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Korle Lagoon: design and supervision

General description of the project

The Ministry of Works & Housing of the Governmentof Ghana decided to bypass all the existing dry weather wastewater around theKorle Lagoon.

In order to reduce the flux of pollution arriving inthe Korle Lagoon and to provide the downstream section of the future wastewaterdrainage system for Accra, the dry weather flows entering the lagoon are to beintercepted by a wastewater collector system that discharges to a sea outfall.

The project consists mainly of three structures:

Theinterceptor weir.Thepumpstation with a preliminary treatment.Thesea outfall.

The Interceptor

To intercept the dry weather wastewater flows from theKorle canal, the Kaneshie - and the Agbogbloshie drain, an interceptor weir isdesigned upstreams of the upper lagoon.

The interceptor is a 77,50m long weir in reinforcedconcrete with a total height of 4,85m from top to bottom, able to hold up thehigh tide sea water level.

Twenty heavy steel flap gates with a clearance of 3,00x3,50 m each are provided in the interceptor weir to allow to pass theflood flows during the rain season conditions (open flap gates ) withoutovertopping the upstream embankments.

During the dry season the flap gates are closed andthe dry weather flows are intercepted and pumped over to the sea outfall.

To remove the flap gates for important maintenance orrepair works and to unload them onshore, a railway trolley is running on top ofthe interceptor weir.

For small maintenance each flap gate compartment can beclosed by means of stop logs in order to permit repair and maintenance works indry conditions.

Furthermore, a garage is provided onshore to store thetrolley.

Pumpstation

During the dry season a pumpstation with a max.capacity of 2m3/s will pump the dry weather wastewater to a gravitary seaoutfall pipe.

The pump station consists of:

  • A double mechanical intake screen for apreliminary wastewater treatment. Thisbar screen with a space of 50mm will be cleaned by hand
  • A screw pump with dia. 2,95 m and a length ofabout 20 m will pump up the water fromlevel 0,00m to +7,85m
  • A screw pump with dia. 2,95 m and a length ofabout 20 m will pump up the water fromlevel 0,00m to +7,85m
  • Fine screen with screw conveyor. The stainlesssteel stepscreen is built with two groups bars, one is fixed, the other isrotating. The bar spacing is 6mm
  • Sandtrap and settling tank.
  • Oil skimmer to remove the grease by hand.

The pump station is provided with a complete equippedservice building for the electrical equipments to provide the power to allow the full functionality of the station and the mechanical treatment works.

The service building also includes a control room andall necessary office and sanitary accommodations.

Sea outfall

The outfall pipe with a dia. of 1200 mmconsists of two strings with ballast weights, nominated as the Lagoon stringwith a length of 880 m and the offshore string with a length of 920 m providedwith diffusers.

The strings are jointed together by a coupling stressinhibitor.

The treated wastewater is flowing gravitary fromthe outlet of the settling tank through the outfall pipe to the sea. 

Contact us

For more information about this project, contact:
dredging@imdc.be