Soil erosion and sediment delivery to surface waters impact the human-water cycle in several ways. Eroded soil, along with nutrients, travels from intensive crop and grazing systems to waterbodies, reducing the fertility of agricultural land, degrading the integrity of freshwater ecosystems, and negatively impacting water quality on which the human population and other sectors depend. Furthermore, sedimentation reduces the functional capacity of vital energy and agricultural infrastructure, such as reservoirs and irrigation canals, resulting in reduced productivity and profitability of food and energy production systems. A few hydrologic models have accounted for the effects of soil erosion on water quality by implementing soil erosion models into their simulations. To our knowledge, soil erosion has not yet been included in large-scale hydrologic models. Our research adds an erosion-sediment transport module to the hydrological Community Water Model (CWatM). That is to assess soil erosion on a regional to a global scale and to simulate the concentration of suspended sediments in surface waters. CWatM is a fully-distributed, large-scale, open-source hydrological model. It runs on a daily time step and high resolution of up to 30 arc seconds (approximately 1 km at the equator). The model can account for human activity and management of water systems, including reservoir operations, water demand, and crop-specific irrigation requirements. A global dataset of 5 arc minutes is available for an easy simulation setup at a catchment, region, and global scale. The implementation of soil erosion and sediment delivery from terrestrial sources will rely on the Modified Universal Soil Loss Equation (MUSLE) and the stream network density within each grid cell. Further, simulating instream erosion uses a power law approach. Finally, the routing algorithm would move suspended soil particles downstream. For that purpose, we combine input datasets with CWatM variables, e.g., surface runoff. We apply this module to a case study in Uganda’s share of the Victoria Lake Basin at five arc minute resolution, where high soil erosion rates challenge the ecological integrity of the natural environment, as well as agricultural productivity and water quality. We further discuss the model sensitivity to input parameters’ variation (e.g., the fraction of daily rainfall in the half-hour of highest intensity).

How to cite: Sorger-Domenigg, F., Tang, T., and Fridman, D.: Including soil erosion and sediment delivery to surface waters in a high-resolution global hydrological model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13155, https://doi.org/10.5194/egusphere-egu23-13155, 2023.

In Mediterranean areas, where water scarcity is a common and recurrent problem, reservoirs play a key role in water resources management. Water allocation for different uses (e.g., urban, agricultural, hydroelectric, and ecological) can be affected by numerous external and internal factors limiting  their water quality condition in the reservoir and in the downstream areas. On the one hand, the loads of substances that alter water quality standards (e.g., sediments, nitrogen, phosphorus). On the other hand, the influence of the management and operation of the reservoir affects the streamflow natural regime. An example of these effects is found in the Guadalquivir river basin (Southern Spain), a highly regulated basin (113 reservoirs) with a relevant problem of sediment inputs throughout the river. The high sediment load is a consequence of the existence of high rates of erosion, favored by the complex orography, the high slopes, the extreme rainfall and the land uses, which partially or totally expose the surface of the land (e.g., olive groves). In this context, the objective in this work is to assess how water quality dynamics are affected by the management and operation of the Guadalquivir’ reservoirs system.

Historical information available for the study period 2011-2022 in 9 control points located in the Guadalquivir river and the main contributing subbasins was compiled,  including: 1) inflow, outflow, stored water volume and precipitation data in reservoirs on a monthly and daily basis, and 2) suspended solids concentration data on a monthly and hourly scale, all of them provided by public regional government data networks.

As result, the sediment loads received by the reservoirs located in the main axis of the Guadalquivir were estimated at daily, monthly, and annual time scales, showing direct relationships with water inputs. Two different scenarios depending on discharges and precipitation in the contributing subbasins were found to cause different effects in water quality: ordinary operation scenario and flood operation scenario. 

Therefore, the combined  understanding of the operational (discharges) and natural (rainfall events) drivers constitutes a relevant step for the effective, efficient, and sustainable management of water resources in reservoirs contributing to one of the challenges of society to comply with the Water Framework Directive in the current context of global warming.

Acknowledgements: This work has been funded by the project Integrated Management for the control of water inputs and sediments in reservoir systems in the Guadalquivir basin, with the economic collaboration of the European Funding for Rural Development (FEDER) and the Office for Economy, Knowledge, Enterprises and University of the Andalusian Regional Government.

