HS9.5

EDI
Ecohydraulic processes in rivers, lakes and reservoirs: restoration and mitigation approaches

Water and sediments interact at different spatial and temporal scales in freshwaters promoting the development of highly dynamic systems. Erosion, transport and sedimentation are vital processes that shape river morphology. These dynamic processes, in turn, are essential to provide a mosaic of diverse habitat patches for aquatic species and to freshwater ecosystems functioning.
Anthropogenic activities such as flow regulations or dams lead to fragmentation and ecosystem degradation, interfering with natural hydro-morphodynamics and affecting aquatic ecology. In Europe, large efforts are set to restore disturbed river sections to meet the goals of a good ecological status, set by the Water Framework Directive. Experience to date indicates that integrating both physical and ecological processes in river restoration efforts is critical to freshwater ecosystems conservation. In this context, the interdisciplinary field of Ecohydraulics represents the link between abiotic components (e.g. hydrology, hydraulics, geomorphology) and riverine biota (e.g. vegetation, fish, macroinvertebrates). Advances in this field of research are therefore paramount to make future management decisions in freshwater systems.
This session aims at integrating the core research disciplines forming Ecohydraulics, from hydrology, hydraulics, fluvial geomorphology, and biology, but also social aspects to ensure a holistic assessment of rivers, lakes and reservoirs, and to enable the implementation of sustainable restoration measures.
We welcome both fundamental and applied research, presenting approaches at different spatio-temporal scales. They may include holistic tools and methods to improve the assessment, prediction and management of restoration and mitigation measures in aquatic systems, with a focus on the hydrological, fluvial geomorphological, and biological interactions.
Contributions may refer, but are not restricted, to:
- sediment transport, fluvial dynamics and sediment budgets in rivers
- risk analysis and mitigation in fluvial systems
- reservoir sedimentation: processes and management
- large wood and microplastic in aquatic systems
- nature-compatible river engineering and river development
- nature based solutions
- revitalization of river systems (from successful studies to failures in restoration)
- tools and methods (concepts, measurements, monitoring, modelling) to understand the interactions between fluvial processes and their biological responses

Co-organized by BG4/GM3
Convener: Stefan Haun | Co-conveners: Roser Casas-Mulet, Markus Noack, Lennart SchönfelderECSECS
vPICO presentations
| Wed, 28 Apr, 11:00–12:30 (CEST)

vPICO presentations: Wed, 28 Apr

Chairpersons: Roser Casas-Mulet, Markus Noack, Lennart Schönfelder
11:00–11:05
11:05–11:07
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EGU21-16042
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ECS
Andrés Peredo Arce, Martin Palt, Martin Schletterer, and Jochem Kail

In the degraded European landscapes riparian corridors had have become key features to maintain connectivity between habitat patches for multitude of organisms. This role of riparian forests has been assessed from the purely structural point of view, to complex models specific for particular species or groups of species, from mammals to plants, from endangered to invasive species.

Dispersion is a key part of the lifecycle of EPTs (Ephemeroptera, Plecoptera and Trichoptera) as they live most of their lives as aquatic juveniles, being drifted downstream, and disperse back upstream when they become short-lived winged adults. These three families of aquatic macroinvertebrates are widely used as bioindicators because of their sensitivity to water pollution and habitat degradation, but little is known about how the riparian vegetation impacts their ability to disperse and recolonize. For example, riparian vegetation could help EPTs dispersion by protecting them from harsh weather conditions, or by helping them to orientate themselves by changing how the reflexion of the light on the water polarises.

Nevertheless, connectivity is not the only driver of the EPT community as other parameters can have a direct effect on the community composition. For example, water pollution is an important driver of the freshwater macroinvertebrate community and in locations where pollution is high is not expected to find almost any EPTs individual regardless of the landscape connectivity. Furthermore, other landscape features can hinder the role of riparian forests as corridors for being a barrier to EPT dispersion, like dams or coniferous forests.

In this study we compare the EPT communities on 120 pairs of sites, each pair located in the same river at 1 to 5 km distance, with different riparian vegetation conditions in Western Germany. The communities are characterised by their overall dispersion capacity using the Species Flying Propensity index (Sarremejane et al. 2017). The riparian vegetation is identified using areal images in the 10 meters and 30 meters buffer from the river.

We expect that riparian forest fragmentation will directly impact functional connectivity, and therefore, in locations with less fragmented riparian forests the EPT community will be mainly composed by weak dispersers (and vice versa). Nevertheless, covariates that can impact or mask this effect were taken into account: catchment land use, saprobic pollution, naturalness, hidromorphological hydromorphological degradation and also other features as coniferous forests or dams.

How to cite: Peredo Arce, A., Palt, M., Schletterer, M., and Kail, J.: Effects of riparian woody vegetation on EPT functional connectivity in Western Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16042, https://doi.org/10.5194/egusphere-egu21-16042, 2021.

11:07–11:09
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EGU21-14342
Ronald E. Pöppl, Hannah Fergg, Maria T. Wurster, Anne Schuchardt, and David Morche

It is well known that in-stream large wood (LW) can have significant effects on channel hydraulics and thus water and sediment connectivity, i.e. by creating hydraulic resistance that decreases flow velocity and transport capacity. The relationship between an in-stream LW structure and its hydraulic function (incl. the related effects on water and sediment connectivity) is generally quantified through drag force. Drag analyses, however, are data-demanding and often not straightforward - especially in complex debris jam settings where LW accumulations consist of wood pieces of widely variable sizes. Here, we introduce a simple LW dis-connectivity index (calculated based on visually estimated, field-derived LW parameters such as the degree of channel blockage), which has been applied in different sediment management contexts in medium-sized mixed-load streams in Austria.

 

How to cite: Pöppl, R. E., Fergg, H., Wurster, M. T., Schuchardt, A., and Morche, D.: The effects of large wood (LW) on water and sediment connectivity in river systems: a new LW dis-connectivity index and its application in sediment management contexts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14342, https://doi.org/10.5194/egusphere-egu21-14342, 2021.

