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

Authors: MAINA, CAROLINE - Jomo Kenyatta University; SANG, JOSEPH - Jomo Kenyatta University; RAUDE, JAMES - Jomo Kenyatta University; MUTUA, BENEDICT - Jomo Kenyatta University; Moriasi, Daniel

Submitted to: Grazinglands Research Laboratory Miscellaneous Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2019
Publication Date: 7/1/2019
Citation: Maina, C.W., Sang, J.K., Raude, J.M., Mutua, B.M., Moriasi, D.N. 2019. Sediment distribution and accumulation in Lake Naivasha, Kenya over the past 50 years. Lakes and Reservoirs. 24:162-172. https://doi.org/10.1111/lre.12272.
DOI: https://doi.org/10.1111/lre.12272

Interpretive Summary: Surface waterbodies play important socio-economic and ecosystem services roles. However, these functions are highly threatened by sedimentation, loss of storage capacity, and water pollution due to land management and climate changes. In this study, state-of-the-art bathymetric survey equipment manufactured and commonly used in the United States was used to quantify sedimentation in Lake Naivasha, Kenya, for the last 20 and 50 years spanning the period between 1966 and 2016. As would be expected, the thickness of the sediment accumulation over the years varied from one part of the lake to another. The thickness of the sediment that had accumulated in the past 20 (1996-2016) and 50 (1966 -2016) years was 0.55 m and 1.9 m, respectively. The rate of sedimentation was higher in the later years as shown by an average annual sediment load of 2.78 x 105 and 4.61 x 105 metric tons/yr for the periods 1966 -1996 and 1996-2016, respectively. Reservoir sedimentation rates determined in this study will help water resource managers in Kenya to develop action plans to reduce sedimentation and extend the life of reservoirs. This research fits into research conducted under the National Program (NP) 211, Water Availability and Watershed Management.

Technical Abstract: Despite the vital importance of surface waterbodies as water sources for socio-economic activities and ecosystems, their functions are highly threatened by sedimentation. Sedimentation of lakes and reservoirs results in loss of storage capacity and decreases water quality. This study assesses the status of sedimentation in Lake Naivasha, Kenya over the past 50 years using a Bathymetric Survey System (BSS). The BSS uses multifrequency Acoustic Profiling System (APS) to map recently deposited sediments. Sediment core samples were collected using a vibra-coring device, dated, and layers corresponding to a period of past 20 and 50 years identified. The collected depth data from APS and dated cores were processed using DepthPic and Surfer software. For the 20 and 50 year periods, sediment distribution varied from one part of the lake to another with high sediment thickness observed in the southwest and eastern part of the lake. For the period 1996 – 2016 and 1966 – 2016, 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 period was 2.78 x 105 and 4.61 x 105 metric tons/yr, respectively. It was found that sediment load into Lake Naivasha has been increasing in the recent past.