Use and over utilization of surface and ground water
1. Agriculture Needs of Water for the Crops:
As our country is essentially an agricultural based country, the crops are to be developed for the production of different types of food grains. The requirement of water varies from crop to crop.
Different research stations are busy in identifying the water needs of all the crops. Most of these crops are shallow rooted, thus water being extracted from top layers of the soil. Soil moisture available in the top layers is essential for such crops.
Hence, it is advocated to keep the topsoil always moist so that crops do not wilt under no water condition. Several scientific methods of ploughing are developed to maintain the moisture in the topsoil for longer periods.
Requirement of maintaining the water storage for breeding the fish and prawn culture is attaining importance whenever we go for storage project. Since fish cannot travel against flow when the velocity is high, special structures are provided adjacent to the weirs to maintain low velocities. Such structures are known as fish ladders.
The different purposes of the multipurpose projects have their conflicting affect on the environment. However, depending on the priority of the water needs of the area to be served, the planning has to proceed in such a way that the impact on environment is kept to be minimum while serving the urgent and primary needs of the people of the area.
2. Groundwater and Aquifers:
Water that is available in the deeper layers of the earth is known as Groundwater. This water has been trapped inside the earth’s crust for several centuries. The water that is lying under the ground has the capacity to move in general direction of its slope with a very small velocity. The bodies that contain such water are known as Aquifers.
Water from these aquifers can be drawn by digging wells and pumping water from these wells. Some of these wells can supply very large quantities of water. In some cases, the drinking water needs of cities are completely met by the groundwater bodies. In the agriculture sector also, groundwater is supporting the growth of crops enormously in certain agricultural dominated areas.
3. Groundwater and Wells:
Wells are used to bring groundwater to the land surface by means of pumps. Wells can be deep wells and shallow wells depending upon the depth at which ground water is available. Sometimes open dug wells are used where the water table is high. In the case of deeper and hard rock aquifers, Tube wells are constructed. In such cases deep well pumps such as turbine pumps or jet pumps are used to lift water to the surface of the ground.
These tube wells in many cases yield significantly high discharges. In a way, groundwater is the water that is available at the place of its use. Thus this water can be lifted from the wells in the agricultural fields and supplied to the crops raised in that field. Hence, there is no need to send water to long distances. This incidentally reduces the water losses considerably. Use of ground water for nearby areas also does not pose the problems of environmental degradation.
4. Floods and Droughts:
The flood hazard itself cannot be prevented, but thorough understanding of the land conditions which are prone to a given hazard and the processes which could culminate in the damage to life and property it is possible to minimize the damage through preparedness for a particular eventuality. Flooding takes place when the river channels are unable to contain the discharge.
In the tropical countries, floods are caused by various factors:
(i) Climatologically (rain),
(ii) Part climatologically (coastal storm surges, estuarine interactions between stream flow and tidal conditions) and
(iii) Others (failure of dams and other control works, excessive release from dams). Floods could get intensified because of basin characteristics, network characteristics, and channel characteristics, each of which has both stable (unvarying) and variable components (Table 2.1) unvarying and variable characteristics.
The improper land-use practices accentuated the flood devastation. There are hardly any forests left in the catchment area of the rivers. It is well known that the forest areas are characterized by high infiltration capacity and transmissibility. The infiltration capacity of the forest areas is 2-3 times greater than in the open fields. The surface runoff in the forested areas may be as little as one-tenth of that of the open fields.
There is hardly any protective vegetation on the banks of the Save and Limpopo rivers. Crops are grown right to the edges of the rivers, even on river slopes. Thus, the combination of absence of forest cover on one hand, and inappropriate farming practices on the other, intensified the floods. Floods can be mitigated by structural, water control and non-structural measures.
The structural methods include dams, reservoirs, and retarding basins, channel management and embankments. The water control methods include flood proofing and catchment modifications. Schemes of drainage and flood protection, flood forecasting, flood warning and emergency preparedness systems, flood insurance, public information and education, and flood relief constitute the non-structural methods.
Drought is lack or insufficiency of rain for an extended period that causes considerable hydrologic imbalances and consequently water shortages, stream flow reductions and depletion of groundwater levels and soil moisture. Drought is the most serious physical hazard to agriculture in nearly every part of the world.
Drought not only leads to serious economic consequences but also leaves behind untold human misery. Among all the natural disasters, drought affects largest number of people in the world. Shortage of water for even the basic needs is the main problem in the drought areas.
Even the shallow rooted crops do not grow in such areas. Getting sufficient drinking water is another problem needing immediate attention in these areas. Some measures like infiltration wells, underground dams, small watersheds, are being taken up to alleviate the sufferings of the people residing in the drought prone areas.
Certain advance techniques such as Cloud Seeding and Artificial Rains are also being tried with varying successes. However, these methods are quite expensive and unpredictable in their success. Scant rains for extensive periods also lead to ecological changes. Ultimately, Government has found reasonable remedies in the form of development of small watersheds in such areas.
5. Dams: Benefits and Problems:
Dams are the major structures in any reservoir from the point of view of structural importance; design details and cost. The dams are of different types depending on different criteria. Depending on the material used for construction, dams can be: masonry dams, concrete dams, earthen dams, rock fill dams, steel dams and timber dams.
Based on the design, the dams can be: gravity dams, arch dams, buttress dams, and multiple arch dams. Similarly, based on the purpose, the dams are known as overflow dams and non-overflow dams.
The masonry and concrete dams are more or less leak proof and hence seepage is not possible. However in the case of earthen and rock fill dams, seepage of water can be expected, in good quantities and therefore, possibilities of water logging on downstream side will be the adverse effect on the environment.
The water resources projects are constructed to several purposes depending on the needs of people of the area to be served. Whenever the projects are developed to supply water for different purpose, the projects are termed as multi-purpose projects.
The different purposes can be: irrigation and agriculture, hydropower generation, drinking water supply, water for Industries, flood control, navigation, recreation and amusement parks and afforestation. Of all the above purposes, irrigation and agriculture occupies higher priority, as the production of necessary food grains for one billion population of the country is the primary concern to us.
In order to develop the industries and other power needs, the next priority is the Hydropower development. The emphasis is increasing on the hydropower, as the natural resources for other forms of energy such as thermal, are becoming scarce. Due to rapid development of urban areas, scarcity of drinking water has surfaced in most of the cities. Hence, the present emphasis is on bringing water to the cities from storage reservoirs.
Slowly, water needs for drinking purposes is occupying priority when compared to other needs. In the flood plains, the problem of inundation of adjacent habituated areas is a priority, as during every flood the losses in respect of human and cattle life, crops, property and fertile soils, are bringing misery to the people.
With every increasing movement of men and material, the transportation by navigation is also recognized as a viable mode. In the recent times, water has been used for recreational purposes also. In some countries, water sports are gaining popularity. In order to develop greenery in many dry areas, Government is encouraging people to go in for tree plantations on a large scale resulting in afforestation.