Department of Water Science and Engineering, IHE Delft Institute for Water Education, Westvest 7, 2611 AX, Delft, the Netherlands.
Department of Water Science and Engineering, IHE Delft Institute for Water Education, Westvest 7, 2611 AX, Delft, the Netherlands; Faculty of Civil Engineering and Geosciences, Delft University of Technology, Building 23, Stevinweg 1, 2628 CN, Delft, the Netherlands.
Sci Total Environ. 2019 Nov 15;691:896-907. doi: 10.1016/j.scitotenv.2019.07.189. Epub 2019 Jul 13.
The Lower Mara River and Wetland, Tanzania, is an important ecosystem and unique water resource for a vast semi-arid area. The river, an affluent of Lake Victoria, and the wetland are experiencing morphological and vegetation changes resulting in channel avulsions and wetland expansion. This study analyses the changes over the last 100 years and investigates natural and anthropogenic behaviors to explain the increase of the Mara Wetland area. We collated historical topographic maps and satellite images. We conducted two field surveys in low and high flow condition with an unmanned aerial vehicle, a sonar and an ADCP. We mapped selected areas as well as the bed topography in some stretches of the river, measured discharges, and collected river bed and suspended sediment samples. The analysis of the sediments shows that the wetland system, dominated by papyrus sp., is very efficient in trapping sediment, releasing clear water to the Lake Victoria. The historical reconstruction using topographic maps, satellite images and a multivariable analysis including hydrology and land cover, shows that 4 major avulsions occurred in the last 70 years due to a combination of natural behaviors, hydrological fluctuations and anthropogenic factors such as basin deforestation, farming and grazing along the river banks and in the wetland. Each avulsion led to substantial expansion of the wetland. Combined, they increased the wetland area by a factor of 3.6. Describing the Lower Mara River dynamic behavior, this work provides relevant information for sustainable future water and sediment management in order to preserve wetland habitats and natural resources.
坦桑尼亚的Lower Mara 河和湿地是一个重要的生态系统，也是广阔半干旱地区独特的水资源。这条河流是维多利亚湖的一个支流，以及湿地正在经历形态和植被变化，导致河道改道和湿地扩张。本研究分析了过去 100 年的变化，并调查了自然和人为行为，以解释 Mara 湿地面积的增加。我们整理了历史地形地图和卫星图像。我们在低流量和高流量条件下进行了两次无人机、声纳和 ADCP 现场调查。我们绘制了选定区域的地图以及河流某些河段的河床地形，测量了流量，并收集了河床和悬浮泥沙样本。沉积物分析表明，以纸莎草为主的湿地系统在捕获沉积物方面非常有效，将清澈的水释放到维多利亚湖。使用地形地图、卫星图像和包括水文学和土地覆盖在内的多变量分析进行的历史重建表明，在过去的 70 年中，由于自然行为、水文波动以及流域森林砍伐、河岸和湿地周围农业和放牧等人为因素的综合作用，发生了 4 次大的河道改道。每次改道都导致湿地的大幅扩张。综合起来，它们使湿地面积增加了 3.6 倍。描述 Lower Mara 河的动态行为，这项工作为未来可持续的水沙管理提供了相关信息，以保护湿地生境和自然资源。
