PRIORITIZATION OF FLOOD PREVENTION MEASURES IN WASTEWATER SYSTEMS IN NORWEGIAN CITIES Geir Torgersen Assistant professor, Ostfold University College, Norway PhD-student, Norwegian University of Life Sciences geir.torgersen@hiof.no Source: ODDMUND MIKKELSEN
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Background for this study Increasing number of flooding in basements in Norway More claims from insurance companies to municipalities for underdimensioned sewers Using non-piped systems - more sustainable THE GOALS FOR THIS STUDY HAS BEEN: What are the triggering reasons and methods when renewing sewers in Norwegian cities today? Are there any single factors that influence on the current practice? 3
Theory / methodology / survey The climatic changes will lead to more focus on flooding and use of SuDS-methods in urban areas There is a transition towards a «Regime shift» from piped to more use of non-piped solutions for urban drainage systems (de Haan and Rotman, 2011) To find the «state of art» in Norway, a survey among the 25 largest cities was carried out 4
Triggering reason - renewing sewers in the largest cities 2010 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% Pollution Flooding water supply project Other infrastructure project others Norway Denmark Sweden Fig. 1: Triggering reasons to renovate sewers in 2010 5
Methods - renewing sewers in the largest cities 2010 80% 70% 60% 50% 40% 30% 20% 10% 0% Open trench Nodig Pumps etc SuDS Others Norway Sweden Denmark Fig. 2: Methods for renovating sewers in 2010 6
Characteristics for Norwegian cities when renewing sewers in 2010 Pollution reduction is normally the triggering reason Open trench is the far most dominating method Flooding has low priority, and SuDS is hardly used at all Norwegian cities compared to other Scandinavian countries: Flood prevention - has lower priority NoDig-methods are less used Use even more traditional methods, as open trenches 7
Model prioritization of renewing projects in sewers Fig. 3: Model of factors that influate when renewing sewers 8
From the Norwegian survey in 2010 Conditions: The conditions 2/3 acceptable, 1/3 bad or reduced Water leaks (43%) implies that open trench may be prioritized No big events (yet) that results in Governmental flooding focus Instruments 95% reports good or acceptable economic conditions 60% reports they the competent people are not enough Methods Open trench (78%) / SuDS 3% Goals The last 10-20 years, focus from the authorities have been on emissions from waste water treatment plant Renewing rate on sewers has so far high focus 9
Lack of requirements - possible consequenses Lack of requirements from authorities in relation to emissions from CSOs The municipalities do not prioritize monitoring or modelling emissions from CSOs Difficult to prove the impact of renewing project Difficult to determine optimal measures Difficult to estimate the consequenses of flooding in the cities 10
Conclusion The survey from the largest Norwegian cities indicates: High rate of water leaks lead to more use of open trench Competent people are not enough - this may lead to little innovation etc. Lack of requirements may have turned the focus to activities and to a lesser degree analyzing the impacts of renewing projects There is: Little progress in the transition from the former to a new «storm water regime» A need to change from traditional engineering approach to more flexible SuDS-design to meet uncertainties related to climate changes Stricter requirements from Norwegian authorities in relation to the impacts of renewing projects may be a first step towards a more sustainable storm water regime 11
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