HS10.10 | Modeling and Design of Natural and Nature-Based Features with a particular focus on rivers and ecosystems affected by hydropeaking
Modeling and Design of Natural and Nature-Based Features with a particular focus on rivers and ecosystems affected by hydropeaking
Convener: Gabriele Chiogna | Co-conveners: John Kucharski, Marie-Pierre Gosselin, Daniel S. Hayes, Marriah Abellera, Bregje van Wesenbeeck, Mauro Carolli
| Thu, 27 Apr, 10:45–12:30 (CEST)
Room 2.31
Posters on site
| Attendance Thu, 27 Apr, 16:15–18:00 (CEST)
Hall A
Posters virtual
| Attendance Thu, 27 Apr, 16:15–18:00 (CEST)
vHall HS
Orals |
Thu, 10:45
Thu, 16:15
Thu, 16:15
Using natural and nature-based features (NNBFs) in designing new infrastructure while preserving impacted ecosystems are long-standing goals in civil and environmental engineering. These goals are also an increasing focus of scientific research, as the demand for environmentally- friendly solutions to traditional engineering challenges grows. This session invites presentations on two emergent and highly multi-disciplinary topics in the field of water resources planning and management: (1) The incorporation of NNBFs in new infrastructure designs, and (2) the management of river systems impacted by hydropeaking- the discontinuous release of turbined water in response to peaks in energy demand that causes artificial flow and river stage fluctuations downstream of hydropower plants. Under the first topic area, a particular focus is given to innovation that advances the methods, models, and techniques used to capture the co-evolution of biological and physical processes that contribute to the performance of NNBFs in infrastructure designs. Under the second topic area, a particular focus is given to research that advances our understanding of the hydrologic, sediment transport, biotic and hydrogeochemical processes affected by fluctuations in river flows. Presentations under both topic areas are expected to cover a range of computational, field, and laboratory experiments that address multiple spatial and temporal scales in various riverine and coastal environments. The session’s presentations will focus on interactions between ecohydrological processes and new and existing water resources infrastructures.

Orals: Thu, 27 Apr | Room 2.31

Chairpersons: Gabriele Chiogna, Marriah Abellera, Daniel S. Hayes
On-site presentation
Peter Herman

The application of nature-based solutions for flood protection in low-lying coastal areas has recently received much attention. The solution is attractive because it may lower the costs for coastal defense, increase the effectiveness and resilience of defense measures, curb negative trends in biodiversity of globally important animal populations and contribute to carbon capture and storage.

Nature-based flood defense measures are based on relatively well-established biogeomorphological principles of self-organisation in coastal landscapes. Vegetated foreshores in particular contribute to wave damping, accumulation and stabilization of sediments maintaining a shallow bathymetry, capacity to adjust bed level to sea level rise and, in some conditions, provision of accommodation space for storm surges. Uncertainties in the contribution of ecosystems to flood safety arise from incomplete modeling capacity for sediment dynamics, inclusion of sub-grid phenomena, complex spatial structure, limited understanding of edge dynamics and sparse knowledge of ecosystem behavior under extreme loading. For application at regional scale, the most difficult problem is that nature-based solutions are needed most where natural processes are weakest, e.g. due to extreme encroachment of the coast.

In the broader context of use of nature-based solutions as measure to adapt to increased relative sea level rise, a crucial question is how these solutions will behave at longer term. Geological evidence shows that increased rates of sea level rise forces coastal wetlands to become narrower and to move faster inland. An important factor determining this behavior is the sediment mass balance, inhibiting the vertical rise of an ever-larger surface of marshes with increasing sea level. A second factor is the stability of the seaward edge under conditions of increased wave attack in deeper coastal profiles. These phenomena are observed in contemporary systems with high rates of subsidence.

Future-proof nature-based solutions for flood defense will have to resolve the issues related to the regional sediment mass balance and long-term stability of the coastal ecosystems. Whether the strategy is to hold the line of the coast or to withdraw, future coastlines will need sufficient sediment sources, sufficient sediment transport capacity and sufficient ecosystem resilience to provide extended services combining flood defense and biodiversity conservation. Major scientific challenges in the design and use of nature-based solutions are identified at this system scale.

How to cite: Herman, P.: Nature-based solutions for flood protection in a systems perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17143, https://doi.org/10.5194/egusphere-egu23-17143, 2023.

Virtual presentation
Patrick Ray and Jacob Tracy

The fundamental water resources problem to be solved in adaptation to climate change is increasing rainfall variability: generally, flood peaks are increasing, and dry-season water availability is decreasing. Large, centralized adaptation strategies such as reservoirs impounded behind tall dams typically perform well at both attenuation of flood peaks, and augmentation of dry season flows. They come with substantial costs, however, in terms of capital cost outlays and damages to local ecological and human environments. The Intergovernmental Panel on Climate Change, the United States (US) Government, the European Union, the United Nations, and many other institutions and agencies are currently advocating for the adoption of “nature-based solutions” (NbS), which are believed able to reduce adverse climate change impacts at community scale, while supporting biodiversity and securing ecosystem services. However, the potential of NbS to provide the intended benefits has not been rigorously assessed. This talk presents a preliminary assessment of climate change vulnerabilities for the Chimanimani biosphere reserve in Zimbabwe, and an evaluation of the tradeoffs between conventional “hard” civil infrastructure and decentralized NbS.

