In this article we will discuss about the environmental impact that results from faulty management of irrigation water. The environmental impacts are: 1. Rise in Water Table 2. Water-Logging 3. Soil Salinisation 4. Lowering of Water Table.
Environmental Impact # 1. Rise in Water Table:
In many canal command areas, faulty irrigation water management practices have resulted in rising of water table leading to problems of water-logging and secondary Stalinization. The problem of raising water table is more serious in arid and semiarid areas, where ground water table has often been several meters below the land surface prior to introduction of irrigation.
Rise in water table is largely due to increased recharge through seepage from main canals, distributaries and field channels, deep percolation of excess water applied to field and inappropriate cropping patterns.
The problem is so acute in some irrigated areas of arid and semiarid regions that the lands, where dryland agriculture was practiced a few years back have become unfit for upland crops during monsoon. Water table has been rising at 0.6 m year-1 in command areas of Western Yamuna Canal.
Once the water table rises to shallow depths, the land lose the productivity due to unfavourable conditions like poor aeration, reduced microbial activity, waterlogging and upsetting of salt water balance.
Environmental Impact # 2. Water-Logging:
Poor drainage and faulty management of irrigation water resulted in problems of waterlogging in many productive soils. In fact salinity and waterlogging are the interlinked problems. Total waterlogged area in India is estimated at 8.5 M ha. Highest waterlogged area (1.3 M ha) is in Uttar Pradesh followed by Gujarat (1.2 M ha) and Rajasthan (1.1 M ha).
Environmental Impact # 3. Soil Salinisation:
Rise of water table in arid and semiarid areas usually mobilise the salts present in soil profile and groundwater. Once the ground water table rises within 2 to 3 m of soil surface, it contributes substantially to evaporation from soil surface and water uptake by plants.
The upward flux of water leads to gradual increase in concentration of salts in shallow depths of soil profile. Initially, crop yields may be reduced due to salinity. As the severity of increases, the lands may have to be abandoned, since excess salts render the soils completely unproductive.
Salt affected soils occur all over India, the most affected states being Uttar Pradesh, Gujarat, Rajasthan, West Bengal and Andhra Pradesh. Largest salt affected area (1, 3 M ha) is in Uttar Pradesh. Extent of salinity under some important command areas is given in Table 10.9. In east coast plains region, coastal saline soils exist to the extent of 0.28 M ha in Andhra Pradesh and 0.08 M ha in Tamil Nadu.
Environmental Impact # 4. Lowering of Water Table:
In Punjab, Haryana and western Uttar Pradesh, indiscriminate instillation of shallow pumping sets for irrigating crops like rice and sugarcane has caused serious overdraft of groundwater from good quality aquifers leading to lowering of water table.
In Punjab where, the number of tube-wells increased from 192 thousand in 1970 to almost 800 thousand in 1990s, resulting on an average 0.2 m year-1 decline in water table. In Haryana, where the number tube-wells has increased 15-fold in past two decades, the average decline in water table has been 0.14 to 0.33 m year-1.
Over exploitation of ground water is causing continuous decline of water table, reduction in well yield, drying up of shallow wells, deterioration of ground water quality, sea water intrusion into coastal aquifers and high cost of energy to lift the water from great depths, which becomes uneconomical to poor farmers to continue agriculture.