daylight & "scour setback" 2

[EngineerofSteel]

I designed a footbridge traversing a run-off stream. It is dry much of the year and flows occasionally between September and February.

The City of Atescadero returned a review asking for "minimum daylight and scour setbacks". This phrase does not even appear on a Google search!

Anyone know what they are requesting, and how to calc it?

I am guessing it is the distance from the top of bank to the high elevation mark...

 

[RWF7437]

I have no idea. Have you tried posting your question here:

http://www.atascadero.org/index.php?option=com_content&task=view&id=193&Itemid=761

good luck

 

[cvg]

dry washes typically migrate laterally during high flows. (try googling "lateral migration") If the banks of the wash are not lined with riprap or other erosion protection, then you are required to "set back" from the edge to protect your structure. Another option is to do the scour calc's and then set your footing below the scour depth. Be aware that this could be 10 feet or more below the bottom of the existing channel.