Magazine et Edition

Volume 70 (2022): Edition 3 (September 2022)

Volume 70 (2022): Edition 2 (June 2022)

Volume 70 (2022): Edition 1 (March 2022)

Volume 69 (2021): Edition 4 (December 2021)

Volume 69 (2021): Edition 3 (September 2021)

Volume 69 (2021): Edition 2 (June 2021)

Volume 69 (2021): Edition 1 (March 2021)

Volume 68 (2020): Edition 4 (December 2020)

Volume 68 (2020): Edition 3 (September 2020)

Volume 68 (2020): Edition 2 (June 2020)

Volume 68 (2020): Edition 1 (March 2020)

Volume 67 (2019): Edition 4 (December 2019)

Volume 67 (2019): Edition 3 (September 2019)

Volume 67 (2019): Edition 2 (June 2019)

Volume 67 (2019): Edition 1 (March 2019)

Volume 66 (2018): Edition 4 (December 2018)

Volume 66 (2018): Edition 3 (September 2018)

Volume 66 (2018): Edition 2 (June 2018)

Volume 66 (2018): Edition 1 (March 2018)

Volume 65 (2017): Edition 4 (December 2017)

Volume 65 (2017): Edition 3 (September 2017)

Volume 65 (2017): Edition 2 (June 2017)

Volume 65 (2017): Edition 1 (March 2017)

Volume 64 (2016): Edition 4 (December 2016)

Volume 64 (2016): Edition 3 (September 2016)

Volume 64 (2016): Edition 2 (June 2016)

Volume 64 (2016): Edition 1 (March 2016)

Volume 63 (2015): Edition 4 (December 2015)

Volume 63 (2015): Edition 3 (September 2015)

Volume 63 (2015): Edition 2 (June 2015)

Volume 63 (2015): Edition 1 (March 2015)

Volume 62 (2014): Edition 4 (December 2014)

Volume 62 (2014): Edition 3 (September 2014)

Volume 62 (2014): Edition 2 (June 2014)

Volume 62 (2014): Edition 1 (March 2014)

Volume 61 (2013): Edition 4 (December 2013)

Volume 61 (2013): Edition 3 (September 2013)

Volume 61 (2013): Edition 2 (June 2013)

Volume 61 (2013): Edition 1 (March 2013)

Volume 60 (2012): Edition 4 (December 2012)

Volume 60 (2012): Edition 3 (September 2012)

Volume 60 (2012): Edition 2 (June 2012)

Volume 60 (2012): Edition 1 (March 2012)

Volume 59 (2011): Edition 4 (December 2011)

Volume 59 (2011): Edition 3 (September 2011)

Volume 59 (2011): Edition 2 (June 2011)

Volume 59 (2011): Edition 1 (March 2011)

Volume 58 (2010): Edition 4 (December 2010)

Volume 58 (2010): Edition 3 (September 2010)

Volume 58 (2010): Edition 2 (June 2010)

Volume 58 (2010): Edition 1 (March 2010)

Volume 57 (2009): Edition 4 (December 2009)

Volume 57 (2009): Edition 3 (September 2009)

Volume 57 (2009): Edition 2 (June 2009)

Volume 57 (2009): Edition 1 (March 2009)

Détails du magazine
Format
Magazine
eISSN
1338-4333
Première publication
28 Mar 2009
Période de publication
4 fois par an
Langues
Anglais

Chercher

Volume 64 (2016): Edition 3 (September 2016)

Détails du magazine
Format
Magazine
eISSN
1338-4333
Première publication
28 Mar 2009
Période de publication
4 fois par an
Langues
Anglais

