Diversion capacity of curved capillary barrier, which is defined as the distance from the starting point of a funneled flow along the boundary of a layered slope to the diversion point, was measured experimentally. Comparing with the known diversion capacities of flat capillary barriers that have been described in published papers, the information and even the discussions on the diversion capacities of curved capillary barriers, generally seen for example in natural slopes, in covering soils of artificially formed landfills, and in the ceiling of ancient tombs, are quite few. We measured the diversion capacity along flat, convex, and concave boundaries in experimentally devised layered slopes within a container of 80 cm wide, 2 cm thick and 90 cm high under an artificial rainfall simulator which was adjusted to generate the rainfalls from 40 to 200 mm/h. The bottom layer in the container was filled with coarse glass beads of 1 mm diameter in average and the top layer was filled with Toyoura sand so as to form the boundaries to be flat, convex, or concave, respectively. We chose the catenary as the typical curved boundaries. Eight runs for flat boundaries, 6 runs for convex boundaries, and 6 runs for concave boundaries were carried out under different rainfall intensities and different slope angles. The equation by Steenhuis et al. (1991), who modified the Ross equation (1990), agreed well with the experimentally measured diversion capacity along the flat boundary. In case of the curved capillary barriers, the equation by Steenhuis et al. ,

L=tan A {1/b(Ks/q - 1)+Ks/q(ha-hw)}

was applied at every point on the curved capillary barrier by changing the value of tan A, where L is the length of diversion capacity, A the angle of the tangential line at every point on the curving boundary, b the parameter in the unsaturated hydraulic conductivity function, Ks the saturated hydraulic conductivity of the top layer, q the rain intensity, ha the air entry suction of the top layer, and hw the water entry suction of the top layer. This equation was capable of predicting the diversion capacity on concave capillary barriers. The value of tan A, determined by the tangential line along the curving boundary defined by the catenary, decreases along the concave capillary barrier resulting in the decrease of the length of diversion capacity, L. On the other hand, the accumulated funneled flow, qL, along the concave capillary barrier increases with L. Only when the accumulated funneled flow exceeds the diversion capacity, the capillary barrier is destroyed. The estimated diversion capacities agreed well with the measured values. The equation by Steenhuis et al. was not able to predict the diversion capacity on a convex capillary barrier. Further theoretical research is needed to estimate the diversion capacity on those convex capillary barriers.