Impact of Post-mining Transformations on Slope Stability and Sustainability Processes in the Base Titanium Mining Area, Kenya

Abstract

The gradual transformations of the open-pit titanium mining legacy in the south coast of Kwale, County in Kenya, has led to the formed gently rolling terrains into steep, unstable slopes that have endangered both the environmental and community safety. This study delves to (1) measure changes of landforms caused by post mining modifications at base titanium geosites, (2) assess how these changes impact slope stability, and (3) identify opportunities designing more sustainable post mining landforms and practices. Using drone (UAV) photogrammetry and satellite images, the research generated high-resolution digital surface and terrain models which were applied to compare pre- and post-mining topography within a transected area of 2 km x 2 km. Slope angles derived from the normalized digital surface model were categorized into stable (<30°) and high-risk (>30°) groups. Changes in vegetation cover were analyzed with the normalized difference vegetation index (NDVI) and field measurements were used to verify remote sensing data on slopes and land cover. Results show that unclaimed mine pits have an average slope of 35°, which is above the stability threshold. Areas that have been actively reclaimed through topsoil replacement and strategic revegetation have slopes below 25° and dense plant cover. High-risk zones match closely with bare-soil tailings dumps and eroded pit walls where poor drainage has increased the risk of mass wasting; however, reclaimed embankments with engineered drainage and early-stage vegetation are resistant to rainfall-induced erosion. These results prove that integrated planning for slopes, drainage systems, and ecological restoration is important in securing post-mining landscapes. In conclusion, sustainable landforms after mining can be actualized when the reclamation focus is on (a) optimization of steep slope angles to below 30°, (b) installation of cut-offs and controlling water flows using toe drains, and (c) quick establishment of  native plants for soil stabilization and reduction of surface runoffs. Lastly, adopting these mitigation practices would enhance geo-hazards adaptation and resilience. In addition, this will also enhance promotion of ecological succession and enabling future sustainable resource nexus land use approaches such as water storage, water recharge, agroforestry and ecotourism, thus resulting in transformations of former mining area into stable multifunctional and sustainable landscapes.