Hydro-geomorphic connectivity has emerged as a significant conceptual framework for understanding the transfer of surface water and materials (e.g., sediment, plant propagules, and nutrients) through landscapes. The concept has had particular success in the field of catchment hydrology and fluvial geomorphology, but has also been employed in, for example, studies of soil erosion and hydrochory, and in neurosciences and social sciences. Connectivity as applied in various disciplines can be a transformative concept in understanding complex systems, allowing analyses of how such systems behave in terms of scaling, catastrophic/phase transitions, critical nodes, emergence and self-organization. However, recent research also highlights the widespread nature of natural longitudinal disconnectivity in river systems, such as beaver dams, log jams, lakes and wetlands. These and other forms of natural disconnectivity can have large spatial and temporal implications on ecological, geomorphic, hydrological and biogeochemical processes through buffering water and material fluxes. We aim to create a diverse interdisciplinary session that reflects a broad range of research seeking to illustrate the role of connectivity on various spatial scales as well as implications of and temporal and spatial variability of disconnectivity. We hope to use the session to develop a discussion of the dual roles of connectivity and disconnectivity to generate a basis for an integrated framework to be applied across the sciences in hydro-geomorphic systems and for managing complex systems and guiding river restoration.

Public information:

1) General introduction by the conveners (“setting the context”) – 5 min

2) ‘Mentimeter’ poll (conveners, authors, audience) – 5 min

3) Displays (max. 7 min per display):

• Invited “speakers” first (Gordon Grant, Ellen Wohl, Rebekah Levine)
• Then following the order as shown in the official EGU session programme (and in your panel to the right of the chat window)

Procedure: Each display will be announced by the session moderators asking the “speakers” to post key messages related to their display material. Then the audience is kindly asked to post questions/statements for discussion.

4) Concluding remarks (conveners) – 5 min

Co-organized by HS13/SSP3, co-sponsored by IAG
Convener: Ronald PöpplECSECS | Co-conveners: Lina Polvi Sjöberg, Laura Turnbull-Lloyd, Manuel López-Vicente, Jantiene BaartmanECSECS, Lovisa Eirell, Anthony Parsons
| Attendance Wed, 06 May, 16:15–18:00 (CEST)

Files for download

Session materials Download all presentations (123MB)

Chat time: Wednesday, 6 May 2020, 16:15–18:00

Chairperson: Ronald Pöppl, Lina Polvi Sjöberg
D1014 |
Stuart Lane

One of the primary challenges of understanding hydro-geomorphic connectivity is to move from static to dynamic representations of connection. This is particularly important when linkages are made between hydro-geomorphic connectivity and habitat. In response to external drivers, notably extreme events, the spatial locations of suitable habitat within an ecosystem may migrate spatially, potentially rapidly. A resilient ecosystem, in one sense, is one where organisms can either “weather-it-out” or migrate to newly suitable habitat to find temporary refuge from those extreme events. In this paper, I show that is it the spatio-temporal evolution of connectivity that determines the resilience of braided stream ecosystems to geomorphic perturbation. Using a validated model of the spatial distribution of instream macroinvertebrate habitat, that combines both known organism preferences with the risks of geomorphic perturbation, I show that during high flow events, suitable habitat shifts rapidly from the primary braid plain channels to secondary ones. The connectivity between primary and secondary channels determines the extent to which secondary channels can be used as refugia; but this connectivity varies continually during the flow event. This can be captured in connectivity metrics based upon notions of percolation. The work has important implications for stream management. First, it shows that the availability of habitat within an ecosystem at high flows is not a sufficient descriptor of the system resilience. The ability of organisms to access suitable habitat as flow rises, and to return to the low flow channel as it falls, is critical; connectivity is primordial. Second, it emphasises that a focus on connectivity as a static state or metric is not sufficient to describe the extent to which a system is resilient. The accessibility of habitat suitable zones at high flows depends upon the how connectivity evolves during the event, which controls accessibility. Thirdly, analyses of connectivity, and wider assessment of stream resilience, need to couple geomorphology and hydrology, and not just focus on environmental flows. The latter provide only a very partial representation of connectivity.

How to cite: Lane, S.: Dynamic connectivity as a determinant of the resilience of stream habitat to geomorphic perturbation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18770, https://doi.org/10.5194/egusphere-egu2020-18770, 2020.

D1015 |
Rebekah Levine, Megan Tarmichael, and Grant Meyer

Beaver activity can segment a stream corridor through dam building which locally affects channel slope and sediment transport.  We have found, however, that long-term beaver presence within a river corridor has impacts beyond dam sites that affect system-wide stream morphodynamics and riparian willow recruitment. Along study streams (basin areas 20 – 125 km2) in southwestern Montana, USA, beaver-chewed willow stems (beaver cuttings) from dam construction, food caches and herbivory float downstream and commonly accumulate within 1 km of dam sites. At the 90 randomly selected sites surveyed, beaver cuttings accumulated on 81% of point bar sites and 51% of all surveyed sites. The accumulated beaver cuttings can sprout, adding roughness, thus enhancing sediment accumulation on point bars and at abandoned dam sites. Sprouting stems were present at 25% of all sites, indicating that beaver cuttings commonly provide a secondary pathway for willow recruitment and influence sediment dynamics.

As beaver cuttings and sediment accumulate on point bars, the channel migrates laterally, burying the cuttings. High resolution aerial imagery has been used to calculate migration rates for twenty-six 200 m reaches in the study streams. Migration rates range from 0.07 – 2.91 m/yr (mean 0.43 m/yr) over a 14 year period from 1995-2009. Thirty-four radiocarbon (14C) ages found in fluvial terraces 1.2 – 3 m above the bankfull channel, show that beaver cuttings range in age from ~6030 – 380 cal yr BP, demonstrating that deposition and burial of beaver cuttings on point bars has been a common process over millennia. The long-term preservation of beaver-chewed wood in point-bar sequences also attests to the importance of beaver activity for enhancing carbon storage in beaver-occupied stream systems.

The mosaic of sites created by beaver includes intact dams, recently breached or abandoned dams, and long-abandoned dams, interspersed with reaches unsuitable for beaver. The beaver produced habitat heterogeneity interacts with sediment and beaver cutting transport to enhance riparian plant colonization and meander development.

How to cite: Levine, R., Tarmichael, M., and Meyer, G.: Willow recruitment and channel patterns in beaver dominated stream systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1210, https://doi.org/10.5194/egusphere-egu2020-1210, 2020.

D1016 |
| Highlight
Alan Puttock, Hugh Graham, and Richard Brazier

The connectivity of landscapes is increasingly recognised as being a key control over their hydrological function and provides a valuable conceptual approach for understanding the environmental impacts of the return of beaver to European landscapes.

