A Comparison of Future IDF Curves for Southern Ontario

Transcription

1 A Comparison of Future IDF Curves for Southern Ontario John Henderson, P. Eng. Essex Region Conservation Authority Presented at Latornell Conservation Symposium November 18, 2015

2 Presentation Outline: What is an IDF Curve? Need for the Study Evolution of the Partnership IDF Study and Findings Climate Adaptation Strategies Next Steps

3 What is an IDF Curve? Intensity-Duration-Frequency Curve Used to design water management infrastructure Common applications Drainage works Storm sewers Stormwater management facilities Delineation of floodplains Characterization of flood risk Based on historic rainfall records

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5 Driving Forces Behind the Study: Essex Region experienced several extreme short duration rainfall events Flooding Municipalities receiving pressure to address flooding Projected trends were suggesting increased frequency of extreme events Reality of Climate Change needs to be considered 2014 PPS IDF curves are used extensively for design of water management structures Other regions were updating IDF curves as part of Climate Adaptation Strategies

6 Street Flooding

7 Street Flooding with Surcharged Sewer

8 Evolution of the Partnership: Part 1 Partnership with ERCA and Local Municipalities Individual Municipalities were considering IDF studies ERCA was aware of other IDF studies in Southern Ontario Need for consistent regional approach CA well suited to manage regional studies Based on watershed boundaries One study for entire region substantial cost savings Organized meetings with Municipal staff to encourage a regional approach 7 of 9 local Municipal partners financially supported study Reviewed other IDF studies and prepared requests for proposals Planned to move forward with a single approach to update the local IDF curves

9 Part 2 Partnership with ERCA, TRCA and OCC Additional review was undertaken by ERCA Many methods to choose from No guidelines or selection parameters Results between methods were not consistent No comprehensive comparison of methods ERCA attended an OCC meeting in Toronto IDF discussion TRCA had same concerns OCC Partnership was formed Partnership benefits additional partners/funding, cost savings, more in-depth study, shared knowledge/resources between CA s

10 IDF Study and Findings Researchers were selected: Dr. Paulin Coulibaly, McMaster University Dr. Donald Burn, University of Waterloo Study Objectives Review emerging techniques ( ) Identify the most robust techniques Apply selected methods for updating IDF curves in Essex and Toronto Region Compare results, document strengths, limitations, uncertainty Report on results with recommendations (if possible)

11 Study Approach (ref. Coulibaly, Burn et al., 2015)

12 Historic Rainfall Data Very difficult to obtain appropriate data Minimum 20 years of Data Annual maximum rainfall for different durations: 15 min, 30 min, 1 hr, 2 hr, 3 hr, 6 hr, 12 hr, 24 hr 15 Stations were selected (EC and NOAA (USA)) Data quality control ensure no anomalies/inconsistencies

13 (ref. Coulibaly, Burn et al., 2015)

14 Selection of Distribution Function (used to estimate the rainfall intensity for different return periods) Literature review Comparison of 7 distribution functions Evaluation using 11 goodness of fit criteria Selection of Climate Models Literature review Best performing models in North America 3 potential emission (GHG) scenarios

15 Selection of Downscaling Techniques (used to improve climate model data) Literature review 2 Methods selected Delta Change Approach Bias Correction Method Peer Review

16 Summary of IDF Projections (ref. Coulibaly, Burn et al., 2015)

17 (ref. Coulibaly, Burn et al., 2015)

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19 (ref. Coulibaly, Burn et al., 2015)

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21 Study Results There is significant variability among future IDF projections which reflects a high level of uncertainty Given the uncertainty in future IDF curves, caution should be exercised in the use of the results Some partners were concerned that they weren t getting a specific curve like other municipalities (singular approach) Variability was greater in the Windsor area compared to Toronto

22 Study Results The Gumbel distribution, which is used by many who develop IDF curves, was the poorest fit of all distributions considered in this study Generalized Extreme Value (GEV) distribution emerged as the best distribution for the study areas Further study is needed to better understand and refine uncertainties likely before major changes in infrastructure design standards in the study area Investigation of regional IDF development methods is recommended

23 Climate Adaptation Strategies 2014 PPS requires municipalities to address climate change Updated IDF Curves may form part of a Climate Adaptation Strategy Stormwater infrastructure is being reviewed for vulnerability Original IDF information Estimated 2090 IDF information Different percentile Some initial thoughts focused on increasing sewer sizes inlet capacity, moving problem downstream

24 Climate Adaptation Strategies Many things must be considered new vs. retrofit, major overland routes for the higher projections Need to changing the public perception - flooded roads, it s a municipal problem (many private servicing issues and opportunities to address flooding issues) Other Strategies being considered in the Essex Region Downspout disconnection, backwater valves, enhanced sewer inspections/maintenance, flow restrictors at road cwb s, seal manhole covers, storm/sanitary cross-connection, education, LID s (rain gardens, permeable pavements, infiltration systems, etc.)

25 Next Steps Further study is needed to better understand and refine the uncertainties involved in future IDF statistics The science is continuing to evolve. Continued updating of IDF curves is required The researches and end users must communicate Utilize opportunities such as FloodNet and OCC programs to assist with further research Climate adaptation requires multiple considerations Continue to build partnerships to pool knowledge and limited resources

26 Questions Reference: Coulibaly, P., Burn, D., Switzman, H., Henderson, J., Fausto, E., 2015, A Comparison of Future IDF Curves for Southern Ontario