Computing Geomorphologically Salient Networks via Discrete Morse Theory

Abstract

Rivers, estuaries, intertidal zones, and other hydrological systems often give rise to complex networks of interconnected channels. Even today, such networks are typically drawn manually by domain experts. Traditional watershed methods for automating this process, where water flows are assumed to follow steepest descent, fail to capture behavior particular to low-relief terrains. At SoCG 2017, Kleinhans et al. proposed a method to construct a network of source-to-sink paths separated by sufficient sediment volume. However, this method is unstable with respect to minor changes of the input terrain, and constructs only channels that flow from one side of the terrain to the other, thereby failing to detect the dead-end channels ("fingers") that characterize intertidal zones. We show how to compute geomorphologically salient networks that avoid these issues. After extending elevation data to a discrete Morse function on the terrain, we identify channels that flow through saddles and have sufficient volume of sediment on both sides. We then detect fingers, which follow the boundary of "spurs" that have sufficient volume of sediment above a particular height. The main challenge here lies in meaningfully modeling salient spurs and determining suitable heights to measure volume. We implemented our method and applied it to real-world data. Our expert users have validated the mathematical modeling by confirming that the resulting (finger) channels indeed constitute a geomorphologically salient network