Marmot Dam Site after 6 years of the removal
The Marmot Dam was built in 1913, and it was
removed in 2007. Before that, the area was logging land. The dam was operated
by PGE (Portland General Electric), and all the land around was also owned by
PGE. Environmental agencies realized that the dam was obstructing the natural
flow of salmon upstream, and they proposed to remove the dam to let the river
flow free. Finally in 2007 the dam was removed, the land was acquired by the
Western Rivers Conservancy, and then transferred to the federal government to
be restored.
After almost 7 years since the removal, the
area doesn't appear like it had a man made structure in the past. The Sandy
River flows free, and there is no major obstruction of sediments. The land on
the north of the river is recovering, trees have been planted in the land where
there used to be a building. This building was also removed, the cement was
broken and the soil was treated to avoid compaction, so the new seedlings can
grow. To the south of the river, the forest looks intact. Mossy Western
Redcedar and Big Leaf Maple trees cover the shaded ground where Sword Fern
grows.
The reason why the dam was removed is
because it was obstructing the flow of salmon upstream. The Sandy River offers
primordial habitat for four species of salmon: Spring Chinook, Fall Chinook,
Steelhead, and Coho. A salmon ladder was built for salmon to swim upstream, but
this was not really effective. PGE realized that the expenses of removing the
dam were significantly lower than the expenses of operating the dam.
Succession is taking place now. The soils
where the building was are now more fertilized, and the young seedlings are
growing, some of them are reaching about 5 feet tall. There are a few invasive
weeds in the area like Vinca, Scotch Broom, and Himalaya Blackberry. The Sandy
River Basin Watershed Council is working in removing the noxious weeds and
restoring the site. They have an idea, they want the replanted area to grow,
and when the trees are mature, they are going to build some facilities like
campgrounds, a boat ramp and a kiosko, but vegetation succession has to be
fully in place.
Steve Wise was explaining about the
hydrology and geology of the Sandy River. The river originally serves as a
channel for lahar coming from Mt Hood. The river has its source in the Sandy
Glacier. The glacier erodes the rocks of the mountain and deposits huge amounts
of sediments into the river (that is why it is called “Sandy”). The last lahar
was about 300 years ago. The bottom of the river is very young; the rocks are
composed mainly by basalt. After the removal of the dam, most of the sediments
were washed downstream in just a couple of days after. These did not affect the
wildlife of the river because of the natural sedimentation regime of the river
and the low toxicity content. The sediments found today are from after the dam
removal.
The forest is categorized as late succession
according to Steve Wise. The average age of the trees is about 200 years, so
the forest is not considered old growth. The dominant species is Western
Redcedar (
Thuja plicata) and Big Leaf
Maple (
Acer macrophyllum). The forest
floor is composed of woody debris and a thick and soft layer of humus (dead
needles and leaves). The canopy is very open, so there is plenty of sunlight
reaching the forest floor. The understory dominant species are Sword Fern (
Polystichum munitum) and Huckleberry. The
branches of the trees are covered by thick layers of moss. Some species of fern
form roots and soil on the branches of the Big Leaf Maple and create habitat,
such as the Licorice fern (
Polypodium
glycyrrhiza). This is a peculiarity of this forest.
