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In March 2008, February 2009 and April 2011 heavy floods occurred  in northern Namibia. Especially the town of Oshakati was severely affected. Oshakati is the second largest town of Namibia and an important commercial, industrial and administrative center.

A consortium of four companies (BAR, IMDC, Grontmij and Tractebel Engineering) was assigned to design, tender and supervise the flood protection measures. IMDC is responsible for the hydrodynamic modeling and the hydraulic design of these measures, the supervision of the geotechnical design and cost calculations and the interaction with the EIA team.

The Oshakati Flood Protection measures consist of:

  • The construction of a dike, 23 km long and 1.5 to 3.0m high.
  • The excavation of new connections between the existing oshana‘s, i.e. ephemeral rivers conveying water during the rainy season.
  • The construction of 4 new bridges across the new connections.
  • The construction of a sluice enabling a controlled entry of water into Oshakati.
  • The construction of 11 harvesting basins for water storage, that can be used for agricultural purposes.
  • The construction of a new siphon, 1000m long, for the NAMWater canal, securing the supply to the drinking water processing plant.

A quasi-2D hydroynamic model was built as main tool for the hydraulic design. This hydrodynamic model takes into account the rainfall over the entire catchment (which is mostly situated in Angola) to calculate discharges, water levels and flood contours. Rainfall data were taken from worldwide satellite measurements processed by the Climate Prediction Center of the National Oceanic and Atmospheric Administration of the USA.

The model was calibrated based on SPOT satellite images of flood contours and on water levels measured by the Ministry of Agriculture, Water and Forestry of Namibia.

As a result of the flood protection measures a total area of 50 km2 will be flooding free and available for the future development of the town of Oshakati.

As for every large project communication with the client, the partners as well as with the different stakeholders is very important.

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