How to cite: Ray, P. and Tracy, J.: Quantitative assessment of the tradeoffs between conventional “hard” civil infrastructure and nature-based solutions for climate change adaptation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16603, https://doi.org/10.5194/egusphere-egu23-16603, 2023.

On-site presentation
Jennifer Olszewski, John Kucharski, Matthew Smith, Marriah Abellera, and Todd Steissberg

Nature-based features (NNBFs) have emerged over the past two decades as tools to leverage natural processes that provide a range of functions from flood reduction to pollutant removal. Despite their growing popularity, a notable gap remains between our understanding of internal NNBF processes and our ability to design NNBFs for specific objectives (e.g., x% reduction of peak storm flow, x% nitrogen reduction) by leveraging such processes. NNBF benefits are, as a result, difficult to quantify, making them a riskier investment compared to tried-and-true grey infrastructure alternatives. This knowledge gap must be filled if we want to design effective and sustainable NNBFs that are viewed on equal footing with grey infrastructure. This presentation will discuss the development of a non-tidal constructed wetland model for the purpose of evaluating design suitability across a range of performance metrics. This model, written in MATLAB, couples hydrologic, hydraulic, and water quality modules. It also allows the user to adjust the constructed wetland configuration (i.e., shape, area, grid cell water depths, vegetation placement, etc.) to maximize specific performance objectives including flood control, wildlife habitat, and water quality. Current efforts are also underway to build upon this design model concept to (1) expand to tidal wetland environments like salt marshes, (2) incorporate vegetation growth/death and morphologic processes, and (3) to incorporate future uncertainty into the design process to support the development of robust and sustainable NNBFs across a range of potential futures and landscape contexts. The overall aim of this work is to develop a framework that allows engineers and policy-makers to evaluate NNBF performance on level footing with grey infrastructure alternatives.

How to cite: Olszewski, J., Kucharski, J., Smith, M., Abellera, M., and Steissberg, T.: Nature-Based Features: developing a framework to shift them from risky investments to reliable and robust solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3548, https://doi.org/10.5194/egusphere-egu23-3548, 2023.

On-site presentation
Jesse Bootsma, Bas Borsje, Daphne van der Wal, and Suzanne Hulscher

Intertidal vegetation is renowned for its capacity to reduce wave energy and thereby enhance coastal safety. At present, this concept is well established on local scales (meters to marsh-mudflat system) and relatively short terms (hours to years). However, the development of intertidal vegetation on larger scales (i.e. the spatial scale of an estuary and the temporal scale of decades) is unknown. Consequently, it is impossible at the moment to quantify the wave damping capacity at these scales. In this paper, the decadal spatiotemporal characteristics and dynamics of intertidal vegetation are studied by combining available data (e.g. from field surveys) and remote sensing techniques (Combining SAR and optical remote sensing). For this analysis, the Scheldt estuary, with a tidal reach of more than 160km from the mouth near Vlissingen, the Netherlands, till Gent, Belgium, is used as study area. Intertidal vegetation located in salt, brackish and freshwater environments is considered to cover the changes in salinity regimes in estuaries. More specifically, the vegetation species considered in this study are: Common glasswort (Salicornia europaea), Common cordgrass (Spartina anglica), Saltmarsh bulrush (Scirpus maritimus), Common reed (Phragmites australis) and Common willow (Salix alba). The variability in vegetation distribution in this study has three components: (1) the areal extent i.e. total marsh dimensions and associated variability in this (expansion/retreat); (2) the variability in vegetation characteristics e.g. density, biomass, height and seasonality; and (3) shifts in vegetation species i.e. going from one species to another at the same location over time. Since the wave damping capacity of a vegetated intertidal area is a combination of the wave attenuation from the bottom friction and the attenuation due to the presence of vegetation, the bed topography corresponding to the vegetation pattern is established from laser altimetry (LiDAR) data. Ultimately, the wave damping capacity of intertidal vegetated areas under various storm conditions is determined using a Simulating WAves Nearshore (SWAN) model, based on the spatial vegetation patterns and characteristics, as well as the variation in bathymetry. Quantification of the decadal dynamics of intertidal vegetation in estuaries and its impact on the wave damping capacity will help us to give recommendations for the effectiveness and the design of nature-based coastal protection measures.

How to cite: Bootsma, J., Borsje, B., van der Wal, D., and Hulscher, S.: Decadal intertidal vegetation development in an estuary and its effect on the wave damping capacity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11683, https://doi.org/10.5194/egusphere-egu23-11683, 2023.

On-site presentation
Guido Zolezzi, Francesca Vallefuoco, Anna Casari, Stefano Larsen, Valentina Dallafior, and Maria Cristina Bruno

