A New Approach To Sediment Transport In The Design And Operation Of Irrigation Canals

The transport of sediment greatly influences the sustainability of an irrigation system. Erosion and deposition not only increase maintenance costs, but may result in an inequitable and inadequate distribution of irrigation water. Understanding the behaviour and transport of sediment allows efficient planning and reliable water delivery schedules,

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 effi cient 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.

This study focuses on sediment transport in irrigation canals which may have a serious impact on design, operation and maintenance activities. Using a mathematical model, and examing ways in which this model can be applied to real-world situations, this text is highly useful for theoreticians and students alike.

Sediment deposition threatens the performance of many irrigation systems. Because of the high impact on irrigation performance and crop production, many studies have been done on how to deal with sediment deposition. In this research, the Delft3D model, originally developed for hydro-morphologic modeling of rivers and estuaries, was adapted for the use in irrigation systems simulations and applied to different case studies. This research addresses two shortcomings of previous studies of sediments in irrigation systems. Firstly, while previous studies primarily used 1D models, this research uses a 2D/3D model. The use of 2D/3D models in irrigation systems is significant because the non-uniform flow around structures such as offtakes, weirs and gates, leads to asymmetric sedimentation patterns that are missed by 1D simulations. Secondly, whereas previous studies mostly considered non-cohesive sediments, this research simulates cohesive, non-cohesive and a mix of both sediment types. This is important for irrigation systems that draw water from natural rivers that carry a mix of cohesive and non-cohesive sediments. The findings of this research are important for irrigation system maintenance and gate operation. It is also essential for the development of canal operating plans that meet crop water requirements and at the same time minimizes sediment deposition by alternating gates.

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 effi cient 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.

Siltation in reservoirs has become an important problem when dams are getting older and stop functioning when the sediment has accumulated to a certain extent. With proper sediment management techniques, negative effects of sediment can be avoided and reservoir life and performance can be improved. This volume deals with reservoir sedimentation, deposition and removal. It provides the principles of sediment transport and gives guidelines to predict reservoir life. It presents several removal techniques, accompanied with detailed operation descriptions. With the help of the RESCON open source software, cost analysis tools to determine the optimum method for maintenance and operation of a reservoir can be applied. To illustrate practice and to assist the reader in setting up a sediment management operation, a number of case studies of existing large dams are included. Written by two experts on reservoir operation, this volume is intended for professionals and advanced students working on dam and reservoir design, construction, operation, maintenance and rehabilitation.

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. An improved approach based on a rational concept of the design of canals for sediment transport is proposed. By using the sediment transport model SETRIC, a water delivery plan has been designed and tested for changing water and sediment inflow conditions that can be implemented with the existing canal infrastructure. The research also shows that flexibility of operation and efficient sediment management are difficult to achieve at the same time. A compromise has to be made and this needs to be reflected in the design. All methods to transport, exclude or extract the sediment are temporary measures and just transfer the problem from one place to the other. A better understanding of sediment movement helps to identify the problems beforehand and to find the best possible solutions.

This work describes the role of sediment transport in the operation and maintenance of demand-based downstream controlled irrigation canals. Sediment deposition in these irrigation canals severely affects the operation of the automatic flow control system. The book also discusses sediment transport modelling in irrigation canals. A simplified 1-D mathematical model SETRIC (SEdiment TRansport in Irrigation Canals) has been improved with the inclusion of downstream control component for the downstream controlled irrigation canals. Based on field measurements and sediment transport modelling, a number of approaches have been proposed for sediment management in such irrigation canals by improvement in their design and operation. This book will be of interest to Irrigation Engineers and Managers, Hydraulic Engineers, Water Resources Engineers and Managers, Civil Engineers, and Agricultural Engineers.