ABSTRACT. Operating Urban Drainage Systems (UDSs) is becoming increasingly challenging due to growing complexity and performance demands. These challenges can be effectively addressed through digitalization and innovative decision-support solutions, such as Digital Twins (DTs). However, establishing and operating a DT involves numerous technical and organizational difficulties. To enable wider adoption of this technology in the urban water sector, the development of integrated and interoperable tools is essential. This paper presents a Data–Information–Knowledge–Wisdom (DIKW) pipeline designed to support the operation of DTs for asset management in UDSs. The approach is demonstrated through a Belgrade case study, highlighting the benefits of connecting diverse tools, such as machine learning and physically based models within a unified framework.

ABSTRACT. Canal de Isabel II, the company responsible for the management of the urban water cycle in the Community of Madrid, is taking the role of a beneficiary in the Horizon Europe project AI:LINER (Data-Driven Sewer Asset Management: a path toward the resilient transformation of Europe´s Sewer Infrastructure). Within this collaboration, AI-driven software for sewer inspection prioritization and long-term rehabilitation planning will be developed and tested for the asset management of part of its sanitation facilities. Asset management in the urban drainage network represents a major advance for water managers today. In addition to its widespread application, it overcomes previous adversities while allowing an adequate level of service to be achieved at the lowest possible cost (Cherqui et al., 2024). Canal de Isabel II, being sensitive to this issue, has keen interest in evaluating the efficiency of this alternative management criteria, based on massive inspection data analysis.

ABSTRACT. Urban Drainage Systems (UDSs) are increasingly challenged by ageing infrastructure, rapid urbanization, and the impacts of climate change. Nature-Based Solutions (NBSs), such as green roofs and swales, can enhance UDS performance and resilience, yet traditional Asset Management (AM) approaches primarily focus on grey infrastructure. To ensure optimal functionality, both grey and blue–green components must be systematically monitored and maintained. This study presents a Digital Twin (DT)-based framework for the rapid assessment of NBS conditions through continuous model updating. The proposed method employs a Proportional–Integral–Derivative (PID) controller to dynamically adjust simulation model parameters (e.g., surface roughness, hydraulic conductivity) based on real-time sensor observations. Parameter changes are interpreted as indicators of NBS condition, serving as early warnings for maintenance or intervention. The methodology will be tested on a section of the Belgrade UDS, focusing on a hypothetical green roof scenario. Water level data collected from the nearby sewer network will be assimilated into the model to update NBS parameters. The results aim to demonstrate the potential of DTs as effective asset management tools for monitoring and maintaining hybrid urban drainage systems.

ABSTRACT. Sustainable management of urban water systems can be supported by integrated models representing system components as interconnected sub-models. However, a careful balance of completeness and parsimony is to be looked for in model development. A modelling framework integrating multiple sub-models was defined to simulate water quantity and water quality dynamics in the CSO-impacted urban canals network of Padua. Heterogeneous (0D vs 1D-2D) sub-model complexity reflects different data availability and the study focus on urban streams multifunctionality. A preliminary simple 0D representation of drainage dynamics in one key node of the water system gave promising results.

ABSTRACT. The integration of Digital Twins into drainage management systems offers unprecedented opportunities for real-time monitoring, predictive modeling, and adaptive control of urban water infrastructure. One of the main challenges, especially in countries with underdeveloped infrastructure monitoring, lies in acquiring accurate (near) real-time data with high temporal resolution to capture flow dynamics across diverse hydraulic conditions. Videographic (camera-based) measurement techniques offer an opportunity to fill such gaps, as they provide non-intrusive, scalable, and visually verifiable data to be used in conjunction with traditional, but often very costly, monitoring approaches. While videographic measurement techniques have been successfully deployed in riverine systems in the past, their introduction to closed-conduit municipal systems has been lagging. The DIGIDRAIN project aims to create a framework for setting up Digital Twins for urban sewage systems. This effort is also to include the application of custom-made low-cost camera-based solutions in key network locations, and investigate the opportunities and challenges which they provide – (1) the choice of best-fitting image-processing methods depending on flow and ambient conditions, (2) cost effectiveness, (3) hardware reliability, and (4) the usefulness and uncertainty of such data for the creation, calibration, and exploitation of the resulting Digital Twin. Preliminary results from a real-world test of a low-cost camera-based setup are presented. The tests are performed in harsh low-light winter conditions with a device installed for autonomous operation inside a maintenance hole. While the acquired data is analysed and provides good agreement with reference measurements, several key challenges – persistent power supply, low-light visibility, visibility issues due to aerosol dispersion, etc. – have been identified with adequate mitigation strategies considered for future work.

ABSTRACT. This study presents a cost-effective workflow combining consumer-grade mobile LiDAR (iPhone) with 2D hydraulic modeling (HEC-RAS) for urban stormwater assessment. Applied to a university campus, the method successfully identified critical drainage zones, flow pathways, and areas of water accumulation during storm events. Results demonstrate that accessible mobile sensing technology can provide engineering-grade hydraulic analysis without expensive equipment or specialized expertise, significantly lowering barriers to stormwater modeling. This framework enables rapid assessment of urban runoff characteristics and establishes a foundation for evaluating Low Impact Development (LID) strategies in different urban settings.

ABSTRACT. Per- and polyfluoroalkyl substances (PFAS) –also known as forever chemicals– are synthetic compounds characterized by their strong carbon–fluorine bonds, which confer exceptional chemical stability and resistance to degradation. This persistence has led to widespread environmental contamination and bioaccumulation. PFAS transport and accumulation are strongly influenced by adsorption at environmental interfaces, particularly the air–water and water–sediment boundaries. To investigate the impact of these processes in a coastal setting, a numerical modeling approach was embraced to investigate the Mar Menor coastal lagoon (southeastern Spain) using the Delft3D 4 suite. Hydrodynamics and wave dynamics were simulated with Delft3D-FLOW and Delft3D-WAVES, while adsorption–desorption processes and Lagrangian particle transport were represented through Delft3D-WAQ and Delft3D-PART. This study provides insights into PFAS behaviour in aquatic environments and supports improved understanding of their environmental fate.

ABSTRACT. Nutrient pollution in rivers remains a major environmental challenge, demanding modelling tools that can guide effective basin-scale water management. Water quality prediction at large scales is often affected by limited monitoring and high uncertainty in complex biogeochemical processes. This work introduces an integrated framework that couples a hydrological model with a reactive–transport module to simulate nutrient dynamics in large catchments. A spatially regularized calibration using the PEST++ iterative ensemble smoother estimates distributed nutrient loads while estimating predictive uncertainty. The method was applied to the Arno River basin in Italy, simulating eight water quality variables including biological oxygen demand, dissolved oxygen, nitrogen, phosphorus, and algal biomass over 2011–2020. Calibration used 8151 spot observations from 70 sampling points, showing good predictability of constituents. The model identified pollution hotspots, particularly urban-linked ammonium and organic loads, and provided spatially explicit nutrient estimates with uncertainty, offering a practical tool for decision-making in data-scarce catchments.

ABSTRACT. The appropriate location of effluent discharge points in aquatic environments such as estuaries and coastal areas is critical to minimizing environmental impacts and ensuring compliance with water quality regulations. Even when treated, effluent discharges can significantly alter the physicochemical and ecological conditions of the receiving environment, particularly in areas of low dilution, high ecological sensitivity, or intensive human and economic use. This work presents a technical assessment supporting the selection of the location and operating regime of an effluent discharge point associated with a proposed aquaculture facility in the Cabedelo area, Figueira da Foz. The discharge is planned for the Mondego Estuary, near a RAMSAR zone of high importance for marine birdlife. Several scenarios were considered, based on several pre-selected discharge locations, including continuous discharge throughout the tidal cycle and intermittent discharge, with suspension during tidal conditions most favorable to upstream dispersion. The study integrates environmental data, physical model experiments, and numerical simulations. The adopted methodology enabled the assessment of flow behavior, pollutant dispersion, and interactions with local hydrodynamic conditions (tides, currents, morphology).

ABSTRACT. The coastal fjord systems in the East of Iceland are increasingly exposed to interacting environmental pressures, including climate-driven changes linked to extreme weather events that affect the entire water system. These climate-driven changes include rising water temperatures, altered mixing patterns and shifts in the water-column structure as observed in sub-arctic fjords of Eastern Iceland (Hansen & Ingólfsson, 1993). Additional pressures arise from harmful algal blooms and nutrient enrichment, which can be amplified by aquaculture discharge, industrial emissions, and untreated municipal sewage (Taranger et al., 2015). Together, these pressures highlight the need for integrated methodologies capable of identifying system vulnerabilities before impacts cascade across ecosystems, local economies, and communities.

