Protecting Ghana’s coastline & more

Published: July 31, 2013

Ada Coastal Erosion Problems

 

Rising sea levels are raising concern globally; driving governments and municipalities to seek expert advice on smart coastal defence solutions. Fortunately in Ghana, Tractebel Engineering’s subsidiary IMDC was present and prepared for everything; from wave modelling to groyne design and turtle protection…

S.O.S – OUR TOWN IS WASHING AWAY

Ada Foah, a coastal town in Ghana,. located along the Volta River is threatened by sea erosion.  IMDC (International Marine & Dredging Consultants) leading water and hydrology experts, is busy on a 2-phase coastal defence scheme for Ghana’s Government while creating opportunities for tourism, …  Read more

KEY STEPS TO EFFECTIVE COASTAL DEFENCE

Phase 1 of the Ada Foah Coastal Defence project began in 2010. But as is always the case working with water, specialised studies were needed to fully understand all of the conditions to be dealt with, on land and at sea… Read more

TAILOR-MADE SOLUTION

For any developing country with many pressing priorities, allocation of investment is a difficult choice. But as IMDC are proving in Ghana, that’s no reason why a sustainable solution can’t be found to meet a client’s long-term needs and budget… Discover the responsible approach to design and construction in Ghana

READ MORE:


  • Ada Coastal Erosion Problems © Jos SMits (IMDC) Ada Coastal Erosion Problems © Jos SMits (IMDC)
  • Ada Coastal Erosion Problems © Jos SMits (IMDC) Ada Coastal Erosion Problems © Jos SMits (IMDC)
  • Ada Coastal Erosion Problems © Jos SMits (IMDC) Ada Coastal Erosion Problems © Jos SMits (IMDC)
  • Ada Foah © Jos SMits (IMDC) Ada Foah © Jos SMits (IMDC)

 

S.O.S – OUR TOWN IS WASHING AWAY

Ada Foah, a coastal town in Ghana,. located along the Volta River is threatened by sea erosion.  IMDC (International Marine & Dredging Consultants) leading water and hydrology experts, is busy on a 2-phase coastal defence scheme for Ghana’s Government while creating opportunities for tourism, …

THE CURRENT ISSUE
Erosion is a major problem on the Ada Foah coastline, 100k m east of Accra and just west of the Volta River mouth. In 50 years, about 300 m of land (6 m per year) has been lost – largely due to its exposed position on the bulge of Africa which faces large waves, arriving unbroken, from the Antarctic. On the top of that there is the dramatically reduced river sand transportation by the Volta River since the construction of the Akosombo Dam in 1963. As a result the town of Ada Foah is under threat with several buildings and roads falling to erosion.

TRUSTED EXPERTISE
IMDC and Dredging International (contractor) have worked in Ghana for 16 years; constructing a wastewater interceptor and providing ongoing dredging and sanitation of Korle Lagoon in Accra. IMDC was also the engineering partner in a design and build contract for the execution of the restoration project of the Elmina Fishing Harbour and the Benya Lagoon. When the Ministry of Water Resources Works & Housing needed an answer to the Ada Foah problem, IMDC was there to support their application for a state loan – and provide the solution.

CLEAR GOALS
Today the project is well underway with the goal to prevent further erosion and encourage natural rebuilding of the beach:

  • Phase I – the critical 5 km coastline stretch running westwards from the Volta delta past the town of Ada Foah. Arrested erosion will help to create a more stable economic environment for the town and local population. Long term, the government’s plan is also to develop the area (with its long beaches and famous turtle breeding grounds) as an international tourist destination.
  • Phase II – will focus on the 10 km coastline stretch west of Ada Foah. Measurements and modelling already begun will define the number and strategic placement of groynes needed to protect a few isolated infrastructure clusters. Beach nourishment is also foreseen; building up the sand dunes to prevent sea overwash into the palm plantations behind.

  • Ada Coastal Erosion Problems Map © IMDC
  • Investigations Locations Measurement Instruments © IMDC
  • Tidal wave and current measurements © IMDC
  • Investigations Hydrodynamic Modelling 3D © IMDC
  • Investigations Dredged Channel © IMDC
  • Investigations Wave Height © IMDC
  • Investigations Locations Groynes © IMDC
  • Groyne Modelling © IMDC
  • Physical modelling © IMDC
  • Physical modelling © IMDC
  • Groyne Design © IMDC

 

KEY STEPS TO EFFECTIVE COASTAL DEFENCE

Phase 1 of the Ada Foah Coastal Defence project began in 2010. But as is always the case working with water, specialised studies were needed to fully understand all of the conditions to be dealt with, on land and at sea.

MEASUREMENT & MODELLING CAMPAIGN
Many elements influence the effect a defence solution can have on a coastline. In Ghana, a short-term estuary and tide measurement campaign and a longer, six month campaign were undertaken to establish the variations in sea states and hydraulic conditions. Supplemented by oceanographic data sets and satellite pictures of the coastline, all data was translated into numerical models, allowing IMDC to define the coastal defence solution (large rock groynes of decreasing length spaced along the coastline) and the final design through:

  • Wave modelling: The wave direction, period and heights, which are used to determine the loading forces that can be expected on each groyne structure.
  • Hydrodynamic modelling: The coastal and estuarine current flows and sediment transport
  • Morphological modelling: How the number, spacing and length of the groynes will interact with the coast and sediment flow, in order to optimise the defence system and predict what the effect would be over some years.

DESIGN & PHYSICAL MODELLING
With knowledge of all forces that would be imposed, the next step was to design the groynes in terms of size, shape and materials. Different 1:20 scale models were built in a laboratory, complete with small scale waves, to test the stability of various design options under constantly changing sea conditions. The ideal structure in this case was found to be a rock groyne of +/- 200 m long, with a 25 m wide smaller rock base (to allow filtration and prevent the structure from sinking into the sand), topped by a 10 m wide heavy armour of 2-4 ton rocks.

