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Punys Petras - One of the best experts on this subject based on the ideXlab platform.
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2D hydrodynamic modelling for identification of dewatered or flooded Stream Channel areas downStream large hydropower plant
'Vytautas Magnus University', 2021Co-Authors: Šilinis Linas, Kasiulis Egidijus, Punys PetrasAbstract:Article Number: jws2019004Hydropower is oldest available source for renewable energy generation in Lithuania and the world. However, because of unequal demand of electricity during the day large hydropower plants are adapted to work in hydropeaking regime, which causes rapid water level and discharge fluctuations and has impact on the environment. To assess the e x- tent of this impact in this study 2D numerical hydrodynamic modelling was carried out to reveal the dewatered or flooded Stream Channel areas at the Nemunas R iver downstrea m Kaunas H ydropower P lant. Such estimation of dewatered or flooded areas, considering different operating modes of hydropower plant, was carried out for the first time in Lithuania. It was revealed that largest areas are flooded when Kaunas hydropower plan t starts its operation with two and four tur bine s and accordingly are dewatered when the plant stops such operations . During this study the impact of water level and discharge fluctuations on river ecosystems was not analysed, however the obtained results will be the initial data for more detailed assessment of fish habitats quality under impact of hydropeakingVandens ūkio ir žemėtvarkos fakultetasVytauto Didžiojo universiteta
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2D hydrodynamic modelling for identification of dewatered or flooded Stream Channel areas downStream large hydropower plant
'Vytautas Magnus University', 2020Co-Authors: Šilinis Linas, Kasiulis Egidijus, Punys PetrasAbstract:Hydropower is oldest available source for renewable energy generation in Lithuania and the world. However, because of unequal demand of electricity during the day large hydropower plants are adapted to work in hydropeaking regime, which causes rapid water level and discharge fluctuations and has impact on the environment. To assess the e x- tent of this impact in this study 2D numerical hydrodynamic modelling was carried out to reveal the dewatered or flooded Stream Channel areas at the Nemunas R iver downstrea m Kaunas H ydropower P lant. Such estimation of dewatered or flooded areas, considering different operating modes of hydropower plant, was carried out for the first time in Lithuania. It was revealed that largest areas are flooded when Kaunas hydropower plan t starts its operation with two and four tur bine s and accordingly are dewatered when the plant stops such operations . During this study the impact of water level and discharge fluctuations on river ecosystems was not analysed, however the obtained results will be the initial data for more detailed assessment of fish habitats quality under impact of hydropeakin
Mathias G Kondolf - One of the best experts on this subject based on the ideXlab platform.
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geomorphological Stream Channel classification in aquatic habitat restoration uses and limitations
Aquatic Conservation-marine and Freshwater Ecosystems, 1995Co-Authors: Mathias G KondolfAbstract:1Land managers in western North America have embraced classification of Stream Channels based on geomorphological characteristics as the importance of Channel stability in successful restoration of aquatic and riparian habitat has become widely recognized. 2Classification can permit rapid inventory of large regions, provide a stratified geomorphological framework within which more detailed observations can be organized, and provide an initial basis for selecting restoration strategies. 3Existing classifications are arbitrary, developed by creating classes out of a continuum of Channel form. Moreover, Stream Channels are dynamic, and the existing condition does not necessarily reflect former, long-term, or future conditions. 4The user should not confuse the classification exercise with a complete understanding of the Channel. Before any Channel works are actually undertaken, site-specific studies are essential, including historical studies to determine former Channel conditions and to shed light on underlying causes for degradation of aquatic or riparian resources. 5When applying a classification system, the raw data collected should be reported, not simply the resultant Channel classes. Channels that do not fit neatly within pre-existing classes should be reported as such and not lumped in classes where they ‚should’ be.
Stanley W. Trimble - One of the best experts on this subject based on the ideXlab platform.