The East Fjords Reyðarfjörður and Seyðisfjörður in Iceland are a Case Study for the ongoing EU-funded project NATALIE (Accelerating and mainstreaming transformative NATure-bAsed solutions to enhance resiLIEnce to climate change for diverse bio-geographical European regions). Within these fjords aquaculture, a new rising industry, plays an important socio-economic role. Part of the project’s core objective has been identifying climate-related natural hazards that may affect society. The approach combines participatory hazard identification, cascading failure modelling, and digital environmental monitoring to better understand how extreme weather events and environmental stressors may disrupt critical community functions. This provides a foundation for developing and co-designing Nature-Based Solutions (NBS) that strengthen local resilience and support adaptive coastal management.

ABSTRACT. We continuously monitored water quality in two catchments with predominantly agricultural loading to evaluate how the implementation of extensive natural flood management (NFM) measures influences the catchment-scale loads in boreal-northern temperate climate conditions. NFM measures such as two-stage channels (TSCs), wetlands and rocky sills decreased the suspended sediment and total phosphorus loads. Part of the reductions were likely caused by simultaneous adoption of conservative cultivation practices.

ABSTRACT. Several restoration measures are planned for the Enz, the longest left tributary of the Neckar, Germany. These include river widening, groynes, and flow concentrations. Due to the location of these measures in the downstream area of a hydroelectric power plant, it is necessary to clarify the extent to which a possible rise in the water level resulting from the conversion measures could affect energy production. Since 1D and 2D approaches are not ideal for detailed investigations involving local disturbance zones, a 3D simulation tool must be used for the assessment. FLOW-3D HYDRO was used to determine the impact of the planned measure on the water level in the downstream area of the power plant. The potential impact of individual measures on water level changes can also be analysed. The investigation reviews the overall measure's effectiveness in creating habitats and assesses its impact on the upstream hydroelectric power plant.

ABSTRACT. See the uploaded Extended Abstract

ABSTRACT. Hydropower is a key renewable energy source that provides both base load and flexibility to balance variable solar and wind power. This study presents two planned cases that combine energy flexibility with ecological restoration through pumping solutions. The first case, part of the EU project ReHydro, involves pumping water from a downstream reservoir to a bypassed river section to restore flow and improve trout spawning habitat. The second case explores pumping water from the River Driva to an existing reservoir, with potential for pump-turbine installation to enhance grid balancing. Preliminary results indicate ecological benefits, such as improved salmon habitat and reduced impacts on spawning areas, alongside increased energy flexibility. Future work will focus on optimizing operations under changing climate conditions and assessing biodiversity, thermal impacts, and ice cover dynamics.

ABSTRACT. Hydrological input data can have significant impact on the results of hydraulic simulations. This study compares three methods for generating average annual hydrological datasets – an average flow duration curve (M1), an average annual hydrograph (M2), and an interpolated monthly average hydrograph (M3) – and their effects on simulating riparian areas with an approach based on inundation time. The simulations revealed substantial differences in predicted riparian areas and the extent of vegetation belts. The findings suggest that while averaged hydrographs retain temporal flow information, averaged flow duration curves may be more suitable for ecohydraulic applications where the flow amplitude is more relevant.

ABSTRACT. This study examines the vertical profiles and seasonal variations of water temperature and dissolved oxygen in a mountain stream pool. The study was carried out in Harmankaya Stream, which flows through a mountainous area located in the vicinity of Zonguldak, northwest Black Sea coast of Turkey. The stream has a drainage area of approximately 12 km². Measurements of temperature and dissolved oxygen concentration were made in a natural pool located on the course of this stream. The dissolved oxygen concentration is found to decrease with depth in the majority of the observations, whereas a decreasing temperature profile is only observed under the condition of net heating at the pool surface. The measurements revealed a seasonal dependence of the dissolved oxygen concentration, coherent with the seasonal variations of the water temperature. The presence of riparian vegetation significantly influences both of the measured parameters, particularly during the summer months. The findings of this study may have important implications for river restoration projects on habitat improvements and providing hydraulic and thermal refuges for fish.

ABSTRACT. Hydropeaking generates abrupt sub-daily fluctuations that alter river hydraulics and morphology, affecting fish populations and their respective habitat use. Understanding how small-bodied leuciscids respond to these pressure-driven flow changes at the microhabitat scale remains difficult. However, fish use the lateral line system to detect hydrodynamic changes in their surroundings through local changes in pressure. Traditionally, fish–habitat relationships are described by microhabitat use metrics (depth, substrate, velocity), but these often overlook fluid-body interactions that fish use to sense and respond to the flow field. This study related fish detections (presence vs. avoidance, presence vs. avoidance vs. mobility) to hydrodynamic conditions immediately after a pulsed-flow event downstream of a small hydropower plant. A 150-m reach was surveyed, 133 PIT-tagged leuciscids were tracked over five days, and three pressure-derived variables were measured with an artificial lateral line, representing streamwise flow (front pressure), turbulence (front fluctuations) and cyclic flow patterns (pressure asymmetry). The analysis identified pressure asymmetry and pressure fluctuations as the main drivers of fish presence, showing that fish were consistently present in microhabitats with lower asymmetry and fluctuations. These results highlight the value of this non-invasive pressure-sensing technology for quantifying the hydrodynamic conditions that drive habitat selection in hydropeaking-impacted rivers.

ABSTRACT. The vulnerability of bridges to scour, the primary cause of bridge failures, is being exacerbated by climate change-induced hydrological extremes, thereby increasing the risk of structural failure. The BriSK project addresses this critical issue by developing an innovative, risk-based methodology for the assessment and enhancement of bridge resilience to scour effects. By integrating advanced hydrological, hydraulic, and climate modelling techniques, BriSK provides tools to facilitate the prioritization of bridge maintenance and inform the hydraulic design of new structures. The project methodology incorporates probabilistic approaches and cutting-edge numerical models, thereby offering scalable and adaptable solutions for the evaluation of vulnerabilities under diverse climate scenarios. By aligning with the global sustainability goals set out by the United Nations, namely the Sustainable Development Goals (SDGs) 9 and 13, the BriSK project delivers significant benefits not only to Portugal but also on a global scale. It represents a significant advancement in the field of civil engineering, thereby ensuring the long-term safety of critical infrastructure.

ABSTRACT. This study numerically investigates the interaction between two-layer stratified opposing flows and side-by-side circular bridge piers. A three-dimensional open-channel configuration is considered, where warm and cold water layers enter the domain from opposing directions, creating a stable density interface and cross-flow conditions. The analysis focuses on the development of mean flow features and turbulence structures, including gap flow acceleration, wake interaction, and recirculation zones. Results from a representative simulation case illustrate how density stratification and velocity contrast modify the flow field around the piers. The findings provide insight into flow–structure interaction in stratified environments relevant to rivers, estuaries, and thermally influenced channels.

ABSTRACT. An in-house numerical model is employed for the investigation of the hydrodynamic effects of Artificial Reefs (ARs) deployment on wave propagation and attenuation. The model is based on the solution of the 3D Navier–Stokes equations using a Large-Eddy Simulation framework for turbulence modeling. The air-water flow is treated as a single-fluid flow, the Immersed Boundary method is implemented for the imposition of the boundary conditions on solid surfaces, while the evolution of the free surface is based on the Level-Set method. The porous media approach is used to model the ARs presence and flow resistance. The analysis focuses on evaluating the influence of ARs layout on wave transmission. Simulations with one and two rows of ARs are compared to assess the overall impact of their presence, followed by an assessment of the effect of streamwise and spanwise spacing between units on wave attenuation performance.

ABSTRACT. When constructing roads, culverts must be installed to safely convey surface water and runoff at stream crossings. Typically, two main types of culverts are used: rectangular and circular. These culverts are usually sloped, and the flow area decreases as water enters the culvert, leading to increased flow velocity. This acceleration can lead to soil erosion and leaching near the outlet, potentially damaging road substructures and surrounding land. While numerous studies have investigated energy dissipation methods for rectangular culverts, more limited research has been conducted on circular culverts. To address this gap, the Nebraska Department of Transportation (NDOT) funded the current research to identify optimal designs for energy dissipation structures at the outlets of circular culverts. The footprints of these dissipation structures must be minimized due to land availability limitations. The study focuses on using baffles to reduce flow energy, exploring optimal baffle placement and height for maximizing energy dissipation. In the first phase of this project, Admiraal and Zhang (2023) modeled dissipation at the outlet of a 48-inch-diameter circular culvert at a 15° slope using a 1:4.8 scale physical model. The system included an inlet tank, the sloped model culvert, a horizontal runout section, and a scaled dissipation structure inside an outlet tank. Two baffle configurations were tested in the rectangular dissipation structure: (1) full-length baffles acting as weirs across the entire width, and (2) staggered baffles consisting of a central baffle and two side baffles separated by a small gap. Weir and baffle heights of D/8, 2D/8, 3D/8, and 4D/8 (where D is the model pipe diameter) were tested. Results indicated that the optimal configurations were 3D/8 for full-length weirs and 4D/8 for staggered weirs, with the latter achieving optimum energy dissipation for the tested configurations. The second phase of this project was designed to identify optimal baffle heights and spacing for the staggered configuration, as geometries tested during the first phase were limited. The team developed an improved experimental setup featuring movable baffles on rails, allowing precise adjustment of horizontal baffle positions. Figure 1 shows three examples of configurations, but the system allows for a much wider range of configurations. Modifications to the outlet tank and the inflow culvert also raised the maximum testable flow rate from 1.4 to 2.0 cfs, and adjustments to other parts of the test apparatus expanded the range of inflow Froude numbers from 3.5–4.5 in Phase 1 to as low as 2.18 in Phase 2. The results for a baffle height of 0.45D indicate that the optimal placement of the central baffle varies with flow rate. For lower flow rates, the optimal baffle position occurs at 1D, whereas for higher flow rates, it shifts to approximately 1.3D,while the side baffles perform best when positioned 0.3D–0.4D downstream from the central baffle. Ongoing tests aim to determine the optimal height combination between the central and side baffles (e.g., 4D/8 for the center and 3D/8 for the sides, or vice versa) and to evaluate how these variations affect energy dissipation at different flow rates. The ultimate goal is to identify the baffle design that maximizes energy dissipation downstream of circular culverts under various hydraulic conditions.

