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Welland River Floodplain Mapping - Round 2 Public Information Presentation

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June 2016 presentation to residents about technical aspects of floodplain mapping for the Welland River. Presentation prepared by MMM Group and WSP.

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Welland River Floodplain Mapping - Round 2 Public Information Presentation

  1. 1. WELLAND RIVER FLOODPLAIN MAPPING UPDATE Public Information Meeting June 2016 Diego Torres Silvestre ((CC BY 2.0) 1
  2. 2. Presentation Outline 2 • Project Vision • Project Overview • Consultation Summary • Where We Are Now • Technical Overview
  3. 3. Project Overview To successfully complete a Floodplain Mapping Update Study that is Connected, Accurate, Reliable, and founded on Empirical data and observations using state-of-the-art tools and methodologies. Project Vision Statement • This means that new floodline mapping will be in place for the Welland River. The new line may affect what you can do on your property. • The project will fully engage affected landowners. • Awareness, understanding and input are key principles of the consultation program. 3
  4. 4. Project Overview Study Area Limit - Lower Study Area Limit - MiddleStudy Area Limit - Upper 4
  5. 5. Project Overview Awareness Meetings (February 2016) occurred during the beginning of the study and focused on describing the project and listening to community ideas and concerns. Technical Understanding & Input Meetings (June 2016) are occurring now that some modeling work has been completed. Draft Floodline Maps (once policy work is ready) will be presented once the technical work is complete and the policies are drafted. Community input will be considered before NPCA Board makes a final decision. Public Input A series of Meetings open to the public, interested landowners and stakeholders are scheduled. 5
  6. 6. Consultation Summary Meeting #1: 131 Meeting #2: 104 Meeting #3: 63 Meeting #4: 109 Total Sign-In: 407 6
  7. 7. Consultation Summary The word cloud reflects themes expressed throughout the February consultations. The size of the words reflects the frequency and relative emphasis expressed during discussion and from the comment cards, as interpreted by the project team. It is not meant to include every issue raised but rather the key themes that need to be addressed as the project progresses. 7
  8. 8. Consultation Summary Mandate and Need to Update Floodline Mapping • NPCA’s legislative mandate as set out in Section 20 of the Conservation Authorities Act is to establish and undertake programs designed to further the conservation, restoration, development and management of natural resources. • In addition, under the Provincial Planning Act Conservation Authorities have been delegated the responsibility to reduce the potential for public cost or risk to Ontario’s residents from natural or human made hazards. Section 3.1 of the Provincial Policy Statement (2014) indicates that development shall be directed away from areas of natural or human-made hazards where there is an unacceptable risk to public health or safety or of property damage, and not create new or aggravate existing hazards. • As such, the Conservation Authorities require that Planning Act development applications identify areas of flood hazard and undertake development such that the risk to the public is mitigated. • NPCA Board agreed with Staff recommendation that the 30 year old floodline mapping be updated in an effort to ensure that the established line reflects the best available information, is up to date, and is technically defensible. • climate change • improved technology (e.g. greater resolution - Digital Elevation Models, more data). 8
  9. 9. Consultation Summary Flood Event Selection • In order to determine what risk of flood to protect against, a flood event must be selected and modeled. • 100-year flood event is the minimum standard. • This is also the flood event used to create the 1985 line. • Means that 1% chance of that flood happening in any given year OR if thinking of a typical home mortgage, there is a 22% chance of the 100- year flood event occurring during the term of the mortgage. 9
  10. 10. Consultation Summary Ontario Power Generation • OPG has a presence in the area and the Welland River plays a significant role in OPG operations. There is a strong perception that: • various structures and facilities affect the flow of water in and down the River • controls on water level and flow have a direct impact on the River’s ability to naturally accommodate flood events and as such the impact flood events have on property • operations contribute significantly to the level of sedimentation • The impact of current OPG operations will be taken into consideration when developing floodplain mapping for the Welland River. • While there has been public discussion about potential changes to OPG operations, this project must assume that OPG will continue to operate their facility in the same manner until OPG declares otherwise. 10
  11. 11. Consultation Summary Siphons • The Siphons are perceived to have a significant impact on the Rivers response to flood events. • The impact of the Old and New Siphons on the Welland River floodplain will be analyzed as part of this study. • It is noted that the NPCA is not responsible for clearing the Siphons however these concerns have been passed along to the City of Welland and the St. Lawrence Seaway Management Corporation. • It is unknown when the next clearing of the siphons will occur. 11