Beavers are the archetypal keystone species, which can profoundly alter ecosystem structure and function through their engineering activity, most notably the building of dams. Beaver dams, associated ponds and other structures such as canals can reduce downstream connectivity. However, conversely beaver engineering can also increase lateral connectivity pushing water sideways, connecting the channel and floodplain, creating complex wetland environments.

Changes in hydrological connectivity associated with beaver, has the potential to alter flow and sediment regimes, biogeochemical cycling and freshwater ecology. Results will be presented from hydrological monitoring across a range of sites in Great Britain where the Eurasian beaver (Castor fiber) has been reintroduced. Analysis will consider (1) does beaver engineering result in flow attenuation across scale and landuse? (2)  Is flow attenuation manifested during both low and high flow conditions?

The return of beaver to intensively managed European landscapes may provide ecosystem service benefits, including natural flood management, water quality, sediment storage and habitat creation (Puttock et al., 2017, 2018). However, beaver activity such as damming and tree felling can also cause management issues (Auster et al., 2019). Therefore, it is critical to understand where and in what density beaver damming may occur. A modelling approach will be presented for determining beaver habitat suitability and dam capacity, which in conjunction with empirical monitoring aims to provide understanding at management and policy relevant scales.


Auster, R. E., Puttock, A., & Brazier, R. (2019). Unravelling perceptions of Eurasian beaver reintroduction in Great Britain. Area, area.12576. https://doi.org/10.1111/area.12576

Puttock, A., Graham, H. A., Cunliffe, A. M., Elliott, M., & Brazier, R. E. (2017). Eurasian beaver activity increases water storage, attenuates flow and mitigates diffuse pollution from intensively-managed grasslands. Science of The Total Environment, 576, 430–443. https://doi.org/10.1016/j.scitotenv.2016.10.122

Puttock, A., Graham, H. A., Carless, D., & Brazier, R. E. (2018). Sediment and Nutrient Storage in a Beaver Engineered Wetland. Earth Surface Processes and Landforms. https://doi.org/10.1002/esp.4398

How to cite: Puttock, A., Graham, H., and Brazier, R.: Does changing connectivity due to beaver engineering result in changing hydrological function? Understanding the impacts of the return of the Eurasian beaver to Great Britain., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2158, https://doi.org/10.5194/egusphere-egu2020-2158, 2020.

D1017 |
Marco Tangi, Simone Bizzi, and Andrea Castelletti

Sediment connectivity is a fundamental property of river network, which directly influences the geomorphological processes regulating the formation and development of the different in-channel geomorphic units and leading to different river types. Alterations of sediment connectivity, e.g. caused by human disturbances such as dam construction or bed mining, are often followed by changes in channel patterns resulting in potential radical shifts in river types, e.g., from braided systems to sinuous single channel, with consequent loss of river ecosystems associated with specific river types.

In this work, we analyze the connections between basin-scale sediment connectivity indices and river types with the aim of advancing our quantitative ability to inter-relate channel forms and processes with type and amount of sediment fluxes available to the river channel. Our study focuses on the Vjosa river, Albania, which due to the limited anthropogenic bias still showcases a large variety of fluvial forms, including ample sections of braided channels, some of the few remaining in Europe and well renewed as ecological hotspots. The Vjosa river is now interested by large scale hydropower development plans, which may threaten the river unique ecological and morphological value. We estimate sediment transport using the CASCADE model, a modelling framework for basin-scale sediment transport simulation, which generates spatially distributed information on sediment movement and connectivity in river networks. The model has been validated using available data on bed load transport in a braided section close to the basin outlet and surficial grain size distributions collected across the river network.

By integrating CASCADE outputs (i.e., sediment fluxes and size distributions) with available geomorphic information at the network scale (e.g., channel slope and water discharge), we successfully tested an empirical formula proposed in literature based on sediment concentration, median grain size, channel slope and bankfull discharge, to disentangle the drivers of braided or single channel patterns. We then tested the same threshold for different dam development portfolios, showing how even few new dams would alter current conditions in terms of type and amount of sediment availability, leading to multiple channel type shifts from braided to sinuous single channel across the network.

For the first time, the incorporation of the CASCADE model with more traditional geomorphic analysis of river system demonstrate how CASCADE sediment connectivity information advances our ability to interpret existing river system processes, to assess stability of the different channel forms and to evaluate resilience and identify tipping points of fragile system like the Vjosa basin.

How to cite: Tangi, M., Bizzi, S., and Castelletti, A.: Network scale sediment connectivity to explore stability and resilience of channel forms and river types in the Vjosa basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8936, https://doi.org/10.5194/egusphere-egu2020-8936, 2020.

D1018 |
Anuschka Buter, Tobias Heckmann, Lorenzo Fillisetti, Antonia Spitzer, Luca Mao, Bernhard Gems, and Francesco Comiti

Sediment connectivity has been receiving increased attention in the last years. Several approaches have been applied to analyse where and to what extent sediment sources are connected to the main fluvial network and/or to depositional areas. Especially in mountain environments, sediment transport is temporally and spatially variable, and thus assessing sediment connectivity is challenging. Within this work, a graph theory-based approach is presented, with the aim to identify changes in space and time within the sediment transport network during the main sediment transport periods of the year.

A network, built up by nodes and directed edges, was manually digitized for the Sulden/Solda river basin (Vinschgau/Venosta valley, Italian Alps). The nodes represent landforms delineated within a previously developed geomorphological map, which features 32 different landform categories and seamlessly covers the entire basin (~130 km²). The directed edges are connecting nodes if sediment transport is (potentially) occurring from one to the subsequent geomorphological unit. This evaluation was made based on visual evidences from orthophotos and geomorphological as well as topographical characteristics of the respective landforms. Furthermore, a sediment transport process type was assigned to each edge.

Snow and glacier melt scenarios are defined by the occurrence of specific sediment transport processes, hence activation or deactivation of the related edges. Scenarios representing potential sediment transport networks during intensive heat periods and intense rain storms are included for both melt seasons, taking into consideration the expected higher frequency of these meteorological conditions in the future decades. For example, rain storm scenarios include edges showing potential debris flow trajectories, whereas these connections are not present in scenarios representing just snow- and ice-melt events. Therefore, functional connectivity changes within the proposed sediment transport network scenarios. For all the events, graph theory measures are calculated, as e.g. the betweenness centrality index to identify “hot-spot” nodes of the sediment cascades. Furthermore, the quantity and the composition of the sediment cascades reaching the catchment outlet can be identified in order to highlight the most relevant transport processes as well as to derive the most typical sediment cascades for a specific area.

