Increase In Total Flow Research Articles

On the Challenges of Simulating Streamflow in Glacierized Catchments of the Himalayas Using Satellite and Reanalysis Forcing Data

Abstract Hydrologic assessment of climate change impacts on complex terrains and data-sparse regions like High Mountain Asia is a major challenge. Combining hydrological models with satellite and reanalysis data for evaluating changes in hydrological variables is often the only available approach. However, uncertainties associated with the forcing dataset, coupled with model parameter uncertainties, can have significant impacts on hydrologic simulations. This work aims to understand and quantify how the uncertainty in precipitation and its interaction with the model uncertainty affect streamflow estimation in glacierized catchments. Simulations for four precipitation datasets [Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG), Climate Hazards Group Infrared Precipitation with Station (CHIRPS), ERA5-Land, and Asian Precipitation–Highly Resolved Observational Data Integration Toward Evaluation (APHRODITE)] and two glacio-hydrological models [Glacio-Hydrological Degree-Day Model (GDM) and Hydrological Model for Distributed Systems (HYMOD_DS)] are evaluated for the Marsyangdi and Budhigandaki River basins in Nepal. Temperature sensitivity of streamflow simulations is also investigated. Relative to APHRODITE, which compared well with ground stations, ERA5-Land overestimates the catchment average precipitation for both basins by more than 70%; IMERG and CHIRPS overestimate by ∼20%. Precipitation uncertainty propagation to streamflow exhibits strong dependencies to model structure and streamflow components (snowmelt, ice melt, and rainfall-runoff), but overall uncertainty dampens through precipitation-to-streamflow transformation. Temperature exerts a significant additional source of uncertainty in hydrologic simulations of such environments. GDM was found to be more sensitive to temperature variations, with >50% increase in total flow for 20% increase in actual temperature, emphasizing that models that rely on lapse rates for the spatial distribution of temperature have much higher sensitivity. Results from this study provide critical insight into the challenges of utilizing satellite and reanalysis products for simulating streamflow in glacierized catchments. Significance Statement This work investigates the uncertainty of streamflow simulations due to climate forcing and model parameter/structure uncertainty and quantifies the relative importance of each source of uncertainty and its impact on simulating different streamflow components in glacierized catchments of High Mountain Asia. Results highlight that in high mountain regions, temperature uncertainty exerts a major control on hydrologic simulations and models that do not adequately represent the spatial variability of temperature are more sensitive to bias in the forcing data. These findings provide guidance on important aspects to be considered when modeling glacio-hydrological response of catchments in such areas and are thus expected to impact both research and operation practice related to hydrologic modeling of glacierized catchments.

Energy loss mechanism of a full tubular pump under reverse power generation conditions using entropy production theory

This paper investigates the energy dissipation mechanism of the internal flow field of the full tubular pump during reverse power generation and pump conditions, utilizing CFD and model test methods to research the device’s hydraulic characteristics, internal flow field and entropy production. The results indicate that the reverse power generation and pump conditions’ performance curves have opposite trends. Under PRPG conditions, the flow uniformity and weighted average angle of the impeller inlet flow field are smaller and the inlet flow field is poor. The stator-rotor gap flow under PRPG conditions increases with the increase in total flow, the gap flow under the design flow is 2.88 L/s, and the torque is 7.35 N·m. Under the PRPG condition, the turbulent and wall entropy production ratio increases gradually with the flow increase. Under the design flow rate, the entropy production rate of the impeller is 55.07%, and the entropy production rate of the impeller is the largest among the components under different flow rates. The entropy production of the outlet channel rises significantly with the flow rate. The research results of this paper provide a theoretical basis for the distribution of energy loss in reverse power generation of the full tubular pump.

Simulating the Hydrological Impact of Green Roof Use and an Increase in Green Areas in an Urban Catchment with i-Tree: A Case Study with the Town of Fontibón in Bogotá, Colombia

