Plantation forestry impacts on sediment yields and downstream channel dynamics in the UK: a review

Abstract

The impact of coniferous plantation forest on erosion and sediment yields in the UK uplands over the past three decades is reviewed by examining background or natural suspended sediment yields (SSY), bed load yields (BLY) and bank erosion and comparing with studies of‘disturbed’catchments. This paper collates all the UK studies that have monitored changes in erosion and sediment yields at the forest establishment, mature forest and timber harvesting phases of the forest cycle. A simple model based on this comprehensive examination of studies to date suggests that mean sediment yields increase at the initial ground disturbance phase, recover as the forest matures and increase again more significantly at the timber harvesting phase. The likely downstream impacts of these changes in sediment yields on channel dynamics and management is discussed, introducing sediment wave theory with particular reference to the generation of bed load waves downstream of forested catchments. Modelling of downstream changes in unit stream power has implications for the accumulation of nonpoint source sediment in sediment waves. Published studies in which channel changes have resulted from the passage of sediment waves are collated and it is concluded that the translating wave model is best supported. The paper concludes with a discussion of the broader implications for river management and presents advice for river managers.