HR: 17:25h
AN: H24A-06    [Abstracts]
TI: Stormflow runoff in Eastern Amazonia, Brazil: The role of riparian wetland valleys
AU: * Wickel, A J
EM: bwickel@xolo.conabio.gob.mx
AF: Center for Development Research (ZEF), University of Bonn, Walter-Flex-Str. 3, Bonn, 53113 Germany
AU: * Wickel, A J
EM: bwickel@xolo.conabio.gob.mx
AF: CONABIO, Av. Liga Perfiferico, Insurgentes Sur 4903, Col. Parques de Pedregal, Tlapan, Mexico City, 14010 Mexico
AU: Van de Giesen, N C
EM: N.C.vandeGiesen@CiTG.TUDelft.NL
AF: Center for Development Research (ZEF), University of Bonn, Walter-Flex-Str. 3, Bonn, 53113 Germany
AU: Van de Giesen, N C
EM: N.C.vandeGiesen@CiTG.TUDelft.NL
AF: Dept. of Water Management Civil Engineering & Geosciences, TU Delft, Stevinweg 1, Delft, 2628 CN Netherlands
AB: Analysis of 245 rainfall-runoff events over a one and a half year study period at two small (10 and 35 ha.) watersheds in the Eastern Amazon region revealed a strong correlation between rainfall and stormflow volume. From this relationship it was deducted that only 0.6% of the total watershed area is estimated to contribute to stormflow generation, while only 1.5 % of the total annual runoff is made up by stormflow. The main factors controlling stormflow generation seem to be topography (shallow canyon like incision pattern of the creeks), which confines the source area of stormflow to the flat valley bottoms with riparian forest, and the high permeability of the surrounding area. Analysis of field measurements revealed that the minimum observed infiltration rate (80 mm/hr) still exceeds the maximum rainfall rates (66 mm/hr), meaning that saturation overland flow or Hortonian overland flow conditions hardly ever occur. Similar stormflow dynamics were found for catchments with comparable topography and soil characteristics in various studies in Central Amazonia and for a watershed in Guyana. In none of these studies though, the relation between rainfall and stormflow was so strong that even the filling of the wetland storage with the onset of the rainy season could be observed. The hypothesis of a fixed contributing area for the streams of the current study region is confirmed by the chemical analysis of stormflow nutrient concentrations, which seems to be entirely controlled by the riparian vegetation. After a short period of strong flushing of nutrients from the canopy at the onset of the rainy season the stormflow shows only a slight decline in nutrient concentrations. A second, delayed peak in stream nutrient exports, typical for overland flow during or right after a storm, was absent. The current study illustrates that the variable source concept posed by Hewlett and Hibbert in 1967 is limited by topography and substrate under certain conditions, and that the stormflow generating ``source area'' for stream in Eastern Amazonia does not extend further than the riparian valley.
DE: 1813 Eco-hydrology
DE: 1834 Human impacts
DE: 1838 Infiltration
DE: 1850 Overland flow
DE: 1876 Water budgets
SC: Hydrology [H]
MN: Fall Meeting 2005