5th International Conference on Rain Water Cistern Systems
"Rainwater Catchment for Future Generations"
Keelung, Taiwan, R.O.C. - August 1991

Section 7: Agricultural Uses of Cistern Water

Page 381

Rainwater, Water Table And Soil Moisture In A Hillslope

Jose de Oliveira Leite & Antonio Cadima Zevallos
Cacao Research Centre, Brazil.

Abstract

The objective of this work was to stud y the relationships between the rainfall, the water table and the soil moisture regimen in a hillslope planted with cacao. These parameters were measured daily during 270 days.

The water table was observed in a set o 5 wells located in a contour line of the hillside. Beside the middle well two sets of tensiometers were installed at 15, 30, 60, 90 and 135 cm depths. Also, the soil composition, density of aggregates and moisture equivalent were measured. It was found that, horizontally, the soil profile can be divided into three zones: the op zone (from 15 to 30 cm depth), not submissive to the water table rise under rainy conditions. This zone presents an average soil moisture content of 0.48 (cm3/cm3). In the middle zone (30.- 90 cm), the average moisture content ranges from 0,50 to 0,55 f the water table. is below or above 4m depth, respectively, and th bottom zone, below 90 cm, is more submissive to that saturation although its moisture content is not statically different than o the upper zone. The peculiarity of the middle zone, which is composed of B21 and B22 horizons, is associated with its high clay content. Also this zone represents a water reservoir to the cacao' tree. In general, the results suggested that the water table height, associated with the rainfall conditions, controls the moisture content in the whole soil profile. However at the 30 - 90 cm depth, the transpiration flow of the cacao tree may also play an important role in the soil moisture regimen.

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