Project context and challenge
The Jangwani valley, some 2.5 km upstream of the mouth of the Msimbazi River, is one of the most flood-prone places in Dar es Salaam. Here Morogoro Road, the link between the city centre and the northwestern part of the city, crosses the river. During high river flows, the road and the Jangwani Bridge are submerged and traffic comes to a standstill.
Right next to the bridge lies the main depot of the city’s Bus Rapid Transit system. It was not designed for flooding: water and sediment regularly flow in, damaging buildings, blocking the drainage system and damaging the buses parked inside. In 2018 alone, the depot flooded four times, and the frequency had been increasing since 2011.
As part of the World Bank funded Dar es Salaam Urban Transport Improvement Project, TANROADS asked CDR to identify feasible long term options to protect these major public investments, and to prepare detailed designs and tender documents.
CDR’s approach and contribution
CDR led the assignment with Deltares and the Tanzanian firms WEMA Consult and Sapphire. In the first stage, hydraulic modelling and preliminary designs were used to compare measures: dredging a wider and deeper river channel, temporary protection of the depot, a ramp to connect the depot to a raised road, and a new bridge with a longer span and more clearance. CDR also proposed a low cost alternative for the depot: a flood early warning and evacuation plan to move the buses to safety in time.
In the second stage, the team carried out topographic surveys and geotechnical investigations and prepared a basis of design, including design water levels for floods of different return periods. Together with Deltares, a hydraulic and morphological study verified the river channel design. It showed that a uniformly widened channel would quickly fill with sediment, so the channel was adjusted to keep sediment moving.
The detailed designs and tender documents were prepared as separate lots, allowing TANROADS to decide on each intervention. An ESIA scoping study under World Bank safeguards completed the work.
Result
TANROADS selected a new bridge combined with river dredging. CDR delivered the detailed design of the New Jangwani Bridge, a multi-span bridge with a total span of around 390 metres and a raised Morogoro Road, together with the dredging design and tender documents. Relocating the bus depot to a safer site was recommended as the most feasible long term solution.
In 2024, a follow-up study by CDR confirmed that the bridge remains safe even during a 1 in 1,000 year flood under severe climate change.
