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Upstream Side (upstream + side)

Distribution by Scientific Domains
Earth and Environmental Science60%

Selected Abstracts

Flow reversal over a natural pool,riffle sequence: a computational study

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2003
Zhixian Cao
Abstract A computational study is presented on the hydraulics of a natural pool,rif,e sequence composed of mixed cobbles, pebbles and sand in the River Lune, northern England. A depth-averaged two-dimensional numerical model is employed, calibrated with observed data at the ,eld site. From the computational outputs, the occurrence of longitudinally double peak zones of bed shear stress and velocity is found. In particular, at low discharge there exists a primary peak zone of bed shear stress and velocity at the rif,e tail in line with the local maximum energy slope, in addition to a secondary peak at the pool head. As discharge increases, the primary peak at the rif,e tail at low ,ow moves toward the upstream side of the rif,e along with the maximum energy slope, showing progressive equalization to the surrounding hydraulic pro,les. Concurrently, the secondary peak, due to channel constriction, appears to stand at the pool head, with its value increasing with discharge and approaching or exceeding the primary peak over the rif,e. The existence of ,ow reversal is demonstrated for this speci,c case, which is attributable to channel constriction at the pool head. A dynamic equilibrium model is presented to reconstruct the pool,rif,e morphology. A series of numerical modelling exercises demonstrates that the pool,rif,e morphology is more likely produced by shallow ,ows concentrated with coarse sediments than deep ,ows laden with low concentrations of ,ne sediments. It is concluded that channel constriction can, but may not necessarily, lead to competence reversal, depending on channel geometry, ,ow discharge and sediment properties. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Contradictory results from different methods for measuring direction of insect flight

FRESHWATER BIOLOGY, Issue 10 2004
Kate H. Macneale
Summary 1. Stream ecologists have been puzzled by the apparent paradox that invertebrate populations persist in headwater streams despite the high frequency with which individuals drift downstream. To resolve this ,drift paradox', directions and distances of both larval and adult movement must be identified. Using over 50 interception traps in combination with results from several mark,capture experiments using 15N as a label, we tested the assumption that interception traps accurately represent the ultimate direction of adult insect flight. 2. In several streams in the Hubbard Brook Experimental Forest, 76% of 15N-labelled stoneflies (Leuctra ferruginea) had flown upstream from where they emerged to where they were captured. In contrast, over 60% of stoneflies were flying downstream when captured, i.e. on the upstream side of an interception trap. 3. The instantaneous direction, as indicated by the side of the interception trap on which they were captured, indicated the ultimate flight direction for fewer than 1/3 of the individuals captured. Thus, such traps did not accurately reflect the ultimate flight patterns of individuals, as indicated by mark,capture data. 4. Conclusions drawn from interception trap counts regarding the direction of movement and the distribution and persistence of populations may need to be re-evaluated. We suggest that better tracking methods, including mass mark,capture studies using stable isotopes, be used to evaluate the potentially complex patterns of adult insect movement and the consequences of that movement for individuals and populations. [source]

Föhn as a response to changing upstream and downstream air masses

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 635 2008
Georg J. Mayr
Abstract Observations of föhn from the field phase of the Mesoscale Alpine Programme (MAP) are used to study how differences between the air masses upstream and downstream of the central Alpine crest determine whether the flow can descend to the lee as either shallow föhn, when it passes through passes in the mountains, or deep föhn, when it overflows the Alpine crest. First, the föhn case of 30 October 1999 is examined using ECMWF analyses and radiosonde data at various upstream and downstream locations. Additional measurements from aircraft, dropsondes, an instrumented car and automatic weather stations are then used for a detailed study of the föhn flow across the Brenner Pass. Advection of cold air around the eastern edges of the Alps and warm air around the western edge of the Alps ahead of a synoptic ridge set up a reservoir of colder air on the south side of the Alps and a reservoir of warmer air to the north. The depth to where the air was colder on the southern side was sufficient for a shallow föhn to flow through the pass. After the passage of the ridge axis, synoptic cold air advection provided another source of colder air, this time from the southwest, growing deeper with time and having a synoptically imposed cross-barrier flow component. The maximum depth to where the air upstream was colder than downstream extended just above the peaks of the highest mountains. An analysis of the detailed measurements across the Brenner Pass showed that this depth was also the top of the layer that descended and accelerated down the lee slopes of the Wipp Valley. Upstream, air above the föhn layer had an even stronger cross-barrier component yet did not descend because it did not have lower potential temperatures than the downstream side at that level. Deep föhn never developed. An examination of other well-documented MAP föhn cases confirmed the conclusion from the 30 October event that shallow and deep föhns , at least for the central Alps , are mostly a response to differences in air masses between the upstream and downstream side. A cross-barrier component of the flow was only a modification but in itself not sufficient to cause the flow to both descend and accelerate down the lee slope, unless potential temperatures on the upstream side were lower in this layer than on the downstream side. Copyright © 2008 Royal Meteorological Society [source]

The effect of rotation on the pressure drag force produced by flow around long mountain ridges

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 608 2005
Helen Wells
Abstract The impact of rotation on the orographic drag experienced by air flowing around a wide mountain is investigated. The work builds on numerical modelling studies performed by Ólafsson and Bougeault, who investigated the effect of rotation and surface friction on the drag experienced by flow around a single elongated mountain perpendicular to the direction of the flow. The region of parameter space they explored is extended by performing a series of idealized model experiments with a larger range of ridge lengths. The drag force in these simulations is compared with the predictions of a heuristic flow-blocking model devised by Shutts. The results show that Shutts's model overestimates the effect of rotation upon the drag force. However we find that Shutts's model predicts both the drag force exerted on the upstream side of the ridge and the upstream features reasonably well. Finally the implications of the results for NWP parametrizations of subgrid-scale orographic drag are discussed. Copyright © 2005 Royal Meteorological Society [source]

Interest of industrial actors in biorefinery concepts in Europe

BIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 3 2009
Klaus Menrad
Abstract To satisfy the rising demand for agricultural and forestry products it is becoming more and more important to use biomass as efficiently as possible. One way of achieving that goal is to implement biorefinery systems in which biomass can be utilized entirely by conversion through multiple processes into a number of valuable products. To pursue the implementation of biorefinery systems, it is important to know to what extent the industry is interested in such concepts. This perspective deals with the results of a cross-European survey investigating the interests of potential industrial actors in biorefinery concepts. A high resonance was identified amongst companies belonging to the biofuels industry; companies active in this sector, therefore, could possibly provide access to further integrated concepts. On the whole, the results reflect a very positive attitude toward biorefinery concepts. But there are also problems with respect to the political and legal framework; policy and legislation may be required to establish stable framework conditions and provide planning security for investment decisions. Oilseed and lignocellulosic feedstock is primarily utilized within the surveyed companies; fuel, heat and power are the primary products produced from biomass. Additionally, the survey showed that biorefinery concepts are highly influenced by aspects concerning regional value chains. On the upstream side ,feedstock issues' appear to be especially important for biorefineries. In general, sustainability aspects are considered to be a benefit of biorefinery concepts. This suggests opportunities for the design of marketing and communication strategies based on ecological aspects of biorefinery implementation. © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd [source]