Comparing morphological investigation with χ index and gilbert metrics for analysis of drainage rearrangement and divide migration in inland plateaus

Abstract

Drainage rearrangements and consequently divide migration are important processes in the dynamic evolution of landscapes. Two approaches have been used to identify, analyze, and describe these processes: traditional studies based on morphological and sedimentary evidence; and topographic metrics analysis, highlighting the χ index and Gilbert's three metrics (gradient, relief, and elevation). However, the two approaches have not been tested together for catchments located in areas of tectonic stability and low relief (i.e., inland plateaus). The present study uses traditional methods (morphological evidence) and topographic metrics to analyze drainage rearrangements and divide migration in an inland volcanic plateau: the high drainage divide between the Uruguai and Paraná rivers (two of the largest basins in South America). The results indicate that drainage divides in low reliefs with symmetrical characteristics on both sides have different behaviour of divide migration than asymmetrical ones. For symmetrical divides, past, present and future trends of mobility may occur in different directions, resulting in a back-and-forth movement. Because of similarities on both sides of the divide, local factors such as structural lineaments can be the lead causes of the imbalance that induces bidirectional migration. In this sense, current/future migration trends predicted by topographic metrics may not relate to the way the divide moved in the past. On the other hand, traditional analysis of evidence of stream capture does not guarantee that the drainage divide behaves the same in the present and/or in the future. Therefore, the combination of the two approaches can be helpful to better understand drainage divide migration dynamics through time, especially in areas of low relief such as inland plateaus.