Kitsault Dam Case Study
The Kitsault Dam was constructed in approximately 1948 as a rock-fill timber crib structure. Its main purpose was to provide storage support of a small secondary diversion structure used to create power for the Torbrit Silver Mine. The dam was built 8 metres high by 23 metres long and impounded up to 17 million cubic metres at full supply level (FSL). The reservoir at an elevation of 800 metres discharges to the Kitsault River with an average slope of 2.6 percent and is deeply entrenched in canyons until approximately 5 km upstream of the community of Alice Arm. The channel then spreads out to a wide floodplain as it approaches the community and the ocean.
Figure 1: Arial View of the Kitsault Dam (August 19, 2002)
Figure 2: Reservoir (1996)
Figure 3: Kitsault River floodplain upstream of Alice Arm, to picture right. (1996)
The community of Alice Arm on Alice Arm is approximately 70km south of Stewart and 120 km north of Terrace, B.C. and has a fluctuating population of approximately 20 people. There are remnants of emergency protection works, which some consider a dike that protected the community from high water events on the Kitsault River in the past, however, inspections of these works indicate the community may be at risk from high water events including a sudden breach of the dam.
Figure 4: The community of Alice Arm (1996)
Inspections of the Dam are by float plane or helicopter only. Vehicle access on Provincial highway 82 and 83 from Alice Arm to the old powerhouse became impassable in several locations from washouts during high water events. The powerhouse was removed and some work was performed to determine the extent and condition of the bedrock in 1981. The recommendations from that inspection indicate removal of the dam by the end of 1983 was the preferred option.
On December 15, 1983, the Water Management Branch acknowledged the abandonment of FWL 14294 rendering the dam that remained as abandoned. The former licensee was made aware of their liability outlined in Section 25 of the Water Act which states:
Liability of owner for damage remains
25 The abandonment, suspension, termination or cancellation of all or part of the rights held under a licence or approval does not relieve the owner of the land, mine or undertaking to which the licence or approval is or was appurtenant of liability for damage resulting from the works constructed, operated or maintained by the owner, or from a defect, insufficiency or failure of the works.
The state of the dam was dilapidated and it was deteriorating at an accelerating rate. The sheet metal covering the spillway in 1999 had completely disappeared promoting the decay in the spillway area. The timber cribbing forming the main structural component was also deteriorating suffering from rot and crushing.
The wooden shiplap upstream face was showing deterioration at a slower rate due to the submergence in the reservoir. The protective housing covering the outlet control tower had fallen off in 1995. The tower began to lean and was expected to be inoperable. Access to the tower was difficult to impossible making an adequate inspection unfeasible and unsafe.
Figure 5: Crushing and rot on downstream face (2002).
Woody debris was found on and over the dam suggesting the reservoir overtopped the dam during high runoff flows. Woody debris was also expected to be hampering the low level outlets. The overtopping events likely caused the sinkhole, or otherwise removal of rock fill, in the structure as observed in the September 26, 2001 inspection. Seepage through the dam was evident at various locations and could not be adequately assessed or quantified. It was anticipated that the phreatic zone reached the down stream slope and seepage was occurring around the low level outlets.
Approximately 5 km downstream of the Kitsault Dam, a secondary diversion dam exists but no inspections have been performed due to lack of access; fly-over visuals are the only mention of this structure. This dam was built as a concrete gravity structure with a very small impoundment of <1000m3 and formed the intake for the penstock. There were no anticipated problems with this structure.
The deteriorating status of the Kitsault Dam concerned the Dam Safety Unit . The previous owner was found and informed of the status. The concern for the stability of the Dam culminated to the issuance of an Order in December, 2001. The Order required the owner to develop a remedial works plan subject to acceptance by the Dam Safety Officer and finally implement the plan by September 30, 2002. Discussions with the owner and the approved remedial works plan, the Order was replaced with a new one. The new Order extended the time for completion of the remedial works plan and requested further information about the structure. The dam must also be removed or replaced by October 31, 2007.
Engaging in open communication and working with the owners has produced an amicable and workable solution. The remediated dam has reduced the concern for public safety and also reduced the liability for the owner. Again, working closely with the owner has produced a win-win scenario for all involved.
Please review this PowerPoint presentation on the remediation. Slideshow is set for automatic display of the next slide.
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