In the catchment area of the volcano Nevado del Huila, more specifically in the Paez River basin, debris flows have occurred in recent periods, as occurred in 1994 (source seismotectonic) and 2007 (of volcanic origin). Based on the evidence left by debris flows occurred in 1994 and 2007, were collected geologic and topographic data directly in the field to model the behavior of flows along the Paez River basin, following the methodology Lahar -Z proposed by Iverson and others (1998). The results show that the obtained values overestimate the cross-sectional areas of flooding and underestimate the volumes involved when compared with the respective actual values obtained from field surveys. We conclude that the formula obtained has a better correlation between theoretical data and measurements in the field.