Artykuły w czasopismach na temat „Stream flow”
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1
Jones, Jeremy B., i Amanda J. Rinehart. "The long-term response of stream flow to climatic warming in headwater streams of interior AlaskaThis article is one of a selection of papers from The Dynamics of Change in Alaska’s Boreal Forests: Resilience and Vulnerability in Response to Climate Warming." Canadian Journal of Forest Research 40, nr 7 (lipiec 2010): 1210–18. http://dx.doi.org/10.1139/x10-047.
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Warming in the boreal forest of interior Alaska will have fundamental impacts on stream ecosystems through changes in stream hydrology resulting from upslope loss of permafrost, alteration of availability of soil moisture, and the distribution of vegetation. We examined stream flow in three headwater streams of the Caribou–Poker Creeks Research Watershed (CPCRW) in interior Alaska over a 30-year period to determine (i) how stream flow varied among streams draining watersheds with varying extents of permafrost and (ii) evaluate if stream hydrology is changing with loss of permafrost. The three streams drained subcatchments with permafrost extents ranging from 4% to 53%. For each stream, runoff data were analyzed by separating base and storm flow contributions using a local-minimum method and with analysis of flood recession curves. Mean daily runoff during the ice-free season did not significantly vary among streams (mean = 0.57 mm·d–1), although the watersheds with lower permafrost had a greater contribution of base flow. Across years, flow was variable and was related with summer temperature in the watershed with low permafrost and with precipitation in the watershed with high permafrost. With climate warming and loss of permafrost, stream flows will become less responsive to precipitation and headwater streams may become ephemeral.
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Lancaster, Jill, i Alan G. Hildrew. "Characterizing In-stream Flow Refugia". Canadian Journal of Fisheries and Aquatic Sciences 50, nr 8 (1.08.1993): 1663–75. http://dx.doi.org/10.1139/f93-187.
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Flow in nine streams was examined in relation to refugia for invertebrates. Areas of bed maintaining low hydraulic stress throughout the discharge hydrograph could provide flow refugia for animals during spates. In one stream, near-bed shear stress and velocity were repeatedly measured in discrete patches. Three types were identified: "fast" patches maintained high hydraulic stress, "variable" patches showed the greatest change in stress, and "slow" patches maintained low stress and thus were potential refugia. Average stress increased with discharge, but potential refugia were prominent throughout and could be important for invertebrates. Abundances of refugia in eight comparison streams were characterized by changes in the frequency distribution of flow forces with discharge. Three stream types were identified that did not simply reflect channel size or morphology. Such stream-specific flow patterns could affect the structure of comunities through the differing provision of refugia. Longitudinal transport processes in these streams were investigated by solute dilution experiments and by the application of a model to measure an aggregated "dead zone". Transport (and dead zone volume) varied among streams and further reflected their refuge potential. Clearly, flow habitat features could intervene in population and community dynamics by providing refuge from spates.
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DeWalle, David R., Bryan R. Swistock i William E. Sharpe. "Episodic flow–duration analysis: a method of assessing toxic exposure of brook trout (Salvelinus fontinalis) to episodic increases in aluminum". Canadian Journal of Fisheries and Aquatic Sciences 52, nr 4 (1.04.1995): 816–27. http://dx.doi.org/10.1139/f95-081.
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Episodic flow–duration curves were developed that summarize stream flow data by considering the duration of sustained flows at or above specified levels. These curves and relationships between dissolved aluminum concentrations and stream flow were combined for five Appalachian (Pennsylvania) streams to determine the frequency of occurrence of acutely toxic aluminum conditions for brook trout (Salvelinus fontinalis). Concentrations of total dissolved aluminum (AlTD) increased with stream flow in all streams, but reached a plateau or decreased during extreme high flows in some streams. AlTD was dominated by inorganic monomeric species in all streams except Benner Run and Baldwin Creek. Episodic AlTD concentrations and durations were compared with a toxicity curve developed using caged wild and hatchery-reared brook trout. Results predicted that lethal episodes occurred on Linn, Stone, and Roberts runs, but not on Benner Run and Baldwin Creek. With the exception of Stone Run, brook trout populations were largest in streams without predicted lethal episodes (Benner Run and Baldwin Creek) and were smallest in streams with predicted lethal episodes (Linn and Roberts runs). This analysis could be adapted for prediction of toxic conditions in streams for other pollutants where toxicity varies with both concentration and duration of exposure.
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Hughes, JMR, i B. James. "A hydrological regionalization of streams in Victoria, Australia, with implications for stream Ecology". Marine and Freshwater Research 40, nr 3 (1989): 303. http://dx.doi.org/10.1071/mf9890303.
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Annual, monthly, low and peak flow data were used to classify and ordinate 138 stream gauges in Victoria. Sixteen hydrological variables were used and low-flow and entire-flow regionalizations were derived. The low-flow regionalization was spatially indistinct and therefore unusable, but the entire-flow regionalization produced five distinctive and spatially significant regions. Least-squares relationships were calculated between mean annual runoff, catchment area and coefficient of variation of annual flows, and the 16 variables. Rivers in the dry western districts of Victoria exhibit high variability of annual, monthly and peak flows, and low specific low flows. The converse is true for rivers in the western highlands of Victoria. Stream regionalizations are a useful tool for stream ecologists, and may be used for generating hypotheses, for detecting representative rivers and for producing baseline stream surveys.
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Nolan, Kevin P., i Tamer A. Zaki. "Conditional sampling of transitional boundary layers in pressure gradients". Journal of Fluid Mechanics 728 (9.07.2013): 306–39. http://dx.doi.org/10.1017/jfm.2013.287.
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AbstractStatistical analysis of transitional boundary layers in pressure gradients is performed using the flow fields from direct numerical simulations of bypass transition. Laminar–turbulent discrimination separates the streaky laminar flow from turbulent regions. Individual streaks are identified and tracked in the flow field in order to obtain statistics of the amplitude of the streak population. An extreme value model is proposed for the distribution of streak amplitudes. It is also possible to differentiate those streaks which break down into turbulent spots from innocuous events. It is shown that turbulence onset is due to high-amplitude streaks, with streamwise perturbation velocity exceeding 20 % of the free stream speed. The resulting turbulent spots are tracked downstream. The current analysis allows for the measurement of the lateral spreading angles of individual spots and their spatial extent and volumes. It is demonstrated that the volumetric growth rate of turbulent spots is insensitive to pressure gradient.
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Whillans, I. M., i C. J. Van Der Veen. "New and improved determinations of velocity of Ice Streams B and C, West Antarctica". Journal of Glaciology 39, nr 133 (1993): 483–590. http://dx.doi.org/10.1017/s0022143000016373.
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Abstract Measurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.
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Whillans, I. M., i C. J. Van Der Veen. "New and improved determinations of velocity of Ice Streams B and C, West Antarctica". Journal of Glaciology 39, nr 133 (1993): 483–590. http://dx.doi.org/10.3189/s0022143000016373.
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AbstractMeasurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.
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Mrzljak, Vedran, Jasna Prpić-Oršić i Tomislav Senčić. "Change in Steam Generators Main and Auxiliary Energy Flow Streams During the Load Increase of LNG Carrier Steam Propulsion System". Pomorstvo 32, nr 1 (20.06.2018): 121–31. http://dx.doi.org/10.31217/p.32.1.15.
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In this paper is presented an analysis of main and auxiliary steam energy flow streams from steam generators during the increase in steam system load at conventional LNG carrier. During the steam system load increase was presented differences in steam pressure and temperature between main and auxiliary steam flow streams. Energy power of the auxiliary flow stream is higher than energy power of the main flow stream only at the lowest steam system loads after which main flow stream takes over primacy at middle and high steam system loads. Cumulative auxiliary energy flow stream was divided on energy flow streams to each auxiliary device and energy power consumption of each auxiliary device was also investigated throughout number steam system loads. Analysis of steam production from marine steam generators presented in this paper provides insight into the operation dynamics of the entire steam propulsion system.
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Stephenson, S. N., i R. A. Bindschadler. "Is Ice-Stream Evolution Revealed By Satellite Imagery?" Annals of Glaciology 14 (1990): 273–77. http://dx.doi.org/10.3189/s0260305500008740.
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Ten Landsat Thematic Mapper images together show Ice Streams E, D and most of Ice Stream C on Siple Coast, West Antarctica. The images are interpreted to reveal aspects of both spatial and temporal evolution of the ice streams. Onset of ice-stream flow appears to occur at distributed sites within the ice-stream catchment, and the apparent enhanced flow continues in channels until they join, forming the main ice stream. Most crevassing on these ice streams is associated with features of horizontal dimensions between 5 and 20 km. We suggest these features are caused by bed structures which may be an important source of restraint to ice flow, similar to ice rumples on ice shelves. A pattern of features near the grounding line of the now-stagnant Ice Stream C are interpreted as having formed because there was a period of reduced flux before the ice stream stopped.
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Stephenson, S. N., i R. A. Bindschadler. "Is Ice-Stream Evolution Revealed By Satellite Imagery?" Annals of Glaciology 14 (1990): 273–77. http://dx.doi.org/10.1017/s0260305500008740.
