Sammendrag
We assessed three different flood mitigation options, based on simple models, to reduce flooding problems in Bjørkelangen town. The mitigation options i) small debris dams, ii) re-meandering of Lierelva, and iii) restoration of Liermåsan and Bliksrudmåsan were considered for current and future flow scenarios in a climate change context. We evaluated flood reduction potential for peak flow episodes with return periods of 100 years. Restoration of Liermåsan and Bliksrudmåsan may store approximately 4-5% of the total water volume comprising maximum daily peak flow and approximately 2-3% in context of future climate change. Importantly, however, the total water storage capacity increases non-linearly with increasing area of peat land and establishing peat land in 5% of the catchment would create a 10% flooding reduction. Construction of small debris dams in forested areas at approximately 1,000 sites may store approximately 5% of the total water volume comprising the 1-day peak flow and approximately 2-3% in context of future climate change. Re-meandering of Lierelva was not found to have significant effects on flood mitigation in Bjørkelangen. Restoration of Liermåsan and Bliksrudmåsan should receive highest priority due to a combination of highest cost-efficiency and high flood mitigation potential.