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 '~A OS COUNCIL REPORT =E:-:-:N=G--:1~4-::2-=-0-=-=15:::--"1 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 (/) C'a ~ c. Q) 'u Q) (/) ::l ~ o(/) E ... Q) -; 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. nhc I '<: 1iI:~ii:t~J water resource specialists I Ln · . N 0- UJ ; ~ 0- cll ~ I I I f- I II U( 0- I I I ! I II I I I !± }t( E ".. I ! 0 (l() 0 r-. ! 0 I.D f-- -~. ~ 0- 0:: 0:: 0- UJ .... >- 0- l- i o ! --- I i V vf;r ~l - I--- I .-t o I 11' - IkV 1 'I ~ ~I ·~Wrl - a !- 1- 1 (w) NOll\f/\313 I I ciiE z r ~ I I! t- 1'" : I+- @ " o .-----;~----r----,'~--;!---=E,...,.I--r---, ~ I .. I"'+----+- V I J 1 - I -+H _- "" .§ 1 c.. - I-I----i---j-/ ""- w N ~ ....o N o M o 1~~-4·~~4-~~~~1 ~ __ - I ~~ II-Y-JbW I)f' ~ ,~VI Nt_:~~ f (w) N011V'1\313 o o o In ~ (w) ~NIHUION Alternative C - Dredging Options ---------- Sumas Bar 15 10 I 11 _ -o 5 .s (!) 0 i!= -5 en _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ -SOOyrwaterl8V81 020 yrwaterlevel yrwater level tl. W C -10 -_ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - __ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - __ - - - - - - - - - - - - - - black line· existing conditions red line· widening option __ I -15 ~- ----------- ---------------------------------------- ------------------------------------------------------------------- ------------- ------ -20 0 H to V ratio 1()0 200 ' 300 400 500 ' 600" 700 DISTANCE FROM SOUTH BANK (m) aoo 900 ' = 0.1 10'00 Matsqui Bar 15 r l- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- -- - - - - - - - - - - - - - - - - - - - - - - , __ 1: r m--n--------n-n---mm--m--------n---m----nnnmm-----m--m_m _____ : :~~~:::::: o en C) 0 ..§. i!= -5 c -10 a.. w 0-- black line· existing conditions ~- -- ----------------- - -------- ----- -- --- --- - ------------------- - ---- --- !-~~- ~~':'~ --- ~-~!~~~- ~~!- !~~~~~I_ ~I?~!~':'- - -15 H to V ratio -20 0 100 200 300 400 500 600 700 aoo 900 =0.1 10'00 DISTANCE FROM SOUTH BANK (m) nhc I. '<:: lir:~ii:t:~J~ water resource specialists Alternative C - Channel Widening ---- Present Conditions Post-dredging Conditions Elevation (m GO) Elevation - (m GO) 2 o -2 -4 2 o -8 -2 -4 -6 -8 -10 -12 -10 -12 -14 -14 -6 -16 -16 -18 -20 -22 -24 -18 -20 -22 -24 Dredge volume =310~ m 3 ,::;, lH:10V nhc I , liltla~tmsJ water resource specialists Alternative C - Matsqui Bar Dredging - - ----- ----- ----- Present Conditions Post-dredging Conditions Elevation (m GD) Elevation - - (m GD) 2 o -2 -4 -6 -8 2 o -2 -4 -6 -8 -10 -12 -10 -12 -14 -16 -18 -20 -22 -24 -14 -16 -18 -20 -22 -24 Dredge volume =380,000 m3 lH:l0V nhc I '<: lildliltI:l~J water resource specialists Present Conditions Elevation (m GO) Elevation (m GO) - 2 o -2 -4 -6 -8 -2 -4 -6 -8 -10 -12 -14 -10 -12 -14 -16 -18 -20 -22 -24 -16 -18 -20 -22 -24 Dredge volume nhc I '<: lit~I1IJ 2 o =690,000 m3 water resource specialists a rJ E r 00 rJ N L Ul z Cl «.....I Cl « IJJ 0- :r: o.....I .....I « U Ul IJJ b b0::: 0- Cl IJJ > 0::: Z ~ ~ IJJ « • • • Dike option still being evaluated further. 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. nhc I.'<:. Iu:~at~i.I water resource specialists
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