INTRODUCTION Mining in many countries continues to be a widespread and most important economic activity today
Mining in many countries continues to be a widespread and most important economic activity today. (Walsh et al. 2017). This is more so in most of the developing countries, (Ayree, 2001). The need for land development and urbanization has led to an increase in river sand mining activities. During the construction of roads and buildings sand and gravel have been used as aggregated source needed for construction. Rapid development in recent years, has led to an increased demand for river sand that is used as a source for construction materials. This is so because the mining activities have a remarkable potential for employment, distribution, economic and social development of both local and national scale. (Tianen et al, 2014). The increase in demand for sand for construction purposes has an enormous pressure on the environment. According to Kondolf et al, 2008.
Some disturbances that occur are from the methods used in mining and machines used. The extraction of sand from rivers, streams, flood plains has conflict with the manner the riverine ecosystem function. (Kori et al, 2012). The sand mining activities have various problems that include river bank erosion, river buffer zone encroachment, river bed degradation and deterioration of river water quality. The excessive removal of the sand may distort the natural equilibrium of a river system significantly. Investigating the river on the sand mining capacity further is very important as it helps come up with recommendations for long-term management of sand mining activities.
The extraction of sand as a free resource has an impact on the costs and income of economic sectors and also the local livelihoods, (Kondolf, 1997). There have been a construction boom in rural and urban areas, so rivers around greater Gaborone virtually have no river sand, this development has led to sand miners to source river sand from as far as Mahalapye.( The voice, 2016). Both the positive and negative impacts of river sand mining were examined in the study conducted at Mahalapye River.. Qualitative and quantitative research designs were carried out and used to collect data from selected sampled points.
Environmental aspects of man in mining areas have been impacted by sand mining activities. However, people now resorted to the trade of sand to earn themselves a living. In the past, since the sand mining has economic gains, the lands within the domain of leaders were sold to miners, so that people can derive their livelihoods from sand mining to ensure their survival and this was done from the natural resources available and accessible to them.
Sand is normally used for all kinds of projects for example the construction of artificial islands, land reclamation these projects have economic and social value, moreover environmental problems can be brought about by sand mining. (Ashraf et al, 2013). When the rate of extraction of sand exceeds the rate at which natural processes generate the material, environmental problems occur. (Mattamana et al, 2013). Throughout the world mining of natural aggregates such as sand serves are used as the main source of construction. However, operations of sand mining are disruptive to the environment whether small-or-large-scale. (Musa, 2009).
The environment and mine cannot be protected at the same time as the two variables are not mutually exclusive argues as suggested by Chapman et al. Despite the significance of the extraction of sand and gravel from river mines in most developing nations, the points of interest of its financial, natural, and social geology are not completely clear. The proper evaluation of environmental impacts is often a hard task in light of the fact that the impacts appear after a long period of time. The fundamental issue is the need to reinforce a holistic approach for planning and managing these resources. The continued illegal extraction of sand in most river systems aggravates the situation. As a result, it is important to increase public knowledge and control the extraction of the sand and gravel.
This research aims at presenting effective mechanisms to control sand extraction in order to conserve the local communities; the main objectives are determination and evaluation of environmental impacts of sand mining, evaluation of environmental impacts of sand mining. There is also ensuring that sand mining is carried out in a sustainable way, and finally avoiding pollution which can lead to water quality deterioration. The river is to be ensured that is protected from bank and bed erosion beyond its stable profile.
Instream mining will produce other costly effects beyond the immediate mine sites. Several hectares of fertile streamside land are lost annually, further as valuable timber resources and wildlife habitats within the bank areas. Degraded stream habitats result in loss of fisheries productivity, diversity, and recreational potential. Severely degraded channels might lower land and aesthetic values.
All species need specific surroundings conditions to ensure long-term survival. Native species in streams are unambiguously adapted to the surroundings conditions that existed before humans began large-scale alterations. These have caused major environment disruptions that favored some species over others and caused overall declines in biological diversity and productivity. In most streams and rivers, environment quality is strongly connected to the stability of channel bed and banks. Unstable stream channels are inhospitable to most aquatic species.
Factors that increase or decrease sediment supply usually destabilize bed and banks and lead to dramatic channel readjustments. for instance, human activities that accelerate stream bank erosion, like riparian forest clearing or instream mining, cause stream banks to become net sources of sediment that usually have severe consequences for aquatic species. Anthropogenic activities that artificially lower stream bed elevation cause bed instabilities that lead to a net release of sediment within the native vicinity. Unstable sediments simplify and, therefore, degrade stream habitats for several aquatic species. Few species have the benefit of these effects.
The most vital effects of instream sand mining on aquatic habitats are bed degradation and alluviation, which might have substantial negative effects on aquatic life. The steadiness of sand-bed and gravel-bed streams depends on a fragile balance between streamflow, sediment supplied from the watershed, and channel form. Mining-induced changes in sediment provide and channel form disrupt channel and surroundings development processes. Moreover, movement of unstable substrates ends up in downstream deposit of habitats. The affected distance depends on the intensity of mining, particles sizes, stream flows, and channel morphology.
The complete removal of vegetation and destruction of the profile destroys habitat each above and below the bottom as well as among the aquatic ecosystem, leading to the reduction in faunal populations.
