Sediment Budgets in Forested and Unforested Basins in Upland Scotland.

The downstream impact of afforestation and deforestation is being studies in paired basins, one forested (6.8 km2) and the other moorland (7.7 km2), at Balquhidder in the steep wet Scottish Highlands. Preliminary sediment budgets are given based on three years' output data and one year's source data. Suspended sediment output from the forested basin varies more closely with water discharge, and is three times higher in total, than that from the moorland basin where it is deduced that less sediment is available. The delivery ratio from first order tributaries to mainstream outlet is close to 1.0 for suspend sediment in both basins, and for bed load in the forested basin, but much lower for bed load in the moorland basin; this presumably reflects channel storage but this has not yet been detected in cross section surveys because bed load fluxes are very low. Mainstream bank erosion accounts for less than 5% of sediment outputs and a landslide into the moorland mainstream in 1985 has not yet affected basin outputs