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

#### Chercher

- Accès libre

A head loss model for homogeneous slurry transport for medium sized particles

Pages: 1 - 12

#### Résumé

Slurry transport in horizontal and vertical pipelines is one of the major means of transport of sands and gravels in the dredging industry. There exist 4 main flow regimes, the fixed or stationary bed regime, the sliding bed regime, the heterogeneous flow regime and the homogeneous flow regime. Of course the transitions between the regimes are not very sharp, depending on parameters like the particle size distribution. The focus in this paper is on the homogeneous regime. Often the so called equivalent liquid model (ELM) is applied, however many researchers found hydraulic gradients smaller than predicted with the ELM, but larger that the hydraulic gradient of liquid. Talmon (2011, 2013) derived a fundamental equation (method) proving that the hydraulic gradient can be smaller than predicted by the ELM, based on the assumption of a particle free viscous sub-layer. He used a 2D velocity distribution without a concentration distribution.

In this paper 5 methods are described (and derived) to determine the hydraulic gradient in homogeneous flow, of which the last method is based on pipe flow with a concentration distribution. It appears that the use of von Driest (Schlichting, 1968) damping, if present, dominates the results, however applying a concentration distribution may neutralise this. The final equation contains both the damping and a concentration distribution giving the possibility to calibrate the constant in the equation with experimental data. The final equation is flexible and gives a good match with experimental results in vertical and horizontal pipelines for a value of A_{Cv} = 1.3. Data of horizontal experiments D_{p} = 0.05-0.30 m, d = 0.04 mm, vertical experiments Dp = 0.026 m, d = 0.125, 0.345, 0.560, and 0.750 mm.

#### Keywords

- Slurry transport
- Homogeneous transport
- Viscous sub layer
- Mixing length

- Accès libre

A comparative study of friction factor correlations for high concentrate slurry flow in smooth pipes

Pages: 13 - 20

#### Résumé

A number of correlations for friction factor determinations in smooth pipes have been proposed in the past decades. The accuracy and applicability of these friction factor formulas should be examined. Based on this notion the paper is designed to provide a comparative study of friction factor correlations in smooth pipes for all flow regimes of Bingham fluids. Nine models were chosen. The comparisons of the selected equations with the existing experimental results, which are available in the literature, were expressed through MARE, MRE^{+}, MRE^{-}, RMSE, Ѳ, and S. The statistical comparisons were also carried out using MSC and AIC. The analyses show that the Wilson-Thomas (1985) and Morrison (2013) models are best fit models to the experimental data for the Reynolds number up to 40000. Within this range, both models can be used alternately. But beyond this Re value the discrepancy of the Wilson-Thomas model is higher than the Morrison model. In view of the fact that the Morrison model requires fewer calculations and parameters as well as a single equation is used to compute the friction factor for all flow regimes, it is the authors’ advice to use this model for friction factor estimation for the flow of Bingham fluids in smooth pipes as an alternative to the Moody chart and other implicit formulae.

#### Keywords

- Bingham fluid
- Smooth pipe
- Laminar flow
- Turbulent flow
- Friction factor
- Reynolds number
- Correlations
- Statistical parameters

- Accès libre

Spatial interpolation of point velocities in stream cross-section

Pages: 21 - 28

#### Résumé

The most frequently used instrument for measuring velocity distribution in the cross-section of small rivers is the propeller-type current meter. Output of measuring using this instrument is point data of a tiny bulk. Spatial interpolation of measured data should produce a dense velocity profile, which is not available from the measuring itself. This paper describes the preparation of interpolation models.

Measuring campaign was realized to obtain operational data. It took place on real streams with different velocity distributions. Seven data sets were obtained from four cross-sections varying in the number of measuring points, 24-82. Following methods of interpolation of the data were used in the same context: methods of geometric interpolation arithmetic mean and inverse distance weighted, the method of fitting the trend to the data thin-plate spline and the geostatistical method of ordinary kriging. Calibration of interpolation models carried out in the computational program Scilab is presented. The models were tested with error criteria by cross-validation. Ordinary kriging was proposed to be the most suitable interpolation method, giving the lowest values of used error criteria among the rest of the interpolation methods.

