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29-404: The Terror Lake main dam is 2100 feet long and 156 feet high and is a rockfill dam faced with concrete. A spillway with a 600-foot crest is adjacent to the north side of the dam. The lake acts as a reservoir with a surface area of 850 acres. It can store 78,000 acre-feet of water at a lake surface elevation of 1383 feet. The power tunnel is 10 feet in diameter and extends 26,300 feet from the dam to

58-643: A steel structure or a concrete block. Under normal flow conditions the water will spill over the fuse plug and down the spillway. In high flood conditions, where the water velocity may be so high that the dam itself may be put in danger, the fuse plug simply washes away, and the flood waters safely spill over the dam. Fuse plugs are used in many dams throughout the world. For example, the Warragamba Dam in New South Wales has fuse plugs that are approximately 14m high. This article about

87-443: A baffle of concrete blocks but usually have a "flip lip" and/or dissipator basin, which creates a hydraulic jump , protecting the toe of the dam from erosion. Stepped channels and spillways have been used for over 3,000 years. Despite being superseded by more modern engineering techniques such as hydraulic jumps in the mid twentieth century, since around 1985 interest in stepped spillways and chutes has been renewed, partly due to

116-565: A plunge pool, or two ski jumps can direct their water discharges to collide with one another. Third, a stilling basin at the terminus of a spillway serves to further dissipate energy and prevent erosion. They are usually filled with a relatively shallow depth of water and sometimes lined with concrete. A number of velocity-reducing components can be incorporated into their design to include chute blocks, baffle blocks, wing walls, surface boils, or end sills. Spillway gates may operate suddenly without warning, under remote control. Trespassers within

145-404: A spillway gate can result in the stranding of fish, and this is usually avoided. Fuse plug A fuse plug is a collapsible dam installed on spillways in dams to increase the dam's capacity. The principle behind the fuse plug is that the majority of water that overflows a dam's spillway can be safely dammed except in high flood conditions. The fuse plug may be a sand-filled container,

174-507: Is a structure used to control water release on a routine basis for purposes such as water supply and hydroelectricity generation. A spillway is located at the top of the reservoir pool. Dams may also have bottom outlets with valves or gates which may be operated to release flood flow, and a few dams lack overflow spillways and rely entirely on bottom outlets. The two main types of spillways are controlled and uncontrolled. A controlled spillway has mechanical structures or gates to regulate

203-460: Is designed like an inverted bell , where water can enter around the entire perimeter. These uncontrolled spillways are also called morning glory (after the flower ), or glory hole spillways. In areas where the surface of the reservoir may freeze, this type of spillway is normally fitted with ice-breaking arrangements to prevent the spillway from becoming ice-bound. Some bell-mouth spillways are gate-controlled. The highest morning glory spillway in

232-443: Is set by dam safety guidelines, based on the size of the structure and the potential loss of human life or property downstream. The United States Army Corps of Engineers bases their requirements on the probable maximum flood (PMF) and the probable maximum precipitation (PMP). The PMP is the largest precipitation thought to be physically possible in the upstream watershed. Dams of lower hazard may be allowed to have an IDF less than

261-486: The penstock , from an inlet 143 feet below the nominal surface of the lake. The penstock that connects the power tunnel to the powerhouse is steel-lined and runs for 3,400 feet, varying from 56 to 96 inches in diameter. The station discharges water to the Kizhuyak River. Other civil works for the project include several dikes, smaller dams and diversion channels to collect water into the lake. A 17-mile private road

290-463: The PMF. As water passes over a spillway and down the chute, potential energy converts into increasing kinetic energy . Failure to dissipate the water's energy can lead to scouring and erosion at the dam's toe (base). This can cause spillway damage and undermine the dam's stability. To put this energy in perspective, the spillways at Tarbela Dam could, at full capacity, produce 40,000 MW; about 10 times

319-407: The capacity of its power plant. The energy can be dissipated by addressing one or more parts of a spillway's design. First, on the spillway surface itself by a series of steps along the spillway (see stepped spillway ). Second, at the base of a spillway, a flip bucket can create a hydraulic jump and deflect water upwards. A ski jump can direct water horizontally and eventually down into

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348-437: The dam down a smooth decline into the river below. These are usually designed following an ogee curve . Most often, they are lined on the bottom and sides with concrete to protect the dam and topography. They may have a controlling device and some are thinner and multiply-lined if space and funding are tight. In addition, they are not always intended to dissipate energy like stepped spillways. Chute spillways can be ingrained with

377-414: The difference in height between the intake and the outlet to create the pressure difference required to remove excess water. Siphons require priming to remove air in the bend for them to function, and most siphon spillways are designed to use water to automatically prime the siphon. One such design is the volute siphon, which employs volutes or fins on a funnel to form water into a vortex that draws air out of

406-405: The electrical rates for the city of Kodiak, since this displaces most of the oil that would otherwise be consumed by diesel generator sets. 57°41′09″N 152°53′42″W  /  57.68583°N 152.89500°W  / 57.68583; -152.89500 Spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee , typically into

