Browsing by Author "Kasvi, Elina"
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Item Data Processing and Quality Evaluation of a Boat-Based Mobile Laser Scanning System(2013) Vaaja, Matti; Kukko, Antero; Kaartinen, Harri; Kurkela, Matti; Kasvi, Elina; Flener, Claude; Hyyppä, Hannu; Hyyppä, Juha; Järvelä, Juha; Alho, Petteri; Department of Civil and Environmental Engineering; Department of Real Estate, Planning and Geoinformatics; Department of Built EnvironmentMobile mapping systems (MMSs) are used for mapping topographic and urban features which are difficult and time consuming to measure with other instruments. The benefits of MMSs include efficient data collection and versatile usability. This paper investigates the data processing steps and quality of a boat-based mobile mapping system (BoMMS) data for generating terrain and vegetation points in a river environment. Our aim in data processing was to filter noise points, detect shorelines as well as points below water surface and conduct ground point classification. Previous studies of BoMMS have investigated elevation accuracies and usability in detection of fluvial erosion and deposition areas. The new findings concerning BoMMS data are that the improved data processing approach allows for identification of multipath reflections and shoreline delineation. We demonstrate the possibility to measure bathymetry data in shallow (0–1 m) and clear water. Furthermore, we evaluate for the first time the accuracy of the BoMMS ground points classification compared to manually classified data. We also demonstrate the spatial variations of the ground point density and assess elevation and vertical accuracies of the BoMMS data.Item Empirical Modeling of Spatial 3D Flow Characteristics Using a Remote-Controlled ADCP System: Monitoring a Spring Flood(Multidisciplinary Digital Publishing Institute (MDPI), 2015) Flener, Claude; Wang, Yunsheng; Laamanen, Leena; Kasvi, Elina; Vesakoski, Jenni-Mari; Alho, Petteri; Department of Real Estate, Planning and Geoinformatics; Department of Built EnvironmentItem Flow patterns and morphological changes in a sandy meander bend during a flood-spatially and temporally intensive ADCP measurement approach(2017) Kasvi, Elina; Laamanen, Leena; Lotsari, Eliisa; Alho, Petteri; Department of Built Environment; MeMoThe fluvio-geomorphological processes in meander bends are spatially uneven in distribution. Typically, higher velocities and erosion take place near the outer bank beyond the bend apex, while the inner bend point bar grows laterally towards the outer bank, increasing the bend amplitude. These dynamics maintain the meander evolution. Even though this development is found in meandering rivers independent of soil or environmental characteristics, each river still seems to behave unpredictably. The special mechanisms that determine the rate and occasion of morphological changes remain unclear. The aim of this study is to offer new insights regarding flow-induced morphological changes in meander using a novel study approach. We focused on short-term and small-spatial-scale changes by conducting a spatially and temporally (daily) intensive survey during a flood (a period of nine days) with an ADCP attached to a remotely controlled mini-boat. Based on our analysis, the flood duration and the rate of discharge increase and decrease seems to play key roles in determining channel changes by controlling the flow velocities and depth and the backwater effect may have notable influence on the morphological processes. We discuss themes such as the interaction of inner and outer bend processes and the longer-term development of meander bends.Item The impacts of near-bed flow characteristics on river bed sediment transport under ice-covered conditions in 2016–2021(Elsevier, 2022-12) Lotsari, Eliisa; Lintunen, Karoliina; Kasvi, Elina; Alho, Petteri; Blåfield, Linnea; Department of Built Environment; University of TurkuGlobal climate change has been projected to affect hydrology, the ice-covered flow period and river morphology (including changed sediment transport conditions) in northern high-latitude regions. To understand the impact of the expected shortening of the ice-covered period on bedload transport, one needs to understand the present sediment transport in these high-latitude rivers with annually occurring ice cover. Thus, the aims are (1) to define the impacts of ice cover on near-bed flow characteristics during hydrologically varying years, and (2) to analyse the impacts of these mid-winter flow characteristics on the bed sediment transport potential. The analyses are based on Acoustic Doppler Current Profiler (ADCP: 2016–21) and Acoustic Doppler Velocimeter (ADV: 2020–21) measurements performed in mid-winter ice-covered conditions of the sandy and small (circa 20 m wide) Pulmanki River in northern Finnish Lapland. Despite the ice-covered river conditions in winter, sediment transport occurs even during these harshest mid-winter conditions. The critical velocities and shear velocities of mid-winter conditions were exceeded in winters 2016–2021, and bedload transport occurred according to bedload measurements. Three different situations occurred regarding the bed sediment transport and near-bed velocity conditions: (1) high measured mid-winter discharges indicate high velocities throughout the meander bend; (2) low measured mid-winter discharges cause low near-bed velocities throughout the meander bend; (3) winters having intermediate discharges indicate near-bed velocities and sediment transport potential being higher at the upstream inlet and apex sections of the meander bend but clearly lower downstream of the apex. The confinement by the river ice cover, i.e. bottom-fast ice, explains the velocity variation. The near-bed velocities were the highest at the upstream inlet section of a symmetrical meander bend, where the measurement cross-sections were narrower and shallower. The velocities were the lowest downstream of the apex, where the channel changed from