Hill-slopes can have considerable development potential because of the views and attractive setting they provide. Historically, construction on hill-slopes had been conceived on short-term benefits with the rights of the individual prevailing. However, there are rising community expectations concerning the maintenance of visual values, natural habitat and biodiversity around urban and growth centres. Hill-slopes are often prone to hazards such as soil erosion and landslide as is evident from past incidences, resulting in loss of lives and property. Development in these areas can compound such hazards and render them highly visible and costly to deal with. There is, therefore, a need to better manage and control construction activities on hills to reduce environmental impacts and to reduce loss of lives and property. Future management decisions on hill-slope development should also be based on the principle of sustainable development because of the unique values associated with them, which makes them a natural resource in their own right. In this context, sustainable development means that resources should be used in ways that do not jeopardize future use of the resource. Strategic planning, which recognizes visual, conservation and recreational values, can provide clearer directions for future uses and management.
Environmental Impacts
The major adverse environmental impacts of hill-slope development are:
Slope erosion- Site clearing during earthworks result in the removal of vegetation and the creation of cleared surfaces, which become vulnerable to the erosive action of rain and surface runoff. Erosion on exposed slopes starts with rain splash leading to sheet, rill and gully erosion creating badlands if the site is left exposed for too long or abandoned altogether. Cuts and fills change the slope angle, often creating steeper slopes. The steeper the slope, the faster the surface runoff flows and the more force it will have to remove material down-slope.
Slope stability- Landforms are the product of the local balance between weathering, erosion and deposition and are continuously evolving. Natural slopes that have been stable for years may suddenly fail because of development activities on hills. Changes to the terrain and hydrology through construction or earthworks may cause erosion, which create conditions conducive to mass movement if exposed surfaces are not protected within a short period. Exposed rocks will be weathered at a faster rate and the weathered material is susceptible to movement especially when saturated with water. Over cutting of slope or over steepening of the slope gradient can induce instability. Slope cutting changes the slope topography and releases residual horizontal stresses and cause expansion of the slope. Joints or weak zones may be exposed along which sliding may occur. Placement of fill will also lead to increase in shear stresses acting on slopes and may lead to slope failure. Drainage patterns of an existing terrain may be altered as a result of construction. The change in groundwater flow patterns may cause changes detrimental to the stability of the newly constructed slopes of the existing in-situ slopes that were stable prior to construction.
Landscape impacts- The impact on landscape is the direct physical change to existing landscape features such as vegetation, topographical, geomorphological features and recreational facilities as well as buildings and structures. Visual impact is a change to the appearance of the landscape and the subsequent effect on the views of groups of people at particularly sensitive viewpoints. Visual impact can vary from overall improvement to degradation. Construction on hills will bring about a change in the landscape and will thus have a visual impact on landscape quality.
However, all is not doom and gloom, the solution to most of the environmental problems lie in our hands. If only every Sierra Leonean can opt to plant at least one tree on the hill-slopes, we will be sure of preventing major environmental problems. Finally, environmental problem anywhere is an environmental problem everywhere. Environmental problems do not obey physical geographic boundries.
Environmental Impacts
The major adverse environmental impacts of hill-slope development are:
Slope erosion- Site clearing during earthworks result in the removal of vegetation and the creation of cleared surfaces, which become vulnerable to the erosive action of rain and surface runoff. Erosion on exposed slopes starts with rain splash leading to sheet, rill and gully erosion creating badlands if the site is left exposed for too long or abandoned altogether. Cuts and fills change the slope angle, often creating steeper slopes. The steeper the slope, the faster the surface runoff flows and the more force it will have to remove material down-slope.
Slope stability- Landforms are the product of the local balance between weathering, erosion and deposition and are continuously evolving. Natural slopes that have been stable for years may suddenly fail because of development activities on hills. Changes to the terrain and hydrology through construction or earthworks may cause erosion, which create conditions conducive to mass movement if exposed surfaces are not protected within a short period. Exposed rocks will be weathered at a faster rate and the weathered material is susceptible to movement especially when saturated with water. Over cutting of slope or over steepening of the slope gradient can induce instability. Slope cutting changes the slope topography and releases residual horizontal stresses and cause expansion of the slope. Joints or weak zones may be exposed along which sliding may occur. Placement of fill will also lead to increase in shear stresses acting on slopes and may lead to slope failure. Drainage patterns of an existing terrain may be altered as a result of construction. The change in groundwater flow patterns may cause changes detrimental to the stability of the newly constructed slopes of the existing in-situ slopes that were stable prior to construction.
Landscape impacts- The impact on landscape is the direct physical change to existing landscape features such as vegetation, topographical, geomorphological features and recreational facilities as well as buildings and structures. Visual impact is a change to the appearance of the landscape and the subsequent effect on the views of groups of people at particularly sensitive viewpoints. Visual impact can vary from overall improvement to degradation. Construction on hills will bring about a change in the landscape and will thus have a visual impact on landscape quality.
However, all is not doom and gloom, the solution to most of the environmental problems lie in our hands. If only every Sierra Leonean can opt to plant at least one tree on the hill-slopes, we will be sure of preventing major environmental problems. Finally, environmental problem anywhere is an environmental problem everywhere. Environmental problems do not obey physical geographic boundries.
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