That's alot of water!!! It reads to me that they are using...

That's alot of water!!! It reads to me that they are using flexible (HDPE) pipe culverts and rockfill to get the road open again in the short term.

I'd be interested to see if this is just a stop gap measure while a more substantial structure such as a multi cell concrete box culvert or bridges can be designed and a contractor procured to do the work. Given that amount of water, I think something more substantial that HDPE pipes are needed to stop this from happened frequently.

In saying that, it's great to see the effort from the government to get the road open again, whatever it takes.