Quel est le rapport entre les rochers et l'eau, l'assainissement et l'hygiène ?
L'Inde utilise plus d'eaux souterraines que la Chine et les États-Unis réunis, et ses réserves s'épuisent rapidement. Arjen Naafs, conseiller technique de WaterAid pour l'Asie du Sud, s'intéresse à l'hydrogéologie qui pourrait aider les communautés à gérer efficacement les réserves.
As a hydrogeologist, I was pleased to join 35 colleagues from WaterAid India recently on a course provided by one of our knowledge partners, ACWADAM, who have a unique focus on groundwater in India. The situation of groundwater in India is a silent and hidden crisis that will affect many, particularly poor people.
- India is by far the largest user of groundwater in the world, consuming more than China and the USA combined (the next two in line).
- Total consumption of groundwater, spread over all 1 billion people adds up to 616 litres per person per day.
- Since the 1970s groundwater abstractions have sky-rocketed because of the green revolution.
- There are over 30 million wells in India – every fourth farmer has one.
- More than 3 million springs ensure the constant flow (base flow) in Indian rivers, but very little is known about them.
- Traditional sources of drinking water for poorer people – such as springs, shallow wells and shallow tubewells – are drying up because of dropping groundwater levels.
The path to depletion
Throughout India alarm bells are going off that groundwater is depleting. These days people prefer to blame this on climate change. But although links may be present, the main causes are limited knowledge leading to poor management and unregulated and excessive extraction.
Agriculture and associated irrigation have been key developments in India, which the Government has provided since the 1970s subsidies for electricity for irrigation pumps. This has had excellent results for crop production but has used up a lot of water – too much water. In order to improve this situation, or at the very least avoid further deterioration, we need to understand where the groundwater is coming from, how much there is, and how we can make the best use of it. That is where hydrologeology comes in.
Now for the science bit
To know more about groundwater, you need to look at the ground – or, in many cases, at the rocks. To be more precise, we need to look at the spaces between the rocks – the porosity. The community we visited – Randullabad, in Pune in Maharashtra, is covered with beautiful layered basalts. These rocks have lots of little holes, and this primary porosity (this is the open space that rocks themselves have) looks quite promising to hold water. However, the holes are not connected to each other and are therefore empty (the holes are actually old air bubbles from when lava cooled down and became rock about 66 million years ago).
However, as the area has moved and shifted in those 66 million years, these rocks have high secondary porosity – this is the space ‘between’ the rocks, such as the cracks and fractures. These fractures are many and well connected, and can hold and transport considerable amounts of water (a layer that holds water is called an aquifer). The ‘speed’ (or, more appropriately, the ‘slowness’) by which water flows through the ground is called the transmissivity – which can vary wildly from a few millimetres per year to a few centimetres a day.
A hydrogeologist will therefore look at which layer is most fractured, which direction the fractures have, and where this layer comes to the surface – that is the ‘recharge area’. Using rainfall data, borehole logs, transmissivity, and a lot of further puzzling and conceptualising, it becomes possible to know where the water from springs comes from and how deep your borehole should be. The final step is to calculate how much water is available and, based on that, regulate the extraction and demand.
In Randullabad this understanding had led people to change the crop pattern, allocate a specific well for drinking water, and increase their access to water by building a small dam for recharging the aquifer.
Radullabad is quite unique, as they now have been able to achieve real water security. They know what they have, they know how much more is coming, and, based on this, they plan their abstraction. And, importantly, they have dedicated the deepest well to drinking water alone.
What is WaterAid doing?
As per our water security framework, WaterAid is committed to provide safe and sustainable water to enable long-lasting WASH services. Inspired by experiences in Randullabad, our 35 colleagues will work with communities and government, to get a deeper (pun intended) understanding of the local context.
We will explore the idea of training community hydrogeologists (also called para-hydrogeologists, or barefoot hydrogeologists) to increase communities’ awareness of the size and limits of their groundwater source, and will work to make their data available to others (using, for example, mwater).
The course I attended also included a special session on water conflicts. This social aspect to the hard science of hydrogeology is important, as water security can only be achieved by regulating the extraction and demands. Helping people to balance water demands in a community (or in a district, a town, or anywhere) requires tact, patience and tenacity, and highlights that achieving sustainability requires stamina.