Tracing Sediment Provenance in Kilindini Harbour, Mombasa Using Heavy Minerals and Natural Radionuclides

Abstract

Harbours are essential gateways for trade, but they often face challenges like sedimentation, which can obstruct navigation channels and hinder ship movement. Understanding sediment dynamics is crucial to managing this issue. Various methods, such as using Rare Earth Elements (REEs), artificial radionuclides, and exotic particles, have been explored globally. However, these methods can be costly, pose safety risks, or are impractical for large-scale studies. This study applied sediment fingerprinting using selected elements and natural radionuclides to trace sediment transport and sources in Kilindini Harbour, Mombasa. Samples were collected from River Mwache, Mteza Creek, and Port Reitz, about 10 km from the harbour's main channel, and analyzed using EDXRF and gamma spectroscopy. The analysis showed that elemental concentrations generally decrease as sediments move through the system, with the lowest levels found in Port Reitz. This was a clear indicator of sediments being transported downstream from River Mwache and into Kilindini Harbour through Port Reitz. Zircon (Zr) behaved differently due to its resistance to weathering, remaining consistent throughout the transport. This proved that Zr would be an essential tracer element for future studies. Radionuclide activity patterns revealed regions of sediment accumulation, particularly along River Mwache and its banks. Natural radionuclides were therefore proven as an effective, cheap and safe method to determine sediment deposition areas. In conclusion, the study determined a major source of sediments in Kilindini harbour to be Mwache River and Mteza creek. Future research can refine these methods for more accurate quantification of sediment sources