HR: 10:35h
AN: H22D-02    [Abstracts]
TI: Plantation Forestry and Peak Flow Responses in Experimental Catchments and Large River Basins in Chile
AU: * Iroume, A
EM: airoume@uach.cl
AF: Universidad Austral de Chile, Faculty of Forest Sciences, PO Box 567, Valdivia, Chile
AU: Huber, A
EM: ahuber@uach.cl
AF: Universidad Austral de Chile, Faculty of Sciences, PO Box 567, Valdivia, Chile
AB: Land use changes are inextricably linked to water resources and the consequences of such changes are a problem faced by water managers and governments across the world. This particular study considers the impact of changes in plantation forest cover on the hydrological response, with a specific focus on the issue of peak flow conditions and variation. The research still in progress is focused in small catchments and large river basins of Chile. The analysis of the data and the preparation of this document were carried out within the framework of the INCO- CT2004-510739 EPIC FORCE Project. EPIC FORCE aims to improve the integrated management of forest and water resources at the river basin scale through the development of policies based on sound science, focusing on extreme rainfall/snowmelt events. The focus areas are four Latin American countries (Costa Rica, Ecuador, Chile and Argentina.), which represent a range of humid forest and rainfall/snowmelt regimes with major flood and erosion problems and which suffer from a lack of integrated water and forest policies. Much of the controversy surrounding changes in peak flows following forest treatment arises from uncertainty over the response from different sizes of storms; whilst most studies agree that mean peak flow generally increases (even for only a short period) in the post harvesting period, there have been a number of different conclusions regarding influence of forest cover on peak flows from small storms compared with the flows from large events. In Chile, this research is been carried out in experimental catchments (less than 1 km2) and in large river basins (greater than 94 and up to 1,545 km2). Results from La Reina (34.4 ha), where peak flows from the pre-harvesting period (years 1997 to 1999, plantation of Pinus radiata established in 1977 covering the 79.5% of the area) were compared with those from the post- harvesting period (plantation clearcut between end of 1999 and first months of 2000 and replaced by an Eucalyptus nitens plantation) show that in average peak flows increased by 32% after forest removal. Analyzing pre and post-harvesting peak flows from different sizes of rainfall events (rainfall "small" events from 5 to 10 mm, "medium" events from 10 to 50 mm, and "large" events greater than 50 mm), the median of the peak flows increased by 67% for the small events and 32% for the large events. Besides, comparing the pre-harvesting condition with each of the years of the post-harvesting period (years 2000 to 2005), the analysis showed that in all cases post-harvesting peak flows were still significantly higher than before forest clearing. Decreases in annual runoff were noticed in the large river basins where forested area almost doubled between the beginnings of the 1970 up to present. These decreases in annual runoff are well explained by the increases in evapotranspiration capacity of the new planted forests, calculated using the Zhang model and through direct measurements done in experimental plots by the authors. However, the increases in planted area within these large river basins seem not to affect peak flows, as peak flows from the "pre plantation development period" were not statistically different from those of the "post plantation development" one. This research is allowing the generation of evidence based management proposals to support forest certification processes of Chilean companies.
DE: 1800 HYDROLOGY
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 1860 Streamflow
SC: Hydrology [H]
MN: 2007 Joint Assembly