11:09–11:11
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EGU21-9815
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ECS
Karla Campagnolo, Danrlei de Menezes, and Masato Kobiyama

Headwater streams are mainly responsible for providing sediments and nutrients to the downstream regions. In addition, the riparian vegetation of these streams is a source of large wood (LW) for the water channel. Sediments and LW play an ecologically-important role in maintaining aquatic habitat, meanwhile sometimes execute serious intensification of the impact of downstream large floods. The quantity and size distribution of sediments on the channel bed and LW certainly influence on channel hydraulics and stability as well as the quality of aquatic habitats. Hence, the characterization of sediments and LW supports the renaturalization and conservation of streams/rivers. Therefore, the objective of the present study was to evaluate the influence of the LW deposition and the channel morphology on the bed sediment grain size along a reach (700 m) inside a headwater catchment (15 km2), southern Brazil. The mean slope of the reach channel is 0.33% which can be considered low. This catchment is characterized with the Mixed Ombrophilous Forest, the climate is the Cfb according to Köppen classification and the average annual rainfall is 1881 mm. Hydrological (rainfall and discharge) and LW dynamics monitoring has been carried out in this catchment since 2017. The step, pool and cascade are observed as channel morphologies along the study reach, which were divided into three parts (upstream, middle, and downstream). Furthermore, 26 cross-sections of the stream were established for field survey, such as measurement of the diameter (axis -a, -b, and -c) of the bed sediments (D90, D84, D50, D16, D10, and Dmax) and LW presence verification. The definition of the sampling points sought to ensure a correct representation of the fluvial geomorphology. The present study reported the results obtained through the field survey carried out on August 8th, 2020, using caliper, tree caliper, metric tape and GPS. The grain sizes varied from 324.64 mm to 2.76 mm (particles smaller than 2 mm were not computed). The results showed that the presence of LW in the section induced a smaller value of the sediment grain size. In the pool formation a greater variation in the sediment granulometry was found than in cascades and steps. Furthermore, within the pool, the sediment sizes tended to increase from upstream to downstream. It is concluded that the LW acts as natural barriers for sediment deposition, avoiding the sediments exhaustion and generating low-velocity zones, favoring the maintenance of aquatic habitat. Also, the difference in the granulometry of the sediments within the pool formation may be a function of the flow velocity. In Brazil, the importance of fieldwork involving the monitoring of LW and bed sediments should be highlighted as a tool for understanding the hydrogeomorphic processes and for conserving the riparian zone, because such fieldworks are still few.

How to cite: Campagnolo, K., de Menezes, D., and Kobiyama, M.: Influences of channel morphology and large wood on bed sediment grain size characteristics along a headwater stream, southern Brazil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9815, https://doi.org/10.5194/egusphere-egu21-9815, 2021.

11:11–11:13
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EGU21-243
Ingo Schnauder

Drag coefficients convert flow velocity into the force exerted on a body and hydraulic head loss. They spatially integrate all properties of a given configuration into one single parameter. Therefore, drag coefficients are widely used in engineering, including environmental flow applications such as large wood log. However, the scatter in drag coefficients reported from previous studies clearly indicate that universality is no longer given and predictions underlie large uncertainties. Deeper analyses are mostly restricted due to insufficient hydraulic data – which in many studies is simply the discharge and the derived cross-sectionally averaged velocity.

It is obvious, that the ‘ideal’ drag coefficients from infinite and low-turbulence wind tunnel studies with the iconic cD = 1.1 for the subcritical regime (104 < Re < 105) do not apply anymore. Instead, disturbances play a major role. For large wood, these are typically (i) blockage of the finite river cross-sectional area, (ii) the proximities of the bed below and the free-surface above, (iii) interaction with the free-stream turbulence, (iv) wake interference and (v) 3D-effects such as free ends of the cylindrical or channel aspect ratio.

To search for a more robust predictive scheme, we started flume experiments with horizontal cylinder configurations and measured the flow field in vertical profiles as well as the overall drag. First results shifted our emphasis from drag to velocity coefficients like the ones used in energy and momentum equations to account for non-uniformity. This seems reasonable, both because of the the squared represention of velocity in the drag term and because of the significant non-uniformities in large wood constellations.

How to cite: Schnauder, I.: Drag coefficients of large instream wood – mystery or science?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-243, https://doi.org/10.5194/egusphere-egu21-243, 2020.

11:13–11:15
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EGU21-16197
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ECS
Kshitiz Gautam, Sanjay Giri, Biswa Bhattacharya, and Gennadii Donchyts

Himalayan rivers in Nepal flow through the mountains with high gradient to emerge in lowlands as large rivers carrying enormous amount of discharge and sediments. They release significant quantity of sediment forming alluvial fan as a result of sudden decrease in gradient when they enter the lowland and gain braided form. This braided form has made the river morphologically more dynamic in nature. Division of channels into numerous anabranches leads to formation of temporary or permanent islands in between them. These islands in long run are either eroded gradually by the river channel or develop into vegetated islands. The development of vegetation may be long term with growth of trees or they may develop into grasslands that may be seasonal which is usually inundated during floods. The river channels and islands along with the surrounding floodplain with vegetation act as perfect recipe for the development of complex wetland ecosystem.

Koshi River in Nepal is among such rivers emerging from the mountains to flat plains of Terai thereby flowing into multiple channels within a large width of about 5 km, which is then controlled by Koshi Barrage at 41 km from the gorge. This dynamic river system feeds the Koshi Tappu Wildlife Reserve, a Ramsar site in the reach. The change in river course and vegetation of this large area which otherwise would be challenging to study can be done rather easily by the use of satellite imageries and cloud computing. Google Earth Engine (GEE) has been used in this study for analysing the morphological changes of the river as well as vegetation changes within the study area using the multiple satellite images taken at different times. NDWI has been calculated and used to identify the occurrence of water in the river channels, thus the morphological changes. While NDVI is used for intensity of vegetation. The temporal and spatial analysis of the morphodynamics and corresponding changes in vegetation is performed from 1987 to 2020 within the selected area.

