Sediment distribution and accumulation in Lake Naivasha, Kenya over the past 50 years

Abstract

Although surface waterbodies are water sources for socio‐economic activities and ecosystems, their functions are threatened by sedimentation. Sedimentation of lakes and reservoirs can result in a loss of storage capacity and altered water quality. The present study assessed the sedimentation status of Lake Naivasha, Kenya, based on sediment distribution and accumulation over the past 50 years, using a Bathymetric Survey System (BSS). The BSS uses multi‐frequency Acoustic Profiling System (APS) to map recently deposited sediments. Sediment core samples were collected with a vibe‐ coring device and dated. Sediment layers corresponding to a period of the past 20 and 50 years were identified. Sediment cores and acoustic images were subsequently used to determine sediment thickness within the lake. The collected depth data from multi‐frequency APS, and dated cores were processed in DepthPic and Surfer software. The sediment depth was extracted in DepthPic, while the sediment volume and distribution were generated from Surfer software. The results from present study indicated that sediment distribution varied from one part of the lake to another for the past 20 and 50 years. High sediment thickness observed in the south‐west and eastern parts of the lake. Between 1996–2016 and 1966–2016 periods, the maximum accumulated sediment thickness was found to be about 0.55 and 1.9 m, with an average sediment thickness of 0.25 and 0.56 m, respectively. The mean sediment load corresponding to the 1966–1996 and 1996–2016 periods was 2.78 × 105 and 4.61 × 105 t/year, respectively. It was found that sediment load into Lake Naivasha has been increasing in the recent past. Based on the present the study, it was found that combined use of BSS, sediment cores and dating can be adopted in many lakes and reservoirs to determine sediment thicknesses even where no prior bathymetric surveys exist for comparison.

Investigation of Flood Management and Mitigation Measures in Ungauged NATURA Protected Watersheds

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“…The capacities and surface area differences derived from numerous bathymetric surveys for a reservoir provide an estimate of water capacity loss over time due to sediment deposition (Iradukunda et al, 2020;White, 2005). Several scholars have carried sedimentation studies on lakes and reservoirs using various methods including mathematical modeling, bathymetric surveys, remote-sensing, sediment coring, and multi-frequency acoustic systems (Dargahi, 2012;Gadissa et al, 2018;Icold, 2009;Maina et al, 2019;Rahmani et al, 2018;Rakhmatullaev et al, 2011;Schleiss et al, 2008). However, little or no information is known about the Murera reservoir and yet the watershed is dotted with anthropogenic activities that would contribute to sedimentation and the consequent pollution of the water resource.…”

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