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

1. WELLAND RIVER
FLOODPLAIN
MAPPING UPDATE
Public Information Meeting
June 2016
Diego Torres Silvestre ((CC BY 2.0)
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2. Presentation Outline
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• Project Vision
• Project Overview
• Consultation Summary
• Where We Are Now
• Technical Overview

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.
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4. Project Overview
Study Area Limit - Lower
Study Area Limit - MiddleStudy Area Limit - Upper
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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.
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6. Consultation Summary
Meeting #1: 131
Meeting #2: 104
Meeting #3: 63
Meeting #4: 109
Total Sign-In: 407
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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.
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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).
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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.
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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.
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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.
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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.
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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
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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
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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
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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
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A

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
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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
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X

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
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P3P2P1

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)
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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
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22. Overland Flow (Rain – Land – Flow)
Church Road Gauge
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Peak Flow
Observed
Flow
Observed
Rain
3 days
Precipitation / Runoff Response

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
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24. Stream Flow – Mapping
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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. 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
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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)
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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.
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Stream Flow – Flowing Water

28. Flood line
Flood level
Normal level
Looking downstream…
Elevation(m)
Flood Level and Floodline
Flood level
Normal level
Flood level
Normal level
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C

29. Summary – Floodplain Model
Overland Flow
(Runoff)
A
A Stream Flow
(Elevation)
B+ = C Floodline
Flood Line
Normal Level
B C
Flood
Level
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30. Facilitated Q&A
Diego Torres Silvestre ((CC BY 2.0)