Assessment of Geothermal Gradient in Samaru, Zaria, Northwestern Nigeria: Implications for Groundwater and Subsurface Engineering

Abstract

Background: Geothermal gradient is an essential parameter in subsurface thermal analysis, geothermal resource calculation, and hydrogeological studies. This research was aimed at determining the shallow geothermal gradient at Samaru, Zaria, Northwestern Nigeria, and examining the potential implications on groundwater development and subsurface engineering. Methods: A cross-sectional research design was used, where data were systematically obtained from 45 randomly sampled hand-dug wells. Data was collected from January to March 2024. Water surface temperatures were obtained using a UTi80 thermal imaging camera, while water table depth was recorded using a meter rule. Coordinates and elevations were obtained using a handheld GPS device. Linear regression analysis was used to establish the relationship, while contour maps were used to establish spatial relationships. Results: Water surface temperatures ranged from 22.4°C to 28.4°C, while the water table depth ranged from 1.30 m to 7.79 m. Linear regression analysis showed that the shallow geothermal gradient was 0.4708°C/m, which is way above the global average of 0.025°C/m. Contour maps showed deeper water tables in the west and east, which are potential sites for boreholes, while the northwest showed shallow water tables, indicating high groundwater vulnerability. Conclusion: The high gradient values indicate local conditions of shallow subsurface environments rather than deep crustal heat flow. The results provide critical background information for groundwater management, borehole placement, and shallow engineering in crystalline basement environments. The results add to Nigeria’s developing geothermal resource database.