ABSTRACT. This extended abstract presents preliminary results from an ongoing series of laboratory experiments investigating how the geometry of propeller-induced scours near quay walls depends on wall-roughness characteristics. The experiments are conducted over a granular sediment bed using a free Wageningen propeller and different wall configurations (smooth glass walls and sheet pile walls with different orientations). Differences in scour geometry are evaluated under comparable propeller rotational speeds, wall distances, and bed-clearance conditions. The preliminary results indicate variations in scour geometry associated with wall roughness, and the final results will be presented at the conference.

ABSTRACT. It is shown that the low-head dam downstream-part energy dissipation intensity depends on the underwater vortical pattern, which extends toward obstruction located downstream of the weir in the lower course of river. The specific energy function and momentum equation of the non-rectangular cross-section channels can be used to perform a hydraulic analysis for both the hydraulic jump and rapids-type flow situations (Laanearu, 2024). The quadratic-type channel hydraulic framework is used for this purpose, i.e. the low-head dam downstream flow characteristics are explained for pre- and post-reconstructed situations. It is shown that the underwater vortical pattern of pre-rebuilt weir is considerably changed as it is compared to the post-rebuilt situation. The rapidly varying flow at weir and rapids, depending on extreme river flow events, are discussed to explain the hydraulic modelling challenges due to climate changes and future river-basin restoration studies.

ABSTRACT. The developed eddy viscosity (Oldekop et al., 2019), based on Reynolds stresses, the modified mean velocity, its gradient, and turbulent kinetic energy, was computed from experimental data for a plunging breaker wave. This formula was integrated into a wave model, and the results were compared with those obtained from an identical numerical model. It was concluded that the eddy viscosity beneath a plunging wave on a sloping bottom demonstrates more intricate variation throughout the wave cycle and water depth than previously indicated by earlier models.

ABSTRACT. Field measurement data and internal-flow hydraulics are used to interpretate annual changes in water renewal processes within the Ebro Delta estuary (NW Mediterranean Sea) over past field measurement periods. Observed changes to the threshold heights of estuarine bed sediment features are attributed to several mechanisms related to cross-shore sediment transport driven by the river flow that erodes sediment bed features, and sea level changes in the Mediterranean that can increase or decrease bed threshold heights due along-shore sediment transport driven by wave action. It is shown that the stratified-flow processes in the Ebro Delta estuary switch between one- and multi-layer modes in different seasons, depending on variations of river discharge and sea water level. Results obtained from an internal-flow hydraulics model and a numerical modelling approach (BOM) are used to gain understanding of the varying stratification structure within the Ebro Delta estuarine exchange due to variations in the upstream freshwater outflow from the Ebro river and the water level within the Mediterranean Sea. The river cross-sections interfacial characteristics are compared.

ABSTRACT. It is shown that the low-height leveled point source exhausted pollutant causes seasonally dependent plumes in a city environment due to marine winds. An in-house developed CFD tool is used to generate smellscape maps, which includes the air temperature and pollution fields in pedestrian zone, near buildings and inside greenery areas. Four scenarios, considering distinct marine–urban areas temperature contrasts over one year period, are used to demonstrate the stratified-flow dynamics and access air-pollutant impacts in an urban canopy. The winter and summer times scenarios are used to demonstrate the air pollution distribution with less and most worst impact of pollutant in the close vicinity of point source, respectively. The spring and autumn times scenarios correspond to different inversed-temperature situations, where the point-source pollutant is trapped due to development of the stratified flow in the urban canopy.

ABSTRACT. It is shown that a low-height, thermally varying point source in a coastal-city environment produces dispersion patterns that depend strongly on local microclimate and land–sea temperature contrasts. A combined Gaussian–CFD smellscape framework is established, where the Gaussian model is first calibrated against CFD in an open, obstacle-free domain. For calibration, a non-stratified, unified-temperature case is used. The resulting dispersion parameters are then applied to the coastal configuration, enabling consistent pollution modelling in the original urban setup. When comparing the calibrated Gaussian solution with the CFD results, the CFD model reveals plume rise, lateral deflection, and recirculation features that the analytical approach cannot reproduce. When comparing CFD and Gaussian, the CFD solution reveals plume rise, deflection and recirculation effects that the Gaussian model cannot reproduce. The comparison confirms that the Gaussian approach is suitable only when the ambient wind exceeds the stack exit speed and the source is well-exposed above nearby obstacles, whereas under weak winds or within the urban canopy, CFD is required for realistic predictions. The presented workflow provides a practical tool for estimating near-field pollutant distribution, offering interpretable smellscape maps for communication, planning and operational support in coastal districts.

ABSTRACT. The UN SDG 6 on clean water and sanitation aims to ensure access to water and sanitation for all. The main global deficits on SDG 6 are connected to developing countries, while Europe and North America have neglectable fractions of their populations underserved. But the data from the UN reflects the situation in the Arctic region poorly. Greenland holds 10% of the world's freshwater reserves in its icecap, which is melting faster than ever, and efforts to utilize this water for energy production and to meet the increasing global water demand are developing. Still, however, a significant fraction of Greenland’s population continues to suffer from water scarcity, insecurity, and quality deterioration. Here I present the status of SDG 6 in Greenland and discuss environmental and health implications and prospected consequences of climate change. I also reflect on the application of a community based participatory approach in the strive for solutions.

ABSTRACT. Rewetting of peatlands remains the key measure to improve their ecological status. Although every peatland is different, hydrological processes standing behind the restoration of the formerly drained peat soil remain universal. Wishing to make peatland rewetting more feasible and wishing to provide the potential peatland managers with quantified benefits, we developed, programmed and published the SERVIPEAT software.

ABSTRACT. Nature-based Solutions (NbS) are increasingly promoted in European river basins to address intensifying hydrological extremes while supporting ecological restoration. Yet their hydrological functioning, spatial context-dependence, and governance requirements remain insufficiently understood in engineered lowland systems. This extended abstract synthesizes insights from two complementary NbS research strands: (1) qualitative, expert-based research on the hydrological and socioecological impacts of Eurasian beavers (Castor fiber) and (2) quantitative modelling research on riverine wetlands in a Dutch lowland catchment. Together, these studies examine how ecosystem-driven and designed NbS enhance retention, delay runoff, and increase hydrological connectivity, and how their combined insights can guide integrated, multifunctional river-resilience strategies.

