- 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

Sand dune vegetation-biocrust interaction as a source of spatial heterogeneity

Pages: 145 - 155

#### Résumé

Vegetation and biocrust play crucial roles in dune stability and mobility, and their interaction can lead to bistability, temporal oscillations, and hysteresis. We studied a two-dimensional (2D) mathematical model of vegetation and biogenic crust cover dynamics on sand dunes. Under a certain parameter range, the space-independent version of the model exhibited the bi-stability of an oscillatory state and a steady state, and we studied the 2D dynamics of the model under these parameters. The patterns developed by the 2D model showed a high degree of spatial heterogeneity and complexity depending on the initial conditions and on the state type across the front. The results suggest that spatial heterogeneity and complexity can evolve from the intrinsic dynamics between vegetation and biocrust, even without natural geodiversity and spatiotemporal climate fluctuations. In the real world, these two types of intrinsic and extrinsic heterogeneity processes interact such that it is difficult to distinguish between them.

#### Mots clés

- Sand dunes
- Biocrust
- Bistability
- Relaxation oscillations
- Drift potential
- Mathematical modeling

- Accès libre

The spatial and temporal variability of hydrological drought in the Polish Carpathians

Pages: 156 - 169

#### Résumé

The aim of the study was to evaluate the climate and geographic factors controlling the hydrological drought of the rivers located in the Upper Vistula catchment in the Polish Carpathians. Drought was identified based on the daily flow (based on water stage measered once a day at 6 UTC) series dating from between 1975 and 2019 at 49 gauging cross-sections. Four physico-geographical regions were identified in the Polish Carpathians and spatial variabilities of the basic drought characteristics were developed within these regions. Such spatial distributions were treated as maps indicating drought hazard areas in the region. In addition, an analysis was undertaken to study the seasonality of the start and end times of the drought (all in the multi-annual period), the longest duration of droughts, the droughts of the highest volume in multi-annual period, as well as the number of drought days. Multi-annual variability of the number of drought days was also analysed.

The results suggest that droughts in the Polish Carpathians are events characteristic of summer and autumn, whereas in the Tatra Mountains and the Podhale region - of autumn and winter. The greatest hazard of a prolonged and high-volume drought occurs in the Podhale region and the Tatra Mountains, while the lowest hazard is observed in the Bieszczady Mountains and the eastern part of the studied area.

#### Mots clés

- Hydrological drought
- Long-term variability
- Seasonal variability
- Vistula
- the Polish Carpathian
- Drought hazard

- Accès libre

Experimental investigation of hydrophobic bentonite effects on reducing evaporation from water surfaces

Pages: 170 - 177

#### Résumé

In recent years, due to the occurrence of water shortage and drought problems, particularly in arid and semi-arid regions of the world, new methods to reduce evaporation from the surface of dam reservoirs, lakes, and other water-free surfaces are investigated. This study aimed to use hydrophobic bentonite to reduce water evaporation from water surfaces, on a laboratory scale, and field conditions for the first time. Bentonite initially became hydrophobic by stearic acid (SA). Under such conditions, hydrophobic bentonite floats on the surface of water and forms a thin coating layer. The produced hydrophobic bentonite had a contact angle of 150°, indicating its superhydrophobicity. Evaporation reduction was measured under laboratory and field conditions and it was compared to hexadecanol as the reference material. The results demonstrated that the hydrophobic bentonite efficiency under laboratory conditions was similar to that of hexadecanol and prevented water evaporation by 36%. However, under field conditions, hydrophobic bentonite and hexadecanol efficiencies were 40% and 23% to reduce evaporation for 30 days, respectively. In terms of stability, hexadecanol needed to be re-injected after three days, while hydrophobic bentonite was stable and remained on the surface for more than 100 days under laboratory conditions and for more than 15 days under field conditions without needing re-injection. This coverage with method can be used to reduce evaporation from lakes, tanks, and reservoirs of small dams.

