Hillslope processes, drainage density, and landscape morphology

TLDR

Catchment morphology and drainage density are strongly influenced by hillslope processes. The study investigates how different hillslope process laws affect drainage basin evolution using numerical experiments. A numerical model incorporating five hillslope process laws—diffusive‑advective transition, runoff generation threshold, erosion threshold, and two threshold‑activated landsliding types—derives expressions linking drainage density to rainfall, relief, and mean erosion rate. These hillslope processes modify landscape appearance and the slope‑contributing area relationship, with the sign of drainage density versus relief varying by threshold type and climate: positive in semiarid, low‑relief settings and negative in humid or high‑relief landscapes dominated by saturation or landsliding thresholds.

Abstract

Catchment morphology and drainage density are strongly influenced by hillslope processes. The consequences of several different hillslope process laws are explored in a series of experiments with a numerical model of drainage basin evolution. Five different models are considered, including a simple diffusive‐advective process transition, a runoff generation threshold, an erosion threshold, and two types of threshold‐activated landsliding. These different hillslope processes alter both the visual appearance of the landscape and the predicted relationship between slope and contributing area. On the basis of the different threshold theories, we derive expressions for the relationships between drainage density and environmental factors such as rainfall, relief, and mean erosion rate. These relationships vary depending on the dominant hillslope threshold. In particular, the sign of the predicted relationship between drainage density and relief is positive in semiarid, low‐relief landscapes and negative in humid landscapes dominated by a saturation threshold and/or in high‐relief landscapes dominated by simple threshold landsliding.