This is further aided by the failure to appreciate the environmental services provided by wetlands, lakes, rivers and groundwater. Water resources will be exposed to the increasing withdrawal, storage, flow regulation and consumptive use by evaporation and transpiration, and to the pollution. Flow regulation, fragmentation, sediment imbalance, shift from permanent flow to seasonal flow, salinization, contamination (physical, chemical and biological), acidification and eutrophication are factors putting significant pressure on water resources. (Meybeck, 2003).

Rivers are central to the planet’s ecology. Humanizing, taming rivers and fighting with nature will damage rivers and other parts of the ecosystem. Since aquatic life cannot live long without water, large reductions in stream flows, even for short duration of time, can be damaging. Richness of freshwater biodiversity can be gauged from the fact that, according to some estimates, the total diversity of animal life per unit area of rivers is 65 times greater than the seas.

The main competition for water over the next century will be between the agriculture and environment. Globally, the agriculture uses between 70 to 90 per cent of the developed water supplies and livelihood of 70 per cent of the world’s poor depends on farming.

Despite the benefits, large-scale irrigation systems have led to pollution in rivers and the drying up of wetlands. A recent global study calculated that at least 30 per cent of the world’s river flows need to be used to maintain the condition of freshwater ecosystems worldwide.

In the case of Indus River, historical flows downstream the Kotri Barrage (1962) indicate that on an average only 21 per cent, or 1.7 cubic km of the historical Rabi flow now reaches the delta. Prior to the commissioning of the Kotri Barrage there were no days per season with zero flow, but after the Kotri, Mangla and Tarbela were built, zero flow not only appears during the low flow season but also during the high flow season (Lannerstad, 2002).

According to the IUCN (World Conservation Union), average flows downstream the Kotri Barrage in 1880 was 185 cubic km/year (150 million acre-feet – MAF/year). In 1965, the flow reduced to 99 cubic km/year (80 MAF/year) and, in 1992, it was 12 cubic km/year (10 MAF/year).

The notion that any runoff to the sea is a “wasted flow,” reflects a narrow view of how a river’s system works. Runoff to sea delivers nutrients to sea, with their complex food webs; sustaining economically and culturally important fisheries; protecting wetlands with their capacity to filter out pollutants; providing habitat for a rich diversity of aquatic life; safeguarding fertile deltas; protecting water quality; maintaining salt and sediment balances and offer awesome aesthetic beauty (Postel, 1995).

According to the US dam building department, the dam building era in the US is now over. The department now believes in water conservation, demand management, efficiency improvements and reuse. The department’s funding assistance would now be for those investments where a portion of the saved water can be dedicated to environmental restoration or enhancement.

Large dams and river diversions have proven to be the primary destroyers of aquatic habitat, contributing substantially to the destruction of fisheries, the extinction of species and overall loss of the ecosystem services on which the human economy depends. (Postel, 1995).

There are presently over 45,000 large dams (15 meters high) which obstruct the world’s rivers, completing changing their circulation systems. Large dams change water-land relationship, destroying the existing ecosystem balance which, in many cases, has taken thousands of years to create. The negative impacts of dams have become well-known now. Most countries have stopped building them altogether. Some are now forced to invest their money into fixing the problems created by the existing dams. The problems include soil erosion, species extinction, diseases (river blindness, dengue fever, malaria and schistosomiasis).

According to some scientists, large dams cause changes to the earth’s rotation because of the shift of water weight from the oceans to reservoirs. Due to the number of dams which have been built, the Earth’s daily rotation has apparently sped up by eight-millionths of a second since the 1950s.

Key options: Not only people should learn to share water among themselves they should also share the water with nature. This could be done, if the policies give more priority to the ecology. Once the ecology gets the priority over politics, a series of measures can be taken, which would save water for the nature. These include switching of crops that are less water intensive, using drip system for irrigation (or low-pressure sprinklers), canal lining, use of saline agriculture and drought-resistant crops, water conservation, and water demand management.

One of the most widely supported pathways towards freeing up water for the environment and other uses is to improve water productivity - which means extracting more value from each drop of water used though the increased crop yields, fish production, livelihoods and environmental values.

Improved crop varieties combined with better tillage methods and more precise drip or micro irrigation can reduce water consumption and make a huge difference to crop yields. Drought resistant seeds, water harvesting schemes and small plot technologies such as the manually operated treadle pumps have the potential to boost yields by 100 per cent in many areas of sub-Saharan Africa where most farmers depend on the rain-fed agriculture.

According to the Stockholm International Water Institute and Colombo-based the International Water Management Institute, if water productivity can be improved over the next 25 years, the global need for extra water for irrigation will be zero.

Other possible options for reducing the need for more water include one to influence peoples’ diets. Western diets based on meat from grain fed cattle account for as much as 5,000 litres per capita per day while vegetarian diets deplete less than half as much water.

“With the prevailing land and water management practices, a balanced diet requires 3,287 litres of water per day compared to the 50 used for an average household’s domestic needs. Wastewater of one city upstream becomes the drinking-water source of a downstream town. It is estimated that up to one-tenth of the world’s population eats food produced using wastewater from the towns and cities.

In water scarce areas increasing the use of urban wastewater for irrigation is another alternative, which can be effectively used. In addition, full use should be made of the rain-fed irrigation. In water-scarce areas, the rain-fed irrigation has great potential. Rainwater can be stored behind small embankments and dykes.

Water accounting: In order to meet water scarcity, it is essential to do away with the “business-as-usual” approach. One such approach is water accounting. Most resource engineers are of the view that the water used in irrigation is “wasted” or is “lost,” (after its use). These perceived losses are, in fact, not losses. Water is used downstream. So the productive use of downstream water can increase the water productivity and mitigate the river depletion.

David Molden (1997), at the International Water Management Institute, has developed an accounting model that accounts the water uses, depletion and productivity, in an open-basin perspective.

According to the model, the water consumed, so-called “losses” can be, and are often recovered and reused downstream. Water lost to evaporation or to different sinks, which are not available immediately are real losses. The “open-basin” describes a basin where uncommitted water of usable quality is flowing to the sea.

In an open basin further water resources can be captured and developed without negative effects to neither in-basin nor down-stream users. When all the water is fully committed, the basin is considered “closed.” The model was developed in an irrigation perspective and the most important implication of the paradigm is that the productivity of water should be treated as seriously as the productivity of land.

http://dawn.com/2005/07/18/ebr7.htm