1. 6.1
BASIC ENGINEERING
New ‘modernised’ diversion structures have promoted larger inequity in the distribution of irrigation water between upstream and downstream farmers due to the collapse of traditional evolving water rights.

2. Irrigation infrastructure
Three types of engineering structures:
Diversion and ephemeral river training structures
Spate canals and water diversion structures
Field structures

3. Importance of sedimentation
Management of sedimentation:
Less important in traditional systems
More important in permanent diversion structures:
Limit diversion of coarse sediments
Cope with future rise in field levels

4. Diversion and ephemeral river training structures
Requirements for successful intakes:
Divert low and spate flows
Prevent large flood flows
Limit high coarse sedimentation concentrations
Function over the longer term

5. Traditional intakes Two basic forms:
Diversion spur extending into ephemeral river bed
Cross bund across ephemeral river bed

6. Advantages of traditional diversion structures:
Traditional intakes
Advantages of traditional diversion structures:
Flexibility
Appropriate and low cost
Relatively efficient
Limit diversion of high flows and high sediment loads

7. Disadvantages of traditional diversion structures:
Traditional intakes
Disadvantages of traditional diversion structures:
Enormous input of labour
Not always possible to divert water where needed

8. Low cost improvements to traditional diversions
Improvement options:
Use of bulldozers and backhoes
Bed sills
More durable diversion spurs
Improved diversion bunds
Controlling the flows admitted to canals
Basic gated intakes
Rejection spillways

9. New permanent diversion structures
Disadvantage multiple intake improvements:
Increase in costs
Disadvantage single intake improvement:
Increase in inequity between water users

10. New permanent diversion structures
Recommendations:
Provide multiple diversion points for systems containing numerous intakes and canals
Participation of farmers in design and development
Introduction of spate irrigation to new areas on small tributary ephemeral rivers

11. Bank protection and river training
Combination of substantial structures and natural vegetation
Controlling river beds:
Bunds constructed by bulldozers across the ephemeral river will cause siltation and avoid scour

12. Spate canals and water diversion structures
Objective: divert maximum amount of water to the fields in a short time period

13. Traditional canals and water control structures
Characteristics:
No drop structures and steeper slope
Unequal distribution of bed sediments
Often not well-maintained – ‘everybody’s land’
Several types of water control structures

14. Improved traditional canals and water control structures
Design based on slopes and cross sections of existing traditional canals
Check and drop structures:
Structure design for maximum canal discharge
Expensive gates
Upstream off takes allow down flow?
Need to raise canal bed?
Spill capacity?

15. Improved traditional canals and water control structures
Flow splitting structures:
Diversion of flows to manageable discharges
Fixed shares?

16. Field-to-field irrigation
Field off-takes
Field-to-field irrigation
Advantages
Quick apply of water
No investment in canal system
Disadvantages
Damage of crops
Less water to downstream fields
Requirement flow capacity of field off-takes:
Sufficient for full incoming canal flow

17. In-field structures
Fields form into series of level terraces:
Drop structures between fields prevent erosion

18. Requirements for successful engineering interventions:
Recommendations
Requirements for successful engineering interventions:
Be easy for farmers to operate
Prevent large flood flows
Distribute water in line with rules and rights
Continue to function with sedimentation
Cope with unstable ephemeral river channels