The Manning formula is one of the most used to calculate the average velocity of water flow in ungauged channels. In order to be applied, it is necessary to measure in field the hydraulic radius (RH), the slope of the water surface (S), and to obtain the roughness coefficient (n), usually through tables created for this purpose. This involves a difficult, inefficient and subjective data collection in the field. This study evaluates the possibility to obtain these parameters in a more efficient manner, reducing the time of the process and allowing to work in larger areas. To achieve these objectives, the data used in this work were: 1) digital terrain models generated from airborne LiDAR data with a density of 2 points/ m2 , acquired when the channel was dry; 2) the height of the waterline and channel geometry measurements in the field using GPS; 3) Flow measurements. With this information, the velocity (Ve) was estimated and related to the average velocity of water flow (Vc) calculated from data measured in the field. The coefficient of determination between both velocity values was 73.52%, suggesting that the proposed methodology is useful to obtain the average velocity of flow, especially in remote areas or dry riverbeds.