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Ten Landsat Thematic Mapper images together show Ice Streams E, D and most of Ice Stream C on Siple Coast, West Antarctica. The images are interpreted to reveal aspects of both spatial and temporal evolution of the ice streams. Onset of ice-stream flow appears to occur at distributed sites within the ice-stream catchment, and the apparent enhanced flow continues in channels until they join, forming the main ice stream. Most crevassing on these ice streams is associated with features of horizontal dimensions between 5 and 20 km. We suggest these features are caused by bed structures which may be an important source of restraint to ice flow, similar to ice rumples on ice shelves. A pattern of features near the grounding line of the now-stagnant Ice Stream C are interpreted as having formed because there was a period of reduced flux before the ice stream stopped.
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Hicks, Peter D., i Pierre Ricco. "Laminar streak growth above a spanwise oscillating wall". Journal of Fluid Mechanics 768 (6.03.2015): 348–74. http://dx.doi.org/10.1017/jfm.2015.98.
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The use of spanwise wall oscillations to attenuate the growth of laminar streaks within the incompressible Blasius boundary layer is investigated. As in the case of the flow above a stationary flat plate, studied by Leib et al. (J. Fluid Mech., vol. 380, 1999, pp. 169–203), free-stream convected gusts interact with the boundary layer to drive the streak growth. Spanwise wall oscillations can either reduce or increase the total energy of the laminar streaks, depending upon the wall oscillation amplitude and frequency, as well as the free-stream gust properties. Reductions in streak energies of up to 90 % are obtained, indicating that spanwise wall oscillations are an effective technique for attenuating the laminar streak growth. Therefore they may suppress secondary boundary-layer instabilities and delay transition. The laminar boundary-layer base flow matches the Blasius profile in the streamwise and wall-normal directions, while in the spanwise direction a generalized version of the classical Stokes layer profile (generated by a wall oscillating beneath a quiescent fluid) occurs, which evolves downstream due to non-parallel flow effects. Via a Wentzel–Kramers–Brillouin–Jeffreys analysis, this generalized Stokes layer is shown to approach the classical Stokes layer in the limit of large downstream distances or high-frequency plate oscillations. The laminar streaks forced by the generalized and the classical Stokes flows differ significantly, which implies that the choice of the spanwise base flow may affect the secondary instability and transition in this flow. The analysis also proves that the use of the classical Stokes layer as spanwise base flow, as employed by Hack & Zaki (Phys. Fluids. vol. 24 (3), 2012, 034101), is inappropriate.
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Larter, Robert D., Kelly A. Hogan, Claus-Dieter Hillenbrand, James A. Smith, Christine L. Batchelor, Matthieu Cartigny, Alex J. Tate i in. "Subglacial hydrological control on flow of an Antarctic Peninsula palaeo-ice stream". Cryosphere 13, nr 6 (5.06.2019): 1583–96. http://dx.doi.org/10.5194/tc-13-1583-2019.
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Abstract. Basal hydrological systems play an important role in controlling the dynamic behaviour of ice streams. Data showing their morphology and relationship to geological substrates beneath modern ice streams are, however, sparse and difficult to collect. We present new multibeam bathymetry data that make the Anvers-Hugo Trough west of the Antarctic Peninsula the most completely surveyed palaeo-ice stream pathway in Antarctica. The data reveal a diverse range of landforms, including streamlined features where there was fast flow in the palaeo-ice stream, channels eroded by flow of subglacial water, and compelling evidence of palaeo-ice stream shear margin locations. We interpret landforms as indicating that subglacial water availability played an important role in facilitating ice stream flow and controlling shear margin positions. Water was likely supplied to the ice stream bed episodically as a result of outbursts from a subglacial lake located in the Palmer Deep basin on the inner continental shelf. These interpretations have implications for controls on the onset of fast ice flow, the dynamic behaviour of palaeo-ice streams on the Antarctic continental shelf, and potentially also for behaviour of modern ice streams.
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Rauch, Martina, Saša Mudrinić i Antun Galović. "Detailed Analysis of Exergy Destruction of All Basic Types of Heat Exchangers". Processes 10, nr 2 (27.01.2022): 249. http://dx.doi.org/10.3390/pr10020249.
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Dimensionless expressions of exergy destruction, normalized to ambient temperature and heat capacity of the weaker stream, for all basic types of recuperators are derived. The analytical expressions for maximum exergy destruction were calculated using the GNU Octave software for all recuperators, namely parallel-flow and counter-flow recuperators, and all forms of cross-flow heat exchangers, namely without mixing of streams, only mixing the streamlines of the weaker stream, only mixing the streamlines of the stronger stream and mixing the weaker and stronger streams. For parallel-flow and counter-flow recuperators, as well as for their special cases, expressions for local and total exergy destruction are given. It is shown that the maximum exergy destruction, as a local extreme, is the same for all recuperators for mutually equal values of the quantities π3 (ratio of the heat capacity of the weaker stream to the heat capacity of the stronger stream) and πT (ratio of the inlet temperature of the stronger stream to the inlet temperature of the weaker stream). The ratio of exergy destruction to effectiveness of each basic type of recuperator is further analyzed. The obtained results are presented and interpreted in appropriate dimensionless diagrams.
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Gröbner, Katharina, Wolfgang Gadermayr, Giorgio Höfer-Öllinger, Harald Huemer i Christoph Spötl. "Karst hydrogeology of Lamprechtsofen (Leoganger Steinberge, Salzburg)". Austrian Journal of Earth Sciences 112, nr 1 (1.01.2019): 50–61. http://dx.doi.org/10.17738/ajes.2019.0004.
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AbstractThe Leoganger Steinberge are a heavily karstified massif largely composed of Dachstein dolomite and limestone hosting the deepest through-trip cave in the world, Lamprechtsofen, whose frontal parts are developed as a show cave. Many parts of this 60 km-long and 1724 m-deep system are hydrologically active. 1.5 km behind the lower cave entrance Grüntopf stream and Kneippklamm stream merge to form the main cave stream. Another underground stream, Stainerhallen stream, flows through the eponymous hall of the show cave. Since 2007 water temperature, electrical conductivity and water level have been monitored in the Grüntopf and Kneippklamm stream. Water temperature and water level in the Stainerhallen and main cave stream have been measured since 2016.The long-term dataset (2013–2017) shows that the water temperature of the cave streams (Grüntopf stream: 3.7–5.2°C; Kneippklamm stream: 5.1–5.9°C) is largely invariant, but the electrical conductivity varies strongly (Grüntopf stream: 107–210 µS/cm; Kneippklamm stream: 131–248 µS/cm) in response to snowmelt and precipitation events. The event water of the Kneippklamm stream is characterized by a low electrical conductivity and is then followed by slightly warmer and higher mineralized water derived from the phreatic zone. This dual flow pattern also explains the asymmetrical changes of the water level during snowmelt: the fast event water flows directly through vadose pathways to the measurement site, whereas the hydraulic (phreatic) response is delayed. The Grüntopf stream reacts to precipitation and snowmelt events by changes in the karst-water table, which can be explained by a piston flow-model. The Kneippklamm stream reveals evidence of a lifter system.The altitude of the catchments was calculated using δ18O values of water samples from the underground streams and from surface precipitation. The Grüntopf stream shows the highest mean catchment (2280 m a.s.l.), which is in agreement with its daily fluctuations of the water level until August caused by long-lasting snowmelt. The Stainerhallen stream has the lowest catchment (average 1400 m a.s.l.). The catchments of the other two streams are at intermediate elevations (1770–1920 m a.s.l.). The integration of the catchment analyses and observations from tracer tests conducted in the 1970s showed that the latter reflected only one aspect of the karst water regime in this massif. During times of high recharge the water level rises, new flow paths are activated and the karst watershed shifts.
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Harmon, Russell S., Deborah L. Leslie, W. Berry Lyons, Kathleen A. Welch i Diane M. McKnight. "Diurnal chemistry of two contrasting stream types, Taylor Valley, McMurdo Dry Valley Region, Antarctica". E3S Web of Conferences 98 (2019): 01020. http://dx.doi.org/10.1051/e3sconf/20199801020.
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Numerous ephemeral streams flow within the McMurdo Dry Valley Region of Antarctica that transport glacial meltwater to perennially ice-covered, closed-basin lakes during the austral summer. The diurnal behavior for two Taylor Valley streams of different character was examined during the summer of 2010-11. Andersen Creek is a short, 1st-order proglacial stream, whereas Von Guerard Stream is a long, high-order stream with an extensive hyporheic zone that has a substantial cyanobacterial algal mat community in its middle reaches. Both streams display strong daily cycles for temperature, electrical conductivity, dissolved oxygen, and pH. Conductivity varies in concert with flow, with solute dilution occurring during the daily high-flow pulse. Dissolved oxygen co-varies strongly with pH at Andersen Creek but not for Von Guerard Stream. Each stream has a distinct geochemical character that for Andersen Creek is a direct reflection of its glacial source, unmodified by secondary effects, whereas that for Von Guerard Stream is modulated by its resident algal mat community and through extensive hyporheic zone interaction and exchange.
