What Is A Dam Spillway?
Dams are important structures that are constructed to store water. This water, generally from a channel, can later be used for work involving electricity and irrigation. Dams are also critical in flood control. What is a dam spillway and why are they important?
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Although the majority of dams are built using high tech designs, some experience an overflow of water. If this occurs, the whole structure and design of the dam can become damaged. Therefore, excess water needs to be discharged successfully to avoid any potential disasters.
What Is A Dam Spillway?
What is a dam spillway? A spillway offers a way for the stored excess water to discharge. This is why most dams should be designed with at least one spillway. Whether water is required downstream or the stored water behind the dam has become overwhelming, just about every dam requires a spillway to safely discharge certain amounts of water.
Here at Gracon Industrial Construction, we specialize in providing hydroelectric constructions, dam constructions, piping services, food manufacturing and process, and electrical services for various government agencies and privately held companies.
Gracon has industry-leading capabilities which allow us to perform dam maintenance with our expert dam construction contractors. Our experts specialize in replacement and rehabilitation services for all sizes of dam mechanical equipment. Dam repair is what Gracon specializes in. Find out more about our services here.
A Dam Spillway Explained and the Different Types of Spillways
Designing dams would be more straightforward if environmental factors such as rainfall and snowmelt were consistent throughout the year. As a matter of fact, since most dams exist because of hydrologic variability, they wouldn’t be necessary if rainfall was consistent.
Dams exist to provide storage for water and to smooth out the varying nature of inflows. These structures protect us from flooding so the stored water can be used for different purposes during the year.
Those varying inflows are not always modest, however. Some can be gigantic with various watersheds generating the majority of their annual volume of water in just one storm event. In such a scenario, these inflows can race to a reservoir with little to no warning. Therefore, dams need to be ready to withstand and handle any major storms.
Because of each season’s variability in terms of weather, engineers can not predict the exact volume of floodwater due to melting snow and rainfall. Therefore, designing a dam for a specific discharge of water through its channel is nigh on impossible.
To combat this, spillways are included in most dams. If there is a sudden rise of water upstream of a dam, a spillway will allow the water to discharge through it and stop the dam from overflowing.
Spillways are made with the aid of a penstock and a large cross-sectional tube. A connection is made between the inlet of the spillway upstream and the outlet of the spillway downstream from the dam.
Spillways are classed into four distinct categories:
Overflow spillway
Chute spillway
Side-channel spillway
Limited service spillway
Each of these serves specific purposes for specific conditions. But, they all share the role of discharging water to inhibit any flooding from rising water levels. What is a dam spillway and different types? We’re explaining more here:
Overflow Spillway
An overflow spillway is typically used with concrete gravity dams. These are usually gated or ungated and allow water to overflow if it builds up behind the dam.
Chute Spillway
A chute spillway is usually constructed for earth or rock-filled dams. Nevertheless, some concrete dams also use chute spillways. If this is the case, the dam would typically be located in a small canyon where there wouldn’t be enough space for an overflow spillway.
You will generally find a chute spillway through the abutment. This is adjacent to the dam itself. It can also be located in a saddle, found a little away from the dam.
Side Channel Spillway
Side-channel spillways are used in similar circumstances to chute spillways. Compared to other spillways, a side-channel has a more unique shape. This allows it to be built on a narrow dam abutment.
In general, these spillways are ungated but they can be designed with gates if required.
Limited Service Spillways
A limited service spillway is designed if the spillway will only be operated infrequently and, when this occurs, damage is possible. However, this damage can not be so bad that it causes a catastrophic release of water from the reservoir.
Other types of spillways include:
Siphon spillway
Shaft spillway
Auxiliary spillway
Ogee spillway
Siphon Spillway
A siphon spillway works as the name suggests, like a siphon. These are built with a hood over a standard spillway which forms a conduit. When the reservoir’s water level rises, it will start to flow over the crest. This is regarded as an ogee spillway.
This flowing water creates tiny air bubbles. Once the air in the crest is removed, the siphon action begins. This type of spillway has a larger discharging capacity meaning more water can flow.
Shaft Spillway
This spillway uses a circular crest that is built into the surface of the reservoir. Here, the water flows over having been carried by a sloping or vertical tunnel that travels to a horizontal tunnel around the stream bed level. Eventually, this travels to the downstream side. Diversion tunnels constructed during the construction of the dam can later be used as the horizontal conduit in some cases.
Auxiliary Spillway
Most large dams are constructed with two spillways with one called the service spillway and the other the emergency spillway. The emergency spillway, also known as an auxiliary spillway, is operated when there is an excess flow of water located upstream of the channel.
