GOVERNMENT OF THE REPUBLIC OF GHANA

MINISTRY OF WORKS AND HOUSING

  KLERP - Korle Lagoon Ecological Restoration Project

Introduction

1.1 Overview

The flooding, sewage, siltation and solid waste pollution problems seen in Accra and specifically around and in the Korle Lagoon have been reported for decades as the drains of Accra have been used as open sewers and convenient disposal points for all solid and liquid waste, due to a highly inadequate sewerage and garbage collection service. The low levels of dissolved oxygen do not facilitate the complete breakdown of organic waste entering the Lagoon. The stench and visual pollution associated with this is evident in the entire area.

The objective of the project is to restore the Korle Lagoon, as far as possible, to its former state in which marine life was abundant and offered substantial improvements to the drainage systems in Accra by way of ensuring efficient floodwater conveyance to the sea. These improvements will lead to an increased health, reduced poverty and a general increase in the quality of life for the people of Accra.

1.2. Background

IMDC was selected as the consultants to do the design, tender documentation and site supervision. The successful contractor is a joint venture between Dredging International and Gulf Dredging. The Quantity Surveyors is Antwi - Donkor, Krakue and Partners from Ghana are also the Clients representative.

During the first stage (2000 to 2002), the lagoons were cleared of the mangrove swamps in the flood water flow path. The first stage also included the dredging of the Lagoon to a suitable depth, disposal of material, landscaping and soil protection. The mountainous dumps of domestic waste were sealed by capping with clay (obtained from the dredged material) and top soiled, with a final covering of grass. The Odaw river (now Korle canal), Kaneshie and Agbogbloshie canals were re- aligned, excavated and earth dyke side walls were constructed with slope protection where appropriate.

1.3  Project Details- Stage 2

The proposed solution for the second stage is to intercept and divert all dry weather flow into the lagoon. This waste water will be pre-treated and pumped offshore via a proposed new sea outfall pipe.

An initial offshore investigation was done (early 2003) to determine the parameters for the sea outfall line. A further offshore soil investigation is programmed for the end of 2003 to determine the geotechnical conditions of the sea bed. A  re-design of the Interceptor and Pump Station was done during the middle of 2003. This re-design proposed a shorter 75m ( previous 140m) long flapgate Interceptor. The redesigned flap gate interceptor allows for low level evacuation of the flood waters and the retention of downstream lagoon waters. The Flap gates will open at a water level difference of 100mm above tide level (previous weir +1.2m) which will allow for early and low level flood evacuation resulting in lower upstream inundation levels. This will also allow for flushing of siltation towards the ocean during flood conditions. The Interceptor height could be increased from +1.2 to + 1.7m NLD with an improved retention height for the lagoon waters resulting in less frequent backwater overtopping of lagoon water into the canal system during the high spring tides.  A single screw 2m³/sec Pump (previously 1.2 m³/sec)  with 2 sets of screens (50mm coarse and 6mm fine), a settling basin and oil skimmer were also introduced. The Screw Pump system together with the stepped screens is a more reliable option which requires less maintenance thus resulting in reduced maintenance costs. This waste water will be screened down to 6mm and pumped to a sufficient height to allow for a gravitational offshore drainage via a 1.4 km landline of 1.2m Dia. which will connect to the same diameter 850m sea outfall pipe.

KLERP Vital Statistics

General Description: Marine, Drainage & Landscaping Works

Location: Korle Gonno - Accra, Ghana

Contract Value: $ 89,52 Million

Contract Duration: 20 months for each of 2 stages

Donors: KUWAIT Fund; BADEA; OPEC Fund

Technical

Site Area: 150 Ha (excluding Sodom & Gomorra:33 Ha)

Area of Lower Lagoon: 13.1 Ha

Area of Upper Lagoon: 5.9 Ha (excluding Mangrove Island: 3.9 Ha)

Total area of Lagoon: 19 Ha

Length of Upstream Canals: 2.5 Km

Contract Quantities Stage 1

            Dredged:                    600 000 m³

            Canal Excavation:      300 000 m³

            Soil Replacement:      500 000 m³ (250 000 m³ Excavation/ 250 000 m³ Fill)

            Dike Construction:      50 000 m³

Material re-handled:   150 000 m³

            Total:                            1 600 000 m³

            Surface Protection (Rip-rap & Gabions): 40 000 m²

            Landscaping: 70 Ha (19.1 Ha reclaimed).

            Grassing: 34 000m²

Stage 2 Works:

Korle Interceptor weir dimensions: 75m long x 8.1m wide base x 4.1m high,        Concrete  900 m³  ,20- 3m x 3.4m steel flap gates. Steel sheetpiles 162 ton.

Korle Pump Station and Settling Tanks capacity: 2 m³/sec 3m Ø X 20m long Archimedes screw with electric motor- 355kW, 2 electrical Step Screens & 280 m³  Settling tank with flushing.         Concrete 1010 m³

Landline dimensions; Ø 1.2m x 1.4 Km-   PE pipe

Outfall Characteristics:  Capacity: 2m³/sec. Diffuser -1mm openings

                                           Dimensions: Ø x 1.2m x 0.85 Km- PE Pipe

                                           Design Life: 30 years

Key Dates

Cleint

  Consultant

Contractor

Sub- Contractor

Photos