Stormflow generation and flowpath characteristics in an Amazonian rainforest catchment

The Amazon basin covers an area of roughly 7 x 10(6) km(2) and encompasses diverse soil-landscape types with potentially differing hydrological behavi our. This study was conducted in the Ultisol landscape of the western Amazo n basin in Peru. Processes of stormflow generation were investigated on an event basis in a first-order rainforest catchment to establish a causal lin k between soil physical and precipitation characteristics, hillslope flowpa ths and stormflow hydrograph attributes. A sharp decrease in soil hydraulic conductivity with depth and high rainfall intensity and frequency favour r apid near-surface flowpaths, mainly in the form of saturation-excess overla nd flow and return flow. The latter results in an almost random occurrence of overland flow, with no obvious topographic control. Hillslope flowpaths do not vary much with respect to the hydrograph attributes time of rise, re sponse time, lag time and centroid lag time. They have the same response ti me as streamflow, but a somewhat lower time of rise and significantly short er lag times. The recession constant for hillslope hydrographs is about 10 min, in contrast to the streamflow recession constants of 28, 75 and 149 mi n. Stormflow generation in this Ultisol rainforest catchment differs strong ly from that reported for Oxisol rainforest catchments. These two soilscape s may define a spectrum of possible catchment hydrological behaviour in the Amazon basin. Copyright (C) 2000 John Wiley & Sons, Ltd.