How to cite: Contreras, E., García, G. S., Polo, M. J., and Pimentel, R.: The role of reservoir operation in sediment contribution to water quality: an spatiotemporal scale analysis along the Guadalquivir river, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15564, https://doi.org/10.5194/egusphere-egu23-15564, 2023.

Pesticides are chemicals used in various agricultural practices to control pests, weeds and plant diseases. They are responsible for many negative impacts on the environment and human health. In addition, they are linked to the intensive use of agricultural machinery and equipment, and to mass production, often associated with monoculture. These non-ecological practices contribute to the contamination of freshwater by pesticides, as well as to the continuous soils degradation and the erosive processes increase. In this context, Rouzies et al. (2019) developed the dynamic and continuous model PESHMELBA with the aim of simulating pesticide transfers at the watershed scale, and comparing scenarios by explicitly taking into account the landscape spatial organisation. This model has a modular structure, which allows to improve the representation of some processes or landscape elements (such as plots, vegetative filter strips, ditches, rivers, etc.), or to add new ones. The current version of the model only estimates the pesticides transfer in solution (water), which may underestimate the impact of these solutes, as the part of them absorbed in the soil particles is not yet taken into account in the simulations.
Thus, an erosion module was developed in order to integrate the transfer of pesticides in the particulate phase into the PESHMELBA model, and to quantify the soil loss and the particles transfer at the watershed scale. This model differs from other existing erosion models by performing continuous dynamic simulations, i.e. it takes into account the variation of sediment concentrations in space and time, and the continuity between precipitation events. The developed model simulates soil detachment by rainfall (interrill erosion) and by runoff (rill erosion), transfer of particles by laminar and concentrated surface runoff, and deposition of particles when transport capacity is exceeded, in particular inside landscape elements as vegetated strips or hedges, or where slope decreases. This deposition consolidates along time between two surface runoff events.
This module integration inside PESHMELBA allows the comparison of different scenarios of agricultural practices and land use, by taking into account different configurations of the landscape elements. This first version of the erosion model is still in the testing phase, where the first simulations show consistent results and illustrate the interest of a continuous dynamic simulation, essential to represent pesticide transfer. Despite the current constraints and limitations of this model, it shows great potential to represent erosive processes in a more realistic way, by further refining and improving this first version in subsequent contexts.

How to cite: Lima, T., Carluer, N., Rabotin, M., Moussa, R., and Lauvernet, C.: Development of an erosion and transfer particulate phase pesticides model at the watershed scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5845, https://doi.org/10.5194/egusphere-egu23-5845, 2023.

The Geul river, a nearly 60 km long transboundary stream in the northeast of Belgium and southeast of the Netherlands, suffers from excessive fine sediment inputs. This causes the gravel bed to become clogged, which, in turn, hampers the reintroduction of salmonids in the river. To examine the occurrence and origin of fine sediments on the gravel bed of the Geul river, the fine sediment layer was mapped and sampled along the entire reach of the river from near the source to the mouth in late Spring 2021. The bed sediment samples were analysed for trace metal concentrations. The results from the trace metal analysis show that the diffuse ‘uncontaminated’ sediment inputs from the catchment resulting from soil erosion cannot fully explain the declining pattern of the zinc and lead concentrations in the bed sediments of the Dutch reach of the Geul river, downstream from the historic mining sites in the Belgian part of the catchment. This implies that additional sources of fine sediment that is less contaminated than the bed sediment exist. Assuming a model of a constant area-specific sediment yield from the catchment and a constant bank erosion rate per unit river length, the contribution of bank erosion in the Geul river was estimated to increase from 35% at the Belgian-Dutch border to about 67% at the river mouth. This model explains about 56% of the variance of measured zinc and lead concentrations in the bed sediments. The residual concentrations (modelled – measured) correlate negatively with the rubidium concentration in the bed sediment, which is a proxy for the clay mineral content of the sediment. The rubidium concentration explains about three quarters of the variance unexplained by the above sediment delivery model. The model assumptions and results are discussed against independent observations of suspended sediment transport and bank erosion in the Geul river.

How to cite: van der Perk, M., Hemstra, R., Visschers, S., Winteraeken, H., de Redelijkheid, M., and Lemmens, D.: The contribution of stream bank erosion to downstream dilution of mining-contaminated stream bed sediment in the Geul river in the Netherlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16317, https://doi.org/10.5194/egusphere-egu23-16317, 2023.

