ENG 014-2015 Fraser River Bank Erosion - update

aS 1~A
COUNCIL REPORT
ABBOTSFORD
Report No. ENG 14-2015
COMMITEE OF THE WHOLE
Date: March 9, 2015
File No:5225-30
To:
From :
Subject:
Mayor and Counci l
Rob Isaac, Director, Wastewater and Drainage
Fraser River Bank Erosion - Update
RECOMMENDATION
THAT Report No. ENG 14-2015, dated March 9, 2015, from the Director, Wastewater and
Drainage regarding Fraser River Bank Erosion - Update, be received for information.
SUMMARY OF THE ISSUE
In July 2014, the City engaged the services of Northwest Hydraulics Consultants (NHC) to
undertake the Fraser River bank erosion study. The intent of the study is to assess the causes
of the Fraser River bank erosion and the risk posed to the Matsqui dyke, to prioritize locations
where future erosion mitigation work may be required and to recommend the most feasible
solutions. A key finding of the study is that much of the south bank of the Fraser River, between
Sumas Mountain and the tip of Matsqui Prairie, is unstable and other erosion arcs could develop
and potentially undermine the dyke in the near future. This report provides an update regarding
the proposed mitigation options and costs.
BACKGROUND
Five erosion arcs have formed along the south bank of the Fraser River, between the northerly
tip of Matsqui Prairie and Sumas Mountain, since 1997. The latest Beharrell Road erosion arc
appeared unexpectedly after the 2013 freshet and was only 30 m away from the Matsqui dyke.
The repair work was completed by March 31,2014 and cost $2.8M, of which $1.2M was funded
from a previous Flood Protection Program funding and $250K from a Provincial grant.
To understand the causes of the erosion issues and identify mitigation options, Council
approved a budget of $180,000 (Attachment A) in July 2014 and the City engaged the services
of Northwest Hydraulics Consultants (NHC) to undertake the Fraser River erosion study.
DISCUSSION
The intent of the study is to assess the causes of the Fraser River bank erosion and the risk
posed to the Matsqui dyke, to prioritize locations where future erosion mitigation work may be
required and to recommend the most feasible solutions. Details of the tasks of the study are
included in Attachment B.
The Province has been involved with reviewing of the work plan of the study, and providing
guidance throughout the study. In addition, other potential stakeholders in the vicinity such as
Mission, Chilliwack, Fraser Valley Regional District, Metro Vancouver, and the Fraser Basin
Report No. ENG 014 -2015
Page 2 of 4
Council were kept informed of the study progress and provided inputs during progress webinars.
The study is approximately 90% complete.
A key finding of the study is that much of the south bank of the Fraser River, between Sumas
Mountain and the tip of Matsqui Prairie, is unstable. Large sections of underwater bank are
over-steepened and near point of failure (slopes steeper than 1.7H:1V). In addition, only a
fraction of the bank shows good riprap condition. The unstable bank is evident with the
unexpected appearance of the Beharrell Road erosion arc immediately after a normal freshet in
2013 (1:5 years event), which was not present in 2012. Other erosion arcs could develop and
potentially undermine the dyke in the near future.
Other findings of the study include:
SUbstantial morphological changes occurred in the Matsqui reach particularly during the
period 1984 to 1999. These include deposition (up to 8m) along the north side of the river
and general bed lowering (up to 6.5m) along the south bank. This created a well-defined
trench along the south bank. These changes were slowed down after 1999, with little
systematic bed lowering along bank between 2005 and 2014;
Risk assessment identified some areas with high bank failure risk overlapping with minimum
dyke setback (less than 80m). These are identified as areas of highest priority that require
mitigation to protect the dyke (Attachment C).
The proposed mitigation options and costs are summarized in the table (Attachment D):
Option
A
B
C
D
E
Note:
Description of Option
Upgrade existing bank protection with continuous
rock armouring
Upgrade existing bank protection with rock spurs
Dredge north side of river
Rock protection of arcs when they form to ensure
the dyke is not directly attacked
Relocation of the dyke
Costs
$6M to $20M
$4M
$6M to $10M
(every 2 years)
$2M
(Refer to Attachment D)
See note below
These costs are Class D estimates and are rounded off to the nearest $2M. Updated costs may
be provided at the Council meeting on March 23, 2015. Option E is currently being reviewed and
will be available on March 23, 2015.