The study basin is characterized by a high sediment availability due to large glacio-fluvial deposits present at the glaciers forefield and to the wide areas covered with talus deposits. However, the connectivity analysis demonstrates that a vast portion of these sediment sources is not connected to the main channel under the modelled melt runoff scenarios. Only in case of intense rainstorms talus deposits might become a coupled sediment source due to the potential occurrence of debris flows. Hence, areas connected only occasionally due to the (re-)activation of specific sediment cascades can be mapped. Additionally, a relative connectivity degree is calculated for every scenario, introducing a better comparability.

How to cite: Buter, A., Heckmann, T., Fillisetti, L., Spitzer, A., Mao, L., Gems, B., and Comiti, F.: Graph theory-based sediment connectivity analysis of a glacierised Alpine basin for different event scenarios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17926, https://doi.org/10.5194/egusphere-egu2020-17926, 2020.

D1019 |
Steven G. Sandi, Patricia M. Saco, Jose F. Rodriguez, Mariano Moreno-de las Heras, and Samira Azadi

Over the last few years, the concept of hydrological connectivity has emerged as a useful framework to quantify how changes in water redistribution and sediment production may lead to land degradation. Here, we illustrate the use of the connectivity framework for several examples of dryland systems that are analysed at a variety of spatial and temporal scales using both modelling approaches and remote sensing data analysis. We show that hydrological connectivity is particularly useful in drylands where human and/or natural disturbances can alter the surface water availability and pathways, and therefore the system connectivity. In doing so, we also focus on the analysis of co-evolution of system structures and function, and how they may drive threshold behaviour leading to desertification. We apply the framework to different dryland systems, starting with the analysis of semi-arid rangelands, where feedbacks between the decline in vegetation density and landscape erosion reinforces degradation processes driven by changes in connectivity. We then focus on semi-arid floodplain wetlands, where decreases in water volumes promote terrestrial vegetation encroachment that changes drainage conditions and connectivity, potentially reinforcing redistribution of flow paths to other wetland areas. In both cases, crossing a system threshold might lead to degradation in which the return to a functional system is unlikely. The examples presented highlight the need to incorporate a co-evolutionary framework for the analysis of changing connectivity patterns and the emergence of thresholds in arid and semi-arid systems. This framework can be used for the identification of early warning indicators of transitions from healthy to degraded states, which are useful for management applications.

How to cite: Sandi, S. G., Saco, P. M., Rodriguez, J. F., Moreno-de las Heras, M., and Azadi, S.: Hydrological Connectivity: A Useful framework to identify degradation thresholds in semiarid landscapes., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11934, https://doi.org/10.5194/egusphere-egu2020-11934, 2020.

D1020 |
Ellen Wohl, Julianne Scamardo, and Emily Iskin

Large wood historically influenced diverse geomorphic and ecological processes in channels from first-order streams to major rivers. Centuries of deforestation and wood removal from channels have significantly reduced the presence of wood. The presence of large wood tends to decrease longitudinal connectivity, but increases lateral and vertical connectivity that arises from the presence of wood as an obstacle in the channel. Channel-spanning logjams, in particular, enhance vertical connectivity via hyporheic exchange flow and lateral connectivity via overbank flow, channel avulsion, lateral channel migration, or formation of secondary channels. In mountain streams, these effects are likely to be more pronounced in relatively wide, low gradient reaches with thicker alluvium and greater space for floodplain development and channel lateral mobility. River restoration increasingly includes maintaining or reintroducing large wood to channels, but there are relatively few studies that can be used to constrain management targets by providing data on instream large wood loads in unmanaged streams in diverse geographic settings. Here, we document the longitudinal distribution and persistence of logjams in the US Southern Rocky Mountains over a period of a decade. Key results include: (1) The longitudinal distribution of logjams varies significantly between successive stream reaches. Reaches are hundreds to thousands of meters in length and defined based on consistent stream gradient and channel lateral confinement. (2) Individual logjams change on an annual basis and typically persist less than a decade, although new logjams form frequently. (3) Individual logjams are more persistent in wide, low gradient reaches. (4) The population of logjams within a reach is more resilient to major floods in wide, low gradient reaches. The continuing breakup of jams and formation of new jams underscores the importance of ongoing wood recruitment in a natural river corridor. The results also imply that large wood reintroduction may be most effectively focused on specific types of wood process domains where the persistence and geomorphic effects of large wood are enhanced.

How to cite: Wohl, E., Scamardo, J., and Iskin, E.: Large wood and stream longitudinal disconnectivity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10411, https://doi.org/10.5194/egusphere-egu2020-10411, 2020.

D1021 |
Alexander Orkhonselenge, Odmaa Bulgan, Dashtseren Gerelsaikhan, Tuyagerel Davaagatan, and Nyamdorj Altansukh

This study aims to reconstruct paleoclimate change in eastern Mongolia inferred from sedimentological and geochronological records from Lake Yakhi in the drainage basin of the Pacific Ocean. In a context of the study goal the hydroclimatic fluctuation in eastern Mongolia resulted from Lake Yakhi is presented here. Result from changes in lake area of Lake Yakhi shows it decreased from 79.72 km2 in 1970 to 53.76 km2 in 1986 and 35.03 km2 in 2018. The hydraulic dynamics and field observation show that Lake Yakhi is shifting into a playa lake. For shrinking Lake Yakhi, shifting toward a playa lake is directly related to the global warming, i.e., it implies the lake is extremely sensitive to climate change in the late Holocene. This coincides with those conditions of large lakes in the Govi region in southern Mongolia (Orkhonselenge et al., 2018). The major element compositions of the lake sediments show that the core Y18-1 is dominated by SiO2, Al2O3, K2O and Na2O, while the cores Y18-2 and Y18-3 largely contain SiO2, Al2O3, CaO and Fe2O3. In addition to the dominant semimetal and transition metal, presence of oxides of alkali earth metals in the core Y18-1 and of alkaline earth metals in the cores Y18-2 and Y18-3 show a derivation of intermediate sedimentary and volcanic rocks in the drainage basin of Lake Yakhi. This coincides with the tectonostratigraphic terrane structure of the cratonal clastic sedimentary rocks (Badarch et al., 2002) in the Lake Yakhi area. Further detail geomorphological and geochronological records from Lake Yakhi would not review only the hydrogeochemical evolution, but the paleoclimate changes in eastern Mongolia. Leading the dates would precisely determine the paleohydroclimatic fluctuations in eastern Mongolia.

How to cite: Orkhonselenge, A., Bulgan, O., Gerelsaikhan, D., Davaagatan, T., and Altansukh, N.: Hydroclimatic fluctuation in Lake Yakhi, eastern Mongolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-686, https://doi.org/10.5194/egusphere-egu2020-686, 2020.

