The groundwater system underneath Pakistan’s flowing rivers in the Indus plains has at least 400 million acre feet (MAF) of pristine water. This storage is so large that it is equivalent to more than three years of the mean annual flow of the Indus (or 1,000 days of storage, after excluding polluted areas). This should now be seriously considered in the mainstream planning of Pakistan’s water resources.
More than a thousand years ago, Alberuni wrote, “India has once been a sea which by degrees has been filled up by the alluvium of the streams.” This view was later endorsed in the late 19th century by Austrian geologist Eduard Suess, who named the sea ‘Tethys Ocean’. Mike Searle, in his 2013 book Colliding Continents explains that the Himalayas resulted from collision of the Indian plate with the Eurasian plate 50 million years ago.
The Indus river and its Sutlej tributary both existed prior to this collision and drained into the Tethys Ocean. The collision gradually closed the sea and the remnants of the Tethys were filled by the material of eroding mountains deposited by the flowing rivers.
The Indus rivers have carried huge silt loads for millions of years, depositing them in the plains all the way to the delta. In their 1988 book, Irrigated Agriculture of Pakistan, Nazir Ahmad and Ghulam Rasul Chaudhry explained that high sediment loads in the Indus river system have created nearly 200,000 square kilometres of flatlands. These flatlands, to a considerable depth, are made up of unconsolidated and granular formations, capable of holding large volumes of water. “This reservoir of water is so vast, it ranks among the natural wonders of the world,” the authors write as they describe the groundwater resources of the Indus basin.
Aloys Arthur Michel, in his 1967 book, The Indus Rivers, describes these alluvial deposits as unconsolidated material, deeper than one mile, forming a large homogeneous groundwater reservoir with a capacity “at least ten times the annual runoff of the Indus rivers”.
This begs the question, that if we knew about this groundwater storage potential for decades, why has it never been discussed in the mainstream planning for sustainable exploitation to benefit the inhabitants of the Indus basin?
The reasons could have been many. The military dictatorship in place at the time of the signing of the Indus Water Treaty set a future discourse on the harnessing of surface waters only; a drift into debt economy and the lure of easy dollars in mega infrastructure projects for water; interest groups pushing large dams in the 1950s and 60s – an era when the whole world was going on a binge of building large dams; a lack of capacity at home to scrutinise proposals being advised by foreign ‘experts’ with vested interests; the obvious advantages of the visibility of big structures which can be loudly publicised in political arenas and so on. The result was that Pakistan chose the path of building mega-dams, river diversions and gravity-based flood irrigation systems. In doing so, we severely deteriorated our aquifers through waterlogging, salinity, unmanaged abstractions and indiscriminate pollution.
But that was the past. Is it possible to pursue a different path now?
First, given the fact that this vast aquifer sits on top of a filled-up sea, its deeper formations are naturally saline. In the northern parts of the alluvial plains, the aquifer may hold sweet water up to a depth of a thousand feet or so, but as one moves south, the depth of sweet water gradually reduces.
In the Indus delta, sweet groundwater may occur only within the top hundred feet or less. Similarly, as we horizontally move away from main river beds, the water quality becomes brackish. The existence of deep high-capacity tube wells in previous Salinity Control and Reclamation (SCARP) projects and many deep tube wells in the private sector today, have contaminated the shallower fresh water with saline upwelling. In many areas away from the rivers, shallow layers of groundwater have been exploited by irrigation tube wells and what remains now is brackish to saline groundwater.
Such uninformed groundwater pumping, besides deteriorating the aquifers, has also exacerbated secondary salinisation and loss of fertile soils.
The map in Figure 1 shows the extent of freshwater aquifers in the Indus plains. It excludes the areas where water quality is saline, brackish or of marginal quality. Out of 200,000 square kilometres of the Indus plains, the current fresh groundwater occurrence in Pakistan is approximately spread over 88,000 square kilometres.
