Challenges in GWI: Saline Intrusion

Challenges in GWI: Saline Intrusion

In this blog I want to focus on one of the most challenging areas of management for groundwater irrigation; coastal aquifer resource management. As we have previously discussed, groundwater is an incredibly important development resource in Africa, but this development has to be sustainable.

In coastal East Africa, specifically coastal areas of Kenya, Tanzania and Comoros, there is a heavy reliance on large aquifers. An aquifer is a large underground layer of water-bearing permeable rock, unconsolidated materials or rock fractures from which groundwater can be extracted.  The resource is theoretically infinite, however we will go on to discuss the fact that the availability of this resource is determined by societal factors, as well as by physical and environmental factors (Comte et al, 2016). The latter of which dictating the ultimate renewability of the resource.

As previously discussed, aquifers hold the potential to provide a reliable and long-term solution to agricultural irrigation. Aquifers provide natural water purification, meaning that crops can be grown from the water pumped straight out of the ground. Aquifers also provide flood management as when it rains heavily, the porous rock absorbs water. Due to unprecedented demographic growth in East Africa in the past few decades, water demand has increased. This has caused a number of the coastal aquifers to become stressed. The demographic usage pressure alongside environmental change minimising rainfall events has led to saline intrusion (Oiro, 2019).

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Saline or saltwater intrusion is the movement of saltwater into freshwater aquifers. Saline intrusion occurs when coastal aquifers are overused, and the negative pressure difference draws in coastal water (Alfarrah, 2018).  This process contaminates the water in the aquifer.

Analysis of long-term records shows that unsustainable groundwater abstraction is the main driver of aquifer and borehole salinization. Whilst saline intrusion can occur naturally in some areas, the process is dramatically enhanced where there are failures of governance.

Arguably the greatest problem with overusing aquifers is that the saline intrusion contaminates the water, leading to many long-term knock-on effects. Saline intrusion obviously means that the water is no longer drinkable and has to be filtered straight from the pump. However, groundwater is rarely filtered for irrigation and long-term use of saline water to irrigate crops has led to soil quality deterioration (Comte et al, 2016). When soil is irrigated with saline water, natural ions and minerals are lost, and the effective fertility of the soil is dramatically reduced (Kourgialas, 2016). The effect of this is long-term damage to agricultural land.

A strategic aquifer in the coastal region of Kenya has been surveyed and mapped for a number of decades. Analysis of data has found that the saltwater front has risen by 80 m and “advanced toward the well-field by up to 2 km” in the last 30 years (Oiro, 2019). Significant new hydrological insight is needed in order to substantially cut down on saline intrusion.

With results confirming the levels of saline intrusion put alongside the critical need to take advantage of groundwater for irrigation and overall development, sustainable hydrological practises and governance are required. Groundwater in East Africa lacks monitoring infrastructure and the recent urban and agricultural success from utilising groundwater has meant that people are reluctant to change their ways. Sustainable practices don’t have to just be limiting the use of the resource, they can also include reliance on alternative methods of groundwater extraction such as traditional shallow wells (Fluence, 2017). However, encouraging the re-implementation of large numbers of shallow wells is a governance issue in itself.

I hope this blog has provided sufficient explanation into one of the greatest problems with groundwater irrigation in coastal regions, as well as provided insight into the complex governance that defines almost every non-physical issue.