ABSTRACT. 1 Introduction Agricultural drought (AD) is a critical natural disaster that evolved primarily from soil moisture (SM) deficiencies, threatening food security. Recently, the frequent drought events have considerably affected crop productivity, particularly in semi-arid regions such as Pakistan. Understanding drought variability at different soil depths offers valuable insights into the mechanisms of soil–atmosphere connectivity and their impacts on agricultural sustainability. Therefore, this study aims to characterize AD in Pakistan using SSMI across multiple soil layers and to elucidate its relationship with climatic variables and vegetation health. 2 Methodology Monthly soil moisture (SM) data for the period 1981–2020 were acquired and processed for three soil depths of 0–7 cm (surface), 7–28 cm (sub-surface), and 28–100 cm (deeper layer). The SSMI was analyzed for each depth to quantify agricultural drought frequency and intensity. The Mann–Kendall test and Sen’s slope estimator were used to test drought trends and their slope. The Standardized Precipitation Index (SPI) at multiple time scales (SPI-1, SPI-6, and SPI-12) was employed to determine the impact of meteorological drought on soil moisture anomalies. Additionally, the NDVI was used to reveal vegetation responses to SM deficits and to evaluate lag correlation between vegetation health and soil dry conditions. Moreover, the impact of climatic factors on drought conditions in different soil layers was manifested using conventional correlation analysis. 3 Results The SSMI effectively recorded the major drought events experienced in Pakistan, particularly during 2000, 2001, 2002, 2004, and 2018. The frequency of drought was comparatively higher in the surface soil layer (0–7 cm) with shorter durations, while deeper layers (28–100 cm) experienced fewer but longer drought events. Drought transition over different soil layers analysis shows that dry conditions propagated from surface to sub-surface and deeper soils with less than one month and one month lag time, respectively. The association of SSMI with different time scales of SPI varied by depth, exhibiting the higher correlation between SSMI and SPI-1 for surface soil, SPI-6 for sub-surface soil, and SPI-12 for deeper soil layers. This suggests that shallow SM is more susceptible to short-term precipitation variabilities, whereas deeper layers are associated with longer-term meteorological drought conditions. The association of SSMI with NDVI was significantly higher in vegetation-rich areas of Pakistan, while at the northern mountain site and sparse vegetation areas, a poor correlation between both factors was observed in this study. Moreover, NDVI exhibited comparatively strong correlations with deeper soil SSMI than surface soil layer SSMI, suggesting that vegetation health depends more on deeper SM availability than surface conditions. Moreover, the impact of climatic variables, including precipitation, potential evapotranspiration, temperature, evapotranspiration, and shortwave radiation, on drought conditions in the surface soil layer was more prominent than in deeper soil layers. Additionally, seasonal analysis elaborated that the relationship between climatic forces and SSMI was most pronounced during the crop-growing period, indicating the significance of climate, soil, and vegetation interactions in AD dynamics. 4 Conclusion This study explores the effectiveness of various soil layers SSMI in characterizing AD across Pakistan. Results show that surface soil SSMI can efficiently detect short-term droughts, while deeper soil layers capture long-duration drought conditions. The propagation of drought through soil profiles and its lagged association with NDVI provide crucial insights for drought monitoring and risk assessment. Understanding these depth-dependent relationships between soil moisture, precipitation, and vegetation health can significantly improve AD assessment and offer climate-resilient water management strategies in water-scarce and arid and semi-arid regions.

ABSTRACT. Climate-induced variations in thermal regimes can influence hydrological dynamics, crop growth and productivity, and ecosystem stability. As one of the largest components of water balance, agricultural water consumption is highly impacted by such thermal variations. Shifts in temperature patterns affect germination, flowering, and maturation processes, which can either enhance or constrain productivity depending on crop type and regional climatic conditions. Therefore, understanding the spatiotemporal evolvement of thermal condition is essential for evaluating the impacts of climate change on crop development. This study analyses the long-term dynamics of growing degree days (GDD) across Finland from 1961 to 2023 to quantify spatiotemporal variations in heat accumulation and their implications for crop development. Daily mean air temperature data from the Finnish Meteorological Institute, provided at a 10-km spatial resolution, is analysed using an analytical framework. GDD values were computed with a base temperature of 5 °C and accumulated through each growing season to capture temporal trends, regional variability, and changes in thermal thresholds relevant to key crops such as potato faba bean, barley, oats, and wheat. Trend detection using the non-parametric Mann–Kendall is employed to test the significancy of GDD variations throughout the record. The findings suggest rapid transformation in the thermal condition over Finland, reshaping agricultural timing and productivity potential. This spatiotemporal assessment provides a robust foundation for modeling climate adaptation strategies and supports sustainable management of northern agro-ecosystems under warming climate.

ABSTRACT. Water scarcity and rising energy costs in Mediterranean agriculture demand precision irrigation tools. Conventional scheduling often relies on static, tabulated FAO-56 crop coefficients (Kc), which fail to capture the significant intra-annual variability of multi-cut crops like alfalfa. This can lead to water over-application, particularly during the lower-demand spring and autumn cycles. This paper presents an adaptive computational framework within the OASIS IoT network to model this dynamic Kc. We first demonstrate that static FAO-56 values are only accurate during peak summer months, while observed Kc is significantly lower in early and late season. We then validate this seasonal pattern using two independent methods: (1) a satellite-based Kc derived from Sentinel-2 NDVI (Kc = -0.2190 + 1.6198·NDVI) and (2) an in-situ Kc derived from measured soil moisture depletion curves. Finally, we propose a novel and continuous model using harmonic functions to mathematically describe the seasonal evolution of the FAO-56 parameters (e.g., Kc_ini, Kc_max). This harmonic model provides a robust, low-effort pathway for significant water savings. It enables a truly adaptive management system that can be initialized with FAO standards and then progressively self-calibrates as local data is collected, optimizing the food-water-energy nexus for alfalfa and other multi-harvest crops.

ABSTRACT. Climate extremes increasingly threaten crop production, yet the nonlinear and interacting nature of weather drivers makes it difficult to define actionable thresholds at which yields decline. This study presents a transferable, data-driven workflow that detects and evaluates agroclimatic stress thresholds (ST) and stress types using standard weather and yield records. Using 1 km gridded daily data and regional potato yields (1990–2022) from Finland and the Netherlands, we computed six ETCCDI-style indicators for the potato growing season: RX5day (maximum 5-day precipitation), RX1day (maximum 1-day precipitation), CDD (consecutive dry days < 1 mm), CWD (consecutive wet days ≥ 1 mm), CSU (consecutive hot days TX > 25 °C), and CFD (consecutive cool-night days TN < 5 °C). The workflow combines collinearity screening, Random Forest (RF) modeling, SHAP-based feature selection, and partial-dependence analysis to derive initial thresholds (STᵢ). These are refined using class-density diagnostics to obtain adjusted thresholds (STₐ) and integrated through a multivariate majority-vote system for classifying stressed (Sh) and non-stressed (NSh) seasons. Additionally, stress types (wet, dry, heat, cool) are identified for each shocked year. Results reveal that early-season wetness dominates yield shocks in Finland, particularly when May RX5day > ~27 mm or CWD > 6 days, while mid-season dryness and heat drive losses in the Netherlands (e.g., July CDD > 9 days, RX5day < 25 mm). The model achieved strong multivariate performance (F1 ≥ 0.8 for most regions) and accurately detected historical shock years (e.g., 2018). To enable operational use, we defined “screen–confirm–modify” rules by month: screen with key indicators (e.g., RX5day₅ or CDD₇), confirm with secondary cues (CWD or CSU), and modify management (drainage, irrigation, heat mitigation) when thresholds are crossed. The framework thus converts complex climate–yield relationships into interpretable, month-resolved thresholds suitable for early-warning and decision support in climate-resilient agriculture.

ABSTRACT. Regulated rivers often contain engineered structures, such as dams, that obstruct fish migration. To mitigate these impacts, a variety of fish-passage solutions have been developed, including bypass channels and technical, semi-technical, and nature-like fishways. Rock-ramp fishways are a type of nature-like fishway, consisting of an inclined channel with boulders arranged to mimic natural riffles. These boulder arrangements create preferential migration corridors and low-velocity resting areas for fish. Reservoir operations can cause substantial fluctuations in flow depth within rock-ramp fishways, thereby changing the relative submergence of the boulders. The relative submergence, RS=h/H, is defined as the ratio of flow depth h to boulder height H. Variations in RS have been shown to modify the local hydraulic conditions, including the mean velocity distribution and turbulence characteristics (Nilsson et al., 2025). Silva et al. (2012) showed that fish altered their spatial use of the flow and tail-beat frequency in response to changes in turbulence intensity (TI), preferentially occupying regions with moderate TI while avoiding highly turbulent cores. They also identified Reynolds shear stress (RSS) as a key turbulence parameter, with variations in RSS being strongly linked to fish passage performance. Motivated by these findings, the present study examines how changes in RS at approximately constant bulk velocity, modifying the spatial distribution of TI and RSS in a laboratory-scale rock-ramp fishway.

