Fix for reduced drain capacity 1

[amphora]

I have inherited a construction project where the contractor has installed 6inch electrical ducts through the 3’-0”Wide x 2’-0”Deep box drain, thus reducing the drain’s capacity. The pipes cannot be raised as they also cross an adjacent roadway. As a solution, I am considering adding another box drain that attaches to the existing box drain before the pipes, goes around the pipe, then converge downstream, similar to a river bifurcation. The size of the branched drain will be to account for the required overall capacity. Any thoughts?

 

[Pinwards]

You may want to first look at the tributary area that drains to the box, and/or check the Flow that it was designed to accommodate. While the conduit through the box will certainly restrict flow and be a long-term maintenance issue (e.g. is there still room to vacuum out any accumulated sediment/debris? Public or private owner?), it's possible that the Q to this drain is small and the restriction may not affect its function. I would also be carefully checking the project plans and spec's as what the contractor did is highly irregular and not something to just accept without careful review of the options they had and their decision-making that led to that irregular situation.

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[amphora]

Thank you for your response. I have calculated the catchment area and used the rational formula to determine the discharge. The peak flow was calculated for a 50 year return period as recommended by state agency. Under normal rainfall conditions I believe the drain will be fine but it’s the abnormal conditions I’m concerned about. I have reviewed the project plans in their entirety and confirmed that it was a major error on the contractors part. I am now attempting to concoct a solution.