Chercher

10 Articles
access type Accès libre

Vertical and lateral soil moisture patterns on a Mediterranean karst hillslope

Publié en ligne: 08 Jul 2016
Pages: 209 - 217

Résumé

Abstract

The need for a better understanding of factors controlling the variability of soil water content (θ) in space and time to adequately predict the movement of water in the soil and in the interphase soil-atmosphere is widely recognised. In this paper, we analyse how soil properties, surface cover and topography influence soil moisture (θ) over karstic lithology in a sub-humid Mediterranean mountain environment. For this analysis we have used 17 months of θ measurements with a high temporal resolution from different positions on a hillslope at the main recharge area of the Campo de Dalías aquifer, in Sierra de Gádor (Almería, SE Spain). Soil properties and surface cover vary depending on the position at the hillslope, and this variability has an important effect on θ. The higher clay content towards the lower position of the hillslope explains the increase of θ downslope at the subsurface horizon throughout the entire period studied. In the surface horizon (0-0.1 m), θ patterns coincide with those found at the subsurface horizon (0.1-0.35 m) during dry periods when the main control is also exerted by the higher percentage of clay that increases downslope and limits water depletion through evaporation. However, in wet periods, the wettest regime is found in the surface horizon at the upper position of the hillslope where plant cover, soil organic matter content, available water, unsaturated hydraulic conductivity (Kunsat) and infiltration rates are higher than in the lower positions. The presence of rock outcrops upslope the θ sampling area, acts as runoff sources, and subsurface flow generation between surface and subsurface horizons also may increase the differences between the upper and the lower positions of the hillslope during wet periods. Both rock and soil cracks and fissures act disconnecting surface water fluxes and reducing run-on to the lower position of the hillslope and thus they affect θ pattern as well as groundwater recharge. Understanding how terrain attributes, ground cover and soil factors interact for controlling θ pattern on karst hillslope is crucial to understand water fluxes in the vadose zone and dominant percolation mechanisms which also contribute to estimate groundwater recharge rates. Therefore, understanding of soil moisture dynamics provides very valuable information for designing rational strategies for the use and management of water resources, which is especially urgent in regions where groundwater supports human consume or key economic activities.

Mots clés

  • Soil moisture
  • Soil water content
  • Hillslope
  • Soil properties
  • Runoff
  • Karstic
  • Mediterranean
access type Accès libre

Applying profile- and catchment-based mathematical models for evaluating the run-off from a Nordic catchment

Publié en ligne: 08 Jul 2016
Pages: 218 - 225

Résumé

Abstract

Knowledge of hydrological processes and water balance elements are important for climate adaptive water management as well as for introducing mitigation measures aiming to improve surface water quality. Mathematical models have the potential to estimate changes in hydrological processes under changing climatic or land use conditions. These models, indeed, need careful calibration and testing before being applied in decision making. The aim of this study was to compare the capability of five different hydrological models to predict the runoff and the soil water balance elements of a small catchment in Norway. The models were harmonised and calibrated against the same data set. In overall, a good agreement between the measured and simulated runoff was obtained for the different models when integrating the results over a week or longer periods. Model simulations indicate that forest appears to be very important for the water balance in the catchment, and that there is a lack of information on land use specific water balance elements. We concluded that joint application of hydrological models serves as a good background for ensemble modelling of water transport processes within a catchment and can highlight the uncertainty of models forecast.

Mots clés

  • Runoff
  • SWAT
  • COUP
  • DRAINMOD
  • HBV
  • INCA
  • Model harmonization
  • Model comparison
access type Accès libre

Rainfall timing and runoff: The influence of the criterion for rain event separation

Publié en ligne: 08 Jul 2016
Pages: 226 - 236

Résumé

Abstract

Rain is not uniform in time and space in semiarid areas and its distribution is very important for the runoff process. Hydrological studies usually divide rainfall into events. However, defining rain events is complicated, and rain characteristics vary depending on how the events are delimited. Choosing a minimum inter-event time (MIT) is a commonly used criterion. Our hypothesis is that there will be an optimal MIT that explains the maximum part of the variance of the runoff, with time to runoff used as a surrogate. The objective is to establish a procedure in order to decide upon this optimal MIT. We developed regressions between time to runoff (T0) and three descriptive variables of rain. Our results show that the optimum MIT is 1 hour, which seems to be the minimum period of time required for water in larger macropores to drain and sufficiently modify the effect of antecedent soil moisture on the runoff generation process. Rain events are classified into three significantly different groups: (1) large and intense rains, (2) light rains on wet soil, and (3) light rains on dry soil. Intense rains produce most of the runoff, but there were significant differences between small events in the runoff generated. Of rain events, 63.75% are single-tip events, and many could be dew.

