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I research the flow of water and the transport of sediment and nutrients in rivers, streams, and ditches, with a special focus on developing and assessing environmentally friendly solutions in river and agricultural water management. I am particularly interested in the complex interactions between flow, vegetation, and riverine transport and retention processes.
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 through the TSC design was 2.4 times higher than the total costs. We demonstrate how TSCs can be made eligible for the obligatory vegetated riparian buffer of the European Union agri-environmental subsidy scheme (CAP-AES) by optimising their spatial application with respect to other buffer measures, and recommend to publicly finance their additional costs compared to conventional dredging at priority sites. Further studies on biodiversity impacts and long-term performance of two-stage channels are required.
Kaisa Västilä; Sari Väisänen; Jari Koskiaho; Virpi Lehtoranta; Krister Karttunen; Mikko Kuussaari; Juha Järvelä; Kauko Koikkalainen. Agricultural Water Management Using Two-Stage Channels: Performance and Policy Recommendations Based on Northern European Experiences. Sustainability 2021, 13, 9349 .
AMA StyleKaisa Västilä, Sari Väisänen, Jari Koskiaho, Virpi Lehtoranta, Krister Karttunen, Mikko Kuussaari, Juha Järvelä, Kauko Koikkalainen. Agricultural Water Management Using Two-Stage Channels: Performance and Policy Recommendations Based on Northern European Experiences. Sustainability. 2021; 13 (16):9349.
Chicago/Turabian StyleKaisa Västilä; Sari Väisänen; Jari Koskiaho; Virpi Lehtoranta; Krister Karttunen; Mikko Kuussaari; Juha Järvelä; Kauko Koikkalainen. 2021. "Agricultural Water Management Using Two-Stage Channels: Performance and Policy Recommendations Based on Northern European Experiences." Sustainability 13, no. 16: 9349.
Natural riparian vegetation generally presents a complex hydrodynamic behavior governed by plant morphology and flexibility. By contrast, hydrodynamic processes in partly vegetated channels are conventionally simulated by using simplified model vegetation, such as arrays of rigid cylinders. The aim of this study is to investigate the impacts of embedding natural plant features in the experimental simulation of flow in partly vegetated channels. Unique comparative experiments were carried out with both reconfiguring vegetation made of natural‐like shrubs and grasses, and with rigid cylinders. While the lateral distributions of flow properties presented a high similarity governed by the shear layer differential velocity ratio, the bulk vegetative drag, and the presence of large‐scale vortices, the flexibility‐induced mechanisms of natural‐like vegetation markedly affected the flow at the interface. Differences in plant morphology and spacing, and the dynamic motion of flexible foliated plants induced deeper vortex penetration into the vegetation. The normalized shear penetration was 6‐10 times greater than observed for rigid cylinders, resulting in wider zones significantly exchanging momentum with the adjacent open water. The efficiency of lateral momentum transport for flexible foliated vegetation was up to 40% greater than the corresponding rigid cylinder case. Overall, the results indicated that improving the representativeness of model vegetation is a critical step toward the accurate simulation of hydrodynamic and transport processes in natural settings.This article is protected by copyright. All rights reserved.
Gerardo Caroppi; Kaisa Västilä; Paola Gualtieri; Juha Järvelä; Maurizio Giugni; Paweł M. Rowiński. Comparison of Flexible and Rigid Vegetation Induced Shear Layers in Partly Vegetated Channels. Water Resources Research 2021, 57, 1 .
AMA StyleGerardo Caroppi, Kaisa Västilä, Paola Gualtieri, Juha Järvelä, Maurizio Giugni, Paweł M. Rowiński. Comparison of Flexible and Rigid Vegetation Induced Shear Layers in Partly Vegetated Channels. Water Resources Research. 2021; 57 (3):1.
Chicago/Turabian StyleGerardo Caroppi; Kaisa Västilä; Paola Gualtieri; Juha Järvelä; Maurizio Giugni; Paweł M. Rowiński. 2021. "Comparison of Flexible and Rigid Vegetation Induced Shear Layers in Partly Vegetated Channels." Water Resources Research 57, no. 3: 1.
