Methods to Drain Surface Water

[Stinja]

A current project I'm working on is creating a bus facility over an existing open lot.

Right now, the lot is bare soil and so runoff drainage occurs throughout. With the proposed design, about 85% of the lot will be covered in asphalt or building increasing the amount of surface runoff.

A soils report found that the groundwater table ranges from 5 to 8 feet below the surface.

I planned to have 8ft drywells but now with the GWT at that depth, does not sound like a good idea.

What are other ways I could consider to help decrease the amount of surface runoff?

 

[Ron]

I'm not sure where you're located, but that's usually mandated by some local or regional authority. Many of them limit the post development runoff to pre-development runoff, not necessarily in total volume, but in peak flows. You can attenuate those peaks in a variety of ways, most commonly with on-site detention and retention ponds.

Since you have 85 percent developed area, you'll have to work a bit harder to balance the remaining area with retention/detention. Many authorities will limit impervious development to 70 or 75 percent of the site.

You might also look at state roads nearby and their retention facilities...they will often take part of your runoff if you ask.

With 5 to 8 feet above the water table, you have plenty of depth for ponds, assuming you have adequate surface area.