Contents preface (VII) introduction 1—37

5.14.2.4. Accumulation of Salts
As a result of the high water table in waterlogged areas, there is an upward capillary flow of water to the land surface where water gets evaporated. The water moving upward brings with it soluble salts from salty soil layers well below the surface. These soluble salts carried by the upward moving water are left behind in the root zone when this water evaporates. The accumulation of these salts in the root zone of the soil may affect the crop yield considerably.
5.14.3. Remedial Measures for Waterlogging
The main cause of waterlogging in an area is the introduction of canal irrigation there. It is, therefore, better to plan the irrigation scheme in such a way that the land is prevented from getting waterlogged. Measures, such as controlling the intensity of irrigation, provision of intercepting drains, keeping the full supply level of channels as low as possible, encouraging economical use of water, removing obstructions in natural drainage, rotation of crops, running of canals by rotation, etc., can help considerably in preventing the area from getting waterlogged.
In areas where the water table is relatively high, canal irrigation schemes should be planned for relatively low intensity of irrigation. In such areas canal irrigation should be allowed in the Kharif season only. Rabi irrigation should be carried out using ground water. Intercepting drains provided along canals with high embankments collect the canal water seeping through the embankments and, thus, prevent the seeping water from entering the ground. The full supply level in the channels may be kept as low as possible to reduce the seepage losses. The

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level should, however, be high enough to permit flow irrigation for most of the command area of the channel. For every crop there is an optimum water requirement for the maximum yield. The farmers must be made aware that the excessive use of water would harm the crop rather than benefit it. The levelling of farm land for irrigation, and a more efficient irrigation system decrease percolation to the ground and reduce the chances of waterlogging. The improvement in the existing natural drainage would reduce the amount of surface water percolating into the ground. A judicious rotation of crops can also help in reducing the chances of waterlogging. Running of canals by rotation means that the canals are run for few days and then kept dry for some days. This means that there would not be seepage for those days when the canal is dry. This, of course, is feasible only in case of distributaries and watercourses.

The combined use of surface and subsurface water resources of a given area in a judicious manner to derive maximum benefits is called conjunctive use of water. During dry periods, the use of ground water is increased, and this results in lowering of the water table. The use of surface water is increased during the wet season. Because of the lowered water table, the ground water reservoir receives rainfall supplies through increased percolation. The utilisation of water resources in this manner results neither in excessive lowering of the water table nor in its excessive rising. The conjunctive use of surface and subsurface water serves as a precautionary measure against waterlogging. It helps in greater water conservation and lower evapotranspiration losses, and brings larger areas under irrigation.
The most effective method of preventing waterlogging in a canal irrigated area, however, is to eliminate or reduce the seepage of canal water into the ground. This can be achieved by the lining of irrigation channels (including watercourses, if feasible). In areas which have already become waterlogged, curative methods such as surface and subsurface drainage and pumping of ground water are useful.