NEED TO KNOW? A groyne is a long, low wall-like structure that extends straight out from the beach into the sea with the aim of deflecting shore currents, slowing water flow and trapping the sea sediments (sand) needed to rebuild the shoreline. This picture shows a model of a groyne.

  • Groyne Design © James Geskiere (Tractebel Engineering) Groyne Design © James Geskiere (Tractebel Engineering)
  • Groyne finished © Jos SMits (IMDC) Groyne finished © Jos SMits (IMDC)
  • Construction of temporary jetty © Jos SMits (IMDC) Construction of temporary jetty © Jos SMits (IMDC)
  • Construction of temporary jetty © Jos SMits (IMDC) Construction of temporary jetty © Jos SMits (IMDC)
  • Construction of temporary jetty © Jos SMits (IMDC) Construction of temporary jetty © Jos SMits (IMDC)
  • Construction of Groyne © Jos SMits (IMDC) Construction of Groyne © Jos SMits (IMDC)

 

TAILOR-MADE SOLUTIONS

For any developing country with many pressing priorities, allocation of investment is a difficult choice. But as IMDC are proving in Ghana, that’s no reason why a sustainable solution can’t be found to meet a client’s long-term needs and budget…

COST EFFECTIVE DESIGN
Groynes were chosen as the most stable, lasting and low maintenance (an important future cost saving) solution. While the initial concept was to build these groynes using cast concrete shapes, a lower cost option was found using rocks from a local quarry. With 200,000 tons of rock needed (smaller rocks for the groyne base and 2 – 4 ton rocks for the armour core layer on top), using a locally sourced material and involving local contractors, is a good socio-economic solution. A bonus is that the very natural look of rock groynes don’t hinder the future tourism ambitions of the Ada Foah beach.

INNOVATIVE CONSTRUCTION
IMDC’s design, lowering the height of the groynes as much as possible, called for a a temporary jetty used as platform for the cranes to deposit the rocks. This jetty is then dismantled and moved to the next location for each groyne. Coffer walls are also erected under the jetty to prevent backwash erosion of the site excavations and potential flooding of the many km2 flat palm plantation and agricultural land beyond Ada Foah’s low beach sand dunes.

“IMDC has been involved in every aspect of this project from the planning to the scientific research; measuring and data analysis, modelling, design of structures and defining technical specifications, into feet-on-the-ground project management, always keeping our client’s interests top of mind. Our ability to tailor-make diverse and cost effective solutions is intrinsic to the value we add in working this way.” Jos Smits, CEO of IMDC

  • © Jos SMits (IMDC)
  • Turtle Leatherback Turtle Leatherback © Jos SMits (IMDC)

 

GOOD NEWS FOR TURTLE POPULATIONS

Ada Foah coastline is an important nesting site for 3 turtle species:

  • Olive Ridley turtle
  • Leatherback (the world’s largest sea turtle)
  • Green turtle

While environmental aspects don’t fall in IMDC’s scope in Ghana, the contractor still has to ensure that no nests are damaged during construction – and as Owner’s Engineer IMDC must supervise this.

Turtles lay and bury their eggs on the beach at night so each morning the site is checked for new eggs which are then moved to protected beach hatcheries and reburied in the sand where they are monitored until ready to hatch. Hatched baby turtles are then carried down to the sea and released. By playing a part in the programme to protect the eggs and baby turtles, construction works are actually contributing to an increased turtle population!


  • ANTIFER LNG Terminal ANTIFER LNG Terminal
  • ANTIFER LNG Terminal ANTIFER LNG Terminal
  • ANTIFER LNG Terminal ANTIFER LNG Terminal
  • Mundra new LNG-terminal Mundra new LNG-terminal
  • Mundra new LNG-terminal Mundra new LNG-terminal
  • Mundra new LNG-terminal Mundra new LNG-terminal

 

EXTENDED EXPERTISE FOR OFFSHORE WIND, PORTS AND LNG TERMINALS

The interest in coastal defence systems to secure and protect high-value sea-front, real-estate and quality of life in coastal towns and cities is increasing worldwide; yet the protection and stability of key installations and important infrastructure has long been a reality.

Whether designing a groyne, a breakwater for an LNG terminal or harbour, protection for nuclear installations or the underwater foundations of offshore wind turbines, the hydrodynamic studies and design knowledge required are very similar. IMDC have over 25 years of experience in this field and have lent their talents to bring value to many different projects, working alongside Tractebel Engineering in Power & Gas and Renewable Energies, as well as Smart & Sustainable Infrastructure.

IMDC Shore protection and breakwaters for LNG terminals:

To know more about IMDC, visit their website

Coastal Defence?

Ada Foah Coastal Defence project will mainly: stop erosion; restore the coastline; create a stable environment by securing the town and nearby villages; restore Ada Foah’s tourism potential.

WHO’S WHO

Key players working together to resolve Ghana’s Coastal Defence:

CLIENT
Ministry of Water Resource Works and Housing

CONSULTING ENGINEERS

IMDC (Design & Owner’s Engineer)

SUB-CONSULTANTS

Project Management International (Project Management)

CONTRACTOR

Dredging International (Construction & Execution of works)

PROJECT TIMELINE

2010 Contract awarded
Measurement Campaigns
Design Phase: groyne system

2011 Phase I construction begins (4,7 km protected coast)

2013 Phase II measurement and modelling begins
Phase I due to be completed in December

2014 Phase II construction begins (10 km protected coast)

2015 Project completes

More information

Annelies Bolle, Project Manager
Jos Smits
, CEO IMDC
Alexander Lesser, Marketing & Communications

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