How can human activity affect slopes?
A slope is defined as an inclination or slant. Slopes are complex systems that include a series of inputs, processes and outputs that interact together. Slopes form and change over time due to the external natural elements such as climate or internal factors such as rock structure and permeability or due to human processes, the latter that occurs fastest and has the greatest impact on the surrounding site. There are various different types of slopes that can be identified by the angle and curvature of the landform; rectilinear slopes often have an even, relatively straight form.
Convex slopes often curve outwards whereas concave slopes slump inwards. However, exact replicas of a single slope cannot usually be found because of the varying conditions in which they form. Natural processes that affect slopes often have a minimal effect and occur over a long period of time. For instance, a scree slope can form in a matter of years whereas human management or even error, can have a profound impact on the slope itself as well as the areas surrounding it and even the smallest change in conditions can have a significant effect.
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There are several ways in which human activity can alter a slope, most of which are due to human demands and pressure on the land literally and physically. As the population continues to expand, more land will be needed for various uses and activities, whether it is for housing, farming or industrial use. The multitude of ‘needs’ that humans require are often for recreational activities such as skiing, mountain biking and hang gliding are in demand for relaxation and leisure, however, in demanding areas of land for use for recreation, land is often being abused and changed dramatically due to overuse.
An example of this is Aosta Valley in Italy, a skiing resort that has been weathered to an extreme extent and been subjected to severe debris disposal on public surfaces. The tourist attractions that are often visited by millions of people a year are being damaged and are not managed with care. Coastal areas experience problems in that buildings constructed on cliff tops increase the instability of the cliff and the risk of slope failure. The Holbeck Hall Hotel in Scarborough began descending downhill after a few sudden months of rainfall.
Another human action that influences slopes is the construction of buildings and establishments and often has a notable effect on the soil beneath. The sheer weight of the building foundations as well as the machinery needed to fabricate the buildings condenses the soil, making it more compact and denser. This in turn prevents infiltration and percolation through the soil, increasing overland flow and therefore, flooding of bodies of water. Grace Lau The vibrations produced from the machinery can also trigger slope movements, however large or small.
Also, different forms of constructions such as road cuttings and embankments can create hazardous slopes. The appropriate precautions need to be taken in order to maintain them safely. The action of gravity, precipitation and climate can cause soil creep, even on the seemingly gentlest of slopes, making them unstable. Rotational slip can be occurring, such as in the Isle of Wight where retirement bungalows are thought to be slipping and to cause a landslide eventually.
Generally, the land in certain areas are only suitable for particular uses, in farming, slope angles in conjunction with other factors can be crucial for determining the aptitude of the land in question. While steep slopes at low altitudes have a greater potential, there are limits that need to be considered, for instance, the ability for operation of heavy machinery. An example of skilful slope management is the Champagne region in France, where the slopes are assessed for their carrying capacity and the suitable number of vines are planted.
This has proved very successful in combining slopes for human uses and not provoking natural disasters. However, the erosion of soil is still an ongoing problem, especially on agricultural land when the land is not taken into consideration. Once initiated, soil erosion reinforces itself and continues and can only be stopped with human intervention. Another case of poor management of slopes is in Hong Kong, where the vast majority of the natural terrain is hilly and mountainous and slope safety is a priority.
However, in the past 50 years, landslides on man-made slopes have killed more than 470 people. Poor maintenance of slopes is a major contributory factor in many landslides in Hong Kong and prevention schemes are constantly in motion. The removal of natural vegetation on a site also contributes to hazards and disasters. The roots of plants and trees often serve as a binding agent in the soil and soft sedimentary rocks. Material is ‘anchored’ to the soil that would otherwise be easily removed, occasionally causing landslides.
Trees usually benefit the slopes, increasing coil cohesion and friction. Humans also aim to control the flow of water, and change the balance of infiltration and runoff both intentionally and unintentionally with surface paving, water channelling and other activities. However, having identified some possible human causes to disasters associated with slopes, it is rarely one action that induces accidents, it is often the accumulation of activities that cause disasters.
It is found that urban areas are more susceptible to mass movement disasters and having occurred, the repair of various articles is expensive. It is also not natural slopes alone that require management, industries producing masses of waste heaps need careful stabilisation. These artificial slopes require the necessary knowledge to prevent potentially serious hazards. In Aberfan, Wales, 147 people died, most of them children, due to the instability of a coal mine spoil heap.
Since then, Grace Lau spoil heaps have been reduced in gradient to stop the occurrence of similar events. The frequency of human-induced disasters seem to outweigh the naturally occurring accidents and therefore, better consideration of the uses and effects of slopes need to be contemplated in order to address this and end such events. But, with current successes in managing slopes, the revaluation of certain schemes and ideas are required in order to increase the number of successes.
The hazards often cause a loss of lives, property damage and countless problems and the awareness and knowledge of the danger of disasters, natural or caused by human activity, can be the best prevention of them. Hill slopes and vegetation play a critical role in defining slope stability and the removal of vegetation needs to be considered to an appropriate extent. The importance of planning in terms of human activities needs to be emphasised in order to minimise hazards.