Thousands of micropollutants, emitted every day from numerous anthropogenic sources, end up in surface waters posing a risk to human health and the environment. Conventional monitoring approaches for an EQS-based assessment with e.g. monthly grab samples miss situations with high concentrations of total suspended solids (TSS) and associated chemicals. This is a clear shortcoming, especially in the context of load observations. To address this gap, we devolved a monitoring concept with event-driven sampling and applied it for the assessment of persistent micropollutants representative for different pollution sources and pathways in three Austrian rivers, namely the Wulka river and two of its tributaries.

The selected compounds belong to the groups of industrial chemicals with wide dispersive use, pharmaceuticals, herbicides, fungicides, and metals. An online monitoring station at each river measured water level/discharge, turbidity/TSS, and conductivity in 1 min timesteps, for the period of 20 months. Turbidity was measured to capture the river’s TSS variability on a high-resolution basis and to trigger automated autosamplers for sampling during specific flow events. Samples from high and base flow periods were analysed for concentration of the selected micropollutants in total and filtered samples.

The research allowed us to gain insights regarding the TSS and the related micropollutant transport dynamics of events and for the entire period. Preliminary results show that without event consideration the annual loads are underestimated for heavy metals and overestimated for pesticides.

The outcomes provide a better understanding of the transport of TSS and related chemicals and quantify the essential relevance of sampling during high-flow events for the assessment of transported loads of some micropollutants in rivers.

The monitoring was conducted within the EU Interreg Project Danube Hazard m3c.

How to cite: Weber, N., Kittlaus, S., Milacic, R., Zoboli, O., Zessner-Spitzenberg, M., and Krampe, J.: River load estimation of micropollutants: The Importance of event-driven sampling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6452, https://doi.org/10.5194/egusphere-egu23-6452, 2023.

Soils in the Gulf of Lions region (NW Mediterranean) show some of the highest copper (Cu) levels in Europe (Ballabio et al, 2018). The episodic and erosive nature of rainfall in the Mediterranean area (González-Hidalgo et al, 2007), historical intensive agricultural practices using Cu to fight the downy mildew and its relatively high solubility make the study of its transfer and consequences along the land-sea continuum a major issue. The main objective is to quantify the Cu fluxes from coastal rivers discharging in the Gulf of Lions and characterise their temporal variability highlighting the importance of floods on the transfer processes of matter and associated contaminants in the Mediterranean region.

Since 2006, the SNO MOOSE, a multi-platform and multi-site observation network designed to monitor the evolution of the Mediterranean basin in a context of global change, has been carrying out. Therefore, on a monthly monitoring basis, trace metal concentrations in suspended particulate matter (SPM) have been estimated in the five main small coastal rivers of the Gulf of Lions as well as the Rhone River.

These observations coupled with a sediment flux model (Sadaoui et al, 2016) allow the estimation of elemental fluxes. Small rivers have the highest average Cu content in suspended matter (80.3 µg/g) and in the soils of the catchment areas (79.7 µg/g) (approximatively a factor of 2 compared with the Rhone). Mean annual estimation of Cu fluxes are about 316T/year with an interannual variability of 36%. The Rhone River is by far the major contributor to the fluvial exports of particulate copper to the Gulf of Lion. However, although small coastal rivers account only for 6% of SPM inputs, their contribution to particulate Cu fluxes averages 9.7%.

Interannual variability of fluxes is controlled by the occurrence of episodic flash floods on coastal rivers typical of the functioning of Mediterranean watercourses (Roussiez et al, 2011, 2012).

The SPM transport originating from surface soil erosion and associated copper mainly takes place during these brief events for small coastal rivers (annual average of 66% of total Cu export against 19% for the Rhone). According to the number of events occurring each year their relative contribution of Cu fluxes compared to the Rhone is highly variable (from 2 % in 2012 up to 41% in 2011). Thus, the influence of coastal rivers on the global Cu budget to the Gulf of Lions is not negligible.

Moreover, copper transferred in rivers from the erosion of wine-growing soils is mainly in extractable form, which is more hazardous for the environment because it is both mobile and potentially assimilable by organisms.

How to cite: Machu, Y., Aubert, D., Ludwig, W., Charrière, B., Sola, J., and Sotin, C.: Contribution of small coastal rivers to copper export to the Gulf of Lions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3346, https://doi.org/10.5194/egusphere-egu23-3346, 2023.

