Utbedring av og problemer med kvist- og stokkdammer sett i et geomorfologisk perspektiv, med utgangspunkt i teori og observasjoner fra Soknedal, Norge

Abstract

Small branch and log dams are a new type of check dam used in small(~1km²) basins to prevent infrastructure damage resulting from heavy precipitation. These dams are built to deposit sediments, reduce flood volume and mitigate hillslope processes. From a geomorphological perspective, this thesis addresses problems with small branch and log dams, and how to make them more resilient and sustainable in regard to erosion, sediment deposition, and flood control. During 2014 four dams were constructed in Soknedal, Norway, an area prone to flooding and landslides. Alterations in the dams were recorded during fieldwork undertaken throughout the Autumn and Winter of 2014-2015. These records are combined with theory to answer the aforementioned problems.

A dry Autumn and Winter resulted in low dam activity, with no flooding or erosion recorded, nevertheless there was a noticeable amount of fine sediment deposition in two of the dams. Observations and theory suggest that these sediments will be subsequently eroded and transported downstream during a flood. One might consider constructing taller dams if rapid sediment deposition in a short time span is a problem. Taller dams require better erosion control, but would reduce the flood volume more efficiently. This thesis suggests that using step-pool morphology as inspiration when constructing several dams would result in a large amount of energy dissipation. Further research is needed to better record how dams respond to floods in respect to reducing flood volume, erosion and sediment transportation.