Muskoka Floodplain Mapping Study + + February 18, 2020 Presented by Alfred Breland and Bethany Heppner

‒ Over 100 years of experience in ‒ Hatch offers a regional team with hydrology and flood hazards studies advanced technical capabilities and dedicated to the project a commitment to delivering a high- quality study. ‒ Core Team ‒ Alfred Breland, Senior Consultant/Manager ‒ Attendance at Annual Floodplain 35 years Mapping Knowledge Transfer ‒ Stu Bridgman, Project Sponsor Workshops held by MNRF and CA’s 45 years ‒ Mark Orton, Hydrology 45 years ‒ Greg Schellenberg, Hydrology 5 years ‒ Bethany Heppner, Hydraulics 5 years

‒Provide new baseline topographic data/maps ‒ Old data: 5 m contour mapping based on photogrammetry ‒ New data: 1m Bare Earth DEM based on LiDAR survey (0.5 m contours) ‒Provide updated and new flood plain mapping for Muskoka River Watershed ‒ Concentrating on Urban and High Risk areas ‒ Major Lake Chains

‒ Lake Chains ‒ Lake Vernon - Peninsula - Fairy Lake ‒ Lake Joseph – Rosseau – Muskoka ‒ Spence Lake ‒ Port Severn shores of Georgian Bay ‒ Populated areas ‒ Huntsville, Bracebridge, Bala, Port Carling ‒ At risk River Sections ‒ Big East, Purbrook, Springdale

Copyright © Hatch 2020. All Rights Reserved. History of the Muskoka River Watershed Flood Risk Management ‒Extensive development ‒Flood Damage of area in the last 100 Reduction Program years ‒ Original Mapping ‒ Population 60,599 ‒ 1980s and 1990s (2016 Census) ‒ Deterministic ‒ 74 million annual Hydrology Models tourist visits ‒ 100-Year Annual Exceedance Probability

‒2013 ‒2019 ‒ Flood of record on the ‒ Flood of record in Big East River majority of Muskoka ‒ Motivation of this study basin ‒ First major flood after ‒ Required update of decades minimal hydrology study flooding ‒ Third major flood in 6 years

Rainfall Depth Snow-Water Equivalent Depth 02EB013 - Big East 02EB004 - North Branch 02EB008 - South Branch 02EB006 - Muskoka R. below Bala

200 0 180 20 160 40 140 60 120 80 100 100 80 120 Flow Flow (cms) 60 140

40 160 Precipitation Depth (mm) 20 180 0 200

Date

April 2013 Precipitation Event April 2019 Precipitation Event

Total P - Beatrice Climate Total P - Muskoka Total P - Beatrice Climate Total P - Muskoka Total P - Algonquin E. Snow on Ground - Beatrice Climate Total P - Algonquin E. Snow on Ground - Beatrice Climate Snow on Ground - Muskoka A Snow on Ground - Algonquin E. Snow on Ground - Algonquin E. Temp. - Beatrice Climate Temp. - Beatrice Climate 80 30 80 30

70 70 20 20 C) 60 ° 60 10 10 50 50

40 0 40 0

30 30 -10 -10 20 20 Mean Daily Temperature (°C) Temperature Daily Mean -20 ( Temperature Daily Mean -20

10 Total Precip (mm)or Snow Ground on (cm) 10 Total Precip (mm) or Snow on Ground (cm) Ground on Snow or (mm) Precip Total 0 -30 0 -30

Copyright © Hatch 2020. All Rights Reserved. Return Period (years) -2.500 -2.000 -1.500 -1.000 -0.500 0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500 2 5 10 100 1,000 Flood Frequency Analysis 1,000 Statistical Distribution Annual Max. Daily Q (1916-2019) 95% Confidence [CELLRA Interval NGE][CELLRA ‒Port Sydney (02EB004) has [CELLRA NGE] over 100 years of record NGE] /s) ‒2019 event exceeds 3 100 [CELLRA estimate for 100-Year AEP NGE] Streamflow(m ‒Flood of Record supersedes other events if larger

3 Gauge Recorded Peaks (m /s) 1:100-yr AEP 95% Confidence Number Gauge Name 2013 Flood 2019 Flood Estimate (m 3/s) Range (m 3/s) Big East River near 02EB013 230 168 220 168 –271 Huntsville 02EB004 North Branch Muskoka 201 234 214 191 –237 River at Port Sydney 02EB008 South Branch Muskoka 139 167 147 128 –165 River at Baysville Muskoka River below 02EB006 390 435 417 372 –461 Bala

Copyright © Hatch 2020. All Rights Reserved. Climate Change in the Muskoka River Watershed “While it is not yet possible to precisely define future climates, the growing expertise in climate science makes it possible to set out plausible and likely climatic conditions for future periods, given specific assumptions about how the global economy grows and its pattern of energy use changes. We have used data generated by the Intergovernmental Panel on Climate Change (IPCC CMIP5 Project) to extract information on the midcentury values for temperature and precipitation in Muskoka that are expected if the world follows each of two plausible scenarios for economic growth and greenhouse gas emissions reductions. We have compared these data with equivalent measurements of temperature and precipitation in our current climate. While there will still be warm years and cold ones, wet ones and dry ones, the typical year at mid-century is likely to be 3-4ºC warmer each month than at present, and about 10% wetter . The midcentury projections for Muskoka reveal about a 10% increase in the total amount of precipitation in a typical year. Nearly all of this increase is likely to occur in late fall to early spring (November through April) for a 17% increase in the total for those 6 months (524 mm compared to 446 mm at present).”

