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HECRas modeling / piers in an overbank

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dwolford

Civil/Environmental
Nov 10, 2010
12
US
Several rows of circular columns support a house above the base flood within the overbank of a large river. I have established cross-sections through each set of piers, and include natural sections just upstream and downstream of the piers. Each pier is modeled as an obstruction. My question is: should additional cross-sections be established between the rows of piers to account for open areas between the piers, or do the obstructions not project (extend) between cross-sections? If there is a reference that addresses this specifically that would be helpful.
 
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The house is to be higher than the base flood. Only the piers will be in flow area. I'm mainly wanting to know if anyone has a reference that indicates whether obstructions set in adjacent cross-sections are interpolated between the sections. In this case, does HECRas see adjacent piers as a wall between piers or is the area between the cross-sections treated as open area by the model?
 
You should read the Hydraulic Reference Manual. HEC-RAS is a 1-dimensional model. The model doesn't "see" anything, it calculates a friction loss at the point of the entered cross-section and determines the HGL accordingly.

You should also read HEC-18 and HEC-20 to see how scour occurs at round piers and how the spacing between them affects the scour.
 
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