Juha Järvelä | Aalto University (original) (raw)

Papers by Juha Järvelä

Research paper thumbnail of New formulas addressing flow resistance of floodplain vegetation from emergent to submerged conditions

International Journal of River Basin Management, 2022

Hydraulic modelling of natural floodplain vegetation using leaf area index (LAI) has been applied... more Hydraulic modelling of natural floodplain vegetation using leaf area index (LAI) has been applied successfully for non-submerged conditions whereas its suitability for submerged conditions requires further development. This study investigates the vegetative flow resistance at low relative submergences and extends existing LAI-based approaches building upon new flume data and prior experiences from field-scale applications. We provide advanced LAI-based formulas for modelling the flow resistance from emergent to submerged conditions, with water depth up to three times higher than the vegetation height. Such low relative submergences are highly relevant in hydraulic analyses of riverbank and floodplain flows but not adequately represented in existing formulas. The use of the deflected vegetation height as the characteristic height provided the most accurate modelling results, whereas the use of undeflected height resulted in significant errors. As a new development for submerged conditions, we proposed von Kármán scaling factor for improved model predictions. Overall, the results proved that LAI-based modelling is suitable also at low relative submergences for a wide range of vegetation densities (LAI = 1-5) and mean flow velocities (0.05-1.2 m s −1). For both emergent and slightly overtopped vegetation the JAR and VAS approaches outperformed the BAPmod-LAI approach that does not account for reconfiguration. For modellers, we provide a workflow and guidance on the use of the newly developed LAI-based formulas in 1D/2D hydrodynamic models for both emergent and submerged conditions.

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Research paper thumbnail of Flow and Wake Characteristics Associated with Riparian Vegetation Patches: Results From Field‐Scale Experiments

Hydrological Processes

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Research paper thumbnail of Article Determining Characteristic Vegetation Areas by Terrestrial Laser Scanning for Floodplain Flow Modeling

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Research paper thumbnail of Physically-based modeling of drag force caused by natural woody vegetation

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Research paper thumbnail of Luonnonmukainen vesirakentaminen peruskuivatuksessa

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Research paper thumbnail of Agricultural Water Management Using Two-Stage Channels: Performance and Policy Recommendations Based on Northern European Experiences

Sustainability

Conventional dredging of ditches and streams to ensure agricultural drainage and flood mitigation... more Conventional dredging of ditches and streams to ensure agricultural drainage and flood mitigation can have severe environmental impacts. The aim of this paper is to investigate the potential benefits of an alternative, nature-based two-stage channel (TSC) design with floodplains excavated along the main channel. Through a literature survey, investigations at Finnish field sites and expert interviews, we assessed the performance, costs, and monetary environmental benefits of TSCs in comparison to conventional dredging, as well as the bottlenecks in their financing and governance. We found evidence supporting the expected longer-term functioning of drainage as well as larger plant and fish biodiversity in TSCs compared to conventional dredging. The TSC design likely improves water quality since the floodplains retain suspended sediment and phosphorus and remove nitrogen. In the investigated case, the additional value of phosphorus retention and conservation of protected species throug...

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Research paper thumbnail of Effect of floodplain vegetation on flow and transport of cohesive particles in an environmental two-stage channel

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Research paper thumbnail of Determination of flow resistance of vegetated channel banks and floodplains

Flow resistance due to vegetation may greatly affect the conveyance of a channel, and thus evalua... more Flow resistance due to vegetation may greatly affect the conveyance of a channel, and thus evaluating the resistance is a critical task in river engineering and restoration. Therefore, flow resistance of natural willows and sedges was studied in a laboratory flume. The aim was to investigate, how type, density and combination of vegetation, flow depth and velocity influence vegetal drag or friction losses. Friction fac- tors, f, and vegetal drag coefficients, C'd, were determined for a selection of 170 test runs. The results showed large variations with depth of flow, velocity, Reynolds number and vegetal characteristics. E.g. the vegetal drag coefficient for the leafy willows was three to seven times that of the leafless willows. The experimental drag coefficients for the leafless willows were compared to the values predicted by four methods, which were developed based on theory and experiments on rigid cylinders.