NHC recommends addressing high priority areas with long term solution, i.e. Option A or Band
monitoring lower priority areas and potentially addressing with Options A, B or D.
It was discussed that Option C is a temporary measure and will not stabilize the failing banks. It
would only result in a small impact to the south bank and would be required once every two
years to be effective.
Option E - relocation of the dyke is being evaluated and would require the design and
construction of the dyke to meet the current seismic standards. It is anticipated that the costs
would be significantly higher than any of the other options; however, since it has the least
environmental and fisheries impact, this option was recommended by the Province to be
included in the review.
Page 3 of 4
Report No. ENG 014 -2015
8ased on the cost estimates shown in the above table and the effectiveness of the proposed
options, the preferred option is Option 8 - upgrade existing bank protection with rock spurs,
along the entire project reach.
Once the study is complete, the recommended next step is to prepare a proposal to senior
governments for funding to correct the Fraser River bank erosion issue. The proposal would
include potential solutions and comparisons to potential flood damages to Abbotsford.
Note: Fraser 8asin Council is undertaking the Lower Mainland Flood Management Strategy Phase 1 work. While the erosion issues in Abbotsford are identified in the current phase, the
objective to advance infrastructure flood protection projects and funding is currently identified in
Phase 2 of the work. Their projected timeline to complete the whole strategy is 2019 and would
likely include other priorities outside Abbotsford.
FINANCIAL PLAN IMPLICATION
There is no impact to the financial plan at this stage.
Date reviewed and approved by the Chief Financial Officer; March 8, 2015
IMPACTS ON COUNCIL POLICIES, STRATEGIC PLAN ANDIOR COUNCIL DIRECTION
Understanding the causes of the erosion issue and identifying mitigation solutions is a prudent
step to solve the Fraser River bank erosion problem. It aligns with Strategic Objective #1 continue improving our financial outlook.
SUBSTANTIATION OF RECOMMENDATION
In July 2014, the City engaged the services of Northwest Hydraulics Consultants to undertake
the Fraser River bank erosion study. The intent of the study is to assess the causes of the bank
erosion on the Fraser River and the risk posed to the Matsqui dyke, to prioritize locations where
future erosion mitigation work may be required and to recommend the most feasible solutions. A
key finding of the study is that much of the south bank of the Fraser River, between Sumas
Mountain and the tip of Matsqui Prairie, is unstable and other erosion arcs could develop and
potentially undermine the dyke in the near future. The proposed mitigation options and costs are
summarized in this report.
g.L.
Rob Is c,
Oirec r, Wastewater and Drainage
Jim Gor on, P.Eng.
General Manager, Engineering and Regional
Utilities
ATTACHMENTS
Attachment "A":
Attachment "8":
Attachment "C":
Attachment "0":
SC:sj
Report No. ENG 47-2014
Fraser River bank erosion study and stabilization concepts - scope
Areas of highest priority that require mitigation
Proposed mitigation options
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COUNCIL REPORT
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ABBOTSFORD
Report No. ENG 47-2014
Attachment A
Executive Committee
June 26,2014
File No:
5225-30
To:
From:
Subject:
Mayor and Council
Stella Chiu, Senior Drainage and Wastewater Engineer
Fraser River Bank Erosion
RECOMMENDATION
THAT a budget amendment be made in the 2014 Budget to fund the proposed Fraser
River Bank Erosion Study, in the amount of $180,000, from General Capital Reserves.
SUMMARY OF THE ISSUE
The Beharrell Road Erosion Arc was successfully repaired before the 2014 freshet.
However, a long-term solution is prudent to solve the Fraser River erosion issues. Based
on past engineering studies, new erosion arcs are expected to form along the south
bank until the sources that cause the change of flow in the river are understood and
problems mitigated. This report discusses the recommended next steps.
