Defining sustainable sand mining rates through the lens of alluvial underground water loss in ephemeral rivers in Arid and Semi-Arid Lands

点击翻译按钮获取中文摘要

Defining sustainable sand mining rates through the lens of alluvial underground water loss in ephemeral rivers in Arid and Semi-Arid Lands A case study of Makueni County in KenyaAggregates are the unrecognized foundational material of our economies. They are mined the world over, accounting for the largest volume of solid material extracted globally (Peduzzi, 2014). Between 47 and 59 billion tons of material is mined every year, globally (Steinberger et al., 2010), of which sand and gravel account for both the largest share (from 68 per cent to 85 per cent). These materials are also undergoing the fastest increase in extraction rates (Steinberger et al., 2010) as a result of ever-increasing population and economic (Koehnken et al., 2020), and yet are one of the least regulated activities in many regions (UNEP, 2019).Rivers and wetland ecosystems of the world are fast degrading as a consequence of indiscriminate sand and gravel mining from river beds and related areas. The construction industry prefers sand from river beds, flood plains and from shores of the lakes which is angular in shape, a factor that promotes strength of concrete, unlike desert sands which have circular and smooth grains(Kondolf, 1997). The demand for sand and gravel from rivers has seen unprecedented growth since the 1970s(Hackney et al., 2021) and evidence of the adverse environmental effects of river sand and gravel mining are increasing annually. A study done on river Kivou in Kitui (Muiruri et al., 2020) showed that sand mining that exceeds the natural replacement rates leads to alteration of the river morphology, with adverse environmental impacts such as lowering of the water table impounded in sand reserves, stream bank instability and loss of riverine vegetation, channel erosion, river incision among others. It is observed that most of the research done has focused on perennial rivers in Asia, Americas and Europe and there is limited research on the impact of river sand mining on alluvial ground water in ephemeral rivers in ASALs in Africa. Alluvial aquifers of ephemeral rivers provide a viable alternative source of water to the low yielding and unreliable groundwater aquifers ((De Hamer et al. 2008). Additionally, the latest decadal climate predictions indicate continued warming and decreasing rainfall over North and Southern Africa leading to increased water stress in the region. River sand mining in Makueni County is carried out in ephemeral streams and rivers that are the defining characteristic of many watersheds in dry, arid and semi-arid regions, and serve a critical role in the protection and maintenance of water resources, human health, and the environment (Levick et al., 2008).To this end, the project aims to examine the intricate relationship between instream river sand mining and alluvial groundwater availability in sandy ephemeral rivers in arid and semi-arid areas.Research Questions1. What is the natural relationship between the availability of sand and that of alluvial ground water in ephemeral rivers?2. How does the relationship change when the sand is mined? 3. To what degree can instream sand mining be carried out without adversely affecting alluvial ground water in sandy ephemeral rivers ? 4. What are the potential tradeoffs between river sand mining for economic use and the ecosystem services provided by sand in ephemeral rivers?5. What key success indicators can be observed in Makueni rivers since the regulation of instream sand mining in 2015?