Thermal bulk polymerization of cholesteryl acrylate

The thermal bulk polymerization of cholesteryl acrylate was carried out in the solid phase, the mesomorphic phase, and the liquid phase to study the effect of monomer ordering on polymerization rate and polymer properties. The rate increased with decreasing ordering (or enhanced mobility) of the monomer. Formation of inhibitive by-products during the polymerization limited conversions to 35%. The sedimentation constant S0 = 6.2 S was the same for the polymers obtained in the three phases. The weight-average molecular weight (w) was 480,000 as determined by ultracentrifugation. Poly-(cholesteryl acrylate) formed in bulk is randomly coiled when dissolved in tetrahydrofuran. The thermal properties of the monomer are given

Modelling water flow and seasonal soil moisture dynamics in analluvial groundwater-fed wetland

International audienceComplex interactions occur in riparian wetlands between groundwater, surface water and climatic conditions. Knowledge of the hydrology of these systems is necessary to understand their functioning and their value and models are a useful and probably essential tool to capture their hydrological complexity. In this study, a 2D-model describing saturated-unsaturated water flow is applied to a transect through a groundwater-fed riparian wetland located along the middle reach of the river Dijle. The transect has high levees close to the river and a depression further into the floodplain. Scaling factors are introduced to describe the variability of soil hydraulic properties along the transect. Preliminary model calculations for one year show a good agreement between model calculations and measurements and demonstrate the capability of the model to capture the internal groundwater dynamics. Seasonal variations in soil moisture are reproduced well by the model thus translating external hydrological boundary conditions to root zone conditions. The model proves to be a promising tool for assessing effects of changes in hydrological boundary conditions on vegetation type distribution and to gain more insight in the highly variable internal flow processes of riparian wetlands. Keywords: riparian wetland,eco-hydrology, upward seepage, floodplain hydrolog

Modelling water flow and seasonal soil moisture dynamics in analluvial groundwater-fed wetland

Complex interactions occur in riparian wetlands between groundwater, surface water and climatic conditions. Knowledge of the hydrology of these systems is necessary to understand their functioning and their value and models are a useful and probably essential tool to capture their hydrological complexity. In this study, a 2D-model describing saturated-unsaturated water flow is applied to a transect through a groundwater-fed riparian wetland located along the middle reach of the river Dijle. The transect has high levees close to the river and a depression further into the floodplain. Scaling factors are introduced to describe the variability of soil hydraulic properties along the transect. Preliminary model calculations for one year show a good agreement between model calculations and measurements and demonstrate the capability of the model to capture the internal groundwater dynamics. Seasonal variations in soil moisture are reproduced well by the model thus translating external hydrological boundary conditions to root zone conditions. The model proves to be a promising tool for assessing effects of changes in hydrological boundary conditions on vegetation type distribution and to gain more insight in the highly variable internal flow processes of riparian wetlands.</p> <p style='line-height: 20px;'><b>Keywords: </b>riparian wetland,eco-hydrology, upward seepage, floodplain hydrolog

Analysis of the spatial variation in the parameters of the SWAT model with application in Flanders, Northern Belgium

International audienceOperational applications of a hydrological model often require the prediction of stream flow in (future) time periods without stream flow observations or in ungauged catchments. Data for a case-specific optimisation of model parameters are not available for such applications, so parameters have to be derived from other catchments or time periods. It has been demonstrated that for applications of the SWAT in Northern Belgium, temporal transfers of the parameters have less influence than spatial transfers on the performance of the model. This study examines the spatial variation in parameter optima in more detail. The aim was to delineate zones wherein model parameters can be transferred without a significant loss of model performance. SWAT was calibrated for 25 catchments that are part of eight larger sub-basins of the Scheldt river basin. Two approaches are discussed for grouping these units in zones with a uniform set of parameters: a single parameter approach considering each parameter separately and a parameter set approach evaluating the parameterisation as a whole. For every catchment, the SWAT model was run with the local parameter optima, with the average parameter values for the entire study region (Flanders), with the zones delineated with the single parameter approach and with the zones obtained by the parameter set approach. Comparison of the model performances of these four parameterisation strategies indicates that both the single parameter and the parameter set zones lead to stream flow predictions that are more accurate than if the entire study region were treated as one single zone. On the other hand, the use of zonal average parameter values results in a considerably worse model fit compared to local parameter optima. Clustering of parameter sets gives a more accurate result than the single parameter approach and is, therefore, the preferred technique for use in the parameterisation of ungauged sub-catchments as part of the simulation of a large river basin. Keywords: hydrological model, regionalisation, parameterisation, spatial variabilit

Development of a conceptual model of the hydrologic response of tropical Andean micro-catchments in Southern Ecuador

