Continuous measurement of flow direction and streamflow based on travel time principles using a triangular distribution of acoustic tomography systems

[Display omitted] •Monitoring river dynamics using three underwater tomographic systems.•Estimating continuous cross-sectional mean velocity and runoff based on travel-time.•Proposing new equations to estimate continuous mean flow direction using travel-time.•Flow direction in unidirectional river can be estimated using three acoustic stations. Monitoring flood dynamics is important to provide optimal flood mitigation practices and understand their hydrological responses. Recently, applications of travel time principles have gained a growing interest in hydrological research and river engineering. In this study, flood dynamics were monitored using the fluvial acoustic tomography system (FAT), based on travel time principles. The primary objective of this study is to continuously measure the mean cross-sectional velocity, river flow direction, and river discharge using an innovative tomographic system during two flood events. In this regard, three FAT systems were placed in a gravel bed stream forming a triangle shape to measure stream velocity along two cross-sections. By investigating the magnitude of the cross-sectional mean velocity vectors and the cross-sectional areas, we proposed new equations to evaluate the expected flow direction. The performance of flow measurement by the FAT system was verified with another reference record. Importantly, we demonstrated that the minimum number of acoustic stations to determine river flow direction in unidirectional streams can be reduced to three stations which can be more practical and easier. Further, one of the novel aspects of this study is offering new guidelines to continuously estimate flow direction using a triangular distribution of tomographic systems. In general, this study presents a promising method for monitoring flow dynamics in rivers.