Et paleohydrologisk studie av Sagbekken, Hedmark fylke : en rekonstruksjon av Sagbekkens flomhistorie gjennom holosen

The location for this thesis has been the river Sagbekken. Sagbekken is a small river in Foldal municipality in Hedmark county in Norway, and it ends it’s journey in lake Butjønna. The river is not directly connected to Glomma, but through a couple of other streams the water from lake Butjønna meets Glomma in Alvdal.This thesis describes a paleohydrological study of lacustrine sediments. The idea behind this project was to determine wether the conservation-potential of Sagbekken’s flood-signals in lake Butjønna was of good enough quality to make a reconstruction of Sagbekken’s flood-history.Two sediment-cores each 5 m long were taken from the bottom of lake Butjønna. The making of a visual log and loss-on-ignition analysis showed a clear lamination between the mineral flood-signals and the organic matter. Floods of a certain magnitude deposit enough mineral material to create a horizontal layer in the cores. The magnitude of the flood determine how thick the layer is. Altogether 68 flood-layers was recorded from Storofsen in AD 1789 to 9500 BP. Carbon-dating methods was used to determine the age. With such a long time-span it’s easy to see how the flood-regimes have changed from periods with frequent floods to periods without floods at all.A recurrence-interval was estimated for Sagbekken and it was found to be 137 years. This estimation rests on the assumption that a constant sedimentation has taken place in lake Butjønna. The floods have duration from a few hours to a couple of days, and are therefore kept out.The maximum grain-size, the competence, Sagbekken could carry during the spring-flood was estimated with indirectly methods. Observation of flood-marks along the river channel was the basis for a reconstruction of the water surface. With the use of Manning’s formula was the speed, discharge and competence estimated for the spring flood in Sagbekken. The competence was estimated to 4 mm +/- 1 mm, and that fits well with the observations of sand along the river-channel