Integrating Bedload Sediment Tracing and Suspended Load Monitoring for Comprehensive Sediment Transport Analysis in an Intermittent River of the Balearic Islands

For far too long, sediment transport research has largely focused on perennial rivers, leaving Intermittent Rivers and Ephemeral Streams (IRES) underexplored, despite their prevalence in global river networks. This status quo is starting to change partly due to the advent of climate change impact that is ramping up the frequency of periodic drying and pushing rivers towards intermittence and ephemerality, thereby necessitating a paradigm shift towards the research frontier on IRES. This study addresses that need by examining bedload and suspended load transports behavior in the Sant Miquel River, an intermittent river located on the Balearic Islands of Spain. The Sant Miquel River is a significant water body in the region, known for its unique hydrological characteristics and its importance to the local ecosystem. This work represents the first instance of employing passive tracers to study sediment transport in an intermittent river and offers a pioneering approach by simultaneously monitoring and analyzing both bedload and suspended load transport, along with their relative magnitudes. Three survey campaigns were conducted between January 2023 to June 2024 and parameters on the transport of both bedload and suspended sediment loads were characterized on an inter-survey basis. Morphological characterization of the study reach revealed weak riverbed armoring (i.e., the ratio between surface and subsurface grain-size metrics), a characteristic commonly found in other IRES. The tracer-based sediment mobility analysis showed nearly equal mobility across different grain sizes, diverging from the size-selective transport typically reported in perennial rivers. Suspended sediment dynamics in the Sant Miquel River displayed strong seasonal patterns, aligning with observations from other Mediterranean and mountainous catchments. Overall, the findings suggest that the Sant Miquel River exhibited rates of bedload and suspended load transport similar to those observed in other IRES. Notably, a positive correlation was found between suspended sediment load and tracer travel distance, supporting the evidence that finer grain sediment can enhance bedload mobility. This research contributes valuable data to the limited body of knowledge on sediment transport in IRES, emphasizing the importance of further investigation into these unique fluvial systems.