We investigated the ecohydraulic effects of a recently implemented hydropeaking mitigation measure in the Upper Noce Stream (NE Italy, Italian Alps), which also allows for additional hydropower production. The Upper Noce, a 3rd order gravel-bed stream, was affected since the mid-1920s by storage hydropower production and associated hydropeaking. The mitigation measure consisted in the diversion of most of the released hydropeaks into a sequence of three newly-installed, cascading run-of-the-river power plants, fed by a penstock running almost parallel to the former hydropeaking reach. The hydropeaking-diversion mitigation measure markedly reduced hydropeaking on a 10-km stream reach, and hydropeaking is now released immediately upstream the confluence with a major free-flowing tributary, which increases the hydropeaking baseflow. The flow regime in the mitigated reach shifted from hydropeaking-dominated to baseflow-dominated regime in winter, with flow variability represented only by snowmelt and rainfall in late spring and summer. We applied two sets of indicators (the Hydropeaking Indicators HP1, HP2 and the COSH method) and conducted a simplified hydraulic analysis of the hydropeaking wave propagation. We assessed the ecological effects of the mitigation measure using three complementary data sources: the analysis of (a) the benthic and (b) hyporheic invertebrate communities, based on datasets collected before and after the implementation of the diversion measure, and (c) ancillary data monitored by the diversion plant manager for required environmental monitoring, which included the suspended sediment regime and the Extended Biotic Index, measured yearly from the year before to the four subsequent years after the implementation of the mitigation measure.

Three main changes in eco-hydraulic processes associated with hydropeaking mitigation were detected. i) The flow regime in the mitigated reach changed to a residual flow type, with much less frequent residual hydropeaks, with an average two-fold increase in downramping rates that were recorded downstream the junction with a major tributary. ii) The functional composition of the macrobenthic communities shifted slightly in response to flow mitigation, but the taxonomic composition did not recover to conditions typical of more natural flow regimes. This was likely due to the reduced dilution of pollutants and resulting slight worsening in water quality. iii) The hyporheic communities conversely showed an increase in diversity and abundance of interstitial taxa, especially in the sites most affected by hydropeaking, and this effect was likely due to changes in the interstitial space availability, brought by an alteration of the previous time-space pattern of fine sediment transport, which eventually resulted in reduction of fine sediments clogging of the gravel bed interstices.

Besides illustrating a feasible hydropeaking mitigation option for Alpine streams, this work suggests the importance of monitoring both benthic and hyporheic communities, together with the flow and sediment supply regimes, and physico-chemical water quality parameters, for carefully detecting changes in eco-hydraulic processes associated with hydropeaking mitigation that may not be fully expected in the design phase.

How to cite: Zolezzi, G., Vallefuoco, F., Casari, A., Larsen, S., Dallafior, V., and Bruno, M. C.: Assessing the eco-hydraulic effects of a hydropeaking mitigation measure with increased energy production in the Noce River (Italian Alps), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14621, https://doi.org/10.5194/egusphere-egu23-14621, 2023.

On-site presentation
Zeeshan Virk

Zeeshan Tahir Virka, Faisal bin Ashrafa,b, Ali Torabi Haghighia, Bjorn Klovea, Seppo Hellstenc, Hannu Marttilaa

a University of Oulu, Faculty of Technology, Water, Energy, Environmental engineering Research Unit

b Stockholm Environment Institute (SEI)

c Finnish Environment Institute (SYKE)




Fluctuating energy prices in the Nordic region call for short-term river flow regulation at hydropower plants (HPPs). This short-term regulation leads to Hydropeaking – the pulsating water flow downstream of an HPP. Hydropeaking is detrimental to the overall health of the river, impacting all riverine and riparian ecosystem services. One of the major ecosystem services affected by hydropeaking in Nordic rivers is the socio–recreational ecosystem service (SRES), which holds significant value for Nordic culture and human wellbeing. We examine how SRES are affected by hourly hydropeaking events in a large Nordic River reach. Employing two indicators based on normalized daily maximum flow difference and sub-daily flow ramping we estimated annual and seasonal trends of hydropeaking in the studied reach of the Kemijoki River system. The study reach was found to be under “High Pressure” peaking class in all seasons. For SRES impact assessment, we applied a novel methodological approach to multiple layers of high-resolution spatio-temporal data. An overlay analysis of inundation maps derived from 2D-hydrodynamic modeling and a customized land classification map based on a machine learning algorithm resulted in identification of SRES areas under influence of sub-daily hydropeaking within the study reach. The degree of impact on SRES corresponded to seasonal variations of sub-daily hydropeaking where the highest impact was observed in the summer season The most affected recreational land uses were the shore and litorine areas. Furthermore, as intraday flow ramping results in peaking waves downstream of the HPP, our results show that most part of the river channel becomes hydraulically unsafe during hydropeaking events, especially in summer, which is popular in the context of Nordic culture and tourism. Consequently, hydropeaking can seriously impact the social, and recreational services offered by Nordic rivers; therefore, regulation practices at the HPPs should also consider SPES aspects.  We recommend further research to evaluate these services so that tradeoffs between energy production at HPPs and ecosystem services of rivers can be balanced.

How to cite: Virk, Z.: Nordic socio-recreational ecosystem services in a hydropeaked river system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4122, https://doi.org/10.5194/egusphere-egu23-4122, 2023.