#### Keywords

- Open channel
- Current meter
- Cross-validation
- Arithmetic mean
- Inverse distance weighted
- Thin-plate spline
- Kriging

- Accès libre

Hydrodynamic modeling of stratified estuary: case study of the Jadro River (Croatia)

Pages: 29 - 37

#### Résumé

The Jadro River with total length of 4.3 km and average annual discharge of 7.9 m3 s-1 is a relatively small river on the east coast of the Adriatic Sea, close to Split. Field campaign measurements were made to estimate salt intrusion in the Jadro estuary in July 2012. This measurement confirmed the stratified character of the estuary where fresh water flows in a thin layer over denser sea water. Furthermore, a numerical model was set up for simulating unsteady stratified flow without mixing between the layers. The model is applied for the Jadro River and field measurements are used for calibration. In addition, the steady state of stratification within the estuary is analyzed by a box model which assumes mixing between layers. Results of the numerical and the box models were compared. The flushing time estimated with the box model is approximately 1.5 day for summer steady conditions. Numerical analysis however shows that the residence time is much larger owing to flow unsteadiness

#### Keywords

- Estuary
- Salinity
- Numerical model
- Box model
- Jadro
- Croatia

- Accès libre

Investigation of seasonal thermal flow in a real dam reservoir using 3-D numerical modeling

Pages: 38 - 46

#### Résumé

Investigations indicate that correct estimation of seasonal thermal stratification in a dam reservoir is very important for the dam reservoir water quality modeling and water management problems. The main aim of this study is to develop a hydrodynamics model of an actual dam reservoir in three dimensions for simulating a real dam reservoir flows for different seasons. The model is developed using nonlinear and unsteady continuity, momentum, energy and k-ε turbulence model equations. In order to include the Coriolis force effect on the flow in a dam reservoir, Coriolis force parameter is also added the model equations. Those equations are constructed using actual dimensions, shape, boundary and initial conditions of the dam and reservoir. Temperature profiles and flow visualizations are used to evaluate flow conditions in the reservoir. Reservoir flow’s process and parameters are determined all over the reservoir. The mathematical model developed is capable of simulating the flow and thermal characteristics of the reservoir system for seasonal heat exchanges. Model simulations results obtained are compared with field measurements obtained from gauging stations for flows in different seasons. The results show a good agreement with the field measurements.

#### Keywords

- Real dam reservoir
- Thermal stratification
- Mathematical model
- Density flow
- Divergence flow

- Accès libre

Treated wastewater irrigation effects on soil hydraulic conductivity and aggregate stability of loamy soils in Israel

Pages: 47 - 54

#### Résumé

The use of treated wastewater (TWW) for agricultural irrigation becomes increasingly important in water stressed regions like the Middle East for substituting fresh water (FW) resources. Due to elevated salt concentrations and organic compounds in TWW this practice has potential adverse effects on soil quality, such as the reduction of hydraulic conductivity (HC) and soil aggregate stability (SAS). To assess the impact of TWW irrigation in comparison to FW irrigation on HC, in-situ infiltration measurements using mini disk infiltrometer were deployed in four different long-term experimental orchard test sites in Israel. Topsoil samples (0-10 cm) were collected for analyzing SAS and determination of selected soil chemical and physical characteristics.

The mean HC values decreased at all TWW sites by 42.9% up to 50.8% compared to FW sites. The SAS was 11.3% to 32.4% lower at all TWW sites. Soil electrical conductivity (EC) and exchangeable sodium percentage (ESP) were generally higher at TWW sites. These results indicate the use of TWW for irrigation is a viable, but potentially deleterious option, as it influences soil physical and chemical properties.

#### Keywords

- Hydraulic conductivity
- Soil aggregate stability
- Irrigation
- Treated wastewater
- Israel

- Accès libre

Estimating the rainfall erosivity factor from monthly precipitation data in the Madrid Region (Spain)

Pages: 55 - 62

#### Résumé

The need for continuous recording rain gauges makes it difficult to determine the rainfall erosivity factor (Rfactor) of the Universal Soil Loss Equation in regions without good spatial and temporal data coverage. In particular, the R-factor is only known at 16 rain gauge stations in the Madrid Region (Spain). The objectives of this study were to identify a readily available estimate of the R-factor for the Madrid Region and to evaluate the effect of rainfall record length on estimate precision and accuracy. Five estimators based on monthly precipitation were considered: total annual rainfall (P), Fournier index (F), modified Fournier index (MFI), precipitation concentration index (PCI) and a regression equation provided by the Spanish Nature Conservation Institute (R_{ICONA}). Regression results from 8 calibration stations showed that MFI was the best estimator in terms of coefficient of determination and root mean squared error, closely followed by P. Analysis of the effect of record length indicated that little improvement was obtained for MFI and P over 5- year intervals. Finally, validation in 8 additional stations supported that the equation R = 1.05·MFI computed for a record length of 5 years provided a simple, precise and accurate estimate of the R-factor in the Madrid Region.