D1022 |
Kamini Singha, Megan Doughty, Sawyer McFadden, Audrey Hucks Sawyer, and Ellen Wohl

Logjams increase hydraulic resistance and create hydraulic head gradients along the streambed that drive groundwater-surface water exchange. Here, we quantify changes in hyporheic exchange flow due to channel-spanning logjams using field measurements and numerical modeling in MODFLOW and MT3DMS. Electrical resistivity (ER) imaging was used to monitor the transport of solutes into the hyporheic zone during a series of in-stream tracer tests supplemented by in-stream monitoring. We conducted experiments in a variety of reaches in Little Beaver Creek, Colorado (USA) of varying complexity: a control reach with no logjams, a reach with a single, channel-spanning logjam, and additional jams with greater logjam complexity. Our results show that 1) higher hyporheic exchange flow occurs at reach with logjams, 2) logjams create complex hyporheic exchange flow pathways that can cause bimodal solute breakthrough behavior downstream, and 3) higher discharge rates associated with spring snowmelt increase the extent and magnitude of hyporheic exchange flow. The numerical modeling supports all three field findings, and also suggest that lower flows increase solute retention in streams, although this last conclusion is not strongly supported by field results. This study represents the first use of ER to explore hyporheic exchange flow around a naturally occurring logjam over different stream discharges and has implications for understanding how logjams influence the transport of solutes, the health of stream ecosystems, and stream restoration and conservation efforts.

How to cite: Singha, K., Doughty, M., McFadden, S., Sawyer, A. H., and Wohl, E.: Mapping increases in hyporheic exchange from channel-spanning logjams, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1342, https://doi.org/10.5194/egusphere-egu2020-1342, 2020.

D1023 |
Rajiv Sinha and Manudeo Singh

The surface processes are dynamic and act at multiple spatio-temporal scales and contain embedded hierarchies to generate complex landscapes.  It is, therefore, necessary to understand the linkages or ‘connections’ of landscapes across various scales and levels to gain insights on their interactions and feedbacks in association with such processes. Recently, there has been a surge in the application of the concept of connectivity to the multitude of geomorphic systems with varying scales, objectives, and field of study. A large number of review articles and special issues published in the last few years is a testament to the utility of this concept. It, therefore, implies that the connectivity concept could be a way forward to understand the earth’s surface processes and dynamics and their associations with the landforms. This work presents a ‘connectivity framework’ by establishing (a) the interrelationship and interdependencies among its types (sediment connectivity, hydrological connectivity, landscape connectivity), components (structural and functional connectivity), and dimensions (spatial and temporal), (b) the inherent feedback among various components under a process-response framework and under varying terrain characteristics, and (c) its utility in different geomorphic systems at variable scales and physical settings.

In a geomorphic system, connectivity accounts for static and dynamic properties of the landscape, and therefore, establishes structural and functional frameworks of the landscapes and process-response systems. This concept is applicable at all spatial and temporal scales and can be used to understand evolutionary pathways of landscapes and their dynamics. Further, the connectivity approach has the potential to be applied extensively to the hydro-geomorphic systems to understand their complexity as well as for designing effective management practices for river systems and wetlands, water resources for agriculture, and for assessment of ecological flows in rivers. It can also be aligned to a multitude of problems from river basin management to hazard and risk assessment to wetland management and restoration. We, therefore, argue that the connectivity concept is emergent as well as a fundamental property of landscapes and the connectivity framework presents a robust tool to understand the surface processes and dynamics.

How to cite: Sinha, R. and Singh, M.: The connectivity framework: a way forward in understanding the surface processes and dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2898, https://doi.org/10.5194/egusphere-egu2020-2898, 2020.

D1024 |
Anthony Parsons and Ronald Pöppl

In 2019 a new IAG (International Association of Geomorphologists) Working Group on “Connectivity in Geomorphology” has been established. In bringing together the experience and expertise of researchers in the emerging field of connectivity in geomorphology, this IAG-WG aims to enable the transitions a) from parallel projects to concerted research (incl. a transdisciplinary framework with strong linkages to practitioners/applied aspects, e.g. management of water and sediment in catchments), b) from a plethora of case studies to more generic, comparable research, c) from a multiplicity of definitions, concepts and methodological approaches to coordinated, theory-guided research activity along agreed lines, which will provide both immediate benefit for existing projects and a springboard for the development of future research projects. The overarching aim of this WG is to form an international network of Connectivity scientists, to share expertise and develop a consensus on the definition and scientific agenda regarding the emerging field of connectivity in geomorphology. With this poster presentation we would like to communicate our mission statement to the EGU audience, further discussing about recent and future activities of the Working Group

How to cite: Parsons, A. and Pöppl, R.: IAG Working Group on “Connectivity in Geomorphology”: Introduction and status report, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2907, https://doi.org/10.5194/egusphere-egu2020-2907, 2020.

D1025 |
Hanoch Lavee

In humid temperate areas, where infiltration rate and soil moisture are high the hillslopes are draining mainly via shallow subsurface flow. Overland flow is seldom generated on the very low parts of hillslopes when the soil is saturated up to the surface. This spatial pattern is known as “partial area contribution”.

In contrary, in arid areas, where the soil moisture is hygroscopic most of the time, overland flow is generated not because of soil saturation conditions but only when rainfall intensity is higher than the infiltration rate.  

Nevertheless, we found a “partial area contribution” pattern in several arid and semi-arid areas due other controlling factors:

  1. In eastern Sinai, under rainfall simulation experiments on scree slopes, due to high spatial differences in the soil texture, runoff coefficient in the gullies was almost 100% while in the very permeable interfluves runoff wasn’t generated at all. Overland flow was generated, therefore, only in the gullies (Lavee ,1973; Yair & Lavee ,1976).
  2. In an instrumented experimental watershed in the Northern Negev, the specific overland flow yield from long plots ,extending from the divide to the slope base (around 60m in length), was consistently lower than the combined specific overland flow yield from the adjacent two short plots (around 30m in length), draining the upper and the lower sections of the hillslope, respectively. This means that the overland flow is discontinuous and at least part of the overland flow that was generated at the upper part of the hillslope infiltrated, in most overland flow events, into the soil, before reaching the slope base. In other words, only the lower part of the hillslope contributes, in most cases, overland flow to the channel. Such overland flow discontinuity is controlled by: 1. The typical short duration of rain showers in arid areas. As more than 80% of the rain showers last for less than 15 minutes, the total flow duration is usually shorter than the concentration time. 2. The spatial distribution of infiltration rate. In this case it was mainly the relatively high infiltration rate in the colluvial cover at the lower part of the hillslopes in part of the study area that absorbed large amount of the water flowing from the upper part of the hillslopes (Lavee, 1982; Yair & Lavee, 1985; Lavee & Yair, 1990).
  3. In an experimental project along a climatological transect, running from the Mediterranean climate near Jerusalem to the extreme arid climate near the Dead Sea, the main reason for the overland flow discontinuity, especially in the semi-arid area, was the mosaic pattern of “source patches”, on which overland flow was generated, and “sink patches”, in which at least part of the direct rain and the incoming overland flow infiltrated. This pattern is produced by different processes, mainly via the effect of vegetation, but also due to the effects of micro-topography, big stones, especially if they are partly embedded in the soil, and livestock grazing (Lavee & Poesen, 1991; Lavee et al., 1998; Stavi et al., 2008).