On-site presentation
Isabel Boavida, Renan Leite, Maria João Costa, Anthony Merianne, Daniel Mameri, Fernando Afonso, José Maria Santos, and António Pinheiro

The artificial pulsed flows occurring downstream of hydropower plants due to electricity demand, i.e. hydropeaking, affect habitat selection by fish. This effect is particularly unknown for cyprinids, which are the most representative freshwater fish family in European rivers. This study aimed to evaluate the utility of two types of flow-refuge by Iberian barbel (Luciobarbus bocagei) at an indoor flume (6.5m x 0.7m x 0.8m) as a potential solution to mitigate the effects of pulsed flows associated to hydropower production. Based on previous comprehensive research conducted on cyprinids and with the results of this study, the best type of flow-refuge was selected, up-scaled and implemented downstream of small hydropower plants. Two different approach angles with the flume wall - 45⁰ and 70⁰ - were tested to assess the effectiveness of the created hydraulic conditions on attracting fish to the flow-refuge. For each type we tested a base flow event (7 l.s-1), simulating river natural conditions, and a peak flow event (60 l.s-1), simulating pulsed flows. For each setting, two flow-refuges (downstream and upstream) were installed in the flume and tested with a school of five Iberian barbels. The utility of the flow-refuges was assessed by the frequency and time of use by fish at two distinct flow-refuge locations i.e., downstream (area between the flume and the adjacent flow-refuge walls), and inside (the effective covered area of the flow-refuge). Blood glucose and lactate levels were quantified to identify potential physiological adjustments associated with the pulsed flows and the flow-refuge type. Preliminary results indicate that fish behavior differs according to flow event and the type of flow-refuge. The frequency of a single fish using the flow-refuge was higher in the 45⁰ refuge during pulsed flows than in the 70⁰. Overall, the average time spent inside the flow-refuges was higher during pulsed flows for both types and higher in the 45⁰ refuge.  After the 60 l.s-1 events, the blood glucose and lactate levels were higher than in the 7 l.s-1 events. In addition, lactate levels for the 45⁰ flow-refuge during the 60 l.s-1 events, were the highest when compared to 7 l.s-1 events. These results may be explained by the higher velocities created in the presence of the 45⁰ flow-refuge, shown by ADV results, that favoured individual use and rheotactic behaviour, setting off physiological adjustments, increasing residency time and the efficiency to use the flow-refuge.

How to cite: Boavida, I., Leite, R., Costa, M. J., Merianne, A., Mameri, D., Afonso, F., Santos, J. M., and Pinheiro, A.: Mitigating the hydropeaking using flow refuge: an experimental case-study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16568, https://doi.org/10.5194/egusphere-egu23-16568, 2023.

On-site presentation
Simon Führer, Daniel S. Hayes, Thomas Hasler, David R. M. Graf, Felix Stoisser, Elora Fauchery, Anna Coudrais, Antonin Olejarz, Daniel Mameri, Stefan Schmutz, and Stefan Auer

Artificial sub-daily flow fluctuations caused by peak-operating hydropower plants are considered one of the most significant impacts on riverine ecosystems downstream of dams. These rivers have, therefore, been subject to numerous studies in recent decades. However, cyprinid fish, in contrast to salmonids, have hardly been addressed in hydropeaking studies yet, and extensive knowledge gaps remain. Therefore, our experimental study aims to assess the effects of rapid flow reductions on the early life stages of two European cyprinid indicator species, the common barbel (Barbus barbus L.) and the common nase (Chondrostoma nasus L.).

We conducted mesocosm experiments (2.25×2 m) under semi-natural conditions at an outdoor experimental facility (http://hydropeaking.boku.ac.at), simulating different hydropeaking scenarios with varying down-ramping rates during day and night. At each trial, 100 fish from one species (body length <20 mm) were stocked at peak flow (80 L.s-1). After an acclimation time (15 min.), the flow rate was reduced with variable ramping rates (0.3–1.8 cm.min-1) to constant low flow conditions (10 L.s-1). As a response parameter, larval stranding on a gently sloped shoreline mimicking typical nursery habitats was quantified during day and night.

The results reveal distinct diurnal patterns for both species, with increased stranding rates at night for all experimental scenarios. In addition, the data indicate differences between the tested down-ramping rates and show interaction effects between both parameters. The difference between species may result from water temperature and ecological factors. The study outcomes will benefit the ongoing discussion on species-specific hydropeaking mitigation by providing first insights on the direct effects of artificial flow down-ramping on early life stages of cyprinid fish.

How to cite: Führer, S., Hayes, D. S., Hasler, T., Graf, D. R. M., Stoisser, F., Fauchery, E., Coudrais, A., Olejarz, A., Mameri, D., Schmutz, S., and Auer, S.: Stranding of early cyprinid life stages: effects of artificial flow down-ramping on Barbus barbus L. and Chondrostoma nasus L. under experimental conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5678, https://doi.org/10.5194/egusphere-egu23-5678, 2023.

On-site presentation
Giulio Dolcetti, Sebastiano Piccolroaz, Maria Cristina Bruno, Elisa Calamita, Stefano Larsen, Guido Zolezzi, and Annunziato Siviglia

