The Mirror Pond Steering Committee released a series of images and plans on Wednesday, offering a glimpse into what Mirror Pond could look like years into the future.

Mirror Pond is changing, with or without our help. The Mirror Pond Steering committee is considering three scenarios that leave the Newport Avenue Dam in place and four that remove it. Here are the possible long-term outcomes, according to the Mirror Pond Management Board.

Option A1: ‘Do nothing’ scenario (dam in place)

Mirror Pond has been left alone for roughly 30 years and no work has been done. New invasive vegetation has populated the areas that are currently mudflats. The channel location typically follows its current alignment. The system is at full capacity for sediment and sediment continues to move downstream through the system.
Total cost: $0.

Option A1: Do nothing scenario (dam in place)

Option A2: ‘Do nothing’ scenario (5 years after dam removed)

After Mirror Pond has been left alone for roughly 30 years, with nothing else having been done, the dam is removed. Side slopes down to the river are graded and replanted as required by federal and state regulations. Emergent marsh areas left isolated by the receding water are populated by a riparian shrub community.
Total cost: $10.9 million (Cost of removing the dam is the responsibility of the owner, currently Pacific Power.)

Option A2: Do nothing scenario (5 years after dam removed)

Option B1: Sediment removal (dam in place)

Mirror Pond is dredged much as it was in 1984. The existing concrete and stone walls adjacent to public parks have been removed and a more natural edge has been planted. After 30 years, emergent wetland zones have developed along the river’s edge and the accumulation of sediment continues. Mirror Pond is once again at full capacity of sediment storage. Dredging will be needed in the future.
Total cost: $5.7 million

Option B1: Sediment removal (dam in place)

Option B2: Sediment removal (5 years after dam removed)

Mirror Pond is dredged much as it was in 1984. The existing concrete and stone walls adjacent to public parks have been removed and a more natural edge has been planted. After 30 years, the dam is removed. Existing shallow waters retreat to the original channel. The sediment deposits that reaccumulated over 30 years are now left exposed. The channel will be regraded and planted with additional emergent and riparian shrub plantings.
Total cost: $11 million (Cost of removing the dam is the responsibility of the owner, currently Pacific Power.)

Option B2: Sediment removal (5 years after dam removed)

Option C1: Sediment reuse on site (dam in place)

Mirror Pond is partially dredged and the removed sediment is reused on site. The dredged sediment is used to create new lawn areas next to public park lands and a natural edge condition of riparian shrubs. Thirty years from now, the emergent zones and riparian shrub zones are fully mature. Mirror Pond is once again at full sediment capacity.
Total cost: $3.5 million

Option C1: Sediment reuse on site (dam in place)

Option C2: Sediment reuse on site (5 years after dam removed)

After partially dredging Mirror Pond and reusing the sediment on site, the dam is removed 30 years from now. When the dam is removed, the existing shallow waters retreat to the original channel. New lawn areas next to public park lands remain. The emergent zones and riparian shrub zones are regraded to meet the new channel and require additional plantings for these zones.
Total cost: $8.8 million (Cost of removing the dam is the responsibility of the owner, currently Pacific Power.)

Option C2: Sediment reuse on site (5 years after dam removed)

Option D: Changing the channel (dam is removed)

The dam is removed as part of the project and the channel has been modified to a new location. Adjusting the location of the channel accommodates creating lawn areas adjacent to parks and reduces the extent of wetlands adjacent to homes. Thirty years from now, the plantings are fully mature and sediment is moving through this section of the Deschutes River in a more natural river process.
Total cost: $10.6 million (Cost of removing the dam is the responsibility of the owner, currently Pacific Power.)

Option D: Changing the channel (dam is removed)

Source: Images and descriptions from Jim Figurski, Mirror Pond Management Board

7 options for Mirror Pond’s future

Staff reports / The Bulletin /

Published Jun 13, 2013 at 05:00AM

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