Flow channels work by using gravity to allow slurry to flow from under cattle to a store outside the shed. They are more complicated than having an 8ft-deep tank under the slats but there are scenarios where they have a role and offer savings in the cost of building or labour:
Where a farmer wants to build a large-scale, cost-effective store in the form of a lined lagoon or overground tank. With this in place, any subsequent sheds can empty their slurry into it.Where there is already large existing slurry storage on the farm. Directing the slurry from any new shed into this store saves the cost of building tanks under the shed.More unusually, where the presence of bedrock or a high water table would make it costly to dig down for new underground tanks.Where an existing bedded shed is converted to slats to end use of bedding, etc.There are examples of all of the above on Irish farms. In most cases, flow channels are used in conjunction with a lagoon or overground store.
Usually, a flow channel will empty directly into a lagoon, availing of the fact that a lagoon is at least partly underground and below the shed floor and, overall, making for a simple system. Where the slurry ends up in an overground tank, the flow channel will usually feed into a reception tank from which slurry will be pumped into the store.
I recently featured a set up in Co Meath where – by raising the site about 20ft – a parlour and cubicle house were built above the nearby overground tank, allowing dairy washings and slurry flow directly into the store without need of pumps or a reception tank. Once working properly, channels have advantages:
They reduce building costs. They can operate automatically and reduce labour.No in-shed agitation.Design
Flow channels have to be carefully designed and need management. You’re trying to get a semi-solid mix of dung and urine to flow. If moisture is lost, the material quickly becomes stiffer and adheres strongly to concrete. Blockages can and will happen.
A flow channel works by trapping a shallow bed of liquid slurry behind a low dam wall (see figure 1). A wedge of slurry builds up on top of the pool and gradually flows over the wall and onwards. After a few weeks of cattle housing, this hill becomes sloped: it’s lowest where the slurry is slipping over the dam wall, a bit higher at the far end of the channel. Some points are:
The weight of the slurry at the high end pushes a flow over the dam wall at the other end. When the flow channel is working well, the slurry settles to a stable slope. For cattle slurry in Irish sheds, this is typically a slope of 1.5% to 2%. For drier, more stiff slurry, the slope will be steeper – more weight is required to push material over the edge of the dam walls.The floor of a slurry channel should be flat. It’s the incline on the mass of slurry that gives a flow. The trapped pool of liquid slurry at the bottom of the channel acts as a lubricant layer. It allows the mass of slurry above it to slide slowly along the channel. Without this trapped pool, the slurry would stick to the concrete floor of the channel. The stiffness of cattle slurry can vary, depending on diet. Cattle fed on grass silage with low or moderate levels of concentrates will produce a relatively liquid slurry mixture. Cattle fed on hay, haylage and/or high levels of concentrate will produce drier slurry that is slower to flow and that, in a flow channel, will sit at a steeper slope.The dam wall is generally recommended to be 6in to 9in in height. It runs across the full width of the channel, typically 1m to 1.5m. Given that slurry must be pushed over the dam wall, its top should be rounded or edged. The dam wall itself can be narrow. Slurry will slide more readily over a 2in-wide wall than one that is 6in wide. The length of a channel has to be taken into account. This is best shown by some examples. If a channel is 40ft (12m) long and the slurry under cattle settles at 2%, the bed of slurry will be 10in higher at the end furthest from the dam wall. If the channel is a lengthy 80ft (25m), the bed of slurry will be 20in high at its furthest end.Now take drier slurry from cattle on a high concentrate diet which stabilises at a 3% slope. In a 40ft channel, the slurry bed will be 14in high at the furthest end. On an 80ft channel, the top of the slurry will be 29in high.The depth of a slurry channel is therefore determined by its length. For a longer run, the bed of slurry will be higher at its high end, so the floor needs to be lower. A 250mm (10in) freeboard (safety space) must be left between the top of the slurry bed and the underside of the slats. If building a new shed, it is best to build it for a 3% fall – that should cater for times when the slurry is a bit drier.If 3% is chosen as the target slope, the depth of the floor can be calculated by a simple formula: Freeboard (mm) + [length (mm) x 0.03] = depth of channel floor below shed floor.The maximum length for a flow channel is recommended to be 25m. If slopes permit a flow channel can feed into another, lower one. The second channel will generally be 1-3ft lower than the first one.A minimum channel width of 1m is generally recommended. Small width increases the risk of blockage by dry slurry sticking to the side walls. Any wider than 1m brings little advantage but raises the building cost. In dairy cubicle sheds, automatic scrapers can be used to bring slurry down standing and feed passages to a flow chamber at one end of the shed.
