A COMPARISON OF NUMERICAL AND ANALYTICAL TECHNIQUES FOR DESCRIBING CAPILLARY RISE1

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Abstract
Using two new approaches to solving Richards' equation, we calculated capillary rise in Yolo light clay soil. Both techniques have already been tested for infiltration and are now being applied to capillary rise. Comparison of the two calculations shows good agreement at short and long times and less agreement at intermediate times. This divergence is greater with capillary rise than with downward infiltration for Yolo light clay soil. Possible reasons for this divergence are discussed. Results are in general agreement with the experimental capillary rise data of Moore (1939); however, the initial and boundary conditions used in our calculations varied considerably from his. FINDIT is a method of solving the general flow equation with finite-difference and iteration techniques resulting in two-term equations for either cumulative inflow or inflow rate valid for any time and direction. OPTIMIZATION, like the Green and Ampt solution, uses cumulative inflow to calculate the time. The simplicity and ease of solution are marked advantages of the latter. Using two new approaches to solving Richards' equation, we calculated capillary rise in Yolo light clay soil. Both techniques have already been tested for infiltration and are now being applied to capillary rise. Comparison of the two calculations shows good agreement at short and long times and less agreement at intermediate times. This divergence is greater with capillary rise than with downward infiltration for Yolo light clay soil. Possible reasons for this divergence are discussed. Results are in general agreement with the experimental capillary rise data of Moore (1939); however, the initial and boundary conditions used in our calculations varied considerably from his. FINDIT is a method of solving the general flow equation with finite-difference and iteration techniques resulting in two-term equations for either cumulative inflow or inflow rate valid for any time and direction. OPTIMIZATION, like the Green and Ampt solution, uses cumulative inflow to calculate the time. The simplicity and ease of solution are marked advantages of the latter. © Williams & Wilkins 1985. All Rights Reserved.

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