The Use of Delft3D to Simulate the Deposition of Cohesive and Non-Cohesive Sediments in Irrigation Systems

by Shaimaa Abd Al-Amear Theol

Overview

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.

Product Details

ISBN-13:	9780367496913
Publisher:	Taylor & Francis
Publication date:	04/20/2020
Series:	IHE Delft PhD Thesis Series
Pages:	158
Product dimensions:	6.69(w) x 9.44(h) x (d)

About the Author

Shaimaa Abd Al-AMear Theol is a Ph.D. fellow in the Water Science and Engineering Department/ Land and Water Development for Food Security in IHE Delft, and Wageningen University & research in the Netherlands. She obtained MSc in Hydraulic Engineering from IHE-Delft (was named UNESCO-IHE), Delft, the Netherlands in the year 2011. Her study abroad is fully supported by the Iraqi Ministry of Higher Education and Scientific Research. She has a background in engineering. Her primary research interests are the cohesive and non-cohesive impacts on the irrigation systems, and the 2D/3D modelling in irrigation systems.

Table of Contents

The use of Delft3D to simulate the deposition of cohesive and non-cohesive sediments in irrigation systems i

The use of Delft3D to simulate the deposition of cohesive and non-cohesive sediments in irrigation systems iii

Acknowledgments v

Summary vi

1 Contents vii

1 Introduction 1

1.1 Importance of irrigated agriculture 2

1.2 Sediments problems in irrigation canals 2

1.3 Operation of canals 4

1.4 Mathematical models 6

1.5 Previous studies & research gap 6

1.6 Research objective 9

1.7 Methods 10

Modelling using Delft3D 10

1.8 Structures of the thesis & Scope of the study 14

2 The use of DELFT3D for irrigation systems simulations 15

2.1 Introduction 17

2.1.1 Delft3D 18

2.2 Methods 19

2.2.1 Model set-up 19

2.2.2 Description of the hypothetical case study 19

2.2.3 Scenarios 21

2.2.4 Model calibration 21

2.2.5 Initial conditions 21

2.2.6 Boundary conditions 21

2.3 Results 22

2.3.1 Scenario 1a: rectangular canals with different sizes and different b/h ratios 22

2.3.2 Scenario 1b: trapezoidal canals with different sizes and different b/h ratios 25

2.3.3 Scenario 1c: canals with structures (rectangular and trapezoidal) 26

2.3.4 Scenario 2: simulations with cohesive sediments 27

2.4 Discussion 33

2.4.1 Adapting Delft3D for irrigation systems 33

2.5 Conclusions 36

3 The use of 2D/3D models to show the differences between cohesive and non-cohesive sediments in irrigation canals 37

3.1 Introduction 39

3.2 METHODS 40

3.2.1 Modelling using DelftSD Governing equations in the Delft3D model 40

3.3 Model setup 42

3.3.1 Grid construction, bathymetry, and other parameter assumptions 42

3.3.2 Model runs 43

3.3.3 Scenarios 44

3.4 RESULTS 47

3.4.1 Impact of variable sediment concentrations 47

3.4.2 Variable flow discharges (Q) 50

3.4.3 Behaviour of cohesive and non-cohesive sediments under very high concentrations 53

3.4.4 Interaction between non-cohesive, and cohesive sediments 55

3.5 DISCUSSION 58

3.6 CONCLUSION 60

4 What is the effect of gate selection on the non-cohesive sedimentation in irrigation schemes? - A case study from Nepal 63

4.1 INTRODUCTION 65

4.1.1 Delft3D 66

4.1.2 Study Area 66

4.2 METHODS 68

4.2.1 Data 68

4.2.2 Model setup 69

4.2.3 Validation 70

4.2.4 Scenarios 73

4.3 RESULTS 75

4.3.1 Scenario 1 Reference case (SGO1) all gates are opened 75

4.3.2 Scenario 2 Gate Operation 76

4.3.3 Other parameters 81

4.4 DISCUSSION 85

4.5 CONCLUSIONS 88

5 The role of gate operation in reducing problems with cohesive and non-cohesive sediments in irrigation canals 89

5.1 Introduction 91

5.2 Materials and Methods 92

5.2.1 Model Selection 92

5.2.2 Case study 95

5.2.3 Model setup 96

5.2.4 Scenarios 99

5.3 Results 100

5.3.1 Reference scenario 100

5.3.2 Effect of weirs 1 and 2 105

5.3.3 Effect of gate settings 106

5.4 Discussion 109

5.5 Conclusions 112

6 Conclusions and Recommendations 115

6.1 CONCLUSIONS 116

6.1.1 How can Delft3D be used in irrigation setting? 117

6.1.2 Cohesive and non-cohesive sediments 120

6.1.3 The impact of gates operation on the sediment transport in the irrigation schemes 123

6.2 Reflection 123

6.3 Recommendation 124

6.4 Research contributions 125

6.5 Further studies 125

References 127

List of acronyms 137

List of Tables 140

List of Figures 141

About the author 145