Environmentally sensitive plot-scale timber harvesting: impacts on suspended sediment, bedload and bank erosion dynamics

摘要

The impact on sediment pollution of environmentally sensitive harvesting of 15 ha plot(20/100 the catchment area)of amture coniferous plantation forest in the 0.89 km~2 Afon Tanlwyth catchmet, Plynlimon, was investigated for 12 months before harvesting began and a further 18 months after. The results revealed:(a)a steepening of the suspended sediment concentration vs. Discharge rating resulting in a 39/100 increase in suspended sediment yield(as compared to the adjacent forested Hafren catchment)during the year in which the harvesting operation took place; (b)a statistically significant increase in main channel bank erosion rates, as compared with the nearby Afon Cyff; main channel banks are estimated to have contributed around 80/100 of the total catchment suspended yield during the two year period(1995-1996), and (c)no significant change in bedload yields over the duration of the study, though a longer post-harvesting time series of bedload data will be required to properly assess the impact of the harvesting operation upon behload yields.