Impacts of sand mining on shared perennial rivers and ephemeral watercourses in Namibia
Silvanus Kweenda Uunona(1)
(1) MINISTRY OF AGRICULTURE, WATER AND FORESTRY, PRIVATE BAG 13193, WINDHOEK, 9000, Namibia
Sand mining is one of the main threats to the rich biodiversity supported in Namibian wetlands particularly alongside our perennial rivers and ephemeral watercourses. This process can destroy riverine vegetation, cause erosion, pollute water sources and reduce the diversity of animals supported by these woodlands habitats.
An earlier study by an IRBM intern has identified that the lower Okavango River in Namibian has good potential to be considered for designation as a Ramsar Site (Kavari 2006). Yet, according to Mendelsohn & el Obeid (2001) about 49% of the riverine vegetation alongside the Okavango River in Namibia was cleared between 1972 and 1996 mainly for cultivation. In the same period the human population increased by 5% per year (Mendelsohn & el Obeid, 2003). The vegetation along these riverbanks is further threatened by unsustainable sand mining to supply building sand needed for the development of this rapidly expanding population, particularly around the urban centres such as Rundu and Divundu. This study focuses on the potential threat of ever-increasing sand mining activities to provide sand to the construction industry, not only alongside the Okavango River, but also along ephemeral, seasonal and perennial rivers throughout the country.
Sand mining is a type of opencast mining that provides material for the construction sector in Namibia. Alluvial sand from riverbeds is the most used sand and has been illegally mined in the ephemeral rivers and river banks throughout the country although the new Forestry Act expressly prohibits any disturbance of vegetation within 100 m of any watercourse (Forestry Amendment Act, 2005). Furthermore, the process of sand mining has accelerated environmental degradation to an alarming rate in many areas. According to Kaangu (2005), sand mining was the main activity he observed on many occasions being done on a large scale in the ephemeral Klein Windhoek River, in the central part of Namibia. The sand needs to be exploited to satisfy human demands but this requires efficient and effective resource management to ensure economically and environmentally sustainable utilization (Youba, et al., 2002). This study will provide baseline information for a concerted effort by policy makers, sand contractors, engineers, and local residents to find a solution to the threatening crisis.
Many species of trees and shrubs in dry riverbeds are supported by groundwater retained by the river sand in these alluvial aquifers at varying depths, e.g. Acacia erioloba, Salvadora persica, Faidhelbia albida,& Combretum imberbe. Therefore the extraction of sand from the riverbed may affect their survival and recruitment ability (Nair, 2005). Dust caused by trucks can impede the photosynthesis of plants by blocking the leaves’ stoma (Muller, 2005). Sand mining may have an adverse affect on biodiversity as loss of habitat caused by sand mining will affect burrowing animals and insects, as well as plants, and to a lesser extent larger mammals and reptiles because they can easily migrate to uninterrupted places (Muller, 2005). As sand mining destabilises soil structure, river banks and often leaves isolated islands of trees, subsequent flow will erode this banks and islands further. Sand mining activities alongside rivers and in floodplains involves removal of top soil, and vegetation cover. This also contributes to future soil erosion.
Soil contamination is mainly caused by oil spills by trucks and machinery used to extract sand. Even though the area of contamination would be localised, the presence of any hydrocarbons on the ground is undesirable and can lead to surface and ground water pollution (Gillian, 1999). After the rain, contamination may subsequently spread over larger areas. Thus sand mining not only causes serious disturbance to soil, severe soil erosion, loss of topsoil and removal of top cover but can indirectly cause soil and water pollution too. It is feared that the operation may invoke profound ecological changes that could affect the entire ecosystem and change the landscape of an area (Nair, 2005).
This study concentrates on both the positive and negative impacts of sand mining. Positive in terms of financial gain and provision of building material and negative in terms of environmental impacts on ephemeral, seasonal and perennial wetlands. This study aimed to determine the main factors that hinder more sustainable management and to identify challenges in the development of a national sand mining policy and its effective implementation. This project forms part of a broader initiative by the Department of Water Affairs to assess the impacts of sand mining and develop a National Policy that will prevent further environmental degradation to our ephemeral, seasonal and perennial wetlands.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,