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Vaughan, David G., Hugh F. J. Corr, Andy M. Smith, Hamish D. Pritchard i Andrew Shepherd. "Flow-switching and water piracy between Rutford Ice Stream and Carlson Inlet, West Antarctica". Journal of Glaciology 54, nr 184 (2008): 41–48. http://dx.doi.org/10.3189/002214308784409125.
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AbstractRutford Ice Stream and Carlson Inlet are neighbouring glaciers in West Antarctica. Rutford Ice Stream flows at speeds greater than 350 m a−1, whereas Carlson Inlet, which has some similar dimensions and supports a similar driving stress, flows 10–50 times slower. We discuss a range of observations concerning Carlson Inlet, and conclude that there is good indirect evidence that it is a relict ice stream, which ceased streaming more than 240 years BP, but sufficiently recently that its surface morphology, basal water content and basal morphology still retain characteristics produced by streaming. An analysis of expected subglacial drainage pathways indicates that Carlson Inlet is not streaming because it is currently starved of subglacial water, which is currently directed beneath Rutford Ice Stream. This current state of water piracy by Rutford Ice Stream is, however, sensitive to minor thickness changes on the ice streams; a ∼120 m (<4%) thickening of Rutford Ice Stream would divert almost all the subglacial water in the system towards Carlson Inlet and could reactivate its flow. The result highlights the importance of subglacial drainage in controlling ice-stream evolution and the requirement for ice-sheet models to couple ice flow with subglacial drainage.
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Childress, Evan S., Keith H. Nislow, Andrew R. Whiteley, Matthew J. O’Donnell i Benjamin H. Letcher. "Daily estimates reveal fine-scale temporal and spatial variation in fish survival across a stream network". Canadian Journal of Fisheries and Aquatic Sciences 76, nr 8 (sierpień 2019): 1446–58. http://dx.doi.org/10.1139/cjfas-2018-0191.
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Environmental drivers of population vital rates, such as temperature and precipitation, often vary at short time scales, and these fluctuations can have important impacts on population dynamics. However, relationships between survival and environmental conditions are typically modeled at coarse temporal scales, ignoring the role of daily environmental variation in survival. Our goal was to determine the importance of fine-scale temporal variation in survival to population dynamics of stream salmonids. We extended the Cormack–Jolly–Seber model to estimate daily survival rates from seasonal samples of individually marked brook trout (Salvelinus fontinalis) in a stream network. Daily variation in temperature and flow were strongly associated with survival, but relationships varied between juvenile and adult trout and among streams. In all streams, juveniles had higher mortality in warm, low-flow conditions, but in the two larger streams, cold, high-flow conditions also reduced juvenile survival. Adult survival decreased during low flows, particularly in the fall spawning period. Differing survival responses among stream network components to short-term environmental events created shifts in optimal location for maximum survival across life stages, seasons, and years.
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Knight, Jasper, G. McCarron Stephen i A. Marshall McCabe. "Landform modification by palaeo-ice streams in east-central Ireland". Annals of Glaciology 28 (1999): 161–67. http://dx.doi.org/10.3189/172756499781821616.
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AbstractIn eastern Ireland, subglacial bedforms including drumlins and Rogen moraines were modified by headward erosion along two ice streams which had overlapping flow tracks. The ice streams, which had tidewater termini, are dated by geochronometric and morphostratigraphic methods to <15.014 C kyr BP (Castleblaney ice stream) and ~13.814C kyr BP (Armagh ice stream). Bedforms along ice-stream tracks show a morphological continuum which reflects a down-ice increase in the degree of modification by ice-stream activity (i.e. resulting in unmodified →remoulded/overprinted →crosscut →streamlined bedforms). The down-ice changes in bedform types are inferred to relate to changes in subglacial drainage and sediment-transport mechanisms. Bedform and sedimentary evidence suggest that discrete subglacial meltwater channels which developed up- ice changed in a down-ice direction to unchannelized flows which deepened towards the ice margin. Meltwater release from subglacial cavities, and produced by strain heating at sheared ice-stream margins, probably helped support ice-stream flow, which ended as the volume of subglacial meltwater discharge decreased. Dated millennial-scale cycles of ice activity may be related to instability at tidewater margins, followed by complex thermal and hydraulic responses within the ice mass.
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Kobayashi, Sohei, Takashi Gomi, Roy C. Sidle i Yasuhiro Takemon. "Disturbances structuring macroinvertebrate communities in steep headwater streams: relative importance of forest clearcutting and debris flow occurrence". Canadian Journal of Fisheries and Aquatic Sciences 67, nr 2 (luty 2010): 427–44. http://dx.doi.org/10.1139/f09-186.
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This study shows that debris flow disturbances that alter in-channel physical conditions or displace organisms exert greater impacts on stream macroinvertebrate community structure than clearcutting disturbances that change energy inputs in steep headwater systems. We surveyed abiotic characteristics and macroinvertebrate communities of 10 steep headwater streams in central Japan that contained a chronosequence of forest stands and debris flow occurrences. Streams of recently logged forests had higher light levels, nitrate concentrations, and stream temperature ranges than streams of mature forests. Streams of middle-aged forests, which experienced debris flows in recent years (1989–1998), had lower abundance of shredders, crawlers, and headwater-adapted taxa than the other streams. A shredder taxon, Gammarus nipponensis , was completely absent in the streams with recent debris flows, despite their dominance in the other streams. Decreases of depositional environment associated with depletion of large wood and loss of channel structure as well as replacement of community members by rapid colonizers appear to be the major mechanisms of structural changes in macroinvertebrate communities affected by debris flows.
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Briggs, Martin A., Phillip Goodling, Zachary C. Johnson, Karli M. Rogers, Nathaniel P. Hitt, Jennifer B. Fair i Craig D. Snyder. "Bedrock depth influences spatial patterns of summer baseflow, temperature and flow disconnection for mountainous headwater streams". Hydrology and Earth System Sciences 26, nr 15 (4.08.2022): 3989–4011. http://dx.doi.org/10.5194/hess-26-3989-2022.
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Abstract. In mountain headwater streams, the quality and resilience of summer cold-water habitat is generally regulated by stream discharge, longitudinal stream channel connectivity and groundwater exchange. These critical hydrologic processes are thought to be influenced by the stream corridor bedrock contact depth (sediment thickness), a parameter often inferred from sparse hillslope borehole information, piezometer refusal and remotely sensed data. To investigate how local bedrock depth might control summer stream temperature and channel disconnection (dewatering) patterns, we measured stream corridor bedrock depth by collecting and interpreting 191 passive seismic datasets along eight headwater streams in Shenandoah National Park (Virginia, USA). In addition, we used multi-year stream temperature and streamflow records to calculate several baseflow-related metrics along and among the study streams. Finally, comprehensive visual surveys of stream channel dewatering were conducted in 2016, 2019 and 2021 during summer low flow conditions (124 total km of stream length). We found that measured bedrock depths along the study streams were not well-characterized by soils maps or an existing global-scale geologic dataset where the latter overpredicted measured depths by 12.2 m (mean) or approximately four times the average bedrock depth of 2.9 m. Half of the eight study stream corridors had an average bedrock depth of less than 2 m. Of the eight study streams, Staunton River had the deepest average bedrock depth (3.4 m), the coldest summer temperature profiles and substantially higher summer baseflow indices compared to the other study steams. Staunton River also exhibited paired air and water annual temperature signals suggesting deeper groundwater influence, and the stream channel did not dewater in lower sections during any baseflow survey. In contrast, Paine Run and Piney River did show pronounced, patchy channel dewatering, with Paine Run having dozens of discrete dry channel sections ranging from 1 to greater than 300 m in length. Stream dewatering patterns were apparently influenced by a combination of discrete deep bedrock (20+ m) features and more subtle sediment thickness variation (1–4 m) depending on local stream valley hydrogeology. In combination, these unique datasets show the first large-scale empirical support for existing conceptual models of headwater stream disconnection based on spatially variable underflow capacity and shallow groundwater supply.
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Mišetić, Stjepan, Željko Pavlin, Milorad Mrakovčić i Vedran Jurić. "Defining environmentally acceptable flow downstream intake structures in Croatia". Management of Environmental Quality: An International Journal 14, nr 4 (1.10.2003): 520–32. http://dx.doi.org/10.1108/14777830310488720.
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Determining minimum water flows that will continuously run through a natural channel downstream of a water intake (Q0) is a multidisciplinary problem. It is, however, not approached in a multidisciplinary way in most countries. This paper offers an overview of the main methods and proposes a practical and environmentally more acceptable way of determining the retained flow, namely the environmentally acceptable flow (EAF). It is proposed that until the conditions are created for use of more complex methods and/or biological response techniques, the EAF be defined by determining whether the retained flow is sufficient for sustaining and developing indigenous wildlife in the streams by ensuring of the essential living conditions for the bioindicator species. The proposed bioindicators are characteristic fish populations of a specific type of stream and stream reaches. Being the final link in the ecological food chain, fish species are reliable indicators of bioecological balance in a stream.
