1. Structures: Design and construction of stream crossings
Training of Trainer Personnel on Environmentally Sound Design and Implementation of Public Works-Community Roads of the Productive Safety Net Program (PSNP)

2. Design and construction of stream crossings: culverts, other STs, concrete work
Types of stream crossing structures
Pipe culverts: crossing of water is under the structure,
Fords: crossing of water is over the structure,
Cause ways or vented fords: a combination of a culvert and ford (ford-culvert),
Bridges: most expensive river crossing as compared to the above 3 options,
Box culvert: used in special cases, weak foundation
Steel pipe culvert: mostly used by machine bending

3. Stream crossing structures (cont’d)
Detail properties of stream crossing structures
Pipe culvert: The common type, its construction involves
Concrete pipe production (60 – 120 cm),
Filling foundation – by lateritic, granular material, sand,
Slope: 2%, max. 5% to avoid scouring problems,
Head walls for fill retaining and traffic sign, and
Scour control measures (apron, riprap)

4. Stream crossing structures (cont’d)
Detail properties of stream crossing structures
(2) Drift or Ford: The cheapest option of stream crossing,
Level of ford is almost same as river bed, however a little bit of raising, cm required for sedimentation,
Slope is about 3% or same as slope of stream,
Surface options: concrete, packed stone or gabion,
Up and downslope walls: can be masonry or gabion,
wing wall or sign post can be provided at the approaches for traffic.

5. Stream crossing structures (cont’d)
(3) Cause way or vented ford or vented spillway:
Its function is a combination of culvert and ford,
In dry season water flows underneath the structure,
In wet season, water flows on top of the structure,
Flow in the pipe during flood is pressurized, Thus,
Design: The creation of downstream hydraulic pressure could be a problem that necessitates the provision of strong apron,
Apron should be concrete or well-compacted stone with adequate length down stream of the vented ford,
Requires care to build

6. Stream crossing structures (cont’d)
(4) Bridges: some characteristics
Most expensive stream or river crossing structure option,
Major structure that require skills, detailed hydrological, hydraulics and foundation study,
Very high budget/expensive unless need or requirement is critical,
Mostly planned for year-round rivers, ……

7. Stream crossing structures (cont’d)
Some times local materials like timber used,
Some times a combination of wooden bridge deck on proper abutment foundation used,
Cost versus foundation are the main factors to be considered i.e short crossing & good foundation,
Last but not least, Bridge crossing or locations are sited at straight river stretches, river bend and meandering stretches are not feasible since the river will eventually break at bends.

8. Stream crossing structures: concrete technology(cont’d)
Concrete: a mixture of 3 materials
Ingredients: cement, sand, aggregate (crushed gravel),
Mix proportion: depends on the required quality of the concrete or quality of work,
Different qualities or mix types of concrete:
Lean concrete, mass concrete, dense concrete, dense/plastic concrete depending on respective proportion/volume of cement, sand and aggregate

9. Stream crossing structures: concrete technology(cont’d)
Concrete quality or mixes:
Lean concrete for culvert bedding, 1:4:8 (147 kg cement/m3 concrete),
Mass concrete for foundation and non-reinforced concrete structures, 1:3:6 (185 kg/m3),
Dense concrete for culvert pipes, light reinforced concrete structures, 1:2:4 (263 kg/m3),
Dense, plastic concrete for heavy reinforced concrete structures, 1:2:3 (313 kg/m3).

10. ILO Video for Module 15 Structures
Video Show
ILO Video for Module 15 Structures

11. Questions or comments from trainees or other trainers?

12. June 13-24, 2011 Ghion Ambassel Hotel Dessé, Ethiopia
Training of Trainer Personnel on Environmentally Sound Design and Implementation of Public Works-Community Roads of the Productive Safety Net Program (PSNP)
June 13-24, 2011
Ghion Ambassel Hotel
Dessé, Ethiopia