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Abstract
Drainage of sloping lands is an important problem that affects the productivity of agricultural lands. The increase in groundwater levels, especially in the downslope part,
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causes waterlogging. Therefore, a suitable drainage system for sloping land should be
carefully designed.
In the present study, the problem of draining sloping lands bounded by two streams was
treated numerically using the finite element technique. A computer program, named SEEP ]LOW, was written in MATLAB 6.5 and prepared to determine the location of the water table, the seepage discharges, and to draw streamlines and I or equipotentiallines. Three cases were studied. In the first case, a system of equally-spaced pipe drains is analyzed. A system of pipe drains laid at unequal spacing is studied in the second case. For the two cases, the upper pervious layer is underlain by a horizontal impervious one. In the third case. two conditions for the bottom boundary were studied. The first condition considered different slopes for the impervious sublayer. In the second condition, the lower layer was assumed to be highly pervious with a specific piezometric head.
The results indicated that constant drain spacing is not suitable for sloping land. One or two rows of pipe drains, at the upper part, may not receive any drainage water. On the other hand, drains at the lower part may become totally full, thus waterlogging occurs. Closer drain spacing is required to lower the water table and to prevent waterlogging at the bottom of the slope. Results also indicated that the system of unequal spacing may ensure a constant drainage depth all over the slope. Rearranging the pipe drains layout made them receive equal seepage discharges and work in a full capacity and hence, waterlogging was minimized and soil conditions were improved. The slope of the bottom boundary gave a small effect on the seepage characteristics. The bottom layer may act as a source or a sink according to the value of the piezometric head. When the bottom layer acts as a source, the pipe drains receive drainage water from both the recharge rate and the upward flow. and when it acts as a sink. pipe drains may have no function because of vertical drainage to the
bottom layer.