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Eder, A., M. Exner-Kittridge, P. Strauss i G. Blöschl. "Re-suspension of bed sediment in a small stream – results from two flushing experiments". Hydrology and Earth System Sciences 18, nr 3 (17.03.2014): 1043–52. http://dx.doi.org/10.5194/hess-18-1043-2014.
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Abstract. Streams draining small watersheds often exhibit multiple peaking sedigraphs associated with single peaking hydrographs. The process reasons of the multiple sediment peaks are not fully understood but they may be related to the activation of different sediment sources such as the stream bed itself, where deposited sediments from previous events may be available for resuspension. To understand resuspension of stream bed sediments at the reach scale we artificially flooded the small stream of the HOAL Petzenkirchen catchment in Austria by pumping sediment-free water into the stream. Two short floods were produced and flow, sediment and bromide concentrations were measured at three sites with high temporal resolution. Hydrologically, the two flood events were almost identical. The peak flows decreased from 57 to 7.9 L s−1 and the flow volumes decreased from 17 to 11.3 m2 along the 590 m reach of the stream. However, a considerably smaller sediment load was resuspended and transported during the second flood due to depletion of stream bed sediments. The exception was the middle section of the stream, where more sediment was transported during the second flood event which can be explained by differences between flow velocity and wave celerity and the resulting displacement of sediments within the stream. The results indicate that the first peak of the sedigraphs of natural events in this stream is indeed caused by the resuspension of stream bed sediments, accounting for up to six percent of the total sediment load depending on total flow volume.
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Zhang, B., J. L. Tang, Ch Gao i H. Zepp. "Subsurface lateral flow from hillslope and its contribution to nitrate loading in streams through an agricultural catchment during subtropical rainstorm events". Hydrology and Earth System Sciences 15, nr 10 (18.10.2011): 3153–70. http://dx.doi.org/10.5194/hess-15-3153-2011.
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Abstract. Subsurface lateral flow from agricultural hillslopes is often overlooked compared with overland flow and tile drain flow, partly due to the difficulties in monitoring and quantifying. The objectives of this study were to examine how subsurface lateral flow generated through soil pedons from cropped hillslopes and to quantify its contribution to nitrate loading in the streams through an agricultural catchment in the subtropical region of China. Profiles of soil water potential along hillslopes and stream hydro-chemographs in a trenched stream below a cropped hillslope and at the catchment outlet were simultaneously recorded during two rainstorm events. The dynamics of soil water potential showed positive matrix soil water potential over impermeable soil layer at 0.6 to 1.50 m depths during and after the storms, indicating soil water saturation and drainage processes along the hillslopes irrespective of land uses. The hydro-chemographs in the streams, one trenched below a cropped hillslope and one at the catchment outlet, showed that the concentrations of particulate nitrogen and phosphorus corresponded well to stream flow during the storm, while the nitrate concentration increased on the recession limbs of the hydrographs after the end of the storm. All the synchronous data revealed that nitrate was delivered from the cropped hillslope through subsurface lateral flow to the streams during and after the end of the rainstorms. A chemical mixing model based on electricity conductivity (EC) and H+ concentration was successfully established, particularly for the trenched stream. The results showed that the subsurface lateral flow accounted for 29% to 45% of total stream flow in the trenched stream, responsible for 86% of total NO3−-N loss (or 26% of total N loss), and for 5.7% to 7.3% of total stream flow at the catchment outlet, responsible for about 69% of total NO3−-N loss (or 28% of total N loss). The results suggest that subsurface lateral flow through hydraulically stratified soil pedons have to be paid more attention for controlling non-point source surface water pollution from intensive agricultural catchment particularly in the subtropical areas with great soil infiltration.
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Eder, A., M. Exner-Kittridge, P. Strauss i G. Blöschl. "Re-suspension of bed sediment in a small stream – results from two flushing experiments". Hydrology and Earth System Sciences Discussions 10, nr 10 (7.10.2013): 12077–104. http://dx.doi.org/10.5194/hessd-10-12077-2013.
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Abstract. Streams draining small watersheds often exhibit multiple peaking sedigraphs associated with single peaking hydrographs. The process reasons of the multiple sediment peaks are not fully understood but they may be related to the activation of different sediment sources such as the streambed itself where deposited sediments from previous events may be available for resuspension. To understand resuspension of stream bed sediments at the reach scale we artificially flooded the small stream of the HOAL Petzenkirchen catchment in Austria by pumping sediment-free water into the stream. Two short floods were produced and flow, sediment and bromide concentrations were measured at three sites with high temporal resolution. Hydrologically, the two flood events were almost identical. The peak flows decreased from 57 to 7.9 L s−1 and the flow volumes decreased from 17 to 11.3 m3 along the 590 m reach of the stream. However, a considerably smaller sediment load was resuspended and transported during the second flood due to depletion of stream bed sediments. The exception was the middle section of the stream where more sediment was transported during the second flood event which can be explained by differences between flow velocity and wave celerity and the resulting displacement of sediments within the stream. The results indicate that the first peak of the sedigraphs of natural events in this stream is indeed caused by the resuspension of streambed sediments, accounting for up to six percent of the total sediment load depending on total flow volume.
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Chester, E. T., i B. J. Robson. "Do recolonisation processes in intermittent streams have sustained effects on benthic algal density and assemblage composition?" Marine and Freshwater Research 65, nr 9 (2014): 784. http://dx.doi.org/10.1071/mf13239.
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When intermittent streams flow, benthic algae develop from both colonising propagules and regrowing dried biofilm. We aimed to determine whether colonisation processes influence algal densities and taxonomic composition beyond the period immediately following commencement of winter flows, and whether regulation modifies those processes, in the Victoria Range, Australia. Stones were placed in two unregulated streams, and upstream and downstream of weirs in three regulated streams, after dry biofilm was removed. Epilithic algae on treatment and control stones were collected after winter flows (12 weeks). Treatment effects were still apparent in one (unregulated) stream, but not in the other streams. Algal assemblages and densities upstream and downstream of weirs differed, but there was no systematic pattern among streams. In intermittent headwater streams, recolonisation processes may influence algal assemblages until spring; but in most streams, the duration of influence will be shorter, depending on the assemblage composition in regrowth and refuges, which is also shaped by conditions during the previous flow season. If the effects of regulation depend on how idiosyncratic flow regimes and assemblage compositions influence recolonisation, they may be difficult to predict. Similarly, recovery trajectories for stream communities after drought will differ among streams, depending on whether biofilm can develop during potentially short seasonal flows.
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Shabtaie, S., C. R. Bentley, R. A. Bindschadler i D. R. MacAyeal. "Mass-Balance Studies of Ice Streams A, B, and C, West Antarctica, and Possible Surging Behavior of Ice Stream Β". Annals of Glaciology 11 (1988): 137–49. http://dx.doi.org/10.3189/s0260305500006455.
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Recent airborne radar sounding has made it possible to map accurately three of the West Antarctic ice streams that flow into Ross Ice Shelf. In previous work we have shown that ice streams A and Β have negative mass balances, whereas inactive Ice Stream C has a strongly positive balance. In this paper we examine in more detail the balance of ice streams A and Β by constructing several gates across them where velocities and ice thicknesses have been measured. We then examine the net fluxes in blocks of the ice streams delimited by successive pairs of gates.Ice Stream A as a whole is apparently discharging more ice than is being accumulated in the catchment area, and currently thinning at the rate of 0.08 ± 0.03 m a−1. The situation on Ice Stream Β is more complex. We have calculated separately the fluxes from tributary ice streams Bl and B2, and examined their individual fluxes within Ice Stream Β by tracing the suture zone between them down-stream of their confluence. The flow band that is the farthest up-stream (girdle), encompassing both Ice Stream Bl and Ice Stream B2, shows a strongly negative net flux that we attribute to lateral and headward expansion of the ice streams within the band. Such expansion can occur by lateral movement of an ice-stream boundary, by temporally accelerating ice flow at the head of the ice stream, or by activation of formerly slowly moving “island” or “peninsula” ice.The imbalance in this flow band, 8 ± 2 km3 a−1 (equivalent mean rate of change in ice thickness, is nearly half of the total excess outflow for the Ice Stream Β system (20 ± 4 km3 a−1), — the remainder is mostly the difference between flow through the uppermost gate and mass input to the catchment area .When for the whole of Ice Stream Β is plotted against the distance along the entire Ice Stream B, the overall pattern appears to be of mild thinning in the catchment, intense thinning in the girdle, and thickening in the main body of the ice stream, which decreases with distance from the girdle. This global behavior is suggestive of a major transient response, resulting from either a change in the internal dynamics or an internal adjustment to a change in the external forcings. We argue that there are a number of conditions which could lead to this type of response pattern. One possibility is a surge. Although the distribution of the changes in thickness is one characteristic of a surge, we caution that this alone is not sufficient to classify the behavior as a surge. Several other possibilities that support a picture of Ice Stream Β as a system in the process of dynamic change and in unsteady state are discussed.At present, Ice Stream C and its catchment area are thickening over their entire area The present surface elevation does not suggest that Ice Stream Β has captured part of Ice Stream C. Moreover, the shut-down of Ice Stream C and the large mass imbalance of Ice Stream Β are not related.
