Management strategies for excess and deficit water imbalances
Water is essential for life. However, if it is present in excess or deficit quantities than that required for normal life sustenance, it may cause either flood or drought. This section deals with some issues related to the above imbalance of water, and strategies to mitigate consequential implications. Much detailed discussions is presented in Lesson 6.2.
Flood control and management
• There should be a master plan for flood control and management for each flood prone basin.
• Adequate flood-cushioning should be provided in water storage projects, wherever feasible, to facilitate better flood management.
• While physical flood protection works like embankments and dykes will continue to be necessary, increased emphasis should be laid on nonstructural measures such as flood forecasting and warning, flood plain zoning, and flood proofing for minimization of losses and to reduce the recurring expenditure on flood relief.
Drought prone area development
• Drought-prone areas should be made less vulnerable to drought associated problems through soil conservation measures, water harvesting practices, minimization of evaporation losses, and development of ground water potential including recharging and transfer of surface water from surplus areas where feasible and appropriate.
Terms referred to above are explained below:
Flood cushioning:
The reservoirs created behind dams may be emptied to some extent, depending on the forecast of impending flood, so that as and when the flood arrives, some of the water gets stored in the reservoir, thus reducing the severity of the flood.
Embankments and dykes:
Embankments & dykes also known as levees are earthen banks constructed parallel to the course of river to confine it to a fixed course and limited cross-sectional width. The heights of levees will be higher than the design flood level with sufficient free board. The confinement of the river to a fixed path frees large tracts of land from inundation and consequent damage.
Flood forecast and warning:
Forecasting of floods in advance enables a warning to be given to the people likely to be affected and further enables civildefence measures to be organized. It thus forms a very important and relatively inexpensive nonstructural flood-control measure. However, it must be realized that a flood warning is meaningful if it is given sufficiently in advance. Also, erroneous warnings will cause the populace to loose faith in the system. Thus the dual requirements of reliability and advance notice are the essential ingredients of a flood-forecasting system.
Flood plain zoning:
One of the best ways to prevent trouble is to avoid it and one of the best ways to avoid flood damage is to stay out of the flood plain of streams. One of the forms of the zoning is to control the type, construction and use of buildings within their limits by zoning ordinances. Similar ordinances might prescribe areas within which structures which would suffer from floods may not be built. An indirect form of zoning is the creation of parks along streams where frequent flooding makes other uses impracticable.
Flood proofing:
In instances where only isolated units of high value are threatened by flooding, they may sometimes by individually flood proofed. An industrial plant comprising buildings, storage yards, roads, etc., may be protected by a ring levee or flood wall. Individual buildings sufficiently strong to resist the dynamic forces of the flood water are sometimes protected by building the lower stories (below the expected high-water mark) without windows and providing some means of watertight closure for the doors. Thus, even though the building may be surrounded by water, the property within it is protected from damage and many normal functions may be carried on.
Soil conservation measures:
Soil conservation measures in the catchment when properly planned and effected lead to an all-round improvement in the catchment characteristics affecting abstractions. Increased infiltration, greater evapotranspiration and reduced soil erosion are some of its easily identifiable results. It is believed that while small and medium floods are reduced by soil conservation measures, the magnitude of extreme floods are unlikely to be affected by these measures.
Water harvesting practices:
Technically speaking, water harvesting means capturing the rain where it falls, or capturing the run-off in one’s own village or town. Experts suggest various ways of harvesting water:
• Capturing run-off from rooftops;
• Capturing run-off from local catchments;
• Capturing seasonal flood water from local streams; and
• Conserving water through watershed management.
Apart from increasing the availability of water, local water harvesting systems developed by local communities and households can reduce the pressure on the state to provide all the financial resources needed for water supply. Also, involving people will give them a sense of ownership and reduce the burden on government funds.
Minimization of evaporation losses:
The rate of evaporation is dependent on the vapour pressures at the water surface and air above, air and water temperatures, wind speed, atmospheric pressure, quality of water, and size of the water body. Evaporation losses can be minimized by constructing deep reservoirs, growing tall trees on the windward side of the reservoir, plantation in the area adjoining the reservoir, removing weeds and water plants from the reservoir periphery and surface, releasing warm water and spraying chemicals or fatty acids over the water surface.
Development of groundwater potential:
A precise quantitative inventory regarding the ground-water reserves is not available. Organization such as the Geographical Survey of India, the Central Ground-Water Board and the State Tube-Wells and the Ground-Water Boards are engaged in this task. It has been estimated by the Central Ground-Water Board that the total ground water reserves are on the order of 55,000,000 million cubic meters out of which 425,740 million cubic meters have been assessed as the annual recharge from rain and canal seepage. The Task Force on Ground-Water Reserves of the Planning Commission has also endorsed these estimates. All recharge to the ground-water is not available for withdrawal, since part of it is lost as sub-surface flow. After accounting from these losses, the gross available ground-water recharge is about 269,960 million cubic meters per annum. A part of this recharge (2,460 million cubic meters) is in the saline regions of the country and is unsuitable for use in agriculture owing to its poor quality. The net recharge available for ground-water development in India, therefore, is of the magnitude of about 267,500 million cubic meters per annum. The Working Group of the Planning Commission Task Force Ground-Water Reserves estimated that the usable ground-water potential would be only 75 to 80 per cent of the net groundwater recharge available and recommended a figure of 203,600 million cubic meters per annum as the long-term potential for ground-water development in India.
Recharging:
Artificial recharge provides ground water users an opportunity to increase the amount of water available during periods of high demand--typically summer months. Past interest in artificial recharge has focused on aquifers that have declined because of heavy use and from which existing users have been unable to obtain sufficient water to satisfy their needs.
Transfer of surface water:
Basically, it's the movement of surface water from one river basin into another. The actual transfer is the amount of water not returned to its source basin. The most typical situation occurs when a water system has an intake and wastewater discharge in different basins. But other situations also cause transfers. One is where a system's service area covers more than one basin. Any water used up or consumed in a portion of the service area outside of the source basin would be considered part of a transfer (e.g. watering your yard). Transfers can also occur between interconnected systems, where a system in one basin purchases water from a system in another basin.