I thought it might be useful to define a few things, so I’ve put together some scribble notes on related issues.
These comments are made without reference to a particular content that the object will hold, what material is used in manufacturing the object, the type of design or how it interacts with its environment.
Note that cattle manure is fairly watery, especially when mixed with urine. For contrast, horse manure tends to be relatively solid and clumps together.
The word ‘slurry’. I think that the general population might be more aware of the word being used in the manure context than in a mining / industrial context. The quote “Bob had to clean himself up after getting splashed by some slurry.” only conjures up an image of one type of slurry. In a mining / industrial context, I suspect slurries are mostly used for transporting or processing material, not storing it - most minerals would separate quite quickly from water if it was stored.
Slurry tanks and pits are used to store slurry, for use as fertiliser and/or biogas. Slurry can’t be used all-year round, as heavy rain will tend to wash it into waterways (causing pollution) and can’t be used when the weather is too dry (risk of chemical burns to crops).
Silo - container for storing bulk solids of a granular (gravel, grain) or powdered (cement, flour) nature.
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- Primary axis must be vertical.
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- Typically circular, octagonal or square on plan.
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- Must empty at the lowest point and typically has a funnel base. This means that most silos are wholly above ground.
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- Sizes and construction vary hugely.
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- Design will normally avoid having corners, where material may be trapped.
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- Typically fed with a conveyor, hoist or air-blown system.
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- Typically covered - may have a sloping roof.
There are other concepts that borrow the word ‘silo’, e.g. bunker silo.
Tank - container for storing bulk fluids (liquids and gases).
- Primary axis may be horizontal or vertical.
- Where the primary axis is horizontal, tanks with liquids tend to have planar vertical ends, whereas tanks with gases tend to have curved or domed ends.
- May be any shape, but larger tanks tend to be circular, whether on plan or cross-section.
- Typically has a flat or gently sloping base, sloping enough so that it can empty fully. May have a sump (a small area with a lower floor level). As fluids can be pumped, a tank can be underground. Tanks for gases can be fitted with inlets / outlets at any level and need not be emptied at the lowest point nor filled at the highest point.
- Sizes and construction vary hugely.
- Design will normally avoid having corners, where material may be trapped.
- Typically fed with a hose or pipe.
- May be covered, uncovered or sealed:
- Covered - has a roof.
- Uncovered / open - has no roof. Low cost construction and typically used for low value contents, e.g. rainwater.
- Sealed - tanks for gases need to be sealed to prevent the gas escaping.
Pit - hole in the ground. May rise marginally above ground level. May have a variety of uses, not just storage.
- Low cost construction and typically used for low value contents.
- May be covered or uncovered.
- If it is covered, then it might be a tank, not a pit. If it is sealed, then it is likely a tank, not a pit.
Silos and tanks should probably be rendered (yeah, I went there) like buildings - they have walls and a roof. Admittedly, this can be difficult argument with uncovered tanks, as they don’t have a roof. However, in day to day usage, most people can’t see whether a tank is covered or not, so I think they should probably be rendered the same. Some tanks are truly huge - the size of a stadium or bigger: Way: Whiddy Island Oil Terminal (1046578828) | OpenStreetMap - they aren’t minor objects that can be left off a general purpose map.
Pits that can’t be described as basins, salt pans, tailing ponds ……………… [my brain went blank] should probably be mapped as landforms, that is landuse=*, embankments, etc.
This means the contents of a slurry pit will tend to have a higher percentage of solids than municipal sewage. That said, cattle manure is fairly watery.