The use of tension infiltrometers to assess routes and rates of infiltration in a clay soil

Abstract

SUMMARYThis paper describes the design and operation of a simple tension infiltrometer which imposes pressure potentials at the soil surface (hb) of –0.5, – 2 and –9 cm water, corresponding to equivalent diameters (ed) of the largest conducting pore of 6, 1.5 and 0.3 mm respectively. Infiltration measurements obtained in Evesham series clay soil were fitted to Philip's (1957) two‐term infiltration equation. Results were interpreted using information on the number, type and size of conducting macropores obtained in a dye tracing experiment. Significantly larger values of effective hydraulic conductivity at hb=–0.5 cm were attributed to the flow of water in large shrinkage cracks which constituted nearly 90% of the total conducting macroporosity. Measured fluxes at hb=–9 cm were related to sorption and swelling in the clay matrix, since within the range of infiltration times considered (t<0.5 h), the gravity or steady state component of infiltration was negligible. Rainfall intensity/duration data for a large number of storms at Silsoe were used to demonstrate that in dry soil nearly 70% of rainfall infiltrates in the clay matrix, and that the infiltration capacity of macropores of ed≤1.5 mm is only rarely exceeded.