Estimation of baseflow recession constants and effective hydraulic parameters in the karst basins of southwest China

2012 ◽  
Vol 43 (1-2) ◽  
pp. 102-112 ◽  
Author(s):  
Xi Chen ◽  
Yan-fang Zhang ◽  
Xianwu Xue ◽  
Zhicai Zhang ◽  
Lingna Wei
Keyword(s):  
Southwest China ◽  
Low Permeability ◽  
Hydraulic Parameters ◽  
Slow Flow ◽  
Drought Period ◽  
Near Surface ◽  
Aquifer Characteristics ◽  
Break Points ◽  
Fast Flow ◽  
Basin Area

By analysing the hydrographs of karst basin outflow, it is possible to identify aquifer characteristics and, accordingly, the main features of a karst basin. In this study, 19 basins with daily observed flow discharges during drought periods between October and April 1973–1983 were selected to analyse the master recession curve (MRC). During a drought period, the MRCs were separated into segments of fast flow exponential recession and slow flow exponential recession. Break points of the fast and slow recession segments were identified and the recession constants α were determined. Relationships between α and basin area were identified. According to the estimated baseflow recession constants, hydraulic parameters including aquifer thickness and hydraulic conductivity were estimated. Hydraulic conductivities in the near-surface epikarst aquifer are of the order 10−3 m s−1, much larger than 10−5 m s−1 in the low-permeability aquifer.

scholarly journals Effects of passive storage on modelling hydrological function and isotope dynamics in a karst flow system in southwest China

2021 ◽  
Author(s):  
Guangxuan Li ◽  
Xi Chen ◽  
Zhicai Zhang ◽  
Lichun Wang ◽  
Chris Soulsby
Keyword(s):  
Southwest China ◽  
Flow System ◽  
Hydrodynamic Dispersion ◽  
Slow Flow ◽  
Model Structure ◽  
Tracer Transport ◽  
Coupled Flow ◽  
Heterogeneous Aquifers ◽  
Improved Model ◽  
Fast Flow

Abstract. Representing passive storage in coupled flow-isotope models can facilitate simulation of mixing and retardation effects on tracer transport in many natural systems, such as catchments or rivers. However, the effectiveness of incorporating passive storages in models of complex karst flow systems remains poorly understood. In this study, we developed a coupled flow-isotope model that conceptually represents both “fast” and “slow” flow processes in heterogeneous aquifers to represent hydrological connections between hillslopes and low-lying depression units in cockpit karst landscapes. As this model originally included a varying number of passive storages at different positions of the flow system (e.g. fast/slow flow reservoirs combined with different hillslope/depression units), the model structure and relevant parameters were optimized using a multi-objective optimization algorithm. This was used to match detailed observational data of hydrological processes and isotope concentration in the Chenqi catchment in southwest China. Results show that the optimal structure for a coupled flow-isotope model incorporated only two passive storages in fast flow and slow flow paths of the hillslope unit. Using fewer or greater numbers of passive stores in the model could lead to under- or over-mixing of isotope signatures. This optimized model structure could effectively improve simulation accuracies for outlet discharge and isotope signatures, with > 0.65 of the modified Kling-Gupta efficiency. Additionally, the optimal tracer-aided model yields reasonable parameter values and estimations of hydrological components (e.g. more than 80 % of fast flow in the total discharge). Furthermore, results imply that the solute transport is primarily controlled by advection and hydrodynamic dispersion in steep hillslope unit, which is a remarkable phenomenon in the karst flow system. The study resulted in new insights, more realistic catchment conceptualizations and improved model formulation.

Improving the global modeling of soils in JULES and the Unified Model: Updating from UM/HWSD to SoilGrids soil properties and from the Brooks & Corey to the van Genuchten soil-hydraulics model

2021 ◽  
Author(s):  
Patrick C. McGuire ◽  
Pier Luigi Vidale ◽  
Martin J. Best ◽  
David H. Case ◽  
Imtiaz Dharssi ◽  
...  
Keyword(s):  
Soil Properties ◽  
Land Surface ◽  
Climate Model ◽  
Model Updating ◽  
Unified Model ◽  
Pedotransfer Functions ◽  
Hydraulic Parameters ◽  
Near Surface ◽  
Soil Database ◽  
Soil Hydraulic

