International Journal of Hydrology Effects of continuous fushing on the sediment removal effciency in settling basins of small scale irrigation projects; a case study of kiriku-kiende irrigation project, embu county, kenya Submit Manuscript | http://medcraveonline.com Introduction Surface irrigation is a widely used farming system for crop production as it requires less skilled labour and involves less operational cost. Surface irrigation systems contributed to about 90% of the world’s crop land irrigation promoting furrow irrigation as the main application method. 1 However, poor design and management, non-uniformity of water application, and over-irrigation featured in surface irrigation are responsible for ineffcient irrigation, leading to wastage of water, water logging, salinization, and pollution of surface and ground water resources. 2 Irrigated agriculture is under serious risk due to substantial soil losses from highly erodible soils. 3−5 Irrigated agriculture has been faced with challenges such as sediment loading in the river basins, settling tanks and dams. 6 Many factors such as surface and solids loading rates, tank type, solids removal mechanism, inlet design, weir placement and loading rate affect the capacity and performance of a settling tank. 7 The management of sediments in river basins and waterways has been an important issue for water managers throughout the history as from the ancient Egyptians managing sediment on foodplains. 8 Currently, water managers are faced with similar challenges mainly resulting in siltation of water reservoirs, reduced capacity of water transport, annual irrigation acreage reduction and high maintenance cost for an irrigation project. 9,10 Kenya is not exempted from the dangers posed by sedimentation and siltation in her water bodies. According to, 11 a high proportion of sediments generated in the catchment areas is delivered through soil erosion to the rivers and lakes. Effective management of sediments from rivers during irrigation water abstraction by use of settling basins has become increasingly important from an economic and environmental perspective. Many factors such as surface and solids loading rates, tank type, solids removal mechanism, inlet design, weir placement and loading rate affect the capacity and performance of a settling tank. 7 Sediments in irrigation network causes clogging and blocking of irrigation structures. This contributes to overall low irrigation water delivery to the farms. This study was to examine the effect of continuous sediment fushing versus desilting. This would form a basis for designers of settling basin for consideration of continuous fushing for eventual increase of the overall effciency of irrigation systems. In Kenya, smallholder irrigation development is one of the key strategies for land use intensifcation with expected positive effects on rural incomes and poverty alleviation. About 20% (106,600 ha) of the potential irrigable land is already under irrigation where 50% (53,300) of this area is under smallholder irrigation. 12−14 Table 1 presents the land under irrigation in each basin. 10‒15 Principle of sediment particle settling: The suspended solids in water with a specifc gravity greater than that of water usually tend to settle down by gravity as soon as the turbulence is retarded by offering storage. If a particle is suspended in water, it initially has two forces acting upon it. These forces are represented by two Equations. 16 Equation 1 represents the force of gravity acting on the particles while the buoyant force is given by Equation 2. G p p F g ρ ν = (1) B w p F g ρ ν = (2) Where: F G = Gravitation force (N) F B = Buoyant force (N) Volume 1 Issue 2 - 2017 Patrick N Namu, 1 James M Raude, 2 Benedict M Mutua 3 1 Sustainable Materials Research and Technology Centre, Jomo Kenyatta University of Agriculture and Technology, Kenya 2 Department of Soil, Water and Environmental Engineering, Jomo Kenyatta University of Agriculture and Technology, Kenya 3 Planning, Partnerships, Research and Innovations, Kibabii University, Kenya Correspondence: Patrick N Namu, Sustainable Materials Research and Technology Centre, Jomo Kenyatta University of Agriculture and Technology, Kenya, Email pattinams@yahoo.com Received: August 12, 2017 | Published: August 30, 2017 Abstract Reservoir based irrigation schemes present sediment problems of various types. These problems affect the performance of the settling basin in sediment deposition. One of the major problems is the deposition of sediment in the basin and consequent loss of storage capacity. The design of settling basin involves determination of a combination of width, depth and length of the basin for desired removal efficiency of sediment above a given size. The aim of this study was to compare the effect of continuous removal of sediment from a basin to that of periodic removal. A physical model that was sized to resemble the settling basin of Kiriku-Kiende irrigation project was set up in the Civil Engineering laboratory of Jomo Kenyatta University of Agriculture and Technology. The physical processes for this research involved five experiments on sediment settling in different settling time and same inflow rate. The results obtained shows that settling tanks with continuous sediment removal have a higher sediment removal efficiency of 65.5% against 24.4% for those without a flushing component. Keywords: Efficiency, Flushing, Irrigation, Sediment, Settling basin Int J Hydro. 2017;1(2):49‒53 49 © 2017 Namu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and build upon your work non-commercially. Research Article Open Access