Geomorphological assessment for city of Dar Es Salaam, Tanzania

Location: Dar es Salaam, Tanzania.
Client: World Bank

We worked with the World Bank to carry out an investigation of the geomorphological processes operating in the Dar es Salaam region to consider sediment sources and pathways, and the influence of sediment on flood related issues. We were commissioned by the World Bank in 2018 to undertake this study with the support of UKAID.

Challenge

The river basins within Dar es Salaam currently suffer from an in-balance of sediment. This means that more sediment enters each river system than leaves. This is predominantly as a result of vegetation clearance over many years, rapid urbanisation and a lack of sediment control practices during construction.

If no action is taken, the risk and rate of erosion and soil loss will continue to increase as urban development intensifies. This means that the severity of flood events, made worse by excess sedimentation within the lower urban river basins, will increase. This will cause harm to people and infrastructure. In addition, the rapid rate of sediment delivery has led to dredging, which in the long term is unsustainable and damaging to the environment, especially if it is not undertaken in a managed way.

Solution

Geomorphological assessent, Dar es SalaamThe existing sedimentation problems will continue until long term solutions are implemented and established to reduce sediment entering the river. In this study, we worked closely with the World Bank and local stakeholders to identify long-term, adaptable and sustainable nature based solutions which could be implemented. This included calculating sediment transport rates and identifying key areas within the region susceptible to erosion. Our analysis demonstrated that significant volumes of sediment reach the lower river basins each year.

We made recommendations for long term sustainable solutions including:

  • re-forestation
  • changes to current land management practices
  • promoting the use of better construction site sediment management
  • building gully dams in the upper catchment
  • promoting sustainable urban drainage.

Benefit

Using engagement, citizen science and the delivery of new scientific information, this study has provided new insight into the source of sedimentation in all river basins within Dar es Salam. A future sustainable delivery plan has been developed to tackle the sediment problem for all levels of society to undertake, from government to local communities.

Want to know more?

 Email Matt Hemsworth for more information about this geomorphological assessment project for Dar es Salaam. Discover more of our projects on our International Development webpage.



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