Ogee Spillway
Ogee spillways are usually constructed in rigid dams. These form part of the main dam if there is enough length to do so.
What Is A Dam Spillway?
What Is A Dam Spillway?
Dams are important structures that are constructed to store water. This water, generally from a channel, can later be used for work involving electricity and irrigation. Dams are also critical in flood control. What is a dam spillway and why are they important?
Although the majority of dams are built using high tech designs, some experience an overflow of water. If this occurs, the whole structure and design of the dam can become damaged. Therefore, excess water needs to be discharged successfully to avoid any potential disasters.
What Is A Dam Spillway?
What is a dam spillway? A spillway offers a way for the stored excess water to discharge. This is why most dams should be designed with at least one spillway. Whether water is required downstream or the stored water behind the dam has become overwhelming, just about every dam requires a spillway to safely discharge certain amounts of water.
Here at Gracon Industrial Construction, we specialize in providing hydroelectric constructions, dam constructions, piping services, food manufacturing and process, and electrical services for various government agencies and privately held companies.
Gracon has industry-leading capabilities which allow us to perform dam maintenance with our expert dam construction contractors. Our experts specialize in replacement and rehabilitation services for all sizes of dam mechanical equipment. Dam repair is what Gracon specializes in. Find out more about our services here.
A Dam Spillway Explained and the Different Types of Spillways
Designing dams would be more straightforward if environmental factors such as rainfall and snowmelt were consistent throughout the year. As a matter of fact, since most dams exist because of hydrologic variability, they wouldn’t be necessary if rainfall was consistent.
Dams exist to provide storage for water and to smooth out the varying nature of inflows. These structures protect us from flooding so the stored water can be used for different purposes during the year.
Those varying inflows are not always modest, however. Some can be gigantic with various watersheds generating the majority of their annual volume of water in just one storm event. In such a scenario, these inflows can race to a reservoir with little to no warning. Therefore, dams need to be ready to withstand and handle any major storms.
Because of each season’s variability in terms of weather, engineers can not predict the exact volume of floodwater due to melting snow and rainfall. Therefore, designing a dam for a specific discharge of water through its channel is nigh on impossible.
To combat this, spillways are included in most dams. If there is a sudden rise of water upstream of a dam, a spillway will allow the water to discharge through it and stop the dam from overflowing.
Spillways are made with the aid of a penstock and a large cross-sectional tube. A connection is made between the inlet of the spillway upstream and the outlet of the spillway downstream from the dam.
Spillways are classed into four distinct categories:
Overflow spillway
Chute spillway
Side-channel spillway
Limited service spillway
Each of these serves specific purposes for specific conditions. But, they all share the role of discharging water to inhibit any flooding from rising water levels. What is a dam spillway and different types? We’re explaining more here:
Overflow Spillway
An overflow spillway is typically used with concrete gravity dams. These are usually gated or ungated and allow water to overflow if it builds up behind the dam.
Chute Spillway
A chute spillway is usually constructed for earth or rock-filled dams. Nevertheless, some concrete dams also use chute spillways. If this is the case, the dam would typically be located in a small canyon where there wouldn’t be enough space for an overflow spillway.
You will generally find a chute spillway through the abutment. This is adjacent to the dam itself. It can also be located in a saddle, found a little away from the dam.
Side Channel Spillway
Side-channel spillways are used in similar circumstances to chute spillways. Compared to other spillways, a side-channel has a more unique shape. This allows it to be built on a narrow dam abutment.
In general, these spillways are ungated but they can be designed with gates if required.
Limited Service Spillways
A limited service spillway is designed if the spillway will only be operated infrequently and, when this occurs, damage is possible. However, this damage can not be so bad that it causes a catastrophic release of water from the reservoir.
Other types of spillwaytypes of spillways include:
Siphon spillway
Shaft spillway
Auxiliary spillway
Ogee spillway
Siphon Spillway
A siphon spillway works as the name suggests, like a siphon. These are built with a hood over a standard spillway which forms a conduit. When the reservoir’s water level rises, it will start to flow over the crest. This is regarded as an ogee spillway.
This flowing water creates tiny air bubbles. Once the air in the crest is removed, the siphon action begins. This type of spillway has a larger discharging capacity meaning more water can flow.
Shaft Spillway
This spillway uses a circular crest that is built into the surface of the reservoir. Here, the water flows over having been carried by a sloping or vertical tunnel that travels to a horizontal tunnel around the stream bed level. Eventually, this travels to the downstream side. Diversion tunnels constructed during the construction of the dam can later be used as the horizontal conduit in some cases.