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Research paper thumbnail of Feasibility of laser scanning and photogrammetric 3D approaches for mapping and monitoring a riverine environment

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Research paper thumbnail of Large-scale experiments for vegetated flows with different types of vegetation patch layouts

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Research paper thumbnail of 10th International Drainage Workshop of ICID Working Group on Drainage, 6-11 July 2008, Helsinki, Finland and Tallinn, Estonia

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Research paper thumbnail of Impact of tree scale on drag: experiments in a towing tank

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Research paper thumbnail of Vegetation characteristics and floodplain topography from terrestrial laser scanning for hydraulic analyses

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Research paper thumbnail of Flow resistance in vegetated channels: characteristics of natural woody vegetation

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Research paper thumbnail of Hydraulic and sediment considerations in designing environmentally preferable drainage channels: experiences from a field demonstration site

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Research paper thumbnail of Flow resistance of floodplain vegetation mixtures for modelling river flows

Journal of Hydrology

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Research paper thumbnail of Acoustic Doppler velocimetry (ADV) data on flow-vegetation interaction with natural-like and rigid model plants in hydraulic flumes

Data in Brief

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Research paper thumbnail of Comparative Analysisof Lateral Shear Layers Induced by Flexible and Rigid Vegetationin a Partly Vegetated Channel

38th IAHR World Congress - "Water: Connecting the World"

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Research paper thumbnail of Flume Investigationsusing Natural-Like Vegetation with a View on Fine Sediment Processes

38th IAHR World Congress - "Water: Connecting the World"

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Research paper thumbnail of Physical Modelling of Shrub-Willow Patches in Prototype Scale

38th IAHR World Congress - "Water: Connecting the World"

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Research paper thumbnail of New formulas addressing flow resistance of floodplain vegetation from emergent to submerged conditions

International Journal of River Basin Management, 2022

Hydraulic modelling of natural floodplain vegetation using leaf area index (LAI) has been applied... more Hydraulic modelling of natural floodplain vegetation using leaf area index (LAI) has been applied successfully for non-submerged conditions whereas its suitability for submerged conditions requires further development. This study investigates the vegetative flow resistance at low relative submergences and extends existing LAI-based approaches building upon new flume data and prior experiences from field-scale applications. We provide advanced LAI-based formulas for modelling the flow resistance from emergent to submerged conditions, with water depth up to three times higher than the vegetation height. Such low relative submergences are highly relevant in hydraulic analyses of riverbank and floodplain flows but not adequately represented in existing formulas. The use of the deflected vegetation height as the characteristic height provided the most accurate modelling results, whereas the use of undeflected height resulted in significant errors. As a new development for submerged conditions, we proposed von Kármán scaling factor for improved model predictions. Overall, the results proved that LAI-based modelling is suitable also at low relative submergences for a wide range of vegetation densities (LAI = 1-5) and mean flow velocities (0.05-1.2 m s −1). For both emergent and slightly overtopped vegetation the JAR and VAS approaches outperformed the BAPmod-LAI approach that does not account for reconfiguration. For modellers, we provide a workflow and guidance on the use of the newly developed LAI-based formulas in 1D/2D hydrodynamic models for both emergent and submerged conditions.

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Research paper thumbnail of Flow and Wake Characteristics Associated with Riparian Vegetation Patches: Results From Field‐Scale Experiments

Hydrological Processes

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Research paper thumbnail of Article Determining Characteristic Vegetation Areas by Terrestrial Laser Scanning for Floodplain Flow Modeling

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Research paper thumbnail of Physically-based modeling of drag force caused by natural woody vegetation

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Research paper thumbnail of Luonnonmukainen vesirakentaminen peruskuivatuksessa

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Research paper thumbnail of Agricultural Water Management Using Two-Stage Channels: Performance and Policy Recommendations Based on Northern European Experiences

Sustainability

Conventional dredging of ditches and streams to ensure agricultural drainage and flood mitigation... more Conventional dredging of ditches and streams to ensure agricultural drainage and flood mitigation can have severe environmental impacts. The aim of this paper is to investigate the potential benefits of an alternative, nature-based two-stage channel (TSC) design with floodplains excavated along the main channel. Through a literature survey, investigations at Finnish field sites and expert interviews, we assessed the performance, costs, and monetary environmental benefits of TSCs in comparison to conventional dredging, as well as the bottlenecks in their financing and governance. We found evidence supporting the expected longer-term functioning of drainage as well as larger plant and fish biodiversity in TSCs compared to conventional dredging. The TSC design likely improves water quality since the floodplains retain suspended sediment and phosphorus and remove nitrogen. In the investigated case, the additional value of phosphorus retention and conservation of protected species throug...