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Contribution of Stream Channel Erosion to Sediment Yield from an Urbanizing Watershed
Science, 1997Co-Authors: Stanley W. TrimbleAbstract:Stream Channel erosion has long been suspected as the major contributor to long-term sediment yield from urbanizing watersheds. For San Diego Creek in southern California, measurements from 1983 to 1993 showed that Stream Channel erosion furnished 10 5 megagrams per year of sediment, or about two-thirds of the total sediment yield. Thus, because Channel erosion can be a major source of sediment yield from urbanizing areas, Channel stabilization should be a priority in managing sediment yield.
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Stream Channel erosion and change resulting from riparian forests
Geology, 1997Co-Authors: Stanley W. TrimbleAbstract:Forested Stream banks, compared to grassed ones, can destabilize Stream Channels by promoting erosion. Four reaches of Coon Creek, Wisconsin, each with long-term grassed and forested subreaches were examined. Grassed reaches were narrower and had smaller Channels (bankfull cross sections) than forested reaches, suggesting that grassed Channel reaches stored about 2100 to 8800 m 3 more sediment per kilometre than forested reaches. Available evidence suggests that conversion of riparian forests to grass would allow storage of sediment along Channels, possibly decreasing downStream sediment yields. These findings are important as many grassed riparian corridors are rapidly reverting to forest because of economic conditions and governmental policies.
Francis J Magilligan - One of the best experts on this subject based on the ideXlab platform.
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immediate changes in Stream Channel geomorphology aquatic habitat and fish assemblages following dam removal in a small upland catchment
Geomorphology, 2016Co-Authors: Francis J Magilligan, Keith H Nislow, B Kynard, A M HackmanAbstract:Abstract Dam removal is becoming an increasingly important component of river restoration, with > 1100 dams having been removed nationwide over the past three decades. Despite this recent progression of removals, the lack of pre- to post-removal monitoring and assessment limits our understanding of the magnitude, rate, and sequence of geomorphic and/or ecological recovery to dam removal. Taking advantage of the November 2012 removal of an old (~ 190 year-old) 6-m high, run-of-river industrial dam on Amethyst Brook (26 km2) in central Massachusetts, we identify the immediate eco-geomorphic responses to removal. To capture the geomorphic responses to dam removal, we collected baseline data at multiple scales, both upStream (~ 300 m) and downStream (> 750 m) of the dam, including monumented cross sections, detailed Channel-bed longitudinal profiles, embeddedness surveys, and Channel-bed grain size measurements, which were repeated during the summer of 2013. These geomorphic assessments were combined with detailed quantitative electrofishing surveys of Stream fish richness and abundance above and below the dam site and throughout the watershed and visual surveys of native anadromous sea lamprey (Petromyzon marinus) nest sites. Post-removal assessments were complicated by two events: (1) upStream knickpoint migration exhumed an older (ca. late eighteenth century) intact wooden crib dam ~ 120 m upStream of the former stone dam, and (2) the occurrence of a 10–20 year RI flood 6 months after removal that caused further upStream incision and downStream aggradation. Now that the downStream reach has been reconnected to upStream sediment supply, the predominant geomorphic response was bed aggradation and associated fining (30–60% reduction). At dam proximal locations, aggradation ranged from 0.3 to > 1 m where a large woody debris jam enhanced aggradation. Although less pronounced, distal locations still showed aggradation with a mean depth of deposition of ~ 0.20 m over the 750-m downStream reach. Post-removal, but pre-flood, bed surveys indicate ~ 2 m of incision had migrated 25 m upStream of the former reservoir before encountering the exhumed dam, which now acts as the new grade control, limiting progressive headcutting. Approximately 1000 m3 of sediment was evacuated in the first year, with ~ 67% of the volume occurring by pre-flood, process-driven (e.g., changes in base level) controls. The combination of changes in Channel-bed sedimentology, the occurrence of a large magnitude flood, and the emergence of the new crib dam that is a likely barrier to fish movement was associated with major reductions in abundance and richness in sites downStream and immediately upStream adjacent to the former dam in post-removal sampling. At the same time, we documented the presence of four species of fish, including sea lamprey, which were not present above the dam prior to removal, indicating that upStream passage has been achieved; and we also documented lamprey spawning activity at sites immediately below the dam, which had previously been unsuitable owing to an excessively coarse and armored riverbed. Our results point to the importance of interactions between dam removal and flood disturbance effects, with important implications for short- and long-term monitoring and assessment of dam impacts to river systems.
