Roads interact heavily with the natural environment, both during their construction and afterwards. If this is not anticipated at the planning stage, both risk coming off losers. The durability of the road will be reduced and the local environment damaged. In brief, a road changes the natural equilibrium between them. The task of the planner is to ensure both suffer as little as possible.
Water, falling, flowing or simply standing, is the road’s worst enemy. It attacks it on numerous fronts. It can quickly gouge deep channels along and across the surface, wash away the protective gravel layer, and if left standing, turn the road into an impassable swamp. For this reason, it must be prevented from getting on the road or, if it does, it must be evacuated as quickly as possible. However, measures taken to keep water off the road or to get rid of it can cause problems elsewhere. Upstream preventive measures can interfere with natural flows. Drains for evacuation concentrate and speed up flow, causing flooding and soil erosion downstream. In many cases, measures taken to protect the road will not only be harmful to the natural environment but will interfere with local patterns of water use.
Road construction can also be destructive, particularily when heavy machinery is involved. Their deployment requires a lot more space than is needed for the road and its right of way. As a result a large area is completely stripped of all cover, trees, bushes etc. In addition, areas of land in proximity to the road must be stripped of all cover, both vegetal and topsoil, to provide gravel, leaving exposed areas which are not only impossible to cultivate but may provide loci for further erosion or pits where stagnant water will accumulate.The silt-laden runoff from these deforested areas will rapidly clog up culverts and drains and accelerate the destruction of the road.
Roads can also be the agents of environmental destruction, not only because of increased traffic, but also because they open up hitherto inaccessible areas. This of course is not necessarily bad. However, the availability of transport may encourage commercial activities, highly profitable in the short run, but harmful to the environment, and in the long run to the inhabitants themselves. For example, wholesale destruction of trees to make charcoal often follows road improvement.
Mitigating measures must be incorporated at the design stage since it is far more expensive to implement them retroactively. Negative impacts at the construction stage can best be minimised by using labour-based methods and by ensuring, for example, that gravel borrow pits, once exploited, be restored and replanted. It goes without saying that comparative costing should take account of the additional mitigating costs imposed by the use of heavy equipment. The negative impacts of the road itself can best be dealt with by careful analysis of the natural and human environment, by jointly formulating mitigating measures with the residents, and by ensuring that the additional work required is included in the construction contract.
Powerpoint presentation: Environment