Rivers are increasingly recognised as active players in the global carbon cycle. They are able to transport, transform, and exchange organic matter, and can emit considerable fluxes of greenhouse gases (e.g., CO2) into the atmosphere, with a magnitude comparable to the global carbon input to the oceans. However, the quantification of these processes is still affected by considerable uncertainties, driven by an incomplete understanding of the interplay between physical, geochemical, and biological parameters, and by a lack of spatially and temporally resolved high-quality data. For instance, and despite a potentially strong impact on kilometres of rivers worldwide, the effects of hydropeaking on riverine CO2 emissions have been almost completely neglected until recently (Calamita et al., Unaccounted CO2 leaks downstream of a large tropical hydroelectric reservoir, PNAS 2020). As a contribution to filling this knowledge gap, we present the results of a field-measurement campaign performed in a single-thread Alpine river (River Noce, Italy) during multiple hydropeaking events. Data of water-dissolved CO2, water temperature, and flow discharge, were collected sub-hourly both downstream and upstream of the outlets of a hydropower plant, revealing a complex pattern of variation in time at both locations. Water released from the hydropower plant during hydropeaking had oversaturated CO2 concentrations relative to the atmosphere, in close agreement with water samples collected in the hypolimnion of the upstream reservoir. Higher flow rates during hydropeaking events were associated with higher rates of gas exchange through the water-air interface. Higher exchange rates and higher CO2 concentrations in water during hydropeaking events enhanced CO2 fluxes, as confirmed by measurements with a floating CO2 flux chamber. Meanwhile, the CO2 concentration upstream of the outlets displayed strong diel fluctuations around the atmospheric equilibrium concentration, which were likely driven by primary production within the residual flow during the day. It is shown that the residual flow can have a previously unacknowledged added value as a CO2 sink during the day, fueled by its biological activity. Hydropower releases bypassed the residual flow and discharged hypolimnetic water oversaturated with CO2 at high flow rates during hydropeaking, offsetting CO2 concentration and fluxes downstream of the outlets and increasing emissions on average. These results highlight the ubiquity of hydropeaking impacts also with respect to greenhouse gas emissions. They illustrate the complexity of the riverine carbon cycle and demonstrate the importance of temporally and spatially-resolved data for the accurate assessment of the riverine carbon balance.

How to cite: Dolcetti, G., Piccolroaz, S., Bruno, M. C., Calamita, E., Larsen, S., Zolezzi, G., and Siviglia, A.: Measured temporal variations of CO2 concentration and atmospheric emissions in a hydropeaking-impacted river, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-560, https://doi.org/10.5194/egusphere-egu23-560, 2023.

Posters on site: Thu, 27 Apr, 16:15–18:00 | Hall A

Chairpersons: John Kucharski, Marie-Pierre Gosselin, Mauro Carolli
Gabriele Chiogna, Monica Basilio Hazas, Giorgia Marcolini, Teresa Pérez Ciria, and Francesca Ziliotto

This presentation aims at covering different and interdisciplinary research aspects focusing on hydropeaking, highlighting in particular which temporal scales are relevant at different spatial scales. We will present how the impact of hydropeaking at the catchment scale changed in the past decades due to changes in legislation and the energy market and the role of hydropeaking in the context of energy complementarity. We will then focus on the effects of sudden river stage fluctuations at the reach scale and their impact on surface water-groundwater interaction and eventually on energy and mass transfer processes, considering seasonal, weekly and sub-daily time scales. Finally, laboratory scale investigations will show the effects of hydropeaking on solute mixing in porous aquifers. The environmental impact of hydropeaking on the ecosystem calls for effective mitigation strategies and policies to find a sustainable compromise between energy production and ecosystem preservation which are capable of tackling processes occurring at multiple spatial and temporal scales.

How to cite: Chiogna, G., Basilio Hazas, M., Marcolini, G., Pérez Ciria, T., and Ziliotto, F.: Hydropeaking: a multiscale perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-656, https://doi.org/10.5194/egusphere-egu23-656, 2023.

Davide Vettori and Costantino Manes

Coastal areas are among the most endangered zones worldwide due to ever increasing physical and environmental pressures exacerbated by the effects of climate change. Eelgrass ecosystems represent a promising nature-based solution because they promote biodiversity and carbon capture. Recent works have concluded that eelgrass can also contribute to reduce physical pressures on coastal areas by damping incoming waves. However, the large number of governing physical parameters and the limited amount of data available make it hard to quantify the wave attenuation due to eelgrass in natural scenarios.

In the present work extensive laboratory experiments were conducted to characterise the wave attenuation properties of eelgrass in a range of natural scenarios. Experiments were conducted in a 50m long wave tank wherein a 4m long and 0.1m high meadow of eelgrass replicas was located. Eelgrass replicas modelled a range of eelgrass species (e.g. Cymodocea nodosa, Zostera marina) to a scale between 1:1 and 1:8 depending on the conditions considered. Replicas were designed using both Cauchy and Froude similarities and considering the morphology and flexural rigidity of eelgrass. A total of 330 experiments were performed varying the most important governing parameters, namely: water depth (from 0.15m to 0.6m), plant densities (up to 1338 plant/m2), wave height (up to 0.16m depending on the water depth) and length (between 1m and 4m). Thus, the wave Cauchy number in the tests ranged from unity up to 7000. During experiments the water surface level along the tank and the meadow was measured by means of 8 resistance gauges that recorded at 128 Hz with a relative error up to 2%. From water surface level data, the mean wave height at each location was calculated and the wave attenuation coefficient of eelgrass was estimated based on the variation of mean wave height along the patch.

The resulting wave attenuation coefficients agree well with the model proposed by Lei & Nepf (2019) for submergence ratios larger than 0.2, even though for low attenuations the relative uncertainty is high. The wave attenuation caused by the eelgrass meadow is significantly larger than that due to the friction at the bed and lateral walls for submergence ratios over 0.2 and meadows denser than 251 plants/m2. These values may represent important thresholds for eelgrass contribution to wave attenuation in coastal areas.

How to cite: Vettori, D. and Manes, C.: Characterisation of wave attenuation by eelgrass meadows via laboratory experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2851, https://doi.org/10.5194/egusphere-egu23-2851, 2023.