The preliminary assessment of the results shows that the vegetation dynamics of the area has been affected by the continuous erosion and deposition caused by the morphological changes apparently due to the barrage. Over time, river has been channelizing and branching several times causing the existing islands to erode along with their vegetation as well as forming new islands with vegetation cover. This shifting of the river and resulting vegetation dynamics appear to have affected the habitat of the wild water buffaloes (Arna) as well as, other endangered species native to the area. Additional analysis on the effect of river morphology and vegetation dynamics to the flood pattern and other ecological components will be carried out to support the initial findings and draw generalized conclusions.

How to cite: Gautam, K., Giri, S., Bhattacharya, B., and Donchyts, G.: Impact of morpho- and vegetation-dynamics on flood, erosion and ecology in large lowland rivers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16197, https://doi.org/10.5194/egusphere-egu21-16197, 2021.

11:15–11:17
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EGU21-4966
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ECS
|
Highlight
Gabriel Spreitzer, Isabella Schalko, Robert M. Boes, and Volker Weitbrecht

Large wood (LW) and logjams are common and important elements in rivers, yet knowledge about composition, volume and porosity of wooden structures in streams is still limited. Most studies apply a rectangular approach (manually measuring a rough bounding-box of the logjam) to estimate LW accumulation volume and porosity. However, this method cannot capture the complex dimensions of LW accumulations and may introduce an additional human-made estimation error. Furthermore, there is a risk of accidents involved when obtaining manual measurements on logjams in the field. Drones represent a powerful tool in geosciences, yet their potential has not been fully exploited to date. The application of non-intrusive quantification methods is widely available in geosciences and recently also increasing for research related to LW in rivers. Recent studies demonstrated that drone imagery and Structure-from-Motion photogrammetry provide true replicates of prototype logjams in form of 3D-models. In the present study we used video footage of a LW accumulation, obtained via standard drone (DJI Phantom 4 Pro+), to evaluate its potential for a rapid assessment of geometric measures (e.g. length, width, height, volume) of the LW accumulation. The gained results from the 4k drone video footage (4,096 x 2,160 pixels) were scaled solely from the obtained video georeferencing data and verified with a properly scaled 3D-accumulation-model that has been generated from high resolution drone imagery (5,472 x 3,648 pixels). We are interested in the level of detail and accuracy, that can be obtained from georeferenced drone footage, and aim to introduce a practical and more reliable assessment method as a state-of-the-art alternative to the traditionally applied rectangular approach. Our study may be of interest for river managers and engineers to rapidly and safely assess LW accumulation volume and porosity in the field.

How to cite: Spreitzer, G., Schalko, I., Boes, R. M., and Weitbrecht, V.: Video footage from drones for Structure-from-Motion photogrammetry – A practical and rapid assessment method for large wood accumulations in rivers?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4966, https://doi.org/10.5194/egusphere-egu21-4966, 2021.

11:17–11:19
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EGU21-13100
Jakub Langhammer

High-resolution imaging using unmanned aerial vehicles (UAV, UAS, drones) opened up in the last decade a new potential for a detailed, reliable, operable, and affordable approach for riverscape monitoring. Based on the experience with the pilot research on UAV detection of fluvial dynamics on natural and modified streams, we have proposed a framework for the assessment of the sustainability of stream restoration projects based on UAV imaging and photogrammetry. The approach focuses on aspects where the high-resolution UAV imagery can bring reliable and quantitative information, applicable for assessing restoration success and incorporation into standard assessment schemes.

We distinguish four critical aspects of stream restorations, where the UAV monitoring can provide reliable quantitative information, applicable for assessment of stream restoration success or failure: (i) Restoration effect, (ii) Dynamics of fluvial processes, (iii) Hydrological connectivity, and (iv) Riparian vegetation. For each aspect, there are derived relevant indicators, allowing quantitative assessment and scoring.

We have tested the framework on the evaluation of restorations on three urban streams in the metropolitan area of Prague, Czech Republic, which were subject of revitalization in the past decade. We have maintained regular recurrent UAV monitoring campaigns of these streams over four years, which enabled tracking the restorations since their completion and identifying the positive aspects and the failures in the sustainability of the realized restoration projects. 

UAV monitoring enabled to identify stream restoration features that would be hard or impossible to assess by other mapping techniques. As for the restoration effect, the UAV assessment revealed that although the basic goals of restoration projects were fulfilled, the newly shaped stream patterns significantly differ from the approved restoration plans. The restored channels are typically less complex and featuring simpler geometry than planned. Multitemporal assessment enabled to track stream instability and to measure the extent of bank erosion. UAV monitoring over a low flow period enabled to identify the stream segments where the inappropriate channel transformation led to disruptions in hydrological connectivity, and to detect and measure the extent of eutrophication in the stream and the newly created shallow ponds. UAV monitoring also enabled tracking the progress of vegetation succession after the restoration and quantitatively assessing the extent of riparian shading as a substantial element of sustainability of stream restoration.

Despite the limitations stemming from the nature of optical sensing, UAV monitoring proved to be a highly efficient and reliable technique suitable for evaluating stream restoration projects with versatile applications even in the urban environment’s specific conditions.

How to cite: Langhammer, J.: UAV monitoring of urban stream restoration sustainability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13100, https://doi.org/10.5194/egusphere-egu21-13100, 2021.