ABSTRACT. Rubber dams are increasingly used in hydraulic engineering due to their operational flexibility, and cost of construction and maintenance. They enable reliable regulation of upstream water levels without moving mechanical parts, thereby eliminating issues related to corrosion, sealing, and the use of potentially environmentally harmful lubricants. (Gebhardt et al., 2018). Despite these advantages, concerns remain regarding their ecological impact, particularly with respect to downstream fish passage (Gebhardt et al., 2014). Like any weir structure, rubber dams represent a potential obstacle for migrating fish, and during downstream movement, individuals may experience delayed passage or physical injury upon impact with structural components downstream of the weir (Cox et al., 2023). In practice, the risk of fish injury at weirs is often estimated using criteria based on the ratio between tailwater depth and drop height. This approach, applied for instance in Germany (DWA, 2005) and the United States (USFWS, 2019), provides a simplified proxy for potential risk. However, for rubber dams this metric frequently yields unfavourable results because the nappe commonly impinges on the weir sill, which is often inadequately submerged or lacks sufficient tailwater depth. Moreover, this assessment method, originally developed for bypass channels and spillway systems, has been criticized for oversimplifying the complex hydraulics of weir flow conditions (Baumgartner et al., 2013; Duncan, 2013). In particular, the impinging nappe may locally displace the tailwater cushion, eliminating protective depth at the impact zone (Thorenz et al., 2018). Conversely, under certain conditions, especially at small drop heights or when the overflow jet is thick, fish may remain embedded within the water jet and thus avoid direct collision (Kaminski et al., 2024). The current binary classification of conditions as either “safe” or “lethal” is unrealistic; in practice, intermediate outcomes with varying levels of impact probability and injury severity are far more likely. To assess fish impact probability at rubber dams, a numerical modelling approach was applied (Kaminski et al., 2025). The simulations were conducted using OpenFOAM with the interFoam solver to capture free-surface flow dynamics, combined with passive inertial particles representing fish trajectories during downstream weir passage. Multiple rubber dam geometries and operating conditions were analysed, covering a range of flow scenarios and gate heights. Figure 1 shows representative simulations under different hydraulic conditions. For each simulation, collisions between particles and the concrete weir sill surface were recorded. The resulting data were used to establish a relationship between the impact probability and the dimensionless ratio of overflow depth to maximum gate height. The derived relationship allows for an approximate estimation of the fish impact probability for a wide range of rubber dam configurations and flow scenarios. While the method does not directly quantify biological injury or mortality, it provides a more physically meaningful measure than the conventional tailwater-to-drop-height criterion. The model captures the essential hydrodynamic mechanisms governing fish descent, including nappe embedding and local cushion displacement, offering a better approximation to fish passage safety. Rubber dams are increasingly used in hydraulic engineering due to their operational flexibility, and cost of construction and maintenance. They enable reliable regulation of upstream water levels without moving mechanical parts, thereby eliminating issues related to corrosion, sealing, and the use of potentially environmentally harmful lubricants. (Gebhardt et al., 2018). Despite these advantages, concerns remain regarding their ecological impact, particularly with respect to downstream fish passage (Gebhardt et al., 2014). Like any weir structure, rubber dams represent a potential obstacle for migrating fish, and during downstream movement, individuals may experience delayed passage or physical injury upon impact with structural components downstream of the weir (Cox et al., 2023). In practice, the risk of fish injury at weirs is often estimated using criteria based on the ratio between tailwater depth and drop height. This approach, applied for instance in Germany (DWA, 2005) and the United States (USFWS, 2019), provides a simplified proxy for potential risk. However, for rubber dams this metric frequently yields unfavourable results because the nappe commonly impinges on the weir sill, which is often inadequately submerged or lacks sufficient tailwater depth. Moreover, this assessment method, originally developed for bypass channels and spillway systems, has been criticized for oversimplifying the complex hydraulics of weir flow conditions (Baumgartner et al., 2013; Duncan, 2013). In particular, the impinging nappe may locally displace the tailwater cushion, eliminating protective depth at the impact zone (Thorenz et al., 2018). Conversely, under certain conditions, especially at small drop heights or when the overflow jet is thick, fish may remain embedded within the water jet and thus avoid direct collision (Kaminski et al., 2024). The current binary classification of conditions as either “safe” or “lethal” is unrealistic; in practice, intermediate outcomes with varying levels of impact probability and injury severity are far more likely. To assess fish impact probability at rubber dams, a numerical modelling approach was applied (Kaminski et al., 2025). The simulations were conducted using OpenFOAM with the interFoam solver to capture free-surface flow dynamics, combined with passive inertial particles representing fish trajectories during downstream weir passage. Multiple rubber dam geometries and operating conditions were analysed, covering a range of flow scenarios and gate heights. Figure 1 shows representative simulations under different hydraulic conditions. For each simulation, collisions between particles and the concrete weir sill surface were recorded. The resulting data were used to establish a relationship between the impact probability and the dimensionless ratio of overflow depth to maximum gate height. The derived relationship allows for an approximate estimation of the fish impact probability for a wide range of rubber dam configurations and flow scenarios. While the method does not directly quantify biological injury or mortality, it provides a more physically meaningful measure than the conventional tailwater-to-drop-height criterion. The model captures the essential hydrodynamic mechanisms governing fish descent, including nappe embedding and local cushion displacement, offering a better approximation to fish passage safety. Further research is required to translate impact probability into biological injury metrics, which will necessitate coupling the hydrodynamic simulations with empirical data from laboratory or field studies using live fish or sensor surrogates. Nevertheless, the presented approach represents a significant methodological step toward a more realistic assessment of downstream fish passage over rubber dams. In its current form, the estimated impact probabilities can already be incorporated as correction factors or modifiers in existing evaluation frameworks, providing a more nuanced and defensible assessment of ecological risks associated with rubber dam operation.

ABSTRACT. Hybrid Barriers have emerged as promising technology to guide or deter fish at hydropower facilities while maintaining hydraulic continuity. However, meaningful experimentation in this field requires expertise not only in hydraulics and fish ecology but also in electrical engineering and animal welfare. To address this interdisciplinary challenge, the FishLab Innsbruck was established as a new research infrastructure to conduct controlled live fish experiments under reproducible hydraulic and electrical conditions. The facility enables systematic testing of electrified barriers under realistic flow conditions and provides the necessary monitoring systems for safe animal handling and continuous system supervision.

ABSTRACT. Invasive carp species (silver, bighead, and grass carp) have become a significant problem for native populations of fish in the United States (Kolar et al, 2005; 2007). The carps compete for food resources with native species and they reproduce and spread rapidly throughout connected watersheds. Carps congregate to spawn and the fertilized eggs float freely in the water column until they develop enough to swim. In order to predict egg dispersal and identify control solutions, sophisticated models are needed to assess the transport and dispersion of the free-floating eggs and larvae.

Several models have been developed for predicting egg paths. The models require both a hydrodynamic component and a tracking algorithm. Existing hydrodynamic models that have been used to investigate this problem include one-dimensional models (Garcia et al., 2013) and three-dimensional models (Li et al., 2022). In addition, Li et al. (2022) examined two-dimensional hydrodynamic model implications. Egg tracking algorithms generally combine deterministic results of the hydrodynamic model with information about egg diameter and buoyancy and a statistical model that represents turbulent diffusion. For example, for horizontal displacement of an egg over a short time step, the following equation is used: X_(i,t+∆t)=X_(i,t)+U_i ∆t+R√(2K_h ∆t) (1) where X is the horizontal position vector [m] of the egg, U is the flow velocity vector [m/s], t is a time step [s], R is a random number sampled from a normal distribution, and Kh is horizontal eddy diffusivity [m2 s-1]. A different equation that considers egg fall velocity (affected by egg weight, buoyancy, and drag) and vertical turbulence characteristics is required for vertical displacements. Modeling is complicated by the fact that egg characteristics are time dependent (Li et al., 2022). Due to the stochastic nature of turbulent diffusion, many realizations of egg flow paths must be simulated to get a probabilistic representation of egg dispersion.

For three-dimensional hydrodynamic models, the local flow velocity used in Eq. 1 is a direct result of the solution, but for one- and two-dimensional models, assumptions must be made about the vertical (and horizontal for 1-D) velocity distributions in the river. For example, the vertical distribution is generally assumed to follow the log-law. Then, as each tracked egg changes position, its velocity can be assessed from the local average velocity of the flow, the log-law, and the height of the egg above the bed.

In the present work, egg dispersion is modeled in a 19-km reach of the Platte River in eastern Nebraska. The Platte River is braided with high sediment loads. Typical flow rates range from less than 40 m3/s to more than 300 m3/s throughout the year. The river is about 450-m wide at bankfull and about 1-m deep during low flows. The high aspect ratio of the river favors a two-dimensional hydrodynamic model; therefore, HEC-RAS 2D was utilized. Gaging stations at the ends of the reach provided boundary conditions and were used to calibrate the model. Python scripts were written to process hydrodynamic model results and predict egg paths. The scripts account for changes in egg buoyancy and size, horizontal and vertical egg position, velocities based on the hydrodynamic results, and turbulent diffusion. Vertical variations in velocity utilize the log-law based on the 2-D hydrodynamic model. 5000 virtual carp eggs were tracked for each condition.

For low flows, eggs were significantly retarded by interactions with sandbars and banks, and there were long delays in egg advection when eggs followed side chutes. During higher flows, eggs traveled much more rapidly. This was in part due to increased velocities, as anticipated, but was also due to the submergence of sand bars that would otherwise have forced the eggs to follow longer paths. Additional work is being done to improve model performance near banks and sandbars, where eggs get artificially trapped due to the discretized bathymetry representation and spatial resolution limitations of the hydrodynamic model.