Marek Petreje, Michal Sněhota, Petra Heckova, Bara Rybova, Tomas Chorazy, and Michal Novotny

Implementation of a green roof can require large amounts of natural resources such as water and natural components of the substrate. Therefore, green roof system that uses the principles of a circular economy has been developed and tested. Two studies were performed to evaluate performance of substrate for green roof amended with a recycled crushed brick and pyrolyzed sewage sludge (biochar). In order to design and select a suitable substrate, 8 substrate variants were prepared and tested. Physical properties such as maximum water capacity, retention curves, bulk density, grain size and pH were analyzed in order to selected suitable substrates for case studies.

First case study was performed on green roof size 7x5 m2. The aim was to evaluate the performance of the substrate in real conditions and to compare it with a commercially available substrate. To assess the effect of pyrolyzed sewage sludge, only part of the green roof contained biochar (9.5 vol. %), whereas the crushed brick was part of both substrates (37.5 vol. %).

Second study was performed on two elevated experimental beds in order to verify performance of the novel concept of combination of constructed wetland and extensive green roof irrigated with pre-treated grey water which we call hybrid green roof. The substrates amended with the same recycled materials as in the first study were used.

In hybrid green roof system, greywater is first pumped into the constructed wetland to be treated and then is used for irrigation of green roof. Performance of this hybrid green roof system was assessed on the basis of water balance measurements, laboratory analyses of water samples taken from various parts of the experimental beds, temperature and water content measurements along the experimental bed´s layers height. The hybrid green roof system is viable. There are relatively low concentrations of nutrients (phosphorus and nitrogen) in the leachate from test beds, namely because the irrigation provides the water directly to the drainage layer and nutrient rich substrate enriched with biochar isn't leached by irrigation water. Concentrations of nutrients increases only in response to precipitation. The constructed wetland part of the system proven a high potential to reduce the nutrients concentration in pre‑treated grey water.

The vegetation formed by Sedum spp. carpets is prospering well on both elevated experimental beds in the second study as well as on green roof in the first study. Nutrients from biochar are apparently available for the vegetation. Therefore, the vegetation on the bed and green roof with biochar amended substrate shows more vigorous growth and higher evapotranspiration. Substrates amended with recycled materials developed in the study had comparable properties (maximum water capacity, bulk density, pH) with commercial substrates.

This research has been funded by research projects: TN01000056/03, GA22-25673S

How to cite: Petreje, M., Sněhota, M., Heckova, P., Rybova, B., Chorazy, T., and Novotny, M.: Case study of extensive green roof with growing media amended with recycled materials and hybrid constructed wetland-extensive green roof, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6159, https://doi.org/10.5194/egusphere-egu23-6159, 2023.

Eleanor Pearson, Barry Hankin, Nick Chappell, Keith Beven, and Steve Rose

This poster summarises a range of new findings on monitoring and modelling the effectiveness of Natural Flood Management including from NERC/UKRI NFM programme over the last five years covering a range of nature based solutions designed to slow, store and infiltrate flood water. The updates cover the following areas: Quantitative evidence (monitoring and modelling) of effectiveness of different NFM features or systems of features; Performance failure of NFM measures or systems of measures; Evidence for climate change resilience of measures;  Trade-offs between clusters of NFM features versus large individual NFM features; Evidence for resilience of NFM at high and low flows and; Evidence for integrated benefits including water resources and water quality in combination with flood risk regulation; Advances in distributed modelling of different NFM features and evidence for shifts in effective parameter shifts; Scaling modelled parameter shifts to represent changes at larger scales.

The poster also solicits additional quantitative evidence from international colleagues and will be used to update evidence summaries being used in the UK.

How to cite: Pearson, E., Hankin, B., Chappell, N., Beven, K., and Rose, S.: Compilation of new evidence for the effectiveness of measures to emulate natural flood management (NFM) in the last 5 years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6368, https://doi.org/10.5194/egusphere-egu23-6368, 2023.

David Dorthe, Michael Pfister, and Stuart N. Lane

The thermal regime of regulated rivers is altered by rapid discharge variation downstream of hydropower plants (hydropeaking). This strongly modifies the thermal regime of such rivers, due to both the upstream water storage and the associated regular release to downstream, resulting in a thermal wave as the water temperature is different from the river temperature (thermopeaking). This temperature alteration needs to be considered when managing hydropower installations because of its influence on the health of aquatic ecosystems. On a longer timescale, global climate change is also influencing the natural thermal regime of rivers through changes in air temperature, vegetation, hydrology, etc. Thus, the assessment of the effects of hydropower on streams needs also to consider the extent to which changing climate will modify existing hydropower impacts, and also the mitigation methods that have been developed for current climate situations.

To evaluate the evolution of river temperature under different scenarios, deterministic coupled, hydrodynamic and temperature modelling can be used. Such models have been used previously to replicate the thermal regime of rivers or evaluate the impact of climate change on river temperature. However, there is a growing realisation that external drivers of stream temperature are more complex than hitherto thought, especially in per-Alpine streams. For instance, such streams can have significant shading whose importance changes as a function of time within the year. Equally, between the zone of water off-take and return, the residual flow may not occupy the full channel perimeter meaning that it is also necessary to consider the energy balance effects of water-adjacent sediments.