The presence of vegetation has a significant impact on the flow conditions in streams and rivers by changing the roughness, which has an important effect on flow velocity distribution. The article focuses on modelling and analysing the depth-averaged velocity distribution in a rectangular channel partially covered by submerged grassy vegetation. The possibility of using two selected models (CCHE2D flow model and Shiono and Knight model) has been evaluated using the measurement data from a laboratory experiment. The measurements and modelling have been carried out for different flow conditions. Applied models calibrated for low velocities were found to be extendable to the same vegetative condition during high velocities.
Monika B. Kalinowska; Kaisa Västilä; Adam Kozioł; Paweł M. Rowiński; Adam Kiczko; Janusz Kubrak. Modelling of Velocity Distribution in a Channel Partly Covered by Submerged Vegetation. Flood Risk in the Upper Vistula Basin 2020, 91 -101.
AMA StyleMonika B. Kalinowska, Kaisa Västilä, Adam Kozioł, Paweł M. Rowiński, Adam Kiczko, Janusz Kubrak. Modelling of Velocity Distribution in a Channel Partly Covered by Submerged Vegetation. Flood Risk in the Upper Vistula Basin. 2020; ():91-101.
Chicago/Turabian StyleMonika B. Kalinowska; Kaisa Västilä; Adam Kozioł; Paweł M. Rowiński; Adam Kiczko; Janusz Kubrak. 2020. "Modelling of Velocity Distribution in a Channel Partly Covered by Submerged Vegetation." Flood Risk in the Upper Vistula Basin , no. : 91-101.
This paper investigates the interplay between the flow, suspended sediment concentration (SSC), and net deposition at the lateral interface between a main channel and riverbank/floodplain vegetation consisting of emergent flexible woody plants with understory grasses. In a new set of flume experiments, data were collected concurrently on the flow field, SSC, and net deposition using acoustic Doppler velocimeters, optical turbidity sensors, and weight-based sampling. Vegetation largely affected the vertical SSC distributions, both within and near the vegetated areas. The seasonal variation of vegetation properties was important, as the foliage strongly increased lateral mixing of suspended sediments between the unvegetated and vegetated parts of the channel. Foliage increased the reach-scale net deposition and enhanced deposition in the understory grasses at the main channel–vegetation interface. To estimate the seasonal differences caused by foliation, we introduced a new drag ratio approach for describing the SSC difference between the vegetated and unvegetated channel parts. Findings in this study suggest that future research and engineering applications will benefit from a more realistic description of natural plant features, including the reconfiguration of plants and drag by the foliage, to complement and replace existing rigid cylinder approaches.
Walter Box; Kaisa Västilä; Juha Järvelä. The Interplay between Flow Field, Suspended Sediment Concentration, and Net Deposition in a Channel with Flexible Bank Vegetation. Water 2019, 11, 2250 .
AMA StyleWalter Box, Kaisa Västilä, Juha Järvelä. The Interplay between Flow Field, Suspended Sediment Concentration, and Net Deposition in a Channel with Flexible Bank Vegetation. Water. 2019; 11 (11):2250.
Chicago/Turabian StyleWalter Box; Kaisa Västilä; Juha Järvelä. 2019. "The Interplay between Flow Field, Suspended Sediment Concentration, and Net Deposition in a Channel with Flexible Bank Vegetation." Water 11, no. 11: 2250.
Kaisa Västilä; Chanjoo Lee; Donggu Kim; Sungjung Kim; Jongmin Kim; Juha Järvelä. MEASUREMENT OF LATERAL AND WAKE FLOWS ASSOCIATED WITH STREAMSCALE WILLOW PATCHES. 38th IAHR World Congress - "Water: Connecting the World" 2019, 1 .
AMA StyleKaisa Västilä, Chanjoo Lee, Donggu Kim, Sungjung Kim, Jongmin Kim, Juha Järvelä. MEASUREMENT OF LATERAL AND WAKE FLOWS ASSOCIATED WITH STREAMSCALE WILLOW PATCHES. 38th IAHR World Congress - "Water: Connecting the World". 2019; ():1.
