Effect of Climate Change on Sewer Overflows in Milwaukee

1. WEFTEC 2012 Effect of Climate Change on Sewer Overflows in Milwaukee October 2012 Bridging the gap between climate change research and the risk of overflows from my collection system David Perry Brown and Caldwell, Milwaukee, Wisconsin

2. Presenter David Perry Brown and Caldwell, Milwaukee, Wisconsin Co-Authors • David Bennett, Brown and Caldwell • Urbain Boudjou, Tim Bate, and Karen Sands, • Milwaukee Metropolitan Sewerage District • Michael Hahn, Southeast Wisconsin Regional Planning Commission • Sandra McLellan and Elizabeth Sauer, • Great Lakes WATER Institute, University of Wisconsin, Milwaukee

3. Climate change research is producing a wealth of models and projections on global climate change …What does that mean to my organization in our local context? What is the possible risk of overflows in the future? Will our long range facilities plans be ruined by climate change?

4. Outline • Milwaukee – our context • Regional Climate Change Trends • Downscaling: from Regional to Local • Milwaukee Modeling System • Findings

5. Milwaukee – our context Some background to the key questions

6. Milwaukee • Three rivers meet Lake Michigan • 850 square miles drain to Milwaukee Harbor • Pollution Sources: • Urban runoff • Agricultural runoff • SSOs • CSOs Great Lakes - 20% of Earth’s freshwater Drinking water source for 40M 500 beaches

7. Milwaukee Metropolitan Sewerage District • Serves Milwaukee and 27 metropolitan communities • 1 million people • 5% Combined Sewers, 95% Separated Sewer • Two large water reclamation facilities • Total treatment capacity 690 MGD • Deep Tunnel Storage – 427 MG • CSO and SSO control • Real Time Control • Optimize use of treatment and storage

8. 2020 Facilities Plan Regional Water Quality Management Plan • Innovative watershed-scale approach – Collaborative, Integrated • Wastewater system + water course system • Improve water quality in regional streams/rivers and Lake Michigan. • Facilities plan + Regional water quality management plan • Completed in 2007 • Did not account for climate change.

9. 2020 Facilities Plan Regional Water Quality Plan Will the plan work if climate changes? Can we meet goals for SSO and CSO control?

10. Regional Climate Trends A few observations

11. How will our climate change? Large events may become larger and more frequent Smaller events may become less frequent Total annual rainfall may be similar to existing – but the distribution of rainfall may vary http://www.wicci.wisc.edu/climate-change.php

12. Probability of Snow vs. Rain Late 20thc (1950-1999) Late 21st c (2080-2099) IPCC Scenario A2 Only a 1-month snow season in Milwaukee later this century? Courtesy of Dan Vimont

13. Climate models and uncertainty • Global Climate Models (GCM) • 14 models • Wide range in predicted results Strategy: Use two GCM models that represent the best and worse case scenario for our most sensitive season for generation of CSOs: SPRING RAINFALL

14. Downscaling to Local How to convert regional model results to local data

15. Climate Downscaling UW-Madison Center for Climate Research • Approaches • Statistical downscaling (GCM) • Dynamic downscaling (regional climate models) • Statistically downscaled precipitation and air temperature time series • Projected mid-century climate change conditions • Parent data: Milwaukee airport observed data for the 1940 through mid-2004 period. Local 8 km x 8 km Grid cells GCM Grid Cells

16. Milwaukee Modeling System How do we link climate projections to overflow estimates?

17. Modeling Methods used by MMSD Rainfall and Meteorological Data Regional Hydrologic Model HSPF Continuous runoff and infiltration simulation (used for both wastewater and stormwater/watercourse modeling) Wastewater Flow Generation Model Flow Forecasting System (FFS) Calibrated wastewater hydrographs Simplified Wastewater Flow Generation and Hydraulic Model MACRO System-wide water balance simulation of flow and volume Wastewater Hydraulic Model MikeUrban Detailed simulation of level and flow in all pipes and facilities

18. Modeling Methods used by MMSD Rainfall and Meteorological Data Strong Hydrologic Foundation Regional Hydrologic Model HSPF Continuous runoff and infiltration simulation (used for both wastewater and stormwater/watercourse modeling) Decades of history rapidly simulated to predict SSOs and CSOs Wastewater Flow Generation Model Flow Forecasting System (FFS) Calibrated wastewater hydrographs Simplified Wastewater Flow Generation and Hydraulic Model MACRO System-wide water balance simulation of flow and volume Wastewater Hydraulic Model MikeUrban Detailed simulation of level and flow in all pipes and facilities

19. Findings Will the plan work?

20. Simulation Cases Population and Land Use Condition Facilities Represented in the Model Climate Scenario Case 1: 2010 Existing Facilities + Historic Climate Case 2: Recommended Facilities + Historic Climate Case 3: Recommended Facilities + DSN10% Case 4: Recommended Facilities + DSN90% Baseline 2020 Facilities Plan All cases used Projected Future 2020 Population and Land Use Moderate climate change More extreme climate change

21. Simulated SSO Volume in Each Year 64 year simulation

22. Simulated SSO Volume in Each Year 64 year simulation

23. Simulated SSO Volume in Each Year 64 year simulation

24. Simulated CSO Volume in Each Year 64 year simulation

25. Simulated CSO Volume in Each Year 64 year simulation

26. Simulated CSO Volume in Each Year 64 year simulation

27. Average Annual Simulation Results

28. Summary on climate change • Large events may be larger and more frequent • Small events may be less frequent • The annual average rainfall may have a similar average amount • Increasing spring rainfall is a characteristic of most GCM results • Spring is also the time of greater CSO risk • Increasing temperature may reduce the likelihood of snowmelt events

29. Conclusions – for Milwaukee MSD • Recommended Facilities in the 2020 Plan are designed to reduce overflows (especially SSOs) • Year-to-year variability in overflows is large • For both the existing climate and projected climate scenarios • Climate change may increase CSOs • Up to 20% more average annual CSO volume in the extreme climate scenario • But annual SSO volume may not change significantly • The objectives of the 2020 Plan are not significantly compromised in the climate change scenarios • Additional facilities could be constructed to mitigate the changes

30. Conclusions – in general • Build a team • Climate researchers • Hydrologic and hydraulic modelers • Wastewater system planners and managers • Water quality scientist • Evaluation of climate change on overflows requires: • Downscale GCM to local - statistically modify historic weather • Model with strong hydrologic foundation • Simulate long term response to climate scenarios • Keep hydraulic model simple

31. Let’s talk about it … I welcome your comments and questions Presenter David Perry Brown and Caldwell, Milwaukee, Wisconsin Co-Authors • David Bennett, Brown and Caldwell • Urbain Boudjou, Tim Bate, and Karen Sands, • Milwaukee Metropolitan Sewerage District • Michael Hahn, Southeast Wisconsin Regional Planning Commission • Sandra McLellan and Elizabeth Sauer, • Great Lakes WATER Institute, University of Wisconsin, Milwaukee