Spatial variability of field-measured soil-water properties

Nielsen, D. R.; Biggar, J. W.; Erh, K. T.

doi:10.3733/hilg.v42n07p215

Cited by 952 publications

(433 citation statements)

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“…This was also a smooth bare soil. The soil at this location has been extensively studied [14], [15]. The particular area these measurements were conducted in was a Yolo silt loam (20% sand and 20% clay).…”

Section: Experiments Descriptionsmentioning

confidence: 99%

Soil water infiltration observation with microwave radiometers

Jackson¹,

Schmugge

O'Neill³

et al. 1998

IEEE Trans. Geosci. Remote Sensing

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Abstract-Experiments were conducted using truck-based microwave radiometers operating at 1.41-(L-band) and 2.65-GHz (S-band) horizontal polarization to observe small plots during and following sprinkler irrigation. These experiments were conducted on a sandy loam soil in 1994 and a silt loam in 1995. Sandy loam soils typically have higher infiltration capabilities than clays, and in our studies, we were not able to exceed this with the irri-

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Section: Experiments Descriptionsmentioning

confidence: 99%

Soil water infiltration observation with microwave radiometers

Jackson¹,

Schmugge

O'Neill³

et al. 1998

IEEE Trans. Geosci. Remote Sensing

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“…In natural soils these functions exhibit considerable spatial variability [Nielsen et al, 1973] leading to strongly variable pore water velocity fields which dominate the transport of conservative chemicals. Corresponding features such as highly irregular concentration distributions, concentration hot spots, and a local dispersion much smaller than the global dispersion were found in a number of field-scale experiments on solute transport [van Wesenbeeck and Kachanoski, 1994;Flury et al, 1994;Bronswijk et al, 1995].…”

Section: Introductionmentioning

confidence: 99%

Approximation of asymptotic dispersivity of conservative solute in unsaturated heterogeneous media with steady state flow

Hammel¹,

Roth²

1998

Water Resources Research

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Abstract. The relation between the heterogeneity of hydraulic properties and effective asymptotic transport is studied for microscopically heterogeneous but macroscopically homogeneous unsaturated media with steady flow. Heterogeneity is described by the scaling of the hydraulic functions 0 (½m) and K(0). The study is based on an analytical approximation of asymptotic dispersivity under the assumption that matric potential is spatially constant. For the special case of a water-saturated medium the result of the stochastic continuum theory is recovered. When applied to several published numerical simulations, the approximated asymptotic dispersivities are found to agree well with the numerical values. By exploring the heterogeneous media for various hydraulic states, the approximation resolves some apparent inconsistencies found in the simulations. The cases considered span the entire range from perfect to zero correlation between scaling factors of matric potential and hydraulic conductivity. It is demonstrated that this correlation is crucial for the behavior of asymptotic dispersivity with changing flow rate. Since weak to moderate correlations are often found in soils, this result has significant implications for solute transport through heterogeneous soils. In this work we aim at analyzing the quantitative effect of hydraulic heterogeneity on asymptotic transport by an analytical approximation. The applicability of the approximation is evaluated for the cases considered in the numerical studies mentioned above. In contrast to the stochastic continuum approach of Yeh et al. [1985a, b] and Russo [1993], which assumes a spatially constant water content, our analytical approximation is based on the assumption of gravity flow, that is, spatially constant matric potential. This assumption is motivated by the continuity of the matric potential across any boundary which results from its gradient being a driving force of water flux. Finally, simple expressions for the asymptotic dispersivity for arbitrary parameterization of hydraulic functions, flow rates, and characteristics of heterogeneity are obtained.In the following we will often refer to the results of a particular numerical simulation. For better readability, we introduce the abbreviations given in Table 1 instead of using full citations. 2.Theoretical Framework Description of Heterogeneity by ScalingOur approach for the approximation of the asymptotic dispersivity is based on the scaling of the hydraulic variables to account for the spatial variability of the soil hydraulic functions. These variables are the matric potential era, the water content 0, and the hydraulic conductivity K, which is considered as isotropic. For simplicity we restrict our analysis to the scaling of ½m and K. However, it is straightforward to include the scaling of 0 or that of chemical parameters.Let The simulations are ordered with increasing complexity of the underlying heterogeneity. For simulations S1, S2, and S3 the correlation between scaling of matric potential and hydraul...

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“…Or, les études de terrain ont montré que dans des unités considérées comme homo-gènes persistait une variabilité résiduelle souvent importante : c'est par exemple le cas de flux comme les précipitations (JACQUET, 1960) ou de variables internes comme le stock hydrique (GASCUEL-ODOUX et MÉROT, 1986), ou de paramètres comme les propriétés hydriques des sols (NIELSEN et al, 1973 ;VAUCLIN, 1983 ;BOUMA et BELL, 1983 ;. Cette variabilité est parfois assortie d'une autocorrélation spatiale qui, dans le cas des propriétés des sols, peut amplifier la variabilité des flux hydriques (SHARMA et al, 1987 ;BINLEY étal., 1989b).…”

Section: Paramétrisation Et Variabilité Intra-unitéunclassified

Génèse des débits dans les petits bassins versants ruraux en milieu tempéré : 2 - Modélisation systémique et dynamique

Ambroise¹

2005

rseau

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SUMMARYThe second part of this review on streamflow génération analyses how the knowledge available from field studies (see Part 1) has been used since the 1960s or could be used to improve catchment modelling. After a présentation of the main mode! types, the various problems encountered during the modelling process are discussed.The large variety of hydrologie models available for event or continuous simulation can be reduced to a few main types according to the ways the functional, spatial and temporal aspects of the catchment behaviour are represented. Lumped "blackbox" models are useful for many engineering problems but can not be used in "extrapolation" and give no information on the internai catchment dynamics. Lumped conceptual models, which consider a catchment as a System of interconnected réservoirs and simulate the main global fluxes, use empirical lumped relationships and parameters that often hâve no great physical meaning and are not measurable. Semi-distributed conceptual models use the same réservoir description, but at the scale of "homogeneous" units derived from a space discrétisation, which allows one to take catchment structure explicitly into account. Physicaliy-based distributed models, which use theoretical équa-tions and measurable parameters, provide a dynamic explanation of catchment behaviour but require too much information and are too complex to be easily used at the catchment scale. Physico-conceptual semi-distributed models try to overcome the limits of the previous types, while keeping their advantages, by simplifying the dynamic approach and discrétisation using new concepts.Physically-based or conceptual models, which describe or explain the water cycle at the catchment scale, are very useful for research, but their use in prac- Correspondance : ambroise@geographie.u-strasbg.fr Partie 1 publiée dans Rev. Sci. Eau 11/4 (1998). Les commentaires seront reçus jusqu'au 30 septembre 1999.

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Spatial variability of field-measured soil-water properties

Cited by 952 publications

References 31 publications

Soil water infiltration observation with microwave radiometers

Soil water infiltration observation with microwave radiometers

Approximation of asymptotic dispersivity of conservative solute in unsaturated heterogeneous media with steady state flow

Génèse des débits dans les petits bassins versants ruraux en milieu tempéré : 2 - Modélisation systémique et dynamique

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