Gis–Ahp Groundwater Potential Mapping and Sensitivity Analysis for Public Borehole Planning in Ikorodu, Lagos State, Nigeria

In the rapidly growing coastal city of Lagos, Nigeria, the tap water often fails to reach the people who need it most. As a result, families and communities have turned to digging their own wells and drilling boreholes to access the water hidden beneath the ground. This underground water is a vital resource, but finding it is not as simple as picking a spot in the backyard and starting to dig. The ground is a complex puzzle made of rock layers, soil types, and hidden cracks that either hold water or let it drain away. If a borehole is drilled in the wrong place, it might come up dry, wasting thousands of dollars and leaving a community without a solution. To solve this, scientists use a method that combines satellite images with computer mapping to predict where water is most likely to be found. They look at the shape of the land, how much rain falls, how water flows across the surface, and the hidden cracks in the earth that act as highways for water to move underground.

A team of researchers recently applied this approach to Ikorodu, a large local government area on the edge of Lagos. Their goal was to create a detailed map that could guide public officials and community leaders on where to drill new boreholes with the highest chance of success. Instead of guessing or relying on expensive, time-consuming field tests for every single site, they built a digital model that weighs six different factors. These factors include the height of the land, how steep the slopes are, the amount of rainfall, the density of streams and rivers, the type of land cover like buildings or forests, and the density of lineaments. Lineaments are long, linear features on the surface of the earth, often visible as straight lines in satellite photos, which usually indicate cracks or faults deep underground where water can collect and flow more easily.

The researchers used a computer system to analyze data from satellites and weather records covering the entire Ikorodu area. They assigned a score to each factor based on how much it helps water gather underground. For instance, flat land is better for soaking up rain than steep hills, and areas with many underground cracks are better at holding water than solid, unbroken rock. By layering all this information together, they produced a map that divides the region into five zones, ranging from "Very Low" potential to "Very High" potential. The most important discovery was that the density of these underground cracks, or lineaments, was the single most powerful predictor of where water would be found, outweighing even the amount of rainfall or the slope of the land.

To ensure their map was reliable and not just a lucky guess, the team performed a rigorous test. They asked themselves: "What if our experts were slightly wrong about how important each factor was?" They systematically changed the importance of each factor in their computer model by small amounts, running twenty-six different scenarios to see if the final map would change drastically. The results were reassuring. Even when they tweaked the numbers, the map remained stable, and the conclusion that underground cracks are the most critical factor held true in every single test. This gave them confidence that the map was a robust tool, not a fragile one. They also checked the accuracy of their land cover data, which showed that their computer classification of buildings, vegetation, and bare ground was correct about 89 percent of the time.

The final map revealed a clear pattern for the region. The southern, southeastern, and parts of the central areas of Ikorodu are rich in groundwater potential, with high concentrations of underground cracks and gentle slopes that allow rain to soak in. In contrast, the northern and northwestern parts of the area are much less promising, characterized by higher ground and fewer cracks, making them poor candidates for new wells. The researchers did not stop at just drawing the map; they turned it into a practical guide for decision-makers. They created a four-tier system that tells planners exactly what to do in each zone. Areas marked as "Very High" are the top priority for immediate investigation and drilling. "High" areas are the next step. "Moderate" areas require extra caution and specific tests before any drilling is approved. Finally, the "Low" and "Very Low" zones are places where drilling should be avoided unless there is a very strong, specific reason to do so, as the risk of failure is high.

While the map is a powerful tool, the researchers are careful to explain its limits. They verified their findings by comparing their map to a list of locations where previous geophysical surveys had already suggested water might be found, and the two matched up well. However, they note that this map is a screening tool, not a guarantee. It cannot replace the need for on-the-ground tests, such as electrical surveys and actual drilling, to confirm the depth and quality of the water. They also warn that in the coastal areas near the lagoon, there is a risk of saltwater mixing with the fresh groundwater, a danger that the map does not directly show but must be considered by planners. Ultimately, this study provides a clear, scientifically tested roadmap for Ikorodu. It moves the conversation from random drilling to strategic planning, offering a way to save money and ensure that the communities of Lagos have access to the clean water they need.