Urbanization has produced various social, environmental, and hydrological impacts, such as reduced biodiversity, increased urban temperatures, ecosystem degradation, air and water pollution, changes to hydrological processes, groundwater recharge alterations, increased prevalence of floods, vegetation removal, and potential increases in unstable soils. Finding solutions to mitigate the impacts of urbanization is of vital importance in the development and planning of cities, and particularly so for developing countries. One strategy gaining momentum is the use of green roofs and larger green areas (greater green cover under trees, with the purpose of increasing the permeable area) for runoff control. In this study, a simulation was carried out using the i-Tree Hydro software that involved the urban basin in the Fontibón area of Bogotá, Colombia, with the aim of observing the hydrological benefits of trees, green areas, and permeable zones. Five scenarios were proposed in which green roof coverage was implemented (20% and 50% increases in green areas in Scenarios 1 and 2), coverage under existing trees was enhanced (50% and 100% increase in Scenarios 4 and 5), and finally a complete removal of green zones in Fontibón was simulated (Scenario 3). The town is relatively susceptible to a reduction in its existing green areas, with an increase in total flow of more than 50% for one scenario considered. Thus, an increase in the permeable coverage under trees (50% and 100% increased coverage under existing trees) provided the best strategy for mitigating the impacts of urbanization by reducing the total, maximum, and average impervious flow by 3%, 4%, and 8%, respectively. Finally, an increase in permeable zones corresponding to plants was proposed via the implementation of green roofs. However, this strategy showed a response to the reduction in the lowest total flow at 1%.

Determining exercise‐induced blood flow reserve in lower extremities using phase contrast MRI

To study the changes in limb blood flow during lower extremity exercise using phase contrast (PC) MRI in normal volunteers. Healthy volunteers performed plantar flexion exercise (<1 W) for four minutes. Flow velocity was measured using cardiac-gated, cine PC-MRI sequences (fast gradient recalled echo [GRE]; multishot echo planar imaging [EPI]) on a 3T scanner at the level of the superficial femoral artery (SFA): 1) preexercise; 2) immediately postexercise; 3) during three minutes recovery; and 4) postrecovery. At rest there was a triphasic flow waveform in the SFA. During exercise it changed to a monophasic pattern with an increase in total flow; there were variable changes in vessel size and flow velocity. The waveform regained the triphasic pattern during recovery. The exercise-induced flow reserve (FR) was 167 +/- 90%. PC-MRI demonstrates that the resting triphasic flow waveform transforms into a monophasic pattern with submaximal exercise and returns to baseline with recovery. This increase in the regional blood flow allows for measurement of exercise-induced FR in the SFA.

THE CONTRASTING EFFECTS OF WILDFIRE AND CLEARFELLING ON THE HYDROLOGY OF A SMALL CATCHMENT

A wildfire in an aAorested research catchment presented the rare opportunity to compare the hydrological eAects of wildfire with the eAects of clearfelling in the same catchment in the Jonkershoek Valley, in the south-western Western Cape Province of South Africa. The timber plantation, which occupies 57% of the 2 km 2 catchment, had been clearfelled and re-planted to Pinus radiata roughly five years before the fire. The eAects of the two treatments on total flow, stormflow and quick-flow volumes, peak discharge and storm response ratio were determined by means of multiple regression analysis, employing the dummy variable method to test for the significance of treatments. Both clearfelling and wildfire caused significant increases in all the stream-flow variables analysed. But the clearfelling eAect was dominated by large increases in total flow (96% over three years), of which storm-flow and quick-flow volumes formed only minor parts. After the wildfire, by contrast, increases in total flow were small (12%) but the storm flow increases were three- to fourfold in the first year and roughly double in the second year. The wildfire caused fire-induced water repellency in the soils which led to overland flow on mid-slope sites, where soil infiltrability normally far exceeds local rainfall intensities. It is argued that these results support the hypothesis that stream-flow generation processes were changed by the wildfire in that overland flow made a direct contribution to storm flows, but that clearfelling had no such eAect. #1997 by John Wiley & Sons, Ltd.

Vascular adaptations in rat hindlimb skeletal muscle after voluntary running-wheel exercise

To test the hypothesis that voluntary running-wheel exercise would elicit vascular adaptations in rat skeletal muscle, male Sprague-Dawley rats (202 +/- 5 g) were cage confined (C, n = 11) or housed in cages with free access to running wheels (R, n = 13) for 12 wk. Vascular transport capacity was determined in maximally vasodilated (papaverine) hindquarters of C and R rats with measurements of total and regional (radiolabeled microspheres) flow capacity and capillary filtration coefficient. R rats voluntarily ran 29 +/- 4 km/wk over the 12-wk period; however, performance of individual rats varied greatly (range 4-74 km/wk). Citrate synthase activity was increased in the medial head (81%, P < 0.001) and the red long head (88%, P < 0.001) of the triceps brachii muscle in R rats but not in the white long head (25%, P = 0.06). Capillary filtration coefficient was 27% greater in R compared with C rats (0.040 +/- 0.003 vs. 0.031 +/- 0.002 ml.min-1.100 g-1.mmHg-1, respectively, P < 0.001) suggesting that there was an increase in microvascular surface area available for fluid exchange. Total hindquarters flow was increased in R rats (P < 0.05) at all perfusion pressures examined, indicative of an increased flow capacity. Regional flows revealed that skin flow was unchanged in R rats and that the increase in total flow was due to increased skeletal muscle flow capacity. These results indicate that voluntary running-wheel exercise elicits adaptive increases in skeletal muscle vascular transport capacity and oxidative capacity comparable to those seen in treadmill-trained rats and support the use of voluntary running-wheel exercise as a less stressful training modality in exercise studies using rats.

