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18The parameter consistency of the one-dimensional Hairsine-Rose (H-R) erosion model under 19 conditions of significant rainfall splash was examined. To account for the splash characteristic The observations taken during and after the experiment, as well as surface elevation data, 43 confirmed the noticeable impact of non-uniform flow on the erosion process.44

15This work presents a numerical model able to simulate the effect of biomass growth on the hydrau-16 lic properties of saturated porous media, i.e., bioclogging. A new module for an existing coupled 17 flow and reactive-transport code-PHWAT-was implemented. Laboratory experiments were used to 18 validate the model.. Good agreement with the experimental data was found. Model behavior was 19 satisfactory in terms of numerical discretization errors and parameter calibration, although-grid-20 independent results were difficult to achieve. The new code was applied to investigate the effect of 21 the initial conditions on clogging development. A set of simulations was conducted considering 1D 22 and 2D flow conditions, for both uniform and heterogeneous initial biomass concentrations. The 23 simulation results demonstrated that the rate and patterns of bioclogging development are sensitive 24 to the initial biomass distribution. Thus, the common assumption of an initially uniform biomass 25 distribution may not be appropriate and may introduce a significant error in the modeling results. 26

[1] Transport of contaminants in coastal aquifers subject to tidal fluctuation is an important topic in hydrogeology as a consequence of the significant development of human activities near the shoreline. Despite this, relatively little work has been done to investigate the joint effect of variable water density flow and tidal saltwater head fluctuation. In particular, numerical modeling results have rarely been validated with experimental data. The primary aim of this work was to develop and validate a modeling strategy to incorporate the effect of tides in a variable density simulation using a widely adopted simulation package. The numerical model reproduced data from a laboratory experiment designed to investigate the impact of tides on conservative contaminant transport in a coastal aquifer, where the polluted water is denser than the ambient groundwater. Both the plume shape and size were reproduced when tidal fluctuations were incorporated in the model. Model simulations were then used to examine in detail how the flow patterns are modified during one tidal cycle. According to the simulations, the contaminant was mainly discharged from the beach surface. The model was also used to investigate the contact between the contaminant plume and the saltwater intrusion in the freshwater aquifer. We observed that the two dense water phases never completely mix during the simulation. Instead, a slice was continuously removed from the front of the polluted plume because of the discharge of freshwater. The observed mechanism is cyclical with a frequency compatible with the tide.

Rain splash soil erosion in the presence of rock fragments and different initial conditions was tested in laboratory flume experiments under controlled conditions. The aim of the experiments was to ascertain whether cumulative soil erosion is proportional to the area of soil exposed to raindrop detachment under the condition of constant and uniform precipitation. The surface area exposed to rain splash erosion was adjusted by placing rock fragments onto the surface of identically prepared soil in laboratory flumes. The laboratory results showed that the eroded cumulative mass depended on the cumulative runoff, and that soil erosion was proportional to the soil surface area exposed to raindrops, in situations where an initially dry, ploughed and smoothed soil surface were ensured. The results showed that this relationship was controlled to a smaller extent by the soil's initial moisture content, bulk density and soil surface characteristics.When the initial conditions were more complex, soil erosion was proportional to the area exposed only at steady state. Then, sediment concentrations during the first part of the erosion event were instead more sensitive to the initial state of the soil surface, whereas at steady state it was observed that the concentrations of eroded sediments were controlled mainly by the effective rainfall and area exposed to raindrops. Previously published field data on rain splash soil erosion were analyzed to ascertain whether the same behavior was evident under field conditions. For this case it was found that rain splash erosion is in general not proportional to the area exposed. In contrast to the controlled laboratory experiments, the field experiments were characterized by non-uniform initial surface roughness, surface soil aging and heterogeneous rock fragment size and spatial distribution. However, the presented laboratory results showed clearly that, for soils with negligible surface roughness, erosion depends on (i) the area of soil 3 exposed to rainfall and (ii) the cumulative runoff, and that it is only slightly dependent on other soil variables.Keywords: Soil erosion experiment, Area exposed, Flume experiment, Cumulative discharge, Cumulative eroded mass, Soil initial conditions. IntroductionOver several decades, attention has been given to the effect of the soil surface characteristics (such as surface roughness, crop residues, organic mulches, vegetation cover and rock fragment coverage) on runoff generation, infiltration and soil erosion rates Poesen et al., 1999;Li, 2003;Gyssels et al., 2006;Smets et al., 2008;Knapen et al., 2009;Guo et al., 2010;Zavala et al., 2010). Numerous studies have pointed out the role played by surface rock fragments on erosion as well as on the hydrological response of soils (such as infiltration rate, surface ponding, runoff generation) (Adams, 1966;Poesen et al., 1990Poesen et al., , 1998Poesen et al., , 1999 Parsons, 1991, 1994;Bunte and Poesen, 1994;Ingelmo et al., 1994;Poesen and Lavee, 1994;Torri et al., 1994;van Wesemael et al., 19...