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impact of reach geometry on Stream Channel sensitivity to extreme floods
Earth Surface Processes and Landforms, 2014Co-Authors: Eirik M Buraas, Carl E Renshaw, Francis J Magilligan, W B DadeAbstract:Predicting spatial and temporal variations in bank erosion due to extreme floods presents a long-standing challenge in geomorphology. We develop two methodologies for rapid, regional-scale assessments of Stream reaches susceptible to Channel widening. The first proposes that Channel widening occurs when unit Stream power exceeds a critical threshold (300 W/m2). The second is motivated by the observation that widening often occurs at Channel bends. We introduce a new metric, the bend stress parameter, which is proportional to the centripetal force exerted on a concave bank. We propose that high centripetal forces generate locally high bank shear forces and enhance Channel bank erosion. We test both metrics using the geomorphic signature of Tropical Storm Irene (2011) on the White and the Saxtons Rivers, Vermont. Specifically, we test if reaches where significant Channel widening occurred during Irene required one or both metrics to exceed threshold values. We observe two distinct styles of Channel widening. Where unit Stream power and bend stress parameter are high, widening is usually due to bank retreat. Elsewhere widening is usually due to the stripping of the upStream end of mid-Channel islands. Excluding widening associated with the stripping of the heads of mid-Channel islands, almost all the widening (> 98%) occurred along reaches identified as susceptible to widening. The combined metrics identify up to one-quarter of the reaches lacking susceptibility to Channel widening. Copyright © 2014 John Wiley & Sons, Ltd.
Darlene Wilcox - One of the best experts on this subject based on the ideXlab platform.
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the Stream Channel incision syndrome and water quality
Ecological Engineering, 2010Co-Authors: Douglas F Shields, Richard E Lizotte, Scott S Knight, C M Cooper, Darlene WilcoxAbstract:Abstract Watershed development often triggers Channel incision that leads to radical changes in Channel morphology. Although morphologic evolution due to Channel incision has been documented and modeled by others, ecological effects, particularly water quality effects, are less well understood. Discharge, basic physical parameters, solids, nutrients (nitrogen and phosphorus), chlorophyll and bacteria were monitored for five years at two sites along a Stream in a mixed-cover watershed characterized by rapid incision of the entire Channel network. Concurrent data were collected from two sites on a nearby Stream draining a watershed of similar size and cultivation intensity, but without widespread incision. Data sets describing physical aquatic habitat and fish fauna of each Stream were available from other studies. The second Stream was impacted by watershed urbanization, but was not incised, so normal Channel–floodplain interaction maintained a buffer zone of floodplain wetlands between the study reach and the urban development upStream. The incised Stream had mean Channel depth and width that were 1.8 and 3.5 times as large as for the nonincised Stream, and was characterized by flashier hydrology. The median rise rate for the incised Stream was 6.4 times as great as for the nonincised Stream. Correlation analyses showed that hydrologic perturbations were associated with water quality degradation, and the incised Stream had levels of turbidity and solids that were two to three times higher than the nonincised, urbanizing Stream. Total phosphorus, total Kjeldahl N, and chlorophyll a concentrations were significantly higher in the incised Stream, while nitrate was significantly greater in the nonincised, urbanizing Stream ( p ≤ 0.02). Physical aquatic habitat and fish populations in the nonincised urbanizing Stream were superior, as it supported almost twice as many species and yielded more than four times as much biomass per unit of effort. These results suggest that Channel incision is associated with a complex of ecological stressors that includes Channel erosion, hydrologic perturbation, and water quality and physical habitat degradation. Ecological engineering of Stream corridors must focus at least as much energy on mediating hydrologic perturbations and managing habitat quality as on pollutant loadings.
