Good drainage is essential to a road's lifespan. Water that sits on or under the pavement weakens it, leading to cracks, potholes and washouts. On the 54 km Akwanga project, ICCO installed 16.5 km of longitudinal drainage and 72 culverts to manage water along the route.
Key facts
- Longitudinal drainage: 16.5 km
- Culverts: 72 in total, 1,940 m combined length
- Pipe culverts: 36 × 600 mm, 18 × 900 mm, 11 × 1,200 mm
- Box culverts: 7 reinforced concrete box culverts, 224 m
- Design basis: Hydrological and drainage design by ICCO
- Certified complete: 12 April 2022
Hydrological design
ICCO's design work included hydrological and drainage design. This studies how rainwater moves across the land and where streams and run-off meet the road. The results set the size and position of each drain and culvert.
Sizing matters: a culvert that is too small backs water up against the road, while one that is too large wastes money. Designing from the flow data for each crossing avoids both problems.
Drains along the road
The 16.5 km of longitudinal drainage works collect water from the road surface and the land beside it. The drains then carry it away to safe outlets, keeping it clear of the pavement layers.
Culverts under the road
Where water must cross the road, ICCO built pipe and box culverts of different sizes, matched to the expected flow:
| Culvert type | Number | Total length |
|---|---|---|
| 600 mm dia. reinforced concrete pipe culverts | 36 | 900 m |
| 900 mm dia. reinforced concrete pipe culverts | 18 | 486 m |
| 1,200 mm dia. reinforced concrete pipe culverts | 11 | 330 m |
| Reinforced concrete box culverts | 7 | 224 m |
| Total | 72 | 1,940 m |
Smaller pipe culverts handle minor run-off, while larger pipes and box culverts carry bigger streams. In total, 72 culverts with a combined length of 1,940 m carry water safely under the road.
Protecting the investment
Well-placed culverts stop water from building up against embankments, which can cause them to fail. They also help keep the surrounding land from flooding during heavy rain.
Over 54 km, that works out at about 1.3 culverts for every kilometre of road, a reminder of how often water needs to cross a road in this landscape.
Certified complete
The works were confirmed complete and compliant with the approved drawings and technical specifications in the Certificate of Completion dated 12 April 2022.
More on the Akwanga 54 km road
This article is part of a five-part series on the project:
- ICCO Completes 54 km Road Project in Akwanga LGA, Nasarawa – the scope, value, timeline and completion of the project.
- Moving 2.5 Million m³: Earthworks Behind Akwanga's 54 km Road – the earthworks and layered pavement.
- Seven Bridges Built on the Akwanga 54 km Road in Nasarawa – the seven concrete bridges, bearings and joints.
- Akwanga's 54 km Road Built for Future Utilities and Safer Travel – the HDPE service ducts and flexbeam guardrails.
Frequently asked questions
Why is drainage important for a road?
Water that sits on or under the pavement weakens it, leading to cracks, potholes and washouts. Drainage keeps water away from the pavement layers.
How many culverts are on the Akwanga road?
There are 72 culverts with a combined length of 1,940 m: 36 of 600 mm, 18 of 900 mm and 11 of 1,200 mm reinforced concrete pipe, plus 7 reinforced concrete box culverts.
How much drainage runs along the road?
ICCO installed 16.5 km of longitudinal drainage, which collects water from the road surface and nearby land and carries it to safe outlets.
How were the drains and culverts sized?
ICCO's hydrological and drainage design studied how rainwater moves across the land and where streams meet the road. The results set the size and position of each drain and culvert.
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