BACKGROUND
Five erosion arcs have formed along the south bank of the Fraser River, between the
northerly tip of Matsqui Prairie and Sumas Mountain, since 1997. The latest Beharrell
Road Erosion Arc appeared unexpectedly after the 2013 freshet and is only 30m away
from the Matsqui Dyke. This is the highest priority site of the five arcs because of its
proximity to the dyke. The repair work was substantially completed on March 31, 2014
and cost $2.8M, of which $1 .2M was funded from a previous Flood Protection Program
funding and $250K from a Provincial grant. Attachment A includes pictures of the
Erosion Arc.
The river flow is changing direction, causing scouring and deepening at the base of the
bank. Based on past engineering studies, new erosion arcs are expected to form along
the south bank until the sources that cause the change of flow in the river are
understood and problems mitigated.
DISCUSSION
On December 5, 2013, a statement was provided by the Ministry of Forests, Lands and
Natural Resource Operations (MFLNRO) to support repairing of the Beharrell Road
Erosion Arc before the 2014 Fraser River Freshet (Attachment B). In the same
document, it was stated that:
The longer term solution has to include completing requisite river modelling studies
upstream and downstream of this location to identify the source of the problem, review
mitigation options and implementation of mitigation works.
Page 2 of2
Report No. ENG 47-2014
To understand the causes of the problem and identify the mitigation solutions, staff were
in discussion with a consultant and the Province regarding a work plan of an Erosion
Study ("Study") for the Fraser River.
The intent of the Study is to assess the causes of bank erosion on the Fraser River and
the risk posed to Abbotsford's dyke. As well as prioritize locations where future erosion
mitigation work may be required, define mitigation options and provide recommendations
on the most feasible solution. The cost of the study is estimated $171,000 (excluding
tax) .
It is recommended that a budget of $180,000 be approved, based on the following:
Estimated cost of Study
GST (5%) of $171 000
, Tota[ (Rounded)
$171,000 /
$ 8.550/
$180,000 I
/
I
FINANCIAL PLAN IMPLICATION
There is no current budget established for the Fraser River Bank Erosion Study. It is
recommended that a budget amendment be made to the 2014 Budget to fund the
proposed Fraser River Bank Erosion Study, in the amount of $180,000, from General
Capital Reserves.
~e~d ana approved by the:
Chief Financia[ Officer
IMPACTS ON
DIRECTION
COUNCIL
POLICIES,
STRATEGIC
PLAN
ANDIOR
COUNCIL
Understanding the causes of the erosion issue and identifying mitigation solutions is a
prudent step to solve the Fraser River Bank Erosion problem. It aligns with Strategic
Objective #1 - Continue Improving our Financial Outlook.
SUBSTANTIATION OF RECOMMENDATION
The Beharrell Road Erosion Arc was successfully repaired before the 2014 freshet.
However, a long-term solution is prudent to solve the Fraser River erosion issues. A
hydraulic study is necessary to understand the causes of the Fraser River bank erosion
problem and identify mitigation solutions. [t is recommended a budget amendment be
made in the 2014 Budget to fund the proposed Fraser River Bank Erosion Study, in the
amo~,~ oo, from General Capital Reserves. ~ ~
c~J.
Stella
Senior Drainage and Wastewater Engineer
Jim Gordo , P.Eng.
