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1 Corey, A. T.; Jayawardane, P. H. 1982. Groundwater hydrology in the Mahaweli System H. 43p.
(Location: IWMI-HQ Call no: P 661 Record No: H01653)
A groundwater hydrology study of a watershed in the Mahaweli System H was undertaken to (1) Determine the principle source of water producing high water tables and interfering with the production of upland crops on Red Brown Earth (RBE) soils, (2) Assess the danger of the spread of areas with persistent high water tables (swamps) with continued irrigation, and (3) Assess the feasibility of using artificial drains to control high water tables in the area. It was found that the principal recharge to the groundwater comes from infiltration from flooded basins and irrigation ditches. Water- table elevations are affected by rainfall mainly when rains occur on fully saturated soils. Because the aquifer underlying RBE soils has a substantial transmissibility and the slope is favourable in most places, there is little danger of the high water tables becoming permanent (or spreading indefinitely) if reasonable care is taken in the use of irrigation water. There are localized spots, however, where the natural drainage conditions are such that high water tables can be expected to persist with any type of irrigation procedures. Most of the high water tables on the RBE soils could be avoided by lining the irrigation channels and avoiding cultivation employing flooded basins on RBE soils. Although artificial drains would be physically effective, it would be much less expensive and probably more economical to solve the high water-table problem by preventing the excessive infiltration from channels and growing only upland crops on the RBE soils. Artificial drains of the interceptor type might be practical to use near the boundary of RBE and LHG soils to protect the upland crops on the RBE soils from lateral seepage originating from flooded basins on the LHG soils. In such a case, the interceptor drain should be located parallel to the boundary at perhaps 30 m from the nearest flooded basins. The appropriate distance for a particular site would be determined by simple tests performed at the site. The interceptor drain should be placed at a depth as near as practical to the surface of any restrictive layer underlying the main water conducting stratum.
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