Understanding the statistics of bedload particle motions is of great importance. To model the hop events defined as trajectories of particles moving successively from the start to the end of their motions, recently, Wu et al. (Water Resour Res, 2020) have successfully performed individual-based simulations according to the Fokker–Planck equation for particle velocities. However, analytical solutions are still not available due to (i) difficulties in treating the velocity-dependent diffusivity, and (ii) a knowledge gap in incorporating the termination of particle motions for the equation. In the latest work (Wu et al., J Fluid Mech, 2023), we have specified a Robin boundary condition representing the deposition of particles; and devised a variable transformation to deal with the velocity-dependent diffusivity. The original bedload transport problem is thus found to be governed by the classic equation for the solute transport in tube flows with a constant diffusivity after the transformation. By solving the spatial and temporal moments of the governing equation, we have investigated the influence of the deposition rate on three key characteristics of particle hops. Importantly, we have related the deposition rate to the mean travel times and hop distances, enabling a direct determination of this physical parameter based on measured particle motion statistics. The analytical solutions are validated by experimental observations with different bedload particle diameters and transport conditions.

How to cite: Wu, Z., Jiang, W., Zeng, L., and Fu, X.: On bedload particle deposition and hop statistics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4132, https://doi.org/10.5194/egusphere-egu23-4132, 2023.

Researches on the solute dispersion process with adsorption and desorption at boundaries are common in various fields, such as chemistry, biology and hydraulics. However, the Laplace transform as an available method for the adsorption-desorption boundary conditions, is complicated and difficult to apply. Recently, Jiang et al. (J. Fluid Mech., vol. 947, 2022, A37) proposed a much simpler analytical method based on the classic framework of separation of variables to derive solutions of concentration moments for a tube flow, which is valid for the entire range of the reactive transport process. The key of this approach is to solve the eigenvalue problem for the bulk and surface concentration distributions with the adsorption-desorption boundary conditions. Compared with the Laplace transform method, this new method can effectively avoid the complexity caused by the inverse Laplace Transform. Here we apply this simple approach to solute transport in channel flows with bed adsorption and desorption. We investigate the effect of adsorption-desorption on the dispersion process, and the influence of initial conditions on the non-uniformity of dispersion characteristics over the cross-section before the Taylor dispersion regime.

How to cite: Zhan, J., Jiang, W., and Wu, Z.: Reactive transport in channel flows with bed adsorption and desorption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5963, https://doi.org/10.5194/egusphere-egu23-5963, 2023.

The water authority of Israel has decided to create an unnatural flow starting at a point in the Tzalmon stream into Lake Kinneret (Sea of Galilee) 4 km upstream as a way to manage the lake water level. The national water company “Mekorot” use the existing national water carrier to take water from the desalination plants next to the Mediterranean Sea and transfer it to the Tzalmon river where the water will naturally flow within the stream into the lake. A test flow was conducted at changing discharge rates of 3,100, 4,500, and 6,000 m³ hour^-1 for three hours for each flow rate for two days to examine the new flow system that leads desalinated water into the Tzalmon stream. Nevertheless, the test flow was a great opportunity to study the Tzalmon flow's ability to transport particles, nutrients, and bacteria as well as study their distribution dynamics in the lake. Fifteen temperature sensors were deployed in the Tzalmon river outlet to the lake to capture the mixing dynamics with the lake water during the test flow. During the flow release, profiles of temperature, electrical conductivity (EC), dissolved oxygen (DO), and pH were conducted along the flow path of the water into the lake using a boat in 5 locations. In addition, the boat sampled the water for total dissolved solids (TSS), nutrients, bacteria concentration, and general chemistry in those 5 locations in the river outlet. Along the river, six temperature sensors were deployed in and out of the water in three locations to understand the temperature change along the flow path from the discharging point to the lake. Furthermore, water samples from those 3 locations along the flow path were taken and analyzed to the above-mentioned parameters at each flow rate discharge. The results highlight the ability of the river flow to carry those parameters at different flow velocities along with their distribution dynamics in the lake water. Furthermore, the water reached the lake only at the end of the second flow period and during the third flow period due to losing conditions along the flow path. Therefore, there were only two occasions of river water mixing in the lake, and this mixing dynamic was studied and will be presented at the session. This new water discharge into an ephemeral river will start in the next few years and will change the river area ecosystem and will bring newly dissolved and solid materials into the lake. This test is the first examination of the system in which the constant flow release will potentially influence the lake ecosystem and the flow regime in the lake.

How to cite: Stein, S.: Mixing dynamics of stream water into Lake Kinneret through a short-period flow release test, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4111, https://doi.org/10.5194/egusphere-egu23-4111, 2023.