity of the source increases rapidly at the beginning of the infiltration event and approaches a final value after only several minutes. The objectives of this study were to a) implement into a transient numerical model a system-dependent boundary condition that describes infiltration from subsurface sources and considers the source characteristic curves, b) evaluate the dependence of the transient source discharge rate on the soil and source hydraulic properties, c) carry out laboratory experiments involving transient water flow from subsurface water sources, and d) compare the experimental results with those obtained with the a modified version of the HYDRUS-2D software package. Good agreement was found between transient back pressures measured in the laboratory experiment and those calculated using the HYDRUS-2D. The modified model allows the use of any hydraulic model for soil and source properties, simulation of both short and long duration infiltration events, and consideration of various source geometrical shapes. The modified numerical model also enables complex processes in the root zone involving short-time irrigation and root water uptake. Results of this study are important to improving the efficiency of subsurface drip irrigation.

Technical Abstract: The infiltration rate of water from a subsurface cavity is affected by many factors, including the pressure in the cavity, its size and geometry, and the hydraulic properties of the surrounding soil. When a predetermined discharge of a subsurface source (e.g. a subsurface emitter) is larger than the soil infiltration capacity, the pressure head in the source outlet increases and becomes positive. The increased pressure may significantly reduce the source discharge rate. The main objective of this study was to develop a system-dependent boundary condition that describes this process while considering the source characteristics, and to implement this boundary condition into the HYDRUS-2D software package. The updated numerical model was validated against transient experimental data. Good agreement was found between transient cavity pressures measured in laboratory experiments and those calculated using the updated numerical model.