Stone arch bridges in Tanzania
Innovation rooted in history
Rural communities’ access to schools, hospitals, markets and jobs depends on dangerous river crossings. Safe year-round crossing on a stone arch bridge is therefore a foundation for sustainable development.
Population growth and dispersion in Tanzania puts a major strain on mobility infrastructure. Unfortunately, the national government struggles to cope with the rapidly increasing demand. Much needed infrastructure projects using conventional techniques, such as steel and reinforced concrete, are often very expensive.
The tried and tested technology of stone arch bridges allows for a decentralised approach embedded within local government structures. This cost-effective method with high local ownership guarantees a long-lasting upgrade of rural roads.
The stone arch technology provides a cost saving of 80% compared to concrete or steel bridges and can be implemented by a public tender procedure. Alternatively, the village and Tanzanian Rural Road Agency (TARURA) can be involved with distributed responsibilities: the village provides stones and sand, TARURA provides supervision and Enabel provides technical support. On top of the cost benefit, the approach creates ownership, builds capacity and empowers local leadership.
An average annual TARURA budget can finance 1 concrete bridge via a public tender procedure. The same budget can instead be used to finance 5 stone arch bridges via public tendering or 10 stone arch bridges by involving the local community.
The village involvement includes the supply of stones, sand, water, timber, but the most important contribution is that of casual labour. This transforms the appreciation of the bridge from a government intervention, and thus not a local responsibility, to a community asset that requires community attention before, during and after construction.
Enabel has written a construction manual and translated it to Swahili so it can be used by TARURA.
Thanks to close collaboration with TARURA officials during the project, the technique attracts more and more interest. So far, it has already been promoted by the national director of TARURA. Three arch bridges are currently under construction without Enabel support and outside of Enabel’s intervention area, which is currently limited to the North-Eastern Kigoma region. Within the Kigoma region, TARURA has also started the construction of two stone arch bridges outside of the Enabel project.
The project at a glance
- Tanzania has a population of around 55 million, with annual growth rate of 3%
- Bridge construction started in 2018
- Target for 2022 is 70 bridges completed
- Bridge spans range from 1.1 to 31 m
- Bridge budgets range from € 2.400 to € 35.500. This is financed for 80% by the Enabel project and by 20% by local contribution, which are usually in kind contributions such as stones.
- 97% of villagers say they perceive personal benefits after bridge construction was completed.
- 99% of villagers say they perceive benefits to their community after bridge construction was completed.
- Financial costs are 80% lower than an equivalent conventional reinforced concrete bridge.
- Carbon emissions are 80% lower than an equivalent conventional reinforced concrete bridge. This is thanks to less use of cement, no use of reinforcement steel and thus less transport of industrial materials.
Pictures: © Enabel
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