Levee freeboard in FEMA 44 CFR 65.10

[Erdbau]

From FEMA regulations: "Riverine levees must provide a minimum freeboard of three feet above the water-surface level of the base flood. An additional one foot above the minimum is required within 100 feet in either side of structures (such as bridges) riverward of the levee or wherever the flow is constricted. An additional one-half foot above the minimum at the upstream end of the levee, tapering to not less than the minimum at the downstream end of the levee, is also required."

Does "taper" mean linearly interpolate from 0.5 feet at the upstream end to 0 feet at the downstream end? This makes the most sense to me, but I've also seen 0.5 feet added to the very upstream end and 0 feet everywhere else along the levee.

 

[cvg]

no, it means that if you have a structure near the downstream end and you have 4 feet of freeboard at that structure, then you may begin tapering the levee height beginning at the downstream end of the structure (using linear interpolation) so that you have no less than 3 feet at the end of the levee. Also, FEMA is a stickler that the ends must tie in to high ground. You can't just terminate the levee without a tie back levee and the tie back must also have the minimum 3 feet of freeboard.

 

[Erdbau]

Hmmmm.... I sort of see what you are saying. That would be in the case where you have a structure within 100 feet of the downstream end. But, still, what about the 0.5 feet at the upstream end of the levee? That still seems to be completely independent of the 1-additional-foot-at-structures requirement.

 

[cvg]

I have yet to see a levee where the freeboard was exactly 3.5 feet at the upstream end and 3 feet at the downstream, with uniform taper in between. poorly worded regulation. Also note that this requirement is for "riverine levees", levees on ephemeral streams may occasionally be granted slightly relaxed standardss

 

[Erdbau]

This situation is an existing levee that has 3.5 feet at the upstream end. However, at other locations a bit further downstream, is has more than 3 feet but less than 3 plus taper depending on what "taper" means.