Chicago/Turabian StyleKaisa Västilä; Chanjoo Lee; Donggu Kim; Sungjung Kim; Jongmin Kim; Juha Järvelä. 2019. "MEASUREMENT OF LATERAL AND WAKE FLOWS ASSOCIATED WITH STREAMSCALE WILLOW PATCHES." 38th IAHR World Congress - "Water: Connecting the World" , no. : 1.
Monika B. Kalinowska; Kaisa Västilä; Paweł M. Rowiński. Solute transport in complex natural flows. Acta Geophysica 2019, 67, 939 -942.
AMA StyleMonika B. Kalinowska, Kaisa Västilä, Paweł M. Rowiński. Solute transport in complex natural flows. Acta Geophysica. 2019; 67 (3):939-942.
Chicago/Turabian StyleMonika B. Kalinowska; Kaisa Västilä; Paweł M. Rowiński. 2019. "Solute transport in complex natural flows." Acta Geophysica 67, no. 3: 939-942.
Riparian shrubs and trees present a complex, seasonally variable morphology, with flexible stems and leaves efficiently adapting to the flow forcing (reconfiguration). The aim of this paper is to investigate how foliage and reconfiguration affect the flow and mixing in a partly vegetated channel. Specific attention was placed on the velocity statistics, onset and coherence of turbulent structures, and lateral momentum transport at the horizontal interface between vegetation and open water. The experimental flume arrangement was novel in that it allowed investigating the lateral shear layer induced by flexible riparian plants. The natural-like vegetation consisted of emergent woody plants and a grassy understory, with density, morphology and reconfiguration behavior comparable to those found in real riparian areas. Investigations were conducted under foliated and leafless conditions to determine the seasonality effects. The mean and turbulent flow structure was determined with acoustic Doppler velocimetry, and dynamic plant motions were investigated from video footage. The presence of foliage enhanced the drag discontinuity at the interface, resulting in more pronounced velocity gradients between the vegetated and open areas compared to the leafless conditions. Foliation induced stronger shear layer-scale mixing, whereas, under leafless conditions, the local mixing induced by stems was more important. The reconfiguration decreased the coherence of the two-dimensional large-scale vortices at the interface while their characteristic frequency was consistent with the canonical mixing layer theory. Our results indicated that shear layer dynamics in partly vegetated channels was influenced strongly by morphology and reconfiguration of complex plants, with more efficient lateral momentum transport at the interface in the foliated conditions than previously reported for shear layers induced by simpler vegetation.
Gerardo Caroppi; Kaisa Västilä; Juha Järvelä; Paweł M. Rowiński; Maurizio Giugni. Turbulence at water-vegetation interface in open channel flow: Experiments with natural-like plants. Advances in Water Resources 2019, 127, 180 -191.
AMA StyleGerardo Caroppi, Kaisa Västilä, Juha Järvelä, Paweł M. Rowiński, Maurizio Giugni. Turbulence at water-vegetation interface in open channel flow: Experiments with natural-like plants. Advances in Water Resources. 2019; 127 ():180-191.
Chicago/Turabian StyleGerardo Caroppi; Kaisa Västilä; Juha Järvelä; Paweł M. Rowiński; Maurizio Giugni. 2019. "Turbulence at water-vegetation interface in open channel flow: Experiments with natural-like plants." Advances in Water Resources 127, no. : 180-191.
Flow disturbances generated by individual patches of submerged, flexible aquatic vegetation were investigated for two naturally growing macrophyte species, Potamogeton crispus L. and Myriophyllum spicatum L., in a sandy lowland river. Through acoustic Doppler velocimetry, 24 vertical profiles of the 3D velocity field were recorded downstream of each of the patches. The morphological features and biomechanical properties of the plants were also evaluated. The experiments showed the relationship between biomechanical characteristics and turbulence statistics. M. spicatum, which was stiffer and therefore less prone to dynamic reconfiguration, showed a greater effect on velocity damping, causing an increase in Reynold stresses, turbulence intensities and turbulent kinetic energy downstream of the patch. These effects were present in regions both above and below plant height. In contrast for P. crispus, these effects were present only below plant height. The stiffer plant produced a mixing layer in its wake similar to that of dense plant canopies. The patch of less stiff and more streamlined P. crispus with longer leaves presented a much weaker effect on the flow. In contrast to previous studies conducted with rigid plant surrogates, we concluded that reconfiguration of the living flexible plants allows the plants to minimize drag forces, and therefore, their influence on the flow field was weaker than the effects reported for rigid surrogates.
