subdrain design

[pbh]

Without using Modflow drain modeling, is there a simpler methodology to calculate the approximate quantity of groundwater flow to a road subgrade in a road cut condition?

 

[eschwarzrock]

No. Try estimating the flow rate (relatively), and then try determining whether it is steady (the true groundwater table has been intercepted) or just intermitent. if intermittent and small flow, use 4-6 in. subdrain, if sustained and large flow, use 8 - 12 in. But eventually the groundwater level in the area of the subdrain and adjoining roadway would be lowered to just about the level of the drain and the flow rate would slow. It's kind of a judgement call without extensive investigation. If there's room, a swale directed to an outlet structure may be a better choice.