Mots clés

  • Rain events
  • Minimum inter-event time (MIT)
  • Runoff
  • Macrochloa tenacissima (= Stipa tenacissima)
  • Semiarid
access type Accès libre

Hydraulic characteristics and sediment generation on slope erosion in the Three Gorges Reservoir Area, China

Publié en ligne: 08 Jul 2016
Pages: 237 - 245

Résumé

Abstract

Hydrological processes play important roles in soil erosion processes of the hillslopes. This study was conducted to investigate the hydrological processes and the associated erosional responses on the purple soil slope. Based on a comprehensive survey of the Wangjiaqiao watershed in the Three Gorges Reservoir, four typical slope gradients (5°, 10°, 15°and 20°) were applied to five rainfall intensities (0.6, 1.1, 1.61, 2.12 and 2.54 mm·min-1). The results showed that both surface and subsurface runoff varied greatly depending on the rainfall intensity and slope gradient. Surface runoff volume was 48.1 to 280.1 times of that for subsurface runoff. The critical slope gradient was about 10°. The sediment yield rate increased with increases in both rainfall intensity and slope gradient, while the effect of rainfall intensity on the sediment yield rate was greater than slope gradient. There was a good linear relationship between sediment yield rate and Reynolds numbers, flow velocity and stream power, while Froude numbers, Darcy-Weisbach and Manning friction coefficients were not good hydraulic indicators of the sediment yield rate of purple soil erosion. Among the three good indicators (Re, v and w), stream power was the best predictor of sediment yield rate (R2 = 0.884). Finally, based on the power regression relationship between sediment yield rate, runoff rate, slope gradient and rainfall intensity, an erosion model was proposed to predict the purple soil erosion (R2 = 0.897). The results can help us to understand the relationship between flow hydraulics and sediment generation of slope erosion and offer useful data for the building of erosion model in purple soil.

Mots clés

  • Purple soil
  • Runoff
  • Flow hydraulics
  • Sediment
  • Slope gradient
  • Rainfall intensity
access type Accès libre

Identifying the relationships of climate and physiological responses of a beech forest using the Standardised Precipitation Index: a case study for Slovakia

Publié en ligne: 08 Jul 2016
Pages: 246 - 251

Résumé

Abstract

The paper presents relationship between the Standardised Precipitation Index (SPI) and physiological responses of individual trees in a beech stand using an example of an experimental plot in Bienska valley (Zvolen, Slovakia). SPI is a widely used tool for monitoring both short-term and long-term droughts, and for the assessments of drought impacts on agriculture. Due to the complex ecosystem bonds, monitoring of drought in forests often requires a sophisticated technological approach. The aim of the paper was to correlate the SPI on the physiological responses of trees that were recorded during the performed physiological research (sap flow, and stem circumference increment) at the site in the growing seasons (May to September) of the years 2012-2014. The results revealed a relationship between the index and the physiological responses, although the problem with the impact of other environmental factors has also come up. The secondary correlation, in which soil water potential that significantly affects physiological responses of forest tree species was used as a dependent variable, showed a tighter relationship with the SPI. We found the highest correlation between the soil water potential and the values of SPI aggregated for five weeks. This indicates that the beech forest has a five week resistance to drought stress. The results also enable simple monitoring of the initiation of the drought stress by applying SPI for five weeks.

Mots clés

  • Drought
  • Physiological responses
  • Beech
  • Standardised Precipitation Index
  • Soil water potential
access type Accès libre

Design of a new hybrid artificial neural network method based on decision trees for calculating the Froude number in rigid rectangular channels

Publié en ligne: 08 Jul 2016
Pages: 252 - 260

Résumé

Abstract

A vital topic regarding the optimum and economical design of rigid boundary open channels such as sewers and drainage systems is determining the movement of sediment particles. In this study, the incipient motion of sediment is estimated using three datasets from literature, including a wide range of hydraulic parameters. Because existing equations do not consider the effect of sediment bed thickness on incipient motion estimation, this parameter is applied in this study along with the multilayer perceptron (MLP), a hybrid method based on decision trees (DT) (MLP-DT), to estimate incipient motion. According to a comparison with the observed experimental outcome, the proposed method performs well (MARE = 0.048, RMSE = 0.134, SI = 0.06, BIAS = -0.036). The performance of MLP and MLP-DT is compared with that of existing regression-based equations, and significantly higher performance over existing models is observed. Finally, an explicit expression for practical engineering is also provided.