Channel widening causes shallowing of the bed, producing braided flow or subsurface intergravel flow in riffle areas, clogging movement of fishes between pools. Channel reaches become more uniformly shallow as deep pools fill with grave.
Because of human activities, rivers all over the globe are under pressure and therefore the excessive sand mining is an activity that threatens rivers system. (Kondolf, 1997; Rovira et al., 2005). Due to excessive mining done in the rivers channel erosion below dams is often by a modification in particle size on the bed, as gravels and finer materials are winnowed from the bed and transported downstream, leaving an armor layer, a coarse lag deposit of enormous gravel, cobbles, or boulders. Development of an armor layer is an adjustment by the river to modified conditions as a result of the larger particles is less easily mobilized by the hungry water flows below the dam. (Kondolf, 1997). In the last decades, the environmental impacts of sand mining have been understood and scrutinized. (Sreebha et al Padmalal, 2008).
Rivers all over the globe are under huge pressure due to numerous kinds of anthropogenic activities, among which indiscriminate extraction of sand and gravel is most disastrous, because the activity threatens the very existence of stream ecosystems. (Kondolf 1994; Rovira et al 2005; Lu et al 2007). Due to rapid industrialization, urbanization and associated developments, the rivers are widely exploited for river bed materials like sand and gravel. The need for sand and gravel is rising exponentially throughout the past few decades to satisfy its ever-increasing demand in the construction sector. The quick pace of economic developments, rise in foreign remittances and liberalized housing schemes for building constructions, mainly from banking sector are some of the causative factors liable for intense sand mining from river beds. (Padmalal and others 2008)
Although the received information regarding sand mining in developed countries is reliable (Krausmann et al., 2009), lack of worldwide knowledge regarding the extraction of materials has caused environmental issues and helped to lack of awareness (Unep, 2014). That is why the extraction from these mines ends up in the environmental degradation in each small and large scale (Makweba and Ndonde, 1996). River sand is a non-renewable resource within the human life cycle. If its extraction equals its regeneration, the environmental effects are marginal. However excessive extraction hinders system natural operation (Sreebha and Padmalal, 2008). The destruction of public properties, the destruction of water sources, the degradation of native communities livelihood, and therefore the loss of the standard of the soil are all the results of excessive extraction (Ashraf et al., 2011; Viswanathan, 2002) and it also results in such effects as noise, dust, pollution, heavy traffic around the mine, and landscape modification (Aryee, 2001; Willis and Garrod, 1999)
More often, over-mining occurs and in return it turns to jeopardize the health of the river and the environment in general. The morphology of the riverbed can be changed by the degradation, which constitutes the aspect of the aquatic habitat. When there is rapid bed degradation the bank may be induced to collapse and also erosion which is caused by increasing the heights of banks. (Collins et al 1990). The economy of Botswana thrives principally from natural resource extraction that includes: Gold, diamond, nickel, gravel and sand that accounts for third of the country’s Gross Domestic Product. On the different hand, this has buoyed the economy greatly due to compliance and strict management of existing mining laws and correct control of mining activities by the relevant authorities in charge. In a bid to exercise its regulative powers over the activities of miners and observe of natural resource extraction, the government of Botswana enacted the Natural Policy on Natural Resources Conservation and Development in 1990 to safeguard the fragile ecosystem around mining sites. This policy created it mandatory for prospective miners to get permit from the relevant authority and must show proof of detailed technique for extraction in addition to Environmental Impact Assessment (EIA) and Environmental Management plan (EMP). The plan behind these conditions is to encourage sustainable resource extraction inside the environment by all parties concerned.
In protecting the environment sand is a very important mineral for our society, but the practice of sand mining is a very concerning issue for the environment as the demand for sand increases in industry and construction. Mining activities can be responsible for a considerable damage on the environment when the activity is carried out without proper guidelines and that can lead to the clearing of the vegetation, and soil erosion. (Ashraf et al 2011).
Vegetation has the power to reduce soil loss through absorbing the precipitation energy of raindrops and reducing runoff, decreasing flow velocities, limiting soil movement by roots and weeds, improving porosity and aggregation and decreasing soil wetness. Sand miners remove vegetation before sand extraction to create access roads into the mining areas. Pits also need massive open lands to be cleared to permit miners to extract quality aggregates. Continuous removal of vegetation exposes the land. Destruction of vegetation may be a serious issue provided that it triggers formation of gullies. (Jaramillo, 2007), Borges et al., 2002
The processes of prospecting, extracting, concentrating, refining and transporting minerals have great potential for disrupting the natural surroundings. (Rabie et al., 1994). Many rivers have plentiful quantities of sand and gravel that are mined conveniently and economically for a spread of uses. Usually the conditions imposed on the approval for sand mining activities are expressed in administrative terms, without technical consideration of their potential impact on the ecosystem. Physical impacts of sand mining include reduction of water quality and destabilization of the stream bed and banks. Mining may also disrupts sediment supply and channel type, which may end in a deepening of the channel (incision) as well as alluviation of habitats downstream.
Channel instability and deposit from instream mining can also damage public infrastructure (bridges, pipelines, and utility lines). Impacts to the biological resources include removal of infauna, epifauna, and a few benthic fishes and alteration of the available substrate. This method may also destroy riverine vegetation, cause erosion, pollute water sources and reduce the variety of animals supported by these woodlands habitats. (Byrnes and Hiland, 1995).