Secord Dam REpair measures

Interim Repairs
These repair measures will be performed from December 2020-February 2021. ​

1. Right Downstream Retaining Wall: repair of the hole in the retaining wall will include a 2-3 foot concrete block. The top of concrete block elevation is labeled as “TBD”. It appears this block protrudes out into the path of flow release from the spillway gate. Disturbance of flows might be avoided by limiting the top of block elevation to or below the top of the existing spillway sill elevation (El. 709.8).
2. Left Downstream Retaining Wall: the embedment depth and reinforcement of C-06, Detail 1 is not shown on the plan. 8-inch embedment as per Detail C-05, Section B, Sheet 6, Dowel #4 should be sufficient.
3. Tailrace Shoreline Protection: the “Displaced material” across the tailrace was present before the flood event. The Boyce operator stated that it was placed there by Gladwin County or MDOT to protect the downstream bridge piers. Confirmation of this could be confirmed by coordinating with Gladwin County or MDOT.

Repairs reference diagrams not included in the full document. Diagrams are Critical Energy Infrastructure Information and have distribution restrictions.

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Future Repairs
​Critical items identified by the Federal Energy Regulatory Commission (FERC) in a series of letters were assessed during the field review in October and will be addressed as soon as possible. This includes repairing a hole in the right retaining wall downstream of the spillway. This dam will need improvements to allow for winter operations. The long-term plan is to rehabilitate the embankment, install crest gates and construct an auxiliary spillway.

Recommendation Follow-up Actions from the TRC Inspection Report of Secord Dam

Critical action

The Secord Focused Spillway Inspection Report dated November 30, 2018 referenced a hole in the right (west) concrete retaining wall at the base near the downstream toe of slope. This hole was also observed during the post-flood inspection by TRC on June 9th. It appears to be the source of back fill erosion contributing to a void behind the wall…It is recommended that the wall be repaired as follows:

1. Lower the tailrace water level for a period of time sufficient to clear debris from the base of the existing retaining wall and prepare a uniform surface for installation of concrete forms located approximately 2-3 feet away from and parallel to the existing retaining wall. Install formwork for the entire length of the existing retaining wall to a uniform height of approximately 3 feet to ensure coverage above the existing hole and provide a closure form at the end of the existing retaining wall. Install dowels in the spillway slab and the side of the existing retaining wall and install a rebar cage tied to the dowels. Pour the form with concrete. Allow appropriate cure time and then remove the forms and re-water the tailrace.

recommended action

1. Repair the southernmost floor beam supporting the powerhouse. The exposed reinforcing steel is showing signs of corrosion and section loss. Due to its position at the beamfascia, it is exposed to the elements and will continue to deteriorate, possibly at an accelerated rate.
2. Repair the spall/undermining of the east wingwall (bulkhead). The exposure of the steel sheet piling can start to corrode due to the moisture present at the site. Extended exposure could lead to failure of the connection between the concrete cap and the steel sheet piling below.
3. Backfill voids behind the retaining walls.
4. To ensure that the right downstream slope is not actively moving, it is recommended that survey hubs be installed along the slope (at the crest, toe, and midslope) to monitor the slope for additional movement - the survey hubs should be initially monitored every other week. 
5. Repair the erosion damage that was observed at the downstream toe of slope at the end of the right concrete wingwall and on the right and left downstream riverbank above the riprap. The erosion does not appear to be an immediate threat to dam safety, but should be repaired when feasible.

​Non-Critical Action/Maintenance Items

1. Remove the trees, cattails and other overgrowth along an approximate 50 foot long section of the far left of the embankment near the left abutment. Once this vegetation is removed, repair the surface sloughs and erosion damage at the toe, and replace the riprap...The dead and fallen trees should continue to be removed as part of regular maintenance activities. Stumps should be removed by either pulling or with machines that can grind them down. All woody material should be removed to about 6 inches below the ground surface and the cavity backfilled with well-compacted clayey soil and grass vegetation established.
2. Clean and repair concrete deterioration to retaining walls and wingwalls (bulkheads). Repairs include cleaning concrete surfaces, patching spalls and delaminated areas, and epoxy-injecting cracks. This will slow the rate of deterioration and extend the service life of the dam.
3. Clean and paint remaining steel equipment supports on the deck. Cleaning and painting should slow or stop active corrosion and extend the usable life of the structures.
4. Place additional riprap on the upstream slope near the right abutment.
5. Perform maintenance of the vegetative cover throughout. Removal of improper vegetation is necessary for the proper maintenance of a dam. All vegetated embankment slopes should be maintained with a maximum grass height of 12 inches…Common methods for control of vegetation include the use of weed trimmers or power brush-cutters and mowers. Chemical spraying to kill small trees and brush is acceptable if precautions are taken to protect the local environment. It is important to remember not to mow when the embankment is wet.
   
6. Although rodents or burrow holes were not observed during the site visit, it is likely they are present. Continue to maintain proper rodent control throughout...They (rodents) are usually discouraged from inhabiting the embankment if the vegetative cover is kept mowed as previously discussed. The rodents can also be controlled by fumigants, trapping or shooting during the appropriate season - local laws and regulations should be checked before trapping and/or hunting. If a burrow or den is observed, it is recommended that it be backfilled by mud-packing - pour a mud-pack mixture (i.e.,a slurry consisting of 90% soil and 10% cement mixture) with the aid of a pipe into the hole with dry soil tamped into the entrance and vegetation re-established.

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Quick Facts

$24 million	2,015	2022-2024
Cost to Repair	Waterfront Properties	Estimated Lake Return Date

Secord Dam will require significant repairs and upgrades to meet the ½ PMF (probable maximum flood) standards. To get the dam up to these standards we will decommission the powerhouse, construct a new auxiliary spillway, install new crest gates and repair the reinforcement embankment.

Example crest gate with gate closed on the far/left side and the gate open on the right side