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Publisher Copyright: © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. 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.

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&ndash, 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.

Maria Forsman: Julkaisut ja tieteen mittaaminen. Bibliometriikan käännekohtia. Enostone 2016.

Gleick, James: Informaatio. Suomentanut Veli-Pekka Ketola. Art House 2013.

VK: T20702 Detailed modeling of floodplain flows and associated processes requires data on mixed, heterogeneous vegetation at river reach scale, though the collection of vegetation data is typically limited in resolution or lack spatial information. This study investigates physically-based characterization of mixed floodplain vegetation by means of terrestrial laser scanning (TLS). The work aimed at developing an approach for deriving the characteristic reference areas of herbaceous and foliated woody vegetation, and estimating the vertical distribution of woody vegetation. Detailed experimental data on vegetation properties were gathered both in a floodplain site for herbaceous vegetation, and under laboratory conditions for 2–3 m tall trees. The total plant area (Atot) of woody vegetation correlated linearly with the TLS-based voxel count, whereas the Atot of herbaceous vegetation showed a linear correlation with TLS-based vegetation mean height. For woody vegetation, 1 cm voxel size was found suitable for estimating both the Atot and its vertical distribution. A new concept was proposed for deriving Atot for larger areas from the point cloud attributes of small sub-areas. The results indicated that the relationships between the TLS attributes and Atot of the sub-areas can be derived either by mm resolution TLS or by manual vegetation sampling.

Funding Information: The authors thank the technician Antti Louhio for his help in arranging the experiments at the Environmental Hydraulics Lab of Aalto University. The authors acknowledge the support from the technicians Antonio Fusco and Domenico Palmiero of the Laboratory of Hydraulics of University of Naples Federico II. The authors acknowledge funding from Maa‐ ja vesitekniikan tuki ry (Grant No. 33271), Maj and Tor Nessling Foundation (Grant No. 201800045), Academy of Finland (Grant No. 330217), and from statutory activities No. 3841/E‐41/S/2020 of the Ministry of Science and Higher Education of Poland. Publisher Copyright: © 2021. The Authors. Copyright: Copyright 2021 Elsevier B.V., All rights reserved. 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.

Hydrodynamic processes in partly vegetated channels have been often investigated by simulating vegetation with arrays of rigid cylinders. By contrast, natural riparian vegetation is generally flexible and presents a complex morphology that influences the dynamic and reconfiguration behavior, deeply affecting the flow structure. 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, in comparison with the rigid cylinder representation. Experiments were carried out with both reconfiguring vegetation made of bushes and grasses, and with rigid cylinders in two facilities. The results on flow structure gained in the two setups are compared. The lateral distributions of normalized mean velocity and lateral Reynolds stress of the considered hydraulically similar vegetated shear layers were observed to depend mainly on the differential velocity ratio and the overall vegetative bulk drag, observing analogous distributions for the two vegetation models. Nevertheless, different shear penetration within the vegetation was observed for flexible and rigid vegetation, with a systematically higher penetration found for natural-like vegetation. The flexibility-induced mechanisms of natural vegetation were found to significantly affect the turbulent flow structure, markedly modifying the lateral exchanges across the interface.

