Scour - house in a floodplain

[Rye1]

I've been asked to conduct a scour analysis and scour protection for a proposed house in a floodplain. Velocity of the 100-year event is about 1.5 ft/s. The proposed house is located at a confluence and the flooding is from a river downstream. The proposed house is in a backwater area from the river. Because of the confluence issue, the existing HEC-RAS models will not work. I could create a new 2d HEC-RAS with the confluence as a junction, but the model would not be close to the existing FIS information. Thoughts?

Robert Billings, PE, PH, CFM

http://www.newrivereng.com

 

[phamENG]

Do you have a FIS cross section near the location of the house? Or are you saying that, because of the location of the site, you feel the FIS data is not accurate for the site?

I deal with tidal flooding, not riverine flooding, so discount my thoughts as you will. If I have to design a footing to resist flooding scour, the usual solution is to go deeper. Nobody really wants to pay for an expensive, detailed analysis (up front cost) when it will only save them 6-12 inches of footing depth anyway (inconsequential when compared to the rest of the financed cost of the structure in most cases). So I use simplified, conservative scour estimates based on FIS data when I can or flood depth when I can't and make sure that the footing will perform as required when that amount of soil is removed.

 

[Ekenny_G]

Is the FIS flow based on a detail hydrology study or estimated from Regression equation?

You can create 2D model with boundary condition that utilize the FIS flow data (Unsteady/steady flow hydrograph),and add breaklines around the house for more detail flow parameter.