Soils of the Upper Río Chagres Basin, Panama

Understanding the relationship between rainfall, and stream flow in mountain terrain requires the quantifying of rates of water movement into and through regolith covered hillslopes. General theory holds that infiltration rates in humid tropical are higher than rainfall intensities so surface runoff is minimal. However, soil profile characteristics can vary significantly on a hilslope, with concomitant changes in soil hydrologic characteristics. The pattern of soils within two small first order drainages was evaluated within the upper Río Chagres basin. Two main influences on soil distribution were identified. Mass movements primarily translational sliding and treefall result in stripping of the upper soil horizons and exposure of weathered saprolite. Soils forming in the deposits are characterized by higher infiltration rates and a more uneven surface topography than the stable soils. A catenary relationship was also observed with stable, oxidizing soil profiles in upper slope positions and reduced (gleyed) soils at the outlet of the drainage basin.