Simplified modelling and numerical simulations of concrete carbonation in unsaturated conditions

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Upscaling Hydrological Processes for Land Surface Models with a Two‐Hydrologic‐Variable Model: Application to the Little Washita Watershed

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Impact of spatial heterogeneities on oxygen consumption in sediments: Experimental observations and 2D numerical modeling

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A soil column model for predicting the interaction between water table and evapotranspiration

International audienceLateral waterfluxes are not realistically taken into account in soil column models, although they influence the dynamic evolution of the vertical soil moisture profile. By neglecting these fluxes, the modeling of the soil‐vegetation‐atmosphere continuum is incomplete, and the feedbacks between these three compartments cannot be fully simulated. These fluxes have an importance in the different fields where soil column models are used: hydrology, hydrometeorology, biogeochemical cycles, ecology, and soil weathering. This paper introduces a novel Hydrological Hillslope‐based Soil Column model (H2SC) that simulates the temporal evolution of the water table depth and evapotranspiration fluxes and their interaction. The interconnected processes are infiltration, evapotranspiration, vertical soil water movements, and the nonexplicitly modeled lateral fluxes flowing through the soil column. These lateral fluxes are modeled as a drainage function built from physically based equations that describe a simplified hillslope hydrology. This drainage function can be easily implemented in any soil column model without penalizing computational times. The H2SC model was validated on numerical experiments where a 2‐D hillslope simulation performed with an integrated hydrologic model was compared with simulations using the H2SC 1‐D model. Each of the H2SC simulations represents a specific location of a soil column along the hillslope. Different climate forcings, soil properties, and geometric shapes of the hillslope were tested. The model was then applied at the locations of two piezometers in the Strengbach catchment, France. The model reproduced the temporal evolution of the water table level fairly well for both the numerical experiments and for the real test case

Influence of vegetation‐induced water table seasonality on groundwater chloride concentration dynamics in a riparian fen peatland

International audiencePeatlands are environments that rely mainly on high water levels to accumulate organic matter. Depending on the chemical species observed, the lowering of the water table can change biogeochemical equilibriums, with various impacts. This paper aims to understand the effect of shallow groundwater seasonality on chloride concentrations in a French riparian peatland by combining water table monitoring, geochemical and stable water isotopes analysis. Water table levels and groundwater samples were recorded and collected for 3 years, every 2 months, in nine observation wells and the nearby river. Chloride concentrations were highly variable in space and time, ranging from 10 to 100 mg L À1. They are shown to be related to the wate

Combining experimental and modelling approaches to monitor the transport of an artificial tracer through the hyporheic zone

International audienceIn order to advance methodologies used in the investigation of Hyporheic Zone (HZ) mixing processes, this article combines experimental and modelling tools to follow a tracer injected into the river and infiltrating into the HZ. A highly concentrated sodium chloride solution was injected into the river; (i) the river conductivity, (ii) the riverbed resistivity by Electrical Resistivity Tomography (ERT) and (iii) vertically distributed chloride concentrations within the HZ were monitored. Both ERT and concentration measurements showed an infiltration depth of the tracer of 35 cm, and a partial recovery after injection, which was faster within the superficial layer that was found to be more resistive according to the ERT initial image. The modelling approach used the HydroGeoSphere code to model the coupling between river surface flows and HZ groundwater flows and transport processes. The model set-up involved a 50 cm high existing riverbed step, a vertical contrast in HZ saturated hydraulic conductivity and the aquifer discharge flux. Fitting the vertical chloride profile, the adjusted values were 5 × 10−2 m s−1 for the saturated hydraulic conductivity of the first highly permeable layer below the riverbed, and 4 × 10−6 m s−1 for the aquifer discharge flux. The bottom layer saturated hydraulic conductivity was found to be at least 10 times lower than the value within the first layer. Numerical simulations showed that the two main parameters controlling the mixing within the HZ were the groundwater discharge and the saturated hydraulic conductivity first sediment layer of the riverbed. The riverbed step was found to be less significant here compared to these two parameters. The combination of experimental and modelling tools allowed us to quantify the aquifer discharge flux, which is complicated to investigate in the field without any model. Results of this study showed that combining modelling with ERT and vertically distributed chloride sampling allows the quantification of the main factors controlling the hyporheic exchange

