discharge regime
Recently Published Documents


TOTAL DOCUMENTS

70
(FIVE YEARS 22)

H-INDEX

18
(FIVE YEARS 2)

2021 ◽  
Vol 118 (49) ◽  
pp. e2111215118
Author(s):  
Predrag Popović ◽  
Olivier Devauchelle ◽  
Anaïs Abramian ◽  
Eric Lajeunesse

Understanding how rivers adjust to the sediment load they carry is critical to predicting the evolution of landscapes. Presently, however, no physically based model reliably captures the dependence of basic river properties, such as its shape or slope, on the discharge of sediment, even in the simple case of laboratory rivers. Here, we show how the balance between fluid stress and gravity acting on the sediment grains, along with cross-stream diffusion of sediment, determines the shape and sediment flux profile of laminar laboratory rivers that carry sediment as bedload. Using this model, which reliably reproduces the experiments without any tuning, we confirm the hypothesis, originally proposed by Parker [G. Parker, J. Fluid Mech. 89, 127–146 (1978)], that rivers are restricted to exist close to the threshold of sediment motion (within about 20%). This limit is set by the fluid–sediment interaction and is independent of the water and sediment load carried by the river. Thus, as the total sediment discharge increases, the intensity of sediment flux (sediment discharge per unit width) in a river saturates, and the river can transport more sediment only by widening. In this large discharge regime, the cross-stream diffusion of momentum in the flow permits sediment transport. Conversely, in the weak transport regime, the transported sediment concentrates around the river center without significantly altering the river shape. If this theory holds for natural rivers, the aspect ratio of a river could become a proxy for sediment discharge—a quantity notoriously difficult to measure in the field.


Author(s):  
A. Tihonov ◽  
A. Pol'shin ◽  
N. Lyubimyy ◽  
M. Gerasimov

The purpose of the article is to analyze the main results of the works that are used in the calculations of elevators with moderate speed modes, to clarify the suitability of their individual positions for developing the parameters of centrifugal unloading of high-speed elevators. Works devoted to the study of the operation of high-speed elevators, the results of which have not received a decent interpretation and development, are of considerable interest. As the efficiency of high-speed elevators is determined by the quality of centrifugal unloading and by the operation of the belt-drum mechanism without slipping, there is a need to analyze the work aimed at solving this problem. The paper presents known solutions for determining the parameters of centrifugal unloading, which are based on various hypotheses of the movement of material particles inside the bucket. The physical and mechanical phenomena that affect the movement of material particles in the elevator bucket are studied. The advantages and disadvantages of each hypothesis are revealed. The theoretical study of the process of centrifugal unloading is complicated by the fact that during the movement and exit of the material from the bucket, there is an unstable movement of the bulk material under the influence of a changing system of forces: the forces of attraction, centrifugal and coriolis forces, and the friction force. Meanwhile, even the simplest cases of material motion under a gravitational or mixed discharge regime are difficult to analyze theoretically. In this regard, the dependencies and methods of constructing the trajectories of the material movement are established, as well as the relevance of using a particular equation.


2021 ◽  
Author(s):  
Santiago Gómez-Dueñas ◽  
Allen Bateman ◽  
Germán Santos ◽  
Raúl Sosa

<p>Magdalena's river basin represents a quarter of Colombia's surface, yet neighbouring ecosystems remain ignored while enduring unacceptable environmental conditions. At its outlet in the Caribbean Sea, several channels link it to Cienaga Grande de Santa Marta (CGSM), a deltaic coastal-lagoon ecosystem (4200 km<sup>2</sup>) from which around 15 to 20 % are water bodies. According to several studies, Magdalena River's overflows represent its primary freshwater source. However, the recorded discharge has gradually reduced, though the basin's rainfall shows a rising tendency. Additional discharge measurements close to the outlet evidenced that it was even lesser than records upstream counterintuitively. Consequently, the energy gradient from the river to the sea through the ecosystem is reversing more frequently. That has resulted in a continuous salinisation process of the lagoons, diminishment of the mangrove forest and lagoons extension, fauna migration and low water quality. This research aims to elaborate on the Magdalena River's outlet discharges vulnerabilities in Colombia, thus providing better insight into impact-based decision-making. </p><p>Results suggest that the discharge regime responds to the El Niño Southern Oscillation (ENSO) phenomenon as it controls the country's dry/rain season. Further analysis indicates that a) low flows relate to El Niño periods and high flows to La Niña; b) the flow duration curve's slope is getting milder, meaning that high flows are decreasing whereas low flows are increasing; c) extreme discharges are getting smoother, and less disperse so that high and low flow peaks are within a smaller range; d) the dispersion diminishes radically during severe El Niño events, and e) although a priori the assumption is that the more severe El Niño events might bring lower discharge values, the minimum values recorded are more significant than in neutral ENSO conditions. </p><p>Moreover, extreme discharge values during ENSO events, despite their severity, tended to have a horizontal asymptote that suggests human-driven control upstream, especially during El Niño periods. The Magdalena basin holds Colombia's hydropower network representing more than 70% of its electricity supply distributed in 33 operating plants. On the one hand, it is clear that during El Niño, the plants guarantee a minimum discharge downstream, as it is when the National Hydrometeorological Agency only considers drought protocols. However, during neutral ENSO conditions, the flows are not controlled and thus, impacts downstream arise. On the other hand, reservoirs have increased evaporation due to a large accumulated open water surface (611 km<sup>2</sup> in total). Results show that water loss represents 40% to 80% of the current average discharge at the outlet (7000 m<sup>3</sup>/s), adding to the ecosystem depletion. The results urge decision-makers to reconsider the drought protocols applying an impact-based approach.</p>


2021 ◽  
Vol 9 (1) ◽  
pp. 47-70
Author(s):  
Kumar Gaurav ◽  
François Métivier ◽  
Rajiv Sinha ◽  
Amit Kumar ◽  
Sampat Kumar Tandon ◽  
...  