#### Mots clés

- Water evaporation
- Water surface
- Hydrophobic bentonite
- Hexadecanol monolayer

- Accès libre

Correlation between climate and flood indices in Northwestern Italy at different temporal scales

Pages: 178 - 194

#### Résumé

The occurrence of river floods is strongly related to specific climatic conditions that favor extreme precipitation events leading to catchment saturation. Although the impact of precipitation and temperature patterns on river flows is a well discussed topic in hydrology, few studies have focused on the relationship between peak discharges and standard Climate Change Indices (ETCCDI) of precipitation and temperature, widely used in climate research. It is of interest to evaluate whether these indices are relevant for characterizing and predicting floods in the Alpine area. In this study, a correlation analysis of the ETCCDI indices annual time series and annual maximum flows is presented for the Piedmont Region, in North-Western Italy. Spearman’s rank correlation is used to determine which ETCCDI indices are temporally correlated with maximum discharges, allowing to hypothesize which climate drivers better explain the interannual variability of floods. Moreover, the influence of climate (decadal) variability on the tendency of annual maximum discharges is examined by spatially correlating temporal trends of climate indices with temporal trends of the discharge series in the last twenty years, calculated using the Theil-Sen slope estimator. Results highlight that, while extreme precipitation indices are highly correlated with extreme discharges at the annual timescale, with different indices that are consistent with catchment size, the decadal tendencies of extreme discharges may be better explained by the decadal tendencies of the total annual precipitation over the study area. This suggests that future projections of the annual precipitation available from climate models simulations, whose reliability is higher compared to precipitation extremes, may be used as covariates for non-stationary flood frequency analysis.

#### Mots clés

- Flood tendency
- ETCCDI indices
- Flood and climate variability

- Accès libre

Performance analysis of rectangular SIT (sediment invert trap) for stormwater drainage system

Pages: 195 - 212

#### Résumé

Deposition of solid particles in the stormwater sewers reduces the discharging capacity, causing inundation. A sediment invert trap (SIT) is an option that can be installed at the bottom of the stormwater sewer drain to intercept the flowing solid particles. In the present study performance of rectangular SIT were analyzed experimentally and computationally. Variation of particle trapping efficiency of rectangular SIT fitted at the bottom of the open channel flume has been studied under the interpretation of invert trap depth, flow depth, particle size, particle shape, and slot width. To predict the flow field and trap efficiency of a rectangular invert trap, 2D-VOF-DPM-CFD modelling has been carried out using ANSYS Fluent 2020 R1 software. For velocity field determination, the volume of fluid (VOF) model was used along with realizable

#### Mots clés

- Sediment invert trap
- Trap efficiency
- Shape factor
- Volume of fluid model
- Discrete phase model

- Accès libre

Adaptive stochastic management of the storage function for a large, open reservoir using learned fuzzy models

Pages: 213 - 221

#### Résumé

The design and evaluation of algorithms for adaptive stochastic control of the reservoir function of a water reservoir using an artificial intelligence method (learned fuzzy model) are described in this article. This procedure was tested on the Vranov reservoir (Czech Republic). Stochastic model results were compared with the results of deterministic management obtained using the method of classical optimisation (differential evolution). The models used for controlling of reservoir outflow used single quantile from flow duration curve values or combinations of quantile values from flow duration curve for determination of controlled outflow. Both methods were also tested on forecast data from real series (100% forecast). Finally, the results of the dispatcher graph, adaptive deterministic control and adaptive stochastic control were compared. Achieved results of adaptive stochastic management were better than results provided by dispatcher graph and provide inspiration for continuing research in the field.

#### Mots clés

- Stochastic
- Artificial intelligence
- Storage function
- Optimisation

- Accès libre

Analytical and numerical investigation of mechanical energy balance and energy loss of three-dimensional steady turbulent flows in open-channels

Pages: 222 - 233

#### Résumé

Study about the mechanical energy balance and the energy loss of 3-D turbulent flows in open-channels has its own complexities. The governing equation of the mechanical energy in turbulent flows has been previously known and includes turbulence parameters that their calculations or measurements are not easy. In this study, a form of the total mechanical energy equation that leads to a number of significant physical insights is analytically investigated, from which analytical relationships for the energy loss estimation in 3-D turbulent flows are defined. The effect of different turbulence parameters is reflected on the new relationships and analyzed by equalizations replacing unknown correlations with closure approximations using the numerical turbulence simulation. In order to investigate the application of the analytical relationships, numerical simulations are performed by using OpenFOAM software to solve the Navier-Stokes equations with the RSM turbulence model in open-channels with different geometries. Then, the contribution of the turbulence parameters to the total mechanical energy balance is evaluated in uniform and nonuniform turbulent flows and their difference is analyzed, that leads to identify the parameters affecting the friction and local losses. The results demonstrate that the magnitudes of the turbulent diffusion, the work done by the viscous stresses pertaining to the mean motion and the viscous diffusion of the turbulence energy are substantially smaller than the other terms of the total energy equation for turbulent flows in open-channels with different geometries, while the effect of the variations of the turbulence kinetic energy and the work done by the turbulence stresses, that has not been considered in the previous mechanical energy equations, is more important in complex flows. From a practical viewpoint, in order to study the details of the total mechanical energy balance and the energy loss in 3-D turbulent flows with the presence of the secondary currents, the proposed method can be useful.