To address this challenge this paper identifies the necessary ingredients of deterministic coupled hydrodynamic and temperature modelling for hydropower impacted streams. This is supported by a unique and very high-quality stream temperature dataset which we use to identify the minimum process representation required for such models. In order to reproduce such data, we show that such models need to have a spatially-explicit and time-dependent correction of two key processes: (1) solar shading; and (2) stream bed sediment effects.

How to cite: Dorthe, D., Pfister, M., and Lane, S. N.: The necessary ingredients for deterministic modelling of hydropower management and climate change impacts on stream temperature in peri-Alpine streams, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7088, https://doi.org/10.5194/egusphere-egu23-7088, 2023.

Kim van den Hoven, Carla J. Grashof-Bokdam, Pieter A. Slim, Ludolph Wentholt, Patrik Peeters, Davy Depreiter, André R. Koelewijn, Carolien Kroeze, and Jantsje M. van Loon-Steensma

Managed realignment is the landward relocation of flood infrastructure to reintroduce the tide on former reclaimed land. A managed realignment site is an ecological restoration site. At the same time, it forms a new type of hybrid flood defence that makes use of Natural and Nature Based Features. Nature-based flood protection is provided by the flood risk reduction capacity of the restored habitat such as saltmarshes, complemented by the landward relocated flood defence infrastructure, i.e., the realigned dike. The realigned dike is either a (reinforced) existing or newly constructed dike. The realigned dike can be built or reinforced from local resources such as the saltmarshes and formerly reclaimed land. Material from the removed dikes can also be re-used. In history, saltmarsh sods have been used as building material for the dikes themselves and for their revetment. The sods were also used as emergency dike repair material. In addition to the use of local resources as building material for flood infrastructure, the mining of local resources can simultaneously support nature restoration under the dynamic circumstances of the coast.
      We tested the historic sod technique for dike revetments at a managed realignment project in progress where the dikes were available for real size experiments. On a dike with grass revetment, we studied the erosion resistance of transplanted dike grass sods after one growth season. Grass sods were transplanted to the inner and outer dike slope. The erosion resistance of the transplanted sections was tested under calm and extreme conditions with a grass pull test, a wave impact simulator, an overflow generator, and by analysing roots development. After one growth season, we found that the vegetation of transplanted sods continued to grow and started to connect to the original dike revetment. While some erosion occurred under extreme circumstances, the grass pull test revealed the transplanted sod revetment was stronger than a bare clay revetment. The erosion resistance of transplanted sods after one growth season is promising when compared to for instance a newly seeded grass revetment.
      In conclusion, the sod application technique can provide local resources for the revetment of realigned dikes. Sod transplantation can also be used to introduce target species at for instance the dike toe. At the same time, mining of (grass) sods from former land or saltmarshes can support nature restoration and development. Our results can hereby contribute to increase our ability to design flood infrastructure with Natural and Nature Based Features.

How to cite: van den Hoven, K., Grashof-Bokdam, C. J., Slim, P. A., Wentholt, L., Peeters, P., Depreiter, D., Koelewijn, A. R., Kroeze, C., and van Loon-Steensma, J. M.: Local resources for dike revetment in managed realignments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7770, https://doi.org/10.5194/egusphere-egu23-7770, 2023.

Prasanta Sanyal, Santrupta Samantaray, and Ritwick Mandal

In general, availability of groundwater have shaped human settlement and land-use patterns by providing water for the people living in an area. However, anthropogenic activities including the agricultural practice impacted the quality and quantity of groundwater significantly. Therefore, it is crucial to monitor and quantify the human impact, and to find pathways towards more sustainable use of groundwater. The Hindon basin in the north-west part of Indo-Gangetic plain in India which once witnessed the Indus valley civilisation, now negatively affected by human influences. The river basin covers an area of ca. 7000 km2 and is inhabited by more than 10 million people. The catchment of the Hindon river hosts sugar mills, paper mills, textile industry and intensified agricultural activities. The land-use pattern data shows that 66% of land is utilised for agriculture including orchards, 15% is used for settlements, 0.5% for industrial purposes, and less than 2% of the basin area has forest cover which is of poor quality. The main crops in the area is sugarcane, and urea is used extensively in the agricultural field. The run-off of nutrients and agrichemicals from the fields deteriorating the water quality, making the Hindon one of the most polluted stretches in the Indo-Gangetic plain.

To quantify the impact of agricultural activities in groundwater, water isotopes (δ2H and δ18O) and dual isotopes of dissolved nitrate (δ15N and δ18O) been measured in groundwater. The water isotope data suggest that impact in groundwater is so severe that the canal water, sourced from the glacier melt of the Himalaya, which pass of though the basin is recharging into the groundwater. The dual isotopes of nitrate suggest that the dissolved nitrate which is much above the WHO prescribed limit is mostly sourced from the fertilizer urea. Our result suggests that for sustainability, a multi-crop agricultural practice with less demanding water crop with reduction of use of urea is the need of the hour.

How to cite: Sanyal, P., Samantaray, S., and Mandal, R.: Understanding the impact of agricultural activity in groundwater by water isotopes and dual isotope of dissolved nitrate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8797, https://doi.org/10.5194/egusphere-egu23-8797, 2023.

