Capillary conductivity data estimated by a simple method

Abstract

For the determination of capillary conductivity much rather tedious laboratory work is needed. Many people are materially or mentally not equipped for such kind of work but nevertheless need the data. A less laborious, simple technique is described which can give good results. A vertical column of soil is allowed to evaporate at the top; all other sides are completely closed. Every day the total weight of the column is read and determinations are made of the moisture content and moisture tension at a number of depths. The velocity of flow for different depths can be calculated from the changes in moisture content and weight. The potential gradient can be read from the moisture tension readings, making it possible to calculate the capillary conductivity. A difficulty is that a pF-curve is needed when moisture content or moisture tension is determined. In the latter case, used in this paper, the total amount of moisture in the column determined from tension data and the pF-curve does not agree with the amount determined from the total weight. This means the flow velocity cannot be calculated exactly. The reason is that the pF-curves used lack sufficient reproducibility. They can be fitted to the soil column used by the iteration technique described. The capillary conductivity values, determined with the aid of Bouyoucos' electrical nylon units, are fairly accurate at moisture tensions between 0.1 to 20 atmospheres. Below 0.1 atmosphere they lack accuracy. An advantage of this method is, that it is a true imitation of some moisture flow processes which occur in nature and to which knowledge of the capillary conductivity has to be applied. RESUME : Le travail de laboratoire necessite pour la determination de la conductivite capillaire peut etre considere comme assez fatigant. Beaucoup de gens ne sont pas equipes, materiellement et mentalement, pour un tel travail et cependant doivent posseder ces donnees. Une technique moins laborieuse, plus simple est ici decrite : elle peut donner de bons resultats. International Association of Scientific Hydrology Proceedings of the Wageningen Symposium — June 1966 — Water in the unsaturated lone