Pakistan has one of the world’s largest aquifers (fourth after China, India and the USA). This is the most reliable resource as it provides more than 60% irrigation water, over 90% drinking water and almost 100% water used in the industry. The number of tubewells has increased from 0.2 million to over 1.2 million over the last two and a half decades with countless number of small to large size tubewells installed at the household and industrial level. Groundwater has played a major role in increasing the overall cropping intensity in Pakistan from about 63% in 1947 to over 170% in 2021.
In the absence of any regulatory framework for groundwater use, indiscriminate drilling and operation of tubewells, water tables are depleting in more than half of the canal commands and in almost all urban centres. This phenomenon is more common in the central and lower parts of the doabs (the area between two rivers) and towards the tail ends of all the canal commands. The depleting aquifers have caused a manifold increase in tubewell installation and operational costs.
In a recent article1, we have shown that climate change and its variability is resulting in extreme events of floods and droughts. One major outcome of climate variability is urban flooding as recently witnessed in Karachi, Lahore and Islamabad. It is obvious that groundwater provides resilience against extreme climate events for which it is essential that the resources be managed sustainably by maintaining balance between abstraction and recharge. However, under the current scenario, it is hard to reduce the abstraction due to competing demands for various sectors, which makes increasing recharge as the only option to bring about balance between abstraction and recharge.
The increased climate variability is resulting in wet years/seasons becoming wetter and dry years/seasons becoming drier. Most parts of the country receive heavy rainfalls in the monsoon months of July to September with scanty rains during the rest of the year. Due to changes in land use patterns, catchment modification and urbanization, the flow velocities tend to increase with consequent decrease in lag time. This immediately turns runoff into flash floods, damaging infrastructure and causing loss to human life. Any activity that reduces the flow velocity and increases lag time can help in increasing recharge. Thus, it is important to develop vegetative cover by planting trees and grass in the catchments and in urban areas.
PCRWR’s Work on Rainwater Harvesting and Groundwater Recharge
Pakistan Council of Research in Water Resources (PCRWR) has initiated a number of rainwater harvesting and groundwater projects in the country. One such project is the construction of over 100 rainwater harvesting ponds in Cholistan desert. Following it, the Cholistan Development Authority also constructed an almost similar number of ponds in the desert. These ponds are a buffer against drought and provide resilience against climate change and variability. Similar kind of ponds have been constructed in D.I. Khan, Thar and Chagi Kharan deserts.
The Council has introduced simple, smart and cost effective recharging techniques in Balochistan such as leaky dams and inverted wells, etc. Unlike a delay action dam, a leaky dam slowly releases rainwater while trapping the sediment on its upstream side. The slow flowing water has more surface area to recharge the aquifer2.
The inverted or recharge wells collect rainwater and inject it into the groundwater through a well-developed filtration system that removes the debris and sediments from runoff to allow only silt free water into the bore to avoid the choking of wells (Figure 1). The pre-filtration is provided by making a pit and filling it with different natural filtering material in layers such as gravels, stone crush and sand. This filter acts both ways i.e., removes sediments from runoff as well as enhances the recharge rate from the surface. More than 80% of the water diverted towards the well recharges the aquifer. The Council has installed these wells at a number of sites throughout the country. The techniques developed by PCRWR are now being adopted by various development agencies such as Capital Development Authority (CDA), Islamabad and Rawalpindi Chamber of Commerce and Industry. However, there is a need to upscale these technologies on a larger scale to cope up with the issues of climate change and variability. Groundwater recharge should be an integral component of any water development scheme. Rainwater collected from rooftops, public parks and playgrounds should be diverted to aquifers through recharge wells. The recharged water would help sustain the existing tubewells which otherwise have to deepen or re-drilled after every few years.
All important policy documents emphasize on protecting and recharging the depleting groundwater aquifers. The national water, food and climate change policies provide the guiding principles for the management and better governance of vital resources. These policies place great emphasis on artificial groundwater recharge.