Impact of land-use change on the hydrology of North Lao PDR watersheds

International audienceWe investigated the impact of land-use change on the hydrology of different major Lao tributary watersheds of Mekong River. The region is the North of Laos centred on Luang Prabang and the watersheds are the Nam Khan, Nam Ou, Nam Suong, Nam Lik and Nam Ngum. An additional small agricultural catchment called Houay Pano close to the Nam Khan, is also considered. We used the lumped rainfall–-runoff conceptual models GR4J and GR2M, developed by Irstea in France, the Mekong River Commission hydro-meteorological database and the Japanese Aphrodite meteorological database. The objective was to detect in the hydrological regime of the watersheds an impact of de(re)forestation, processes known to have occurred since the 1980s, but at a degree which has not been quantified. For this purpose we adopted the cross simulation methodology developed by Irstea which has proved to be efficient to detect trends in long term watershed hydrology. The results did not show any significant hydrological change since 1960. On the other hand the application of the same methodology to the small catchment Houay Pano surveyed since 2001 proved to be convincing. We saw evidence of the impact of slash and burn practice, followed by a long fallow period, on a catchment's hydrology over a seven year period

Experimental and modelling evidence of short-term effect of raindrop impact on hydraulic conductivity and overland flow intensity

International audienceTropical montane areas of Southeast Asia are exposed to high-intensity rainfall during the monsoon period. This is particularly problematic in areas where soils on steep slopes are cultivated as it can lead to heavy runoff, high soil erosion, and water pollution. The objective of this paper is to analyse the effect of the impact of raindrops on the dynamics of runoff on such steep fields. Experiments under simulated rainfall were performed at the plot scale (1 m2) to quantify water export from the surface of upland agricultural soils during overland flow events. Four 1 m2 plots were divided in duplicated treatment groups: (a) control with no amendments, and (b) amended with pig manure. Each plot was divided into two 0.5 m2 rectangular subplots. One subplot was designated as a rain splash treatment; the other sub-plot was covered with a 2 mm grid size wire screen that was located 12 cm above the soil surface. The purpose of the screen was to break the raindrops into fine droplets and to reduce fall height in order to drastically reduce their kinetic energy. Runoff was measured for each sub-plot. The results show that raindrop impact drastically enhances runoff generation on both bare soils and on manure amended soils. When the impact of raindrops was limited by screening, runoff was higher on amended soils than on bare soils.The temporal evolution of runoff was correctly modelled using a soil hydraulic conductivity that exponentially decreases over time of exposure to rainfall. Both experimental and modelling results showed that droplet energy induces a rapid evolution of the hydraulic properties of the soil surface due to crusting, resulting in a reduction of hydraulic conductivity and a concomitant increase in runoff rate

Experimental and modelling evidence of splash effects on manure borne Escherichia coli washoff

International audienceIn tropical montane South-East Asia, recent changes in land use have induced increased runoff, soil erosion and in-stream suspended sediment loads. Land use change is also contributing to increased microbial pathogen dissemination and contamination of stream waters. Escherichia coli (E. coli) is frequently used as an indicator of faecal contamination. Field rain simulations were conducted to examine how E. coli is exported from the surface of upland, agricultural soils during runoff events. The objectives were to characterize the loss dynamics of this indicator from agricultural soils contaminated with livestock waste, and to identify the effect of splash on washoff. Experiments were performed on nine 1 m2 plots, amended or not with pig or poultry manure. Each plot was divided into two 0.5 m2 sub-plots. One of the two sub-plots was protected with a mosquito net for limiting the raindrop impact effects. Runoff, soil detachment by raindrop impact and its entrainment by runoff, and E. coli loads and discharge were measured for each sub-plot. The results show that raindrop impact strongly enhances runoff generation, soil detachment and entrainment and E. coli export. When the impact of raindrops was reduced with a mosquito net, total runoff was reduced by more than 50%, soil erosion was on average reduced by 90% and E. coli export from the amended soil surface was on average 3 to 8 times lower. A coupled physics-based approach was performed using the Cast3M platform for modelling the time evolutions of runoff, solid particles detachment and transfer and bacteria transport that were measured for one of the nine plots. After estimation of the saturated hydraulic conductivity, soil erodibility and attachment rate of bacteria, model outputs were consistent with measured runoff coefficients, suspended sediment and E. coli loads. This work therefore underlines the need to maintain adequate vegetation at the soil surface to avoid the erosion and export of soil borne potential pathogens towards downstream aquatic systems