Łukasz Przyborowski; Anna Maria Łoboda; Robert Józef Bialik; Kaisa Västilä. Flow field downstream of individual aquatic plants—Experiments in a natural river with Potamogeton crispus L. and Myriophyllum spicatum L. Hydrological Processes 2019, 33, 1324 -1337.
AMA StyleŁukasz Przyborowski, Anna Maria Łoboda, Robert Józef Bialik, Kaisa Västilä. Flow field downstream of individual aquatic plants—Experiments in a natural river with Potamogeton crispus L. and Myriophyllum spicatum L. Hydrological Processes. 2019; 33 (9):1324-1337.
Chicago/Turabian StyleŁukasz Przyborowski; Anna Maria Łoboda; Robert Józef Bialik; Kaisa Västilä. 2019. "Flow field downstream of individual aquatic plants—Experiments in a natural river with Potamogeton crispus L. and Myriophyllum spicatum L." Hydrological Processes 33, no. 9: 1324-1337.
Riparian plants exert flow resistance and largely influence the flow structure, which affects erosion, deposition and transport processes of fine sediments. Predicting these vegetative effects is important for flood, sediment and nutrient management. However, predictions on the fate of sediments are complicated by uncertainties associated with the suitable parameterization of natural plants and the associated effects on the turbulent flow field and on the variables in the transport equations. The aim of this study is to quantify deposition and transport of fine sandy sediment in a partly vegetated channel under laboratory conditions. Care was taken to reproduce conditions typical of vegetated floodplain flows including dense flexible grassy understory as a starting point. The experiments were conducted in a flume that is specifically designed to recirculate fine sediment. We measured suspended sediment concentrations with optical turbidity sensors and determined patterns of net deposition over the vegetated parts of the cross section. The flow field was determined with acoustic Doppler velocimetry. Our investigations are intended to improve future predictions of fine sediment storage and transport in natural or constructed vegetated channels, and the first results reported herein were useful in designing further, on-going experiments with complex combinations of vegetation and channel geometry. Key words: sediment transport, suspended sediment, deposition, riparian vegetation, flow field.
Walter Box; Kaisa Västilä; Juha Järvelä. Transport and deposition of fine sediment in a channel partly covered by flexible vegetation. E3S Web of Conferences 2018, 40, 02016 .
AMA StyleWalter Box, Kaisa Västilä, Juha Järvelä. Transport and deposition of fine sediment in a channel partly covered by flexible vegetation. E3S Web of Conferences. 2018; 40 ():02016.
Chicago/Turabian StyleWalter Box; Kaisa Västilä; Juha Järvelä. 2018. "Transport and deposition of fine sediment in a channel partly covered by flexible vegetation." E3S Web of Conferences 40, no. : 02016.
New sustainable, cost-effective solutions are urgently needed for river management since conventional practices have posed serious ecological threats on streams, rivers and the surrounding riparian areas. Besides addressing the societal needs e.g. for flood management, river management should increasingly address the ecosystem requirements for improved water quality and biodiversity. We argue that it is not feasible to solve existing and future river management challenges with intensive restoration projects. Instead, we believe that less resource-intensive solutions using natural channel processes and features, including vegetation, should be investigated. Besides directly supporting biota, aquatic and riparian vegetation traps, takes up and helps to process nutrients and harmful substances, and thus this paper emphasizes vegetation as a tool for nature-based solutions (NBS) in river management. In this paper, emphasis is placed on the usage of vegetation as a NBS in river management. We synthesize findings from key literature, showing that the fate of substances in channel systems is largely controlled by abiotic and biotic processes facilitated and modified by vegetation, including flow hydrodynamics, channel morphology, and sediment transport. Subsequently, we demonstrate how vegetation can be incorporated into channel designs, focusing on a two-stage (compound) design to improve resilience to flooding, control the transport of substances, and enhance the ecological status. As a conclusion, clever use and maintenance of vegetation present unused potential to obtain large-scale positive environmental impacts in rivers and streams experiencing anthropogenic pressures.