11:19–11:21
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EGU21-3069
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ECS
Alessio Cislaghi, Paolo Fogliata, Emanuele Morlotti, and Gian Battista Bischetti

River channels and floodplains have been highly modified over the last 70 years to mitigate flood risk and to gain lands for agricultural activities, settlements and soft infrastructures (e.g., cycle paths). River engineering measures simplified the geomorphologic complexity of river system, usually from braided or wandering channels to highly-confined single-thread channel. Meanwhile, rivers naturally adjust and self-organise the geomorphologic function as response of all the disturbances (e.g., flood events, river-bed degradation, narrowing, control works) altering sediment and water transfer, exacerbating bank erosion processes and streambank failures, and exposing bare sediment that can be subsequently colonized by pioneer species. In this context, river management has to address river dynamics planning sustainable practices with the aim to combine hydraulic safety, river functionality, and ecological/environmental quality. These actions require the detection of river processes by monitoring the geomorphological changes over time, both over the active riverbank and the close floodplains. Thus, remote sensing technology combined with machine learning algorithms offers a viable decision-making instrument (Piégay et al., 2020).

This study proposes a procedure that consists in applying image segmentation and classification algorithms (i.e., Random Forest and dendrogram-based method) over time-series high resolution RGB-NIR satellite-images, to identify the fluvial forms (bars and islands), the vegetation patches and the active riverbed. The study focuses on three different reaches of Oglio River (Valcamonica, North Italy), representative of the most common geomorphic changes in Alpine rivers.

The results clearly show the temporal evolution/dynamics of vegetated and non-vegetated bars and islands, as consequence of human and natural disturbances (flood events, riparian vegetation clear-cutting, and bank-protection works). Moreover, the procedure allows to distinguish two stages of riparian vegetation (i.e., pioneer and mature vegetated areas) and to quantify the timing of colonization and growth. Finally, the study proposes a practical application of the described methodology for river managers indicating which river management activity (including timing, intensity and economic costs) is more appropriate and sustainable for each studied reach.

 

References: Piégay, H., Arnaud, F., Belletti, B., Bertrand, M., Bizzi, S., Carbonneau, P., Dufour, S., Liébault, F., Ruiz‐Villanueva, V. and Slater, L.: Remotely sensed rivers in the Anthropocene: state of the art and prospects, Earth Surf. Process. Landf., 45(1), 157–188, https://doi.org/10.1002/esp.4787, 2020.

How to cite: Cislaghi, A., Fogliata, P., Morlotti, E., and Bischetti, G. B.: Towards a better understanding of river dynamics in semi-urbanised areas: a machine learning analysis on time-series satellite images, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3069, https://doi.org/10.5194/egusphere-egu21-3069, 2021.

11:21–11:23
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EGU21-1880
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ECS
Yao Yue, Yuanfang Chai, Shitian Xu, and Xiaofeng Zhang

Seasonal change of water and sediment fluxes is an important issue in flood/drought control and ecosystem protection. Based on trend analysis in dry and flood seasons during 1960–2014 at six major gauging stations on the Yangtze River, the largest river in China, significant homogenization of intra-year water discharge was found, while sharp decrease of sediment load in both seasons was tested. By reconstructing water and sediment series without the human interference, contributions of precipitation change, large dam constructions on the mainstream, and other human activities in each of the sub-basins of the Yangtze River were separated and quantified. It shows that precipitation change attributed for 9.5–23.6% to discharge homogenization in the middle and lower reaches of the Yangtze River, and increased sediment yield by 1.9–25.5% in both dry and flood seasons. Being the largest hydraulic project in the world, the Three Gorges Dam only explains 17.5–27.2% of the downstream homogenization in water flux, and 3.2–23.9% of sediment reduction in both seasons. Relatively small but massive human interference in the sub-basins was recognized as the primary factor, contributing over 60% to discharge homogenization and over 70% to seasonal sediment reduction, most notably in the Hanjiang sub-basin for water flux and in the Jianglingjiang sub-basin for sediment load.

How to cite: Yue, Y., Chai, Y., Xu, S., and Zhang, X.: Seasonal variation in water and sediment fluxes of the Yangtze River under precipitation change and human interference, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1880, https://doi.org/10.5194/egusphere-egu21-1880, 2021.

11:23–11:25
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EGU21-13519
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ECS
Pia Laue, Paul Quinn, Mary Bourke, Darragh Murphy, Mark Wilkinson, Simon Harrison, and John Weatherill

In recent decades, land-use and climate change have dramatically altered catchment runoff rates. For example, agriculture intensification has led to increased flood risks by decreasing  soil permeability and reducing channel-floodplain connectivity. Natural Water Retention Measures (NWRM) is an approach that has been adopted European-wide for the attenuation of peak floods and the provision of wider ecosystem services. A reduction in peak flow is achieved by increasing water storage potential in the landscape and by modifying natural flow pathways. In agricultural areas (~70% of Irish land use),  runoff attenuation features such as offline ponds, earthen bunds, sediment traps and leaky dams are frequently deployed natural retention measures.

Despite the growing evidence across Europe of their efficacy for flood peak reduction, water quality enhancement and biodiversity on the local scale, NWRM features have not been adopted in Ireland as a flood mitigation approach. In order to build a case that will help address this, this presentation will detail a NWRM demonstrate site in Ballygow, Co. Wexford.  The construction and instrumentation of a network of features developed at the field-scale (~1km2) is shown. This site is an intensive pasture, small-hold farm. We aim to quantify the effectiveness of these NWRM features to demonstrate their potential to attenuate flood peaks on agricultural areas using temporary storage, whilst minimising the impact on farming.

The constructed measures consist of a flood swale that connects the channel to the floodplain during high flows, an earthen bund, an offline pond with a sediment trap, that can retain the water from the channel and contributing field slopes, for <12 hours. On-site video footage and eyewitnesses confirm that the flood water flows along the field without draining back into the stream. At approximately 800m across the field, the water is retained temporarily, permitting water storage and the opportunity for suspended sediment to settle out of the water column. Flood water is returned to the channel via a perched 20 cm diameter pipe in the bund. Four automated water level recorders (In-Situ Rugged Troll 100) continuously monitor water levels in the stream and the offline pond at 5 min intervals. In addition, local rainfall (EML Event Logger) is monitored. These data are used to identify the hydrograph characteristics of several storm events and are used to determine the effectiveness of the NWRM structures for flood attenuation. The quantification of the effectiveness of NWRM features will use the observed time series combined with hydraulic and hydrological modelling. 

