## Bulkhead in flood zone V

## Bulkhead in flood zone V

(OP)

I am working on a very small bulkhead and the AHJ is requiring that it be designed for Flood Zone V. The wall is a freestanding log bulkhead with a 1' exposed height and is 50' shoreward of the high tide line so it almost never gets any water on it. The only time that the water gets there is at extreme tides combined with wind waves. The property owner says that has happened only once in the last 20 years. the main function of this wall is to provide a demarcation between the beach sand/native vegetation and his lawn.

How do you calculate the load on the wall in these conditions? All of the calculations in ASCE-7 section 5.4 deal with ds with is the local still water depth and they do not seem to apply to a wall that is normally high and dry.

How do you calculate the load on the wall in these conditions? All of the calculations in ASCE-7 section 5.4 deal with ds with is the local still water depth and they do not seem to apply to a wall that is normally high and dry.

## RE: Bulkhead in flood zone V

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## RE: Bulkhead in flood zone V

## RE: Bulkhead in flood zone V

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## RE: Bulkhead in flood zone V

## RE: Bulkhead in flood zone V

## RE: Bulkhead in flood zone V

## RE: Bulkhead in flood zone V

Haydenwse- IMHO, it is time to take a semi-graphical look at this problem. ASCE 7-10 appears to assume that the still water depth (d_{s}) plus the height of the reflected wave (1.2 d_{s}) is always less than the height of the wall. That is not true for this problem.The wall is 1 foot high, with backfill.

From the diagram below, the worst case breaking wave loading will occur when d

_{s}is 0.45 feet above the base of the wall. If d_{s}is higher, the waves just wash over the top without exerting any force on the wall. If d_{s}is lower, the crest of the reflected wave does not reach the top of the wall.Using C

_{p}= 1.6 (Risk Category I), Unit Weight of Sea Water = 64 pcf, and solving the equations (5.4-5) and (5.4-6), I get:P

_{max}= 81 lb / ft^{2}F

_{t}= 54 lb / ftwww.SlideRuleEra.net

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## RE: Bulkhead in flood zone V

## RE: Bulkhead in flood zone V

.not additiveIf this is correct than you just need to apply the 54 plf load at the Stillwater height.

If they are additive than the wall would be designed for 2*54 plf

## RE: Bulkhead in flood zone V

Haydenwse- Figure 5.4-1 is a simplification of a breaking wave, but a pretty good one. The two equations give accurate results based on the assumptions.P

_{max}(lb/ft^{2}) and F_{t}(lb/ft) both have to be considered individually to design the wall. This 1 foot high wall could be somewhat confusing since it is so short; not much pressure or force.It may help to consider at more typical height wall, say 6 feet. Then, d

_{s}= 2.73 feet. From this I get:P

_{max}= 490 lb/ft^{2}F

_{t}= 1984 lb/ftWith these numbers, it may be clearer that designing a wall for a pressure of 490 lb/ft

^{2}is different than designing a 6' high wall for a total force of 1984 lb/ft. The wall has to meet both of these criteria.www.SlideRuleEra.net

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