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

通过干旱和半干旱土地冲积地下水流失的透镜确定可持续的采砂率以肯尼亚马库埃尼县为例集料是我们经济中未被认识到的基础材料。它们在世界各地被开采，占全球开采的固体材料的最大数量(Peduzzi，2014)。全球每年开采的材料在470亿至590亿吨之间(Steinberger等人，2010年)，其中沙子和砾石所占份额最大(从68%到85%)。由于不断增长的人口和经济(Koehnken等人，2020年)，这些材料的开采率增长最快(Steinberger等人，2010年)，但却是许多地区监管最少的活动之一(UNEP，2019年)。由于不分青红皂白地从河床和相关地区开采沙子和砾石，世界河流和湿地生态系统正在迅速退化。建筑业更喜欢来自河床、洪泛平原和湖岸的棱角状的沙子，这是提高混凝土强度的一个因素，而沙漠沙子具有圆形和光滑的颗粒(Kondolf，1997)。自20世纪70年代以来，河流对砂石的需求出现了前所未有的增长(Hackney等人，2021年)，河沙和砂石开采对环境不利影响的证据每年都在增加。对基图伊的基伍河进行的一项研究(Muiruri等人，2020年)表明，超过自然替代率的采砂会导致河流形态的改变，带来不利的环境影响，如沙地保护区的地下水位降低、河岸不稳定、河床植被丧失、河道侵蚀、河流切割等。据观察，已完成的研究大多集中在亚洲、美洲和欧洲的多年生河流，而关于非洲ASAL中河流采砂对临时河流冲积地下水影响的研究有限。短暂河流的冲积含水层为低产和不可靠的地下水含水层提供了一种可行的替代水源(De Hamer等人。2008年)。此外，最新的十年气候预测表明，非洲北部和南部地区持续变暖和降雨量减少，导致该地区水资源紧张加剧。Makueni县的河流采砂是在干旱、干旱和半干旱地区的许多流域的典型特征--短暂溪流和河流中进行的，在保护和维护水资源、人类健康和环境方面起着至关重要的作用(Levick等人，2008年)。为此，该项目旨在研究干旱和半干旱地区沙质短暂河流冲积地下水有效性之间的复杂关系。在短暂河流中，沙子的可获得性与冲积地下水之间的天然关系是什么？2.当沙子被开采时，这种关系会发生怎样的变化？3.在不对沙质短暂河流中的冲积地下水造成不利影响的情况下，在多大程度上可以进行河流沙子开采？4.出于经济用途的河沙开采与临时河流中沙子提供的生态系统服务之间的潜在权衡是什么？5.自2015年对河流沙子开采进行管制以来，马库埃尼河可以观察到哪些关键的成功指标？

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?