photo: Carlos Andrés Lopez Franco
By Nathalie Jean-Baptiste and Stéphanie Lacombe
Dar es Salaam is known for experiencing flooding during the rainy season. During rainfalls, the water is not well evacuated and has an impact on the infrastructure (e.g. bridges, roads and buildings). The existing storm water drainage system is insufficient, underserviced and cannot cope with new constructions rising in planned and unplanned areas. The 2010 Dar es Salaam Infrastructure Development Program considered the rehabilitation and construction of a 228 km storm water drainage across its then three municipalities (Ilala, Kinondoni and Temeke) a priority. The project was estimated to cost $ 67million USD.
At a microscale, the current drainage system of the Ardhi University campus may provide some insight on the multiple challenges and opportunities for designing, planning and maintaining storm water drainage systems in Dar es Salaam. The campus is located on an observation hill bordering the Tanzanian military ground and comprises several building blocks connected through pathways made of concrete slabs. The grounds has been largely landscaped by alternating sealed surfaces and porous grounds with grass, shrubs and trees to form a well-balanced green campus with large open areas.
photo: Stéphanie Lacombe
The drainage system comprises small canals connected with larger drainage channels following the natural inclination of the ground. In some parts, one can observe that the canals follow the topography and natural downstream path of the land towards the Indian Ocean. In addition, some drainage canals are designed and incorporated to building’s architecture, which suggests that a more holistic approach was taken to protect the buildings and the environment from heavy rainfalls.
As the Ardhi campus continues to grow and new buildings are being constructed, so as the amount of surface runoffs. Hence, today’s drainage system is less adequate due to reduced vegetation and less porous surfaces as well as lack of maintenance in some drainage channels. A transect walk across the campus as well as observations of the different use and functions of the current drainage system reveals the following challenges and opportunities:
- Lack of and/or limited maintenance at the lower part of the campus with solid and green waste clogging the existing drainage
- Limited rain water catchment, less capacity to retain and collect rainwater. Urban storm water runoff is the leading contributor of water pollution
- Seepage of pollutant through the soil as the water from the channels is used for domestic use (washing clothes and cleaning)
- Manpower and willingness to collect water for everyday use. A proper rainwater harvesting system would ensure the accumulation of water for reduce on site and reduce the amount of run-off
- Considering green spaces and the green infrastructure (seen as a planned network of quality green spaces) as a necessity for flood reduction and not an amenity.
- Revitalizing the available natural landscape with the adequate vegetation, handling eroding peat moorland and maintaining the existing drainage holds long term social and environment benefits
photo: Stéphanie Lacombe