Mots clés

  • Decision tree
  • Incipient motion
  • Multilayer perceptron (MLP)
  • Froude number
access type Accès libre

Modeling of sand-water slurry flow through horizontal pipe using CFD

Publié en ligne: 08 Jul 2016
Pages: 261 - 272

Résumé

Abstract

The paper presents three-dimensional CFD analysis of two-phase (sand-water) slurry flows through 263 mm diameter pipe in horizontal orientation for mixture velocity range of 3.5-4.7 m/s and efflux concentration range of 9.95-34% with three particle sizes viz. 0.165 mm, 0.29 mm and 0.55 mm with density 2650 kg/m3. RNG k-ε turbulence closure equations with Eulerian multi-phase model is used to simulate various slurry flows. The simulated values of local solid concentration are compared with the experimental data and are found to be in good agreement for all particle sizes. Effects of particle size on various slurry flow parameters such as pressure drop, solid phase velocity distribution, friction factor, granular pressure, turbulent viscosity, turbulent kinetic energy and its dissipation have been analyzed.

Mots clés

  • CFD
  • Slurry flow
  • Particle size
  • Solid concentration
  • Pipeline
access type Accès libre

Measurement of turbulent flow in a narrow open channel

Publié en ligne: 08 Jul 2016
Pages: 273 - 280

Résumé

Abstract

The paper presents the experimental results of turbulent flow over hydraulically smooth and rough beds. Experiments were conducted in a rectangular flume under the aspect ratio b/h = 2 (b = width of the channel 0.5 m, and h = flow depth 0.25 m) for both the bed conditions. For the hydraulically rough bed, the roughness was created by using 3/8″ commercially available angular crushed stone chips; whereas sand of a median diameter d50 = 1.9 mm was used as the bed material for hydraulically smooth bed. The three-dimensional velocity components were captured by using a Vectrino (an acoustic Doppler velocimeter). The study focuses mainly on the turbulent characteristics within the dip that were observed towards the sidewall (corner) of the channel where the maximum velocity occurs below the free-surface. It was also observed that the nondimensional Reynolds shear stress changes its sign from positive to negative within the dip. The quadrant plots for the turbulent bursting shows that the signs of all the bursting events change within the dip. Below the dip, the probability of the occurrence of sweeps and ejections are more than that of inward and outward interactions. On the other hand, within the dip, the probability of the occurrence of the outward and inward interactions is more than that of sweeps and ejections.

Mots clés

  • Flow measurement
  • Turbulent flow
  • Dip-phenomenon
  • Turbulent bursting
  • Open channel flow
access type Accès libre

Modelling free surface flow with curvilinear streamlines by a non-hydrostatic model

Publié en ligne: 08 Jul 2016
Pages: 281 - 288

Résumé

Abstract

This study addresses a particular phenomenon in open channel flows for which the basic assumption of hydrostatic pressure distribution is essentially invalid, and expands previous suggestions to flows where streamline curvature is significant. The proposed model incorporates the effects of the vertical curvature of the streamline and steep slope, in making the pressure distribution non-hydrostatic, and overcomes the accuracy problem of the Saint-Venant equations when simulating curvilinear free surface flow problems. Furthermore, the model is demonstrated to be a higher-order one-dimensional model that includes terms accounting for wave-like variations of the free surface on a constant slope channel. Test results of predicted flow surface and pressure profiles for flow in a channel transition from mild to steep slopes, transcritical flow over a short-crested weir and flow with dual free surfaces are compared with experimental data and previous numerical results. A good agreement is attained between the experimental and computed results. The overall simulation results reveal the satisfactory performance of the proposed model in simulating rapidly varied gravity-driven flows with predominant non-hydrostatic pressure distribution effects. This study suggests that a higher-order pressure equation should be used for modelling the pressure distribution of a curvilinear flow in a steeply sloping channel.