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Shabtaie, S., C. R. Bentley, R. A. Bindschadler i D. R. MacAyeal. "Mass-Balance Studies of Ice Streams A, B, and C, West Antarctica, and Possible Surging Behavior of Ice Stream Β". Annals of Glaciology 11 (1988): 137–49. http://dx.doi.org/10.1017/s0260305500006455.
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Recent airborne radar sounding has made it possible to map accurately three of the West Antarctic ice streams that flow into Ross Ice Shelf. In previous work we have shown that ice streams A and Β have negative mass balances, whereas inactive Ice Stream C has a strongly positive balance. In this paper we examine in more detail the balance of ice streams A and Β by constructing several gates across them where velocities and ice thicknesses have been measured. We then examine the net fluxes in blocks of the ice streams delimited by successive pairs of gates. Ice Stream A as a whole is apparently discharging more ice than is being accumulated in the catchment area, and currently thinning at the rate of 0.08 ± 0.03 m a−1. The situation on Ice Stream Β is more complex. We have calculated separately the fluxes from tributary ice streams Bl and B2, and examined their individual fluxes within Ice Stream Β by tracing the suture zone between them down-stream of their confluence. The flow band that is the farthest up-stream (girdle), encompassing both Ice Stream Bl and Ice Stream B2, shows a strongly negative net flux that we attribute to lateral and headward expansion of the ice streams within the band. Such expansion can occur by lateral movement of an ice-stream boundary, by temporally accelerating ice flow at the head of the ice stream, or by activation of formerly slowly moving “island” or “peninsula” ice. The imbalance in this flow band, 8 ± 2 km3 a−1 (equivalent mean rate of change in ice thickness, is nearly half of the total excess outflow for the Ice Stream Β system (20 ± 4 km3 a−1), — the remainder is mostly the difference between flow through the uppermost gate and mass input to the catchment area . When for the whole of Ice Stream Β is plotted against the distance along the entire Ice Stream B, the overall pattern appears to be of mild thinning in the catchment, intense thinning in the girdle, and thickening in the main body of the ice stream, which decreases with distance from the girdle. This global behavior is suggestive of a major transient response, resulting from either a change in the internal dynamics or an internal adjustment to a change in the external forcings. We argue that there are a number of conditions which could lead to this type of response pattern. One possibility is a surge. Although the distribution of the changes in thickness is one characteristic of a surge, we caution that this alone is not sufficient to classify the behavior as a surge. Several other possibilities that support a picture of Ice Stream Β as a system in the process of dynamic change and in unsteady state are discussed. At present, Ice Stream C and its catchment area are thickening over their entire area The present surface elevation does not suggest that Ice Stream Β has captured part of Ice Stream C. Moreover, the shut-down of Ice Stream C and the large mass imbalance of Ice Stream Β are not related.
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ST. Germain, S. L., i B. J. Moorman. "The development of a pulsating supraglacial stream". Annals of Glaciology 57, nr 72 (13.05.2016): 31–38. http://dx.doi.org/10.1017/aog.2016.16.
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ABSTRACTSupraglacial streams are a significant part of the glacial hydrological system and important for understanding the connection between glacial hydrology and glacier dynamics. Here we determine the factors that influence the development of step-pool formation and pulsating flow in a supraglacial stream on Bylot Island, Nunavut. Results show that during the second week of a 2-week study, multiple successive rainfall events occurred, stream temperature increased and ablation decreased; which also caused stream discharge to decrease. In addition, the stream, which flowed over a 13 m high waterfall off the front of Fountain Glacier, rapidly formed 21 step-pools and began to pulsate. The pulsating phenomenon involved the complete stoppage of flow over the waterfall and the subsequent restart between 8 and 20 s later. Pulsating flow resulted from rapid changes in the streambed morphology. In particular, the formation of the step-pool sequence was caused by helical flow around meander bends and hydrologically induced slippage along transverse shear planes, evidenced by observations of high-pressure artesian flow from transverse fractures. Contrary to previous literature, this study shows that high discharge is not necessarily the cause of step-pool formation and pulsating flow within supraglacial streams.
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Marensi, Elena, Pierre Ricco i Xuesong Wu. "Nonlinear unsteady streaks engendered by the interaction of free-stream vorticity with a compressible boundary layer". Journal of Fluid Mechanics 817 (15.03.2017): 80–121. http://dx.doi.org/10.1017/jfm.2017.88.
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The nonlinear response of a compressible boundary layer to unsteady free-stream vortical fluctuations of the convected-gust type is investigated theoretically and numerically. The free-stream Mach number is assumed to be of $O(1)$ and the effects of compressibility, including aerodynamic heating and heat transfer at the wall, are taken into account. Attention is focused on low-frequency perturbations, which induce strong streamwise-elongated components of the boundary-layer disturbances, known as streaks or Klebanoff modes. The amplitude of the disturbances is intense enough for nonlinear interactions to occur within the boundary layer. The generation and nonlinear evolution of the streaks, which acquire an $O(1)$ magnitude, are described on a self-consistent and first-principle basis using the mathematical framework of the nonlinear unsteady compressible boundary-region equations, which are derived herein for the first time. The free-stream flow is studied by including the boundary-layer displacement effect and the solution is matched asymptotically with the boundary-layer flow. The nonlinear interactions inside the boundary layer drive an unsteady two-dimensional flow of acoustic nature in the outer inviscid region through the displacement effect. A close analogy with the flow over a thin oscillating airfoil is exploited to find analytical solutions. This analogy has been widely employed to investigate steady flows over boundary layers, but is considered herein for the first time for unsteady boundary layers. In the subsonic regime the perturbation is felt from the plate in all directions, while at supersonic speeds the disturbance only propagates within the dihedron defined by the Mach line. Numerical computations are performed for carefully chosen parameters that characterize three practical applications: turbomachinery systems, supersonic flight conditions and wind tunnel experiments. The results show that nonlinearity plays a marked stabilizing role on the velocity and temperature streaks, and this is found to be the case for low-disturbance environments such as flight conditions. Increasing the free-stream Mach number inhibits the kinematic fluctuations but enhances the thermal streaks, relative to the free-stream velocity and temperature respectively, and the overall effect of nonlinearity becomes weaker. An abrupt deviation of the nonlinear solution from the linear one is observed in the case pertaining to a supersonic wind tunnel. Large-amplitude thermal streaks and the strong abrupt stabilizing effect of nonlinearity are two new features of supersonic flows. The present study provides an accurate signature of nonlinear streaks in compressible boundary layers, which is indispensable for the secondary instability analysis of unsteady streaky boundary-layer flows.
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Fletcher, Tim D., Geoff Vietz i Christopher J. Walsh. "Protection of stream ecosystems from urban stormwater runoff". Progress in Physical Geography: Earth and Environment 38, nr 5 (27.05.2014): 543–55. http://dx.doi.org/10.1177/0309133314537671.
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There is now widespread recognition of the degrading influence of urban stormwater runoff on stream ecosystems and of the need to mitigate these impacts using stormwater control measures. Unfortunately, however, understanding of the flow regime requirements to protect urban stream ecosystems remains poor, with a focus typically on only limited aspects of the flow regime. We review recent literature discussing ecohydrological approaches to managing urban stormwater and, building on the natural flow paradigm, identify ecologically relevant flow metrics that can be used to design stormwater control measures to restore more natural magnitude, duration, timing, frequency and variability of both high and low flows. Such an approach requires a consideration of the appropriate flow and water quality required by the receiving water, and the application of techniques at or near source to meet appropriate flow regime and water quality targets. The ecohydrological approach provides multiple benefits beyond the health of urban streams, including flood mitigation, water supply augmentation, human thermal comfort, and social amenity. There are, however, uncertainties that need to be addressed. Foremost is the need to define ecologically and geomorphically appropriate flow regimes for channels which have already been modified by existing land use. Given the excess of water generated by impervious surfaces, there is also an urgent need to test the feasibility of the natural flow paradigm in urban streams, for example using catchment-scale trials.
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Balcerak, Ernie. "Modeling ice stream flow". Eos, Transactions American Geophysical Union 92, nr 49 (6.12.2011): 464. http://dx.doi.org/10.1029/2011eo490018.
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Cover, Matthew R., Juan A. de la Fuente i Vincent H. Resh. "Catastrophic disturbances in headwater streams: the long-term ecological effects of debris flows and debris floods in the Klamath Mountains, northern California". Canadian Journal of Fisheries and Aquatic Sciences 67, nr 10 (październik 2010): 1596–610. http://dx.doi.org/10.1139/f10-079.
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Debris flows and debris floods are catastrophic disturbances in steep, mountainous landscapes throughout the world, but little is known about the long-term ecological effects of these events on headwater streams. In 10 basins (10–20 km2) in the Klamath Mountains, northern California, USA, we used a space-for-time substitution to infer the long-term (10–100 years) effects of debris flows on stream ecosystem structure. Debris flows mobilized sediment and wood and removed riparian vegetation from large portions of channel networks. Stream temperatures were significantly warmer in streams that had recent debris flows (<10 years ago). Large wood, benthic organic matter, and detritivorous stoneflies were all very sparse in recent debris flow streams, suggesting that allochthonous energy pathways took decades to recover. Rainbow trout ( Oncorhynchus mykiss ) were abundant in recent debris flow streams, but populations of other vertebrates such as coastal giant salamander ( Dicamptodon tenebrosus ) and coastal tailed frog ( Ascaphus truei ) were virtually absent. Increased frequencies of catastrophic debris flows associated with forest management practices can have significant negative impacts on aquatic biodiversity in forested, mountainous landscapes.