Paweł M. Rowiński; Kaisa Västilä; Jochen Aberle; Juha Järvelä; Monika B. Kalinowska. How vegetation can aid in coping with river management challenges: A brief review. Ecohydrology & Hydrobiology 2018, 18, 345 -354.
AMA StylePaweł M. Rowiński, Kaisa Västilä, Jochen Aberle, Juha Järvelä, Monika B. Kalinowska. How vegetation can aid in coping with river management challenges: A brief review. Ecohydrology & Hydrobiology. 2018; 18 (4):345-354.
Chicago/Turabian StylePaweł M. Rowiński; Kaisa Västilä; Jochen Aberle; Juha Järvelä; Monika B. Kalinowska. 2018. "How vegetation can aid in coping with river management challenges: A brief review." Ecohydrology & Hydrobiology 18, no. 4: 345-354.
Kaisa Västilä; Juha Järvelä. Correction to: Characterizing natural riparian vegetation for modeling of flow and suspended sediment transport. Journal of Soils and Sediments 2017, 18, 3131 -3132.
AMA StyleKaisa Västilä, Juha Järvelä. Correction to: Characterizing natural riparian vegetation for modeling of flow and suspended sediment transport. Journal of Soils and Sediments. 2017; 18 (10):3131-3132.
Chicago/Turabian StyleKaisa Västilä; Juha Järvelä. 2017. "Correction to: Characterizing natural riparian vegetation for modeling of flow and suspended sediment transport." Journal of Soils and Sediments 18, no. 10: 3131-3132.
Riparian vegetation imposes a critical control on the transport and deposition of suspended sediment with important implications for water quality and channel maintenance. This paper contributes (1) to hydraulic and morphological modeling by examining the parameterization of natural riparian vegetation (trees, bushes, and grasses) and (2) to the design and management of environmental channels by determining how the properties of natural floodplain plant stands affect the erosion and deposition of suspended sediment. Laboratory and field data were employed for enhancing the physical description of flow–plant–sediment interactions with a consideration of practical applicability. A drag force parameterization that takes into account the flexibility-induced reconfiguration, and the complex structure of foliated plants was validated for small natural trees under laboratory conditions, while the data from a small vegetated compound channel demonstrated the approaches at the field scale. Based on the field data, we identified three key vegetative factors influencing the net deposition and erosion on the floodplain. The significance of these factors was evaluated for vegetative conditions ranging from almost bare soil to sparse willows and dense grasses. Overall, the investigated conditions covered flexible and rigid vegetation with seasonal differences represented by foliated and leafless states. The drag and reconfiguration of woody plants were reliably predicted under leafless and foliated conditions. Subsequently, we present a new easy-to-use methodology for predicting vegetative drag and flow resistance. The methodology is based on a physically solid parameterization for five widely used coefficients or terms (Eqs. (2)–(6)), with the necessary parameter values presented for common riparian species. The methodology was coupled with existing approaches at the field scale, revealing that increasing vegetation density and the associated decreasing flow velocity within vegetation significantly increased net deposition. Further, deposition increased with increasing cross-sectional vegetative blockage and decreasing distance from the suspended sediment replenishment point. Thus, longitudinal advection was the most important mechanism supplying fine sediment to the floodplain, but long continuous plant stands limited deposition. The proposed parameterization (Eqs. (2)–(6)) can be readily implemented into existing hydraulic and morphological models to improve the description of natural vegetation compared to the conventional rigid cylinder representation. The approach is advantageous for evaluating, for example, the effects of both natural succession and management interventions on floodplains. Finally, guidance is provided on how floodplain vegetation can be maintained to manage the erosion and deposition of suspended sediment in environmental channel designs.
Kaisa Västilä; Juha Järvelä. Characterizing natural riparian vegetation for modeling of flow and suspended sediment transport. Journal of Soils and Sediments 2017, 18, 3114 -3130.
AMA StyleKaisa Västilä, Juha Järvelä. Characterizing natural riparian vegetation for modeling of flow and suspended sediment transport. Journal of Soils and Sediments. 2017; 18 (10):3114-3130.
