Sunday, August 24, 2014

Notes from Ross Dam

Ross Dam is the uppermost and highest dam of the three Seattle Light dams on the Skagit River. It is the key dam for controlling flows and power production on the Skagit. Two additional dams are located down river.
Ross Dam from the south

Note the high steep cliff on the far side of the dam and the fact that the slope from the vantage of where the picture was taken are steep as well. At one time there was a scheme to have an even higher dam matching those higher slopes. A higher dam would have backed water up into Canada. An agreement was reached to do so, but there are no current schemes to build a higher dam.

All three dams are located within a gorge between the broader upper Skagit valley and the broader lower Skagit valley. Ross is at an ideal location for a dam at a deep gorge entrance with a broad valley upstream allowing for a large volume reservoir. The Skagit gorge is thought to have formed during the continental glacial period when glacial ice to the north blocked north flowing rivers and diverted river outlets to the south and over a mountain divide where the Skagit gorge is now located (see Riedel, Haugerud and Clague, 2007). The gorge is incised down through the Skagit Gneiss, a band of high pressure and temperature metamorphic rocks within the core of the North Cascades.

Waffle face of the dam

The potential for a higher dam is also reflected in the waffle concrete face of the dam. The idea was that the waffle face would allow excellent adherence between the existing structure and a higher taller dam structure added on to the dam.

View of gorge below dam
The concrete structures on the left and right are the spillways. They are set up to allow the spilled water to collide and dissipate energy if water is spilled from the dam versus passing through the powerhouse which is located on the upper left of this view.

Boathouse and docks on upstream side of dam

Boat house and dock stairs descending into the water
The floating dock sliding up and down piers according to water levels and the permanent steep stairs  has been great improvement from the previous ladder descent to the dock and boat house.

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