435-576: The fish canning season. Kodiak Electric also operates six 1.5 MW wind turbines . Since the network is isolated from the North American grid , a 3 megawatt battery bank was also purchased to help stabilize system frequency on sudden changes of load or sudden shifts in wind. It is the stated objective of the Kodiak co-op to obtain 95% of their electrical energy from renewable sources by 2020. The low cost of power generated by Terror Lake has stabilized

464-423: The flood is sometimes expressed as a return period . A 100-year recurrence interval is the flood magnitude expected to be exceeded on the average of once in 100 years. This parameter may be expressed as an exceedance frequency with a 1% chance of being exceeded in any given year. The volume of water expected during the design flood is obtained by hydrologic calculations of the upstream watershed. The return period

493-424: The rate of flow. This design allows nearly the full height of the dam to be used for water storage year-round, and flood waters can be released as required by opening one or more gates. An uncontrolled spillway, in contrast, does not have gates; when the water rises above the lip or crest of the spillway, it begins to be released from the reservoir. The rate of discharge is controlled only by the height of water above

522-461: The reservoir is full, operators can prevent an unacceptably large release later. Other uses of the term "spillway" include bypasses of dams and outlets of channels used during high water, and outlet channels carved through natural dams such as moraines . Water normally flows over a spillway only during flood periods, when the reservoir has reached its capacity and water continues entering faster than it can be released. In contrast, an intake tower

551-431: The reservoir's spillway. The fraction of storage volume in the reservoir above the spillway crest can only be used for the temporary storage of floodwater; it cannot be used as water supply storage because it sits higher than the dam can retain it. In an intermediate type, normal level regulation of the reservoir is controlled by the mechanical gates. In this case, the dam is not designed to function with water flowing over

580-459: The river downstream. One parameter of spillway design is the largest flood it is designed to handle. The structures must safely withstand the appropriate spillway design flood (SDF), sometimes called the inflow design flood (IDF). The magnitude of the SDF may be set by dam safety guidelines, based on the size of the structure and the potential loss of human life or property downstream. The magnitude of

609-473: The riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels . Spillways ensure that water does not damage parts of the structure not designed to convey water. Spillways can include floodgates and fuse plugs to regulate water flow and reservoir level. Such features enable a spillway to regulate downstream flow—by releasing water in a controlled manner before

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638-414: The spillway are at high risk of drowning. Spillways are usually fenced and equipped with locked gates to prevent casual trespassing within the structure. Warning signs, sirens, and other measures may be in place to warn users of the downstream area of sudden release of water. Operating protocols may require "cracking" a gate to release a small amount of water to warn persons downstream. The sudden closure of

667-438: The spillway gates. Although many months may be needed for construction crews to restore the fuse plug and channel after such an operation, the total damage and cost to repair is less than if the main water-retaining structures had been overtopped. The fuse plug concept is used where building a spillway with the required capacity would be costly. A chute spillway is a common and basic design that transfers excess water from behind

696-424: The system. The priming happens automatically when the water level rises above the inlets. The ogee crest over-tops a dam, a side channel wraps around the topography of a dam, and a labyrinth uses a zig-zag design to increase the sill length for a thinner design and increased discharge. A drop inlet resembles an intake for a hydroelectric power plant, and transfers water from behind the dam directly through tunnels to

725-414: The top if it, either due to the materials used for its construction or conditions directly downstream. If inflow to the reservoir exceeds the gate's capacity, an artificial channel called an auxiliary or emergency spillway will convey water. Often, that is intentionally blocked by a fuse plug . If present, the fuse plug is designed to wash out in case of a large flood, greater than the discharge capacity of

754-474: The use of new construction materials (e.g. roller-compacted concrete , gabions ) and design techniques (e.g. embankment overtopping protection). The steps produce considerable energy dissipation along the chute and reduce the size of the required downstream energy dissipation basin. Research is still active on the topic, with newer developments on embankment dam overflow protection systems, converging spillways and small weir design. A bell-mouth spillway

783-695: The world is at Hungry Horse Dam in Montana, U.S., and is controlled by a 64-by-12-foot (19.5 by 3.7 m) ring gate. The bell-mouth spillway in Covão dos Conchos reservoir in Portugal is constructed to look like a natural formation. The largest bell-mouth spillway is in Geehi Dam , in New South Wales, Australia, measuring 105 ft (32 m) in diameter at the lake's surface. A siphon uses

812-640: Was licensed in 1981 for a term of 50 years. The project is located within the Kodiak National Wildlife Refuge ; environmental studies were carried out before construction, to evaluate impact on the Kodiak bear . Principal loads for the utility are the city of Kodiak, Alaska (and adjacent unincorporated suburbs), and the U.S. Coast Guard base (and adjacent Kodiak Airport ). The hydroelectric plant replaced earlier diesel engine generators , which are now used only for peak loads during

841-543: Was built between the barge landing site at the head of Kizhuyak Bay to the powerhouse. Major equipment and materials arrive by landing craft at the beach, and then are hauled up the private road. A 17-mile transmission line energized at 138 kV connects the switchyard near the powerhouse to the substation at the City of Kodiak. The project was initially constructed by the State of Alaska for US $ 230,000,000 in 1985. The project

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