Mots clés

  • Curvilinear flow
  • Finite difference method
  • Hydraulic structures
  • Hydrodynamics
  • Non-hydrostatic pressure
  • Nonuniform flow
access type Accès libre

Interpretation of ponded infiltration data using numerical experiments

Publié en ligne: 08 Jul 2016
Pages: 289 - 299

Résumé

Abstract

Ponded infiltration experiment is a simple test used for in-situ determination of soil hydraulic properties, particularly saturated hydraulic conductivity and sorptivity. It is known that infiltration process in natural soils is strongly affected by presence of macropores, soil layering, initial and experimental conditions etc. As a result, infiltration record encompasses a complex of mutually compensating effects that are difficult to separate from each other. Determination of sorptivity and saturated hydraulic conductivity from such infiltration data is complicated. In the present study we use numerical simulation to examine the impact of selected experimental conditions and soil profile properties on the ponded infiltration experiment results, specifically in terms of the hydraulic conductivity and sorptivity evaluation. The effect of following factors was considered: depth of ponding, ring insertion depth, initial soil water content, presence of preferential pathways, hydraulic conductivity anisotropy, soil layering, surface layer retention capacity and hydraulic conductivity, and presence of soil pipes or stones under the infiltration ring. Results were compared with a large database of infiltration curves measured at the experimental site Liz (Bohemian Forest, Czech Republic). Reasonably good agreement between simulated and observed infiltration curves was achieved by combining several of factors tested. Moreover, the ring insertion effect was recognized as one of the major causes of uncertainty in the determination of soil hydraulic parameters.

Mots clés

  • Ponded infiltration experiment
  • Two-parameter infiltration equation
  • Three-dimensional axisymmetric dualcontinuum model
  • Preferential flow
10 Articles
access type Accès libre

Vertical and lateral soil moisture patterns on a Mediterranean karst hillslope

Publié en ligne: 08 Jul 2016
Pages: 209 - 217

Résumé

Abstract

The need for a better understanding of factors controlling the variability of soil water content (θ) in space and time to adequately predict the movement of water in the soil and in the interphase soil-atmosphere is widely recognised. In this paper, we analyse how soil properties, surface cover and topography influence soil moisture (θ) over karstic lithology in a sub-humid Mediterranean mountain environment. For this analysis we have used 17 months of θ measurements with a high temporal resolution from different positions on a hillslope at the main recharge area of the Campo de Dalías aquifer, in Sierra de Gádor (Almería, SE Spain). Soil properties and surface cover vary depending on the position at the hillslope, and this variability has an important effect on θ. The higher clay content towards the lower position of the hillslope explains the increase of θ downslope at the subsurface horizon throughout the entire period studied. In the surface horizon (0-0.1 m), θ patterns coincide with those found at the subsurface horizon (0.1-0.35 m) during dry periods when the main control is also exerted by the higher percentage of clay that increases downslope and limits water depletion through evaporation. However, in wet periods, the wettest regime is found in the surface horizon at the upper position of the hillslope where plant cover, soil organic matter content, available water, unsaturated hydraulic conductivity (Kunsat) and infiltration rates are higher than in the lower positions. The presence of rock outcrops upslope the θ sampling area, acts as runoff sources, and subsurface flow generation between surface and subsurface horizons also may increase the differences between the upper and the lower positions of the hillslope during wet periods. Both rock and soil cracks and fissures act disconnecting surface water fluxes and reducing run-on to the lower position of the hillslope and thus they affect θ pattern as well as groundwater recharge. Understanding how terrain attributes, ground cover and soil factors interact for controlling θ pattern on karst hillslope is crucial to understand water fluxes in the vadose zone and dominant percolation mechanisms which also contribute to estimate groundwater recharge rates. Therefore, understanding of soil moisture dynamics provides very valuable information for designing rational strategies for the use and management of water resources, which is especially urgent in regions where groundwater supports human consume or key economic activities.