“Planning for Climate Change in Muskoka” (Muskoka Watershed Council)

Winter Snow Pack

Average April Temperatures

Maximum Daily April Rainfall

Big East River Gauge (02EB013)

Projected Projected Peak Model Inflow Location ‒Prorated by drainage % Increase Inflow (m 3/s) Williams Port 20 276 Big East Upper* area at the location of Little East River 20 44 Big East at HWY 11 20 324 Big East Lower* the river model Local Inflow 20 12

Huntsville Narrows Lake Vernon Outlet 18 355

‒Projected increase due Baysville Baysville Dam 15 192 to climate change Purbrook* Purbrook Bridge 15 214 Springdale Duck Chutes 15 286

Bracebridge Dam 15 306 Bracebridge South Falls Dam 15 231

Port Carling Port Carling Dam 10 76

Bala Bala Dam 10 479

* Modelled using hydrographs from prorated flood of record hydrographs

Static Lake Level for Flood Mapping Lake ‒Review of existing (m) MNRF regulatory levels Vernon Lake 286.68 Peninsula Lake 285.29 ‒Lake Muskoka peak Fairy Lake 285.29 Mary Lake - Port Sydney 281.74 flood level projected to Spence Lake 269.40 (1) Lake Joseph 226.70

increase due to climate Lake Rosseau 226.70 change Muskoka Lake 226.70 (2) Bala Bay 226.30

Georgian Bay at Port Severn 178.00 m GSC (3)

(1) FDR-143 calculated flood level Hanna Chute Forebay (2) ARSP model calculated flood level Lake Muskoka (3) Great Lakes – St. Lawrence River System and Large Inland Lakes Technical Guides (MNRF, 1997)

‒Airborne Imaging, May 2018 ‒1508 km 2 in the Muskoka region ‒2.5 pts/m 2 in Low Density of Population ‒10 pts/m 2 in High Density of Population ‒1m DEM Full Feature, Bare- Earth and Hydroflattened

‒ Sonar data points at hydraulically significant cross sections ‒ Collected between August - September 2018 ‒ Postprocessed in SMS ‒ Merged with the overbank LiDAR ‒ Seamless cross section in HEC-RAS

Upper Big East Flood Hydrographs

Big East River at Williams Port Little East River 300

250 Start End

200 ³/s)

150

Discharge Discharge (m 100

0 -20 -15 -10 -5 0 5 10 15 20 Days Since Peak

Potential Water Level Increase River Reach Due to Climate Change (cm)

Big East Upper 33

Big East Lower 34

Huntsville Narrows 20

Baysville 31

Purbrook 16

Springdale 27

North Branch 26 Bracebridge South Branch 33

Port Carling 2

Bala Reach 19

‒ Lake Maps contain Static ‒ Site specific or local area Floodline studies are required for ‒ Wind setup and waves each section of lake shore drive water further ‒ New allowances based on onshore actual fetch lengths ‒ Vertical and horizontal ‒ Taking into account allowances are required for shoreline characteristics defining hazardous lands ‒ The Technical Guide for Large Inland Lakes (MNR 1996) provides guidance

‒LiDAR Survey Data ‒Floodplain Maps ‒ 1508 km 2 ‒ 1:2 500 Scale ‒ Classified Point Cloud ‒ Lake Shore ‒ 1m Grid DEM ‒ 1061 km Shore Line ‒ 0.5m Contours ‒ 212 km 2 Lake Shore Area ‒ River Bank ‒Technical Report ‒ 65 km Length of River ‒ 39 km 2 River Bank Area

‒ Lake Maps ‒ Map Set A: Lake Vernon ‒ Map Set B: Peninsula Lake ‒ Map Set C: Fairy Lake ‒ Map Set D: Mary Lake ‒ Map Set E: Lake Joseph ‒ Map Set F: Lake Roseau ‒ Map Set G: Lake Muskoka ‒ Map Set H: Bala Bay ‒ Map Set I: Port Severn ‒ Map Set J: Spence Lake ‒ River Maps ‒ Map Set K: Big East River ‒ Map Set L: Huntsville Narrows ‒ Map Set M: South Branch of the Muskoka River at Baysville ‒ Map Set N: South Branch of the Muskoka River at Purbrook ‒ Map Set O: North Branch of the Muskoka River at Springdale ‒ Map Set P: Muskoka River at Bracebridge ‒ Map Set Q: Indian River at Port Carling ‒ Map Set R: Bala Reach of the Muskoka River.

Policies and Planning Education ‒ All levels of government may use ‒ Education and understanding of this data to consider their the nature of floods within the approaches to basin would help all levels of ‒ Official Plans government and the public gain ‒ Zoning By-laws further knowledge on why flooding occurs and inform ‒ Building regulations everyone of what areas are at risk ‒ Emergency planning during flood events. ‒ Infrastructure ‒ Events similar 2013 and 2019 will occur again

Water Management Flood Forecasting ‒ Dams do not provide any flood ‒ Climate Monitoring control ‒ Climate Stations ‒ Storage too small to contain ‒ Flow Gauges flood volumes ‒ Radar Sensing (snow depth tracking)