The quantitative evidence provided by our findings will contribute to establishing vital evidence for the implementation of local and national NWRM schemes in Ireland.

How to cite: Laue, P., Quinn, P., Bourke, M., Murphy, D., Wilkinson, M., Harrison, S., and Weatherill, J.: Achieving Flood Reduction with Natural Water Retention Measures in Agricultural Catchments in Ireland , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13519, https://doi.org/10.5194/egusphere-egu21-13519, 2021.

11:25–11:27
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EGU21-16414
Jo Halvard Halleraker, Janos Steiner, Ulrich Pulg, Johan Kling, and Knut Alfredsen

Fundamental assessment and understanding of fluvial geomorphological processes are crucial for a sustainable management of riverine ecosystems. There is a huge riverscape diversity across Scandinavia; from low gradient river habitats in the lowland (e.g. meanders and river delta in South of Sweden) to high alpine, post-glacial and morphologically highly variable rivers with water falls in West-Norway.

River basin managers in Sweden and Norway, are facing many of the same challenges related to types of pressures, biogeography, restoration needs and a huge number of water bodies. We have in this project exemplified how unbiased science-justified descriptors and indicators that are realistic to generate for many thousand rivers according to the EU Water Framework Directive (WFD), can be used as basis for ecosystem-based management.  

The coverage of high-resolution laser-scanning-data (lidar) surveyed for mapping purposes are soon covering most of the river basin districts in both countries. Green lidar penetrating water is so far only surveyed only in limited pilot areas. Therefore, we have mainly generated riverscape features from grey LIDAR in all the characterised catchments, like e.g. i) river slope, iii) sinuosity, iv) valley confinement and v) substrate composition.

Cluster riverscape analysis and assessment of more than 7100 unique river segment and ca 2041 km of rivers in 10 diverse catchments in Norway, and about 11 000 river segments and ca 1930 km of rivers in three catchments in Sweden have been included in the GIS databases. These rivers have different management regimes (e.g. several permanent protected rivers in Norway) and key species in focus (several national salmon rivers). Still some of the same hymo pressures (e.g. lack of lateral and/or longitudinal river continuum) seems to be quite prominent across management regimes, and therefore an intensified action plan for river restoration seems to be needed.

We have demonstrated that our GIS-techniques by combining high resolution lidar data and the river continuum concept is a cost-efficient methodology for assessing river habitats for both riparian and riverine biota in riverscapes of Scandinavia. By combining lidar with other georeferenced data publicly available like geomorphological maps, pressure data (e.g., road culverts), segmentations and semi-automatic GIS-techniques, huge areas (like catchments of several thousand km2 and hundreds of river water bodies)  can be assessed in an objective transparent way already publicly available.

Application

The methodology and GIS database we have generated in this project are relevant for managements issues such as

a) defining reference conditions (to classify ecological conditions)

b) large scale analysis of habitat degradation of riverine and riparian biodiversity, (consistent river typologies – "digital twins")

c) pressure index to pinpoint more accurate and sustainable restoration strategies and measures, that also acknowledge climate adaptation (e.g. natural flow retention measures)

d) identifying significance of physical alterations (hymo pressures - e.g. longitudinal barriers for fish) vs climate change effects (e.g. due to changes in ice break up)

e) biodiversity management; habitat fragmentation, rare vs common habitat types (for updating next version of national Red lists of nature types and/or endangered riverine species)

 

How to cite: Halleraker, J. H., Steiner, J., Pulg, U., Kling, J., and Alfredsen, K.: A cost-efficient riverscape methodology for GIS characterisation and planning of river restoration in Scandinavia , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16414, https://doi.org/10.5194/egusphere-egu21-16414, 2021.

11:27–11:29
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EGU21-6152
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ECS
Alcides Aybar Galdos, Stefan Haun, Sebastian Schwindt, Ruslan Biserov, Beatriz Negreiros, Maximilian Kunz, and Noack Markus

Clogging of riverbeds, also referred to colmation, has been frequently reported in residual flow river reaches. In such river reaches, colmation occurs mostly due to regulated (minimum) flow conditions without significant flood events that drive morphodynamics. Consequently, incoming fine sediments continuously deposit, infiltrate, and accumulate in the gravel matrix of the riverbed. The negative effect of such clogged layers on river ecology is well-known, especially with respect to the hyporheic interstitial leading to reduced porosity and hydraulic conductivity. These limitations results in a reduced supply of dissolved oxygen for aquatic species living in the hyporheic interstitial. However, no standardized quantitative measuring technique exists to determine the vertical location and the degree of colmation. Most available measuring methods involve a variety of mapping methods or single-parameter approaches. While mapping methods enable only qualitative assessments, single-parameter approaches are insufficient to describe the complexity of colmation.

The objective of this study is to test a novel multi-parameter approach in a residual flow river reach to assess the effect of river restoration measures on colmation. The multi-parameter approach includes four key parameters to describe colmation: i) the grain size distribution of the riverbed using freeze core sampling and sieving, ii) the hydraulic conductivity using a newly developed double packer system, iii) the porosity identified with a photogrammetric approach, and iv) the interstitial dissolved oxygen content (DOC) using optodes. This novel approach enables a quantitative description of colmation and an identification of clogged layers in stratified riverbeds as the hydraulic conductivity and the DOC are measured in vertical profiles. The entire measuring concept is applied before and after the implementation of river restoration measures to detect the intervention’s effects on colmation.

The first analyses of the measurement show clearly the effects of dredging with an artificial alteration of the riverbed on the sediment matrix. The vertical profiles of hydraulic conductivity and dissolved oxygen show typically high values in the permeable upper sediment layer and significant reductions in deeper sediment layers. The thickness range of the permeable upper layer is between 5 and 15 cm before the intervention and increased up to 30 and 50 cm after the interventions. The analyses of a coarsened grain size distribution and porosity support the observation of this declogging effect, although a direct correlation is challenging because both parameters are not detected in the form of vertical profiles, but rather as a bulk information for every measurement point.