<p>    We have updated the soil properties used in JULES (Joint UK Land Environment Simulator), which is the land-surface component of the UM (Unified Model, the UK Met Office’s climate model). JULES models the interaction of the land surface with the atmosphere, and simulates the energy, water, and carbon fluxes. JULES allows either: (i) the Brooks & Corey (BC) model for estimating soil hydraulic properties, or (ii) the van Genuchten (VG) model but using hydraulic parameters translated from the BC model. One advantage of the VG model over the BC model is the smoother dependence of water retention upon matric potential for nearly saturated soils. Herein, we report on our work towards fully implementing the VG model in JULES and in the UM, through the implementation and evaluation of several VG pedotransfer functions (PTFs) for estimating the soil hydraulic parameters used in the hydraulic functions.</p> <p>    We have tested three VG PTFs in global offline JULES runs (driven with WFDEI data over 1979-2012): the combination of Tóth et al. PTFs 17 & 20, the Weynants et al. PTF, and the Zhang & Schaap ROSETTA3 H1 PTF (modified for sandy soils). We also modernized the soil basic properties that are conventionally used for JULES and the UM, from the UM version of the Harmonized World Soil Database (HWSD) to the SoilGrids database.</p> <p>    Evaluation of JULES simulations shows (i) that the modified version of the Zhang & Schaap ROSETTA3 H1 PTF is the best VG option, and (ii) that it compares favorably with the BC control model (which uses the Cosby et al. PTF and the UM/HWSD soils), in terms of the surface energy balance and the mitigation of near-surface temperature biases over mid-latitude continental regions. This modified version of the Zhang & Schaap ROSETTA3 H1 PTF with SoilGrids soils is also currently being used in coupled land-atmosphere UM runs.</p>

scholarly journals Peripheral Vascular Anomalies – Essentials in Periinterventional Imaging

2019 ◽  
Vol 192 (02) ◽  
pp. 150-162 ◽  
Author(s):  
Maliha Sadick ◽  
Daniel Overhoff ◽  
Bettina Baessler ◽  
Naema von Spangenberg ◽  
Lena Krebs ◽  
...  
Keyword(s):  
Therapeutic Approach ◽  
Vascular Malformations ◽  
Vascular Anomaly ◽  
Flow Dynamics ◽  
Vascular Anomalies ◽  
Vascular Tumors ◽  
Slow Flow ◽  
Peripheral Vascular ◽  
Fast Flow ◽  
Selection Of

Background Peripheral vascular anomalies represent a rare disease with an underlying congenital mesenchymal and angiogenetic disorder. Vascular anomalies are subdivided into vascular tumors and vascular malformations. Both entities include characteristic features and flow dynamics. Symptoms can occur in infancy and adulthood. Vascular anomalies may be accompanied by characteristic clinical findings which facilitate disease classification. The role of periinterventional imaging is to confirm the clinically suspected diagnosis, taking into account the extent and location of the vascular anomaly for the purpose of treatment planning. Method In accordance with the International Society for the Study of Vascular Anomalies (ISSVA), vascular anomalies are mainly categorized as slow-flow and fast-flow lesions. Based on the diagnosis and flow dynamics of the vascular anomaly, the recommended periinterventional imaging is described, ranging from ultrasonography and plain radiography to dedicated ultrafast CT and MRI protocols, percutaneous phlebography and transcatheter angiography. Each vascular anomaly requires dedicated imaging. Differentiation between slow-flow and fast-flow vascular anomalies facilitates selection of the appropriate imaging modality or a combination of diagnostic tools. Results Slow-flow congenital vascular anomalies mainly include venous and lymphatic or combined malformations. Ultrasound and MRI and especially MR-venography are essential for periinterventional imaging. Arteriovenous malformations are fast-flow vascular anomalies. They should be imaged with dedicated MR protocols, especially when extensive. CT with 4D perfusion imaging as well as time-resolved 3D MR-A allow multiplanar perfusion-based assessment of the multiple arterial inflow and venous drainage vessels of arterio-venous malformations. These imaging tools should be subject to intervention planning, as they can reduce procedure time significantly. Fast-flow vascular tumors like hemangiomas should be worked up with ultrasound, including color-coded duplex sonography, MRI and transcatheter angiography in case of a therapeutic approach. In combined malformation syndromes, radiological imaging has to be adapted according to the dominant underlying vessels and their flow dynamics. Conclusion Guide to evaluation of flow dynamics in peripheral vascular anomalies, involving vascular malformations and vascular tumors with the intention to facilitate selection of periinterventional imaging modalities and diagnostic and therapeutic approach to vascular anomalies. Key Points:  Citation Format

scholarly journals Comparison of Quantitative Autoradiographic and Xenon-133 Clearance Methods: Correlation of Gray and White Matter Cerebral Blood Flow with Compartmental Blood Flow Indices

