Smallwood Dam REpair measures

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

1. Powerhouse Turbine Air Vent; the powerhouse fan window is to be closed off. This is the vent that was jetting water during the flood event. The air vent may need to be relocated if found to be relevant to powerhouse operations. 5.
2. Rock Buttresses; bedding material and riprap to be placed in the undermined areas of the concrete walls. This would be considered a temporary measure to protect the retaining wall over the winter. A more permanent remedial measure would include rebar and concrete backfill.

​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. These include placement of larger riprap (loose stone) downstream, repairing the downstream retaining walls, and adapting the dam for winter operations. Long-term, the plan is to rehabilitate the embankment, install crest gates and enhance the auxiliary spillway.

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

Critical action

1. ​Repair and/or replace the left side (north) cutoff wall and missing portion of the retaining wall at the downstream end to prevent future loss of wall sections and backfill.

recommended action

1. Repair Spalling on Spillway Piers.
   
2. Seal the air vent within the powerhouse to prevent inadvertent discharge.
   
3. Monitor the effectiveness of the areas recently repaired that were damaged due to erosion during the flooding. If the vegetation does not take within the hydro-seeded areas, reseed the areas and water until a good stand of grass is established.
   
4. Close Tainter gates for a sufficient period of time to allow tailrace water levels to subside to facilitate visual inspection of the spillway tailrace structures.
   
5. Conduct dive inspection of the submerged structures at the upstream side of the spillway and powerhouse.

​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. M-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

$14 million	721	2022-2024
Cost to Repair	Waterfront Properties	Estimated Lake Return Date

Smallwood Dam will require significant repairs and upgrades to meet the ½ PMF (probable maximum flood) standards, and to avoid the flooding that occurred around the dam in the May 19 flood. To get the dam up to these standards we will construct a new passive auxiliary spillway and install new crest gates and shoreline armor protection for high exit velocities. 

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