On dairy farms, the parlour washings can be also be directed into the flow chamber and this will help give a reliable flow. These further dilute the slurry and make it more liquid.
Some flow channels will work continuously without blockages or other problems. They have been well designed, are not too long and catch liquid slurry, possibly with the added help of dairy washings. However, many flow channels need maintenance. This is usually done by flushing out the channel with a large volume of water, typically using the slurry tanker. I spoke to one farmer who installed a hose access point at the start of his channel to allow him flush it out easily. A channel may not work properly because it wasn’t designed or built correctly or because the slurry entering is too dry.It is advised to fill the pool at the bottom of the channel every autumn with water before cattle are housed. This is to make sure slurry doesn’t stick to the concrete of the channel floor. It is generally advised that you should wash out the bottom of a flow channel every second or third year before the start of housing. This is to remove slurry sticking to the floor of the channel or its side walls.If a channel floor is leaking or if the dam wall leaks, the trapped pool of liquid slurry could disappear to be replaced by drier slurry. It will be a less efficient lubricant and flow of slurry over the dam wall may halt.Flow in a channel may be affected by drying winds or by freezing temperatures. Some farmers have had to hang a curtain over the mouth of a flow channel to keep out the wind. Troubleshooting a blocked flow channel
If a flow channel does not work properly and slurry backs up under the slats, there are some basic points you should consider:
Is the slurry too dry? Cattle on high concentrate levels, on hay or dry haylage will produce relatively dry slurry. Is bedding material getting into the slurry channel? This could include straw, sawdust, lime, etc. Is airflow (a breeze) speeding up evaporation and drying out the slurry? It could be enough to reduce the flow over the dam wall and cause backing up. Adding water may be required to address the above issues. Was the channel flushed out before housing? Was the bed of the channel filled with water? Could it be leaking, possibly at the edge of the dam wall?How wide is the dam wall? Slurry will flow more readily over a 2in, rounded or edged wall than over a 4in wide, flat topped wall.Flow channels require careful design but can reduce building cost.They can reduce labour in winter and mean no in-shed agitation of slurry.Floor of channel must be level.Dam wall is six inches high.Fill bottom with water before housing.It acts as a lubricant – slurry wedge slides on top.Flush out every third summer with slurry tanker.Install an access point for tanker hose at top end of channel.
Flow channels work by using gravity to allow slurry to flow from under cattle to a store outside the shed. They are more complicated than having an 8ft-deep tank under the slats but there are scenarios where they have a role and offer savings in the cost of building or labour:
Where a farmer wants to build a large-scale, cost-effective store in the form of a lined lagoon or overground tank. With this in place, any subsequent sheds can empty their slurry into it.Where there is already large existing slurry storage on the farm. Directing the slurry from any new shed into this store saves the cost of building tanks under the shed.More unusually, where the presence of bedrock or a high water table would make it costly to dig down for new underground tanks.Where an existing bedded shed is converted to slats to end use of bedding, etc.There are examples of all of the above on Irish farms. In most cases, flow channels are used in conjunction with a lagoon or overground store.
Usually, a flow channel will empty directly into a lagoon, availing of the fact that a lagoon is at least partly underground and below the shed floor and, overall, making for a simple system. Where the slurry ends up in an overground tank, the flow channel will usually feed into a reception tank from which slurry will be pumped into the store.
I recently featured a set up in Co Meath where – by raising the site about 20ft – a parlour and cubicle house were built above the nearby overground tank, allowing dairy washings and slurry flow directly into the store without need of pumps or a reception tank. Once working properly, channels have advantages:
They reduce building costs. They can operate automatically and reduce labour.No in-shed agitation.Design
Flow channels have to be carefully designed and need management. You’re trying to get a semi-solid mix of dung and urine to flow. If moisture is lost, the material quickly becomes stiffer and adheres strongly to concrete. Blockages can and will happen.
