INFILTRATION IN THE UPPER RÍO CHAGRES BASIN

Annual runoff hydrographs recorded by the Panama Canal Authority in the Upper Río Chagres basin indicate several peculiar features. First, the annual hydrograph is strikingly seasonal, with very few signs of direct runoff and a continuous decay in base flow during the dry season. Secondly, there are signs of anomalously high runoff production efficiencies early in the wet season. Thirdly, the base flow from the catchment exhibits up to three different “quasi-stable” base flow discharges as the wet season progresses. The objective of our study is to examine runoff generation in the upper Rio Chagres watershed using the US Department of Agriculture, Natural Resources Conservation Service “Curve Number” or “CN” methodology. Specifically, variation curve of the CN was analyzed using rainfall and runoff observations from the basin. Results indicate significant influence of seasonality on the CN. Furthermore, there are significant inter-seasonal changes in the CN that invalidate the applicability of the CN approach in this tropical watershed.