1986 ◽  
Vol 6 (4) ◽  
pp. 481-485 ◽  
Author(s):  
U. I. Tuor ◽  
W. Fitch ◽  
D. I. Graham ◽  
A. D. Mendelow
Keyword(s):  
Blood Flow ◽  
White Matter ◽  
Gray Matter ◽  
Slow Flow ◽  
Stable Measure ◽  
Flow Component ◽  
Primate Brain ◽  
Xenon 133 ◽  
Fast Flow ◽  
Clearance Methods

The relationships between CBF in gray and white matter to those of the fast and slow components of xenon-133 clearance curves remain uncertain. CBF was measured in 13 anaesthetized baboons under a variety of conditions, using both the xenon-133 clearance technique and [14C]iodoantipyrine quantitative autoradiography. There was a linear relationship between CBF, as determined by the stochastic (height/area) analysis of the clearance curve, and mean CBF determined from the autoradiograms ( r = 0.94, p < 0.001, slope = 0.86 ± 0.09). There was also a linear correlation between the fast-flow component (measured with xenon-133) and blood flow in the cerebral gray matter (measured with [14C]iodoantipyrine) ( r = 0.92, p < 0.001, slope = 0.69 ± 0.15) and between the slow-flow component (with xenon-133) and blood flow in white matter (with [14C]iodoantipyrine) ( r = 0.79, p < 0.01, slope = 0.81 ± 0.10). In the primate brain, the fast- and slow-flow indices therefore appear to be representative of CBF in gray matter and white matter, respectively, whereas the stochastic analysis provides a stable measure of mean CBF within the tissue monitored.

scholarly journals Formation and development of supraglacial lakes in the percolation zone of the Greenland ice sheet

2017 ◽  
Vol 63 (241) ◽  
pp. 847-853 ◽  
Author(s):  
CHRISTINE CHEN ◽  
IAN M. HOWAT ◽  
SANTIAGO DE LA PEÑA
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Low Permeability ◽  
Near Surface ◽  
Observable Change ◽  
Supraglacial Lakes ◽  
Run Off ◽  
Lake Formation ◽  
And Storage ◽  
Percolation Zone

AbstractWe examine repeat surface altimetry and radio echo observations of two supraglacial lakes in the percolation zone of the Greenland ice sheet to investigate the changes in firn conditions leading to lake formation and implications for meltwater storage within firn. Both lakes formed in 2011, when an anomalously high melt season was followed by low winter accumulation, resulting in reduced infiltration and storage in the near surface. The lakes expanded during the 2012 record melt season and retained liquid meltwater through the following winter. The lakes then contracted, with one lake slowly draining and refreezing and another rapidly draining to the subsurface. The lack of observable change in firn conditions surrounding the lakes indicates increased run-off in the near surface firn, likely along low-permeability ice layers formed during the previous melt seasons. This implies a reduced ability of the firn to absorb increased meltwater.

scholarly journals Characterization of seasonal glacial seismicity from a single-station on-ice record at Holtedahlfonna, Svalbard

2019 ◽  
Vol 60 (79) ◽  
pp. 23-36 ◽  
Author(s):  
Andreas Köhler ◽  
Valerie Maupin ◽  
Christopher Nuth ◽  
Ward van Pelt
Keyword(s):  
Seismic Velocity ◽  
Temporal Distribution ◽  
Velocity Model ◽  
Ice Dynamics ◽  
Near Surface ◽  
Waveform Modeling ◽  
Single Station ◽  
Glacier Runoff ◽  
Fast Flow ◽  
Seismic Background

ABSTRACTGlacial seismicity provides important insights into glacier dynamic processes. We study the temporal distribution of cryogenic seismic signals (icequakes) at Holtedahlfonna, Svalbard, between April and August 2016 using a single three-component sensor. We investigate sources of observed icequakes using polarization analysis and waveform modeling. Processes responsible for five icequake categories are suggested, incorporating observations of previous studies into our interpretation. We infer that the most dominant icequake type is generated by surface crevasse opening through hydrofracturing. Secondly, bursts of high-frequency signals are presumably caused by repeated near-surface crevassing due to high strain rates during glacier fast-flow episodes. Furthermore, signals related to resonance in water-filled cracks, fracturing or settling events in dry firn or snow before the melt season, and processes at the glacier bed are observed. Amplitude of seismic background noise is clearly related to glacier runoff. We process ambient seismic noise to invert horizontal-to-vertical spectral ratios for a sub-surface seismic velocity model used to model icequake signals. Our study shows that a single seismic sensor provides useful information about seasonal ice dynamics in case deployment of a network is not feasible.

