I Wonder How The Dam Thing Works?

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Bonneville Dam Spillway | Wikimedia Commons - Lost Chain Photo

We all know what they are and what they are used for, but most of us don’t really know how they actually do their job. What am I talking about? I’m talking about a device that a lot of us in Oregon can’t do without, at least not yet. The subject of this column is the dam, specifically the Bonneville Dam.

Bonneville Dam | US Army Corps of Engineers
Bonneville Dam | US Army Corps of Engineers

We all know that dams generate electricity by using the power of a rivers churning waters, but I don’t think we appreciate all of the technology it takes to genetate large amounts of electricity. Man started using waterpower over 2,000 years ago, but it took until the middle of the 20th century to come up with the idea of generating electricity by using the energy of falling water. Technically a dam converts potential energy into electrical energy.

According to the Eugene Water and Electric Board (EWEB) 70% of our electricity comes hydroelectric plants and 52% from the Bonneville Power Administration. That means the Bonneville Dam.

FDR Dedicates Bonneville Dam | The Oregonian
FDR Dedicates Bonneville Dam | The Oregonian

Before we delve into the workings of a  hydroelectric dam let’s explore the history of the Bonneville Dam. It was a Public Works Administration project of the “New Deal.” The dam was named for Captain Benjamin Bonneville who was a soldier, explorer, and a trader. Franklin D. Roosevelt commented about the dam project while he was on the campaign trail in 1932 and he returned in 1935 for the dedication of the Bonneville Dam. FDR had some powerful words to share concerning The Bonneville Dam.

The dam is located near Cascade Locks, OR and North Bonneville, WA which puts it at 145 miles from the mouth of the Columbia River and about 40 miles east of Portland, OR. According to the US Army Corps of Engineers the first powerhouse, spillway, and original navigation lock were finished in 1938 to improve navigation on the Columbia River and provide hydropower to the Pacific Northwest. A second powerhouse was built in 1981 and a larger navigation lock was completed in 1993.

Dam internal parts | Suvo, Bright Hub Engineering
Dam internal parts | Suvo, Bright Hub Engineering

Let’s take a look at the 6 parts it takes to make a dam. Those parts are: a water reservoir, a gate, a penstock, a turbine, an alternator, and the most obvious part which is a river. The last part is the Columbia River where the water comes out of the dam and back into the river. Now I’ll take the other parts in order. The water reservoir is another obvious part without which a hydroelectric dam isn’t possible. The gate controls the flow of water from the dam. The penstock is the sloped channel that the water flows through to get to the turbine which is where the water hits the fan blades that rotate the spindle. The Bonneville Dam uses a special kind of blade called a Kaplan Adjustable Turbine. Many other dams use a paddle wheel type of turbine. The alternator is where rotational energy of the spindle is converted into electricity which is then sent through the grid to your house.

Bonneville Dam Spillway
Bonneville Dam Spillway | US Army Corps of Engineers

The dimensions of the dam will give you some perspective as to its massive size. The spillway dam is 449 meters (1,400 ft.) across and 41 meters (132 ft.) wide for the gravity section. It’s height above lowest bedrock is 61 meters (197 ft.). The height of the gates varies from 15.50 meters (50 ft.) to 18.25 meters (60 ft.). The design capacity (how much water it can push through) is 1,600,000 cubic feet per second. How about the depth of the water behind the dam? The average depth is 23.3 meters MSL (above mean sea level) or 75.6 ft. MSL while the maximum  pool depth is 25.0 meters MSL or 82.5 ft. MSL. My best description of the pool depth is that you surely would not want to fall in if you couldn’t swim because there is no way you could just walk to the shoreline from the bottom.

Bonneville Dam Map Showing Navagation Lock | US Army Corps Of Engineers
Bonneville Dam Map Showing Navagation Lock | US Army Corps Of Engineers

Another part of the Bonnevile Dam that has nothing to do with generating electricity is the Navigation Lock. That is the only way that boat traffic can navigate past the dam either upstream or downstream. There are locks: the original one built in 1938 (76 ft. wide and 500 ft. long) and the new lock built in 1993 (86 ft. wide and 675 ft. long). The way boats navigate through a lock is to drive the boat into the lock. The gate is closed and the lock is filled with water to then open the gate on the other side and the boat can then traverse to the other side of the dam. The reverse is performed to go in the other direction. It takes 20-25 minutes to fill the 1938 lock and 15-20 minutes to empty it as opposed to the more efficient 1993 gate which takes 9-13 minutes to empty or fill.

Bonneville Dam Fish Ladder | Commons.Wikimedia.org
Bonneville Dam Fish Ladder | Commons.Wikimedia.org

Over the years concern has built up over the plight of the fish that have to somehow get by a dam. Fish ladders have been built so that the adult fish can get past the dam to continue the return to their upstream spawning grounds.The fish ladder allows the fish to ascend 60 feet to the upstream level.

Some of the greatest advantages of hydroelectric power are that it uses the natural occurring rivers that already have swift flowing water that can keep a reservoir filled, the energy is made cleanly by not producing air, land, or water pollution, and even when they have problems no pollution can be transported into the river.

Let me know what you would like me to talk about or explain. You can email me at: [email protected].

 

Tim Chuey is a Member of the American Meteorological Society and the National Weather Association and has been Awarded Seals of Approval for television weathercasting from both organizations.

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