Evaluation of sediment (dis-)connectivity due structural changes in a low-order stream

Abstract

Investigating sediment dynamics and delivery in low-order streams still a topic with numerous challenges to be overcome. The processes underlying these dynamics are complex and often not linear, especially due to river emerging feedback processes varying significantly across space and through time as being governed by the connectivity relationships in these systems. Sediment connectivity in fluvial systems is controlled by different environmental factors such as hydrology (e.g. precipitation, overland flow) and structural elements (e.g. hillslope runoff pathways, pools, sinks, or natural barriers such as log jams). Most studies use discharge derived variables to estimate transport of sediment but there is a need to understand how structural elements can control the dynamics. Therefore, the main goal of this work is to study the effects of natural barriers (especially large wood accumulations) and their removal on longitudinal water and sediment (dis-)connectivity and sediment delivery via continuous monitoring/estimating of precipitation, discharge, critical shear stress (CSS), and sediment transport. The monitoring will be carried out in different scenarios, which will be determined according to the structural changes in the river corridor, due to the removal of the currently existing barriers with evident retention of sediments. The study will be conducted in the Baio stream catchment (0.89 km²), located in the Campos Gerais plateau, northeast of the state of Rio Grande do Sul, southern Brazil. In this catchment, there is an intense agricultural activity without any conservation practices, being the main sources of sediments coming from rill, sheet and channel stream erosion. At the same time, there are many sources of recruitment of woody debris, especially due to nearby reforestation activities. By investigating the effect of wood barriers in the stream, we look to understand the sensitivity of the sediment transport to the structural elements.