These very first results provide the conclusion that the measured vertical profiles of hydraulic conductivity and DOC are promising data to assess the location and degree of colmation and their modification as a result of river restoration action. Yet, grain size and porosity analyses provide only little evidence because those represent bulk information only. In summary, the multi-parameter approach represents an innovative and quantitative approach to objectively assess the degree and vertical location of clogged layers in gravel riverbed, which is a major advantage over existing methods for assessing colmation.

How to cite: Aybar Galdos, A., Haun, S., Schwindt, S., Biserov, R., Negreiros, B., Kunz, M., and Markus, N.: A novel multi-parameter approach to assess the effects of river restoration measures on the sediment matrix, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6152, https://doi.org/10.5194/egusphere-egu21-6152, 2021.

11:29–11:31
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EGU21-345
Roser Casas-Mulet, Joachim Pander, Maximilian Prietzel, and Juergen Geist

Increased deposition of fine sediments in streams affects a range of key ecosystem processes across the sediment-water interface, and it is a critical aspect of river habitat degradation and restoration. Understanding the mechanisms leading to fine sediment accumulation along and across streambeds, and their affectation to ecological processes is therefore essential for comprehending human impacts on river ecosystems and inform river restoration. Here, we introduce the HydroEcoSedimentary Tool (HEST) as an integrated approach to assess hydro-sedimentary and ecologically relevant processes together. The HEST integrates the estimation of a range of processes occurring in the interstitial zone, including sedimentary (fine sediment accumulation and fine sediment loss upon retrieval), hydraulic (hydraulic conductivity), geochemical (water quality and temperature) and ecological (with a focus on brown trout early life stages).

We tested the HEST application in two rivers with different degrees of morphological degradation in Germany. The HEST was successful in recording the set of key hydrosedimentary and ecologically relevant factors, and in providing a mechanistic linkage between and biological effect in a site-specific context. The HEST data confirmed that salmonid embryo mortality could be linked to high fine deposition in gravel beds. In addition, the HEST illustrated that such mortality could be linked explicitly to interstitial depths and to different infiltration pathways for fines (e.g. vertical vs. horizontal). Although interstitial water quality and temperature were within ecological thresholds and did not show significant differences with surface water, it was still useful to monitor such variables and to rule out any effect on mortality. Water temperature, for example, could be extremely important to detect local groundwater inputs, which has been demonstrated to have a significant effect on embryo salmonids elsewhere. The HEST also allowed accounting for the loss of fines during retrieval failure and estimating hydrological factors with the HEST illustrates its additional usefulness and reliability.

Compared to other methods, the HEST expands the possibilities to monitor and quantify fine sediment deposition in streambeds by differentiating between vertical, lateral and longitudinal infiltration pathways, and distinguishing between the depth (upper vs. lower layers) at which interstitial processes occur along the streambed column.

How to cite: Casas-Mulet, R., Pander, J., Prietzel, M., and Geist, J.: The HydroEcoSedimentary Tool: an integrated approach to characterise interstitial processes in freshwater systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-345, https://doi.org/10.5194/egusphere-egu21-345, 2020.

11:31–11:33
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EGU21-16229
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ECS
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Highlight
Bendik Hansen and Lennart Schönfelder

Hydropower is a key element in the transition to a green energy future. However, this technology also comes with adverse environmental impacts that should be avoided or mitigated. One of the challenges related to hydropower is its impact on fish, and the FIThydro project (2016-2020) has worked on improving the decision support for commissioning and operating hydropower using both existing and innovative technologies. One of the outputs from the project is the FIThydro wiki, which is a collection of mitigation measures, methods, tools and devices for the assessment and measure implementation of fish-friendly hydropower. The mitigation measures are divided into five categories of challenges: environmental flows, habitat, sediment management, upstream fish migration, and downstream fish migration. Each mitigation measure has a description of which methods, tools, and devices to use during the three separate stages of planning, implementation, and operation/monitoring. They also contain a classification table describing different aspects of the solution, such as TRL, suitable locations, which challenges are mitigated, and costs. Similar articles exist for methods, tools, and devices that can be useful in implementing mitigation measures, as well as for test cases in the project. The wiki is closely linked to a Decision Support System (DSS), which helps guide users to the appropriate mitigation measures. The wiki can support decision-making and contribute to a more transparent and simple communication/negotiation of hydropower-related issues through a clarification of terms and technologies.  

How to cite: Hansen, B. and Schönfelder, L.: Knowledge sharing on fish-friendly hydropower: the FIThydro wiki, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16229, https://doi.org/10.5194/egusphere-egu21-16229, 2021.

11:33–11:35
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EGU21-4903
Lei Xu, Saiyu Yuan, Yuchen Zheng, and Yihong Chen

Knowledge of locomotion of fish with significant rheotaxis at river confluences is critical for prediction of fish distribution at a river network. Recently, less silver carps observed in the Poyang Lake should be related to the hydrodynamic change at the confluence of the lake outlet and the Yangtze River. The operation of the Three Gorges Dam has largely changed the hydrodynamics at this confluence. Silver carp is one of the four major Chinese carps, and has significant rheotaxis. In this study, a series of laboratory experiments were conducted to figure out the behavioral responses of juvenile silver carps to hydrodynamics near the separation zone at the channel confluence. The separation zone at a river confluence is one of the main zones for carp habitat and feeding. The locomotion and trajectory of juvenile silver carps were recorded through infrared thermal imaging at the confluence flume. Flow velocity field near the separation zone was measured by a Particle Image Velocimetry (PIV) system. A total of 40 juvenile silver carps were released from the separation zone and swam to the upstream, among which 24 carps swam to the tributary and the other to the main channel. Almost all 24 carps moved along the beginning of the boundary of the separation zone near the corner where the flow shear was strong. It seems that instead of avoiding places with great vorticity, they preferentially chose the trajectory where the flow vorticity was large continuously. They increased the tail-beat frequency and decreased the tail-beat amplitude to maintain body stability when they encountered the flow with large vorticity. These results are beneficial for the regulation of upstream dams to adjust the hydrodynamics at the confluence and improve local ecology.