ABSTRACT. Dams fragment rivers and interrupt ecological connectivity, posing a serious threat to anadromous and diadromous fish populations. To mitigate the effects of river fragmentation, water managers need to build efficient upstream and downstream fishways. Fishways are usually designed to match the requirements of all target fish, even if the requirements are sometimes contradictory, e. g. flow velocities must be high enough to attract strong swimmers, but should not impede passage by weak swimmers (e.g. Schütz et al. 2024). Simultaneously, fishways must be affordable and constructible, often restricted by limited space. For these reasons, fishways often constitute a compromise between several challenging requirements. Design guidelines must address these challenges by reconciling fish ecological and physiological requirements with feasible and hydraulically effective solutions. Ideally, design criteria would be derived directly from research results. However, due to the multitude of complex interactions between the biotic and abiotic environment, this ambitious goal is often unattainable, and therefore the transfers of research findings into planning practice requires simplifications. These simplifications entail uncertainties and cause far-reaching consequences for the planning and monitoring process of fishways, as well as for fishway research itself. The present contribution is based on the experience of 15 years of construction consultancy and practice-oriented research conducted by fish biologists from the Federal Institute of Hydrology (BfG) and hydraulic engineers from the Federal Waterways Engineering and Research Institute (BAW). The requirements and conflicts associated with the transfer of fishway research into practice are illustrated using the example of vertical slot fishways according to German guidelines, with a focus on the design velocity in the slot. German guidelines (DWA 2014) demand, that flow velocities resulting from the drop height between adjacent pools do not exceed critical velocity limits for fish characteristic in the river region of the barrier. Since only five different river regions are distinguished in Germany, the single limit value for one region and all target species cannot cover the species specific relationship between swimming performance and hydraulics, let alone individual fish. In that case, the compromise between feasibility and fish ecological requirements was already part of the development of the design criterion. From a scientific point of view, the relationships are much more complex. Values for species specific swimming performance are available, but usually based on swimming-chamber experiments which strongly deviate from natural conditions and may significantly underestimate the true ability of free-swimming fish (Castro-Santos et al. 2013). The flow field between two adjacent pools is also extremely complex due to separation processes, eddies and flow velocity fluctuations. The design drop height is calculated using a single characteristic velocity derived from the Toricelli-equation. This means that the turbulent flow field experienced by the ascending fish is not considered in the determination of the flow velocity used for the design of the fishway. Even though the current guidelines greatly simplify the reality as experienced by the fish, they are still the best solution for addressing the swimming performance and the flow velocities when designing fish passages. The practical implications for the planning and monitoring process and for the development of design guidelines itself are given below. Planning process A frequently occurring problematic planning situation arises when site-specific constraints prevent the application of a design criterion. Various strategies can be employed to resolve such conflicts. Accepting the deviation from the criterion will result in the risk of a reduced functionality of the fishway. To reduce these uncertainties, the feasible planning options can be investigated, using hydraulic or ethohydraulic models (i.e. fish tests) or (AI-trained) agent-based models. Depending on the chosen strategy, the remaining uncertainties influence the decision of how to achieve the objective (a functional fishway). However, one strategy that is often encountered in practice should be avoided: applying the highly simplified relationship described for individual fish (with the expectation of a functional fishway), without taking into account the compromises underlying the design criterion. Applying this consideration to the example of the design of the pool-type fishway means: the relationship between flow velocity and fish swimming performance from guidelines cannot be used to guarantee functionality for individual fish species. Irrespective of the applied method to eventually reduce uncertainties: it is important to evaluate the function of the constructed fishway and to make adjustments if necessary (adaptive management) (Silva et al. 2018). Monitoring process Since temporal and spatial flow processes are not represented by guideline threshold values, hydraulics, when monitored in fishways, can deviate from designated values. Especially point measurements of water levels and flow velocities are sensitive to measurement location. Also, hydraulic processes depend on hydrological boundary conditions (i.e. head- and tailwater levels) that will differ from design load cases most of the time. Thus, when fishway design follows geometric demands, hydraulic measurements are usually not meaningful and monitoring should focus on ecological aspects. Development of design guidelines Fishway research has a long way to go before it can establish universal design criteria that serve a wide range of species. For the foreseeable future, dealing with uncertainties regarding functionality will be part of the process. Nevertheless, both fundamental research at the interface between turbulent flow and fish behavior and both, site- and non-site-specific applied research are important for the development of design guidelines, as they reduce uncertainties. With respect to the example used in the present manuscript, BfG and BAW-research activities addressing the interaction of fish swimming performance and pool-hydraulics include, among others, hydraulic investigations of the turbulent flow field (e.g. Sokoray-Varga et al. 2022), etho-hydraulic modelling assessing different slot configurations (e.g. Schütz et al. 2024) or the development of AI-based individual models. Ultimately, they all aim to reduce uncertainties at fishways in German waterways and further improvement of design guidelines. Multispecies fishway design is not a largely proven technology (Silva et al. 2018). However, since the implementation of ecological connectivity is crucial and urgent for many fish species, it is reasonable to build fishways based on best available knowledge and where necessary to adapt them to incorporate new findings derived from scientific results and monitoring of existing fishways in the future.

ABSTRACT. The analysis of turbulent flow over complex natural beds requires numerical frameworks capable of directly resolving roughness-induced structures. This study applies OpenFOAM to simulate flow over a real nonuniform gravel bed using a high-resolution STL (STereoLithography) surface extracted from 3D scanning. Both Unsteady Reynolds-Averaged Navier–Stokes (URANS) and Large Eddy Simulation (LES) were performed. A snappyHexMesh-based workflow was developed to resolve the near-bed geometry with local refinement down to 1 mm. Results demonstrate that OpenFOAM accurately represents mean velocity structure and turbulence characteristics. The LES model more effectively captures vortex shedding, near-bed mixing, and anisotropic turbulent motions. The developed open-source workflow highlights the capability of customized CFD to reproduce gravel-bed hydrodynamics with full access to solver settings and mesh controls.

ABSTRACT. Decentralized wastewater treatment plants (DWWTPs) are commonly used in sparsely populated areas of Finland serving between 100 and 1000 population equivalent (PE), but their ability to remove micropollutants (MPs) is not well known. This study examines the occurrence and removal of selected MPS in ten DWWTPs in northern Finland, considering treatment type and seasonal effects. All in all, results indicate that out of 137 MPs, 108 compounds have been observed at least once in the utilities. Removal efficiencies for most compounds were generally negative and highly variable across sampling events, while caffeine and ibuprofen consistently showed high removal (>80%). Seasonal effects were not significant, whereas the treatment process influenced removal efficiency, with a significant difference observed between the biological rotating contactor (BRC) and Batch Activated Sludge (AS).

ABSTRACT. Antimicrobial resistance (AMR) is one of the most important public health challenges of this time. Small-scale wastewater treatment plants, also known as decentralized wastewater plants, are often overlooked as a potential source of antimicrobial resistance proliferation, therefore, a critical gap is evident and requires investigation. In this study, we collected influent and effluent samples from several small-scale wastewater systems in Finland and Sweden, all of which serving a population equivalent of less than 2 000. Moreover, these plants were selected based on the treatment process each utilize. DNA was extracted from the water samples after which, five candidate genes were quantified using digital PCR to see how much of these genes were removed after treatment processing. We expect a reduction of AMR genes from the small-scale treatment plants. Moreover, we also expect differences in removal for the different treatment processes.

ABSTRACT. This study evaluates the pharmaceutical removal efficiency of a two‑stage vertical‑flow constructed wetland functioning in subarctic climatic conditions in northern Sweden. 23 sampling campaigns were conducted between 2023 and 2025 to assess key physicochemical parameters and pharmaceutical residues in the water before and after each treatment step. Reed and organic deposit from the wetland were also sampled and analyzed for pharmaceuticals. Preliminary results show that the total concentration of pharmaceuticals in the water was reduced, although the treatment performance varied substantially across substances, and seasons. These results provide a comparative understanding of the retention and removal efficiency of emerging contaminants in this type of wetland. It was also seen that pharmaceuticals accumulated in the sludge and were taken up by the reed, indicating possible removal paths.

ABSTRACT. In the Arctic region, advanced WWT is uncommon. Up to 20% of Arctic domestic WW is discharged without any treatment, and a secondary treatment level or higher is accomplished in for as little as 19%, which is significantly less than the 86% reported for Europe and North America overall. Inadequately treated WW in the Arctic region is, thus, a likely source of pollutants in the Arctic region. Emissions could constitute a direct exposure route when local recipients are used for the harvest of seafood for human consumption. Here, we present an overview of the overall Arctic status on wastewater treatment and affiliated contamination, and zoom in on the situation in Greenland and Sisimiut.

ABSTRACT. With the introduction of the Net-Zero Industry Act (NZIA), the European Union has reaffirmed its commitment to achieving climate neutrality by 2050, implying a substantial transformation of the European energy system. According to the Global Energy and Climate Outlook 2024 (GECO) (European Commission, 2025), achieving a 1.5 °C pathway requires a massive expansion of variable renewable energy sources (VRES), with wind becoming the dominant source of electricity generation and solar PV capacities increasing several-fold by mid-century. With this drastic increase in VRES, the need for Energy Storage is evident as it can decouple variable electricity generation from consumption in time, thereby reducing curtailment of renewables and improving overall utilization of existing generation assets. Topalovic et al. (2023) highlight that while pumped-hydro storage (PHS) provides high power capacity and cost-efficient operation, its economic viability is often constrained by suitable geography and high initial investment costs. To address these limitations, the Store2Hydro project investigates the conversion of existing hydropower plants (HPPs) into PSH facilities, reducing environmental, social, and economic constraints associated with new developments. A methodology was developed to identify and classify suitable HPPs across Europe. Plants requiring only minimal modifications to be retrofitted to PSH facilities are defined as Category 1 sites and mapped together with their respective potential storage capacities across Europe. In addition, European wind and solar generation were modelled enabling simulations that combine converted Category 1 sites with surrounding VRES and electricity demand to assess the system-level impacts. This abstract briefly describes the site mapping process as well as the methodology for simulating the impact of the found HPPs.

