Search

Jordan’s water scarcity prompted a national plan whereby treated wastewater is utilized to amend agricultural irrigation water so as to reallocate freshwater to urban/domestic uses. The policy, however, has engendered farmers’ resistance in the Northern Jordan Valley (NJV), causing a stalemate in putting new infrastructure into operation. This research investigated the socio-economic causes of farmer resistance and contestation, and examined the government’s institutional approach to overcome the challenges. We found that the perceived risks of wastewater reuse such as salinization and restrictions from international markets figure prominently in the farmers resistance. As yet, farmers have managed to avoid the shift to treated wastewater use by using the political agency of elite farmers who control the Water Users Associations. These same farmers have adopted informal water access practices to overcome freshwater shortages. At the same time, small producers who don’t have possibilities to access extra water and with less political clout seem more willing to irrigate with treated wastewater. We conclude that understanding the heterogeneous context in which the envisioned wastewater users operate is key to predicting and solving conflicts that arise in treated wastewater reuse projects.

Microplastics are an unavoidable part of riverine systems, altering the natural composition of rivers and the associated processes. Within a riverine system, microplastics can be present throughout the water column or within bedload, implying different transport, deposition, and erosion mechanisms. Some recent models have been developed to predict and understand the depth distribution concentration of microplastics and macroplastics, primarily relying on the Rouse model for sediments. However, the great variety in microplastics shape and size accompanied by the dynamic nature of riverine systems (e.g., variety of flow conditions, sediment composition and bedforms) question how realistic and reliable models for plastic distribution along the water column and within sediments are. Present models are often analogous to suspended sediment models and assume diffusivity to be equal to turbulent viscosity, they often exclude the bedload, neglect the effect of turbulence and bed morphology, and come short in explaining the behaviour of mixtures of microplastics and sediments. Understanding these aspects is crucial to improve present models and to aid mitigation efforts and to optimize collection systems and policy. This project targets employing both physical and numerical modelling techniques to further develop depth concentration models of microplastics. We aim to further examine and quantify the influence of turbulence on microplastics transport and concentration distribution by establishing preliminary estimates for the eddy viscosity and diffusivity of microplastics and further examine a wider range of mixtures of microplastics and sediments with different shapes and sizes.

Mobile components of dynamic river systems are varied, and more than fundamental water and sediment interactions must be considered to assess morphodynamic changes. Here, the effects of instream wood and plastic accumulations on the riverbed are modelled and assessed in the presence of a hydraulic structure. We observe a recent tendency towards considering instream wood and plastics as integral riverine system components. Such shift is driven by a multidisciplinary interest in instream wood and riverine plastic dynamics, including those addressing flood hazards and risk assessments. Like sediment, instream wood and plastics can be transported along the river channels during floods, increasing flooding risks and hazards by accumulating near hydraulic structures. Collection racks, a commonly encountered hydraulic structure, are used for trapping and removing various accumulated material, mitigating any potential risks. However, accumulations at collection racks can cause other risks because of potential backwater rise and local scour development. Accumulations of different densities, such as a combined presence of instream wood and plastics, add further complexity to the process understanding. In this study, a physical model is used to explore the geomorphic effects of accumulations of two different densities at a collection rack. Local geomorphic changes (i.e., scour and deposition), their evolution and the spatial extent around a vertical collection rack were analysed with Structure from Motion photogrammetry. The results show a strong relationship between the accumulation density and the hydraulic and geomorphic changes. Light floating material, forming accumulations closer to the water surface, are associated with the largest geomorphic changes, in contrast to dense material, forming accumulations close to the riverbed. In the presence of different densities, intermediate geomorphic changes were observed. Finally, to discuss the observations, we present a conceptual flow field for different scenarios of accumulation densities. Ultimately, outcomes from this work are essential to improve design practices for river managers.