Davide Vanzo, Looser Michael, David F. Vetsch, Sabine Fink, and Francesco Caponi

Hydropower production has different recognized impacts on river ecosystems. In particular, it alters the natural hydrological regime with extended low-residual flow conditions interrupted by rapid daily and sub-daily flow fluctuations, i.e. hydropeaking. Hydropeaking impacts both biotic and abiotic compartments: an increasing body of literature suggests that it can influence the physiological activity of plants, seed germination, and seedling growth, altering the chance of survival of several plant species.

Riparian vegetation is a key indicator of the status of river hydro-morphological processes. Several riparian plant species are nowadays endangered because of the degradation of river ecosystems worldwide, as a result of the exploitation of river resources. River floodplains, by hosting large amounts of biodiversity and habitat types, are crucial objectives for river management and restoration.

Vegetation establishment in floodplains and in-channel morphologies is linked to river hydro-morphodynamic processes: seeds of many riparian species are transported along the river by water, deposited on shorelines as the water level recedes, and establish depending on different environmental factors. The hydrological regime at seasonal-yearly scale (for example flood-drought seasonality), has recognized effects on seed recruitment.

In this study, we applied a vegetation recruitment model based on the Windows of Opportunity concept to study the main hydro-morphological controls on seed recruitment in an Alpine river subjected to hydropeaking. The study site is a small gravel-dominated floodplain of Moesa River (Switzerland). The model predicts potential colonization sites for vegetation after seed dispersal events by comparing water stress caused by water level fluctuations and time-varying plant resistance to inundations. We test alternative hydrological scenarios, comparing business-as-usual and no-hydropeaking conditions, and also different morphological configurations, using river topographical scans from different epochs (pre- and post- natural floods). We use a two-dimensional depth-averaged hydrodynamic model to simulate water levels in every scenario. The different hydro-morphological configurations are then fed into the seed recruitment model, to finally evaluate spatially distributed maps of successful rate of seed recruitment. Each hydrological and morphological scenario is tested also against different vegetation resistance to water stress, hence comparing stress-intolerant and stress-tolerant plant species. In addition, we qualitatively compared our results with an existing dataset of German Tamarisk (Myricaria germanica) dynamics in the floodplain.

Our results show the influence of vegetation resistance on the successful recruitment rate in terms of spatial extension and distribution. The influence of hydropeaking seems to be increased/smoothed depending on the hydrological year. Morphological variations due to natural floods appear to have relevant impact on vegetation dislocation, but less on total amount. Developing quantitative tools to simulate eco-morphodynamic river processes is supportive for both river managers and scientists. Eventually the understanding of key physical drivers of riparian vegetation dynamics in hydropeaking rivers is crucial for the conservation and restoration of functional river ecosystems.

How to cite: Vanzo, D., Michael, L., Vetsch, D. F., Fink, S., and Caponi, F.: Modelling seed recruitment controls in an Alpine floodplain subject to hydropeaking, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11623, https://doi.org/10.5194/egusphere-egu23-11623, 2023.

Saltmarsh rejuvenation in front of a levee - using a numerical model to inform designs
Jasper Dijkstra, Sarah Dzimballa, Joana van Nieuwkoop, and Madelief Doeleman
Daniel Hayes, Maria Cristina Bruno, Maria Alp, Isabel Boavida, Ramon Batalla, Maria Dolores Bejarano, Markus Noack, Davide Vanzo, Roser Casas-Mulet, Damian Vericat, Mauro Carolli, Diego Tonolla, Jo Halleraker, Marie-Pierre Gosselin, Gabriele Chiogna, and Terese Venus

Hydropeaking has received increasing attention in the last years, but many knowledge gaps remain, potentially hampering effective policy and management efforts in rivers under such type of hydropower production. In this study, we collected open hydropeaking research questions from over 200 experts in river science, practice, and policy across the globe using an online survey available in five languages. We used a systematic method of determining expert consensus (Delphi method) to identify 100 core questions related to the following thematic fields: (i) hydrology, (ii) physico-chemical properties of water, (iii) river morphology and sedimentology, (iv) ecology and biology, (v) socio-economics and energy markets, (vi) policy and regulation, as well as (vii) management and mitigation measures. The consensus list of questions shall inform and guide researchers in focusing their efforts to foster a better science-policy interface, thereby improving the sustainability of peak-operating hydropower in a variety of settings.

How to cite: Hayes, D., Bruno, M. C., Alp, M., Boavida, I., Batalla, R., Bejarano, M. D., Noack, M., Vanzo, D., Casas-Mulet, R., Vericat, D., Carolli, M., Tonolla, D., Halleraker, J., Gosselin, M.-P., Chiogna, G., and Venus, T.: 100 key questions to guide hydropeaking research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5314, https://doi.org/10.5194/egusphere-egu23-5314, 2023.

Wave flume experiments to unravel saltmarsh cliff hydrodynamics
Jos Muller, Bas Borsje, Jebbe van der Werf, Dimitrios Dermentzoglou, Bas Hofland, Suzanne Hulscher, and Alessandro Antonini

Posters virtual: Thu, 27 Apr, 16:15–18:00 | vHall HS

Chairperson: Bregje van Wesenbeeck
Assessing Flow Functionality in Hydropeaking Rivers
Sarah Yarnell
Projecting Future Coastal Hazards for Evaluating the Performance of Mangrove NNBF Systems under Changing Climate
Grace Yan, Marriah Abellera, Tori Tomiczek, and Liesel Ritchie