scholarly journals Elevated 3D structures of PM<sub>2.5</sub> and impact of complex terrain-forcing circulations on heavy haze pollution over Sichuan Basin, China

2021 ◽  
Vol 21 (11) ◽  
pp. 9253-9268
Author(s):  
Zhuozhi Shu ◽  
Yubao Liu ◽  
Tianliang Zhao ◽  
Junrong Xia ◽  
Chenggang Wang ◽  
...  
Keyword(s):  
Air Pollution ◽  
Sichuan Basin ◽  
Southwest China ◽  
Pollutant Emissions ◽  
Atmospheric Environment ◽  
Observation Data ◽  
Free Troposphere ◽  
Near Surface ◽  
Haze Pollution ◽  
The Impact

Abstract. Deep basins create uniquely favorable conditions for causing air pollution, and the Sichuan Basin (SCB) in Southwest China is such a basin featuring frequent heavy pollution. A wintertime heavy haze pollution event in the SCB was studied with conventional and intensive observation data and the WRF-Chem model to explore the 3D distribution of PM2.5 to understand the impact of regional pollutant emissions, basin circulations associated with plateaus, and downwind transport to the adjacent areas. It was found that the vertical structure of PM2.5 over the SCB was characterized by a remarkable hollow sandwiched by high PM2.5 layers at heights of 1.5–3 km and a highly polluted near-surface layer. The southwesterlies over the Tibetan Plateau (TP) and Yunnan-Guizhou Plateau (YGP) resulted in a lee vortex over the SCB, which helped form and maintain heavy PM2.5 pollution. The basin PM2.5 was lifted into the free troposphere and transported outside of the SCB. At the bottom of the SCB, high PM2.5 concentrations were mostly located in the northwestern and southern regions. Due to the blocking effect of the plateau terrain on the northeasterly winds, PM2.5 gradually increased from northeast to southwest in the basin. In the lower free troposphere, the high PM2.5 centers were distributed over the northwestern and southwestern SCB areas, as well as the central SCB region. For this event, the regional emissions from the SCB contributed 75.4 %–94.6 % to the surface PM2.5 concentrations in the SCB. The SCB emissions were the major source of PM2.5 over the eastern regions of the TP and the northern regions of the YGP, with contribution rates of 72.7 % and 70.5 %, respectively, during the dissipation stage of heavy air pollution over the SCB, which was regarded as the major pollutant source affecting atmospheric environment changes in Southwest China.

Turbulent axially directed flow of plasma containing rt-PA promotes thrombolysis of non-occlusive whole blood clots in vitro

2004 ◽  
Vol 91 (03) ◽  
pp. 487-496 ◽  
Author(s):  
Gregor Tratar ◽  
Mitja Štrukelj ◽  
Urša Mikac ◽  
Igor Serša ◽  
Aleš Blinc
Keyword(s):  
Whole Blood ◽  
Spin Echo ◽  
Slow Flow ◽  
Directed Flow ◽  
Specific Lysis ◽  
Magnetic Resonance Contrast ◽  
Blood Clots ◽  
Dynamical Spin ◽  
Fast Flow

SummaryThe rate of thrombolysis markedly decreases after a thrombosed vessel is partly recanalized and the remaining clot poses serious risk for rethrombosis. We studied in vitro how thrombolysis depends on penetration of plasma containing thrombolytic agents – 0.2 μg/ml rt-PA or 250 IU/ml streptokinase (SK) nd the magnetic resonance contrast agent Gd-DTPA (at 1 mmol/l) into non-occlusive clots under conditions of fast (turbulent) or slow (laminar) axially directed flow. Cylindrical non-retracted (fresh) or retracted (aged) whole blood clots were pierced lengthways and connected to a perfusion system. Dynamical spin-echo MRI was used for measuring the penetration of labeled plasma into clots and for assessing the remaining clot size. In both types of clots fast flow enhanced the penetration of Gd-DTPA-labeled plasma into clots in comparison to slow flow. In non-retracted clots, lysis with rt-PA and to a lesser extent also lysis with SK followed the path of plasma penetration into clots. After 40 minutes of fast axially directed flow rt-PA resulted in almost complete lysis and SK left only about a third of the clot undissolved, whereas with slow flow lysis was much slower (undissolved clot: 86 ± 5 % with rt-PA and 95 ± 1 % with SK). In retracted clots, substantial lysis was possible only with rt-PA and rapid flow (53 ± 28% of the clot undissolved after 60 min), whereas the use of SK or slow flow precluded meaningful lysis. We conclude that rapid (turbulent) axially directed flow of plasma along non-occlusive blood clots causes forceful exchange of serum inside the clot with outer plasma which enhances both fibrin-specific and non-fibrin-specific lysis of fresh clots. Dissolution of non-occlusive retracted (aged) clots occurs only under fibrin-specific conditions combined with adequate transport of rt-PA into clots.