Mots clés

  • Soil moisture
  • Soil water content
  • Hillslope
  • Soil properties
  • Runoff
  • Karstic
  • Mediterranean
access type Accès libre

Applying profile- and catchment-based mathematical models for evaluating the run-off from a Nordic catchment

Publié en ligne: 08 Jul 2016
Pages: 218 - 225

Résumé

Abstract

Knowledge of hydrological processes and water balance elements are important for climate adaptive water management as well as for introducing mitigation measures aiming to improve surface water quality. Mathematical models have the potential to estimate changes in hydrological processes under changing climatic or land use conditions. These models, indeed, need careful calibration and testing before being applied in decision making. The aim of this study was to compare the capability of five different hydrological models to predict the runoff and the soil water balance elements of a small catchment in Norway. The models were harmonised and calibrated against the same data set. In overall, a good agreement between the measured and simulated runoff was obtained for the different models when integrating the results over a week or longer periods. Model simulations indicate that forest appears to be very important for the water balance in the catchment, and that there is a lack of information on land use specific water balance elements. We concluded that joint application of hydrological models serves as a good background for ensemble modelling of water transport processes within a catchment and can highlight the uncertainty of models forecast.

Mots clés

  • Runoff
  • SWAT
  • COUP
  • DRAINMOD
  • HBV
  • INCA
  • Model harmonization
  • Model comparison
access type Accès libre

Rainfall timing and runoff: The influence of the criterion for rain event separation

Publié en ligne: 08 Jul 2016
Pages: 226 - 236

Résumé

Abstract

Rain is not uniform in time and space in semiarid areas and its distribution is very important for the runoff process. Hydrological studies usually divide rainfall into events. However, defining rain events is complicated, and rain characteristics vary depending on how the events are delimited. Choosing a minimum inter-event time (MIT) is a commonly used criterion. Our hypothesis is that there will be an optimal MIT that explains the maximum part of the variance of the runoff, with time to runoff used as a surrogate. The objective is to establish a procedure in order to decide upon this optimal MIT. We developed regressions between time to runoff (T0) and three descriptive variables of rain. Our results show that the optimum MIT is 1 hour, which seems to be the minimum period of time required for water in larger macropores to drain and sufficiently modify the effect of antecedent soil moisture on the runoff generation process. Rain events are classified into three significantly different groups: (1) large and intense rains, (2) light rains on wet soil, and (3) light rains on dry soil. Intense rains produce most of the runoff, but there were significant differences between small events in the runoff generated. Of rain events, 63.75% are single-tip events, and many could be dew.

Mots clés

  • Rain events
  • Minimum inter-event time (MIT)
  • Runoff
  • Macrochloa tenacissima (= Stipa tenacissima)
  • Semiarid
access type Accès libre

Hydraulic characteristics and sediment generation on slope erosion in the Three Gorges Reservoir Area, China

Publié en ligne: 08 Jul 2016
Pages: 237 - 245

Résumé

Abstract

Hydrological processes play important roles in soil erosion processes of the hillslopes. This study was conducted to investigate the hydrological processes and the associated erosional responses on the purple soil slope. Based on a comprehensive survey of the Wangjiaqiao watershed in the Three Gorges Reservoir, four typical slope gradients (5°, 10°, 15°and 20°) were applied to five rainfall intensities (0.6, 1.1, 1.61, 2.12 and 2.54 mm·min-1). The results showed that both surface and subsurface runoff varied greatly depending on the rainfall intensity and slope gradient. Surface runoff volume was 48.1 to 280.1 times of that for subsurface runoff. The critical slope gradient was about 10°. The sediment yield rate increased with increases in both rainfall intensity and slope gradient, while the effect of rainfall intensity on the sediment yield rate was greater than slope gradient. There was a good linear relationship between sediment yield rate and Reynolds numbers, flow velocity and stream power, while Froude numbers, Darcy-Weisbach and Manning friction coefficients were not good hydraulic indicators of the sediment yield rate of purple soil erosion. Among the three good indicators (Re, v and w), stream power was the best predictor of sediment yield rate (R2 = 0.884). Finally, based on the power regression relationship between sediment yield rate, runoff rate, slope gradient and rainfall intensity, an erosion model was proposed to predict the purple soil erosion (R2 = 0.897). The results can help us to understand the relationship between flow hydraulics and sediment generation of slope erosion and offer useful data for the building of erosion model in purple soil.