#### Mots clés

- Mechanical energy equation
- Energy loss
- Turbulent flow
- Analytical relationships
- Numerical simulation

- Accès libre

Estimation of hydrodynamic properties of a sandy-loam soil by two analysis methods of single-ring infiltration data

Pages: 234 - 243

#### Résumé

Beerkan infiltration runs could provide an incomplete description of infiltration with reference to either the near steady-state or the transient stages. In particular, the process could still be in the transient stage at the end of the run or some transient infiltration data might be loss. The Wu1 method and the BEST-steady algorithm can be applied to derive soil hydrodynamic parameters even under these circumstances. Therefore, a soil dataset could be developed using two different data analysis methods. The hypothesis that the Wu1 method and BEST-steady yield similar predictions of the soil parameters when they are applied to the same infiltration curve was tested in this investigation. For a sandy-loam soil, BEST-steady yielded higher saturated soil hydraulic conductivity,

#### Mots clés

- Soil hydrodynamic properties
- Beerkan infiltration run
- Data analysis methods
- BEST methodology
- Wu1 method

- Accès libre

Field-scale assessment of the unsaturated hydraulic properties of residual soils in southeastern Brazil

Pages: 244 - 256

#### Résumé

Field tests were carried out to estimate effective unsaturated soil hydraulic properties of layered residual soils in Rio de Janeiro, southeastern Brazil. Data of this type are important for understanding the initiation of rainstorm-induced soil landslides, which often occur in the state of Rio de Janeiro as well as other areas having similar geologic settings and climate conditions. Tests were carried out using a simplified field approach, referred to as the Monitored Infiltration Test, which requires only a tensiometer to measure pressure heads below the wetting front, triggered by flow from a Mariotte bottle which maintains a constant pressure at the top edge of the soil profile. The data can then be analyzed by numerical inversion using the HYDRUS-2D software package. The test is relatively fast since no steady-state flow conditions are needed, and versatile since the test can be carried out quickly on steep slopes with the help of a manual auger. Soil water retention and the unsaturated hydraulic conductivity functions were obtained for a range of young, mature and saprolitic residual soils. The effective hydraulic properties of the distinct residual soil layers can be quite large, reflecting a need to provide a careful analysis of field-scale hydraulic heterogeneity in geotechnical analyses.

#### Mots clés

- Residual soils
- Unsaturated soil hydraulic properties
- Field infiltration tests
- HYDRUS-2D

- Accès libre

Effects of carbonated water injection on the pore system of a carbonate rock (coquina)

Pages: 257 - 268

#### Résumé

CO_{2} injection is a well-known Enhanced Oil Recovery (EOR) technique that has been used for years to improve oil extraction from carbonate rock and other oil reservoirs. Optimal functioning of CO_{2} injection requires a thorough understanding of how this method affects the petrophysical properties of the rocks. We evaluated pore-scale changes in these properties, notably porosity and absolute permeability, following injection of CO_{2}-saturated water in two coquina outcrop samples from the Morro do Chaves Formation in Brazil. The coquinas are close analogues of Pre-salt oil reservoirs off the coast of southern Brazil. The effects of carbonated water injection were evaluated using a series of experimental and numerical steps before and after coreflooding: cleaning, basic petrophysics, microtomography (microCT) imaging, nuclear magnetic resonance (NMR) analyses, and pore network modeling (PNM). Our study was motivated by an earlier experiment which did not show the development of a wormhole in the center of the sample, with a concomitant increase in permeability of the coquina as often noted in the literature. We instead observed a substantial decrease in the absolute permeability (between 71 and 77%), but with little effect on the porosity and no wormhole formation. While all tests were carried out on both samples, here we present a comprehensive analysis for one of the samples to illustrate changes at the pore network level. Different techniques were used for the pore-scale analyses, including pore network modeling using PoreStudio, and software developed by the authors to enable a statistical analysis of the pore network. Results provided much insight in how injected carbonated water affects the pore network of carbonate rocks.

#### Mots clés

- Carbonate rocks
- Coreflooding
- Pore Size Distribution
- Pore Network Analysis
- PoreStudio