Auxiliary Spillway
Most large dams are constructed with two spillways with one called the service spillway and the other the emergency spillway. The emergency spillway, also known as an auxiliary spillway, is operated when there is an excess flow of water located upstream of the channel.
Ogee Spillway
Ogee spillways are usually constructed in rigid dams. These form part of the main dam if there is enough length to do so.
This is a modified version of a drop spillway. In this case, the spillway’s downstream profile coincides with the lower nappe’s shape of the flowing, falling water jet from the crested weir.
Explore more:Is there a code for hydraulic design of barrages?
Dam Spillway & Gracon Services
What is a dam spillway? As explained, the main function of a spillway is to control the overflow of water that is stored upstream of a dam in a reservoir. It is simply constructed to maintain the level of water in the reservoir.
Spillways control this level of water without the need for moving parts or mechanical devices. If the level of water reaches above the spillway, then it will automatically fall through the pool of the spillway and escape through the outlet.
However, on occasions, spillways will require maintenance in order to withstand and allow the safe flow of water.
Here at Gracon, we provide dam construction and maintenance services. In the last ten years alone, Gracon has replaced or repaired over 100 gates in dams. Our team is one of the most knowledgeable and experienced throughout the entire United States. Our expert crews draw on years of project experiences to solve some of the most complicated and technical problems that arise with the complex nature of dams.
Gracon, dam construction company, provides solutions.
Spillway | Definition, Importance, Types, Design, & Facts
spillway, passage for surplus water over or around a dam when the reservoir itself is full. Spillways are particularly important safety features for several types of dams. They may lead over the dam or a portion of it or along a channel around the dam or a conduit through it, and the erosive energy of the water at the foot of the spillway is dissipated away from the foundation.
Serious consequences can follow if a dam is overtopped. Disaster is likely in the case of an earthfill, or embankment, dam that was not designed to permit uncontrolled flow of water on its downstream slope. In the case of an inadequate or missing spillway, overtopping can dramatically erode such dams and their foundations, possibly leading to a catastrophic failure. Indeed, inadequate spillway capacity has been a problem for many older earthen dams built before modern flood data became available. Spillage over a concrete gravity dam is also serious, because the floodwater erodes the foundation at the downstream toe. Arch dams possess greater resistance to failure after overtopping.
More From Britannica
dam: Spillways
Four general aspects of spillways are worth noting. First, the uncontrolled discharge of surplus water past the dam should be automatic and not dependent upon human control. Second, the spillway intake should be wide enough so that the largest floods can pass without increasing the water level in the reservoir enough to cause a nuisance to upstream property owners. Third, the rate of floodwater discharge should not increase much above that experienced before the construction of the dam. An increase in discharge can cause flood problems downstream, but a dam usually reduces the peak discharge rate because of the lag effect caused by a flood passing through the reservoir. Fourth, floodwater discharged over the height of a dam can be destructive to the dam structure itself and to the riverbed unless its energy is controlled and dissipated in harmless turbulence.
Grand Coulee Dam
Grand Coulee Dam is a hydroelectric power station on the Columbia River in Washington state.
With earthfill dams, a separate spillway structure is normally constructed to one side of the dam. With concrete gravity dams, the sloping downstream face of the structure can often serve as the basis for the spillway. Water flowing down a spillway can travel at very high speeds—about 160 km (100 miles) per hour in the case of a dam 100 metres (330 feet) high—and form a standing wave where it enters the riverbed; it proceeds downstream at lower mean velocity but in a highly turbulent state. Grand Coulee Dam in Washington state utilizes a spillway of this type. An obstruction known as a kicker, placed at the toe of the dam to project the water slightly upward, can move farther downstream the area in which erosion of the riverbed is most intense. With higher dams it is possible to deflect the jet of spilling water from a level above the base of the dam; this is known as a ski-jump spillway.
Spillways need not be open to the atmosphere. Shaft and tunnel spillways can carry the water away to a point downstream of the dam. At the upstream end, the intake can be self-priming siphons or bell-mouthed drop shafts; the latter are also known as morning-glory spillways.
Kariba Dam
Kariba Dam, an arch dam on the Zambezi River at the border between Zambia and Zimbabwe.
With arch dams it is convenient to construct gated openings in the shell structure at some distance below the crest of the dam, ensuring that the discharging jets fall well clear downstream. A line of six such floodgates is used in the design of Kariba Dam between Zambia and Zimbabwe.
