Going Underground

Stormwater detention ponds can occupy a significant amount of space on a development site.  Underground detention storage can be used to increase the developable area of a property. This concept was recently used by SKW in the civil engineering design for the redevelopment of Oak Park Plaza in Overland Park, Kan.

Underground detention is not a new concept. Traditionally, cast in place concrete vaults or pipes of various material types have been used for this purpose. At Oak Park Plaza, the material options were limited due to City requirements. After reviewing various alternatives, it was determined that utilizing precast reinforced concrete boxes (RCBs) was the best option for the site – an unusual solution to a typical problem. Using RCBs resulted in the savings of thousands of dollars compared to buried pipes, cast-in-place concrete, and other pre-cast concrete options.

Working with Cretex Concrete Products, the detention system was designed using six parallel rows of 12’x9’ single sell RCBs to achieve the required 84,000 cubic feet of detention storage. Openings were installed in the interior sides of the RCBs to allow the water elevation in the structure to equalize. Manhole risers were installed on top of the structure to allow for easy access for maintenance purposes.