Bedrock Channel Incision along the Upper Río Chagres Basin, Panama

Examination of various types of bedrock channel segments throughout the upper Río Chagres network indicates the influences of lithology, rock-mass strength, jointing, and resistance to weathering on channel geometry. Bedrock channel segments throughout the upper Río the Chagres basin take the form of step-pool sequences, pool-riffle sequences, and knickpoints and gorges. Mafic lithologies in the catchment have the greatest rock-mass strength and the longest exposures along the active channel, and are more likely to exert a strong local control on channel geometry. The longest continuous exposure of resistant rocks in the middle and lower portions of the upper Río Chagres occurs in the Dos Cascadas reach, where upstream migration of two knickpoints has created a gorge. Surface textures (

e.g.

, the presence of potholes) and erosion mechanisms of individual rock units in the Dos Cascadas reach correlate strongly with fracture spacing and rock hardness.