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Spillways constructed to one side of earthen dams are featured in the design of Oroville Dam in California and of Mangla Dam in Pakistan. The spillway at Mangla discharges 28,000 cubic metres (36,600 cubic yards) of water per second; the upper stilling basin has the dimensions of an Olympic Games stadium, including its grandstands.
This is a modified version of a drop spillway. In this case, the spillway’s downstream profile coincides with the lower nappe’s shape of the flowing, falling water jet from the crested weir.
Dam Spillway & Gracon Services
What is a dam spillway? As explained, the main function of a spillway is to control the overflow of water that is stored upstream of a dam in a reservoir. It is simply constructed to maintain the level of water in the reservoir.
Spillways control this level of water without the need for moving parts or mechanical devices. If the level of water reaches above the spillway, then it will automatically fall through the pool of the spillway and escape through the outlet.
However, on occasions, spillways will require maintenance in order to withstand and allow the safe flow of water.
Here at Gracon, we provide dam construction and maintenance services. In the last ten years alone, Gracon has replaced or repaired over 100 gates in dams. Our team is one of the most knowledgeable and experienced throughout the entire United States. Our expert crews draw on years of project experiences to solve some of the most complicated and technical problems that arise with the complex nature of dams.
Gracon, dam construction company, provides solutions.
spillway, passage for surplus water over or around a dam when the reservoir itself is full. Spillways are particularly important safety features for several types of dams. They may lead over the dam or a portion of it or along a channel around the dam or a conduit through it, and the erosive energy of the water at the foot of the spillway is dissipated away from the foundation.
Serious consequences can follow if a dam is overtopped. Disaster is likely in the case of an earthfill, or embankment, dam that was not designed to permit uncontrolled flow of water on its downstream slope. In the case of an inadequate or missing spillway, overtopping can dramatically erode such dams and their foundations, possibly leading to a catastrophic failure. Indeed, inadequate spillway capacity has been a problem for many older earthen dams built before modern flood data became available. Spillage over a concrete gravity dam is also serious, because the floodwater erodes the foundation at the downstream toe. Arch dams possess greater resistance to failure after overtopping.
More From Britannica
dam: Spillways
Four general aspects of spillways are worth noting. First, the uncontrolled discharge of surplus water past the dam should be automatic and not dependent upon human control. Second, the spillway intake should be wide enough so that the largest floods can pass without increasing the water level in the reservoir enough to cause a nuisance to upstream property owners. Third, the rate of floodwater discharge should not increase much above that experienced before the construction of the dam. An increase in discharge can cause flood problems downstream, but a dam usually reduces the peak discharge rate because of the lag effect caused by a flood passing through the reservoir. Fourth, floodwater discharged over the height of a dam can be destructive to the dam structure itself and to the riverbed unless its energy is controlled and dissipated in harmless turbulence.
Grand Coulee Dam
Grand Coulee Dam is a hydroelectric power station on the Columbia River in Washington state.
With earthfill dams, a separate spillway structure is normally constructed to one side of the dam. With concrete gravity dams, the sloping downstream face of the structure can often serve as the basis for the spillway. Water flowing down a spillway can travel at very high speeds—about 160 km (100 miles) per hour in the case of a dam 100 metres (330 feet) high—and form a standing wave where it enters the riverbed; it proceeds downstream at lower mean velocity but in a highly turbulent state. Grand Coulee Dam in Washington state utilizes a spillway of this type. An obstruction known as a kicker, placed at the toe of the dam to project the water slightly upward, can move farther downstream the area in which erosion of the riverbed is most intense. With higher dams it is possible to deflect the jet of spilling water from a level above the base of the dam; this is known as a ski-jump spillway.
Spillways need not be open to the atmosphere. Shaft and tunnel spillways can carry the water away to a point downstream of the dam. At the upstream end, the intake can be self-priming siphons or bell-mouthed drop shafts; the latter are also known as morning-glory spillways.
Kariba Dam
Kariba Dam, an arch dam on the Zambezi River at the border between Zambia and Zimbabwe.
With arch dams it is convenient to construct gated openings in the shell structure at some distance below the crest of the dam, ensuring that the discharging jets fall well clear downstream. A line of six such floodgates is used in the design of Kariba Dam between Zambia and Zimbabwe.
Special 30% offer for students! Finish the semester strong with Britannica.
Learn More
Spillways constructed to one side of earthen dams are featured in the design of Oroville Dam in California and of Mangla Dam in Pakistan. The spillway at Mangla discharges 28,000 cubic metres (36,600 cubic yards) of water per second; the upper stilling basin has the dimensions of an Olympic Games stadium, including its grandstands.
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