Working as natural filter, well-designed vegetation schemes have been widely applied to improve the quality of water (Aiona, 2013; Stefanakis, 2015). Proper design, however, requires appropriate physics-based modelling of their filtering capacity. Several theoretical models predicting sediment transport in vegetated flow have been proposed: Baptist (2005); Yang and Nepf (2018); Wu et. al. (2021); Tseng and Tinoco (2021); Yagci and Strom (2022); Wang et. al. (2023). Some of them have been implemented in numerical tools (e.g. Caponi et al., 2022; Li et al., 2022) and in particular in Delft 3D (Deltares, 2014). However, they have been mostly designed and verified based on bedload processes, and their performance for suspended load should be further investigated. This work compares different approaches on their ability to reproduce the effects of vegetation on suspended solids concentration in two-dimensional models built in Delft3D. The work focuses on emerging vegetation, represented as rigid cylinders, and sediment deposition. Comparisons are based on the ability to reproduce flume experiments available in the literature by analysing both flow field and sediment deposition results.@en

The transboundary Mara River, Kenya and Tanzania, is the only perennial source of inflowing surface water of a vast area including the Mara-Serengeti region. The river sustains millions of wild animals as well as a human population of nearly one million (McClain et al., 2014; Gereta et al., 2009). The basin receives two rainy seasons: a lighter in October- December and a heavier in March-May. The river is rich in suspended sediments, which has further increased by recent deforestation, change of land uses and mining (Defersha & Melesse, 2012). Before flowing into the Lake Victoria in Tanzania, the river forms a wide wetland that acts as a natural filter, sinking the large amount of suspended load and releasing clean water to the lake (Fig. 1). The wetland is fed by sediments and nutrients transported by the river and represents an essential but, at the same time, fragile ecosystem. The vegetation, here dominated by papyrus, plays an important role in the stability of the wetland system. However forest fire and farming are intense along the wetland and have deeply modified the vegetation spatial distribution.@en

In wetlands, water is the primary factor controlling the environment and the associated plant and animal life (Ramsar Convention Secretariat, 2006). Wetlands not only provide diverse ecosystem services but also contribute to the improvement of surface water. In tropical Africa, their supportive role has become progressively highlighted in ongoing studies, but less scientific research has been carried out as compared to other ecosystem forms and wetlands in other parts of the world (Kabii, 2017). This is largely due to the difficulty in field or insitu monitoring owed to their remote locations (Gallant, 2015), with those accessible during periods of low flow, totally cut off during high flows. The lack of timely and reliable information on the status and evolution of tropical African wetlands impedes efforts to sustainably manage and develop them. @en

The Pilcomayo is a very active sand-bed river located in South America, where during the last decades, quick changes in cross-sectional shape and dimensions have been observed. The total amount of sediment transported by the river is around 140 millions of tons per year, being one of the largest in the world (Martín-Vide et al., 2014). Due to hydrological regime, the flood season is from January to March, with a maximum discharge around 4600 m3/s. However, the monthly average flow during floods is 650 m3/s. During the dry season, the river is almost dry, with the minimum measured discharge being 1.5 m3/s. The bed is formed by fine sand (Fig. 1), with a median size D50 equal to 100 μm. Wash load is formed mostly by silt and clay and represents the 89% of the total amount of sediment transported by the river. The high variability of flows and the presence of a highly erodible bed made of fine sand makes the Pilcomayo a very active river with cross-sections responding very fast to the flow. @en

The Mara River is the only perennial river of a vast semi-arid area, including the Mara Serengeti ecoregion in Kenya and Tanzania. The river sustains more than one million inhabitants and millions of wild animals. In its lower reaches, the Mara River forms a wide wetland before flowing into Lake Victoria. The wetland represents a rich ecosystem providing essential services, but it is being threaten by increasing human activities. Farming, grazing, fishing and deforestation to produce charcoal and open new crops have deeply modified the riparian vegetation spatial distribution and the habitat morphology. Additionally, the construction of a new dam is planned immediately upstream of the wetland for irrigation purposes and hydropower. This work is undertaken to set up a hydro-morphodynamic model to predict the short- and long-term effects of human activities on the Mara Wetland habitat. The model will be a tool to evaluate strategies to mitigate the negative effects of the activities. The Lower Mara River is poorly gauged and only a few scattered data and observations are available. Therefore, in October - November 2017 (dry period) and May 2018 (wet period) multidisciplinary field work was conducted along a 130 km stretch of the river. An unmanned aerial vehicle (UAV) was used to produce high resolution orthophoto mosaics and digital elevation models of selected areas. The UAV gave topography and ground observations on vegetation type, size and distribution, and other features of unattainable areas. A sonar was used to map the bathymetry of some stretches of river and wetland. River discharge was measured on 4 locations. Bed sediments and water samples were collected from 8 spots to analyse sediment granulometry and suspended sediment concentration. Results suggest that, at wetland inlet, the river is particularly rich in suspended sediment, with measured averaged concentrations of the order of 500 mg L-1 and peaks of 2700 mg L-1. The wetland, thanks to its extent and dense vegetation cover, traps the 90% of the suspended sediments and releases clear waters to the Lake Victoria. The future placement of the dam may have a strong influence: without an adequate management, the dam solid and liquid discharge regulation may further trigger morphological changes and jeopardize the wetland ecosystem.@en