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Research paper thumbnail of Effect of floodplain vegetation on flow and transport of cohesive particles in an environmental two-stage channel

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Determination of flow resistance of vegetated channel banks and floodplains

Flow resistance due to vegetation may greatly affect the conveyance of a channel, and thus evalua... more Flow resistance due to vegetation may greatly affect the conveyance of a channel, and thus evaluating the resistance is a critical task in river engineering and restoration. Therefore, flow resistance of natural willows and sedges was studied in a laboratory flume. The aim was to investigate, how type, density and combination of vegetation, flow depth and velocity influence vegetal drag or friction losses. Friction fac- tors, f, and vegetal drag coefficients, C'd, were determined for a selection of 170 test runs. The results showed large variations with depth of flow, velocity, Reynolds number and vegetal characteristics. E.g. the vegetal drag coefficient for the leafy willows was three to seven times that of the leafless willows. The experimental drag coefficients for the leafless willows were compared to the values predicted by four methods, which were developed based on theory and experiments on rigid cylinders.

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Research paper thumbnail of Feasibility of laser scanning and photogrammetric 3D approaches for mapping and monitoring a riverine environment

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Large-scale experiments for vegetated flows with different types of vegetation patch layouts

Bookmarks Related papers MentionsView impact

Research paper thumbnail of 10th International Drainage Workshop of ICID Working Group on Drainage, 6-11 July 2008, Helsinki, Finland and Tallinn, Estonia

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Impact of tree scale on drag: experiments in a towing tank

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Vegetation characteristics and floodplain topography from terrestrial laser scanning for hydraulic analyses

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Flow resistance in vegetated channels: characteristics of natural woody vegetation

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Hydraulic and sediment considerations in designing environmentally preferable drainage channels: experiences from a field demonstration site

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Flow resistance of floodplain vegetation mixtures for modelling river flows

Journal of Hydrology

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Acoustic Doppler velocimetry (ADV) data on flow-vegetation interaction with natural-like and rigid model plants in hydraulic flumes

Data in Brief

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Comparative Analysisof Lateral Shear Layers Induced by Flexible and Rigid Vegetationin a Partly Vegetated Channel

38th IAHR World Congress - "Water: Connecting the World"

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Flume Investigationsusing Natural-Like Vegetation with a View on Fine Sediment Processes

38th IAHR World Congress - "Water: Connecting the World"

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Physical Modelling of Shrub-Willow Patches in Prototype Scale

38th IAHR World Congress - "Water: Connecting the World"

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Research paper thumbnail of Hydrodynamics of Vegetated Channels

Rivers—Physical, Fluvial and Environmental Processes, GeoPlanet: Earth and Planetary Sciences, 2015

Hydrodynamics of vegetated channels and streams is a rapidly developing research area, and this c... more Hydrodynamics of vegetated channels and streams is a rapidly developing research area, and this chapter summarizes the current knowledge considering both aquatic and riparian zones. The benefit of an advanced parameterization of plant morphology and biomechanical properties is highlighted. For this purpose, the response of flexible and foliated plants and plant communities to the flow is illustrated, and advanced models for the determination of drag forces of flexible plants are described. Hydrodynamic processes governing flow patterns in vegetated flows are presented for submerged and emergent conditions considering spatial scales ranging from the leaf to the vegetated reach scale.

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Research paper thumbnail of Flow resistance in environmental channels: focus on vegetation

Helsinki University of Technology Water Resources Publications, 2004

This thesis aims to improve the reliability of the determination of flow resistance in environmen... more This thesis aims to improve the reliability of the determination of flow resistance in environmentally acceptable channels and floodplains. Special emphasis was placed on addressing the hydraulic effects of vegetation. For this reason, laboratory flume studies with living vegetation were employed. The most notable finding was that, when compared to leafless conditions, the presence of leaves increased the friction factor up to seven-fold. This was strongly dependent on the flow velocity. In addition, the linkage between flow resistance, channel properties, and physical habitat was investigated. For this purpose, field studies were conducted in degraded, restored, and natural channel reaches.
To determine friction factor f or Manning’s n for non-submerged woody vegetation, a new procedure based on the measurable characteristics of vegetation and flow was developed. A major advantage of this procedure over the old methods was its ability to estimate the flow resistance of woody vegetation in both leafless and leafy conditions. In determining the velocity profile and flow resistance caused by submerged flexible vegetation, the approach developed by Stephan (2002) was found to be suitable. However, a new formulation was proposed for the shear velocity based on deflected plant height. This modification offered better practical applicability than the original formulation, which requires complicated turbulence measurements.
In the field studies, the experimental results for friction factors were, excluding those for low flows, in agreement with the values presented in the literature. Overall, the gathered field data from degraded, restored, and natural channel reaches formed a reference data set, which could be useful in other similar restoration or engineering projects. The field studies showed that both flow resistance and cross-sectional geometry were vital factors in determining local hydraulic conditions. The parameters defining these two factors were found to be simple but nonetheless valuable in evaluating the success of a project which aims to restore local hydraulics. A new procedure for applying the success criteria in the post-project evaluation of local hydraulics was developed.

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