Storm Drain Tolerance

[SiPaul]

OK,here is another scenario that I'm sure everyone has run into. You design a storm drain and have your flow rates and set the line and grade. The contractor sets the drain too shallow and says "gee wiz can't we live with this." You are in the position of forcing him to go back and reset it (let's say the difference is only .2-.3%) or say OK it'll work.

Sometimes you can justify the shallower slope from the computations or reason that the model was too conservative to begin with. But put this in the perspective of a contractor who has made several blunders and you want to "keep him honest."

I have given a fair amount of lattitude to contractors knowing that we are not in the business of rocket science and when I feel that things aren't critical I will use back-up computations and judgement.

Any thoughts on this one?

 

[TerryScan]

Where I design the slopes ARE .2-.3%.

One thought is to have the contractor agree to pay for running the as-built through hydraulic analysis. And...he must agree to reset the pipe if the HGL does not meet tolerances. (Here, the HGL must be 1' below grates).

 

[LHA]

Here in PA, USA, storm sewers are public improvements, and public improvements are bonded. In order for the bond to be released, a final engineering inspection must be made. If anything is out of spec, the developer has to pay for engineering review. This review then stated whether the as-built condition is sufficient or not. So, I guess I am saying what Terry is.

Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve