Spatial distribution of intermittency in a Brazilian Semiarid river

Intermittent and ephemeral rivers are characterized by periods of drying and rewetting which occur along different reaches of the channel. Where the channel dries or develops into ponds related to factors such as discharge, topography, geology and riparian vegetation. The aim of this work is to evaluate the spatial patterns and dynamics of intermittency in reaches of a Brazilian semiarid river. Using repeated surveys with unmanned aerial vehicles (UAVs), we characterize its connectivity by identifying locations with different water condition. The Umbuzeiro River (approximately 80 km long; 6.65°S, 40.41°W) is the main river in the Benguê catchment (~1000 km²) that is controlled by the Benguê reservoir, with a storage capacity of 18 hm³. Umbuzeiro is an intermittent/ephemeral river and spatially coherent streamflow occurs mainly in the wettest months of the rain season. We conducted UAV surveys each month from March to June 2022, allowing us to produce detailed hydrological characterizations along different sections of the river. The imagery sets from different UAVs, i.e. DJI Phantom 4 pro and eBee SQ, provided relatable characteristics for a same reach. Visually analysing the reaches, their water condition was determined for smaller subsets, i.e. ponds or dry spots. Observing the temporal and spatial patterns of the presence of water on the riverbed in the different reaches for each survey, we conclude that the patterns are not only dependent on the contributing area of each section, but also on the river’s natural sinuosity, riffle-pool sequences and riparian vegetation. Our results highlight and provide an explanation for the hydrological diversity of semiarid rivers which is important to understand their ecological role and habitat.