relatively narrow to wider and deeper.Item Improving distribution models of riparian vegetation with mobile laser scanning and hydraulic modelling(PUBLIC LIBRARY SCIENCE, 2019-01-01) Nylén, Tua; Kasvi, Elina; Salmela, Jouni; Kaartinen, Harri; Kukko, Antero; Jaakkola, Anttoni; Hyyppä, Juha; Alho, Petteri; University of Turku; Department of Built Environment; National Land Survey of FinlandThis study aimed at illustrating how direct measurements, mobile laser scanning and hydraulic modelling can be combined to quantify environmental drivers, improve vegetation models and increase our understanding of vegetation patterns in a sub-arctic river valley. Our results indicate that the resultant vegetation models successfully predict riparian vegetation patterns (Rho = 0.8 for total species richness, AUC = 0.97 for distribution) and highlight differences between eight functional species groups (Rho 0.46–0.84; AUC 0.79–0.93; functional group-specific effects). In our study setting, replacing the laser scanning-based and hydraulic modelling-based variables with a proxy variable elevation did not significantly weaken the models. However, using directly measured and modelled variables allows relating species patterns to e.g. stream power or the length of the flood-free period. Substituting these biologically relevant variables with proxies mask important processes and may reduce the transferability of theresults into other sites. At the local scale, the amount of litter is a highly important driver of total species richness, distribution and abundance patterns (relative influences 49, 72 and 83%, respectively) and across all functional groups (13–57%; excluding lichen species richness) in the sub-arctic river valley. Moreover, soil organic matter and soil water content shape vegetation patterns (on average 16 and 7%, respectively). Fluvial disturbance is a key limiting factor only for lichen, bryophyte and dwarf shrub species in this environment (on average 37, 6 and 10%, respectively). Fluvial disturbance intensity is the most important component of disturbance for most functional groups while the length of the disturbance-free period is more relevant for lichens. We conclude that striving for as accurate quantifications of environmental drivers as possible may reveal important processes and functional group differences and help anticipate future changes in vegetation. Mobile laser scanning, high-resolutiondigital elevation models and hydraulic modelling offer useful methodology for improving correlative vegetation models.Item Laserkeilausmenetelmien soveltuvuus jokiympäristöjen mallinnukseen(2016) Vaaja, Matti; Kurkela, Matti; Hyyppä, Hannu; Kukko, Antero; Kaartinen, Harri; Jaakkola, Anttoni; Kasvi, Elina; Lotsari, Eliisa; Virtanen, Juho-Pekka; Saarinen, Ninni; Ahlavuo, Marika; Vastaranta, Mikko; Holopainen, Markus; Jalonen, Johanna; Järvelä, Juha; Alho, Petteri; Hyyppä, Juha; Rakennetun ympäristön laitos; Finnish Geospatial Research Institute; University of Turku; University of Eastern Finland; University of Helsinki; Ahlavuo, Marika; Hyyppä, Hannu; Ylikoski, ElinaLaserkeilausaineistojen käyttö virtavesien tutkimuksessa on lisääntynyt nopeasti viime vuosina. Perinteisesti virtavesiin liittyviä prosesseja on mallinnettu maastonmuotojen poikkileikkauksien ja virtausmittausten avulla. Laserkeilausmenetelmät ovat tuoneet mahdollisuuden kerätä alueellisia aineistoja entistä suuremmalla resoluutiolla ja tehokkuudella. Laserkeilauksella tuotettuja maanpinnan korkeusmalleja, muutostulkintamalleja ja kasvillisuuden kohdemalleja käytetään muun muassa tulva-alueiden ja -riskien kartoitukseen, jokidynamiikan ja geomorfologian tutkimuksiin sekä sedimentti- ja habitaattimallinnuksiin.Item Morphological changes and riffle-pool dynamics related to flow in a meandering river channel based on a 5-year monitoring period using close-range remote sensing(ELSEVIER SCIENCE BV, 2020-03-01) Salmela, Jouni; Kasvi, Elina; Vaaja, Matti Tapio; Kaartinen, Harri; Kukko, Antero; Jaakkola, Anttoni; Alho, Petteri; Department of Built Environment; Geoinformatics; MeMo; University of Turku; Gaze Inc.The maintenance of riffle-pool sequences and morphological changes in the long-term have received little attention in the literature. The aims of this study are to determine morphological changes and riffle-pool maintenance in relation to flow conditions in a meandering river channel over a 5-yr period. Change detection was focused on riffle and pool maintenance in a river reach covering three successive meander bends. Changes in a meandering river channel were studied utilizing detailed digital terrain models and flow data. The results indicated that riffle-pool sequences are maintained by high discharge events and the development of pools and riffles was linked. During high discharges, the riverbed eroded on the concave sides and the inflexion points aggraded, causing riffle–pool sequences, whereas during low discharges, concave sides aggraded and inflexion points eroded, causing pool filling and riffle erosion. While discharge increased, near-bed flow velocities increased faster on the concave sides of the bends than at the inflexion points, becoming higher at a discharge of 8 m3/s, ~20% of the bankfull discharge. Changes in the three successive meander bends were mainly similar, and the geometry of meandering rivers contributed to the locations of riffles and pools. Pools and riffles were not stable in size and shape, but their longitudinal location remained the same, instead of migrating up and down the channel. Morphological changes occurred in meander bends year-round, but they were non-linear. Annual channel change was not similar from year to year owing to different flow regimes and morphological changes during the previous year. However, seasonal detection revealed similarities between high and low discharge periods between the years. Concave sides of meander bends may act to temporarily store sediment; however, storage is preserved only under the effective hydrological discharge.