2021 Mar 22
Water. It is inextricably interwoven with human life, civilisation and advancement. In Sri Lanka, water is a cornerstone of agriculture, industry and hence, the economy. A principal facet of water is groundwater. It is an invaluable resource our little island has been abundantly blessed with; or at least, our island used to be blessed with.
With the demand for water for domestic use increasing about 10% every year, and the industrial water demand continuing to double every 5 to 10 years, our groundwater is becoming increasingly vulnerable and the need for sustainable use of groundwater is becoming imperative. We need only to look at our neighbouring countries like India and Bangladesh to see the inevitable consequences of the indiscriminate use of this resource.
What is groundwater?
Groundwater is simply the water found below the earth’s surface. It stays and travels slowly between the spaces in soil, sand and rock known as aquifers, and connects to surface water sources like rivers, lakes and wetlands. But, not all groundwater is the same. The quantity and the quality of groundwater found in diverse aquifers vary and these repositories can be thousands, and sometimes even millions, of years old.
Groundwater becomes naturally recharged when water from rainfall, flooding and waterways finds its way to these underground systems. Over time, as weather patterns and the climate continues to change, so do the groundwater levels. Groundwater levels are also affected by artificial groundwater extraction using dug wells and boreholes. Human interference actually has the potential to influence the natural flow of groundwater.
Aquifers in Sri Lanka
Did you know that there are 6 main aquifer types in Sri Lanka? They are the shallow karstic aquifer, coastal sand aquifers, deep confined aquifers, lateritic (cabook) aquifer, alluvial aquifers and shallow regolith aquifer. In addition to these, there are also a vast number of small groundwater pockets spread throughout the island.
In the arid Jaffna peninsula, the shallow karstic aquifer plays an integral role in preserving agriculture. It is also utilised for domestic purposes. It is in fact among the most extensively used groundwater resources in the country. Coastal sand aquifers too are a limited yet crucial resource that makes possible agriculture and tourism in the coastal regions around the island. Coastal sand aquifers are recharged primarily during the North-East monsoon.
Deep confined aquifers also occur in the coastal plains and are found in the North-Western part of the island. 7 distinct aquifer basins have been recognised in this region. In the South-Western part of the island, the lateritic aquifer is located. These porous laterite formations have significant water holding capacity depending on the depth of the formation.
Found in coastal and inland flood plains and interior river valleys are the alluvial aquifers. They can be easily recharged and are directly connected to surface water sources. A substantial part of the shallow regolith aquifer of the hard rock region spans across the North Western and North Central provinces. Despite releasing a low volume of groundwater, this aquifer has served immensely in meeting the domestic water needs of our people since the ancient kingdoms millennia ago.
Importance of groundwater
There is a close interrelationship between groundwater and nature. While strengthening the lakes, rivers and wetlands and helping maintain water levels, groundwater gives nourishment to our plant life. Especially during months when there is little rainfall, it is groundwater that nurtures our surface water sources, flora and fauna and our ecosystems.
There is also a close interrelationship between groundwater and our people. A majority of our rural population still depends on groundwater from dug wells or boreholes for clean drinking water and other day-to-day household purposes. Even a considerable percentage of piped water is sourced from groundwater.
Moreover, groundwater is pivotal to our agriculture and has prevailed to be considered as an economic and easy to access source for irrigation. It has allowed farmers to circumvent the impact of droughts and dry season water shortages that limited their farming capacity. These factors have encouraged farmers to invest more in agriculture, improved their livelihoods and enabled them to earn higher incomes by selling greater quantities and higher-value produce. Consequently, groundwater has contributed to alleviate poverty in our rural communities and elevate their quality of life.
Not only that, in recent decades, groundwater has increasingly been used for commercial and industrial purposes. Several factors including low cost and ability to manage autonomously have underpinned this trend and allowed industries to flourish.
Factors affecting groundwater
On the other side of the coin, there are natural as well as human-driven factors influencing the quantity and the quality of our groundwater.
Groundwater recharge is shown to be greatly influenced by variables in climate conditions. Among these, rainfall is the most important. Groundwater recharge is impacted by the frequency, intensity and seasonality of rainfall. Temperature is the second parameter relevant to recharge. It has been found that temperature increases beyond 3 degrees of Celsius can increase evaporation leading to reduced recharge. So, what does this mean for Sri Lanka? Climate predictions for Sri Lanka for the year 2050 indicate reduced rainfall along with increased temperature, the outcome of which would be the natural decrease of groundwater.
Reduced rainfall and higher evaporation would also mean that our agriculture would require more irrigation. Reduced rainfall and longer dry spells have already resulted in a sharp surge in the number of wells dug for agricultural purposes, known as agro-wells, especially in the dry zone of our country. From there, being less than 1,000 agro-wells in the mid-1980s, the number has presently increased to over an estimated 100,000 wells. The stress of excessive extraction on groundwater can be observed in the shallow regolith aquifer in the North Central province.
Withdrawal of groundwater has continued unmonitored, and it has caused not only depletion of groundwater, but also contamination, in some aquifers. The increasing salinity of groundwater in the shallow karstic aquifer and coastal sand aquifers provides evidence of the adverse effects of over-extraction of groundwater resources. Adding to this is the contamination of groundwater caused by the improper use of fertiliser and pesticides in cultivation. Clear examples of this can be found in areas like Kalpitiya, Puttalam and Vanathavilluwa.
Making matters worse, the number of deep groundwater wells utilised by various industries across the island too has increased by literally tens of thousands! Overexploitation of groundwater to meet the rising demands of rapidly expanding industrial estates, tourism industry and urban housing projects can be witnessed in the lateritic (cabook) aquifer. In parallel, impacting the quality of groundwater is the discharge of untreated industrial waste.
Examples from neighbouring countries
Our neighbouring countries were once at the same stage of groundwater development as our island. With rural poverty diminishing and the economy thriving, the future seemed promising. The focus remained solely on the immediate advantages of groundwater usage, and this led to unmonitored exploitation of this finite resource.
In the long term, the groundwater sources depleted or became contaminated, and the inescapable eventuality was the collapse of groundwater based agriculture; limited access to clean, safe water; and depopulation of villages that depended on groundwater.
An example of this could be found on the coast of Gujarat, in West India, which came to be known as ‘the Green Creeper’. During the 1960s and 1970s, groundwater usage enabled farmers along the coastal strip to prosper. However, this was ephemeral as excessive withdrawal of groundwater caused saltwater intrusion and salinisation of freshwater, destroying the economy of the region.
In Yemen, over-extraction of groundwater caused the country’s aquifer levels to reduce by up to 40 metres, preventing many farmers from being able to access the resource. Furthermore, contamination of groundwater used as drinking water by arsenic in Bangladesh now threatens the health and lives of millions.
Management of groundwater
A key aspect of groundwater management is the collection, compilation and synthesis of comprehensive information relating to Sri Lanka’s groundwater resources. A system to assess and monitor the conditions of these resources in real-time would be indispensable in the management process.
This information will enable the relevant authorities and stakeholders to recognise where groundwater extraction needs to be closely surveilled and controlled and where strategic utilisation can be encouraged. This can then be integrated into the formulation of a scientific, evidence-based, multi-disciplinary approach for the conservation and development of this resource.
Employment of strategies including the introduction of robust crop varieties that can be cultivated with limited irrigation and installation of rainwater harvesting and artificial recharge systems can serve as important components promoting the quantity and quality enhancement of our aquifers. Alongside, educating and increasing the awareness of the communities who are reliant on groundwater of the capacities as well as the vulnerabilities of the aquifers will also be paramount in the preservation of groundwater for the future.