Drumz, in the construction areas that I've went to, which installed drainage outlets that support habitats for local residential and commercial areas in form of a retention system (an example is City of Upland Colony Crossroads: http://maps.google.com/maps?q=210+and+highland+ave,+upland,+ca&hl=en&ll=34.127419,-117.630765&spn=0.013695,0.01929&sll=37.0625,-95.677068&sspn=53.080379,79.013672&hnear=Highland+Rd,+Upland,+San+Bernardino,+California+91784&t=h&z=16) a similar system was installed to prevent vortexes. The outlets are actually installed at 50�, and some are at 75�, creating a partial backwash pressure to prevent vortex, with a conical cone 2 to 1 ratio of the pipe diameter covering the pipe with 3-in over the pipe itself, with 6 to 8 plate slit-fan to minimize water circular movement. I'll be glad to take the photo of the outlet next time the water drops.
