Résumé : Hedgerow is one of the most important rural landscapes in the world, especially in Europe. Knowledge about the hydrological role of hedgerows is useful ill many fields Of study, such as hydrological modelling and rural landscape management. The aim of this study was to investigate the impact of a...Hedgerow is one of the most important rural landscapes in the world, especially in Europe. Knowledge about the hydrological role of hedgerows is useful ill many fields Of study, such as hydrological modelling and rural landscape management. The aim of this study was to investigate the impact of a hedgerow oil rainfall distribution, soil-water potential gradient, lateral water transfer and water balance. A hillslope with a hedgerow perpendicular to the slope was monitored. To evaluate hedgerow rainfall interception, rainfall was Measured (hourly, daily, and by rainfall event) both next to and up to 16 m upslope and 12 in downslope perpendicularly away from the hedgerow. The strongest correlation between rainfall next to the hedgerow and rainfall at more distant points was obtained using data measured per rainfall event. The average percentage of rainfall intercepted equalled 28% for the leafed period and 12% for the leafless period. The impact of the hedgerow on spatial rainfall distribution wits related to distance from the hedgerow and rainfall amount. Annual distribution of soil-water potential showed that (lie hedgerow influenced it up to 9 in upslope and 6 m downslope, the area in which most of the hedgerow's roots were observed. The soil wits driest at the end of summer, which delayed soil rewetting during autumn in areas surrounding the hedgerow. Annual groundwater dynamics exhibited three distinct periods due to temporal rainfall distribution and, especially at the end Of summer, root-water uptake. In addition, the total potential gradient showed that unsaturated flow was directed towards the hedgerow in summer and autumn. These results indicate that at the local scale hedgerows influences (1) spatial rainfall distribution, (2) soil rewetting, and (3) groundwater recharge, often at distances well beyond the hedgerow's drip line. Consequently, the processes involved in soil-water dynamics around hedgerows should be integrated into relevant hydrological models, especially For catchments with it dense hedgerow network. Copyright (C) 2008 John Wiley & Sons, Ltd.
Résumé : Variability of suspended sediment concentration (SSC) versus discharge relationships in streams is often high and illustrates variable particle origins or availability. Particle availability depends on both new sediment supply and deposited sediment stock. The aim of this study is to improve...Variability of suspended sediment concentration (SSC) versus discharge relationships in streams is often high and illustrates variable particle origins or availability. Particle availability depends on both new sediment supply and deposited sediment stock. The aim of this study is to improve SSC-discharge relationship interpretation, in order to determine the origins of particles and to understand the temporal dynamics of particles for two small streams in agricultural catchments from northwestern France. SSC and discharge were continuously recorded at the outlets and data were examined at different time-scales: yearly, monthly, with distinction between flood periods and non-flooding periods, and individual flood events. Floods are classified in relation to SSC-discharge hysteresis, and this typology is completed by the analysis of SSC-discharge ranges during rising and falling flow. We show that particles are mainly coming from channel, banks, either by hydraulic erosion or by cattle trampling. Particle availability presents a seasonal dynamics with a maximum at the beginning of autumn when discharge is low, decreasing progressively during autumn to become a minimum in winter when discharge is the highest, and increasing again in spring Bank degradation by cattle is the determining factor in the suspended sediment dynamics. Cattle bank-trampling produces sediment, mostly from spring to autumn, that supplies the deposited sediment stock even outside floods. This hydrologically independent process hides SSC-discharge correlation classically linked to hydraulic erosion and transport. Differences in SSC-discharge relationships and suspended sediment budgets between streams are related to differences in transport capacity and bank degradation by cattle trampling and channelization. Copyright (c) 2007 John Wiley & Sons, Ltd.
Résumé : The aim of this work is threefold: (1) to identify the main characteristics of water-table variations from observations in the Kervidy-Naizin catchment, a small catchment located in western France; (2) to confront these characteristics with the assumptions of the Topmodel concepts; and (3) to...The aim of this work is threefold: (1) to identify the main characteristics of water-table variations from observations in the Kervidy-Naizin catchment, a small catchment located in western France; (2) to confront these characteristics with the assumptions of the Topmodel concepts; and (3) to analyse how relaxation of the assumptions could improve the simulation of distributed water-table depth. A network of piezometers was installed in the Kervidy-Naizin catchment and the water-table depth was recorded every 15 min in each piezometer from 1997 to 2000. From these observations, the Kervidy-Naizin groundwater appears to be characteristic of shallow groundwaters of catchments underlain by crystalline bedrock, in view of the strong relation between water distribution and topography in the bottom land of the hillslopes. However, from midslope to summit, the water table can attain a depth of many metres, it does not parallel the topographic surface and it remains very responsive to rainfall. In particular, hydraulic gradients vary with time and are not equivalent to the soil surface slope. These characteristics call into question some assumptions that are used to model shallow lateral subsurface flow in saturated conditions. We investigate the performance of three models (Topmodel, a kinematic model and a diffusive model) in simulating the hourly distributed water-table depths along one of the hillslope transects, as well as the hourly stream discharge. For each model, two sets of parameters are identified following a Monte Carlo procedure applied to a simulation period of 2649 h. The performance of each model with each of the two parameter sets is evaluated over a test period of 2158 h. All three models, and hence their underlying assumptions, appear to reproduce adequately the stream discharge variations and water-table depths in bottom lands at the foot of the hillslope. To simulate the groundwater depth distribution over the whole hillslope, the steady-state assumption (Topmodel) is quite constraining and leads to unacceptable water-table depths in midslope and summit areas. Once this assumption is relaxed (kinematic model), the water-table simulation is improved. A subsequent relaxation of the hydraulic gradient (diffusive model) further improves water-table simulations in the summit area, while still yielding realistic water-table depths in the bottom land.