The National Food Security Policy (2018) makes it mandatory to conserve groundwater resource along with other resources to ensure food security for the growing population. It advocates enforcement of policies and legislation to protect groundwater through management and technical measures like artificial recharge for the threatened aquifers through provincial governments.
The National Water Policy (2018) stresses on: (i) regulating groundwater withdrawals for curbing over-abstraction and promoting aquifer recharge; building check dams and delay action dams for recharging aquifers and reducing the flow velocities and erosion; (ii) recharging aquifers during floods and surplus water flow periods for later use; (iii) promoting groundwater recharge including artificial techniques wherever technically and economically feasible; and (iv) prioritizing investment in groundwater recharge schemes.
The National Drinking Water Policy (2009) envisages preserving and protecting surface and groundwater resources, which offer sustainable sources of supply for both urban and rural communities. Moreover, it encourages and supports rainwater harvesting at household and local levels to augment the municipal water supplies as well as to recharge aquifers to promote sustainability in water resource use.
The National Climate Change Policy (2012) emphasizes on protecting groundwater through management and technical measures such as regulatory frameworks, water licensing, delay action dams, artificial recharge, especially for the threatened aquifers, and adoption of integrated water resource management concepts. It also encourages development of technological innovations for improved water efficiency for crops, including artificial groundwater recharge and development of technologically efficient equipment.
Actions by the Government and What’s Next
For climate change adaptation, the federal government has started Ten Billion Tree Tsunami Project and Clean and Green Pakistan initiative. Millions of trees have been planted to increase the national forest cover. Similarly, Recharge Pakistan Program would be a remarkable initiative that would not only help protect and augment the natural resources, but would also help mitigate the impact of climate change and variability. These projects are now getting attention and acknowledgement of the international community as well.
The most crucial question now is how and where to recharge the aquifers. PCRWR has mapped the entire Indus Plain Aquifer covering about 24 Mha of land. It has investigated the water quality and hydrogeology of the area that can be used to identify the potential recharging zones.
Co-Climate Benefits of Artificial Recharge
Although the primary benefit of artificial recharge is to enhance or improve groundwater resources, there are multiple climate co-benefits as discussed below.
Reducing Urban Flooding: Due to availability of better facilities for education, health, employment and transportation, there is a trend of people migrating from the rural areas to urban areas. The productive agriculture land is being converted into residential societies, commercial complexes and concrete infrastructure, drastically reducing the capability of natural recharge thus resulting into flash floods. The urban flooding has become a major issue in large cities of Pakistan such as Lahore, Karachi, Islamabad and Rawalpindi. The runoff is ultimately drained through the sewerage system. The surface drainage system is inadequate to safely dispose of floodwater thereby further aggravating the situation. The rainwater harvesting and inverted wells will not only recharge the groundwater but also control urban flooding by conserving the precious resource which otherwise is wasted.
Reducing Pressure on the Existing Stormwater Drainage: As discussed before, with increased rainfall and its intensity, the existing infrastructure has become insufficient to carry the stormwater. With rainwater harvesting, there is less pressure on the streams and storm drains. Therefore, the generated runoff can be safely disposed of with relatively less operational and maintenance costs.
Improving Groundwater Quality: Groundwater in the Indus Basin is mainly saline due to its marine geological formation. Due to the decades-long water development and irrigation activities, a layer of freshwater has developed over saline water due to recharge. The freshwater lens is thick near the river banks and upstream of the canal commands and becomes thinner toward the center and tail end of doabs (the area between two rivers) or a canal command. Under such conditions, a balance between groundwater abstraction and recharge becomes crucial. Overpumping may lead to saline water up-coning resulting in the deterioration of groundwater quality3.
A concern is shown by development agencies that recharging groundwater artificially may result in groundwater contamination. The Electrical Conductivity (EC) of the recharging water is generally less than 0.1 dS/m. Many studies, including those conducted by PCRWR, indicate that groundwater quality after artificial recharge is improved manifold.