Abstract. We propose an innovative methodology to estimate the formative discharge of alluvial rivers from remote sensing images. This procedure involves automatic extraction of the width of a channel from Landsat Thematic Mapper, Landsat 8, and Sentinel-1 satellite images. We translate the channel width extracted from satellite images to discharge using a width–discharge regime curve established previously by us for the Himalayan rivers. This regime curve is based on the threshold theory, a simple physical force balance that explains the first-order geometry of alluvial channels. Using this procedure, we estimate the formative discharge of six major rivers of the Himalayan foreland: the Brahmaputra, Chenab, Ganga, Indus, Kosi, and Teesta rivers. Except highly regulated rivers (Indus and Chenab), our estimates of the discharge from satellite images can be compared with the mean annual discharge obtained from historical records of gauging stations. We have shown that this procedure applies both to braided and single-thread rivers over a large territory. Furthermore, our methodology to estimate discharge from remote sensing images does not rely on continuous ground calibration.


2020 ◽  
Vol 27 (2) ◽  
pp. 9-29
Author(s):  
Petre Gâștescu ◽  
ELENA ȚUCHIU

The Danube is the second largest water course in Europe (after the Volga) in terms of length (2860 km) and area (817,000 km2) The river springs from the central-western part of Europe (Schwarzwald), runs through the central part of the continent, crosses the Pannonian Depression to the confluence with the Drava, then pierces the Carpathian Mountains through the Iron Gate Gorge. Farther down it separates the southern part of the Romanian Plain from the Prebalkan Plateau, and the eastern part of Sea, encompasses the Delta area. In Romania the Danube is 1075 km long and drains 97% of the country’s territory. It flows through European regions affected by Oceanic, Baltic, Mediterranean and temperate-continental climatic influences that stamp their mark on the morpho-hydrographic and hydrologic characteristics of the river. The Danube discharge regime depends on its upper course tributaries which come from the Alps with high waters in June. In its middle and lower course it depends on the Drava and the Sava, with high waters in spring (April –May) and lower ones in autumn (September – October). The Danube’s multiannual mean discharge increases downstream as follows: 1,470 m²/s at Passau, after confluencing with the Inn River; 1,920 m²/s in Vienna; 2,350 m²/s in Budapest and 5,300 m²/s after its junction with the Drava, Tisa and Sava rivers. This water volume enters Romania at Baziaş with 5560 m²/s. Hence forward values continue to rise through the contribution of its lower course tributaries, reaching 6,495 m²/s (over the 1840-2016 period) when flowing into the Delta-Ceatal Chilia. Maximum discharge is recorded during the high spring waters, but occasionally in summer, too: 15,800 m³/sec at Baziaș in April 2006; 15,300 m²/s at Giurgiu, and 15,900 m²/s at Ceatal Chilia. Minimum discharge occur in autumn and occasionally in winter: 1,040 m²/s at Baziaș 1949; and 1,790 m²/s at Ceatal Chilia in 1947.The alluvial discharge (1840-2000) was 53 million tons/ year, respectively 1,681kg/s, of which 2.81 million tons /year represented coarse alluvia (sands). The extreme values during that interval were 4,470 kg/sec (141 million tons/year) in 1871 and only 229 kg/sec (7.2 million tons/year) in 1990. Throughout that period there was a tendency to decrease at an annual rate of 8.3 kg/year, naturally with fluctuations in terms of the liquid discharge. The mineralisation degree is still moderate despite the higher quantities of polluting wastes being spilled into the river in front of large cities – Vienna, Bratislava, Budapest and Belgrade (values coming close to 350 – 400 mg/l due mainly to chlorine and natrium). The Danube’s great self-purification capacity makes it recover in the lower course. The qualitative characteristics of the water was implemented in 1996 by Danube Transnational Monitoring Network - TNMN, the objectives and programs in view of ensuring the concentrations and loads of relevant pollutans and identifyng of the major sources of pollution. The spatial and temporal variation in the pontic sector of the physico-chemical quality indicators, reflect the general characteristics and the effect / impact of the main pressures identified at basin level for the period 1996-2015, in 6 monitoring sections (from Baziaș to Reni). The type of surface water body (river, lake, transient water, coastal water) is an aquatic unit that has an aquatic flora and fauna determined by the climatic, lithological and morphological conditons of the minor riverbed, hydrological and physical. significant anthropogenic unmodified chemicals.


Ecohydrology ◽  
2020 ◽  
Author(s):  
Timothy Storer ◽  
Jo Bannister ◽  
Katherine Bennett ◽  
Evan Byrnes ◽  
David A. Crook ◽  
...  

Sign in / Sign up

Export Citation Format

Share Document