Peatland drainage changes catchment conditions and increases the transport of suspended solids(SS) and nutrients. New knowledge and management methods are needed to reduce SS loadingfrom these areas. This thesis examines sediment delivery and erosion processes in a number ofpeatland drainage areas and catchments in order to determine the effects of drainage on sedimentand erosion dynamics and mechanics. Results from studies performed in peat mining, peatlandforestry and disturbed headwater catchments in Finland are presented and potential sediment loadmanagement methods are discussed for drainage areas and headwater brooks. Particular attentionis devoted to erosion of organic peat, sediment transport and methods to reduce the impacts ofpeatland drainage in boreal headwaters.
This thesis consists of six articles. The first and second papers focus on the erosion andsediment transport processes at peat harvesting and peatland forestry drainage networks. Theresults indicate that in-channel processes are important in drained peatland, since the drainagenetwork often constitutes temporary inter-storm storage for eroding and transporting material.Sediment properties determine the bed sediment erosion sensitivity, as fluffy organic peatsediment consolidates over time. As flashiness and peak runoff control sediment entrainment andtransport from drained peatland areas, water quality management should include peak runoffmanagement.
The third, fourth and fifth papers studies use and application of peak runoff control (PRC)method to the peat harvesting and peatland forestry conditions for water protection. Resultsindicate that effective water quality management in drained peatland areas can be achieved usingthis method. Installation of the PRC structures is a useful and cost-effective way of storing stormrunoff waters temporarily in the ditch system and providing a retention time for eroded sedimentto settle to the ditch bed and drainage network. The main effect of the PRC is on SS and SS-boundnutrients.
The sixth paper is concentrated to test new restoration structure to be used in degradedheadwater brooks. The results show that addition of woody restoration structures to the channel iseffective and simple sediment management methods in headwater areas.
New information provided in this thesis on sediment erosion and transport processes in drainedpeatland areas can help to improve water quality control in these areas. In-channel processes areimportant for both peatland uses, since the drainage network often constitutes temporary inter-storm storage for eroding and transporting material. Therefore, controlling these processes is a keyto effective water quality management, which can be achieved using the PRC method in drainageareas or by utilisation of natural fluvial processes in natural channels downstream.
