Why did coaling towers have raised delivery tracks?

[nickelplate759]

Often I see coaling towers (on model railroads, I don't often see them in the wild) where the coal deliver track is slightly elevated relative to the engine servicing tracks.  I'm wondering why, and how common the practice was.   Was it simply to avoid having to dig underground to make room for an unloading bin?

In case it isn't clear what I'm referring to, it's the rear (raised) track in this picture of the  Walthers Concrete Coaling Tower (that I wish they offered in N-scale):

[Chris333]

I'd look for real prototype photos instead of models.  I have no idea why the track is raised.

No elevation here:
http://4.bp.blogspot.com/-MTtfRJp43Og/UOl4_i3BdBI/AAAAAAAAAj8/f3mbR17DDRY/s1600/Alkem+coal+dock+diiorama.jpg

Elevation here:
http://www.trainweb.org/oldtimetrains/photos/cnr_facilities/coal_tower_Beeton.jpg

Little elevation here:
https://c1.staticflickr.com/8/7232/7181574469_a4691329c7_k.jpg

[nickelplate759]

Hmm - the CN tower looks like they raised the track enough that they didn't have to dig to make room for the unloading hopper, but the Cedar Hill tower drawing clearly shows an elevated track and a below-grade unloading hopper.  That's a big tower!

[nkalanaga]

I suspect that, in some areas, it was partly to avoid having the unloading pit flood in wet weather.  For a modern coaling tower, with power machinery, digging a pit wouldn't be any harder than digging the holes for the tower foundation.

[Ed Kapuscinski]

I'm not sure, but I have a theory... many of these towers were essentially "stock" items from manufacturers. If that were the case, my bet would be that they did this so that they only had to design the hoist machinery once, for one height (starting at 0 elevation).

[thomasjmdavis]

Since we are talking theories, my own theory is that it may have been the simplest and cheapest way to expand the capacity of an existing pit when a higher capacity tower was installed, or when the railroad upgraded to larger hoppers.

[nkalanaga]

Both also good theories.  As many different tower designs as there were, I'd imagine that there were also a lot of reasons.

[narrowminded]

Standardized design that can be installed just about anywhere that you can make a level spot, installation ease, flooding potential, and especially ease of equipment maintenance/ replacement being at or just above grade.  I would suggest it's just good engineering practice given that set of design parameters.