Chicago/Turabian StyleKaisa Västilä; Juha Järvelä. 2017. "Characterizing natural riparian vegetation for modeling of flow and suspended sediment transport." Journal of Soils and Sediments 18, no. 10: 3114-3130.
Riparian vegetation imposes a critical control on transport and deposition of suspended sediment with important implications on water quality as well as channel maintenance. With a view on hydraulic and morphological modeling needs, the objective of this paper is to enhance the parameterization of foliated riparian vegetation and to determine how the properties of plant stands affect the erosion and deposition of suspended sediment on a naturally vegetated floodplain. We show that the drag forces of woody plants can be reliably predicted with a parameterization that takes into account their flexibility-induced reconfiguration and complex structure. Based on field investigations in a vegetated compound channel, a multiple regression model was constructed to explain the net deposition and erosion under vegetative conditions ranging from almost bare soil to sparse willows and dense grasses. Net deposition was positively correlated with the cross-sectional vegetative blockage factor and negatively correlated with the distance from the suspended sediment replenishment point, indicating that longitudinal advection was the most important mechanism supplying fine sediment to the floodplain plant stands under real field conditions. Deposition increased with decreasing flow velocity within the natural stands. As an implication to hydraulic and morphological modeling, the proposed drag force parameterization can be easily implemented into model codes to improve the description of flexible, foliated vegetation. The paper concludes by providing guidance on how floodplain vegetation can be maintained to manage the erosion and deposition of suspended sediment.
Kaisa Västilä; Juha Järvelä. Characterizing natural riparian plant stands for modeling of flow and suspended sediment transport. River Sedimentation 2016, 943 -952.
AMA StyleKaisa Västilä, Juha Järvelä. Characterizing natural riparian plant stands for modeling of flow and suspended sediment transport. River Sedimentation. 2016; ():943-952.
Chicago/Turabian StyleKaisa Västilä; Juha Järvelä. 2016. "Characterizing natural riparian plant stands for modeling of flow and suspended sediment transport." River Sedimentation , no. : 943-952.
The purpose of this study was to quantify how vegetation influences the flow and sediment processes relevant to the design and management of environmental compound channels. Therefore, a two-year field investigation was conducted in a cohesive two-stage channel, focusing on the flow resistance and net deposition in five subreaches with different floodplain vegetation conditions. In the grassy subreaches, the cross-sectional blockage factor was the key vegetation property governing the flow resistance, with a process-based model providing reliable estimates under widely variable hydraulic and vegetative conditions. The net deposition of cohesive sediment was best explained by vegetation height while high stand length and density created supply-limited conditions on the inner floodplain. These results showed that the two-stage approach offers potential for controlling the sediment processes through appropriate vegetation maintenance. The novelty of this research is that straightforward analyses accompanied by a physically-based parameterization of the floodplain plant stands were successfully used to characterize the flow–vegetation–sediment interaction in a practical engineering application. The results are expected to be helpful in designing and managing comparable channels.
K. Västilä; Juha Järvelä; Harri Koivusalo. Flow–Vegetation–Sediment Interaction in a Cohesive Compound Channel. Journal of Hydraulic Engineering 2016, 142, 04015034 .
AMA StyleK. Västilä, Juha Järvelä, Harri Koivusalo. Flow–Vegetation–Sediment Interaction in a Cohesive Compound Channel. Journal of Hydraulic Engineering. 2016; 142 (1):04015034.
Chicago/Turabian StyleK. Västilä; Juha Järvelä; Harri Koivusalo. 2016. "Flow–Vegetation–Sediment Interaction in a Cohesive Compound Channel." Journal of Hydraulic Engineering 142, no. 1: 04015034.
