The performance of irrigation schemes that carry sediment laden water is often poor. Modern irrigation schemes are increasingly demand based, which means that the water flow in the canals is determined by the crop water requirements. Accordingly the flow in the canal network is not constant as the crop water requirement changes with the climate and the growing stages. Also the inflow of the sediment is not constant throughout the irrigation season. Such schemes, particularly having unlined canals in alluvial soils, are difficult to design and to manage without compromising the flexibility or maintenance cost. This research has made an in-depth assessment on the role of sediment in the design and management of an irrigation scheme by using the data of Sunsari Morang Irrigation Scheme, Nepal. An analysis of the velocity and shear stress distribution across a non-wide trapezoidal canal has been made to derive the correction factor for the sediment transport predictors.

Sediment transport in irrigation canals influences to a great extent the sustainability of an irrigation system. Unwanted erosion or deposition will not only increase maintenance costs, but may also lead to unfair, unreliable and unequitable distribution of irrigation water to the end users. Proper knowledge of the characteristics, including behaviour and transport of sediment will help to design irrigation systems, plan efficient and reliable water delivery schedules, to have a controlled deposition of sediments, to estimate and arrange maintenance activities, etc. The main aim of these lecture notes is to present a detailed analysis and physical and mathematical descriptions of sediment transport in irrigation canals and to describe the mathematical model SETRIC that predicts the sediment transport, deposition and entrainment rate as function of time and place for various flow conditions and sediment inputs. The model is typically suited for the simulation of sediment transport under the particular conditions of non-wide irrigation canals where the flow and sediment transport are strongly determined by the operation of the flow control structures. The lecture notes will contribute to an improved understanding of the behaviour of sediments in irrigation canals. They will also help to decide on the appropriate design of the system, the water delivery plans, to evaluate design alternatives and to achieve an adequate and reliable water supply to the farmers.