Urbanization is causing a substantial increase in impervious surfaces and thereby alterations in the hydrological cycle, e.g. by increasing runoff volumes and intensities that can lead to urban flooding. Furthermore, urban runoff is considered as one of the most important surface water pollutant sources. The characteristics of urban runoff are known to vary greatly between land use types and climates. However, in cold climates, only a few studies have tackled urban runoff phenomena and these studies rarely include catchment-based and long-term monitoring on both runoff quantity and quality. Yet, to develop successful urban runoff management practices, knowledge on runoff characteristics from various urban sites that are monitored for several pollutants throughout the year is required. The aim of this thesis was to fill gaps in our knowledge on the effects of urbanization on runoff characteristics and to study the mechanisms affecting runoff generation and pollutant transport during vastly divergent seasons in cold climates. This research was conducted in the city of Lahti, southern Finland, and comprised three urban catchments of varying imperviousness: High catchment (city centre, total impervious area [TIA], 89%), Intermediate catchment (city centre, 62%) and Low catchment (residential, 19%). At each catchment, continuous measurements on runoff flow rate and precipitation were carried out for a period of two years. In addition, runoff samples were taken to determine concentrations for total nitrogen (tot-N), total phosphorus (tot-P), total suspended solids (TSS), total and dissolved heavy metals (Zn, Cu, Cr, Mn, Al, Co, Ni, Pb) and total organic carbon (TOC). I showed that in cold climates, annual runoff volumes, most pollutant loads and some of the pollutant concentrations increased with increasing imperviousness. Furthermore, urbanization altered runoff generation (volume, intensity, duration, number of events) more strongly during the warm than the cold period. However, when the summer was dry and the winter wet, the effects of urbanization on annual runoff volumes diminished most likely due to snow removal. The spring snowmelt period began earlier and occurred as several events at the city centres in comparison to the low-development catchment. In contrast with patterns observed during warm periods, cumulative runoff volumes during cold periods decreased with increasing urbanization when TIA reached about 60%. Nevertheless, urbanization increased both warm and cold period loads for most pollutants. However, the mechanisms controlling runoff event quality were distinct between seasons: during cold periods event loads and concentrations were mainly increased by long event durations, yet, during warm periods the peak intensity of runoff was the main increasing factor whereas concentrations tended to decrease as event durations increased. Because of snow removal in the High catchment with TIA of 89%, snowmelt volumes during spring were not affected by the amount of precipitation. In addition, at the High catchment, warm periods contributed more to annual volumes than cold periods, contrary to the pattern observed at the Low catchment. Irrespective of land use, the largest seasonal pollutant loads and concentrations for several pollutants occurred during spring. However, the importance of the warm season in annual pollutant load generation increased with increasing urbanization. This study provides updated data on pollutant unit loads, especially for city centres and for heavy metals. This thesis - applying a catchment-based approach - also showed, for the first time how the seasonality of runoff volumes and loads change at highly impervious city centres. Kaupungistuminen lisää vettä läpäisemättömien pintojen määriä ja muuttaa veden kiertoa lisäämällä pintavalunnan eli hulevesien määrää ja virtaamahuippuja sekä kaupunkitulvia. Koska hulevedet johdetaan usein puhdistamattomina vesistöihin, ne ovat yksi merkittävimpiä pintavesien pilaajia. Kylmän ilmaston hulevesien määrästä ja laadusta ei kuitenkaan ole ollut kattavaa tietoa, vaikka se on edellytys mm. hulevesien käsittelyn ja lainsäädännön suunnittelemiselle. Hulevesiä tulisi myös tutkia ympärivuotisesti kylmän ilmaston vuodenaikojen erityispiirteiden vuoksi. Väitöskirjan tarkoituksena oli selvittää miten kaupungistuminen vaikuttaa hulevesien muodostumiseen ja laatuun eri vuodenaikoina kylmässä ilmastossa. Kaupungistumista kuvasivat läpäisemättömien pintojen määrä (%) sekä maankäyttömuoto (keskusta tai pientaloalue). Tutkimus toteutettiin Lahdessa kahdella keskustavaluma-alueella, jotka olivat 62 % ja 89 % läpäisemättömiä sekä pientaloalueella, jonka läpäisemättömyys oli 19 %. Alueilla mitattiin kahden vuoden ajan hulevesien virtaamaa sekä sadantaa. Hulevedestä otettiin näytteitä, joista määritettiin kokonaistypen ja -fosforin, kiintoaineen, raskasmetallien (Zn, Cu, Cr, Mn, Al, Co, Ni, Pb) ja kokonaisorgaanisen hiilen pitoisuudet. Tutkimus osoitti, että läpäisemättömyys lisää vuosittaista hulevesien määrää ja haitta-ainekuormaa sekä joidenkin haitta-aineiden pitoisuuksia kylmässä ilmastossa. Sääolosuhteet aiheuttivat kuitenkin vaihtelua, sillä vuonna, jolloin talvi oli sateinen ja kesä kuiva, kaupungistumisen vaikutukset hulevesien määriin pienenivät johtuen lumenkuljetuksesta eli sadannan siirtämisestä valuma-alueen ulkopuolelle. Läpäisemättömyys vaikutti hulevesien muodostumiseen voimakkaammin lämpimänä kuin kylmänä kautena, jolloin kaupungistuminen jopa vähensi hulevesien määrää. Haitta-ainekuormituksen määrä silti kasvoi kaupungistumisen myötä ympärivuotisesti. Kaupungistuneimmalla alueella merkittävin osa vuosittaisesta hulevedestä muodostui lämpimänä kautena, päinvastoin kuin vähiten kaupungistuneimmalla alueella. Kaikilla alueilla suurin vuodenaikainen haitta-ainekuorma esiintyi keväällä, mutta kaupungistuminen lisäsi lämpimän kauden osuutta vuosittaisessa kuormituksessa. Haitta-ainekuormitukseen vaikuttavat hydrologiset mekanismit erosivat kylmän ja lämpimän kautena: kylmänä kautena valunnan kesto lisäsi kuormitusta ja lämpimänä kautena kasvavat huippuvirtaamat kasvattivat kuormaa. Tutkimus osoitti ensimmäistä kertaa miten tiivisti rakennettujen keskustojen hulevesien määrä ja haitta-ainekuorma muuttuvat vuodenaikaisesti. Tutkimus tuotti myös päivitettyä tietoa keskusta-alueiden hulevesien laadusta sekä erityisesti raskasmetallikuormituksesta.