Environmental research

Gabions are wire fabric containers, uniformly partitioned, of variable Size, interconnected with other similar containers and filled with stone at the site of use, to form flexible , permeable, monolithic structures such as retaining walls, sea walls, channel lining, revetments and weirs for earth retention. Gabions baskets are wire mesh baskets filled with cobbles or crushed rocks. They are often filled with locally available materials and therefore have a relatively low capital cost. Because they are flexible and porous they can absorb some wave and wind energy, thereby reducing the scour problems associated with impermeable sea defenses such as concrete seawalls. Gabions can be placed as sloping mattresses or as near vertical cubic baskets. They provide a short term alternative to rock armor structures in areas where large rocks are not available. Gabion structures yield to earth movement but maintain full efficiency and remain structurally sound. Highly permeable, the gabion structure act as self draining units which bleed off ground water, relieving hydrostatic heads. Gabion revetments work better when gabion groins are also constructed at regular intervals to trap the sediment transported in the littoral zone. The workshop activities will include both theoretical and practical field works. The theoretical aspect will include power point presentation- lectures on coastal dynamics, hazards (coastal erosion and flooding) and mitigation measures. In addition, documents related to coastal Erosion and climate change in Liberia coastal areas will be presented and reviewed. The use of equipment such as GPS, maps, and diagrams will be presented. The practical field works will include the collection of oceanographic data ( wave, current, beach profiles, etc.). A 25 meters site will be prepared for demonstration purposes. A small gabion structure will be designed and built by the trainees. There will be careful hand packing of gabion materials, lacing up of individual panels and placement shape. Trainees will use hands to handle rocks and other materials for the establishment of foundation layers of gabion basket. Demonstration will also include regular maintenance of gabions. Method of maintenance of severely damaged baskets to be refilled and closed with new mesh panels will be demonstrated. This will include how replacement mesh should be laid over the entire structure if abrasion or corrosion is wide spread. The maintenance aspect of the training is necessary since under expose conditions a maximum life of 10 years is anticipated, after which time a replacement structure may be required. These experiences will be passed on to the local people so that when the project is accepted, maintenance will also be part of the training. It is estimated that ten (10) CEDA specialists in Liberia will be trained to serve as trainers upon the completion of the training. These trainees will in turn train local people the very technology of constructing gabion baskets, gabion revetments, etc. In order to complete both the theoretical and practical field works, a ten-day workshop has been proposed to successfully complete the entire exercise.

Liberia