Application of two methods to determine hydraulic conductivity with disc permeameters on sloping land

The purpose of the present study was to compare two methods for estimating the hydraulic conductivity near saturation with disc permeameters, and to i dentify their merits when studying runoff on sloping land. The soil's hydra ulic conductivity (K) was measured with disc permeameters at a sequence of nominal pressures (psi) in three blocks with average slope gradients of 11. 0% (two occasions), 21.5% (two occasions) and 29.3% (one occasion), respect ively, within a sloping area, 40 m wide and 100 m long. Two different metho ds were used. In the first, the split-location method, the permeameter was moved to an adjacent spot after measurement at each applied psi. The estima te of K(psi) was based on measured sorptivity, steady-state volumetric flow , initial volumetric water content and the volumetric water content at the applied psi. In the second method, the one-location method, the permeameter was not moved during the measurements at each sequence of applied psi and the estimate of K(psi) was based only on steady-state volumetric flow and p iece-wise application of the exponential relation between K and psi. The la tter method generally gave smaller estimates of K than the former on the ge ntle slopes. These differences were smaller or negligible on steeper slopes . The slope gradient and the conditions in the uppermost soil layers had a definite influence on the values of K obtained. The one-location method is recommended in studies in which disturbance of the soil surface must be kep t to a minimum, as is the case in experimental plots.