General anager, Engineering and Regional
Uti/tiies
Attachment "A": Beharrell Road Erosion Arc Pictures
Attachment "B": Statement from MFLNRO on December 5,2013
ENG 47-2014 - Attachment A
Beharrell Road Erosion Arc Repair
ENG 47-2014 - Attachment A
Beharrell Road Erosion Arc Repair
ENG 47-2014 - Attachment A
Beharrell Road Erosion Arc Repair
ENG 47-2014 Attachment B
Stella Chiu
From:
Sent:
To:
Cc:
Subject:
Flint-Petersen, Lotte FLNR:EX <[email protected]>
Thursday, December 05, 201312:13 PM
Stella Chiu
Rob Isaac
Statement on Erosion Arc
Follow Up Flag:
Flag Status:
Follow up
Flagged
Hi Stella,
Further to your request for a statement on the threat posed by the recent erosion are, in relation to the Matsqui
Dike, I offer the following:
We are aware that a new erosion arc has formed in the Matsqui Prairie in Abbotsford after the 2013 Fraser
River freshet. This new arc is only some 30 metres away from the Matsqui Dike. It appears that the thalweg is
continuing to concentrate along the left bank of the Fraser River (confirmed again by recent 2012 and 2013
bathymetry surveys). The cause of this thalweg concentration is likely a result of the deflection of flows along
the left bank in part due to the growing gravel bars upstream (NHC Matsqui Trail Regional Park, Fraser River
bank Erosion, Site Inspection Memo . September 4, 2013).
This new erosion arc is of pressing concern due to both the proximity of the arc to the Matsqui Dike as well as
the limited time available for repair works before the next freshet. This arc likely started to form underwater as
a result of the high freshet flows and water levels in 2012 but first became evident above water after the 2013
freshet. Given the proximity of this erosion arc to the Matsqui Dike, as well as its rapid rate of erosion
progression towards the water side toe of the dike, if left unrepaired it poses a significant threat to public safety
as it could undermine the dike protecting Matsqui Prairie. This is a high priority site and should be protected
prior to the 2014 freshet.
The longer term solution has to include completing requisite river modelling studies upstream and downstream
of this location to identify the source of the problem, review mitigation options, and implementation of mitigation
works. In the meantime, it is my opinion, that this new erosion arc must be repaired before the 2014 Fraser
River freshet.
Lotte Flint-Petersen M.Eng., MBA., P.Eng
Acting Section Head for Flood and Groundwater
Senior Flood Hazard Management Engineer
Ministry of Forests, Lands and Natural Resource Operations
Suite 200 - 10428 153 rd Street
Surrey, Be
V3R IEl
Phone: (604) 586-3721
Lotte. Flint [email protected]
http:Uwww.env.gov.bc.ca/wsd/publicsafety/flood/fhm-2012/safetyindex.html
Water for Be Safe, Sustainable and Valued by all.
ENG 14-2015
Attachment B
Fraser River bank erosion study and stabilization concepts - scope:
2
Tasks
Site Inspection after
Freshet
Geomorphic Assessment
3
Geotechnical Assessment
4
Hydraulic Assessment
5
Risk Analysis
6
7
Mitigation Plan
Final Report
Project Management
1
8
Description
Assessment of post-freshet bed level changes in areas
where deep local scour was identified
Survey and velocity data will be utilized and compared with
previous hydrographic surveys from 1984,1990,1999,2008 to
understand and forecast future changes
Slope stability analyses will be conducted to provide insight
on when these issues may be triggered by lowered bed
levels along the toe of the slope
A river model will be run to illustrate how the changing river
topography has affected flow patterns and velocities along
the south bank, and assess future scour levels
Identify high risk locations along the bank and to support
long-term planning and future mitigation measures
Develop options to mitigate future erosion threats to the dyke
Report summarizing findings and recommendations
Meetings, webinars, presentations
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Current Alternatives (2015)
Alternative
Description of Alternatives
Comments
Current Alternatives (NHC 2014/2015)
Upgrade existing bank protection with continuous
A
revetment (or in high priority sections first)
Re-establish 1V:2H bank slope
B
Upgrade existing bank protection using spurs
30 m long by 180 m spacing
C
Dredge north side of river
Evaluated dredging Matsqui Bar and Channel Widening along Sumas Bar and Matsqui Bar
Limit expansion of scallops when they form to ensure
D
dike is not directly attacked
Notes:
Dredging and riparian buffer could be combined with A, Band D
Miti gati on measures could be implemented in phases by focusing first on the areas with higher risk.
I
** Concept to rebuild dike currently being considered for further evaluation.
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High priority areas should be addressed with long term solution (Alt A or B).
Lower priority areas should be monitored and potentially addressed with Alternatives
A, B, or D.
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