Multi-source approach for reach scale river bed modeling - a case study on Rambla de la Viuda

Understanding river channel changes induced by floods is crucial for effective flood risk management, as floods dramatically reshape rivers through erosion and deposition impacting infrastructure and ecosystems. Factors like landslide-channel interactions, channel confinement or human induced channel modifications (e.g. sediment extraction) significantly amplify flood risks. Predicting future hazards with this knowledge helps manage development in floodplains, design better flood defenses, and adapt to climate change impacts on river systems.

Thus, we need efficient methods for monitoring the dynamics of the river channel, especially after flood events. Also, as use of Digital Twins is emerging for river management, ability to update the 3D topography of the river Digital Twin rapidly becomes a necessity. Mobile laser scanning (MLS) technology offers a way of direct 3D measurements of the environment, regardless of ambient light. We have developed and tested multi-platform mobile laser scanning (MLS) systems for riverine environment mapping for more than a decade, including deployments since 2012 at the Rambla de la Viuda in Spain. Rambla de la Viuda is an ephemeral  gravel bed channel that remains dry for most of the year, but infrequent flash floods can significantly reshape its geomorphology. During the past years such flooding occasions have become more frequent and powerful, not forgetting the extreme flooding in October 2024.

Three different laser scanning systems were used to obtain 3D point cloud data of the dry river bed in Rambla de la Viuda after a major flood event in March 2025. A 8 km long reach of the river channel was scanned for the first time with drone operated laser scanning system (Riegl VUX-120 scanner and NovAtel CPT7 GNSS-IMU navigation system), and smaller parts of the channel were scanned with two different backpack systems: commercial SLAM system Faro Orbis and FGI developed Akhka system with Riegl miniVUX-3 scanner and NovAtel Pwrpak 7/ISA-100C GNSS-IMU navigation system.

In addition to the aforementioned data acquisition, we have collected time series data of the same area with backpack and ATV based MLS systems in years 2012, 2013, 2016 and 2019, and we present some examples of change in selected parts of the reach.

We compare the operability of these systems, and their feasibility for detailed river bed topography mapping in terms of area coverage, level of detail and ease of operation. Time series data is used for change detection, i.e. erosion and deposition, examples of which are depicted discussed in the presentation.