Morphometric analysis of watershed affected by debris flows in mountain region of rio de janeiro

Abstract

The geomorphological processes related to debris flow are the most catastrophic in nature because of their high velocity, kinematic energy, and large volume of mobilized sediments. The damage and economic losses caused by this movement have been significant for human lives, agricultural lands, settlements, and properties. Thus, understanding the characteristics of the source area and deposition area is essential for debris-flow mitigation. Basin-scale morphometric indices are very useful for understanding debris flow initiation, propagation, and deposition, improving susceptibility assessment and hazard map generation. The present article characterizes the morphometric indices in areas where debris flows occurred affecting four basins (Cuiabá, Príncipe, Vieira, and D'Antas) located on the reverse of Serra do Mar fluminense. The indices herein considered include Slope Angle, Topographic Wetness Index (TWI), Stream Power Index (SPI), and Topographic Factor (LS). The morphometric indices were derived from Digital Terrain Models (DTM) (at 12.5-m resolution) using the Geographic Information System environment. The results show that the debris flow was triggered in amplitude >1200 m, slope angles >45°, by landslides developed in the main channel with high values of TWI, SPI, and LS. Debris flows were deposited at slope angles <2° in watershed with high TWI and SPI (except Príncipe and Vieira watersheds) and low Topographic Factor (LS) values. Therefore, the indices indicated the critical classes for the occurrence of debris flow phases of the analyzed watersheds.