The eternal question.
There is no black and white rule here. Like some of the other parameters, it depends on the particulars of the crossing / site in question.
My (Tom Taggart, NHGS) interpretation of the difference boils down to the answer to this question:
- Is the portion of the culvert we are looking at, and trying to determine if it is a wingwall versus simply a headwall, large enough or structured/situated in such a way to direct (or significantly impact) the direction of water flowing through the crossing? Is it having an impact on this direction of flow at low flows? And possibly at high flows as well?
- Secondly, the presence of wingwalls doesn't go into GC or AOP, but might be used in the hydraulic capacity modeling - take your best stab at determining if their are or are not wingwalls and move on. Don't waste a ton of time in the field trying to sort out whether you have just a headwall or a headwall with wingwalls, or almost no headwall with some wingwalls (which happens with some box culverts) and move on. It can be sorted out in QAQC.
Box culvert with 45 degree wingwalls. Small headwall - box culverts typically have small to non-existent headwalls.
A box culvert that is surrounded by so much armored road fill, that we would consider this to have 90 degree wingwalls, as at high flow periods, water will be slamming into the large concrete blocks on either side of the box culverts main conduit.
This is a crazy situation where bank armoring runs right up to the edge of the crossing - this stream is completely channelized - and the armoring flares at a certain distance away from the structure. so, in essence, this has both armoring, and wingwalls, and the wing walls have different angles at different extents from the upstream inlet of the crossing. I would accept both 45 degree wingwalls or 0 degree wingwalls, and hopefully the assessor took a decent photo (like the one above) and put in some helpful comments.
Box culvert with a small headwall and very extended 75-90 degree wingwalls.
Not a wingwall, bank armoring and headwall.
Two box culverts with a 0 degree common wingwall (center) and 30 - 60 degree wingwalls on the side - ignore the one in the center.
Small dry fit stone wingwalls.
Small headwall, no wingwalls.
Small dry fit stone headwall, no wingwalls.
Concrete headwall, not wingwalls based on photo.
Headwall, with 90 degree wingwalls? Hard to say - they seem to be extensive enough that they might affect the efficiency of the inlet during flood flows.
Wingwalls, 45 degree (SL) and 90 degree (SR).
Small mortared headwall.
That's all for now. Please post pics with Q's for any that are confusing.