Clearcutting effects on streamflow in coppiced Eucalyptus globulus stands in Portugal

Two Eucalyptus globulus catchments in Central Portugal were instrumented to gain some understanding of the hydrological effects of coppicing forest stands of this fast-growing species. Suspected increases in total flow, quick flow and delayed flow after clearcutting were tested statistically using the R-Student statistic for outlier detection. Under normal climatic conditions, significant annual flow increases were found only during the water-year immediately after clearcutting. However, when the water-year following harvesting was extremely dry, no flow increase occurred during that year although flow increases were found during the second water-year. Nevertheless, owing to the rapid regrowth of the stands, the hydrological effects of clearcutting were always short lived. Depending on the dominant runoff-generating processes, increases in total flow were due to increases in both the quick and delayed flow components or to increases only in the quick flow component.

Quantification of collateral blood flow in coarctation of the aorta by velocity encoded cine magnetic resonance imaging.

Knowledge about the volume of collateral flow provides insight into the severity of coarctation of the aorta and may be critical in planning the operative approach. There is currently no method for the quantification of collateral flow in coarctation of the aorta. In this study, we applied velocity encoded cine magnetic resonance imaging (VENC-MR) to establish the flow pattern and volume of collateral flow in the descending thoracic aorta in normal subjects and patients with coarctation, introducing a new possibility to quantify the severity of the coarctation by determining the amount of collateral flow. VENC-MR was used to measure flow in the proximal and distal descending thoracic aorta in 10 normal subjects. In 23 patients with coarctation, flow was measured near the coarctation site and above the diaphragm. Patients were divided into a group with moderate to severe coarctation and a group with mild coarctation on the basis of clinical gradient between upper and lower extremities and the estimation of the gradient across the coarctation by Doppler echocardiography. The gradient across the coarctation and the degree of anatomic narrowing were also assessed by MR imaging. In normal volunteers, VENC-MR showed a 7 +/- 6% decrease in total flow, from proximal to distal aorta. The interobserver reproducibility was 3.9% to 4.9% (mean, 4.4%). In patients with moderate to severe coarctation, VENC-MR demonstrated an 83 +/- 50% increase in total flow from proximal to distal aorta, yielding a significant change compared with normal subjects (P < .01). Patients with mild coarctation showed a normal flow pattern and no significant change in total flow. There was a significant relation between the amount of flow increase in the distal aorta and the reduction in luminal diameter at the coarctation site (r = .94) as well as the clinical gradient (r = .84). This study shows the normal flow pattern in the descending thoracic aorta and its reversal in coarctation due to collateral flow. Thus, VENC-MR can measure collateral flow in coarctation and serves as a unique method for providing this important measurement of the severity of coarctation of the aorta.

Mechanism of coronary vasodilation produced by bradykinin.

Bradykinin has been demonstrated to be an endothelium-dependent vasodilator in the cerebral circulation of the mouse, but the actions of bradykinin on regional tissue perfusion in the canine coronary circulation have not been studied. The mechanism of coronary vasodilation by bradykinin was studied in open-chest, anesthetized dogs. The role of cyclooxygenase stimulation, bradykinin B2 receptor activation, and endothelium-derived relaxing factor in bradykinin-mediated vasodilation was studied in separate groups of dogs. Bradykinin was infused intracoronarily so as to avoid changes in systemic hemodynamics capable of altering the regional distribution of coronary blood flow (radioactive microspheres). Bradykinin produced a preferential increase in subendocardial blood flow. Pretreatment with indomethacin had no effect on bradykinin-mediated increases in total left ventricular flow or the transmural distribution of coronary blood flow. Blockade of bradykinin B2 receptors with the competitive antagonist [Thi5,8, D-Phe7]-bradykinin attenuated both the increase in total flow and redistribution of perfusion to the subendocardium produced by bradykinin. Inhibition of endothelium-derived relaxing factor with quinacrine, occlusion/reperfusion, or NG-monomethyl L-arginine attenuated the total increase in left ventricular flow and blocked the redistribution of flow to the subendocardium produced by bradykinin. The present results demonstrate that intracoronary infusion of bradykinin produces a preferential increase in blood flow to the subendocardium via stimulation of B2 receptors and the release of an endothelium-dependent relaxing factor that may be nitric oxide.