How to cite: Lavee, H.: "Partial area contribution" and "Overland flow discontinuity": from humid to arid hillslopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3059, https://doi.org/10.5194/egusphere-egu2020-3059, 2020.

D1026 |
Nicola Ellis, Richard Brazier, and Karen Anderson

In addition to providing a valuable habitat, semi-natural unimproved grasslands may have significant value as part of natural flood management strategies. However, further understanding of the hydrological functioning of these landscapes is required and this study is developing new methods for using proximal remote sensing techniques to assess surface flow pathway connectivity.

Purple moor grass (Molinia caerulea) dominated fields are seasonally saturated and have a dense tussock structure, hypothesised to result in long surface flow pathways with low hydrological connectivity and greater surface roughness than neighbouring intensively managed improved grassland. Quantifying these surface flow pathways required fine-scale understanding of topography not available from available datasets such as airborne LiDAR. After prescribed burning (a local management practice) at a study site in South West England, the underlying M. caerulea tussock structure and flow pathways were exposed. A DJI Mavic Air quadcopter was flown over the M. caerulea field shortly after to capture this structure. A neighbouring improved grassland field of similar size and slope was also surveyed.

Drone surveys were carried out using an automated flight path over an area of 1.7ha of M. caerulea and 2.2 ha of improved grassland. Imagery was captured with an overlap/sidelap of 85% and with a ground sampling distance of 25m. Ground control points were geolocated, using a GNSS with an accuracy of ~0.03m to constrain subsequent structure from motion (SFM) photogrammetry processing.

SFM was used to create dense point clouds, from which digital surface models (DSM) of the two sites were derived at a resolution of 0.03m. The standard deviation of points within each DSM grid cell was also calculated to describe the uncertainty resulting from converting point cloud data to raster. An automated classification method was developed, in R using the LidR package, to identify individual M. caerulea tussocks. The edges of tussocks were characterised by greater error due to the variability in topography and therefore could be used to identify tussock features.

The resulting DSMs were used to quantify surface flow pathway length in both sites using the Arc GIS flow routing algorithm. This included flow pathway length and drainage density (length of flow path per unit area). M. caerulea had longer, more sinuous surface flow pathways through the dense tussocks, with an average drainage density of 2.54m m¯². This was significantly greater than drainage density in the improved field (1.82m m¯²). Flow pathways in the improved grassland were straighter and more in-line with the slope in comparison. Longer, tenuous surface flow pathways in M. caerulea sites theoretically result in a slower velocity of surface runoff, reduced soil erosion, greater evapotranspiration and root uptake than improved grassland sites. It is proposed that this understanding will be incorporated into hydrological modelling to improve understanding of the hydrological functioning and possible natural flood management potential of these landscapes.

How to cite: Ellis, N., Brazier, R., and Anderson, K.: Assessing surface flow pathway connectivity in semi-natural unimproved grasslands using structure from motion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5053, https://doi.org/10.5194/egusphere-egu2020-5053, 2020.

D1027 |
Yuichi Onda, Shohei Kozuka, Hiroaki Kato, and Yoshifumi Wakiyama

In sandy soil, the step and mound-like formation of the erosion/ deposition structures have been reported (Ribolzi et al., 2011; Mayer et al., 2008) by visual observation or small-scale experiments though it has not been analyzed quantitively in the field. Especially no data are available on the sediment transport distance in such erosion areas. Recently, the development of Unmanned Aerial Vehicle based Structure from Motion (UAV-SfM) technique can provide the hi-resolution and hi-accuracy topographic data. This study aimed to detect the step-like erosion and deposition and discuss the step-like erosion and deposition process.

 Our study site was located in Yamakiya district, Fukushima, Japan. This area was decontaminated in 2014 by the Ministry of Environment to reduce the air dose rate by removing topsoil and overlaying decomposed granite soil (organic matter: 4.6%, sand: 68.8%, silt: 19.7%, clay: 6.9%, measured on 10/10/2019). We installed a USLE soil erosion plot (5 m wide and 21 m long) on the farmland slope. The topography in the plot was measured by the UAV-SfM method. UAV used in this study was Phantom4 Pro and flying height was 5 – 10 m. 200 – 400 photos were taken for each survey. Photos were imported to Photoscan, and 3D point clouds were reconstructed. 3D point clouds were imported to ArcGIS pro and converted to DSM data. Finally, soil surface changes were calculated for each survey period. Transport distances of soil particles were measured by RFID tags. RFID tags were coated with cement, bronze powder, fluorescent paint, and topcoat and had 3 – 5 mm size and 2.0 – 3.0 g cm-3 density. 100 RFID tags were set to the soil surface.

 Step-like erosion and deposition were observed between 8/28/2019 – 10/16/2019. Soil surface change in this period showed that erosion and deposition were repeated and higher erosion on the lower slope position. Topography data also showed steeper step structures in the eroded area than the depositional area. Median transport distance of RFID tags in the interrill areas is 4.1 cm, and 76 cm in the terracet areas. Therefore, we found the effect of soil mounds and the terracettes on the bare soil connectivity significantly increase the sediment connectivity and sediment transport distance.

How to cite: Onda, Y., Kozuka, S., Kato, H., and Wakiyama, Y.: The effect of the formation of the micro-terracetts on the connectivity of the sediment transport on sandy granitic soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6476, https://doi.org/10.5194/egusphere-egu2020-6476, 2020.

D1028 |
Qin Yang, Peng Hu, Jianhua Wang, Qinghui Zeng, Zefan Yang, Huan Liu, and Yiyang Dong

The weakened connectivity of wetland system is the key factor leading to the destruction, degradation and disappearance of wetland. Recently, the researches on the connectivity of wetland system mainly focus on the connectivity of hydrology and geomorphology, the impact of wetland system on habitat is ignored. In this study, an innovative method was applied to evaluate and regulate the Stereoscopic Spatial Connectivity (SSC) of wetland systems in the Heilongjiang River Basin in China (HRBC). In the method, the water requirements of typical organisms in the region was considered, and the evolution trend of landscape area in wetland system and the health condition of SSC were analyzed by GIS. The regulation mode of improving Stereoscopic Spatial Connectivity Index (SSCI) was proposed. The results showed that over the past 35 years, the wetland system in the study area had shrunk significantly with the SSCI decreasing from 41.3% in 1980 to 35.08% in 2015. By comparing the correlation between temperature, precipitation, agricultural land, construction land and wetland system in the same period, it proves that human activity is the major driving factor of wetland system shrinkage. Eventually, the key protected areas for maintaining the SSC of the wetland system are clarified, and the key recovery areas are determined according to the three scenarios of "high-medium-low" feasibility, which greatly improves the SSCI and Generalization Route (GR) after regulation. In general, the proposed SSC evaluation and regulation methods can fully reflect the ecological effect of wetland system. The methods also scientifically quantify the significant effect of regulation mode, which has certain reference significance for the evaluation and regulation of wetland system in other regions.

