TITLE: THIRD STREET DAM PRESENTER: Theodore E. Snure, P.Eng. General Manager

AGENDA NO:

DEPARTMENT: Development Services DATE: August 29, 2008

CLEARANCES:

Treasury

ATTACHMENTS: 1. KGS CV (7 pages) 2. Sketch of Dam (1 page)

APPROVALS:

August 29, 2008 02/09/08 Department Head Date City Manager Date

SUMMARY OF HISTORY/DISCUSSION & FUNDING: In the spring of this year, two of the nineteen piers failed in the Third Street Dam and as a result, the stop logs in each of the three bays affected were no longer restrained and washed downstream allowing for free flow of water through the three bays. The dam serves the purpose of impounding water for the Water Treatment Facility, as well as regulating water levels for recreational purposes. The engineering services of KGS Group were secured to provide both a short and long term solution. The short term solution was implemented, which consisted of a rockfill berm that both regulated river elevation and allowed for inspection of the dam in order to develop a long term solution. KGS has now essentially completed their review on the long term solution for the repair of the dam and are finalizing the report. Given the urgent need to begin permanent construction activities on the river this year, we have summarized the report findings in this council report. KGS was selected as the consultant since they have professional engineering staff who are considered to be leading experts on river structures and river hydraulics. Attached as information are the CV’s for the members of the project team for KGS Group. Continued use of KGS Group for the remediation project is strongly supported by the Engineering Dept. REPORT FINDINGS: Structure Condition – With the temporary rockfill berm in place, Dominion Divers of Winnipeg were retained by KGS Group to perform an underwater video inspection of the spillway bays protected by the rockfill berm. A summary of the inspection findings are as follows: “ - Pier walls appear to be in fair to good condition. Some piers are scaled up to 50 mm deep with

exposed aggregate. - In most bays, steel sheet piling is exposed beneath the slab on the downstream side. Gap between

bottom of base slab and river bed ranges between 25 mm and 100 mm. The sheet piling plays an integral part in the sliding stability of the structure because without it, the self-weight of the structure

would not be sufficient to prevent a sliding failure – especially under ice loading. The gap beneath the structure leaves the 60 year old sheet piling vulnerable to corrosion. It is unknown what the current condition of the sheet piling is, or the extent of corrosion that has already occurred.

- Many of the remaining piers have experienced partial failure, with the interface between the pier and base slab undermined to a depth of 25 mm to 200 mm with exposed reinforcing. This undermining is evidence that at the time of the failure of piers 9/10 and 10/11, several other piers were near to experiencing the same type of failure.

- Several of the piers are vertically out of plumb from 25 mm to 100 mm over the 1.8 m height of the pier. This listing could have been caused by debris impact and could have been exacerbated by the different water levels created by the breach of bays 9, 10 and 11.

Based on the inspection, the existing structure cannot be put back into service with any confidence, and requires substantial structural repairs.”

River Uses – Besides the river being the primary source of water supply for the City of Brandon, there is a variety of recreational uses which rely on the 3rd Street Dam to impound water, namely:

- Pontoon boat tours; - Canoeing and kayaking; - Water ski slalom and jump course; - Ducks Unlimited interpretive ponds; - Testing of watercraft by local business owners; - Hosting of water events.

While the temporary rockfill berm has provided some improvement to river levels and therefore mitigated issues for some users there were some users, like the Riverbank pontoon boat tours, which were required to not offer the event this year as water levels were still too low. Long Term Options – Three options were developed and the KGS Report provides for expanded discussion on advantages and disadvantages of each. A summarized version is provided below:

1. Restore the Dam to Its Original Configuration – Restoring the dam to its current configuration would require not only the repair of the failed section but also rehabilitation of the remaining structure. The repair work would require the construction of two temporary dams adding to the cost. The original configuration does not allow the passage of fish and is difficult and costly to maintain. The estimated cost for this option including an engineering and contingency allowance is $720,000.

2. Eliminate the Dam and Replace the Water Intake Structure at the Water Treatment Plant – The

option of replacing the intake structure at the Water Treatment Facility and eliminating the dam was included as it is the best option in terms of fish passage. The disadvantage is cost and the resulting change in river levels. The lowered river levels would result in the loss of the river for recreational purposes as well as bank stability issues. The work required to modify the water intake would be complex involving the construction of an infiltration gallery below the existing intake. An infiltration gallery is essentially a horizontal trench carved into the river bottom and filled with coarse rock, gravel and sand. Significant disruption of the river bottom and coffer damming would be required to carry out the work. The KGS report does not include an estimate for this option however it is reasonable to assume the cost would be in the millions of dollars.

3. Replace the Dam with Rockfill Weir – Replacing the dam with a rockfill weir would include enhancing the existing temporary rockfill weir with more material and removing portions of the existing dam structure. The weir would allow for fish passage and maintain the river at its current level thus allowing for continued recreational use and eliminate the bank stability issue. The estimated cost for this work is $484,000 allowing for engineering and a contingency allowance. A pictorial sketch of this structure is attached to this report.

Conclusion - The report concludes that the 3rd Street dam not only provides for an assured water supply to the City of Brandon Water Treatment Plant, but also the reservoir it creates is extensively used for recreation, tourism, ecological reserves, and local businesses. These users rely on the levels ensured by a dam being in place in the vicinity of 3rd Street, therefore some water level control device needs to remain in place. Thus there are two options which should be considered namely:

- restore the dam to its original configuration; or - replace the dam with a rockfill weir.

Clearly the replacement of the dam with a rockfill weir presents the most effective solution for the City, especially given the urgent need to have a dam in place this fall. FINANCIAL: With the damage to the dam recognized early in the budget year, and knowing that some remediation work would be required, the Engineering Dept. delayed work on some projects in order to divert these funds to the dam requirements. The following table shows our budget needs for the dam and which projects we will defer to achieve the needed funds.

THIRD STREET DAM REPLACEMENT 2008 Estimated Cost Cost to date (Aug. 21, 2008) 176,323.59 Rockfill Berm 400,000,00 Engineering 40,000.00 Contingency 44,000,00 Total: 660,323.59 Source of Funds 6708 WTF Disinfection Implementation 85,000.00 6713 WTF Hydraulic Upgrade 250,000.00 6714 Elderwood Lift Station 200,000.00 Watermain Grid Improvements 145,000.00 Total: 680,000.00

The deferred WTF and Elderwood projects will be moved into the 2009 budget for completion. Deferral of the recommended projects will not adversely affect our ability to operate the water treatment plant or the Elderwood lift station. The Elderwood lift station project was to upgrade mechanical equipment that is nearing the end of its useful life. The WTF projects are similar in nature.

Watermain grid improvements are budgeted annually at $150,000. and are used to improve the waterflow on the watermain distribution system. A one-year interruption of grid improvement work will not adversely affect the integrity of the water distribution grid. RECOMMENDATION That the 2008 Utility Capital Budget be altered to allow for the construction of a rockfill weir to replace the Third Street Dam and further, that KGS Engineering continue to be engaged to complete the necessary engineering services.