This paper presents basic tests to develop an airborne photogrammetric methodology that derives grain size distributions of pre-alpine gravel bed rivers. The data acquisition was performed by a lightweight action cam and a hand-held digital single lens reflex camera. Image processing comprised structure from motion technique to obtain digital elevation models of gravel beds. Laboratory results indicate that their accuracy is about four to six times lower than laser-scan data when based on action cam data. The model computed via photos taken by the reflex camera is almost of the same order as the accuracy of the laser data. Field experiments were conducted to test the performance of estimating grain size distributions against a manual surface sampling method. Therefore, the action cam was mounted to a low-cost quadrocopter, while the reflex camera was operated in hand-held mode. Results indicate that this measurement combination has a high potential to generate data from which characteristic grain size parameters can be estimated.