Rainbow Falls (Missouri River)
Encyclopedia
Rainbow Falls is a waterfall
on the Missouri River
in Great Falls, Montana
, just upstream from Crooked Falls and downstream from Colter Falls
and Rainbow Dam
. It is 47 feet (14m) high and 1,320 feet (402.3m) wide. The waterfall is part of the five Great Falls of the Missouri. The river spills over a sheer ledge of sandstone in the Kootenai Formation
, forming the falls. The falls used to flow with a great deal of force year-round. In 1914 the river shortly upstream was dammed for hydroelectric power by the Rainbow Dam
, which forms a run-of-the-river reservoir. As a result, the falls can almost totally dry up in the summer with only a few narrow strips of water trickling down its face. A railroad bridge crosses the river directly above the falls.
of the dam are located, and on the left side where the main spillway
structure is positioned. The center section of the dam, which is also a spillway structure, only functions when the flow above the reservoir is too great. The left side of the falls is more heavily eroded
than the right side, and sits a little farther upstream. Expansive and arid hills rise above the canyon on each bank. Below the falls is a long, narrow plunge pool
, and a series of gravel bars.
As the flow over the falls diminishes, usually from summer to early autumn, it splits into two parts hugging both banks. The flow at this point usually still extends across most (70 percent) of the full width of the river, but a section in the center remains dry except for a narrow stream of water that is found when the flow is low enough to separate it from the left-side drop, but high enough to feed it. The river below the falls remains mostly full. Much of the water is still diverted to generate power, but there is still enough water flow in the river to flow over the dam's spillways.
In the autumn, however, the majority of the river is diverted through penstock
s around the right side of the falls. The penstocks continue downstream past 19-ft (5m) Crooked Falls, utilizing the combined drop of over 70 ft (21m) to generate hydroelectricity
through 8 turbines. The falls themselves are reduced to a mere trickle. Some water still continues down the right side of the falls through a few parallel drops, trickling out of the river outlet works. On the right, there are also two drops, each around 10 ft (3m) wide at low flow. Also, water comes out of a pipe at the left bank side of the falls, and trickles into the river in a series of small waterfalls.
Upstream of Rainbow Falls lies Colter Falls
and Black Eagle Falls; the former is buried under the reservoir formed by Rainbow Dam, while the latter is controlled by a dam in a similar way to Rainbow Falls. Downstream are Crooked Falls and the Grand Falls of the Missouri. Crooked Falls, as mentioned, is mostly in its natural state, except for an infill on its right side where the penstocks were constructed. Grand Falls is in a similar situation to Rainbow and Black Eagle falls. However, while Black Eagle and Grand Falls were half obliterated by the construction of power canals, Rainbow Falls remains virtually unaltered.
. Rainbow Falls and downstream Crooked Falls are the only two waterfalls on the Missouri-Mississippi river system to remain in an almost-natural condition. Black Eagle Falls and Great Falls
are half- occupied by their dams' powerhouses, and Colter Falls
is submerged. The waterfall received its name from the frequent presence of rainbows in its spray before the dams were built.
Meriwether Lewis was known to comment on the falls:
The waterfall was named "Beautiful Cascade" and later "Handsom[e] Falls" by Lewis, but was given its present name by Thomas B. Roberts, a railroad engineer, in 1872.
Waterfall
A waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.-Formation:Waterfalls are commonly formed when a river is young. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens...
on the Missouri River
Missouri River
The Missouri River flows through the central United States, and is a tributary of the Mississippi River. It is the longest river in North America and drains the third largest area, though only the thirteenth largest by discharge. The Missouri's watershed encompasses most of the American Great...
in Great Falls, Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, just upstream from Crooked Falls and downstream from Colter Falls
Colter Falls
Colter Falls, also Coulter Falls, waterfall, nearly in width, part of the Great Falls of the Missouri, on the Missouri River in north-central Montana. Downstream of Colter Falls lies Rainbow Falls, and upstream is Black Eagle Falls. The Lewis and Clark Expedition was known to discover Westslope...
and Rainbow Dam
Rainbow Dam
Rainbow Dam is a hydroelectric dam on the Missouri River, high and long, located six miles northeast of Great Falls in the U.S. state of Montana and just upstream of Rainbow Falls, a 45 ft waterfall that is the third of the five Great Falls of the Missouri. The dam, built in 1910, generates...
. It is 47 feet (14m) high and 1,320 feet (402.3m) wide. The waterfall is part of the five Great Falls of the Missouri. The river spills over a sheer ledge of sandstone in the Kootenai Formation
Kootenai Formation
The Kootenai Formation is a Mesozoic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.-See also:* List of dinosaur-bearing rock formations...
, forming the falls. The falls used to flow with a great deal of force year-round. In 1914 the river shortly upstream was dammed for hydroelectric power by the Rainbow Dam
Rainbow Dam
Rainbow Dam is a hydroelectric dam on the Missouri River, high and long, located six miles northeast of Great Falls in the U.S. state of Montana and just upstream of Rainbow Falls, a 45 ft waterfall that is the third of the five Great Falls of the Missouri. The dam, built in 1910, generates...
