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Korle Lagoon: design and supervision of construction of the interceptor


 1.    General description of the project.
The Ministry of Works & Housing of the Government of Ghana decided to bypass all the existing
dry weather wastewater around the Korle Lagoon.
In order to reduce the flux of pollution arriving in the Korle Lagoon and to provide the
downstream section of the future wastewater drainage system for Accra, the dry weather flows
entering the lagoon are to be intercepted by a wastewater collector system that discharges to a
sea outfall.

The project consists mainly of three structures:

  • The interceptor weir.
  • The pumpstation with a preliminary treatment.
  • The sea outfall.

2.    The Interceptor.
To intercept the dry weather wastewater flows from the Korle canal, the Kaneshie - and the
Agbogbloshie drain, an interceptor weir is designed upstreams of the upper lagoon.
The interceptor is a 77,50m long weir in reinforced concrete with a total height of 4,85m from top
to bottom, able to hold up the high 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 the flood flows during the rain season conditions (open flap
gates ) without overtopping the upstream embankments.
During the dry season the flap gates are closed and the dry weather flows are intercepted and
pumped over to the sea outfall.
To remove the flap gates for important maintenance or repair works and to unload them
onshore, a railway trolley is running on top of the interceptor weir.
For small maintenance each flap gate compartment can be closed by means of stop logs in
order to permit repair and maintenance works in dry conditions.
Furthermore, a garage is provided onshore to store the trolley.

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

The pump station consists of:

  • A double mechanical intake screen for a preliminary wastewater treatment.  This bar screen with a space of 50mm will be cleaned by hand.
  • A screw pump with dia. 2,95 m and a length of about  20 m will pump up the water from level 0,00m to +7,85m
  • Fine screen with screw conveyor. The stainless steel stepscreen is built with two groups bars, one is fixed, the other is rotating.  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 equipped service 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 and all necessary office and sanitary accommodations.

4.    Sea outfall
The outfall pipe with a dia. of 1200 mm consists of two strings with ballast weights, nominated as the Lagoon string with a length of 880 m and the offshore string with a length of 920 m provided with diffusers.
The strings are jointed together by a coupling stress inhibitor.
The treated wastewater is flowing gravitary from the outlet of the settling tank through the outfall pipe to the sea.



Contact us

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