Dr Ramani Kanta Thakuria
(The author is the former Chief Scientist (Water Management); Assam Agricultural University, Jorhat. Currently, he is working as Principal Scientist at Khanapara campus, AAU, Guwahati-22. thakuriark@gmail.com)
Water as a whole covers about 70 per cent of the earth's surface, the fresh portion is very small. It is only 3 per cent of total water. Groundwater, the largest source of unfrozen fresh water, serves humankind worldwide in multiple ways. As a groundwater user, India ranks first both in use and depletion amongst the countries in the world. This could be understood from the spectacular rise of the number of bore wells everywhere. The story of Cape Town in South Africa becoming a complete dry situation termed Day Zero for the first time in the world is now going to happen in many other cities, including 21 big cities in India. Studies done in 500 big cities in this line have revealed that one in every four cities is suffering from the problem of acute groundwater depletion. It has been estimated that by 2030, under the present scenario of economic growth, the water demand will be more than the supply by 40 per cent.
In Assam, however, the pattern of groundwater depletion is not similar to that of other parts of India which could be understood by its rate of groundwater development value which is only 14 per cent in Assam against the national average value of 62 per cent. In general, the rate of development of groundwater value signifies the status actually how much replenishable groundwater is being exploited for use e.g. the 14 per cent value in Assam signifies that out of total replenishable groundwater only 14 per cent is used giving scope for further utilization of 86 per cent in future. In Assam, however, this picture is not representative of Guwahati and other cities and towns where the population is significantly high, economic development is fast and monitoring of groundwater utilization is lacking. Guwahati is densely populated with around 15 lakh population, has undergone a vast economic development, the immediate effect of which has been noticed in pressure on its groundwater and environment. It is estimated that Guwahati is experiencing a severe stage of groundwater depletion with much more withdrawal rates than that of the replenishment recording about 61 per cent from 2007 to 2017. Changes in the intensity and patterns of rainfall along with the rising trend of temperature have also catalysed the process of groundwater depletion. The city is primarily dependent on lifting water from the aquifer. Under the present situation, it is expected that the availability of water for drinking and industry will be insufficient shortly. Groundwater depletion at the present pace will also influence its surrounding environment by disturbing the soil-atmospheric continuum subsequently contributing to changing the inherent properties of soil. The soil will not be able to maintain the normal soil moisture at the upper surface because of restricted upward movement of soil water from a deeper groundwater depth affecting the grossly microbial population in the soil. If this trend continues, the soil practically will die leading to reduced natural decomposition of city garbage along with poor growth of vegetation and fruit-bearing ability of crops.
Under the above circumstances, an important aspect concerning groundwater is what extent and how best we can make the groundwater available for a longer period. The groundwater as such we can't see nor can we touch. It only becomes visible after its abstraction either as water or as a product embedded with virtual water. The entire product we eat, use, buy, sell, make, wear daily mostly is from groundwater. It is estimated that cumulatively the water we use directly or indirectly per capita is not lesser than 3500 litres a day. While utilizing this amount of water either as water directly or as a product indirectly; important is the maintenance of balance between supply and demand sides. The present situation, however, does not look to be balanced in Guwahati favouring more the demand side than the supply; for which people's deep concern and government efforts are important. There might have many reasons for the higher demand for water in the city, but every effort to reduce the gap should be adopted. The geographical advantage of the city is situated just at the embankment of the mighty river Brahmaputra will help in this regard. The per capita availability of rainfall though is high because of high rainfall (about 1700mm), the situation in per capita rainfall-aided groundwater availability is reverse. This strongly urges the taking up of a holistic plan covering every possible aspect, including shifting of use of water from groundwater to surface water source, conservation of wetland in and around the city, creation of artificial percolation tank, capturing the surplus monsoon runoff etc. Generally, groundwater use is dependent on the demand side, not on the supply side. Rainwater harvesting including rooftop water with proper design and structure coupled with artificial recharging of groundwater is important. Mere harvesting of rainwater without any provision of percolating the harvested rainwater into the soil can't be so effective under the present situation when the natural entry of rainwater is getting affected due to covering of earth's surface by concrete structures everywhere and deforestation on hills and hillocks. As observed for augmenting groundwater resources, rainwater harvesting along with artificial recharging of harvested water has been proved to be a popular technique globally. Artificial recharge technique is, however, highly site-specific for which in Guwahati, flood problems during monsoon should receive priority so that poor quality rainwater does not enter into the soil.
Groundwater is a critical resource that requires judicious utilization ensuring long-term sustainability. Implementation of regulatory measures in this aspect whenever required is important. Analysis of the availability of water before taking up any water demanding project should be the first and foremost consideration. Control or complete withdrawal of groundwater during the non-monsoon season with a suitable alternative in over-exploited areas needs to be promoted. Works on precise identification and delineation of groundwater potential and recharge zone are the priority in the city. Concerning the availability of groundwater, it is important to aware people of the location-wise availability of groundwater through any form of mass media stating the location's groundwater status as over-exploited, critical, semi-critical etc. Time to time forecasting in this regard is important. Gearing up for the groundwater emergency has become important now for which the government needs to respond properly. Until now, the system of groundwater exploration for domestic use is predominantly in the hands of households because of which people can explore groundwater as per their choice. To avoid this with the objective of the long-term sustainability of groundwater, dependencies on it should be reduced. In this regard, provision of setting up of drinking water plant on a surface water basis with government or private sector participation and supplying water from such plants to the households at an official rate with quality protocol may be a good contingency measure. Presently such supply is groundwater-dependent without any official control with regards to rate and quality specification. In the city, a huge quantum of water is used in the construction of big structures like real estate, bridges etc; use of water for such purposes from a surface water source may be considered.