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Citation EBA Engineering. 2015. Hazard abatement order report, Prepared for Village of Cumberland, Comox Valley Regional District and TimberWest Forest Corporation.
Organization Village of Cumberland
URL http://www.viha.ca/NR/rdonlyres/6B833E7C-E676-4A68-ADD7-03B18C241700/0/hazard_abatement_preventation_order_report.pdf
Abstract/Description or Keywords Tetra Tech EBA Inc. (Tetra Tech EBA) have been retained by The Village of Cumberland (the Village), Comox
Valley Regional District (CVRD) and TimberWest Forest Corporation (TimberWest) to prepare this report in
response to the Hazard Abatement or Prevention Orders, dated August 7, 2015, received from the Medical Health
Officer, Dr. Charmaine Enns, MD., MHSc., FRCPC. Copies of these orders are attached as Appendix B.
The work was authorized by the Village of Cumberland on behalf of the three parties via a Tetra Tech EBA Service
Agreement, signed on August 25, 2015. The scope of services, as well as Tetra Tech EBA’s General Conditions,
were provided in our proposal letter dated August 25, 2015.
2.0 OBJECTIVE AND SCOPE OF WORK
The objective of this study is to provide a report which:
 Identifies feasible options, estimated costs, and the likely effectiveness of means to control, minimize or prevent
bank collapse and otherwise mitigate introduction of sediment into Perseverance Creek; and
 Identifies feasible options, estimated costs, and the likely effectiveness of means to control, minimize and
manage the effects of overflow from Cumberland Creek No. 2 Dam spillway into Perseverance Creek.
The scope of services agreed to was limited to:
 A site visit with the Village of Cumberland staff on August 17, 2015 to observe current conditions along the
creek;
 Discussions with Village of Cumberland staff;
 Meeting on August 27, 2015 with the three parties to review the scope of work and resources available;
 A field visit on August 27, 2015 to Cumberland No. 2 Dam, Cumberland No. 1 Dam, Cumberland Creek between
these two dams and the lower reaches of Perseverance Creek with Village, CVRD and TimberWest
representatives;
 Developing options for reducing the erosion in the spillway channel;
 Developing options for minimizing or eliminating the outflow from Cumberland Creek No. 2 Dam to the overflow
spillway channel;
 Estimating the cost of the various options;
 Comparing the options;
 Preparation of a report presenting the results of the study;
 Discussions regarding the options and comparison with the Village of Cumberland, TimberWest Forest
Corporation and Comox Valley Regional District; and
 Finalizing the report. Cumberland Creek No. 2 Dam, refer to Figure 1, was initially constructed sometime between the late 1890’s and
early 1930’s as a timber crib structure. It was part of a hydroelectric project and also a source of potable water for
the Village of Cumberland. A low level conduit, located near the right abutment, discharges flow to Cumberland
Creek. An air photograph from 1931 indicates that there was also discharge to the southeast, down an un-named
channel, herein called the ‘spillway channel’. Some minor erosion along this channel was evident in the 1931
photograph.
At some point prior to 1972, the timber crib was covered with fill and the dam raised. A concrete weir with three, 1.2
m diameter corrugated steel culverts was constructed at the southeast end of the lake likely during this work. This
weir structure acted as the spillway, discharging flow down the ‘spillway channel’, to Perseverance Creek.
Evidence from air photographs indicate activity around the lake in 1964 and, although not conclusive, an apparent
increase in the rate of erosion after the early 1960’s.
This suggests the raising of No. 2 Dam may have occurred in the late 1950’s or early 1960’s.
On December 19, 1972, a rain-on-snow event was experienced. It is postulated that the three culverts were at least
partially plugged prior to, or by, this event, resulting in a rise of the lake level.
This rise in lake level increased the head differential across the dam, resulting in severe piping and an 11 m wide
breach. Reports from that time indicated the piping may have been due to rotting timbers. This breach resulted in
damage to Cumberland No. 1 Dam as well as overtopping and a breach at Henderson Lake Dam.
During the subsequent repairs to the No. 2 Dam, fill was removed adjacent to the concrete weir and a cofferdam
built across the lake to divert flow to the spillway channel. The flow eroded the base of the channel near the weir to
approximately 1.5 m below the invert of the culverts.
When the repairs to No. 2 Dam were complete, the cofferdam was breached, however the opening at the concrete
weir was left at the eroded elevation.
Historic air photographs show clearcut logging was carried out over much of the Cumberland Creek watershed,
including riparian areas, between 1931 and 1950. However, over the past 20+ years, logging has been limited to
small cutblocks, with water management used to minimize erosion and replanting, based on Equivalent Cutblock
Area management principles.
There has been concern regarding the diversion of the majority of the Cumberland Creek flow down the spillway
channel since the erosion was observed in 2002. It is understood the concerns were for three reasons:
 Water was being diverted between watersheds;
 Loss of land; and
 The ongoing erosion of the spillway channel delivering sediment to Perseverance Creek.
It is understood that there was an issue with erosion in this channel during a high flow event in 2003.
In early December 2014, extreme rainfall caused in an increase in turbidity in Comox Lake resulting in a boil water
advisory. Observations and testing at that time revealed that Perseverance Creek was a source of some portion of
the turbidity.
Information Type report
Regional Watershed Vancouver Island North
Sub-watershed if known Cumberland Creek, Perserverance Creek, Comox Lake
Aquifer #
Comments
Project status complete
Contact Name
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