Local oxygen supply and blood flow regulation in contracting muscle in dogs and rabbits.

1. Multiwire surface electrodes were used to measure local hydrogen clearance curves and tissues PO2 in the sartorius muscle in dogs under resting conditions and during stimulation of the muscle at 1, 2, 4, 8 and 20 Hz via the femoral nerve. Tissue oxygen supply was assessed by means of PO2 histograms; evaluation of the initial slopes of the hydrogen clearance curves enabled the measurement of capillary blood flow. 2. In a further model, the analysis of hydrogen clearance curves measured in the femoral vein using intravascular needle electrodes in rabbits enabled the distribution of blood flow to be evaluated both under resting conditions and during direct 2 Hz stimulation of the vastus medialis muscle. 3. Increased oxygen consumption, induced by stimulation, caused increases in capillary flow which were not necessarily accompanied by augmentation of femoral artery flow. 4. PO2 histograms provided no evidence of cellular anoxia even at the maximum level of oxygen consumption. 5. A two-compartment distribution of flow was measured under resting conditions, whereas only one compartment could be resolved during 2 Hz stimulation of the vastus medialis muscle in the rabbit experiments. A clear redistribution of flow was observed in the absence of any increase in total flow. 6. A model for oxygen-dependent regulation of capillary blood flow involving high-flow and normal-flow compartments is proposed.

Stability of frontal displacement of fluids in a porous medium in the presence of interphase mass transfer and phase transitions

To preserve the stability of the front relative to small perturbations when one fluid is displaced by another the pressure gradient must decrease on crossing the front in the direction of displacement. Initially, this criterion was established for the piston displacement of fluids [1, 2], and later in the case of two-phase flow of immiscible fluids in porous media for the displacement front corresponding to the saturation jump in the Buckley—Leverett problem [3, 4]. Below it is shown that the same stability criterion remains valid for flows in porous media accompanied by interphase mass transfer and phase transitions [5, 6]. Processes of these kinds are encountered in displacing oil from beds using active physicochemical or thermal methods [7] and usually reduce to pumping into the bed a slug (finite quantity) of reagent after which a displacing agent (water or gas) is forced in. The slug volume may be fairly small, especially when expensive reagents are employed, and, accordingly, in these cases the question of the stability of displacement is one of primary importance. These active processes are characterized by the formation in the displacement zone of multiwave structures which, in the large-scale approximation (i.e., with capillary, diffusion and nonequilibrium effects neglected), correspond to discontinuous distributions of the phase saturations and component concentrations [5–10]. It is shown that the stability condition for a plane front, corresponding to a certain jump, does not depend on the type of jump [11, 12] and for a constant total flow is determined, as in simpler cases, by the relation between the total phase mobilities at the jump. An increase in total flow in the direction of displacement is destabilizing, while a decrease has a stabilizing influence on the stability of the front. Other trends in the investigation of the stability of flows in porous media are reviewed in [13].

Effects of dopamine and dobutamine on the distribution of pulmonary blood flow during lobar ventilation hypoxia and lobar collapse in dogs.

Hypoxic pulmonary vasoconstriction was induced in the left lower lobe of fifteen dogs by ventilating the lobe with 7% O2 or by absorption collapse, and the distribution of flow between the lobe and the remainder of the lung was measured with electromagnetic flow probes. The lobar to total blood flow ratio was reduced by lobar ventilation hypoxia and decreased further during lobar collapse. In seven dogs, an infusion of 20 micrograms kg-1 min-1 of dopamine produced an increase in total blood flow, an increase in pulmonary artery pressure (P less than 0.01), and an increase in lobar to total flow ratio (P less than 0.05) during both hypoxic states. There was a significant fall in arterial PO2 (P less than 0.01) during ventilation hypoxia. Similar changes in total and lobar to total flow ratio (P less than 0.01) were observed in eight dogs given 20 micrograms kg-1 min-1 of dobutamine, but there were no changes in pulmonary artery pressure. The greater increase in total flow (+ 111%) resulted in a marked increase in mixed venous PO2 and no significant changes in arterial PO2 in this group of dogs. It is concluded that both drugs produce an increase in lobar to total blood flow ratio and shunt fraction, but that the mechanisms causing the redistribution of flow may differ.

Liver blood flow after partial hepatectomy in the pig.