How to cite: Yang, Q., Hu, P., Wang, J., Zeng, Q., Yang, Z., Liu, H., and Dong, Y.: Evaluation and Regulation of Stereosopic Spatial Connectivity for Wetland System in Heilongjiang River Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6784, https://doi.org/10.5194/egusphere-egu2020-6784, 2020.

D1029 |
David Nezlobin, Hanoch Lavee, and Pariente Sarah

In the last several decades a considerable number of hydrologic connectivity indexes have been suggested both in surface and subsurface hydrology. The hydrologic connectivity indexes can be classified according e.g. to the following criteria:

  • Argumentation – if the index formula is based on a strict theoretical derivation, intuitive assumptions, empiric data, or some combination of the above?
  • Range of applicability – only a very few indexes have been suggested as the universal ones, i.e. applicable on various scales, while the great majority of indexes have been designed exclusively for specific scales and environments.
  • Flow model – even at the same scales and environments the various types of flow may have considerably different morphologies. For instance, in the subsurface hydrology the saturated pressurized flows may have the morphology that is notably different from that of unpressurised flows. Consequently, for the suggested connectivity indexes the addressed flow model should be properly specified.
  • Descriptive adequacy – to what extent the index describes the hydrologic connectivity, and whether its value can be strongly affected by the factors unrelated (at least directly) to the connectivity?
  • Predictive power – what is typical accuracy of the index value (or set of values) and if the index value alterations may predict important changes in the hydrologic connectivity of addressed environments?

Several examples of the suggested classification are provided. We further compare two of the powerful connectivity approaches, such as the percolation theory approach and method of random graphs and consider some of the indexes based on these approaches. It can be shown that although both approaches can hardly lead to accurate description of connectivity in real hydrologic systems, they nevertheless may provide theoretical explanation of critical changes in connectivity. The percolation theory, especially its directional modifications, are more applicable for systems consisting of great number of similar elements, connected via their close neighbors. In turn, the approach of random graphs is preferable for systems having moderate number of elements which are connected not necessarily through their neighbors. The mentioned approaches seem to be the most adequate ones for exploring the sharp changes in the hydrologic connectivity but should be further rectified by considering realistic flow processes and their interactions.

How to cite: Nezlobin, D., Lavee, H., and Sarah, P.: On classification of hydrologic connectivity indexes, their descriptive adequacy and predictive power, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8201, https://doi.org/10.5194/egusphere-egu2020-8201, 2020.

D1030 |
Annegret Larsen, Tony Reimann, Christoph Sperisen, Vincent Robin, and Stuart N Lane

Geomorphology has long considered the role of abiotic factors in geomorphic processes, including tectonics, geology, climate and relief, as well as humans impact upon them. Biotic factors however, including not only plants but also bacteria and protists, biofilms, fungi, insects, invertebrates, and animals are increasingly recognized as governing geomorphic processes on many spatial and temporal scales. We argue that if fauna are important as geological agents, then understanding the complex response of geomorphic systems to fauna is necessary to understand the past, present and future of the fluvial environment. It is not surprising that studies of the Late Quaternary evolution of fluvial morphodynamics have largely focused upon changes in the sedimentary soil-sediment sequences that result from climate change; (ii) vegetation change; and/or (iii) human impacts. Reconstruction of vegetation and climate from pollen and other records facilitates these analyses. But if animals are shown to be an important influence on geomorphic processes today, then it is quite possible that they were also important historically. For example, conclusive interpretation of Holocene river changes may be limited because of an incomplete or partial account of the presence and/or absence of data on the role of ecosystem engineers in modifying the riparian and aquatic ecosystems, including hydro-geomorphic processes. DNA found within historical deposits may be used to constrain the role of past ecosystem engineers. Analysis of ancient environmental DNA up to date includes palaeo-environmental DNA from sedimentary deposits (sedaDNA) from disseminated genetic material found within sedimentary archives, including paleo-dietary ancient DNA. Here, we use an analogue study investigating the present hydro-geomorphic and biogeochemical changes that the ecosystem engineer beaver (Castor fiber) creates at four sites in central Europe to better understand and quantify the effects of beaver ecosystem engineering on a seasonal to decadal scale. We utilize these results to interpret the chrono-stratigraphy of two Holocene beaver sites, including macro-fossil and sedaDNA sampling, and test for the first time if sedaDNA can support the investigation of beaver-induced palao-environmental conditions in river floodplains. We find that sedaDNA data and other palaeo-botanical proxies complement each other showing wider diversity of species than if the methods are used separately. However, care must be taken with regards of experimental setup, and further investigation into the effects of transport processes and/or quantitative representativeness is needed.

How to cite: Larsen, A., Reimann, T., Sperisen, C., Robin, V., and Lane, S. N.: Towards a better understanding of past biotic drivers of river and floodplain geomorphology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11338, https://doi.org/10.5194/egusphere-egu2020-11338, 2020.

D1031 |
François Mettra, Koen Blanckaert, Ulrich Lemmin, and David Andrew Barry

In the main river canyon of a deep peri-Alpine lake (Rhône River canyon in Lake Geneva, Switzerland), occasional turbidity currents have been observed and monitored using acoustic Doppler current profilers (ADCP) during summer. It has been hypothesized that floods at catchment basin scale and slides of sublacustrine deltaic deposits are the main cause of these turbidity currents. Here, using discharge and turbidity measurements in the Rhône River, 6 km upstream of Lake Geneva and observations from small sub-catchments (as small as 4 km2), we show that single isolated storms in such sub-catchments can lead to turbidity currents in the deep Lake Geneva without a significant flood at the catchment basin scale (~5500 km2).

We analyzed several examples of hyper-concentrated and debris flows generated in small sub-catchments, reaching the Rhône channel and leading to turbidity currents in Lake Geneva. The relatively high discharge of the Rhône River and its straight man-made channel induced a rapid and intense transfer of sediment toward Lake Geneva. The continuous measurements in the Rhône River allowed tracking these sediment clouds and estimating sediment volumes. Then, using the ADCP measurements, we were able to mesure the intensity of the subsequent sediment pulses in the form of turbidity currents inside the Rhône River canyon in the deep part of Lake Geneva.

In summary, this study shows that a significant fraction of the annual sediment yield of the whole catchment basin is released from specific high-alpine areas due strong but localized storms. These sub-catchments have the specificity to be highly connected with the main channel of the catchment basin, thus permitting a rapid transfer along the sediment cascade (in one single event).

