Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Engineering Science (Interdepartmental Program)

First Advisor

Richard L. Bengtson

Abstract

A model was developed to predict daily change in WT depth and was used for WT management simulations. The model was calibrated and tested using climatological and WT data for a subsurface drainage system at Louisiana Agricultural Experiment Station's Ben Hur Research Farm, Baton Rouge, Louisiana. Monthly daily reaction factor and daily recharge coefficient were determined. Recharge coefficients were multiplied by a correction factor to account for antecedent soil moisture condition prior to the onset of rain. Two methods considered in the estimate of the correction factor were: Method I, the correction factor was taken as the reciprocal of the number of "dry days" prior to the onset of rain; and Method II, it was the reciprocal of moisture deficit total. The standard error and the average deviation between observed WT and WT simulated by Method I were 24.66 cm and 19.45 cm, respectively. In Method II these values were 23.08 cm and 17.71 cm, respectively. These were comparable with their corresponding values for DRAINMOD, which were 20.79 cm and 15.49 cm, respectively. Method II was used to simulate WT control management for the cropping season. A time increment of 3 minutes (0.05 hr) was used in the simulation under two types of control--(a) fixed weir (FXW), in which the outlet control level was set to 60 cm depth during the whole cropping season, and (b) controlled weir level (CWL), which was the same as the FXW method except that the outlet control was lowered to the drain level when WT rose to 30 cm depth. Irrigation was applied by pumping water into the sump each time the WT would fall to a estimated critical level of 80 cm depth. The performances of both types of control were compared in terms of average WT depth, amount of irrigation used, and excess soil water (SEW30). For FXW these values were 69.95 cm, 130.59 mm and 100.99 cm-days, respectively, and for CWL these respective values were 70.38 cm, 138.01 mm and 99.47 cm-days.

Pages

202

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