Testing the shape-similarity hypothesis between particle-size distribution and water retention for Sicilian soils

Application of the Arya and Paris (AP) model to estimate the soil water retention curve requires a detailed description of the particlesize distribution (PSD) but limited experimental PSD data are generally determined by the conventional sieve-hydrometer (SH) method. Detailed PSDs can be obtained by fitting a continuous model to SH data or performing measurements by the laser diffraction (LD) method. The AP model was applied to 40 Sicilian soils for which the PSD was measured by both the SH and LD methods. The scale factor was set equal to 1.38 (procedure AP1) or estimated by a logistical model with parameters gathered from literature (procedure AP2). For both SH and LD data, procedure AP2 …

Analitical deriving of the field capacity through soil bundle model

The concept of field capacity as soil hydraulic parameter is widely used in many hydrological applications. Althought its recurring usage, its definition is not univocal. Traditionally, field capacity has been related to the amount of water that remains in the soil after the excess water has drained away and the water downward movement experiences a significant decresase. Quantifying the drainage of excess of water may be vague and several definitions, often subjective, have been proposed. These definitions are based on fixed thresholds either of time, pressure, or flux to which the field capacity condition is associated. The flux­based definition identifies the field capacity as the soil m…

A simplified approach to estimate water retention for Sicilian soils by the Arya-Paris model

Application of the Arya and Paris (AP) model to estimate the soil water retention curve requires a detailed description of the particle-size distribution (PSD) because the scale factor a, relating the pore length of an ideal soil to that of the natural one, depends on the particle size distribution parameters. For a dataset of 140 Sicilian soils that were grouped in five texture groups, the logistic and linear models were applied to evaluate a, and the water retention values predicted by the AP model were compared with the measured ones. Using the parameters proposed by Arya et al. (1999), the two models yielded similar unsystematic root mean error of estimate (RMSEu). Therefore, their pote…

The use of soil water retention curve models in analyzing slope stability in differently structured soils

Abstract This study analyzes whether and at what rate the parameterization of the Soil Water Retention Curve (SWRC) affects the analysis of shallow slope stability for differently structured unsaturated soils. Advanced empirical or physically-based equations of SWRCs have been proposed in literature to describe soil systems characterized by the so-called bimodal porous domain. In unsaturated soils, SWRC affects the stability assessment in two ways. It influences the resistance properties in terms of shear strengths, which depend on the soil water suction; and it affects the hydrological process modeling (e.g. infiltration) directly influencing soil moisture patterns and indirectly influenci…

Monitoring water and nitrogen transport at field scale in Mediterranean environment

Predicting the water retention characteristic of Sicilian soils by pedotransfer functions.

Utilizzo di modelli bimodali per la descrizione della curva di ritenzione idrica del suolo

L’approfondimento dell’influenza della struttura sulle caratteristiche di ritenzione idrica del suolo può contribuire alla risoluzione dei problemi legati all’eterogeneità del mezzo poroso ed anche alla quantificazione della qualità fisica del suolo. In particolare, nei suoli naturali strutturati, la presenza di un dominio dei pori strutturali (porosità inter-aggregati) e di un dominio dei pori matriciali (porosità intra-aggregati) può essere descritta mediante un’espressione della curva di ritenzione idrica di tipo bi-modale. L’indagine ha riguardato 40 suoli siciliani, per i quali è stato applicato alle misure sperimentali di ritenzione idrica il modello bimodale proposto da Dexter et al.…

Analyzing the role of soil water retention curve in slope stability for differently structured soils

 We analyzed the mechanical and hydrological effects of soil water retention curve (SWRC) models on the slope stability analyses of soils with unimodal and bimodal behavior.  We used three different SWRC models, two bimodal models (Ross&Smettem and Dexter) vs. the traditional van Genuchten model, to evaluate the Factor of Safety (FS) of a simple designed hillslope, based on the Bishop approach for unsaturated soils. Two formulations for term were also considered.  Results indicate that in cases of clayey soils, changes in FS obtained with different SWRC models especially at soil moisture values within the residual zone. In sandy soils the choice of formulations can be more important…

INFLUENCE OF PARTICLE-SIZE DISTRIBUTION MEASUREMENT METHOD ON THE PREDICTION OF SOIL WATER RETENTION CURVE

Application of the Arya and Paris (AP) model to estimate the soil water retention curve requires detailed particle-size distributions (PSD) that can be obtained by fitting a continuous model to traditional sieve-hydrometer (SH) data or using the laser diffraction (LD) method. The AP model was applied to 40 Sicilian soils for which PSD was measured by both SH and LD methods. The scale factor  was set equal to 1.38 (procedure AP1) or estimated by a logistic model with parameters gathered from literature (procedure AP2). To simplify application of the AP model, a relationship for estimating a soil-specific  value from clay content was developed (procedure OPT). For both SH and LD data, proce…

Monthly Hydrological Indicators to Assess Possible Alterations on Rivers’ Flow Regime

Assessing potential deviations of the fundamental river basins’ hydrological processes and streamflow characteristics from the “natural trajectory” represents a high-priority objective to understand the biological impact of altered flow regime on river ecosystems. Existing approaches are mainly based on the analysis of daily-based indicators of hydrologic alteration, which requires wide database, including “pre-impact” and “post-impact” daily flow data frequently unavailable. The hydrological modeling is commonly used to face data missing problems or reconstruct natural conditions, even if models, especially at the daily scales, are often complex and computationally intensive. The use of si…

Influenza della tecnica di misura della distribuzione granulometrica sulla stima della curva di ritenzione idrica del suolo

Le distribuzioni granulometriche ottenute sia con il tradizionale metodo per stacciatura-sedimentazione (SH) che con il metodo della diffrattometria laser (LD) sono state utilizzate per determinare le curve di ritenzione idrica di 40 suoli siciliani attraverso modello di Arya e Paris (AP). La curve di ritenzione idrica determinate con il metodo SH sono risultate più accurate di quelle ottenute dal metodo LD. Fra le differenti procedure applicative utilizzate, i risultati migliori si sono ottenuti utilizzando per ciascun suolo un valore del parametro  determinato attraverso una procedura di ottimizzazione. Infine, è stata proposta una relazione tra il parametro  e il contenuto in argilla c…