HEC-RAS input 1

[BlastResistant]

I hope you hydraulics experts out there can help out an ignorant structural/bridge engineer. It's a super long story so I'm not gonna explain why, but I need to know how much area upstream and downstream from a bridge needs to be surveyed for a proper hydraulic analysis. Due to issues beyond my control, the surveyors need to complete their work before the civil and geotechnical consultants will be selected, and I need to define their scope of work for contractual purposes. If it matters, the structural/bridge engineer (me) is the prime consultant on a State DOT / Federal Aid bridge rehab project.

Thanks in advance!

 

[RWF7437]

http://www.fema.gov/pdf/fhm/frm_gsaa.pdf

good luck

 

[civilperson]

Instruct the surveyors to go beyond the 100 year flood plain limit width and to include the over-topping of the approach roads as a limiting elevation for surrounding topo, (can be from USGS map with a few hard point shots at centerline roads and top of hills). Go three stations upstream and two stations downstream with the stations equal or greater than maximum channel width before over topping the approach roads..

 

[cvg]

First of all, you cannot get sufficient information to prepare your scope from this forum. You should get some help writing the scope from a hydrologist. Perhaps you can hire one to help you scope the project.

there are existing hydraulic analysis for most rivers. A good place to to start would be to go ask the state or county or FEMA if any any studies have been done in the past. Then start with that study and determine any additional survey that is necessary. You will need to determine if the flow through the bridge is impacting any adjacent property owners so you may need to extend your survey at least to the upstream property lines. Many bridges are also checked against the 500-year flood so you would need to extend the cross sections widen enough to evaluate the 500-year floodplain.

 

[LCruiser]

It also depends on whether it will be subcritical or supercritical flow.