- Détails du magazine
- Format
- Magazine
- eISSN
- 1338-4333
- ISSN
- 0042-790X
- Première publication
- 28 Mar 2009
- Période de publication
- 4 fois par an
- Langues
- Anglais

#### Chercher

- Accès libre

Hydrology and the looming water crisis: It is time to think, and act, outside the box

Pages: 89 - 96

#### Résumé

- Accès libre

Values of rainfall erosivity factor for the Czech Republic

Pages: 97 - 102

#### Résumé

The processing of ombrographic data from 29 meteorological stations of the Czech Hydrometeorological Institute (CHMI), according to the terms of the Universal Soil Loss Equation for calculating long term loss of soil through water erosion, erosion hazard rains and their occurrence have been selected, with their relative amount and erosiveness - R-Factors determined for each month and years. By comparing the value of the time division of the R-Factor in the area of the Czech Republic and in selected areas of the USA it has been demonstrated that this division may be applied in the conditions of the Czech Republic. For the Czech Republic it is recommended to use the average value R = 40 based on the original evaluation.

#### Keywords

- Water erosion
- Rainfall-erosivity factor
- Rainfall

- Accès libre

A numerical investigation of a buoyancy driven flow in a semi-porous cavity: comparative effects of ramped and isothermal wall conditions

Pages: 103 - 111

#### Résumé

Steady two-dimensional natural convection taking place in a rectangular cavity, partially filled with an isotropic porous material, has been investigated numerically using an ADI method. It is assumed that one of the vertical walls of the cavity has a ramped temperature distribution. The vorticity-stream function formulation has been used to solve the set of nonlinear partial differential equations governing the flows in the clear region and the adjoining porous region. The effects of Darcy number and Rayleigh number have been discussed in detail.

#### Keywords

- Rectangular cavity
- Free convection
- Brinkman model
- Coupled flow
- Ramped boundary condition
- Numerical solution

- Accès libre

The combined use of wavelet transform and black box models in reservoir inflow modeling

Pages: 112 - 119

#### Résumé

In the study presented, different hybrid model approaches are proposed for reservoir inflow modeling from the meteorological data (monthly precipitation, one-month-ahead precipitation and monthly mean temperature data) by the combined use of discrete wavelet transform (DWT) and different black box techniques. Multiple linear regression (MLR), feed forward neural networks (FFNN) and least square support vector machines (LSSVM) were considered as the black box methods. In the modeling strategy, meteorological input data were decomposed into wavelet sub-time series at three resolution levels and ineffective sub-time series were eliminated by Mallows’ Cp based all possible regression method. As a result of all possible regression analyses, 2-months mode of time series of monthly temperature (D1_Tt), 8-months mode of time series (D3_Tt) of monthly temperature and approximation mode of time series (A3_Tt) of monthly temperature were eliminated. Remained effective sub-time series were used as the inputs of MLR, FFNN and LSSVM. When the performances of the training and testing periods were compared, it was observed that the DWTFFNN conjunction model has better results in terms of mean square errors (MSE) and determination coefficients (R2) statistics. The discrete wavelet transform approach also increased the accuracy of multiple linear regression and least squares support vector machines.

#### Keywords

- Hybrid model
- Discrete wavelet transform
- Mallows’ Cp method
- Multiple linear regression
- Feed forward neural networks
- Least squares support vector machines
- Reservoir inflow modeling

- Accès libre

Validation of transport and friction formulae for upper plane bed by experiments in rectangular pipe

Pages: 120 - 125

#### Résumé

The paper describes results of validation of authors' recently proposed formulae for sediment transport and bed friction in the upper plane bed regime using laboratory experiments in a pressurized pipe. Flows of mixture of water and fine to medium ballotini (d50 = 0.18 mm) were observed in a rectangular pipe (51 x 51 mm) with a deposit at the bottom of the pipe. A comparison of test results with transport-formula predictions shows a satisfactory match confirming a good prediction ability of the proposed transport formula at high bed shear. A prediction ability of the friction formulae appears to be less convincing but still reasonable. A joint use of the formulae for transport and friction predicts the delivered concentration of transported sediment within the accuracy range of ± 40 per cent for flows in which transported sediments strongly affect the bed friction, i.e. for flows with delivered concentration of sediment higher than say 3 per cent.

#### Keywords

- Sediment transport
- Sheet flow
- Bed load
- Suspended load

- Accès libre

Numerical investigation of solid-liquid slurry flow through an upward-facing step

Pages: 126 - 133g

#### Résumé

The flow of a solid-water mixture through an upward-facing step in a channel is numerically investigated. The effect of expansion ratio, mean solids volume fraction and particle diameter on the velocity field, pressure distribution and solid volume fraction field is studied. Expansion ratios of 0.50 and 0.67, particle diameter of 125 μm and 440 μm and mean solid volume fraction between 0.05 and 0.20 are considered. Particle density is 2465 kg m-3. An Eulerian twofluid model is used to simulate the flow. Due to the lack of experimental data, the model was validated by comparison to other numerical investigations and to experimental data about the horizontal pipe case. Afterwards, it is studied the effect of the above mentioned parameters upon the degree of coupling between the phases and the extension of the disturbance region in the pressure and solid volume fraction fields downstream the step. Parameters of engineering interest, such as the reattachment length and the pressure recovery downstream the enlargement, are investigated.