[1] Both the foliage and stem essentially influence the flow resistance of woody plants, but their different biomechanical properties complicate the parameterization of foliated vegetation for modeling. This paper investigates whether modeling of flow resistance caused by natural woody vegetation can be improved using explicit description of both the foliage and stem. For this purpose, we directly measured the drag forces of Alnus glutinosa, Betula pendula, Salix viminalis, and Salix x rubens twigs in a laboratory flume at four foliation levels, parameterized with the leaf‐area‐to‐stem‐area ratio AL/AS. The species differed in the foliage drag but had approximately equal stem drag. For the foliated twigs, increasing AL/AS was found to increase the reconfiguration and the share of the foliage drag to the total drag. The experiments provided new insight into the factors governing the flow resistance of natural woody vegetation and allowed us to develop a model for estimating the vegetative friction factor using the linear superposition of the foliage and stem drag. The model is novel in that the foliage and stem are separately described with physically based parameters: drag coefficients, reconfiguration parameters, and leaf area and frontal‐projected stem area per ground area. The model could satisfactorily predict the flow resistance of twig to sapling‐sized specimens of the investigated species at velocities of 0.05–1 m/s. As a further benefit, the model allows exploring the variability in drag and reconfiguration associated with differing abundance of the foliage in relation to the stem.
Kaisa Västilä; Juha Järvelä. Modeling the flow resistance of woody vegetation using physically based properties of the foliage and stem. Water Resources Research 2014, 50, 229 -245.
AMA StyleKaisa Västilä, Juha Järvelä. Modeling the flow resistance of woody vegetation using physically based properties of the foliage and stem. Water Resources Research. 2014; 50 (1):229-245.
Chicago/Turabian StyleKaisa Västilä; Juha Järvelä. 2014. "Modeling the flow resistance of woody vegetation using physically based properties of the foliage and stem." Water Resources Research 50, no. 1: 229-245.
Reliable estimation of vegetative flow resistance calls for physically sound and readily measurable plant properties. Laboratory flume investigations were conducted to examine four reference area properties in relation to the drag, reconfiguration, and flow resistance of foliated Black Poplar twigs. The experiments were novel in that three characteristic reference areas (leaf area AL, frontal projected area under flow AP, and still-air frontal projected area A0) as well as the foliage–stem reference area ratio (AL/AS) were evaluated. The drag forces were simultaneously measured for up to eight specimens in a plant stand at both partly and just submerged conditions. Due to the high AL/AS of the twigs, leaves contributed 74–98% of the total drag at mean velocities of 0.1–0.9 m/s. Both the partly and just submerged poplars had similar AP and drag per characteristic reference area. Thus, the derived parameter values could be used to estimate the friction factors of the poplar stands at low to just submerged conditions, with each of the three characteristic reference areas providing satisfactory estimates. The flow resistance estimation with AL may be further improved by using AL/AS as a secondary area parameter to take into account the share of the stem to the total drag. Comparison to literature data on other deciduous species suggested that the foliage–stem reference area ratio was an essential property for explaining the between-species variation in AP and flow resistance per AL.
Kaisa Västilä; Juha Järvelä; Jochen Aberle. Characteristic reference areas for estimating flow resistance of natural foliated vegetation. Journal of Hydrology 2013, 492, 49 -60.
AMA StyleKaisa Västilä, Juha Järvelä, Jochen Aberle. Characteristic reference areas for estimating flow resistance of natural foliated vegetation. Journal of Hydrology. 2013; 492 ():49-60.
Chicago/Turabian StyleKaisa Västilä; Juha Järvelä; Jochen Aberle. 2013. "Characteristic reference areas for estimating flow resistance of natural foliated vegetation." Journal of Hydrology 492, no. : 49-60.
Design of environmentally preferable agricultural drainage channels calls for an improved understanding of cohesive sediment processes. Flow and cohesive sediments were investigated in a new demonstration and test channel where a floodplain was excavated on one side of the existing channel to improve flood conveyance. In this approach, the existing, naturally recovered channel was mostly left intact to reduce environmental impacts. Continuous monitoring of discharge and suspended sediment concentration (SSC) during 1 year revealed that the construction work of the two-stage channel caused 2% of the annual suspended sediment (SS) load. Agricultural areas covering 13% of the catchment were estimated to contribute over half of the annual SS, predominantly during the rising stages. Seasonal positive hysteresis was found in SSC which was explained by different drainage efficiencies of two distinct sediment sources. The temporally varying shares of the two sources caused scatter in the rating curves between discharge and SSC or SS load. Out-of-channel processes were shown to govern the amount and timing of the SS input into the channel, indicating that environmentally preferable agricultural channel design should consider the cohesive sediment processes and sources at the catchment scale.
