Land erosion on a global scale is increasingly annually, whether it is caused by rising sea levels or adverse weather conditions the results are the same, loss of land and subsequent infrastructure attached to that land. It is apparent that urban and rural areas are both affected and once the land is lost it is virtually impossible to replace.
This proposal shall deal solely with Nigeria and the unique circumstances which arise in preventing land erosion within a Nigerian parameter, paying particular attention to riverbank collapse, scouring and wash out effects. Gabion Basket used as Retaining Wall.
AREAS OF RISK
There has always been erosion of land it is a natural and ongoing process which if left unchecked can pose a serious threat to the infrastructure, agriculture and communities of susceptible areas, when this threat arises it is then preventative action that is the only serious option.
Much of Nigeria is crossed by waterways, for generations these have been areas of habitation ranging from rural communities to major towns. Of late we have seen an increase in river bank erosion especially evident in steep sided embankments where in some cases buildings are now under threat. A major cause for this is usually the wash from river traffic or an increase in water flow coming down river, either way the outcome is the same, a collapse of river bank and subsequent loss of any habitation or infrastructure in the immediate vicinity.
Water courses are another cause of erosion, after clearance operations have been completed the vegetation is no longer in place to bind the light top soil or sand in place, this causes a washing away of the lighter top soils during prolonged exposure to heavy rains. Any subsequent buildings or road works constructed on top of these areas suffer severe scouring as the supporting materials is washed out to leave a void. Left unchecked the damage deteriorates requiring a major civil project to begin repair work.
The main methods of erosion prevention can take up two main categories sacrificial or permanent works.
Sacrificial works are normally a temporary solution requiring regular maintenance for upkeep and tend to be used on less critical sites or for economic reasons, they can include sandbagging, beach replenishment, netting , light amour or a combination of techniques to achieve the necessary result, they can be effective but are not an ideal solution and generally are at best used for stop gap purposes only.
Permanent works generally involve a large civil project after major studies to determine the most effective method to prevent erosion over an extended period of time, this can include defending major roadways, and infrastructure, or protecting areas potential construction pilling, rock amour, buttressing are a few of many methods used as a permanent solution to land erosion. As mentioned under the opening foreword heading this proposal will deal with effective solutions within the parameters of Nigeria. While permanent works are necessary to protect areas of importance environmental or commercial they can also incur huge expense, a balance between an effective erosion prevention program which will benefit the environment, infrastructure and communities at risk set within an achievable financial framework is the ultimate aim of this proposal.
Gabion Baskets have a proven track record in combating land erosion; they offer a permanent solution to land erosion problems. There versatility allows them to be used in a wide range of environments in most cases requiring the minimum of back up plant making them ideal as a method of protection for areas of difficult access or remote locations.
Gabions within the Context of Nigeria
The benefits of a land erosion project utilizing Gabions would quickly become apparent. An immediate impact would be an employment program using local community workforces in the assembling and construction of the baskets within the project areas. The communities involved in these projects will benefit by having their environment improved and stabilized, also they will receive an economic boost created by the employment such a program will create. In effect helping local communities help themselves.
In areas of particularly bad erosion or frequent collapse, a constant program of repairs may be required, this would require a storage or depot point to be maintained, alternatively, a small manufacturing plant would be set up to cater for the large number of basket needed.
If localized material is not available or unsuitable to be used as basket, infill it may be necessary to set up a transportation service to supply quarried or naturally occurring stone to the work site.
An established method of shipping large quantities of stone is by barge, in areas requiring a constant maintenance program it may be feasible to establish a centralized storage areas for stone infill a riverside location would be preferable allowing barge access and so a constant supply of materials.
Apart from erosion prevention, Gabions can be used for a variety of other construction projects. They are ideal for jetty construction, flood defenses, bund or containment purposes, within Nigeria, they could be incorporated into a number of land reclamation projects as a viable alternative to sheet piled walls.
Within Nigeria, there is now a huge land reclamation program in place involving swamp reclamation and associated areas. There must also be an emphasis on protecting the land which is already in place. To reclaim 5 acres of swamp only to loss 5 acres through erosion does not make any environmental, economic or practical sense. The methods of erosion prevention we have put forward in this proposal have intentionally include a large participation from the communities whose land is currently affected by erosion. Community relations coupled within a training and employment program is always high on our agenda.
We would envisage forming a strong working relationship with the various State Government or Development Corporation departments whose brief covers erosion and reclamation. Rhino in co ordination with our Nigerian cover a wide range of marine and environmental services which if required could be incorporated into the current push for infrastructure construction and environmental cleanup currently underway in Nigeria both in the public and private sectors.
Working with Enviromesh our Uk Partner, we can design and install shore protection, erosion prevention measures and mass. Bringing into use the latest techniques and design features Rhino offer and innovative approach to combat the serious issue of shore and land erosion.