Mots clés

  • Purple soil
  • Runoff
  • Flow hydraulics
  • Sediment
  • Slope gradient
  • Rainfall intensity
access type Accès libre

Identifying the relationships of climate and physiological responses of a beech forest using the Standardised Precipitation Index: a case study for Slovakia

Publié en ligne: 08 Jul 2016
Pages: 246 - 251

Résumé

Abstract

The paper presents relationship between the Standardised Precipitation Index (SPI) and physiological responses of individual trees in a beech stand using an example of an experimental plot in Bienska valley (Zvolen, Slovakia). SPI is a widely used tool for monitoring both short-term and long-term droughts, and for the assessments of drought impacts on agriculture. Due to the complex ecosystem bonds, monitoring of drought in forests often requires a sophisticated technological approach. The aim of the paper was to correlate the SPI on the physiological responses of trees that were recorded during the performed physiological research (sap flow, and stem circumference increment) at the site in the growing seasons (May to September) of the years 2012-2014. The results revealed a relationship between the index and the physiological responses, although the problem with the impact of other environmental factors has also come up. The secondary correlation, in which soil water potential that significantly affects physiological responses of forest tree species was used as a dependent variable, showed a tighter relationship with the SPI. We found the highest correlation between the soil water potential and the values of SPI aggregated for five weeks. This indicates that the beech forest has a five week resistance to drought stress. The results also enable simple monitoring of the initiation of the drought stress by applying SPI for five weeks.

Mots clés

  • Drought
  • Physiological responses
  • Beech
  • Standardised Precipitation Index
  • Soil water potential
access type Accès libre

Design of a new hybrid artificial neural network method based on decision trees for calculating the Froude number in rigid rectangular channels

Publié en ligne: 08 Jul 2016
Pages: 252 - 260

Résumé

Abstract

A vital topic regarding the optimum and economical design of rigid boundary open channels such as sewers and drainage systems is determining the movement of sediment particles. In this study, the incipient motion of sediment is estimated using three datasets from literature, including a wide range of hydraulic parameters. Because existing equations do not consider the effect of sediment bed thickness on incipient motion estimation, this parameter is applied in this study along with the multilayer perceptron (MLP), a hybrid method based on decision trees (DT) (MLP-DT), to estimate incipient motion. According to a comparison with the observed experimental outcome, the proposed method performs well (MARE = 0.048, RMSE = 0.134, SI = 0.06, BIAS = -0.036). The performance of MLP and MLP-DT is compared with that of existing regression-based equations, and significantly higher performance over existing models is observed. Finally, an explicit expression for practical engineering is also provided.

Mots clés

  • Decision tree
  • Incipient motion
  • Multilayer perceptron (MLP)
  • Froude number
access type Accès libre

Modeling of sand-water slurry flow through horizontal pipe using CFD

Publié en ligne: 08 Jul 2016
Pages: 261 - 272

Résumé

Abstract

The paper presents three-dimensional CFD analysis of two-phase (sand-water) slurry flows through 263 mm diameter pipe in horizontal orientation for mixture velocity range of 3.5-4.7 m/s and efflux concentration range of 9.95-34% with three particle sizes viz. 0.165 mm, 0.29 mm and 0.55 mm with density 2650 kg/m3. RNG k-ε turbulence closure equations with Eulerian multi-phase model is used to simulate various slurry flows. The simulated values of local solid concentration are compared with the experimental data and are found to be in good agreement for all particle sizes. Effects of particle size on various slurry flow parameters such as pressure drop, solid phase velocity distribution, friction factor, granular pressure, turbulent viscosity, turbulent kinetic energy and its dissipation have been analyzed.

