1st Edition
Role of Sediment in the Design and Management of Irrigation Canals
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.
1. Introduction
1.1. General
1.2. Prospects of irrigation
1.3. Essentials of irrigation schemes
1.3.1. Functional requirement
1.3.2. Service requirement
1.3.3. Operation and maintenance requirement
1.4. Sediment transport aspects in irrigation canals
1.4.1. Canal design
1.4.2. Operation and management
1.5. Irrigation in Nepal
1.6. Mathematical modelling
1.7. Objectives
1.8. Set-up of the thesis
2. Irrigation in Nepal
2.1. General overview
2.2. Land and water resources
2.3. History of irrigation development
2.3.1. Ancient Period
2.3.2. Medieval Period
2.3.3. Modern Period
2.4. Issues of the irrigation sector
2.5. Description of the study area
2.5.1. Location and development
2.5.2. Major problems
2.5.3. Modernization works
3. Design of canals for sediment transport
3.1. Background
3.2. Design methods
3.2.1. Regime theory
3.2.2. Tractive force theory
3.2.3. Rational theory
3.3. Water flow hydraulics
3.3.1. Governing equations
3.3.2. Roughness prediction
3.4. Sediment transport aspects
3.4.1. Initiation of motion
3.4.2. Sediment transport under equilibrium
3.4.3. Non-equilibirium sediment transport
3.5. Modelling aspects
3.6. Sediment transport models
4. Assessment of parameters for canal design
4.1. Background
4.2. Irrigation water demand and scheduling
4.3. Estimation of design discharge
4.4. Flow control and sediment movement
4.4.1. Flow control
4.4.2. Sediment movement
4.5. Roughness prediction
4.5.1. General
4.5.2. Roughness in the bed
4.5.3. Roughness in the sides
4.5.4. Equivalent roughness
4.6. Sediment transport in non-wide canals
4.6.1. Effects of canal geometry and flow characteristics in sediment transport
4.6.2. Velocity distribution in a trapezoidal canal
4.6.3. Exponent of velocity in sediment transport equation
4.6.4. Correction factor
4.6.5. Predictability of predictors with correction
4.7. Conclusions
5. Towards a new design approach
5.1. General
5.2. Hydraulic aspects of canal design
5.2.1. Existing canal design approaches in Nepal
5.2.2. Canal design methods in SMIS
5.2.3. Proposed canal design approach
5.3. Management aspect of canal design
5.3.1. Operation aspect
5.3.2. Conveyance aspect
5.3.3. Provision of settling pockets
5.3.4. Maintenance activities
5.4. Modelling aspect of canal design
5.5. Conclusions
6. Model development
6.1. Background
6.2. Water flow
6.3. Sediment movement
6.3.1. Galappatti's depth integrated model for non-equilibrium sediment transport
6.3.2. Equilibrium sediment transport predictors
6.3.3. Framework for concentration prediction
6.4. Roughness prediction
6.4.1. Roughness in the sides
6.5. Canal structures and schematization
6.5.1. General
6.5.2. Hydraulics of flow control structures
6.5.3. Discharge calculation in upstream control
6.5.4. General remarks
6.6. Morphological change and numerical scheme
7. Data collection and scheme analysis
7.1. Definitions and canal nomenclature
7.2. Water requirements and design
7.2.1. Irrigation water requirements
7.2.2. Water delivery plan
7.2.3. Canal alignment, control and design
7.3. Morphological and geometrical data
7.4. Water flow data
7.4.1. Rotation schedule
7.4.2. Calibration of broad crested weir
7.5. Sediment data
7.6. Conclusions
8. Application of improved design approach
8.1. General
8.2. Evaluation of the model SETRIC
8.2.1. Model verification
8.2.2. Model calibration
8.2.3. Model validation
8.2.4. Predictability of equilibrium predictors
8.3. Canal design aspects
8.4. Management aspects
8.4.1. Design water delivery schedule with constant water inflow
8.4.2. Measured water inflow, sediment inflow and water delivery schedule
8.4.3. Proposed water delivery schedule with changing demand
8.4.4. Proposed water delivery schedule with variable inflow of water and sediment
8.4.5. Effects of flow control in sediment transport
9. Evaluation
9.1. General
9.2. Canal design aspects for sediment transport
9.3. Mathematical modelling aspects of canal design
9.4. The Model SETRIC
9.5. Present canal design methods for sediment control in Nepal
9.6. Modernization aspects of Sunsari Morang Irrigation Scheme
9.7. Application of the improved approach for the design in SMIS
9.8. Effects of flow control in sediment transport
9.9. General observations and recommendations for further research
Appendix A: Flow diagrams
Appendix B: Water and sediment data
Appendix C: Predictor-corrector method
Appendix D: Galappatti's depth integrated model for non-equilibrium sediment transport
Biography
Krishna P. Paudel graduated in civil engineering with honours from the University of Roorkee (now IIT Roorkee), India in 1989. In January 2004, he joined the Core Land and Water Development of UNESCO-IHE, the Netherlands as a PhD research fellow. His thesis entitled: "Role of Sediment in the design and management of irrigation canals: Sunsari Morang Irrigation Scheme, Nepal" has made an assessment of existing canal design methods from sediment transport perspective.
He has extensive experience in planning, design and management of irrigation and flood control works. Currently, Mr. Paudel is associated with CMS Nepal (Development Consultants) as Senior Water Resources Engineer and has been involved in the design as well as construction of different irrigation and water resource development projects. His field of interest are hydraulics, sediment transport and mathematical modelling.