COMPARISON BETWEEN ADJUSTMENTS OF WATER RETENTION CURVES IN SANDY SOILS IN AN OUTCROP REGION OF THE BOTUCATU FORMATION IN SÃO CARLOS – SP

Abstract

Soil Water Retention Curves (CRAs) allow you to indirectly evaluate the water content, internal drainage, and hydraulic conductivity in the saturated zone of almost all soil types. Several authors have sought to develop methods to model these curves, and the models proposed by van Genuchten (1980), Fredlund and Xing (1994) and Gitirana and Fredlund (2004) have already been consolidated. The objective of the present study was to choose which of the CRAs with bimodal adjustments, modeled by the Double van Genuchten (DVG) technique proposed by Carducci et al. (2011) and by Gitirana and Fredlund (2004), best represented the actual soil moisture in two different locations in the municipality of São Carlos, compared to the unimodal adjustment also performed. For this purpose, two sets of tensiometers were installed in residual soils of the Botucatu Arenosos Formation and undisturbed samples of these soils were collected and taken to the laboratory. The determination of the retention characteristics of the materials was carried out using the filter paper technique (ASTM, 1992), which allowed the modeling of unimodal and bimodal curves. It was found that the bimodal fits obtained better quadratic correlations and lower mean errors and lower mean means of the errors and the model proposed by Carducci et al. (2011) presented the best fit between the measured and calculated data.