Riach says despite the state of emergency in the region, once the Highlanders arrived, there were no thoughts about postponing the game.
"We've had a lot of conversations over the last 24 hours. Once the Highlanders got here around lunchtime, then our attention was very much around the state of the ground, the state of the city and all those things.
"There's really no reason for the game not to proceed."
Riach says the ground conditions aren't ideal, but there looks to be little surface flooding.
"If you're standing at the top of the field and you look down at the stand it looks not too bad, there's one corner that's got a little bit of surface water and we've got some pumps in there trying to get rid of as much of that as we can. The rest of the ground hasn't got obvious puddles but it is very damp. It's going to be very heavy and very slippery."
Riach is confident things will run smoothly at AMI Stadium, and has advice for fans planning to attend the game.
"It will be wet, and we are asking for people who are coming to the rugby to just give themselves a little extra time to get there - the roads are wet, there's a little bit of surface flooding around the city and we don't want people rushing and having any extra problems with their evening."
"You're going to have to dress warmly, you want your best oilskin and gummies on. It's not going to be a fantastic night's weather, but we're really determined that we'll have an occasion fitting of Super Rugby quarter-final."