In this article we will discuss about:- 1. Introduction to Water Logging 2. Causes of Water Logging 3. Ill-Effects 4. Remedial Measures.
Introduction to Water Logging:
An agricultural land is said to be water logged when its productivity gets affected by the high ground water table. The productivity of the land is affected when the root zone of plant gets flooded with water and becomes ill-aerated. Because of the inadequate aeration of the root zone, oxygen required by the plant to maintain its growth is reduced and thus yield of the crop is reduced.
The depth of water table below ground level, which causes water logging is not same for all the conditions. It depends upon nature of soil and type of the crop. The effect of ground water, above ground water table depends upon the height, of capillary fringes which in turn depend upon the nature of the soil.
The height of capillary fringes above water table, for normal agricultural soils, varies from 90 cm to as much as 1.50 m. The root zone depth, is considered about 0.6 m. Hence if at someplace, root zone depth is 0.6 m and height, of capillary fringes is say 1 m, the land will be called waterlogged if depth of table below ground level is 1 + 0.6 = 1.6 m or less. If depth of water table is more than 1.6 m, then it is not water logged.
Depths of water table below ground level, for different crops are given below which will adversely affect their yield:
The ground water table does not remain constant. There shall be seasonal fluctuations, due to variation in rainfall.
Causes of Water Logging:
Following may be the causes of rise in water table which ultimately leads to water logging of the area:
1. Over and Intensive Irrigation:
When a policy of intensive irrigation is adopted, then, maximum irrigable water is supplied to certain region. This leads to heavy percolation and subsequent rise of water table. For this reason, to avoid water logging, a policy of extensive irrigation (on more area) should be preferred from the policy of intensive irrigation (more water on small area).
In short irrigation water applied to the fields is more than the requirements of crop and this result in deep percolation. Percolated water augments the ground water storage and causes rise in water table.
2. Seepage of Water from Adjoining High Lands:
The water from adjacent high lands may seep into the sub-soil of the affected land and may cause rise in water table.
3. Seepage of Water through the Canals:
In nature the water table is always in a state of equilibrium. In other words amount of inflow is practically equal to the amount of outflow. Due to construction of canal, the seepage through bed and sides of the canal takes place. This increases the inflow into the ground water and thus rise in ground water table occurs.
The rise in water table takes place upto the level when the increased inflow is again balanced by the increased outflow by way of increased soil evaporation, increased transpiration and increased discharge into seepage drains.
4. Impervious Obstruction:
Seeping water below the soil moves horizontally. If this flow finds an impervious obstruction, rise in water table occurs on the U/S side of the obstruction. On the same ground if an impervious stratum occurs below the top layer of pervious soil, seeping water will not be able to go deep and this also causes quick rise in water table.
5. Inadequate Natural Drainage:
Soils having less permeable substrata (such a clay) below the top layers of pervious soils, will not be able to drain water deep into the ground. This will cause rise in water level.
6. Inadequate Surface Drainage:
If the area is not properly drained, the storm water will accumulate into the depressions in the area. This accumulated water remains percolating and causes rise in the water table. If natural drains of the area are obstructed by railway or highway embankments, the water will get accumulated and thus causes water logging.
7. Excessive Rains:
Excessive rainfall may cause temporary water logged conditions. If the area is not properly drained, the area may be subjected to continued water logging.
8. Submergence due to Floods:
If a land is continuously subjected to submergence by floods, water loving plants may grow in abundance. The weed growth will obstruct the natural surface drainage of the soil and chances of water logging get increased.
9. Irregular or Flat Topography:
The water is immediately drained from regular steeply sloped area. If the area is flat and irregular, the drainage of the area is poor. This causes detention of water on the surface for longer periods, longer water table may rise.
10. Inadequate Capacity of Arterial Drains:
If the capacity of the drains dealing with flood water is smaller than the required size, the flood water of local drains will spread over country side for days. This will cause heavy percolation of water and may ultimately lead to water logging.
11. Construction of Reservoirs:
Seepage from reservoirs, canals, may cause water logging of the adjoining areas.
Ill-Effects of Water Logging:
The ill-effects of water logged soils are the following:
1. Water logged fields generally remain wet and their tillage becomes difficult.
2. Sowing of the crops is generally delayed because ploughing and mulching of fields is delayed in water logged areas.
3. The climate of the water logged area becomes damp. Standing water in pools becomes stagnant. The stagnant pools of water become good breeding places for mosquitoes. All these, effects ultimately lead to conditions detrimental to the health of the community.