How to cite: Mettra, F., Blanckaert, K., Lemmin, U., and Barry, D. A.: Sediment connectivity in Alpine basins: from isolated storms to turbidity currents in deep peri-Alpine lakes (examples from the Rhône basin and Lake Geneva, Switzerland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11671, https://doi.org/10.5194/egusphere-egu2020-11671, 2020.

D1032 |
Gordon Grant

Connectivity is an intrinsic property of fluvial systems.  Rivers evolve specifically to carry the water, sediment, wood, and other products collected, generated, and delivered by watersheds, and therefore are fundamentally connected to their co-evolving hillslopes and landscapes.  Moreover, these watershed products inevitably flow downstream to their base levels under the influence of gravitational forces; on geological timescales, connectivity is destiny for rivers.

But on shorter timescales, some of the most interesting behavior of rivers occurs where the flows of mass and energy are interrupted for various reasons.  Disconnectivity can occur due to blockages by dams (natural or artificial), landslides, lava flows, glaciers, or sand dunes, among other mechanisms. Such disconnections invariably result in abrupt loss of energy and momentum of moving material, leading to accumulations of mass:  reservoir sediments, wood jams, organic mats, valley fills. The morphology of many rivers is an expression of the tension between states of connectivity and disconnectivity.

A richer context for understanding this tension emerges from considering the related concepts of continuity and discontinuity in fluvial systems.  Where connectivity and its opposite refer to states, continuity and its antonym refer to processes.  Continuity and discontinuity represent fundamental and complementary perspectives on the mechanisms that organize fluvial systems.  The continuum perspective emphasizes how geomorphic features and mechanisms are expressed along continuous gradients without abrupt changes, transitions, or thresholds.  Key concepts in fluvial geomorphology: -- balance of forces, hydraulic geometry, graded streams – reflect this view.  This view is echoed outside of geomorphology as well in fields as diverse as ecology, paleontology, and evolutionary biology. The continuum perspective is extremely useful as an organizing principle for understanding complex systems, because it allows us to treat processes and their corresponding features as orderly progressions, or manifestations of a dynamic equilibrium of forces and overarching controls. This has immense predictive power.

In contrast, the discontinuum view incorporates non-uniform, non-progressive, and non-equilibrium thinking into our understanding of how landscapes develop and evolve.  Three distinct ways in which this perspective is revealed emerge from considering: 1) discontinuous spatial arrangements of geomorphologic features or singular events; 2) process domains that reflect intrinsic or extrinsic thresholds; and 3) physical mechanisms or dynamics that involve state changes, often threshold-based.  Drawing on examples from a wide range of geomorphic landscapes, I will discuss how in moving beyond the continuum perspective, a fertile set of ideas comes into focus: thresholds, non-equilibrium states, heterogeneity, catastrophe. The range of phenomena that is thereby opened up to scientific exploration similarly expands: punctuated episodes of cutting and filling, discretization of landscapes into hierarchies of structure and control, the work of extreme events. Orderly and progressive evolution towards a steady or ideal state is replaced by chaotic episodes of disturbance and recovery. Similar to connectivity and disconnectivity, both continuum and discontinuum perpsectives are complementary and necessary views for understanding the behavior and evolution of fluvial systems.


How to cite: Grant, G.: Continuity and discontinuity in fluvial systems:  why we need both perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11717, https://doi.org/10.5194/egusphere-egu2020-11717, 2020.

D1033 |
Abolfazl Jalali Shahrood, Ali Torabi Haghighi, Meseret Menberu, Hamid Darabi, and Björn Klöve

Erosion and sedimentation play a significant role in river morphology and are among the most important issues in river engineering. Riverbank protection is one of the common efforts in river engineering to stop or reduce the rate of side erosion in rivers. Riprap is one of the simplest and most economical river protection methods due to construction material availability, operation simplicity, flexibility, easiness to construct and repair.  Anthropogenic disturbances could have several side effects in rivers and subsequently induce a change in river morphology. Hence, morphological analysis is needed to trace the history of channel formation and forecast future changes. Riprap is widely used in the Southern parts of Iran to save the rural and agricultural areas located along the river. The Qareaqaj River is one of the major rivers in the South of Iran that is affected by side erosion in many places due to its high meandering morphology. Hence, a riprap structure was constructed in 2006 to protect the Qasr Ahmad village located in the right bank of the Qareaqaj River. The objective of this study is to evaluate how the river training has affected the channel morphology for 18 years in a 10 Km stretch (5 km above and 5 km below the riprap structure). Five Landsat multispectral images captured in 1995, 1999, 2003, 2010, and 2013 were used as input in the RiMARS (River Morphodynamics Analysis method based on Remote Sensing data) for morphological analysis. The Sinuosity Index (SI) has been estimated for meanders for 18 years and the results indicated that most meanders along the stretch are classified as twisty (about 36%), meandering (22%) and winding (18%). Furthermore, the river is divided into ten sections along the flow path and temporal migration of each section is separately analyzed. The river in its halfway (where the riprap was constructed) has migrated on average by 12.5 m, 2.2 m, 5.5 m, and 9 m in 1999, 2003, 2010, 2013, respectively, when compared to the year 1995. The maximum rate of river migration was observed (6.5 m per year) during 2010-2013 at the 7th decile of the stretch, which is about 2000 m below the protected area. The results clearly indicated that the migration rates increased in the downstream of the riprap protected area after the construction date.

How to cite: Jalali Shahrood, A., Torabi Haghighi, A., Menberu, M., Darabi, H., and Klöve, B.: Analysis of river training in Qareaqaj River in Iran: Application of RiMARS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15867, https://doi.org/10.5194/egusphere-egu2020-15867, 2020.

D1034 |
Martin Tschikof, Stephanie Natho, Thomas Hein, and Elisabeth Bondar-Kunze

In the last centuries, rivers in Central Europe have severely suffered from hydro-morphological alterations and excessive nutrient inputs. Their adjacent floodplains have the ability to retain transported nutrients in case of inundation, but are subject to progressing decoupling from the main river stem. In the Austrian Danube Floodplain National Park, restoration measures have been carried out and are planned for the near future to increase lateral connectivity in accordance with navigation purposes.

We investigated nutrient retention capacity in seven differently connected side arms and the potential effects of further proposed reconnection measures using two complementary modeling approaches. With existing monitoring data on hydrology, nitrate and total phosphorus concentrations for three side arms, we derived a multivariate statistical model and compared these results to a larger scaled semi-empirical retention model (Venohr et al. 2011). We modelled nutrient retention at current state and after completion of side arm reconnections in a dry (2003) and wet (2002) hydrologic year.