#### Keywords

- Rainfall erosivity
- R-factor
- Universal Soil Loss Equation
- Modified Fournier index
- Soil erosion

- Accès libre

Stochastic structure of annual discharges of large European rivers

Pages: 63 - 70

#### Résumé

Water resource has become a guarantee for sustainable development on both local and global scales. Exploiting water resources involves development of hydrological models for water management planning. In this paper we present a new stochastic model for generation of mean annul flows. The model is based on historical characteristics of time series of annual flows and consists of the trend component, long-term periodic component and stochastic component. The rest of specified components are model errors which are represented as a random time series. The random time series is generated by the single bootstrap model (SBM). Stochastic ensemble of error terms at the single hydrological station is formed using the SBM method. The ultimate stochastic model gives solutions of annual flows and presents a useful tool for integrated river basin planning and water management studies. The model is applied for ten large European rivers with long observed period. Validation of model results suggests that the stochastic flows simulated by the model can be used for hydrological simulations in river basins.

#### Keywords

- Stochastic model
- Flow simulation
- Long-term periodicity
- Single bootstrap model SBM

- Accès libre

On the role of rock fragments and initial soil water content in the potential subsurface runoff formation

Pages: 71 - 81

#### Résumé

Stony soils are composed of fractions (rock fragments and fine soil) with different hydrophysical characteristics. Although they are abundant in many catchments, their properties are still not well understood. This article presents basic characteristics (texture, stoniness, saturated hydraulic conductivity, and soil water retention) of stony soils from a mountain catchment located in the highest part of the Carpathian Mountains and summarizes results of water flow modeling through a hypothetical stony soil profile. Numerical simulations indicate the highest vertical outflow from the bottom of the profile in soils without rock fragments under ponding infiltration condition. Simulation of a more realistic case in a mountain catchment, i.e. infiltration of intensive rainfall, shows that when rainfall intensity is lower than the saturated hydraulic conductivity of the stony soil, the highest outflow is predicted in a soil with the highest stoniness and high initial water content of soil matrix. Relatively low available retention capacity in a stony soil profile and consequently higher unsaturated hydraulic conductivity leads to faster movement of the infiltration front during rainfall.

#### Keywords

- Stony soils
- Infiltration
- Stoniness
- Initial soil water content
- Mathematical modeling

- Accès libre

Water table effects on measured and simulated fluxes in weighing lysimeters for differently-textured soils

Pages: 82 - 92

#### Résumé

Weighing lysimeters can be used for studying the soil water balance and to analyse evapotranspiration (ET). However, not clear was the impact of the bottom boundary condition on lysimeter results and soil water movement. The objective was to analyse bottom boundary effects on the soil water balance. This analysis was carried out for lysimeters filled with fine- and coarse-textured soil monoliths by comparing simulated and measured data for lysimeters with a higher and a lower water table. The eight weighable lysimeters had a 1 m^{2} grass-covered surface and a depth of 1.5 m. The lysimeters contained four intact monoliths extracted from a sandy soil and four from a soil with a silty-clay texture. For two lysimeters of each soil, constant water tables were imposed at 135 cm and 210 cm depths. Evapotranspiration, change in soil water storage, and groundwater recharge were simulated for a 3-year period (1996 to 1998) using the Hydrus-1D software. Input data consisted of measured weather data and crop model-based simulated evaporation and transpiration. Snow cover and heat transport were simulated based on measured soil temperatures. Soil hydraulic parameter sets were estimated (i) from soil core data and (ii) based on texture data using ROSETTA pedotransfer approach. Simulated and measured outflow rates from the sandy soil matched for both parameter sets. For the sand lysimeters with the higher water table, only fast peak flow events observed on May 4, 1996 were not simulated adequately mainly because of differences between simulated and measured soil water storage caused by ET-induced soil water storage depletion. For the silty-clay soil, the simulations using the soil hydraulic parameters from retention data (i) were matching the lysimeter data except for the observed peak flows on May, 4, 1996, which here probably resulted from preferential flow. The higher water table at the lysimeter bottom resulted in higher drainage in comparison with the lysimeters with the lower water table. This increase was smaller for the finer-textured soil as compared to the coarser soil.

#### Keywords

- Weighable lysimeters
- Modelling
- Hydrus-1D
- Drainage
- Boundary condition