Groundwater Mapping or Aquifer Mapping

Groundwater mapping or aquifer mapping is the process of delineating the presence of ground water in aquifers, followed by the analysis of its quality, quantity, movement and sustainability.

About 30% of world’s fresh water supply is ground water, i.e., 0.76% of entire world’s water. Researches confirm that it is a most exploited and highly extracted raw material. From irrigation to recharging of lakes, its usage is wide. After safety and quality checking, Groundwater can even be used for drinking purposes.

Now what exactly is ground water?

The water that is held under rocks, beneath earth’s surface is called groundwater. While some of the rain water seeps into deeper layers of the land, some run off to streams and rivers. The former reaches the water table and thereafter to a saturated zone.

It is in this zone where there is significant presence of groundwater. Aquifer is a permeable geological formation that can contain this water. The water-bearing rock beds of aquifers might be – confined or unconfined. The latter have more proximity to the earth’s surface. And therefore, more drastically impacted by conditions like drought.

Now why do we require the mapping of aquifers?

During summers, news headlines are crammed full of articles on ground water crisis. According to UNESCO (United Nations Educational, Scientific and Cultural Organisation), India bags the first for being the biggest ground water extractor in the world.

As far as India is concerned, the north Indian states draw more water as per reports. That’s a sole reason why the Central Government Water Board has proposed a model Bill to regulate and control the development and management of ground water in 2005. So, in order to identify aquifer location and plan the efficient use of ground water, mapping comes into picture.

Salient reasons why to do groundwater mapping –

1. Investigating the influence of key parameters like land use and geology on ground water.

2. Exploration of quality and quantity of water in the aquifers.

3. Analyzing the Pre and Post monsoon water level fluctuations and drops in the aquifer.

4. Evaluating the effect of global environmental and seasonal changes in the water table.

5. Study of spatial and temporal variations in the head of water.

How to proceed with Aquifer mapping –

Three major steps involved in aquifer mapping are data collection, post-processing and reporting. Field investigations and remote sensing are used to collect inputs for mapping. Further, these inputs can prepare groundwater models.

Data collection:

Data Collection – Either from existing data bases and maps or by new field measurements.

1. Exploration and collection of groundwater data

2. Field investigations, collecting information about open and bore wells

3. Geophysical investigations and characterization of groundwater reservoirs

For instance, ground water related data regarding pre and post monsoon water levels in both open (dug) and bore wells are available from Ground Water Departments in respective districts. You can refer India-WRIS website for inputs.

Automatic data generation is an option, instead of manual data collection. Point automatic-collecting systems of various parameters or remote sensing are also reliable. Remote sensing contributes infrared or high-altitude aerial photography for aiding in data generation.

Post-processing:

Geographic Information System and Remote sensing for map preparation –

1. Existing data evaluation (Data can be also in the form of paper maps which are scanned or geo-referenced)

2. Analysis of data gaps if any

3. Filling the data gaps and preparing the database

4. Developing thematic layers like rainfall, slope and drainage density

5. Integrating different thematic layers using the Geographic Information System software

Output:

Following are the expected outputs:

1. Hydro geological and water quality maps

2. Locating recharge and discharge zones

3. Quantification of water in different layers of the aquifer

4. Analysis of results on ground water abstraction

5. Deploying sustainable management action based on output study

Benefits in groundwater mapping

One of the main advantages of mapping is the – Identification and categorization of zones. It can be water heads of low, medium and high level. This helps understand the level of water subjected to seasonal and temporal changes. And above all, help plan the water management principles accordingly.

For example – Groundwater prospect map of the Central Eastern Desert shown below indicates water potentials and well location. The map was prepared using Geographic Information System software and Remote Sensing.

The mapping helps identify cluster of aquifer layers and formulate aquifer management plans on it’s basis. On the other hand, it can help in ground water exploration and drilling programs. Efficient use of software’s like – MODFLOW 6, or ArcGIS. It is possible to map the arid regions with the help of radar images.

Similarly, drawing inferences from output mapping help develop sustainable cropping patterns and practices. The process can also lead to the development of particular management strategies and guidelines for water use.

Again, another scope of mapping is the analysis in terms of water quality. The spatial distribution of quality parameters information is necessary for this. After the evaluation of physical and chemical parameters, the results can be compared with Bureau of Indian Standards and World Health Organization standards.

And, a clear idea on the major minerals in water in parts per million(ppm) may be found afterwards. This can give a clarity before using water for domestic, industrial and irrigation purposes. Laboratory tests followed by Geographic Information System software plotting can serve this study.

Challenges in groundwater mapping

• Now, things are much easier with innovations like satellite imagery to aid in mapping. However, technical knowledge (software skills) is a must.

• Above all, it costs certain amount of time and effort.

• The generated map is an outcome of the processed inputs. And if the data is faulty, it can interfere with the end results.

For instance, while developing thematic layers for fresh water aquifers, there shouldn’t be denial of the possibility of salt water intrusion. Consider the geology of the area.

Today, bore well digging and tapping are familiar sights. In times like now, there is an incomparable degree of groundwater exploitation. In short, the coming generation shall face a crisis they cannot imagine surviving, if we don’t think and act before hand.

Therefore, mapping of aquifers open before us a scope and possibility to try our hands on! The map outcome can contribute to overall development in a sustainable way. It enables different State governments to frame guidelines for water resource utilization in an equitable and efficient manner.

Suggested reads: https://www.thehindu.com/news/cities/Hyderabad/aquifer-mapping-best-to-locate-groundwater/article8521728.ece