Both models show comparable annual retention rates and agree in calculating higher nutrient retention in floodplains where reconnection allows more frequent inundations at low discharges. The semi-empirical approach results in highest retention rates at low hydraulic loads and shows more reasonable results at high floods. On the other hand, the statistical approach predicts increasing retention rates with higher nutrient loads entering the side arms and also takes into account nitrate reduction in the remaining water bodies at times of no surface water connection.

Our results suggest that water quality of the Danube River could be improved by increasing parameters related to lateral connectivity between river and floodplain. These include in particular the frequency and area of inundation, as well as nutrient input loads into the reactive zones of floodplains. Still, a frequently hydrologically connected national park stretch after restoration reduces nutrient loads of the Upper Danube by less than 0.1% due to its small areal extent in relation to transported river nutrient loads. In order to sustain an adequate water quality in future, both a reduction in nutrient emissions and a larger area of functional floodplains along the Danube River are required.


Venohr, M., Hirt, U., Hofmann, J., Opitz, D., Gericke, A., Wetzig, A., ... & Mahnkopf, J. (2011). Modelling of nutrient emissions in river systems–MONERIS–methods and background. International Review of Hydrobiology, 96(5), 435-483.

Key words:

River floodplains, lateral connectivity, nutrient retention, river restoration, floodplain reconnection, water quality

How to cite: Tschikof, M., Natho, S., Hein, T., and Bondar-Kunze, E.: Modelling the impact of increased lateral connectivity on nutrient retention in Austrian Danube floodplains, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18887, https://doi.org/10.5194/egusphere-egu2020-18887, 2020.

D1035 |
Lovisa Lind, Xiaolei Su, Lina Polvi, and Christer Nilsson

Stream networks both integrate abiotic and biotic landscape processes and transect the landscape, connecting different ecosystems and geologies longitudinally. The stream network can be divided into three process domains, as zones with distinct geomorphic processes: rapids, slow-flowing reaches, and lakes. Biotic recovery has been variable after stream restoration and it is therefore important to understand where in the catchment it is most beneficial to focus restoration and how the different process domains influence the restoration outcome. Along a stream network, potential for organism dispersal, usually by hydrochory for riparian plants, control riparian community organization. Thus, we wanted to determine whether differences in recovery of riparian vegetation after restoration are a function of seed dispersal or habitat conditions. Our main objective was therefore to predict how the local and upstream source of riparian vegetation influence the restoration outcome. Our study was located in the boreal region of northern Sweden in the Hjuksån catchment. Hjuksån is a tributary of the free-flowing Vindel River, which in turn is the largest tributary to the Ume River. We studied three major factors: dispersal, germination and establishment success of riparian vegetation. In consistence with previous studies that stagnant waterbodies, such as lakes and fens are efficient seed traps, our study indicate that lakes retain more seeds than rapids and slow-flowing reaches, which will influence the riparian community recovery as less species will continue to downstream restored reaches. However, while the germination experiment showed that lakes had the highest germination success there were no such indications for the establishment. The higher germination success might partly be explained by lakes having a higher soil moisture then rapids, which is important for the germination success. Overall, this study indicated that the dispersal, germination and establishment is very low in naturally disconnected stream networks in northern Sweden and further restoration effort might be needed to aid the slow recovery.

How to cite: Lind, L., Su, X., Polvi, L., and Nilsson, C.: Understanding seed dispersal and germination in naturally disconnected stream networks to evaluate restoration success, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20043, https://doi.org/10.5194/egusphere-egu2020-20043, 2020.

D1036 |
Giuseppe Bombino, Carolina Boix-Fayos, Bruno Gianmarco Carrà, Maria Francesca Cataldo, Daniela D'Agostino, Pietro Denisi, Joris De Vente, Antonino Labate, Antonella Nucera, and Demetrio Antonio Zema

In Mediterranean environments, where soil erosion rates are often not tolerable, sediment connectivity at the watershed scale needs accurate evaluation tools. Quiñonero-Rubio et al. (2013) proposed the Catchment Connectivity Index (CCI) to describe hydrological and geomorphological factors. It requires the combination of considerable skills to data sources and demanding field surveys. In order to improve the index and to simplify its application, in this study we propose a modified version of the CCI, the mCCI, that produces a more efficient description of the hydrological and geomorphological parameters composing CCI and, thanks to the large use of GIS software, making easier its applicability for operators with less field experience.

The mCCI is applied in a torrent of Calabria (Southern Italy) to evaluate the sediment connectivity at the catchment scale, by comparing four scenarios: a combination of check dam presence or not and land use or not, in 1955 and in 2012. This case study has shown how and by what extent the natural and human impacts (climate and land-use changes and check dam installation) have affected the geomorphic processes influencing sediment circulation in the studied basin throughout six decades. From 1955 to 2012, a general decrease in sediment connectivity has been caught by the mCCI, as a result of the combined effects of greening-up processes of the catchment (due to both natural afforestation and human-induced reforestation) and the installation of check dams, which have decreased the catchment potential to circulating sediments. Overall, the mCCI can be used as an analytical tool to evaluate the influence of past or future changes in natural and human-induced changes in land use and climate actions to give support to land planners in watershed management tasks.

How to cite: Bombino, G., Boix-Fayos, C., Carrà, B. G., Cataldo, M. F., D'Agostino, D., Denisi, P., De Vente, J., Labate, A., Nucera, A., and Zema, D. A.: A modified index to evaluate the sediment connectivity at the catchment scale in Mediterranean torrents, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20459, https://doi.org/10.5194/egusphere-egu2020-20459, 2020.

D1037 |
Rajkumari Kaurav and Pranab Gandhinagar

Levee breaching is the process of erosion of the levee material resulting in its failure and causing the water to flood. A levee may breach due to overtopping, piping, foundation defects, and lack of maintenance. The complex process of levee breaching involves hydrodynamics, sediment transport, and soil water interaction. This paper presents the 3D simulation of levee breach due to overtopping using CFD software, FLOW-3D. The numerical model uses Reynolds-averaged Navier–Stokes equations (RANS) for fluid flow, along with the volume of fluid (VOF) equation for surface tracking, as the governing equations. In addition, several turbulence models and different equations for bedload transport in scour model are available in FLOW-3D for simulation. A grid convergence test is used to decide the mesh size. The turbulence model and the parameters used in sediment scour model are calibrated using the experimental results for breach profiles available in literature. Results for evolution of breach and water surface profiles are presented. Additionally, velocity vectors in breach section, turbulence characteristics along the longitudinal and transverse direction and the breach discharge are also presented. The study suggests that the Renormalized group (RNG) turbulence model along with Meyer-Peter Müller equation for bedload transport optimally simulate the breach process for the considered case.

How to cite: Kaurav, R. and Gandhinagar, P.: 3D simulation of Levee breach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22292, https://doi.org/10.5194/egusphere-egu2020-22292, 2020.