As water is collected from rooftops, pavements, green belts etc., it is free from most contaminants except some sediments. The harvested water is passed through the primary filter (gravel, crush stones, and sand) before discharging into the subsurface. Here it again passes through a secondary natural filter before joining the aquifer. Otherwise, the rainwater joins the drainage system and is completely polluted. This polluted water during ponding and flowing seeps into the aquifer thereby contaminating the aquifer. As far as bacterial contamination is concerned, bacteria require retention time to incubate. However, during artificial recharge, the bacteria have less time to incubate at the surface. Moreover, it passes through the primary (at the surface) and secondary (below the surface from well screen to the water table) treatments before joining the groundwater. Hence, chances of groundwater contamination with artificial recharge are less as compared to the natural recharge occurring through natural streams and sewage drains.
Ecosystem Improvement: Ecosystems play a very important role in adaptation to climate change and local environment. Artificial recharge through check structure would create small lakes within local community areas and the general environment would become cleaner. This nature-based solution can also be helpful in the betterment of ecosystem services.
Sedimentation Control: In the absence of rainwater harvesting and artificial recharge, the runoff is converted into flash floods that carry huge sediments. These sediments change the stream morphology by narrowing the channel cross sections. This reduces the water carrying capacity of the local drainage channels resulting in catastrophic losses as recently seen in Karachi and Islamabad. With groundwater recharge structures like check dams and inverted wells, sediment is trapped before getting into the channels, thus avoiding sedimentation and meandering in the streams/rivers.
Control Land Subsidence: One of the major consequences of groundwater depletion is potential land subsidence. Subsidence is the sinking or gradual downward settling of the ground's surface with little or no horizontal motion. It mainly occurs when a large amount of water has been withdrawn from the aquifers. Many countries in the world are experiencing land sinking. For example, Bangkok is sinking at a rate of 12 cm/year, Jakarta is sinking by an average of 1-15 cm a year and almost half the city is now situated below sea level. Quetta city, where groundwater is depleting at the rate of more than 5 m/year, is sinking at the rate of 10 cm/year which is an alarming situation. Land subsidence results in deterioration in infrastructure, such as cracks in roads and buildings. Groundwater recharge helps maintain equilibrium thereby reducing the chances of land subsidence.
Reduction in Climate Migration: The most important consequence of climate change is re-occurrence of severe and extended droughts. Lack of availability of surface water exerts extra pressure on the groundwater resources. Excessive abstraction of groundwater to cope with the requirement causes depletion of this resource beyond economical depth and resultantly, the population has to migrate to other areas. Balochistan is a classic example of this phenomenon. Below average rainfall due to climate variability, drying up of mother wells of karezes, excessive groundwater abstraction and lack of an alternate source have led to the depletion of groundwater aquifers to the extent where it has become economically impossible for the communities to pump more groundwater. As a result, the communities have no other option except to migrate to big cities or urban areas. Artificial recharging of groundwater through rainwater harvesting cannot only rejuvenate the dried karezes but can also minimize groundwater depletion and ultimately contribute towards controlling migration from these areas.
One of the consequences of climate change is increased occurrence of floods and droughts. Water during floods can be used to recharge the depleting groundwater aquifers with multiple climate co-benefits such as reduction in urban flooding, improvement in groundwater quantity and quality, provision of better ecosystem services and control over land subsidence. All the water and environment related policies emphasize the importance of groundwater recharge. The national, provincial and local governments should therefore, invest on nature-based, efficient, cost effective and environment friendly solutions for sustainable groundwater management in the country.
The writer is Chairman, Pakistan Council of Research in Water Resources, Islamabad.
E-mail: [email protected]
1 Ashraf. M. (2021). Changing Climate and Its Implications for Pakistan, Hilal Magazine, August 2021, p. 65-68.
2 Ashraf M., A. A. Sheikh (2017). Sustainable groundwater management in Balochistan. Pakistan Council of Research in Water Resources (PCRWR), p. 34.
3 Ashraf M, Z.A. Bhatti, Zakaullah (2012). Diagnostic analysis and fine tuning of skimming well design and operational strategies for sustainable groundwater management – Indus basin of Pakistan. International Journal of Irrigation and Drainage, 61: 270-282.
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