  12. 12. Where We Are Now • Technical work is advancing. • Some site visits have taken place. • Excellent input and discussion from the Watershed Floodplain Committee. • On track to complete the technical work and determine a recommended floodline. • The Committee recommended that the floodline NOT be finalized until the policy work is complete. NPCA Board agreed with this recommendation. 12
  13. 13. What this Presentation will Cover • An overview of the technical work • How the model is created • Local data input • Overland Flow • Stream Flow • Linkage to the Stream Flow Model Overland Flow (Runoff) A A Stream Flow (Elevation) B + = C Floodline Flood Line Normal Level B C Flood Level 13
  14. 14. Standard Industry Practice Update 1985 mapping using standard industry practice • Build a model using proven software • Add local data Volume of Water Welland River Risk Management 14
  15. 15. Floodplain Model for the Welland River Overland Flow (Runoff) A A Stream Flow (Elevation) B+ = C Floodline Flood Line Normal Level Standard industry practice, build model and input local data B C Flood Level 15
  16. 16. Floodplain Model for the Welland River How much rain falls onto the land 1 How much water sinks into the ground, how much evaporates, and how much runoff gets into the river 2 3 How much water flows down the river once it gets into the river We calculate volume in 3 steps 16 A
  17. 17. Floodplain Model for the Welland River Rain contributes to how much water falls on the land Soil conditions, slope and what land is used for determines how much sinks into the ground 17
  18. 18. Welland River at Church Road – 1957 to present Overland Flow (Rain – Land – Flow) Local data on relationship between rainfall and water level Month(s) # Flood Events on Record Jan – Mar 7 Apr – May 2 Nov - Dec 7 X 18 X
  19. 19. Overland Flow (Rain – Land – Flow) Example of rainfall at Church Road gauge shows valid connection between rainfall and increased flow in river Peak Flow Observed Flow Observed Rain 2006 3 days Discharge Precipitation / Runoff Response 19 P3P2P1
  20. 20. We know from analyzing SOILS MAPS that the infiltration rates are generally consistent across the watershed therefore we can predict, with high confidence, overland flows in areas without long-term data monitors. We also have good information on LAND USE by catchment area for each gauge station so we can adjust soils info for imperviousness due to development and still have a high confidence level that the volume of water getting to the river is accurate. We are CALIBRATING the model using the Church Road gauge and VERIFYING it at all other gauge locations (Wellandport, O’Reillys Bridge, Old Siphon, Material Dock, Oswego Creek, Big Forks Creek). Overland Flow (Rain – Land – Flow) 20
  21. 21. Overland Flow (Rain – Land – Flow) Watersheds draining to Church Road gauge: • West Wolf/Little Wolf/Wolf • Buckhorn • Elsie • Moores/Mill • Local Watershed Characteristics: • Surface Slope • Length of overland flow • Soils/land use Church Road Watersheds draining to Church Road 21
  22. 22. Overland Flow (Rain – Land – Flow) Church Road Gauge 22 Peak Flow Observed Flow Observed Rain 3 days Precipitation / Runoff Response
  23. 23. Overland Flow Links to Stream Flow We looked at cross sections of the river in different locations and at all bridges. This helps us understand the rivers capacity to handle the flood event. shape and condition of the river affects how water flows in the river once it gets there 23
  24. 24. Stream Flow – Mapping 24 B 300 400 500 167 168 169 170 171 172 173 174 175 176 177 Welland River Station (m) Elevation(m) Legend WS 100 Year Ground BankSta .055 .035 .055 100 200 300 166 167 168 169 170 171 172 173 174 175 176 Welland River Station (m) Elevation(m) Legend WS 100 Year Ground Ineff BankSta .055 .035 .055 BridgeTypical Cross Section Elevation(m) Elevation(m) Distance (m) Distance (m) Centre line of River Future Cross Sections Bridge O’Reilly’s Bridge Gauge
  25. 25. In order to determine what risk of flood to protect against we need to select a flood event. 100-year flood event is the minimum standard. Means that 1% chance of that flood happening in any given year OR if thinking of a typical home mortgage, there is a 22% chance of the 100-year flood event occurring during the term of the mortgage. Stream Flow – Flowing Water 25
  26. 26. Stream Flow – Flowing Water Simulated flood event flows used for 1985 mapping (m3/s): 1. Abingdon Road - 75 2. Church Road - 100 3. Brooks Bridge -115 4. Becketts Bridge - 205 5. O’Reillys Bridge - 245 6. Montrose Road - 275 Flood Event = 100 year event (1% chance of occurring each year) 26
  27. 27. Q Q2 Q1 As water moves down the river the flow increases. We have data on the history of flows in the river. The 100 year event was experienced at Church Road in 1959. 27 Stream Flow – Flowing Water
  28. 28. Flood line Flood level Normal level Looking downstream… Elevation(m) Flood Level and Floodline Flood level Normal level Flood level Normal level 28 C
  29. 29. Summary – Floodplain Model Overland Flow (Runoff) A A Stream Flow (Elevation) B+ = C Floodline Flood Line Normal Level B C Flood Level 29
  30. 30. Facilitated Q&A Diego Torres Silvestre ((CC BY 2.0)

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