Second, the aquifer system is unconfined. In other words there is no impervious or confining layer above the groundwater to protect it from surface pollution or contamination. In the complete absence of groundwater management in mainstream planning, there is no concept of well-head protection and management of recharge zones.
Consequently, freshwater shallow aquifers underneath the irrigated areas have mostly been polluted with agro-chemicals (fertilisers, pesticides and herbicides), and urban aquifers have been contaminated with sewage and industrial wastes.
Third, and very alarming, is arsenic contamination in the Indus plains aquifers. A series of collaborative projects by Swiss, Chinese and Pakistani organisations have undertaken comprehensive studies on the occurrence of arsenic in the groundwater of the Indus plains. The studies have revealed occurrence of arsenic above 10 microgrammes per litre (the WHO safe drinking water limit) in many areas and found a significant correlation of this occurrence in areas with extensive agriculture and industrial pollution.
The picture painted in this map is reinforced when one sees the amount of pesticide, herbicide and fertiliser being dumped on top of unconfined aquifers in the irrigated areas. Phosphate-based fertilisers and arsenical pesticides represent the largest single manmade input of arsenic into the environment, and are largely responsible for the poisoning of water resources. According to the Pakistan Bureau of Statistics (PBS), 1.66 million tons of pesticide and 66 million tons of fertiliser have been dumped in irrigated areas since 1990s and the trends of usage in both are on the rise, as seen in the plots based on data from PBS.
Moreover, there is a natural occurrence of arsenic in deep formations, mostly saline aquifers. Again, unsustainable projects involving high capacity deep tube wells continue to increase the concentration of arsenic in freshwater aquifers from deeper formations. The good news, however, is that natural fresh waters in streams and aquifers are free of arsenic.
Comparing the maps in Figure 1 and Figure 2, unfortunately, most of the fresh groundwater aquifers of Indus plains are now contaminated with arsenic and other pollutants.
Practices and investments in water sector over the past six decades or so have exacerbated the deterioration of quality in the aquifers. Pakistan has already compromised a significant chunk of its extremely valuable groundwater resource.
A look at quantity
To discuss the quantity of water, we shall now only focus on areas where aquifers are still free from salinity, pollution and arsenic.
According to a 1964 report published by US Department of Interior on water logging and salinity in Pakistan, about two million acres of the Indus plains are “occupied by river channels and are normally covered by freshwater”.
In this study, we carried out a detailed delineation of riverine corridor exclusive of any canal irrigated areas. This area includes river channels which exhibit perennial flow in braided streams all-round the year, as well as the river bed which gets fully flooded in the monsoon. This area is 21,000 square kilometres or 5.2 million acres, and is government-owned land. These riverine corridors sit atop thick layers of sand and silt filled with uncontaminated fresh waters which are being continuously replenished by freshwater of the flowing rivers – free of arsenic. For the sake of this study, we refer to this delineation as the ‘riverine aquifers’.
The thickness of the riverine aquifers could range from over a thousand feet in the northern plains down to less than 100 feet in parts of the Indus delta. We may safely assume the mean specific yields (or drainable porosity of the formation) for these formations at around 25%. If we only take the mean manageable depth of this aquifer at 100 metres, we already have an existing storage of pristine water exceeding 400 MAF.
Generally, in the northern plains the river corridor is narrower but the aquifer is much deeper, while it is shallower in the south but much wider. The quantity of the resource, therefore, remains quite uniformly distributed all across the landscape. And the layout of this aquifer is such that most major population centres of Pakistan are located within a 100 kilometres from it.
The road ahead
If we plan to supply water to the communities at the rate of 40 gallons per person per day (current standard being followed by WASA – the Water and Sanitation Authority in Pakistan) for a population of 220 million, the total requirement of water supply does not exceed 12 MAF, while the resource can be continuously replenished by nature through flowing rivers.
What the government needs is mechanisms – financial, organisational and structural — capable of delivering water from this resource to the people, and simultaneously ensuring the sustainability of the resource. A well thought-of, integrated, coordinated and robust management plan enveloped in a phase-wise implementation blueprint needs to be chalked out.