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Szybowski, Daniel. "LEGAL DILEMMAS OF STREAMING PROPERTY TAX LOGIC". International Journal of New Economics and Social Sciences 7, nr 1 (29.06.2018): 111–12. http://dx.doi.org/10.5604/01.3001.0012.2691.
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Taxes have the property that they constitute a stream because they are paid by subtracting parts of various other streams generated by business entities. When paying tax, they must pay part of their income - in the case of direct tax or expenditure - in the case of indirect tax; we count both volumes as economic categories called streams. These tax characteristics are called the tax logic stream. The conclusion about the flow of tax is in fact trivial, but fraught with serious consequences - not always noticed. Since the tax itself is a stream, firstly, in its creation as a category of public finances, one should always determine the right reference to the value of some other stream; it should be created in relation to this other stream, for example in terms of income, because only the stream is an effective source of income. The tax is a cash stream and only to the cash flow must be referred.
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Phani Kumar, P., A. C. Mandal i J. Dey. "Effect of a mesh on boundary layer transitions induced by free-stream turbulence and an isolated roughness element". Journal of Fluid Mechanics 772 (7.05.2015): 445–77. http://dx.doi.org/10.1017/jfm.2015.203.
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Streamwise streaks, their lift-up and streak instability are integral to the bypass transition process. An experimental study has been carried out to find the effect of a mesh placed normal to the flow and at different wall-normal locations in the late stages of two transitional flows induced by free-stream turbulence (FST) and an isolated roughness element. The mesh causes an approximately 30 % reduction in the free-stream velocity, and mild acceleration, irrespective of its wall-normal location. Interestingly, when located near the wall, the mesh suppresses several transitional events leading to transition delay over a large downstream distance. The transition delay is found to be mainly caused by suppression of the lift-up of the high-shear layer and its distortion, along with modification of the spanwise streaky structure to an orderly one. However, with the mesh well away from the wall, the lifted-up shear layer remains largely unaffected, and the downstream boundary layer velocity profile develops an overshoot which is found to follow a plane mixing layer type profile up to the free stream. Reynolds stresses, and the size and strength of vortices increase in this mixing layer region. This high-intensity disturbance can possibly enhance transition of the accelerated flow far downstream, although a reduction in streamwise turbulence intensity occurs over a short distance downstream of the mesh. However, the shape of the large-scale streamwise structure in the wall-normal plane is found to be more or less the same as that without the mesh.
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Song, S. J., i M. Martinez-Sanchez. "Rotordynamic Forces Due to Turbine Tip Leakage: Part I—Blade Scale Effects". Journal of Turbomachinery 119, nr 4 (1.10.1997): 695–703. http://dx.doi.org/10.1115/1.2841179.
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An experimental and theoretical investigation has been conducted on rotordynamic forces due to nonaxisymmetric turbine tip leakage effects. This paper presents an actuator disk model that describes the flow response to a finite clearance at the rotor tip. The model simplifies the flow field by assuming that the radially uniform flow splits into two streams as it goes through the rotor. The stream associated with the tip clearance, or the underturned stream, induces radially uniform unloading of the rest of the flow, called the bladed stream. Thus, a shear layer forms between the two streams. The fraction of each stream and the strength of shear layer between the two are found as functions of the turbine loading and flow parameters without resorting to empirical correlations. The results show that this model’s efficiency predictions compare favorably with the experimental data and predictions from various correlations. A companion paper builds on this analysis to yield a model of the three-dimensional disturbances around an offset turbine and to predict the subsequent cross forces.
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Robison, E. George, i Robert L. Beschta. "Characteristics of Coarse Woody Debris for Several Coastal Streams of Southeast Alaska, USA". Canadian Journal of Fisheries and Aquatic Sciences 47, nr 9 (1.09.1990): 1684–93. http://dx.doi.org/10.1139/f90-193.
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Coarse woody debris (> 0.2 m in diameter and 1.5 m long) was measured along five undisturbed low-gradient stream reaches; volume, decay class, and horizontal orientation in relation to channel flow of first-, second-, third-, and fourth-order coastal streams were determined. Debris was also classified into four influence zones based on stream hydraulics and fish habitat. Average debris length, diameter, and volume per piece increased with stream size. Eighty percent of debris volume of the first-order and the smaller second-order streams was suspended above or lying outside the bankfull channel, while less than 40% was similarly positioned in the fourth-order stream. Approximately one-third of all debris was oriented perpendicular to stream flow, regardless of stream size. First-, second-, and third-order streams had a higher proportion of recent debris in the channel than the fourth-order stream ([Formula: see text]19 vs. 8%), most new debris being attributable to a major 1984 windstorm. Tree blowdown had a major influence on debris distribution along the smaller stream reaches. Debris jams and accumulations in the largest stream were formed from floated debris. These characterizations are useful for evaluating the distribution and amount of woody debris associated with land-management activities.
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Silvis, Joshua M., Brian C. Benson, Michael L. Shema i Mark R. Haibach. "A Quantitative Approach to Evaluate Changes in Hydrologic Conditions of Headwater Streams: A Case Study of Restoration and Recovery Following Longwall Mine Subsidence". Hydrology 6, nr 3 (8.08.2019): 67. http://dx.doi.org/10.3390/hydrology6030067.
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Mine subsidence can induce streambed ruptures that pirate surface water from a stream. Current understanding of the effects of longwall mining on streams lacks rigorous analytical approaches to detect hydrologic effects and does not consider the efficacy of streambed restoration techniques to address flow disruption. CONSOL Pennsylvania Coal Company, LLC (CPCC) collected and analyzed pre-mining, post-mining, and post-restoration stream discharge and flow duration data from 51.9 km of streams overlying its Bailey Mine to define pre-mining flow variability, detect post-mining changes, and evaluate post-intervention flow recovery. The primary intervention method for restoring stream flow was bedrock permeation grouting. Pre-mine and post-mine baseflow data were compared using both parametric and non-parametric hypothesis testing, which yielded similar results. An environmental flow assessment method for headwater streams using probabilistic risk assessment and correlation analysis of change threshold criteria was developed to differentiate hydrologic change as induced by mine subsidence or explained by natural variability. The method is objective, pragmatic, and statistically delimited.
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Paredes, Pedro, Meelan M. Choudhari i Fei Li. "Instability wave–streak interactions in a high Mach number boundary layer at flight conditions". Journal of Fluid Mechanics 858 (6.11.2018): 474–99. http://dx.doi.org/10.1017/jfm.2018.744.
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The interaction of stationary streaks undergoing non-modal growth with modally unstable instability waves in a high Mach number boundary-layer flow is studied using numerical computations. The geometry and flow conditions are selected to match a relevant trajectory location from the ascent phase of the HIFiRE-1 flight experiment; namely, a $7^{\circ }$ half-angle, circular cone with $2.5$ mm nose radius, free-stream Mach number equal to $5.30$, unit Reynolds number equal to $13.42~\text{m}^{-1}$ and wall-to-adiabatic temperature ratio of approximately $0.35$ over most of the vehicle. This paper investigates the nonlinear evolution of initially linear optimal disturbances that evolve into finite-amplitude streaks, followed by an analysis of the modal instability characteristics of the perturbed, streaky boundary-layer flow. The investigation is performed with a stationary, full Navier–Stokes equations solver and the plane-marching parabolized stability equations (PSE), in conjunction with partial-differential-equation-based planar eigenvalue analysis. The overall effect of streaks is to reduce the peak amplification factors of instability waves, indicating a possible downstream shift in the onset of laminar–turbulent transition. The present study confirms previous findings that the mean-flow distortion of the nonlinear streak perturbation reduces the amplification rates of the Mack-mode instability. More importantly, however, the present results demonstrate that the spanwise varying component of the streak can produce a larger effect on the Mack-mode amplification. The analysis of planar and oblique Mack-mode waves modulated by the presence of the streaks shows that the planar Mack mode still dominates the instability characteristics of the flow. The study with selected azimuthal wavenumbers for the stationary streaks reveals that a wavenumber of approximately $1.4$ times larger than the optimal wavenumber is more effective in stabilizing the planar Mack-mode instabilities. In the absence of unstable first-mode waves for the present cold-wall condition, transition onset is expected to be delayed until the peak streak amplitude increases to nearly 35 % of the free-stream velocity, when intrinsic instabilities of the boundary-layer streaks begin to dominate the transition process. For streak amplitudes below that limit a significant net stabilization is achieved, yielding a potential transition delay that can exceed 100 % of the length of the laminar region in the uncontrolled case.
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Chen, X. H., W. H. Dong, G. X. Ou, Z. W. Wang i C. Liu. "Opposite distribution pattern of streambed hydraulic conductivity in losing and gaining stream reaches". Hydrology and Earth System Sciences Discussions 10, nr 2 (4.02.2013): 1693–723. http://dx.doi.org/10.5194/hessd-10-1693-2013.