How to cite: Xu, L., Yuan, S., Zheng, Y., and Chen, Y.: Locomotion of juvenile silver carp (Hypophthalmichthys molitrix) near the separation zone at the channel confluence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4903, https://doi.org/10.5194/egusphere-egu21-4903, 2021.

11:35–11:37
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EGU21-15963
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ECS
Siqi Tong, Silke Wieprecht, and Martin Schletterer

This study was carried out in the middle and lower reaches of the Jinsha River in southwest China, which represents the upper Yangtze River. Hydraulic structures (14 cascade hydropower stations) are planned and/or constructed in this system, which is considered as largest hydropower base. We aim to summarize appropriate measures to restore the riverine continuum in the middle and lower reaches of the Jinsha River, where high-head cascade hydropower dams are located or planned.

We distributed a questionnaire to Chinese researchers in the related fields (scientists, hydropower operators and NGOs in China, n = 60). According to the responses, fishways, fish lift, fish lock, trap-and-truck system as well as fish hatcheries (artificial breeding) are recognized to ensure passing respectively preserving fish in the Jinsha River basin.

A longitudinal connectivity assessment of the study area revealed a severely disturbed continuity status. Based on the biological analyses of the demands of the target fish species and review of fish pass technologies, a vertical-slot fishway is proposed.

Considering the dam heights and the geographical conditions, it is recommended to combine the vertical-slot fishway with these alternatives to achieve a higher efficiency in passing fish as well as to recover the river continuity towards regional sustainable development.

How to cite: Tong, S., Wieprecht, S., and Schletterer, M.: Analysis of fishways in the Middle and Lower Jinsha River Basin (China), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15963, https://doi.org/10.5194/egusphere-egu21-15963, 2021.

11:37–11:39
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EGU21-2267
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ECS
Luca Bonacina, Riccardo Fornaroli, Valeria Mezzanotte, and Francesca Marazzi

Phytobenthos is the dominant primary producer in streams and sustains, with the allochthonous organic matter inputs, the higher trophic levels. Among the different groups that constitute the phytobenthos community some, especially diatoms, have been studied deeply while others remain quite overlooked. Hence, a characterisation of the overall phytobenthos community is needed, considering all the main taxonomic groups (diatoms, green algae, cyanobacteria and red algae), as related to the environmental conditions characterizing different alpine streams. Moreover, despite the ecological role played by the phytobenthos the knowledge about the factors that control the variations of the community among streams and throughout the different seasons is still poor. Among the different drivers that regulate the phytobenthos component, a pivotal factor is the occurrence of high-flow events that, controlling the stability of riverbed substrates, influences both the phyto and the zoobenthos composition and distribution. Thus, the frequency and the magnitude of flow disturbances are determinant in regulating the phytobenthos density and the recolonization patterns. The aim of this work was to characterize and compare the phytobenthos communities in different streams highlighting the role of the flow regulation due to hydropower reservoirs accounting for the influence of the lithology and the seasonality. The presented phytobenthos data derive from a one-year sampling campaign in four alpine streams representative of different flow conditions (natural vs regulated flow discharge) and lithology (silicate vs carbonate). The riverbed coverage has been estimated monthly in each stream and the biomass has been quantified. In lab, phytobenthos samples have been analysed to measure the photosynthetic activity and define their composition. The main groups (cyanobacteria, green algae, diatoms and algae with phycoerythrin) have been determined both by phyto-PAM deconvolution and by the quantification of the photosynthetic pigments. In order to estimate the bed disturbance, painted stones of different size classes were located in regular arrays along three transversal transects and the distance travelled was measured during every sampling. The preliminary results indicate that regulated streams seem characterized by a greater algae biomass possibly due to a more stable environment. Concerning the community composition, the percentage of diatoms is significatively higher in silicate substrates. Despite the few hours of light, winter promotes phytobenthos colonisation especially for the low frequency of relevant high-flow events but also for the absence of the shadow due to tree canopy on the riverbed.

How to cite: Bonacina, L., Fornaroli, R., Mezzanotte, V., and Marazzi, F.: Ecological effects of flow disturbance on phytobenthos communities in natural and regulated alpine streams, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2267, https://doi.org/10.5194/egusphere-egu21-2267, 2021.

11:39–11:41
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EGU21-287
Aleksandr Tskhai, Vladislav Ageikov, and Aleksandr Semchukov

The ecosystem of the Novosibirsk reservoir - the largest in West Siberia, is the object of this research aimed at studying the mechanisms of water quality formation, which differs in various parts of the reservoir. The research novelty is in simulation of ecological processes occurring in various water areas and in the reservoir as a whole through reproduction of biogeochemical cycles of limiting elements.

The city of Novosibirsk is the administrative center of the Siberian Federal District, which occupies more than 25% of the territory of Russia. The Novosibirsk reservoir is major source of water supply in Novosibirsk. Still, some features of its water quality formation have been poorly explained.

For instance, it is believed that relatively shallow and low flow sites of water bodies are most susceptible to eutrophication. In such places, water warms up better and phytoplankton biomass is much higher. In the central part of the reservoir, depth at the left bank is much less than that at the right one, through which most riverbed flow passes (from the Ob river to the dam). However, according to long-term observations, in every August, phytoplankton biomass at the right bank is several times higher than at the left one.

One more paradox may be considered. Phytoplankton biomass in the surface water layer during the open water period is usually much abundant than at depth characterized by worse penetration of solar radiation. Nevertheless, in the studied period (August 1981), we observed the inverse ratio when phytoplankton biomass at depth significantly exceeded that in the surface layer.

For better understanding these phenomenon, a comparative assessment of mechanisms of in-water processes was performed through applying 3D simulation methods and reproducing the cycles of biogenic elements transformation.

