Longitudinal interference of small structures in the river’s hydrological and sedimentological connectivity in a Brazilian semiarid basin

Abstract

This study evaluated the longitudinal influences of low-water crossing on the river system and sedimentological connectivity in a Brazilian semiarid basin. The Lower Piancó River basin was chosen as the study area, and four low-water crossings along the catchment were identified and selected for analysis and diagnosis. The effective catchment areas of each structure were delimited, and their impacts assessed over time. Rainfall data from three gauges were used to analyze precipitation events capable of causing significant sedimentological and morphological modifications. These events were classified into three types according to their magnitudes: high, moderate, and low. Sediment samples were collected at each low-water crossing, and lateral profiles were drawn upstream and downstream of the structures to analyze the destruction and deposition of sediments and channel morphology. The analysis showed that the low-water crossings could act as barriers to sediment flow, especially for coarser sediments, and favor the incision of the downstream channel. However, during exceptional flows, the low-water crossings allowed the transmission of sediments due to the clogging of the upstream channel riverbed. This highlighted a unique interaction between the river system and the low-water crossings over time. The results of the connectivity analyses revealed that low-water crossings have a unique impact on the fluvial system compared to other structures, particularly due to their role in the sedimentological connectivity of coarse sediments. Specifically, sediment transport downstream of the crossing emerged as a significant factor in understanding its influence on the surrounding environment. Compared to other types of small longitudinal fluvial interventions, the stage model and low-water crossings displayed structural and aesthetic similarities with floodways and fords. However, functionally, the low-water crossings had strong similarities with check dams, weirs, and sand dams due to their roles in retaining sediments and altering the morphology of the channels in which they are installed.