Kaisa Västilä; Juha Järvelä. Environmentally preferable two-stage drainage channels: considerations for cohesive sediments and conveyance. International Journal of River Basin Management 2011, 9, 171 -180.
AMA StyleKaisa Västilä, Juha Järvelä. Environmentally preferable two-stage drainage channels: considerations for cohesive sediments and conveyance. International Journal of River Basin Management. 2011; 9 (3-4):171-180.
Chicago/Turabian StyleKaisa Västilä; Juha Järvelä. 2011. "Environmentally preferable two-stage drainage channels: considerations for cohesive sediments and conveyance." International Journal of River Basin Management 9, no. 3-4: 171-180.
Adaptation to climate change has become one of the focal points of current development discussion. This article summarises the findings from a multidisciplinary research project looking at climate change impacts and adaptation in the Mekong River Basin in Southeast Asia. The research highlights the central role that the hydrological cycle has in mediating climate change impacts on ecosystems and societies. The findings indicate that climate change should not be studied in isolation, as there are several other factors that are affecting the hydrological cycle. In the Mekong, the most important such factor is the on-going hydropower development that is likely to induce changes at least as radical as climate change, but with shorter timescales. The article concludes that climate change adaptation should broaden its view to consider environmental changes likely to occur due to different factors at various spatial and temporal scales. It is also important to recognise that climate change adaptation is a dynamic, development-orientated process that should consider also broader socio-political context. To enable this, we propose that an area-based adaptation approach should be used more actively to complement the dominant sector-based approaches.
M. Keskinen; S. Chinvanno; Matti Kummu; P. Nuorteva; A. Snidvongs; O. Varis; Kaisa Västilä. Climate change and water resources in the Lower Mekong River Basin: putting adaptation into the context. Journal of Water and Climate Change 2010, 1, 103 -117.
AMA StyleM. Keskinen, S. Chinvanno, Matti Kummu, P. Nuorteva, A. Snidvongs, O. Varis, Kaisa Västilä. Climate change and water resources in the Lower Mekong River Basin: putting adaptation into the context. Journal of Water and Climate Change. 2010; 1 (2):103-117.
Chicago/Turabian StyleM. Keskinen; S. Chinvanno; Matti Kummu; P. Nuorteva; A. Snidvongs; O. Varis; Kaisa Västilä. 2010. "Climate change and water resources in the Lower Mekong River Basin: putting adaptation into the context." Journal of Water and Climate Change 1, no. 2: 103-117.
The flood pulse is a key element characterizing the hydrology of the Mekong River and driving the high ecosystem productivity in the Lower Mekong floodplains, both in the Cambodian lowlands and the Mekong Delta in Vietnam. This paper assesses the impacts of climate change, both in terms of changed basin water balance and sea level rise, on the Lower Mekong flood pulse. The impacts were simulated by a three-dimensional hydrodynamic model using the projected changes in sea level and the Mekong mainstream discharge under the influence of climate change as boundary conditions. The model simulations projected that average and maximum water levels and flood duration increase in 2010–2049. The most consistent and notable changes occurred in the average and dry hydrological years. Sea level rise had the greatest effects in the Mekong Delta, whereas the impacts of changed basin water balance were more notable in the upper areas of the Mekong floodplains. The projected impacts were mostly opposite to those resulting from regional water infrastructure development. Higher and longer flooding could cause damage to crops, infrastructure and floodplain vegetation, and decrease the fertile land area. On the other hand, it might boost ecosystem productivity and enhance dry season water availability.
Kaisa Västilä; Matti Kummu; C. Sangmanee; S. Chinvanno. Modelling climate change impacts on the flood pulse in the Lower Mekong floodplains. Journal of Water and Climate Change 2010, 1, 67 -86.
AMA StyleKaisa Västilä, Matti Kummu, C. Sangmanee, S. Chinvanno. Modelling climate change impacts on the flood pulse in the Lower Mekong floodplains. Journal of Water and Climate Change. 2010; 1 (1):67-86.
Chicago/Turabian StyleKaisa Västilä; Matti Kummu; C. Sangmanee; S. Chinvanno. 2010. "Modelling climate change impacts on the flood pulse in the Lower Mekong floodplains." Journal of Water and Climate Change 1, no. 1: 67-86.