A flow channel works by trapping a shallow bed of liquid slurry behind a low dam wall (see figure 1). A wedge of slurry builds up on top of the pool and gradually flows over the wall and onwards. After a few weeks of cattle housing, this hill becomes sloped: it’s lowest where the slurry is slipping over the dam wall, a bit higher at the far end of the channel. Some points are:
The weight of the slurry at the high end pushes a flow over the dam wall at the other end. When the flow channel is working well, the slurry settles to a stable slope. For cattle slurry in Irish sheds, this is typically a slope of 1.5% to 2%. For drier, more stiff slurry, the slope will be steeper – more weight is required to push material over the edge of the dam walls.The floor of a slurry channel should be flat. It’s the incline on the mass of slurry that gives a flow. The trapped pool of liquid slurry at the bottom of the channel acts as a lubricant layer. It allows the mass of slurry above it to slide slowly along the channel. Without this trapped pool, the slurry would stick to the concrete floor of the channel. The stiffness of cattle slurry can vary, depending on diet. Cattle fed on grass silage with low or moderate levels of concentrates will produce a relatively liquid slurry mixture. Cattle fed on hay, haylage and/or high levels of concentrate will produce drier slurry that is slower to flow and that, in a flow channel, will sit at a steeper slope.The dam wall is generally recommended to be 6in to 9in in height. It runs across the full width of the channel, typically 1m to 1.5m. Given that slurry must be pushed over the dam wall, its top should be rounded or edged. The dam wall itself can be narrow. Slurry will slide more readily over a 2in-wide wall than one that is 6in wide. The length of a channel has to be taken into account. This is best shown by some examples. If a channel is 40ft (12m) long and the slurry under cattle settles at 2%, the bed of slurry will be 10in higher at the end furthest from the dam wall. If the channel is a lengthy 80ft (25m), the bed of slurry will be 20in high at its furthest end.Now take drier slurry from cattle on a high concentrate diet which stabilises at a 3% slope. In a 40ft channel, the slurry bed will be 14in high at the furthest end. On an 80ft channel, the top of the slurry will be 29in high.The depth of a slurry channel is therefore determined by its length. For a longer run, the bed of slurry will be higher at its high end, so the floor needs to be lower. A 250mm (10in) freeboard (safety space) must be left between the top of the slurry bed and the underside of the slats. If building a new shed, it is best to build it for a 3% fall – that should cater for times when the slurry is a bit drier.If 3% is chosen as the target slope, the depth of the floor can be calculated by a simple formula: Freeboard (mm) + [length (mm) x 0.03] = depth of channel floor below shed floor.The maximum length for a flow channel is recommended to be 25m. If slopes permit a flow channel can feed into another, lower one. The second channel will generally be 1-3ft lower than the first one.A minimum channel width of 1m is generally recommended. Small width increases the risk of blockage by dry slurry sticking to the side walls. Any wider than 1m brings little advantage but raises the building cost. In dairy cubicle sheds, automatic scrapers can be used to bring slurry down standing and feed passages to a flow chamber at one end of the shed.
On dairy farms, the parlour washings can be also be directed into the flow chamber and this will help give a reliable flow. These further dilute the slurry and make it more liquid.
Some flow channels will work continuously without blockages or other problems. They have been well designed, are not too long and catch liquid slurry, possibly with the added help of dairy washings. However, many flow channels need maintenance. This is usually done by flushing out the channel with a large volume of water, typically using the slurry tanker. I spoke to one farmer who installed a hose access point at the start of his channel to allow him flush it out easily. A channel may not work properly because it wasn’t designed or built correctly or because the slurry entering is too dry.It is advised to fill the pool at the bottom of the channel every autumn with water before cattle are housed. This is to make sure slurry doesn’t stick to the concrete of the channel floor. It is generally advised that you should wash out the bottom of a flow channel every second or third year before the start of housing. This is to remove slurry sticking to the floor of the channel or its side walls.If a channel floor is leaking or if the dam wall leaks, the trapped pool of liquid slurry could disappear to be replaced by drier slurry. It will be a less efficient lubricant and flow of slurry over the dam wall may halt.Flow in a channel may be affected by drying winds or by freezing temperatures. Some farmers have had to hang a curtain over the mouth of a flow channel to keep out the wind. Troubleshooting a blocked flow channel
If a flow channel does not work properly and slurry backs up under the slats, there are some basic points you should consider:
Is the slurry too dry? Cattle on high concentrate levels, on hay or dry haylage will produce relatively dry slurry. Is bedding material getting into the slurry channel? This could include straw, sawdust, lime, etc. Is airflow (a breeze) speeding up evaporation and drying out the slurry? It could be enough to reduce the flow over the dam wall and cause backing up. Adding water may be required to address the above issues. Was the channel flushed out before housing? Was the bed of the channel filled with water? Could it be leaking, possibly at the edge of the dam wall?How wide is the dam wall? Slurry will flow more readily over a 2in, rounded or edged wall than over a 4in wide, flat topped wall.Flow channels require careful design but can reduce building cost.They can reduce labour in winter and mean no in-shed agitation of slurry.Floor of channel must be level.Dam wall is six inches high.Fill bottom with water before housing.It acts as a lubricant – slurry wedge slides on top.Flush out every third summer with slurry tanker.Install an access point for tanker hose at top end of channel. 
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