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Abstract. In gaining streams, groundwater seeps out into streams. In losing streams, stream water moves into groundwater systems. The flow moving through the streambed sediments under these two types of flow conditions are generally in opposite directions (upward vs. downward). The two opposite flow mechanism will affect the pore size and fine particle content of streambeds. It is thus very likely that the opposite flow conditions affect the streambed hydraulic conductivity. However, comparisons of the hydraulic conductivity (K) of streambeds for losing and gaining streams are not well documented. In this study, we examined the K distribution patterns of sediments below the channel surface or stream banks for the Platte River and its tributaries in Nebraska, USA. Two contrast vertical distribution patterns were observed from the test sites. In gaining reaches, hydraulic conductivity of streambed decreases with the depth of the sediment cores. In losing reaches, hydraulic conductivity increases with the depth of the sediment cores. This contrast patterns in the two types of streams were mostly attributed to flow directions during stream water and groundwater exchanges. In losing reaches, downward movement of water brought fine particle into the otherwise coarse sediment matrix, partially silting the pores. For gaining reaches, upward flow winnows fine particles, increasing the pore spacing in the top parts of streambed, leading to higher hydraulic conductivity in shallower parts of streambeds. These flux directions can impact K values to depth of greater than 5 m. At each test sites, in-situ permeameter tests were conducted to measure the K values of the top streambed layer. Statistical analyses indicated that K values from the sites under losing stream condition are significantly different from the K values from the sites under gaining stream condition.
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Brinkerhoff, Joshua R., i Metin I. Yaras. "Numerical investigation of transition in a boundary layer subjected to favourable and adverse streamwise pressure gradients and elevated free stream turbulence". Journal of Fluid Mechanics 781 (16.09.2015): 52–86. http://dx.doi.org/10.1017/jfm.2015.457.
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Laminar-to-turbulent transition of a boundary layer subjected to streamwise pressure gradients and elevated free stream turbulence is computed through direct numerical simulation. The streamwise pressure distribution and elevated free stream turbulence levels mimic the conditions present on the suction side of highly-cambered airfoils. Longitudinal streamwise streaks form in the laminar boundary layer through the selective inclusion of low-frequency disturbances from the free stream turbulence. The spanwise spacing normalized by local inner variables indicates stabilization of the streaks occurs by the favourable pressure gradient and prevents the development of secondary streak instability modes until downstream of the suction peak. Two distinct processes are found to trigger transition to turbulence in the adverse pressure gradient region of the flow. One involves the development of varicose secondary instability of individual low-speed streaks that results in their breakdown and the formation and growth of discrete turbulent spots. The other involves a rapid amplification of free stream disturbances in the inflectional boundary layer in the adverse pressure gradient region that results in a largely homogeneous breakdown to turbulence across the span. The effect of high-frequency free stream disturbances on the streak secondary instability and on the nonlinear processes within the growing turbulent spot are analysed through the inviscid transport of instantaneous vorticity. The results suggest that free stream turbulence contributes to the growth of the turbulent spot by generating large strain rates that activate vortex-stretching and tilting processes within the spot.
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Yuan, Yao, Dalin Zhang, Lin Tian i Jinglin Shi. "Research on the Extension of SCTP Protocol on the Heterogeneous Wireless Network". International Journal of Interdisciplinary Telecommunications and Networking 8, nr 2 (kwiecień 2016): 69–87. http://dx.doi.org/10.4018/ijitn.2016040107.
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As a promising candidate of general-purpose transport layer protocol, the Stream Control Transmission Protocol (SCTP) has its new features such as multi-homing and multi-streaming. SCTP association can make concurrent multi-path transfer an appealing candidate to satisfy the ever increasing user demands for bandwidth by using Multi-homing feature. And multiple streams provide an aggregation mechanism to accommodate heterogeneous objects, which belong to the same application but may require different QoS from the network. In this paper, the authors introduce WM2-SCTP (Wireless Multi-path Multi-flow - Stream Control Transmission Protocol), a transport layer solution for concurrent multi-path transfer with parallel sub-flows. WM2-SCTP aims at exploiting SCTP's multi-homing and multi-streaming capability by grouping SCTP streams into sub-flows based on their required QoS and selecting best paths for each sub-flow to improve data transfer rates. The results show that under different scenarios WM2-SCTP is able to support QoS among the SCTP stream, and it achieves a better throughput.
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Steiness, Jessen, Spitilli, van’t Veen, Højberg i Engesgaard. "The Role of Management of Stream–Riparian Zones on Subsurface–Surface Flow Components". Water 11, nr 9 (12.09.2019): 1905. http://dx.doi.org/10.3390/w11091905.
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A managed riparian lowland in a glacial landscape (Holtum catchment, Denmark) was studied to quantify the relative importance of subsurface and surface flow to the recipient stream. The hydrogeological characterization combined geoelectrical methods, lithological logs, and piezometric heads with monthly flow measurements of springs, a ditch, and a drain, to determine seasonality and thereby infer flow paths. In addition, groundwater discharge through the streambed was estimated using temperature and water-stable isotopes as tracers. The lowland received large groundwater inputs with minimal seasonal variations from adjacent upland aquifers. This resulted in significant amounts of groundwater-fed surface flow to the stream, via man-made preferential flow paths comprising ditches, drainage systems, and a pond, and via two natural springs. Roughly, two thirds of the stream gain was due to surface flow to the stream, mainly via anthropogenic alterations. In contrast, direct groundwater discharge through the streambed accounted for only 4% of the stream flow gain, although bank seepage (not measured) to the straightened and deepened stream potentially accounted for an additional 17%. Comparison to analogous natural flow systems in the catchment substantiate the impact of anthropogenic alterations of riparian lowlands for the subsurface and surface flow components to their streams.
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Poff, N. LeRoy, i J. V. Ward. "Implications of Streamflow Variability and Predictability for Lotic Community Structure: A Regional Analysis of Streamflow Patterns". Canadian Journal of Fisheries and Aquatic Sciences 46, nr 10 (1.10.1989): 1805–18. http://dx.doi.org/10.1139/f89-228.
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Long-term discharge records (17–81 yr) of 78 streams from across the continental United States were analyzed to develop a general quantitative characterization of streamflow variability and predictability. Based on (1) overall flow variability, (2) flood regime patterns, and (3) extent of intermittency, 11 summary statistics were derived from the entire record for each stream. Using a nonhierarchical clustering technique, nine stream types were identified: harsh intermittent, intermittent flashy, intermittent runoff, perennial flashy, perennial runoff, snowmelt, snow + rain, winter rain, and mesic groundwater. Stream groups separated primarily on combined measures of intermittency, flood frequency, flood predictability, and overall flow predictability, and they showed reasonable geographic affiliation. A conceptual model that incorporates the nine stream clusters in a hierarchical structure is presented. Also, the positions of the 78 streams in a continuous three-dimensional flow space illustrate the wide range of ecologically important hydrologic variability that can constrain ecological and evolutionary processes in streams. Long-term daily streamflow records are a rich source of information with which to evaluate temporal and spatial patterns of lotic environments across many physiographic and ecographic regions. Relative positions of streams in flow space provide a conceptual framework for evaluating a priori the relative importance of abiotic and biotic factors in regulating population and community processes and patterns.
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Brouard, Etienne, i Patrick Lajeunesse. "Ice-stream flow switching by up-ice propagation of instabilities along glacial marginal troughs". Cryosphere 13, nr 3 (22.03.2019): 981–96. http://dx.doi.org/10.5194/tc-13-981-2019.
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Abstract. Ice-stream networks constitute the arteries of ice sheets through which large volumes of glacial ice are rapidly delivered from the continent to the ocean. Modifications in ice-stream networks have a major impact on ice sheet mass balance and global sea level. Reorganizations in the drainage network of ice streams have been reported in both modern and paleo-ice sheets and usually result in ice streams switching their trajectory and/or shutting down. While some hypotheses for the reorganization of ice streams have been proposed, the mechanisms that control the switching of ice streams remain poorly understood and documented. Here, we interpret a flow switch in an ice-stream system that occurred prior to the last glaciation on the northeastern Baffin Island shelf (Arctic Canada) through glacial erosion of a marginal trough, i.e., deep parallel-to-coast bedrock moats located up-ice of a cross-shelf trough. Shelf geomorphology imaged by high-resolution swath bathymetry and seismo-stratigraphic data in the area indicate the extension of ice streams from Scott and Hecla & Griper troughs towards the interior of the Laurentide Ice Sheet. Up-ice propagation of ice streams through a marginal trough is interpreted to have led to the piracy of the neighboring ice catchment that in turn induced an adjacent ice-stream flow switch and shutdown. These results suggest that competition for ice discharge between the two ice streams, which implies piracy of ice drainage basins via marginal troughs, was the driving mechanism behind ice flow switching. In turn, the enlargement of the ice catchment by piracy increased the volume and discharge of Scott Ice Stream, allowing it to erode deeper and flow farther on the continental shelf. Similar trough systems observed on many other glaciated continental shelves may be the product of such competition for ice discharge between catchments.