Coastal groundwater systems can have a considerable impact on sediment transport and foreshore evolution in the surf and swash zones. Process-based modeling of wave motion on a permeable beach taking into account wave-aquifer interactions was conducted to investigate the effects of the unconfined coastal aquifer on beach profile evolution, and wave shoaling on the watertable. The simulation first dealt with wave breaking and wave runup/rundown in the surf and swash zones. Nearshore hydrodynamics and wave propagation in the cross-shore direction were simulated by solving numerically the two-dimensional Navier-Stokes equations with a k-ε turbulence closure model and the Volume-Of-Fluid technique. The hydrodynamic model was coupled to a groundwater flow model based on SEAWAT-2000, the latter describing groundwater flow in the unconfined coastal aquifer. The combined model enables the simulation of wave-induced watertable fluctuations and the effects of infiltration/exfiltration on nearshore sediment transport. Numerical results of the coupled ocean/aquifer simulations were found to compare well with experimental measurements. Wave breaking and infiltration/exfiltration increase the hydraulic gradient across the beachface and enhance groundwater circulation inside the porous medium. The large hydraulic head gradient in the surf zone leads to infiltration across the beachface before the breaking point, with exfiltration taking place below the breaking point. In the swash zone, infiltration occurs at the upper part of the beach and exfiltration at the lower part. The simulations confirm that beaches with a low watertable tend to be accreted while those with a high watertable tend to be eroded.

[1] Two laboratory flume experiments on the effect of surface rock fragments on precipitation-driven soil erosion yields were carried out. The total sediment concentration, the concentration of seven individual size classes, and the flow discharge were measured. Digital terrain models (DTMs) were generated before and after one of the experiments. The results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow, therefore decreasing its sediment transport capacity. Rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale. For short times, the rock fragment coverage reduced erosion of the finer particles (<20 mm). For the midsize classes the protection decreased, while erosion of the larger size classes (>100 mm) was unaffected. At long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops. An area-based modification of the Hairsine and Rose (H-R) soil erosion model was employed to analyze the experimental data. The H-R model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used. Predictions were instead less accurate with low rainfall intensity and high rock fragment cover. The DTM results showed that the presence of rock fragments on the soil surface led to increased soil compaction, perhaps due to higher soil moisture content (from greater infiltration) within the rock fragment-covered flumes.

The availability of reliable constitutive models linking the bulk electric properties of porous media to their inner structure is a key requirement for useful quantitative applications of noninvasive methods. This study focuses on the use of dielectric measurements to monitor fluid saturation changes in porous materials. A number of empirical, semi-empirical and theoretical relationships currently exists that link the bulk dielectric constant with volumetric water content. One such relationship, named complex refractive index model or Lichteneker-Rother model has been extensively applied in recent years. Here we first analyse the characteristics of this Lichteneker-Rother model by means of theoretical considerations. This theoretical analysis indicates that the Lichteneker-Rother exponent is dependent upon the geometrical properties of the porous structure, as well as the permittivity contrast between the different phases. Pore-scale modelling and experimental data further support this result. The parameter estimation robustness in presence of synthetic data error is also assessed. This demonstrates that Lichteneker-Rother parameters cannot, in general, be independently identified on the basis of bulk dielectric constant versus moisture content data