Project context and challenge
The lower Msimbazi valley, a 4 km² area in the heart of Dar es Salaam, is where the city’s most severe flooding takes place. Flash floods carry huge amounts of sediment: more than 1.2 million m³ settled in the flood-prone area in just over three years, raising flood levels even further. More than 2,000 households live in the floodplain, and major roads and the Bus Rapid Transit system cross the valley.
The Msimbazi Opportunity Plan, developed earlier with communities and authorities, set out a bold vision: turning the flood-prone valley into a city park surrounded by flood resilient urban development. PO-RALG asked CDR and NORPLAN to turn this vision into a feasible, bankable and buildable project, in coordination with the new Jangwani Bridge.
CDR’s approach and contribution
CDR led the joint venture with NORPLAN Tanzania, supported by Deltares for hydraulic and morphodynamic modelling and DASUDA for urban design and landscaping. CDR was responsible for the river system analysis, vulnerability mapping, identification of solutions, technical feasibility, cost estimates and detailed design.
The study started with socio-economic, topographic, geotechnical and soil quality surveys, a strategic environmental and social assessment, and a census of affected households for the resettlement action and livelihood restoration plan. Flood and sediment models were used to design a new river profile with floodplains, bank protection and sediment traps.
The key idea is to reuse the material dredged from the river and floodplains to build raised terraces. The cut and fill were balanced, with around 3.3 million m³ of fill for park and urban terraces. An integrated spatial plan tested the quality and capacity of the new urban areas, and a cost-benefit analysis assessed the economic feasibility.
In later stages, CDR prepared detailed designs, bills of quantities, bidding documents and ESIAs for the works packages, including earthworks and bank protection, the city park and infrastructure, supported by stakeholder engagement throughout.
Result
The design transforms the valley into a green lung of about 200 hectares, with room for the river, wetlands, urban agriculture, a city park and 22.5 hectares of mangroves. Around it, 84 hectares of raised urban terraces offer space for nearly 2,900 affordable and social housing units. Flood simulations confirm that the urban terraces stay dry during a 1 in 100 year flood under worst case 2050 climate conditions.
PO-RALG received a complete package ready for implementation under the World Bank supported Msimbazi Basin Development Project.
