We present a new experimental setup dedicated to investigating the dynamics and mechanical properties of gravitary free-surface flows made of complex fluids. Our study is motivated by the need of improving the modeling of hazardous geophysical flows, such as debris flows, mud flows, avalanches. Our experimental setup consists of a 3-m long inclined channel whose bottom is constituted by an upward-moving conveyor belt with controlled velocity. To enforce fluid recirculation, channel upper end is closed by a fixed rigid wall perpendicular to the bottom. We report on experiments conducted with a viscoplastic kaolin slurry. For all the tested slope angles, we observed the existence of a belt velocity range in which stationary surges with immobile fronts spontaneously develop. The shape and height of these surges were monitored using a laser sheet and ultrasonic height sensors. We show that these characteristics can be satisfactorily reproduced, at least at first order, by a simple model based on thin-layer approximation.