The role of liver blood flow in liver regeneration remains controversial. This study in 17 pigs documents the total hepatic blood flow, and portal and arterial components measured with an electromagnetic flowmeter, the portal pressure, and the cardiac output for 6 days after partial hepatectomy (PH) or sham operation. There was a twofold increase in total flow immediately after PH which rose to three- to fourfold by the second postoperative day. Thereafter values decreased but remained elevated above preoperative values; no similar increase was noted in sham animals. The increase in flow was both absolute as well as relative to the proportion of liver remnant remaining. The portal component increased from 74 +/- 3% preoperatively to 84 +/- 3% (P less than 0.05) on the second postoperative day, and portal pressure was apparently increased. These changes in flow precede the previously documented maximum regeneration response between Days 3 and 4. The factors resulting in the increased flow may be responsible in part, for regeneration.

Effect of molecular adsorption on water permeability of microporous membranes

The rate of water permeation through a microporous membrane is affected markedly by adsorption of hydrocarbon impurities and/or trace amounts of organic ions such as H(CH 2 17CO 2 - and H(CH 2) 16NR 3 +. Neutral and cationic hydrocarbon impurities are physisorbed primarily at the microcapillary outlets on the low-pressure side of an electropositive filter. Adsorption of the former at these critical sites causes flow through the affected capillaries to stop, and total flow to decrease accordingly, whereas adsorption of the latter at these sites causes a marked increase in total flow. Organic anions and molecules with electron donor substituents are chemisorbed on the high-pressure side of an electropositive filter. Those molecules that are held only by monodentate adsorption migrate through the microcapillaries to the low-pressure side of the filter as in ion-exchange chromatography, during which time water permeation is impeded significantly. Multidentate adsorbed molecules, such as gelatin or polyvinyl alcohol, are relatively immobile. Filters modified on one side only by such molecules exhibit marked anisotropic permeability, i.e., flow in one direction is much greater than in the other.

Gastric blood flow in anaesthetized cats.

1. The gastric mucosal blood flow has been measured by the amidopyrine clearance technique in anaesthetized cats. The total gastric blood flow has been (a) measured directly and (b) calculated by the Fick principle from the amidopyrine concentrations in gastric arterial and venous blood and the gastric output of amidopyrine.2. Observations on the recovery of added amidopyrine from arterial and venous blood and plasma, and on the rate of transfer of amidopyrine from corpuscles to plasma, support the underlying assumptions of the amidopyrine method of measuring mucosal blood flow.3. If acid solutions are instilled into the stomach the mucosal blood flow of the non-secreting stomach may be measured by the amidopyrine technique.4. Total gastric and mucosal blood flow increased linearly with increase in H(+) secretion, stimulated by histamine or gastrin. The increase in total flow was entirely due to the increase in mucosal flow.5. The relationship between mucosal blood flow and H(+) secretion was the same for histamine and gastrin responses, and was unaffected by maintaining the total flow at a constant level, or by reduction of the circulating blood volume. Increase in blood volume altered the relationship so that there was a greater increment in mucosal blood flow for any increase in H(+) secretion.6. It is concluded that valid observations may be made on secretion and blood flow relationships in acute anaesthetized preparations.

Discussion of “Blood Flow and Secretion in the Stomach”

As Dr. Jacobson has quite correctly emphasized, an answer to the question of a possible relationship between blood flow and secretion in glandular organs necessitates a knowledge of the local blood flow to the secreting portion of those organs-in the case of the stomach, the mucosa of the corpus. A valid method for estimating corpus mucosal blood flow, as distinct from total gastric flow, is therefore essential. To date, this problem has been approached in two ways. One is that of Jacobson and his collaborators,l the measurement of aminopyrine clearance. The other has been made by Delaney and myself,2.3 the measurement of mucosal radiopotassium (K42) clearance. Since these two techniques are based on quite different assumptions, agreement of the results obtained with them can give us some confidence in the validity of both. A few minutes spent in such a comparison seem worthwhile. Comparison must be made with stimulated stomachs, since the aminopyrine technique is not applicable to the nonsecreting mUCO$a. During histamine stimulation, the two techniques have given similar results. With intravenous infusion of this agent for 15 to 20 min at 1 }log per min per Kg of body weight, there is an increase in total flow, most of which goes to the mucosa. Nonmucosal flow is changed very little. Mucosal perfusion with both methods is about 1.5 ml per min per g. With graded sub maximal doses, Jacobson found an increase in mucosal flow only, not in total flow. We have not performed a similar experiment and so cannot compare. With the use of secretory inhibitors, some discrepancies unfortunately have appeared. With pitressin, both techniques showed a profound depression of mucosal

Evidence for the Presence of Shunts in Skin of Forearm

Evidence for the Presence of Shunts in Skin of Forearm