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SCHRADER, L. U., L. BRANDT, C. MAVRIPLIS i D. S. HENNINGSON. "Receptivity to free-stream vorticity of flow past a flat plate with elliptic leading edge". Journal of Fluid Mechanics 653 (27.04.2010): 245–71. http://dx.doi.org/10.1017/s0022112010000376.
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Receptivity of the two-dimensional boundary layer on a flat plate with elliptic leading edge is studied by numerical simulation. Vortical perturbations in the oncoming free stream are considered, impinging on two leading edges with different aspect ratio to identify the effect of bluntness. The relevance of the three vorticity components of natural free-stream turbulence is illuminated by considering axial, vertical and spanwise vorticity separately at different angular frequencies. The boundary layer is most receptive to zero-frequency axial vorticity, triggering a streaky pattern of alternating positive and negative streamwise disturbance velocity. This is in line with earlier numerical studies on non-modal growth of elongated structures in the Blasius boundary layer. We find that the effect of leading-edge bluntness is insignificant for axial free-stream vortices alone. On the other hand, vertical free-stream vorticity is also able to excite non-modal instability in particular at zero and low frequencies. This mechanism relies on the generation of streamwise vorticity through stretching and tilting of the vertical vortex columns at the leading edge and is significantly stronger when the leading edge is blunt. It can thus be concluded that the non-modal boundary-layer response to a free-stream turbulence field with three-dimensional vorticity is enhanced in the presence of a blunt leading edge. At high frequencies of the disturbances the boundary layer becomes receptive to spanwise free-stream vorticity, triggering Tollmien–Schlichting (T-S) modes and receptivity increases with leading-edge bluntness. The receptivity coefficients to free-stream vortices are found to be about 15% of those to sound waves reported in the literature. For the boundary layers and free-stream perturbations considered, the amplitude of the T-S waves remains small compared with the low-frequency streak amplitudes.
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Cornacchia, Loreta, Geraldene Wharton, Grieg Davies, Robert C. Grabowski, Stijn Temmerman, Daphne van der Wal, Tjeerd J. Bouma i Johan van de Koppel. "Self-organization of river vegetation leads to emergent buffering of river flows and water levels". Proceedings of the Royal Society B: Biological Sciences 287, nr 1931 (15.07.2020): 20201147. http://dx.doi.org/10.1098/rspb.2020.1147.
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Global climate change is expected to impact hydrodynamic conditions in stream ecosystems. There is limited understanding of how stream ecosystems interact and possibly adapt to novel hydrodynamic conditions. Combining mathematical modelling with field data, we demonstrate that bio-physical feedback between plant growth and flow redistribution triggers spatial self-organization of in-channel vegetation that buffers for changed hydrological conditions. The interplay of vegetation growth and hydrodynamics results in a spatial separation of the stream into densely vegetated, low-flow zones divided by unvegetated channels of higher flow velocities. This self-organization process decouples both local flow velocities and water levels from the forcing effect of changing stream discharge. Field data from two lowland, baseflow-dominated streams support model predictions and highlight two important stream-level emergent properties: vegetation controls flow conveyance in fast-flowing channels throughout the annual growth cycle, and this buffering of discharge variations maintains water depths and wetted habitat for the stream community. Our results provide important evidence of how plant-driven self-organization allows stream ecosystems to adapt to changing hydrological conditions, maintaining suitable hydrodynamic conditions to support high biodiversity.
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Dolzhanskii, F. V., V. A. Krymov i D. Yu Manin. "An advanced experimental investigation of quasi-two-dimensional shear flow". Journal of Fluid Mechanics 241 (sierpień 1992): 705–22. http://dx.doi.org/10.1017/s0022112092002209.
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Forced shear flows in a thin layer of an incompressible viscous fluid are studied experimentally. Streak photographs are used to obtain the stream function of vortical flow patterns arising after the primary shear flow loses stability. Various flow characteristics are determined and results are compared to the stability theory of quasi-two-dimensional flows. The applicability of the quasi-two-dimensional approximation is directly verified and the possibility of reconstruction of the driving force from the secondary flow pattern is demonstrated.
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Truffer, Martin, i Keith A. Echelmeyer. "Of isbræ and ice streams". Annals of Glaciology 36 (2003): 66–72. http://dx.doi.org/10.3189/172756403781816347.
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AbstractFast-flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of 100 or more. Several mechanisms for fast ice-stream flow have been identified, leading to a spectrum of different ice-stream types. In this paper we discuss the two end members of this spectrum, which we term the “ice-stream” type (represented by the Siple Coast ice streams in West Antarctica) and the “isbræ” type (represented by Jakobshavn Isbræ in Greenland). The typical ice stream is wide, relatively shallow (∼1000 m), has a low surface slope and driving stress (∼10 kPa), and ice-stream location is not strongly controlled by bed topography. Fast flow is possible because the ice stream has a slippery bed, possibly underlain by weak, actively deforming sediments. The marginal shear zones are narrow and support most of the driving stress, and the ice deforms almost exclusively by transverse shear. The margins seem to be inherently unstable; they migrate, and there are plausible mechanisms for such ice streams to shut down. The isbræ type of ice stream is characterized by very high driving stresses, often exceeding 200 kPa. They flow through deep bedrock channels that are significantly deeper than the surrounding ice, and have steep surface slopes. Ice deformation includes vertical as well as lateral shear, and basal motion need not contribute significantly to the overall motion. The marginal shear zone stend to be wide relative to the isbræ width, and the location of isbræ and its margins is strongly controlled by bedrock topography. They are stable features, and can only shut down if the high ice flux cannot be supplied from the adjacent ice sheet. Isbræs occur in Greenland and East Antarctica, and possibly parts of Pine Island and Thwaites Glaciers, West Antarctica. In this paper, we compare and contrast the two types of ice streams, addressing questions such as ice deformation, basal motion, subglacial hydrology, seasonality of ice flow, and stability of the ice streams.
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Tang, J., B. Zhang, C. Gao i H. Zepp. "Subsurface lateral flow from hillslope and its contribution to nitrate loading in the streams during typical storm events in an agricultural catchment". Hydrology and Earth System Sciences Discussions 8, nr 2 (27.04.2011): 4151–93. http://dx.doi.org/10.5194/hessd-8-4151-2011.
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Abstract. Compared with overland flow from agricultural hillslopes, subsurface lateral flow is often overlooked partly due to monitoring difficulties and the lack of quantitative identification its role in nutrient delivery to surface water. The objectives of this study were to examine how subsurface lateral flow generates from hillslopes to streams and to quantify its contribution to nutrient loading in streams. Hillslope hydrology and stream hydrology were simultaneously monitored during two typical storms and subsurface flow was separated by chemical mixing model. Positive soil water potential at the soil depths from 0.60 to 1.50 m was observed at the middle course of the storm events, suggesting soil water was saturated following the storms and the drained after the end of the storms. The hydro-chemographs in the stream in a trench below a hillslope showed that suspended sediment, particulate N and P were dominant in the stream during the storms, while after the end of the rainstorms the nitrate concentration and electricity conductivity (EC) in the stream increased with time on the recession limbs of the hydrographs. Meanwhile, a rebound or delayed curve appeared on the recession limbs for several hours immediately after the end of rainstorms. All the synchronous data confirmed nitrate was delivered from the hillslope through subsurface lateral flow to the streams even after the end of rainstorms. A chemical mixing model based on EC and pH showed that the subsurface lateral flow during the rainstorm events accounted for 29% to 45% of the stream flow and about 86% of total NO3−-N loss (or 26% of total N loss) from the peanut hillslope and for 5.7% to 7.3% of the stream flow about 69% of total NO3−-N loss (or 28% of total N loss) from the catchment outlet. The results suggest that subsurface lateral flow generated within a shallow soil profile have to be paid more attention for controlling non-point source surface water pollution from intensive agricultural catchment.
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Merritt, Angela, Belize Lane i Charles Hawkins. "Classification and Prediction of Natural Streamflow Regimes in Arid Regions of the USA". Water 13, nr 3 (1.02.2021): 380. http://dx.doi.org/10.3390/w13030380.
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Understanding how natural variation in flow regimes influences stream ecosystem structure and function is critical to the development of effective stream management policies. Spatial variation in flow regimes among streams is reasonably well understood for streams in mesic regions, but a more robust characterization of flow regimes in arid regions is needed, especially to support biological monitoring and assessment programs. In this paper, we used long-term (41 years) records of mean daily streamflow from 287 stream reaches in the arid and semi-arid western USA to develop and compare several alternative flow-regime classifications. We also evaluated how accurately we could predict the flow-regime classes of ungauged reaches. Over the 41-year record examined (water years 1972–2013), the gauged reaches varied continuously from always having flow > zero to seldom having flow. We predicted ephemeral and perennial reaches with less error than reaches with an intermediate number of zero-flow days or years. We illustrate application of our approach by predicting the flow-regime classes at ungauged reaches in Arizona, USA. Maps based on these predictions were generally consistent with qualitative expectations of how flow regimes vary spatially across Arizona. These results represent a promising step toward more effective assessment and management of streams in arid regions.