ABSTRACT. Renewable energy is a clean source of energy which naturally renews itself in a short period of time and is available for repeated use. Hydropower energy is found as an important renewable energy source and crucial due to its flexibility and storage capabilities. A pumped storage hydropower system (PSHS) is a sustainable solution for grid stability due to its flexibility as a large-scale battery. The implementation of an efficient rim-driven truster (RDT), a booster pump, with a reversible pump turbine in PSHS may provide a new direction to its development. Current study proposed a systematic MATLAB-based design approach for the rim-driven truster. The design condition has been fixed with some input parameters, such as rotational speed, outer diameter, and flow rate of the pump. A blade-design methodology is developed by adapting classical axial-flow pump principles to the hubless configuration. The workflow consisted of constructing velocity triangles to generate 1D mean-lines, creating 2D blade sections using NACA derived thickness profiles, and stacking these into complete 3D geometries. Moreover, to obtain a better grasp about the performance of the designed truster, computational fluid dynamics (CFD) simulations have been carried out. The high-fidelity RANS calculation with the SST k-ω turbulence model is used to investigate the inner flow characteristics of the pump. To establish the design methodology, a performance characteristic is developed with various operating points. The design optimisation is also performed for two geometrical parameters, Z (blade number) and t (blade thickness). The blade number is found to influence the head delivery, with six blades producing slightly higher head than seven or eight, although these differences remained within the uncertainty margin. Cavitation trends are observed clearly: thicker blades generated lower local pressures and therefore were more prone to cavitation. Blade number had a smaller effect, but fewer blades generally reduced cavitation risk. Furthermore, an Eulerian-Eulerian framework-based approach is also implemented to examine the pump performance with sand-laden flow.

ABSTRACT. Reservoirs and rivers do not only provide services for society through hydropower production but are at the same time used for recreational purposes, like boat use, fishing, swimming and other nature experiences. By changing the water regime of waters with pumped-storage hydropower (PSH) the use of waters by the local community might be affected and consequently impact the local community. Studying the social acceptance of PSH and mapping out the impacts on the local communities will allow development of mitigation measures that maintain or even improve the possibility for recreational use.

1. Methods A systematic literature review was conducted on social acceptance of PSH. Searching the databases “Scopus” and “Web of Science” showed 167 and 112 articles, in total 216 articles after duplicates were removed. 3 particles were added from screening reference lists from relevant articles, bringing the total to 219. After all abstracts were reviewed, 23 articles were included in the next step, where the whole article was assessed. The full text review resulted in 8 articles that were relevant literature on social acceptance of PSH. Semi-structured interviews were conducted with stakeholder groups to gain in-depth knowledge of how environmental effects of PSH in reservoirs are perceived. Interviews were conducted with two key stakeholder groups: 1. Representatives from environmental non-governmental organizations (NGOs) 2. Representatives from the hydropower/pumped storage sector Based on the literature review, themes addressed in the interviews included: • Perceived environmental impacts of PSH • Implications of more frequent reservoir water level fluctuations • Consequences for outdoor recreation and resource user interests • Perspectives on planning processes and social acceptance of PSH • Possible mitigation measures to reduce environmental and recreational impacts

2. Results The motivation for implementing PSH for the hydropower sector is the increased storage and production capacity when needed. The hydropower sector perceive the local community to be positive inclined towards PSH and argument that PSH is less controversial that land-based wind power. In literature, PSH is reported to be preferred over other energy storage technologies due to their close familiarity to conventional hydropower, their grid benefits and association with water, thereby being more “natural”. However, the literature review also shows that there is generally low knowledge and awareness on PSH (Gaede et al. 2020, Jones et al. 2019, Mercer et al. 2020, Thomas et al. 2019).

The interviews with NGOs confirmed that reservoirs and surrounding areas are important sites for recreational use. Both recreational and environmental NGOs agreed that pumped-storage hydropower can pose environmental risks, and affect recreational use. However, the general attitude towards PSH was mixed. The knowledge gap on PSH described in literature (Gaede et al. 2020) was also mentioned in several interviews, making it difficult for stakeholders to assess environmental effects of PSH.

Rapid water level fluctuations, changes in water temperature, altered water chemistry, and potential shift in species composition were perceived as environmental effects that could alter the recreational use of PSH reservoirs and surrounding areas. Ice stability emerged as a particularly important concern, especially for organizations representing recreation users. Despite this concern, a power company reported experience with pumping for almost 5 days in a row wintertime, resulted in a water level increase of 110 cm and no issues with ice safety, except very close to the water outlet.

Recreational NGOs expressed a more context-depended view on PSH, pointing out that case-by-case assessment with attention to potential environmental impacts and their implications for recreation were needed. Two interviewed environmental NGOs expressed notably different perspectives. There was strong skepticism on one side, expressing concern for the intensive regulation of freshwater systems and deterioration of ecological conditions and a generally positive attitude on the other side, pointing out the role of PSH in the transition to low-emission energy systems globally.

As mentioned by Jones et al. (2021), the interviews show that planning and licensing processes for PSH can cause concern when there are limited opportunities for influence, though some organizations have been involved at a early stage in planning and consultation processes and providing input during licensing procedures. Especially the implementation of mitigation measures is a process that needs input from affected communities, this is highlighted in both the interviews and literature (Cantor et al. 2025, Thomas et al. 2019). Suggested mitigation measures from the interviews were restrictions on water level fluctuation during sensitive periods, improved ecological monitoring and better mapping of environmental conditions prior to development.

Though there is no general opposition described in literature against PSH, specific projects can still be opposed (Cantor et al. 2025). Disruption of migration routes on ice covered reservoirs for species like domestic and wild reindeers are issues that can influence social acceptance of PSH. Karambelkar et al. (2025) and Cohen et al. (2014) show that actual deployment of PSH can be hindered by significant environmental justice and procedural issues. Distrust in developers (Jones et al. 2021) and exploitation of rural or Indigenous lands for the benefit of urban areas and global goals (Cantor et al. 2025) are areas causing opposition and need to be addressed prior to PSH development.

ABSTRACT. Here presented is the development of digital twins for hydraulic modelling and sediment management of pumped hydropower storage within the Horizon Europe project Store2Hydro. Initially, the modelling of pumped storage hydropower in existing hydropower infrastructure was performed on generic cases in Work Package 2 (WP2) of the project in order to demonstrate the technology for a wide range of morphologic and hydraulic conditions representing different types of European rivers. The results show that morphologic parameters such as river slope, cross-section shape and river size are important, not only for the storage capacity, but also for the local hydraulic conditions when virtually converting conventional hydropower plants to pumped storage plants. Simulations including the sediment dynamics also show that cyclic pumping influences both sediment deposition/erosion patterns close to the power plant in the short term and the long-term build-up in the reach. These models will be extended to real geometries and test-cases within WP5 during the next two years, which will also include environmental impact assessments.

