Relationships between discharge parameters and cross-sectional channel dimensions of rivers in an active margin influenced by tropical climate: The case of modern fluvial systems in the Indonesian islands

The present study investigates (1) the relationships between discharge parameters and bankfull channel width (Wb) based on statistical analyses of hydrological data obtained from 649 sites at rivers on the Indonesian islands of Java, Sumatra, and Kalimantan, and (2) the relationship between depth parameters and Wb using channel cross sections obtained from 86 sites at rivers on these three large islands. These analyses are used to describe geomorphological and hydrological features of fluvial systems developed in a convergent margin under the influence of a low-latitude tropical climate. The relationship between mean discharge (Qmean) and Wb shows distinct variation within the Indonesian rivers, and reflects regional variations in annual rainfall of a tropical climate. The relationship between bankfull discharge (Qb) and Wb shows only minor variations across the three islands, regardless of bed and bank material types. The Qb–Wb relationship in the Indonesian rivers has a pattern similar to that of fluvial systems in Europe and the North American continent, which are influenced by mid- and high-latitude climates. Minor regional variation in the Qb–Wb relationship, regardless of the tectonic and climatic settings, suggests that the development of fluvial morphology is controlled mainly by flood-related episodic discharge. In contrast, the empirical equations between maximum channel depth (db) and Wb and between mean channel depth (dm) and Wb show distinct regional variations not only within the Indonesian fluvial systems but also in fluvial systems of Europe and the North American continent. These regional variations are thought to reflect the fact that db–Wb and dm–Wb relationships are controlled by the tectonic and climatic settings of a drainage basin, and factors such as the interrelationships between precipitation, vegetation, and slope. Consequently, selection of an appropriate dm–Wb (or db–Wb) equation combined with an appropriate Qb–Wb equation permits us to reconstruct spatial and temporal variations in hydrological features in both modern and ancient fluvial systems more precisely than applying previously proposed equations to fluvial systems formed in active margin and low-latitude climatic settings.