Anion and cation leaching through large undisturbed soil cores under different flow regimes. 1. Experimental results

Soil Research ◽  
1999 ◽  
Vol 37 (4) ◽  
pp. 711 ◽  
Author(s):  
L. K. Heng ◽  
R. W. Tillman ◽  
R. E. White
Keyword(s):  
Unsaturated Flow ◽  
Water Flux ◽  
Flow Regimes ◽  
Breakthrough Curves ◽  
Slow Flow ◽  
Exchange Reactions ◽  
Flow Core ◽  
Sodic Soils ◽  
Undisturbed Soil ◽  
Fast Flow

The movement of anions and cations under different unsaturated flow regimes was studied in 2 large undisturbed cores from a soil under pasture. Sequential leaching of calcium sulfate (CaSO4) and potassium bromide (KBr) solutions was carried out at water fluxes which ranged from a normal 5–20 mm/h rate in one core (the slow flow core), to unusually high values up to 350 mm/h in the other (the fast flow core). The objective was to examine the leaching behaviour of the applied cations and anions under these contrasting flow conditions, and determine the relative influence of soil physical and chemical processes in governing ion movement. A better understanding of this behaviour should help in the development of improved practices to reclaim saline soils, ameliorate sodic soils, and minimise unwanted leaching of nutrients. In the slow flow core, miscible displacement breakthrough curves (BTCs) were observed for bromide, with sulfate movement retarded relative to the bromide. Cation exchange reactions occurred in the slow flow core, with calcium generally the dominant cation balancing anions during their movement through the soil. When KBr solution was substituted for CaSO4, potassium ions replaced calcium ions on the exchange sites, resulting in an increase in the calcium concentration in the effluent. In the fast flow core, however, flow was highly preferential and the water flux very variable. The surface-applied solutes appeared very rapidly in the effluent, irrespective of whether they were cations or anions. Under these conditions, solution cation/anion interactions with the soil surfaces did not appear to approach equilibrium, so that the leaching process was dominated by the soil’s water flow characteristics and showed little influence of surface chemical reactions.

scholarly journals Nature and significance of rift-related, near-surface fissure-fill networks in fractured carbonates below regional unconformities

2020 ◽  
Vol 177 (6) ◽  
pp. 1168-1185 ◽  
Author(s):  
Kit Hardman ◽  
Robert E. Holdsworth ◽  
Edward Dempsey ◽  
Ken McCaffrey
Keyword(s):  
Wall Rock ◽  
Surface Phenomenon ◽  
Low Permeability ◽  
Early Permian ◽  
Near Surface ◽  
Content Type ◽  
Basement Rocks ◽  
Supplementary Material ◽  
Fissure Fill ◽  
Migration Pathways

Fissure-fill networks are a widely recognized, but relatively little described, near-surface phenomenon (<1–2 km) hosted in carbonate and crystalline basement rocks below regional unconformities. Faults and fractures in otherwise tight Devonian carbonate basement rocks of the Tor Bay region, Devon, SW England are associated with the development of millimetre- to decametre-wide fissures containing red-coloured early Permian sedimentary material, vuggy calcite mineralization and wall rock collapse breccia. These features preserve evidence about the style and history of fault deformation and reactivation in near-surface settings and on fluid-related processes, such as elutriation and/or mineralization. Field observations, palaeostress analysis and fracture topology analyses show that the rift-related faults and fractures created a network of long-lived open cavities during the development of the Portland–Wight Basin in the early Permian. Once formed, they were subjected to episodic, probably seismically induced, fluid fluxing events and local karstification. The large, well-connected networks of naturally propped fractures were (and possibly still are) important fluid migration pathways within otherwise low-permeability host rocks. These structures are probably equivalent to those observed in many other rift-related, near-surface tectonic settings and suggest that the Tor Bay outcrops can be used as a global analogue for sub-unconformity open fissure systems hosted in low-permeability basement rocks.Supplementary material: Appendix A is available at https://doi.org/10.6084/m9.figshare.c.5023103

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