For most of the river's course, the gradient is slight. Downstream from its headwaters, it splits into two; one-third of its flow passes through the Brazo Casiquiare (Casiquiare Channel) into a tributary of the Amazon, and the remainder passes into the main Orinoco channel. This passageway allows vessels with shallow drafts to navigate from the lower Orinoco to the Amazon River system after unloading and reloading on either side of two falls on the Orinoco along the Colombian border.