This paper presents a lumped conceptual model designed for simulating the rainfallrunoff response of mountain micro-catchments with natural vegetation located in the south of Ecuador. The conceptual model is mimicking the soil hydrology and consists of a maximum of three linear reservoirs in series. A two and three reservoir model structure were tested, respectively A GLUE uncertainty analysis was applied to assess the model performance. Simulation results of the discharge confirmed the applicability of the soil-based conceptual model structure for the selected study areas, during model calibration and validation. The three reservoir model best predicted the runoff, nevertheless the two reservoir model well captures the rainfall-runoff process of the micro-catchments with páramo vegetation. Although differences in climate regime, vegetation, and soil of the selected catchments runoff is strongly controlled by the precipitation and soil type, and the horizons contributing to runoff are defined by their antecedent wetness. Results confirm that the discharge is mainly controlled by lateral subsurface flow through the organic horizons, while during dry conditions the C-horizon and the bedrock mainly contribute to discharge. Lateral transport through the densely rooted top horizon and the litter layer occurs during storm events, being under those conditions the major discharge component. Overland flow is a local phenomenon, negligible in comparison to the other flow components

Effects of watershed and riparian zone characteristics on nutrient concentrations in the River Scheldt Basin

International audienceThe relative influence of a set of watershed characteristics on surface water nutrient concentrations was examined in 173 watersheds within two subcatchments (Upper-Scheldt and Nete) of the River Scheldt Basin (Flanders, Belgium). Each watershed was described by seasonal rainfall, discharge loading of point sources, morphological characteristics (area, average slope, drainage density, elongation), land use and soil properties (soil texture and drainage). Partial regression analysis revealed that soil drainage variables had the strongest influence on nutrient concentrations. Additional influence was exerted by land use and point source loading variables. Nitrate concentrations were positively correlated with effluent loadings coming from wastewater treatment plants and with the area of agricultural land. Phosphate concentrations were best explained by effluent loadings of industrial point sources and by the area of urban land. Land use close to the river was not a better predictor of nitrate and phosphate concentrations than land use away from the river. This suggests that the mediating impact of riparian zones is rather explained by the hydrologic pathways within the buffer strip

Utilisation de l'expérience de drainage à pas de pression multiples pour la détermination des fonctions hydrauliques du sol par la méthode inverse : résultats expérimentaux

La méthode de drainage à pas de pression multiples, combinée avec la méthode inverse, permet la détermination des fonctions hydrauliques du sol (têta(h) et K(h)) simultanément. Cependant, le choix des fonctions décrivant têta(h) et K(h) du sol est d'une importance capitale dans cette méthode. Les résultats expérimentaux montrent que le modèle de CAMPBELL (1974) dans sa version améliorée par HUTSON et CASS (1987) permet une description raisonnable du processus du drainage en fonction du temps et correspondant à des pas de pression croissants. Les courbes de rétention d'eau déduites des paramètres optimisés par la méthode inverse ont les mêmes allures que celles déterminées par la méthode standard (bac de sable et cellules à basses et hautes pressions). Ces résultats sont plus représentatifs de la réalité lorsque les paramètres têta(s) et K(s) sont fixes et égaux aux valeurs expérimentales, avec une précision sensiblement la même dans les cas d'optimisation, où têta(s) est fixe et têta(s) et K(s) fixes et égaux aux valeurs expérimentales; le premier cas où seulement le paramètre têta(s) est fixe est suggéré (il y a moins de paramètres à mesurer). (Résumé d'auteur

Utilisation de l'expérience de drainage à pas de pression multiples pour la détermination des fonctions hydrauliques du sol par la méthode inverse : présentation et évaluation de la méthode

L'optimisation des paramètres des fonctions décrivant les propriétés hydrauliques du sol têta(h) et K(h), basée sur les résultats de l'expérience de drainage interne à pas de pression multiples est une méthode prometteuse. En effet, cette dernière fournit suffisamment d'informations sur les propriétés hydrauliques essentielles d'un sol. Le modèle utilisé pour décrire les relations entre la teneur en eau volumique têta et la pression de l'eau h, d'une part, et entre la conductivité hydraulique K et h, d'autre part, est celui de CAMPBELL (1974) dans sa version améliorée par HUTSON et CASS (1987). Les résultats montrent que ce modèle décrit raisonnablement le processus du drainage en fonction du temps correspondant à des pas de pressions croissantes. La solution de la méthode d'identification des paramètres est unique tant que les valeurs assignées aux paramètres au départ sont proches (plus ou moins 20 %) de celles du sol étudié. L'effet d'une erreur expérimentale allant jusqu'à 10 % n'est pas significatif pour les résultats des paramètres optimisés. (Résumé d'auteur