#### Keywords

- Two-fluid model
- Numerical analysis
- Slurries
- Two-phase flow
- Upward-facing step

- Accès libre

Determination of hydraulic conductivity of a suspension

Pages: 134 - 139

#### Résumé

The process of sedimentation and subsequent gravity compression of kaolin and water suspensions was investigated experimentally. 45 batch tests were carried out and the time dependence of the height of the suspension column was measured. The one-dimensional equations of Darcian mechanics of two-phase porous media are applied to formulate the studied process mathematically. A very natural assumption makes it possible to find a solution of the forward problem for a starting period of the process. Analysis of the theoretical function and the experimental data gives hydraulic conductivity as a function of the suspension concentration. The obtained results are presented and discussed.

#### Keywords

- Hydraulic conductivity
- Kaolin
- Suspension
- Gravity thickening

- Accès libre

Evapotranspiration changes in the forest-steppe and steppe zones under soil mulching

Pages: 140 - 145

#### Résumé

This paper contains the method and results of calculation evapotranspiration and its structure - transpiration and evaporation from traditionally tilled and mulched soil. The data considered indicate that in the arid regions of territory under study the evapotranspiration when soil is mulched does not change significantly and only the relation between the transpiration and soil evaporation changes. In the wet regions, evapotranspiration decreases when the soil is mulched which can result in a certain disturbance of the natural structure of the hydrological cycle and possible overmoistening soils.

#### Keywords

- Evapotranspiration
- Evapotranspiration structure
- Traditional agricultural practice
- Soil mulching

- Accès libre

Exact analytical solutions for contaminant transport in rivers 1. The equilibrium advection-dispersion equation

Pages: 146 - 160

#### Résumé

Analytical solutions of the advection-dispersion equation and related models are indispensable for predicting or analyzing contaminant transport processes in streams and rivers, as well as in other surface water bodies. Many useful analytical solutions originated in disciplines other than surface-water hydrology, are scattered across the literature, and not always well known. In this two-part series we provide a discussion of the advection-dispersion equation and related models for predicting concentration distributions as a function of time and distance, and compile in one place a large number of analytical solutions. In the current part 1 we present a series of one- and multi-dimensional solutions of the standard equilibrium advection-dispersion equation with and without terms accounting for zero-order production and first-order decay. The solutions may prove useful for simplified analyses of contaminant transport in surface water, and for mathematical verification of more comprehensive numerical transport models. Part 2 provides solutions for advective- dispersive transport with mass exchange into dead zones, diffusion in hyporheic zones, and consecutive decay chain reactions.

#### Keywords

- Contaminant transport
- Analytical solutions
- Surface water
- Advection-dispersion equation

- Accès libre

Comparison of real evapotranspiration measured by weighing lysimeters with simulations based on the Penman formula and a crop growth model

Pages: 161 - 172

#### Résumé

Although the quantification of real evapotranspiration (ETr) is a prerequisite for an appropriate estimation of the water balance, precision and uncertainty of such a quantification are often unknown. In our study, we tested a combined growth and soil water balance model for analysing the temporal dynamics of ETr. Simulated ETr, soil water storage and drainage rates were compared with those measured by 8 grass-covered weighable lysimeters for a 3-year period (January 1, 1996 to December 31, 1998). For the simulations, a soil water balance model based on the Darcy-equation and a physiological-based growth model for grass cover for the calculation of root water uptake were used. Four lysimeters represented undisturbed sandy soil monoliths and the other four were undisturbed silty-clay soil monoliths. The simulated ETr-rates underestimated the higher ETr-rates observed in the summer periods. For some periods in early and late summer, the results were indicative for oasis effects with lysimeter-measured ETr-rates higher than corresponding calculated rates of potential grass reference evapotranspiration. Despite discrepancies between simulated and observed lysimeter drainage, the simulation quality for ETr and soil water storage was sufficient in terms of the Nash-Sutcliffe index, the modelling efficiency index, and the root mean squared error. The use of a physiological-based growth model improved the ETr estimations significantly.

#### Keywords

- Weighable lysimeters
- Modelling
- Real evapotranspiration
- Drainage
- Darcy-equation
- Water balance

- Accès libre

Comparison of daily potential evapotranspiration calculated by two procedures based on Penman-Monteith type equation

Pages: 173 - 176

#### Résumé

Paper presents comparison of the daily reference crop (grass vegetation cover) potential evapotranspiration results calculated by the two modifications of the Penman-Monteith type equation. The first modification was published in FAO recommendation (Allen at al., 1998), PM-FAO, the second is modification according to Budagovskiy (1964) and Novák (1995), PM-BN. Both are used in soil water simulation models HYDRUS-1D and GLOBAL. Calculations were performed for frost-free seasons of the years 2000-2009, using the meteorological station Gabčíkovo (South Slovakia) meteorological data and canopy characteristics. The results indicate significant differences in daily and seasonal potential evapotranspiration. Reasons for those differences are discussed; they should be in different net radiation and aerodynamic resistance estimation methods.

#### Keywords

- Potential evapotranspiration
- Reference crop
- Penman-Monteith equation