, which forms a run-of-the-river reservoir. As a result, the falls can almost totally dry up in the summer with only a few narrow strips of water trickling down its face. A railroad bridge crosses the river directly above the falls.
Description
Rainbow Falls varies widely - whether it is in full flow in the spring, or greatly diminished by the autumn. In peak flow in the springtime, the falls is much like its original form - especially on the right side where the outlet worksOutlet works
A set of outlet works is a device used to release and regulate water flow from a dam. Such devices usually consist of one or more pipes or tunnels through the embankment of the dam, directing water usually under high pressure to the river downstream...
of the dam are located, and on the left side where the main spillway
Spillway
A spillway is a structure used to provide the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed. In the UK they may be known as overflow channels. Spillways release floods so that the water does not overtop and damage or even destroy...
structure is positioned. The center section of the dam, which is also a spillway structure, only functions when the flow above the reservoir is too great. The left side of the falls is more heavily eroded
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
than the right side, and sits a little farther upstream. Expansive and arid hills rise above the canyon on each bank. Below the falls is a long, narrow plunge pool
Plunge pool
A plunge pool can be a natural hydrologic fluvial landform feature or a constructed recreational garden feature...
, and a series of gravel bars.
As the flow over the falls diminishes, usually from summer to early autumn, it splits into two parts hugging both banks. The flow at this point usually still extends across most (70 percent) of the full width of the river, but a section in the center remains dry except for a narrow stream of water that is found when the flow is low enough to separate it from the left-side drop, but high enough to feed it. The river below the falls remains mostly full. Much of the water is still diverted to generate power, but there is still enough water flow in the river to flow over the dam's spillways.
In the autumn, however, the majority of the river is diverted through penstock
Penstock
A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydraulic turbines and sewerage systems. It is a term that has been inherited from the technology of wooden watermills....
s around the right side of the falls. The penstocks continue downstream past 19-ft (5m) Crooked Falls, utilizing the combined drop of over 70 ft (21m) to generate hydroelectricity
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...
through 8 turbines. The falls themselves are reduced to a mere trickle. Some water still continues down the right side of the falls through a few parallel drops, trickling out of the river outlet works. On the right, there are also two drops, each around 10 ft (3m) wide at low flow. Also, water comes out of a pipe at the left bank side of the falls, and trickles into the river in a series of small waterfalls.
Upstream of Rainbow Falls lies Colter Falls
Colter Falls
Colter Falls, also Coulter Falls, waterfall, nearly in width, part of the Great Falls of the Missouri, on the Missouri River in north-central Montana. Downstream of Colter Falls lies Rainbow Falls, and upstream is Black Eagle Falls. The Lewis and Clark Expedition was known to discover Westslope...
and Black Eagle Falls; the former is buried under the reservoir formed by Rainbow Dam, while the latter is controlled by a dam in a similar way to Rainbow Falls. Downstream are Crooked Falls and the Grand Falls of the Missouri. Crooked Falls, as mentioned, is mostly in its natural state, except for an infill on its right side where the penstocks were constructed. Grand Falls is in a similar situation to Rainbow and Black Eagle falls. However, while Black Eagle and Grand Falls were half obliterated by the construction of power canals, Rainbow Falls remains virtually unaltered.
History
Rainbow Falls was first discovered by the Lewis and Clark ExpeditionLewis and Clark Expedition
The Lewis and Clark Expedition, or ″Corps of Discovery Expedition" was the first transcontinental expedition to the Pacific Coast by the United States. Commissioned by President Thomas Jefferson and led by two Virginia-born veterans of Indian wars in the Ohio Valley, Meriwether Lewis and William...
. Rainbow Falls and downstream Crooked Falls are the only two waterfalls on the Missouri-Mississippi river system to remain in an almost-natural condition. Black Eagle Falls and Great Falls
Ryan dam
Ryan Dam is a hydroelectric dam on the Missouri River, ten miles downstream from the city of Great Falls in the U.S. state of Montana. The dam is long and high; its reservoir is long and has a storage capacity of . It is a run-of-river dam. The dam is built on the largest of the five Great...
are half- occupied by their dams' powerhouses, and Colter Falls
Colter Falls
Colter Falls, also Coulter Falls, waterfall, nearly in width, part of the Great Falls of the Missouri, on the Missouri River in north-central Montana. Downstream of Colter Falls lies Rainbow Falls, and upstream is Black Eagle Falls. The Lewis and Clark Expedition was known to discover Westslope...
is submerged. The waterfall received its name from the frequent presence of rainbows in its spray before the dams were built.
Meriwether Lewis was known to comment on the falls:
The waterfall was named "Beautiful Cascade" and later "Handsom[e] Falls" by Lewis, but was given its present name by Thomas B. Roberts, a railroad engineer, in 1872.