Stream Pressure

[ztengguy]

I am checking for sliding and uplift under a buried bridge. Its 180' long, on spread foundations. I have calculated the longitudinal pressure from AASHTO and get about 260psf. How is that applied to a longitudinal footing? Just at the end of the footing? So a 4' wide footing x 2'-6" tall will have 2600lbs of force on it for the whole lenght? We dont usually do these calcs, so you can see how in the dark I am.
Thanks

 

[cvg]

maybe a sketch as well as a freebody would clarify this. is this a culvert?