Reducing sediment connectivity though man-made and natural sediment sinks in the Minizr Catchment, Northwest Ethiopia

Mekonnen, Mulatie and Keesstra, Saskia D. and Baartman, Jantiene E. M. and Stroosnijder, Leo and Maroulis, Jerry (2016) Reducing sediment connectivity though man-made and natural sediment sinks in the Minizr Catchment, Northwest Ethiopia. Land Degradation and Development, 28 (2). ISSN 1085-3278


Man-made and natural sediment sinks provide a practical means for reducing downstream reservoir sedimentation by decreasing soil erosion and enhancing the rate of sedimentation within a catchment. The Minizr catchment (20 km2) in the northwest Ethiopian highlands contains
numerous man-made soil and water conservation (SWC) structures such as soil bunds (Erken), fanya juu ridge (Cab) and micro-trenches and natural sediment sinks such as wetlands, floodplains and grassed waterways. These sediment sinks reduce downstream sedimentation into the
Koga reservoir, located at the catchment outlet, however, a large quantity of sediment is still reaching the reservoir. This study evaluates the function and effectiveness of both man-made SWC structures and natural sediment sinks in reducing sediment export from the Minizr catchment. SWC structures and natural sediment sinks were digitized using Google Earth Imagery. Sediment pins and vertical sampling
through the deposit were used to quantify the amount of deposited sediment. In addition, inflow and outflow of suspended sediment data were used to calculate the sediment-trapping efficacies (STE) of man-made SWC structures (soil bunds and fanya juu ridges) and natural sediment
sinks. Results reveal that 144 km soil bunds and fanya juu ridges trapped 7,920Mg y�1 (55 kgm�1 y�1) and micro-trenches trapped 13·26Mg y�1, each micro-trench on average trapped 23 kg y�1. The 17 ha floodplain located in the centre of the catchment trapped 9,970Mg y�1 (59 kgm�2 y�1), while a wetland with a surface area of 24 ha, located near the outlet of the catchment, trapped 8,715Mg y�1 (36 kgm�2 y�1). The STEs of soil bunds and fanya juu ridges, wetlands and floodplains were 54%, 85% and 77%, respectively.
Substantial differences were observed between the STE of grassed and un-grassed waterways at 75% and 21%, respectively. Existing man-made and natural sediment sinks played an important role in trapping sediment, with 38% (26,600Mg y�1) of transported sediment being trapped, while 62% (43,000Mg y�1) is exported from the catchment and thus enters the Koga reservoir. Therefore, additional
catchment treatment measures are required as an integrated catchment scale sediment trapping approach to help reduce sediment loads entering Koga reservoir. Moreover, to maximize the effectiveness of sediment trapping measures, avoid structural failure and ensure their
sustainability, regular maintenance is needed.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Published online 3 October 2016. Permanent restricted access to ArticleFirst version, in accordance with the copyright policy of the publisher.
Faculty / Department / School: No Faculty
Date Deposited: 24 Jan 2017 05:44
Last Modified: 21 Sep 2017 01:28
Uncontrolled Keywords: soil and water conservation structures; wetland; floodplain; waterway; sediment trapping efficacy; Koga reservoir
Fields of Research : 05 Environmental Sciences > 0503 Soil Sciences > 050302 Land Capability and Soil Degradation
Identification Number or DOI: 10.1002/ldr.2629

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