Due to simulation and its results analysis, we revealed the following:

  • the peculiarities of water exchange influenced by stable wind currents in August-September bring to phytoplankton biomass excess at depth near the right bank in contrast to relatively shallow water area near the left one of the Novosibirsk reservoir;
  • “locking” by thermocline and subsequent fluctuations in vertical water exchange lead to abundant phytoplankton biomass in the water column as compared to the surface layer near the dam.

Thus, simulation demonstrates that the above mentioned paradoxes of phytoplankton development in the Novosibirsk reservoir are induced by specific hydrothermal processes.

The study importance goes beyond only giving insight into the causes of interesting natural phenomena. A detailed analysis of simulation results enables to explain nontrivial features of spatially distributed dynamic ecological processes. The possibilities of forecasting the reservoir ecosystem response to changes in different factors associated with varying external effects have been expanded. To mitigate negative impacts of eutrophication, you can change flow patterns at appropriate times, for example, by selecting a suitable operating mode of a hydro-station. The study demonstrates that contaminated water outflow from some water areas may be executed by directional energy use of natural phenomena.

How to cite: Tskhai, A., Ageikov, V., and Semchukov, A.: Hydrological paradoxes of phytoplankton distribution in the Novosibirsk reservoir , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-287, https://doi.org/10.5194/egusphere-egu21-287, 2020.

11:41–11:43
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EGU21-14773
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ECS
Rick Lotzkes, Vyacheslav V. Kuzovlev, Yuri N. Zhenikov, Kyrill Y. Zhenikov, Silke Wieprecht, and Martin Schletterer

The LTERM project REFCOND_VOLGA is operated continuously since 2006 and collects limnological data (chemical, physical and biological samples as well as catchment characteristics), with the aim to analyse the inter-annual variation at reference or least disturbed sites. Sampling sites are located along the Volga as well as along the tributary Tudovka. This study concentrates on Tudovka River (length 106 km, catchment area 1126 km²), where scientists from Tver State Technical University started hydrochemical investigations in the 1990s and since 2006 also hydrobiological assessments are carried out. Tudovka was selected as a model system, because (1) a large part of its catchment is protected, (2) there are minor anthropogenic impacts and with its paludified catchment the river is typical for the region.

The headwater of Tudovka is located in the transition zone of the Central Forest State Nature Reserve Biosphere Reserve, which was established in 1931 to protect “typical forest associations and animals of the central forest region”, and nowadays the last virgin spruce forests of the Southern Taiga are found here. The river is highly influenced by the surrounding mires. Many diffuse inflows from these mires discharge into the river. E.g., during the survey in 2009, a pH of 2.82 and a conductivity of 51 μS/cm were observed at the edges of “Zherdovsky Mokh”.  Since 1985 this Zapovednik (highest protection status in Russia: “prohibited from disturbance / forever wild“ ) is also classified as UNESCO Biosphere Reserve. In the lower course the Molodoitudskii Zakasnik (area of 80 km² between Redkino and Molodoi Tud), is protected by the regional government since 1992, meeting IUCN criteria III (Natural Monument) and IV (Habitat/Species Management Area).

In its upper reaches, the Tudovka River is heavily influenced by mires located in its catchment area. Flowing near three large mires (Staroselsky Mokh, Zherdovskoye and Pesochinskoye) along 20 km in the upper course, the river receives a large amount of organic-rich water. The minimum measured pH of mire waters in the Tudovka catchment area was 2.8, and the maximum chromaticity value was 1006 degrees on the Cr-Co scale. As a result, in the Tudovka River, the pH of water can drop to 6.1, and the chromaticity can increase to 708 degrees.

Thus, six locations were selected along this 104 km long river in order to analyse longitudinal changes. At these six sites (four of them regularly sampled) macrozoobenthos samples were collected using a modified multi-habitat-sampling method. In our presentation, we focus on the analyses of the data for the years 2010-2019 and provide information on taxa composition, longitudinal distribution and temporal changes of the benthic fauna along the Tudovka. In addition, we analyse choritope-specific distribution of benthic taxa across samples from individual microhabitats.

We exemplify at the monitoring sites the spatial distribution of different choriotope types, according the longitudinal profile of the river. We show that it is historically influenced by the Valdai glaciation (moraines), and nowadays catchment characteristics (peat bogs and forest) as well as morphodynamics in the different river sections governs the zoobenthos fauna accordingly.

How to cite: Lotzkes, R., Kuzovlev, V. V., Zhenikov, Y. N., Zhenikov, K. Y., Wieprecht, S., and Schletterer, M.: Long term research and monitoring along the brownwater river Tudovka (Tver Region, Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14773, https://doi.org/10.5194/egusphere-egu21-14773, 2021.

11:43–11:45
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EGU21-431
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ECS
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Taís Yamasaki and Johannes Janzen

Floating treatment wetlands (FTWs) constitute a nature-based solution that promotes water, stormwater and wastewater treatment by using vegetation growing hydroponically on top of a floating mat. One of the advantages of FTWs is not requiring land space to install them, since FTWs are put directly on the water body's surface. Consequently, FTWs can have the potential to affect the flow field, inducing preferential paths and short-circuit, for instance, which may be controlled by how the FTWs are arranged on the water surface. This study aims to numerically simulate the flow field for three FTW arrangements displayed in a channel reach, in order to assess the hydrodynamic differences between each arrangement. In Arrangement 1, three FTWs in series will be installed at the channel center. Arrangement 2 will be formed by three FTWs in series, each one spanning the channel width. Finally, Arrangement 3 will be formed by two FTWs displayed at each margin of the channel. The total FTW volume will remain constant for all arrangements. The simulations will be performed in Computational Fluid Dynamics (CFD), using a validated FTW model from laboratory experiments.

How to cite: Yamasaki, T. and Janzen, J.: Effects of three floating treatment wetland arrangements on the flow field of a channel, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-431, https://doi.org/10.5194/egusphere-egu21-431, 2021.

11:45–12:30