Bonneville Lock and Dam Earthcache
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This cache leads you to Bradford Island, the site of the Bonneville Lock and Dam Visitor Center. It is accessible from the Oregon side of the river, and is open year round, 9:00 a.m. to 5:00 p.m (except for being closed Thanksgiving, Christmas, and New Year’s Days). You will need to take I-84 east from Portland and take exit 40. And then just follow the signs to the Visitor Center. You will actually drive across part of the dam to get there, which is quite fun. To complete this cache, you will need your GPS, something to write with and on, something with which to time yourself for two minutes, and a digital camera.
Located in the Columbia River Gorge, the Bonneville Lock and Dam consists of several structures that span the river between Oregon and Washington. It was built by the U. S. Army Corps of Engineers during the Great Depression of the 1930s, and was dedicated by President Franklin D. Roosevelt himself in September, 1937. It was named for Army Captain Benjamin Bonneville, an early explorer credited with charting much of the Oregon Trail.
Prior to 1896, before any structures were built on the Columbia River, boats were halted at the Cascades Rapids, located several miles upstream of Bonneville. Boat travelers either had to portage (that means pick up and carry) their boats and supplies around them, or pull the boats up the rapids with ropes. Then, in 1896, a set of locks were opened at the rapids that greatly enhanced travel. Today, however, both the cascades and the old lock structure are submerged by Lake Bonneville, the reservoir that formed behind the dam.
The original structures, a lock and a powerhouse, were built on the south side of Bradford Island, and a spillway was built on the north side. The original lock at Bonneville was, at the time, the largest single-lift lock in the world. That means that the boats drive into just the one step, the water rises or lowers, and they drive out on their way up or downstream. Its use allowed boats to go another 188 miles upstream before they reached another impasse.
A second powerhouse and dam structure was started in 1974 and finished in 1981. The engineers made room for it by widening the river channel on the north side of the river, creating Cascades Island between the new powerhouse and the original spillway. The combined electrical output of the two powerhouses is now over 1 million kilowatts, providing the power needs for 500,000 Northwest homes.
Eventually, several more locks were built upstream on the Columbia and Snake Rivers, allowing ships to transport people and freight for 465 miles from the Pacific Ocean to Lewiston, Idaho. And the original lock at Bonneville was actually the smallest of the eight, so a newer, bigger lock was needed. This new structure was built on the south side, opening in 1993. The old lock is still present, but it is no longer used.
A multi-functional dam, the primary uses of Bonneville are for electrical power generation and river navigation. However, it is also used for fish and wildlife protection, recreation, and flood control. The spillway, still the original, has 18 gates over a length of 1450 feet, and they maintain the reservoir (upstream) at usually 60 feet above the river on the downstream side. Interestingly enough, the water you see coming from the spillway is excess water and does not produce power. However, in the spring, when the juvenile salmon are migrating to the ocean, spillways along the Columbia River system all open to create higher and faster water flows. This helps the salmon get to the ocean in time for their change into salt-water fish.
There are fish ladders, with underwater viewing windows on the bottom level of the visitor center. These ladders help the native salmon and steelhead make it past the dam to get to their spawning grounds. The ones you see at Bonneville (there’s one on both the north and south sides) are called pool and weir. They are one of the oldest styles of fish ladders. They use a series of small dams and pools of regular length to create a long, sloping channel for fish to travel around the dam. The channel acts as a fixed lock to gradually step down the water level. And to head upstream, the fish may either jump up from box to box in the ladder or they can swim through holes cut through the concrete partitions between the steps.
On the Oregon side, there is a fish hatchery with many things to see, including a 10-foot long sturgeon. Believe me, the fish you see through those underwater windows are massive! And if you’re a multi-cache lover, the first waypoint of Sturgeon Fishing (GC1B49) is at the fish hatchery. The dam and fish hatchery are open year round, though the best time to visit the dam, if you’re hoping to see lots of fish using the fish ladders, is in the months of April through September. And during most of the year, more fish use the Washington shore fish ladders, so you may want to visit that visitor center sometime. Due to security reasons, visitors may be required to show ID, and it isn’t possible to cross the entire dam. However it is open to the public and there is no fee for parking or entry.
Today, Bonneville Lock and Dam, located at River Mile 146.1 (meaning that it’s 146.1 miles from the Pacific, if you follow all the twists and turns of the middle of the river), is managed by the U.S. Army Corps of Engineers. More than 100 people are necessary to operate and maintain it each year. The work force includes engineers, powerhouse and lock operators, office administrators, skilled laborers, warehouse workers, biologists and park rangers.
The Columbia is the most dammed river in the world, for its length. The reason that this works is that it drops faster than most. So you can put a lot of dams close together in terms of river miles. One of the effects of turning the river into a succession of lakes, as we have, is that the water slows down. Much of the sediment drops to the bottom at each step, instead of staying in solution and being swept out to sea.
There are three basic types of rocks. There are igneous rocks, metamorphic rocks, and sedimentary rocks. Igneous rocks are formed when magma cools. Metamorphic rocks form when a rock is moved to a different environment and minerals are exchanged in order to find an equilibrium with its new environment. And sedimentary rocks form when layers of loose sediment get compacted and cemented together.
Knowing this, what kind of rock is forming now here in the gorge? What would we see a lot of, if we could see the gorge 1000 years from now?
To log this cache, email me the answers to questions 2 and 3, post online the answers for 1 and 4:
1. Go to the underwater fish viewing level of the visitor center (level 1) and choose one window to stand in front of. For a period of two minutes, how many fish do you see through this one window?
2. On the roof of visitor center (level 5), there is a sign entitled ‘From Forest to Sagebrush.’ What are the names of the two zones that Portland and Vancouver, and the Bonneville Lock and Dam fall into? Please do not post this answer in your online log, or any picture of this sign.
3. Go to N 45.38.560, W 121.56.663 (an easy walk or a quick drive) and count how many spillways are open, letting the water through. How would this compare to other times of year (for example, Spring would find more open, yes?)? And how does this affect the accumulation of sediment and the creation of sedimentary rock at the bottom of the river? Feel free to post the number of open spillways in your online log, as well.
4. And finally, take a picture of yourself (or your GPS, for those of you who are camera shy) with the part of the dam you found most interesting in the background and post it online with your log.
And no internet or armchair finds, please.
If you don’t have access to a digital camera, then email me the answers to these 2 questions, as well. Answers are found on signs on the roof of the visitor center.
1. What is the reason for the abrupt climate change found in the Columbia River Gorge?
2. How fast is the wind that is 'common and may persist for long periods of time?'
There is another visitor center on the Washington side (the one with the greater number of fish coming through), accessed from SR-14, exit 40. It concentrates on electricity generation, and you can take a trip down into a giant turbine. I would encourage you to check it out sometime, though it is not necessary to complete this earthcache.
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