4. Growth of Wild Weeds:
Weed growth in water logged areas is generally very intensive. This reduces the supply of food to the crops, as weed shares the food. Farmers have to do lot of labour to clear the fields from weeds so that they may have good production of crops.
5. If water logged area has canal system of irrigation, the canal water will be used very little as such areas require very little irrigation. This aspect may lead to wastage of canal water, which remains filled up in low areas and may cause water logging of more areas.
6. Inadequate Circulation of Air in Root Zone:
In water logged areas, air circulation in the root zone becomes inadequate, due to which activity of bacteria and consequent growth of the plants is affected.
7. Water Logging Causes Salinity of the Soil:
The water that has risen up continuously evaporates by capillary action. This establishes continuous upward flow of water from the water table to the land surface. With this upward flow, the salts which are present in water and also in lower layers of soil rise towards the surface, resulting in the deposition of salts in the root zone of crops.
The concentration of these salts (which are usually alkaline) has a corroding effect on the roots, which reduces the osmotic activity of the plants and reduces their growth. Such soils which contain large concentrations of harmful salt in the root zone are known as saline soils. From this it can be easily said that wherever there is waterlogging, salinity is a must.
8. In waterlogged areas, temperature of the soil is generally low. Lower temperature does not allow bacteria to function properly and as such supply of food to the plants is reduced.
Remedial Measures for Controlling Water Logging:
It is evident that water-logging can be controlled only if the quantity of water entering the soil is checked and reduced. To achieve this, the inflow of water into the ground water reservoir must be reduced and the outflow from this reservoir should be increased.
Following are some of the measures which can be adopted for controlling water logging:
1. All the canals and water courses, used for irrigation and other purposes, should be lined. It is considered as one of the most effective measure of controlling waterlogging.
2. Intensity of irrigation in the area likely to be water logged should be reduced. In areas where water tale is very high, irrigation during Kharif season may only be allowed. During Rabi season, the cultivators may he asked to irrigate from wells.
3. Cultivators may be educated for economic use of water. They should be made to understand the importance of irrigation water. They should be asked to divide fields into small Kiaries so that deep percolations do not occur.
4. In order to reduce seepage from Kucha canals, they should be designed with lesser depth of water. Lesser depth will induce lesser head for seepage losses.
5. Certain crops require more water than others. If a particular field is always sown with a crop requiring more water the chances of water-logging are more. In order to avoid this, crops requiring lesser, and more quantity of water, should be sown alternately in the fields.
6. Optimum Use of Water:
Certain fixed quantity of water for a particular crop gives best results. Less than that and more than that reduces the yield. But most of our farmers are unaware of this fact. They always think that more the waterings you apply, to the field, the greater is going to be the yield and hence they try to use more and more water. This can be checked by educating the farmers.
7. Revenue should be charged on the basis of quantity of water utilized and not according to the area irrigated. This measure has its own practical drawbacks but theoretically the cultivator would be tempted to irrigate more area with same quantity of water.
8. Providing Intercepting Drains:
Intercepting drains along the canals, particularly in high embankment reaches should be constructed. These drains intercept seepage and percolation from the canals. They should not be laid very close to canals, because then they would be drawing water from the canals directly.
9. Introduction of Lift Irrigation (Well Irrigation):
Well irrigation utilises the underground water for irrigation. Hence the areas which are likely to be water logged in near future should be irrigated from wells and intensity of irrigation from canals should be reduced considerably. Well irrigation would lower the ground water-table and chances of land becoming water-logged are eliminated.
10. Improving the Natural Drainage of the Area:
The natural drainage system of the area should be such that no water is allowed to stand for longer period and as soon as rain water drops on the ground it should be immediately led to drains. For this natural drains should be maintained clear from weed growth and any obstructions should be removed. Natural slopes of drains should be maintained by clearing silt from time to time.
11. Provision of an Efficient Drainage System:
An efficient drainage system should be provided to drain away the storm water. A good drainage system may consist of surface drains as well as sub-surface drains. If area is very intensively water- logged and soil is of poor drainability, underground porous, or tile drains have to be laid to effectively lower down the waterable.
12. Adoption of Sprinkler Method for Irrigation:
This method almost completely eliminates the percolation losses from water courses. Maximum percentage of this water is utilized in form of consumptive use and losses are reduced to minimum.