Lab 4

Sandy River Delta's dam Report

Introduction

Recent research in hydrology and biology has been focused on the impact of stream diversion on the aquatic wildlife after the removal of Marmot dam. Five years ago, the Sandy River Delta dam which was managed by Portland General Electric since 1908 was removed in order to restore fish habitat. The removal of Sandy River Delta dam has attracted the attention the community of scientists to observe a vast amount of sediment collected in a reservoir. This report presents some fundamental geological, hydrological and ecological change observed five years after this removal. This watershed was disturbed by human action for over many decades; in fact, the reestablishment of this biome as it used to be is considered as a secondary succession.

Sandy River Delta dam’s history

Figure 1: The Marmot dam: Photo credit: Kesley Khan

Sandy River dam was built by Portland General Electric (PGE) through the Bull Run Hydroelectric Project between 1909 and 1912 near the Bull Run. In 2007, the Marmot Dam on the sandy river was removed because of its environmental costs. “The powerhouse had a generating capacity of 22 megawatts (MW), enough to power 12,000 homes in 2007”( The Oregonian p. E04 2007)

Sandy River Delta dam’s location

Figure 2: Marmot dam

Dam was located about 3.1 miles down the Roslyn Lake (GNIS, 2010). Latitude 45°24'0.39"N, longitude 122° 7'55.40"W and range 338 m. The Marmot Dam divert water from the Sandy to the Little Sandy by canal and tunnel, it has 30 feet high. The dam was disturbed the salmon from the upper level to migrate to the downstream. In fact, they included a fish ladder to allow the migration of salmon. Despite all, the fish ladder wasn’t effective and efficient. In 1951, the PGE installed fish screen to prevent fish from being drawn in dam.

The impacts of the removal of Sandy River Delta dam .

1.      Ecological Secondary Succession

      Stream Channel

The removal of the dam allows the river to flow naturally. The coarse sediment that was in pool reservoir has made a little change by moving downstream. It has changed the form and the behavior of the downstream. There are two large of point bars in the both side of the site which have accumulated of sands, gravels, cobbles and a few boulders deposited by the stream when its velocity drops along the inner bank after the dam’s removal.

      Aquatic wildlife

Figure 3: Salmon habitat

The sediment that was buried in the reservoir of the dam did not cause damage the salmon habitat and others species aquatic. Contrariwise, the community of salmon has been mixed and diversified which help them to not be extremely endangered species. In the other side, salmon don’t need human help to move down and upper stream anymore. Despite all, the Oregon Department of Fish and Wildlife has a hatchery raised fish; as the result over million fish species such as coho, spring Chinook , and steelhead have removed into the river every year.

      Vegetation

This area is managed by Western Rivers Conservancy which is a non-profit organization that buys land in the western part of USA to conserve critical habitat, create public access in the forest. It cooperates with others environmental agencies to secure the health of the whole ecosystems.The west side of dam’s site is an old young Douglas fir ( Pseudotsuga menziesii ) forest. The manager has introduced some species of hardwood and shrub in an open area where the dam’s building was located. There are many invasive of grasses and shrubs such as Himalaya Blackberry (Rubus armeniacus (syn. Rubus discolor), scotch broom (Cytisus scoparius) in this open area. The east side of the dam’s site is an old growth Western red cedar (Thuja plicata)  forest.

      Soil

Sandy River has a young geologic landscape. This river was formed less than 300 years ago. The river floor is cover of sands, gravels, and cobbles. The stream’s shore is likely beach sand. This soil in western part of the river is volcanic which means the growth rate of the trees is very slow however in the eastern part the soil underneath the Western red cedar is really spongy, rich in nutrients and microorganisms.

Conclusion

The removal of Sandy River dam is considered as a secondary succession because this area has covered with vegetation many years ago. In fact, it will take only a couple of year for this area to regenerate.

References/ edit

http://en.wikipedia.org/wiki/Bull_Run_Hydroelectric_Project ( All references are from Wikipedia)

Jump up

1. ^ "Roslyn Lake". Geographic Names Information System (GNIS). United States Geological Survey. November 28, 1980. Retrieved January 16, 2010.
2. Jump up^ "Bull Run River". Geographic Names Information System (GNIS). United States Geological Survey. November 28, 1980. Retrieved January 16, 2010.