Mots clés

  • CFD
  • Slurry flow
  • Particle size
  • Solid concentration
  • Pipeline
access type Accès libre

Measurement of turbulent flow in a narrow open channel

Publié en ligne: 08 Jul 2016
Pages: 273 - 280

Résumé

Abstract

The paper presents the experimental results of turbulent flow over hydraulically smooth and rough beds. Experiments were conducted in a rectangular flume under the aspect ratio b/h = 2 (b = width of the channel 0.5 m, and h = flow depth 0.25 m) for both the bed conditions. For the hydraulically rough bed, the roughness was created by using 3/8″ commercially available angular crushed stone chips; whereas sand of a median diameter d50 = 1.9 mm was used as the bed material for hydraulically smooth bed. The three-dimensional velocity components were captured by using a Vectrino (an acoustic Doppler velocimeter). The study focuses mainly on the turbulent characteristics within the dip that were observed towards the sidewall (corner) of the channel where the maximum velocity occurs below the free-surface. It was also observed that the nondimensional Reynolds shear stress changes its sign from positive to negative within the dip. The quadrant plots for the turbulent bursting shows that the signs of all the bursting events change within the dip. Below the dip, the probability of the occurrence of sweeps and ejections are more than that of inward and outward interactions. On the other hand, within the dip, the probability of the occurrence of the outward and inward interactions is more than that of sweeps and ejections.

Mots clés

  • Flow measurement
  • Turbulent flow
  • Dip-phenomenon
  • Turbulent bursting
  • Open channel flow
access type Accès libre

Modelling free surface flow with curvilinear streamlines by a non-hydrostatic model

Publié en ligne: 08 Jul 2016
Pages: 281 - 288

Résumé

Abstract

This study addresses a particular phenomenon in open channel flows for which the basic assumption of hydrostatic pressure distribution is essentially invalid, and expands previous suggestions to flows where streamline curvature is significant. The proposed model incorporates the effects of the vertical curvature of the streamline and steep slope, in making the pressure distribution non-hydrostatic, and overcomes the accuracy problem of the Saint-Venant equations when simulating curvilinear free surface flow problems. Furthermore, the model is demonstrated to be a higher-order one-dimensional model that includes terms accounting for wave-like variations of the free surface on a constant slope channel. Test results of predicted flow surface and pressure profiles for flow in a channel transition from mild to steep slopes, transcritical flow over a short-crested weir and flow with dual free surfaces are compared with experimental data and previous numerical results. A good agreement is attained between the experimental and computed results. The overall simulation results reveal the satisfactory performance of the proposed model in simulating rapidly varied gravity-driven flows with predominant non-hydrostatic pressure distribution effects. This study suggests that a higher-order pressure equation should be used for modelling the pressure distribution of a curvilinear flow in a steeply sloping channel.

Mots clés

  • Curvilinear flow
  • Finite difference method
  • Hydraulic structures
  • Hydrodynamics
  • Non-hydrostatic pressure
  • Nonuniform flow
access type Accès libre

Interpretation of ponded infiltration data using numerical experiments

Publié en ligne: 08 Jul 2016
Pages: 289 - 299

Résumé

Abstract

Ponded infiltration experiment is a simple test used for in-situ determination of soil hydraulic properties, particularly saturated hydraulic conductivity and sorptivity. It is known that infiltration process in natural soils is strongly affected by presence of macropores, soil layering, initial and experimental conditions etc. As a result, infiltration record encompasses a complex of mutually compensating effects that are difficult to separate from each other. Determination of sorptivity and saturated hydraulic conductivity from such infiltration data is complicated. In the present study we use numerical simulation to examine the impact of selected experimental conditions and soil profile properties on the ponded infiltration experiment results, specifically in terms of the hydraulic conductivity and sorptivity evaluation. The effect of following factors was considered: depth of ponding, ring insertion depth, initial soil water content, presence of preferential pathways, hydraulic conductivity anisotropy, soil layering, surface layer retention capacity and hydraulic conductivity, and presence of soil pipes or stones under the infiltration ring. Results were compared with a large database of infiltration curves measured at the experimental site Liz (Bohemian Forest, Czech Republic). Reasonably good agreement between simulated and observed infiltration curves was achieved by combining several of factors tested. Moreover, the ring insertion effect was recognized as one of the major causes of uncertainty in the determination of soil hydraulic parameters.

Mots clés

  • Ponded infiltration experiment
  • Two-parameter infiltration equation
  • Three-dimensional axisymmetric dualcontinuum model
  • Preferential flow

Planifiez votre conférence à distance avec Sciendo