Hva skal vi dimensjonere rør og flomveier for i fremtiden og hvordan gjør vi det Tone M. Muthanna Associate Professor Department of Hydraulic and Environmental Engineering NTNU
20% 10% (Lindholm, 2012) 2
Dimensjonering av rør Hva gjør vi i dag: Norsk Vann anbefaler en 20% faktor som legges på toppen som en klimafaktor NOU anbefaler gjentaksintervall på 5,10,20 eller 50 avhengig av konsekvenser (20 i vanlig sentrumsbebyggelse) Hva skal vi gjøre i fremtiden? Ingen fasit på det, dessverre, men noen eksempler som peker ut en prioritering Vi har mye data som vi kan lære mye av med bedre analyse 3
Data Analysis Risvollan Station Stationary vs. Non-stationary FFA
Is Anthropogenic climate change significant enough to abandon stationary models for non-stationary flood frequency analysis models?
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 DATA Analysis Minute Daily Monthly Annual Methods Applied Mann-Kendall Test F- Test T- Test Gurbbs Test 60 50 40 30 20 10 0 Feb.01 Feb. 02 Feb.03 Feb.04 Feb. 05 Feb. 06 Feb. 07 Feb. 08 Feb. 09 Feb. 10 Feb. 11 Feb.12 Feb.13 Feb. 14 Feb. 15 Feb.16 Feb. 17 Feb. 18 Feb. 19 Feb. 20 Feb. 21 Feb. 22 Feb. 23 Feb. 24 Feb. 25 Feb. 26 Feb. 27 Feb.28 Feb. 29 6
Precp. Data 1400 1200 1000 800 600 400 200 0 Annual Data Year Findings Coefficient of Variation (COV) 0.17 Mann-Kendall Statistics (S) 0 Confidence Factor (CF) 49.2% Status of Trend Stable
Month COV S CF Status of Trend January 0.74-25 68.1% Stable February 0.58-2 50.8% Stable March 0.67 34 74.1% NSS April 0.71 32 72.8% NSS May 0.36-82 94.5% Presumably Decreasing June 0.38 37 76.0% NSS July 0.50 30 71.5% NSS August 0.52 30 71.5% NSS September 0.70 65 89.6% NSS October 0.42-3 51.6% Stable November 0.78-6 53.9% Stable December 0.60-42 78.9% Stable NSS = Not statistical significant
1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 30,00 20,00 10,00 0,00 Maximum Precipitation for Different Durations 1 min 2 min 3 min 5 min 60,00 40,00 20,00 0,00 10 min 15 min 20 min 30 min 100,00 50,00 0,00 400,00 300,00 200,00 100,00 0,00 45 min 60 min 90 min 120 min 180 min 360 min 720 min 1440 min
Duration (min) COV S CF Status of Trend 1 0.44 26 68.8 % NNS 2 0.51 63 88.9 % NNS 3 0.55 77 93.3 % Presumably Increasing 5 0.52 79 93.8 % Presumably Increasing 10 0.47 74 92.5 % Presumably Increasing 15 0.44 64 89.2 % NNS 20 0.42 60 87.7 % NNS 30 0.41 56 86.0 % NNS 45 0.39 63 88.9 % NNS 60 0.39 81 94.3 % Presumably Increasing 90 0.34 80 94.0 % Presumably Increasing 120 0.3 72 91.9 % Presumably Increasing 180 0.27 92 96.4 % Increasing 360 0.26 109 98.4 % Increasing 720 0.35 80 94.0 % Presumably Increasing 1440 0.52 86 95.3 % Increasing NSS = Not statistical significant
Climate Change Impact on Norway The continuous increase in temperature to be 5.4 C in northern Norway is the forecast for the end of the 21st century. Increase of precipitation in the autumn 5-30% Norway has also been projected. (Klaus Vormoor, 2016)
Coefficient Variation Mann-Kendall Statistics Seasonal Data Analysis of January February November December 0.74 0.58 0.78 0.60-25 -2-6 -42 Confidence factor 68.1% 50.8 53.9% 78.9% Coefficient Variation Mann-Kendall Statistics of March July August 0.67 0.50 0.52 34 30 30 Confidence factor 74.1% 71.5% 71.5% Precipitation to gain its flood driving momentum than snowmelt driven floods. 13
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Reconstruction of the Alna River flows Data Discharge (stations) Alna (2010 2015; Oslo VAV) Vestli (1984 2015; NVE) Precipitation (stations) 12 stations (inside Alna catchment) Mostly new (2014 2015) Vestli (1974 2014; met.no) High spatial variability Annual precipitation (09.2014 08.2015) 18
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Reconstruction of the Alna River flows Hydrologic modelling (method) Inductive data-based mechanistic models a) Rainfall Runoff Q c P P P e e A t t 1 t 1 p t p 1 t 1 q t q b) Runoff Runoff Q A c Q V Q V Q V eˆ eˆ e t t 1 t 1 p p 1 t 1 q t q t where: t - time, P - precipitation, & - coefficients, q & p - orders (autoregressive & moving average components), & e - error terms, Q A - flow (Alna), Q V - flow (Vestli), Catchments Area (km 2 ) Elevation (m) Alna 64.29 30 438 Vestli 2.80 154 340 20
Reconstruction of the Alna River flows Hydrologic modelling (results) Overall evaluation a) Rainfall Runoff: 4182 models (Nash-Sutcliffe efficiency, NSE > 0.75) b) Runoff Runoff: Calibration (NSE > 0.832) Validation (NSE > 0.858) Flows of 2 nd Sept. 2015 21
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Assessment of the capacity of the Culvert-Tunnel System The Kværnerbyen culvert-tunnel system Diverts Alna River from its natural course Length ~ 2331 m Steel lined tunnel (145 m) Buried culvert (446 m) Unlined blasted tunnel (1740 m) 23
B1 LT B2 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 Assessment of the capacity of the Culvert-Tunnel System Modelling the culvert-tunnel system (results) Flow magnitudes that pressurize the culvert sections Culvert sections with limited capacity to carry the peak flow of 2 nd Sept. 2015 Runoff (m3/s) 40 45 50 65 82.2 92.9 101.5 25
Drivere i systemet Hvordan kan en nedbørshendelse med mindre enn 20års gjentaksintervall resultere i en så stor flom? Ikke stasjonær tidsserie i flomserien Urbanisering! I slike tilfeller er flomveier viktige Exflood gresskledde swales, http://www.bioforsk.no/ikbviewer/page/prosjekt/hovedtema?p_dimension_id=22783&p_menu_id=22 793&p_sub_id=22784&p_dim2=22785 26
Oppsummering Dimensjonering av flomveier for ekstremhendelser Dimensjonere rør for den daglige driften Risikoanayse (sansynlighet og konsekvens) viktig i valg av dimensjoneringsgrunnlag Sammenhengende flomveier, ikke bare ut av egen tomt/prosjekt 27
Tusen takk!