ABSTRACT. The general shape of rivers is influenced by the convergence of flow hydraulic and sediment transport properties, with the latter’s complexity being a topic of high interest among researchers for the last two centuries. Sediment erosion, transport and deposition heavily impact channel evolution, stability and habitat of river systems, thus the understanding of sediment dynamic is crucial to predicting said characteristics. This is further complicated when introducing cohesive sediments, which in addition to the transport processes of bedload and suspended load driven by grain size and flow conditions, also display increased ramifications due to electrochemical bonding and flocculation. Numerical models are widely used to simulate such processes with satisfying results, relying on empirical transport equations describing erosion, deposition and particle entrainment. However, sediment transport modeling is highly sensitive to sediment properties and choice of transport formula. This study will conduct a sensitivity analysis of sediment parameters and transport formulas in HEC-RAS 1D models using monogranular synthetic bathymetries which entail, long-term simulations simulating deposition and erosion conditions. This is aimed at probing relatively simple modelling of river morpho dynamics that is widely used and might be further implemented in a river digital twin layout at low computational cost. 1. Methodology The synthetic bathymetries consist of 8 straight rectangular channels, with varying sloped and dimensions. Each bathymetry was designed to represent a true river channel, with grain sizes ranging from cobbles to silt, although neglecting particle size sorting and planimetric divagation that is typical for large scale 1D approach. The dimensions were based on the Chézy-Strickler formulas for skin and bedform roughness, initially defining the grain size and critical shear stress for particle entrainment, from which the slope of the channel and water velocities are back calculated. Sediment transport functions are based on literature and adapted for each case. The maximum erodible depth is arbitrarily set at 10 meters for all cases. While this value is exaggerated for the smaller rivers, it is a reasonable depth for the larger ones and thus kept constant to avoid variations from the simulations exceeding the maximum erodible depth. The sensitivity analysis is conducted firstly on cross-section distance and computation increments under uniform-steady flow, the equilibrium load and sediment load series boundary conditions (corresponding to equilibrium load), running simulations of 30-day durations. The first boundary condition is used to obtain the sediment volume output, which will be used as input for the sediment load series. The cross-section distances were chosen arbitrarily as multiples of the channel width, within the range Δx=B – 10B, where Δx is cross-section distance and B is channel width. The net sediment volume of the channel is used as evaluation of the analysis, presented as a percentage of the average volume input/output. The best performing test is then used to investigate the influence of the computation increment, which were based on the ratio of Δx/Δt ranging from 0.0001-1, where Δt is computation increment, using the same evaluation criteria. These analyses provide the influence of truncation errors produced by the model geometry and flow computations. Aiming at clarifying hydropower layout possible perturbation on riverbed, long-term simulations of 10-year periods were conducted on all cases, specifically testing deposition and erosion conditions, e.g., dam-upstream and -downstream perturbations, respectively. Deposition experiments further bifurcated in two cases: (1) steady case and (2) oscillating scenarios. Steady case refers to uniform flow, upstream boundary condition, the equilibrium sediment load, and the downstream backwater effect (i.e., water height set to twice the normal depth). In the oscillating case, the upstream flow and sediment input were the same as in the steady case, but the downstream boundary condition features an oscillation of ± 15% of the aforementioned water height. For the erosion experiments, the upstream boundary condition was again a uniform flow, but with zero input load (i.e., sediment starving), and the downstream water height was maintained at normal depth. The oscillating scenarios are supposed to reflect hypothetical powerplant operations and see the effect of oscillating water levels on the sediment deposition/erosion. Investigated outcomes include sediment volume, terrain change, and the expected time of propagation for bed perturbation, i.e., the celerity of the sediment deposition/erosion. More detailed sensitivity analysis was developed on the silt case for uniform-steady flow, due to the availability of parameters with the inclusion of cohesive properties. A comparison between the Laursen and Yang transport function was conducted. In addition, the cohesive parameters of particle erosion threshold (τ_c), particle erosion rate (Kd), mass wasting erosion (τ_MW) and mass wasting erosion rate curve (Kd_MW) were tested along different ranges to note the influence on channel geometry and sediment volume. 2. Preliminary results The preliminary results show that the truncation errors are very minimal, with net volume lower than 1% of the average volume transported, with the exception of Gravel and Very Coarse Sand cases where it is higher than 10%. Deeper insight is needed, but initial suspicions suggest that these discrepancies are due to the grain size being at the limit of the applicable grain size for the transport functions available in HEC-RAS. Cohesive properties showcased significant impact on the results, displaying high erosion and deposition. These also made the impact of the transport function more prevalent. Using Laursen transport function on the silt case resulted in more sediment transport than Yang by one order of magnitude. The long-term simulations give varying but expectable results. Sediment volume transported and terrain change increase proportionally to the grain size applied, ranging six orders of magnitude. As for the celerity, the pattern is less linear, which enhances the effect of different transport functions being applied, although similarly ranging six orders of magnitude. For the cases using Yang and Laursen functions, Yang demonstrates decreasing celerity with decreasing grain size, meanwhile the latter displays the opposite effect. The oscillating scenarios are yet to be analyzed and are to be provided with the full paper.

ABSTRACT. The study explains the dynamics of air-water stratified flow in a sloped pipe with constant diameter and restricted ventilation. The air-circulation process in a real-length hydraulic model with realistic diameter is investigated for a water filling case. This study qualitatively analyses the air-circulation process in a large-diameter pipe, to explain the air inflow and outflow situations, which may be relevant for outdoor air quality analysis in urban environments. For this purpose, the 3D Computational Fluid Dynamics (CFD) model, representing the two-phase flow of immiscible fluids, is used. The numerical model flow regime is chosen to be turbulent, and the air and water phases are considered to be incompressible, isothermal and Newtonian fluids. Interface tracking for the air-water flow is resolved by applying the volume of fluid method. The case study demonstrates the ability of the advanced numerical modelling tool to predict air-water interfacial drag and associated air exchange of the collector, which is ventilated through three venting towers .

ABSTRACT. Air entrainment and dispersed bubble transport can play an important role in the hydraulic behaviour of navigation locks during filling operations. When strong turbulence or local plunging phenomena occur, air can be introduced into the water body in the form of bubbles that rise, diffuse, and interact with the surrounding water. These processes alter the mixture density and thus influence momentum exchange and free-surface dynamics. Bubbles can coalesce and form larger air pockets, which can violently erupt from the water. This potentially endangers both vessels during the locking process and the operational staff of the lock. As a consequence, air entrainment is generally avoided in the planning process of locks with deep culvert systems (PIANC 2025). In this work, a modelling approach is presented that aims to model the flow of air and water on the large scales of a navigation lock. Conventional interface-capturing approaches based purely on the Volume of Fluid (VoF) method do not adequately capture these effects, because dispersed bubbles fall well below the grid resolution and a sufficiently fine grid is not feasible for the spatial scales encountered at a navigation lock. The modeling approach applied here couples Large-Eddy Simulation (LES) concepts with a sub-grid scale model for air bubble transport. Preliminary results for the phenomenological validation of air-water flows at the navigation lock in Hannover-Anderten (Germany) are presented.

ABSTRACT. The simultaneous presence of air and water in a gravity-flow pipe—typical of a Water Collection System (WCS)—creates complex two-phase flow regimes. Ventilation is determined by the drag between the moving water interface and the air in the pipe headspace, resulting in air exchange through connected manholes. A critical knowledge gap exists in urban water engineering: There are currently no hydraulic formulae available for modelling the airflow in headspace and manholes, thus of ventilation of WCS. To address this issue, a custom-built numerical model was developed utilizing the open-source Computational Fluid Dynamics (CFD) library, OpenFOAM. This software uses a two-phase solver (interFoam), features fully custom geometry and meshing (using blockMesh) and appropriate boundary conditions to investigate the air-phase characteristics under varying conditions. The influence of three different pipe slopes on the air flux is investigated in a half filled pipe located between two manholes with atmospheric top ends. The numerical solutions aim at the understanding the fundamental hydraulic principles of air-water stratified flow within gravity-flow pipes.

ABSTRACT. This study investigates the hydraulic and airflow dynamics of a section of the urbanised area combined sewerage system located in a highly populated area through modelling and field-based validation. A detailed hydraulic model was developed using the US EPA Storm Water Management Model (SWMM), incorporating the physical characteristics, operational conditions, and boundary inputs. Simulated flow rates and discharge hydrographs were generated for a range of observed rainfall and dry-weather conditions. To evaluate model reliability, the results were systematically compared with field measurements collected within the Engineering Tools of Stratified-Flow Processes in the Built Environment project, which provided high-resolution discharge data under real-world operating conditions. The comparison enabled the identification of both systematic and event-specific discrepancies. Beyond hydraulic flows, the study also examined air-water interactions within the sewer system. Air volumes and airflow velocities are derived for the modelled network segment.

ABSTRACT. This study presents an endeavour to parameterize the hydraulic-type solutions of air-water stratified flow in a sloped pipe. The air-flow velocity is coupled with the water-flow velocity due to an interfacial drag in the gravity pipe using an air-part force-balance equation with the frictional and pressure-gradient terms. It is shown that if the fluids (air and water) are specifically coupled in terms of gravity, and wet and dry pipe-wall skin friction, then the stratified flow develops, where the air flow inside the pipe interior head space is purely driven by water flow below, i.e. the fluxes are related to the gravity-driven water flow. The Manning roughness scale is related to the Colebrook-White formula friction factor to gain pipe-wall roughness height under changing hydraulic radius. The air-flow part force-balance equation solutions, which are dependent on the frictional and pressure-gradient terms, are coupled with the Manning equation solutions to relate the water-flow fluxes with the air-flow fluxes in a simplified manner due to the air-water interfacial drag without pressure-gradient term.

ABSTRACT. This study presents an attempt to model and simulate the hydraulic-type solutions of air-water stratified flow in a sloped pipe with a large-scale diameter and restricted ventilation through scattered manholes along main. Four dry-weather scenarios and corresponding wet weather cases are considered in the urbanized catchment area to model hydraulically the air-water stratified flow inside the underground pipe, focusing on a hydraulic-gradient dependent formation of air cavity. For this purpose, the Manning-formula based solutions are developed in frames of the CoCoViLa platform application. The model is constructed using primitive building blocks as pipes and manholes, inlets and tanks, and enables computing the water and air flows in the system using standard hydraulic formulae for water flow and complemented parameterised air flow tables. This study gives an insight into the complexity of air-water stratified flow in a poorly ventilated water collection system, which reveals naturally the quasi-steady flow due to the distinct diurnal flow pattern that is characteristic for a large-city type water consumption profile, and the coastal-region stormwater events.