"Thirty foot wall of water" as reported in there is only true in the most technical sense, as that was the height of the roadway with the culvert that got blocked by debris until the weight of the water and erosion from being washed over collapsed it. The long vertical pan from the edge of a washed away road you see was one end of that where the culverted side road met the main road. Actually traveling down the valley it was only about waist high, though that was still quite menacing enough when I was in a car that didn't get swept away only because we saw it coming and backed around a corner and up a hill in the couple seconds between when it surged ahead at the end of a long straightaway and when it reached the bottom. Sadly, "thirty foot wall of water" makes a much better sound bite than "three foot wall of water" and mum is a bit dramatic.

The funny thing about the whole situation was that while every other bridge and culvert etc. for a good fifty miles was washed out, the 20ft wooden bridge I'd built over the river, which had been fully submerged under fast flowing water despite being a good four feet higher than the usual surface of the river for two days and had boulders bouncing over it after the bank on the end without a big old tree to keep it intact with its root system eroded away, was still in exactly the same place on the other end and intact aside from a lot of scuffing due to how much it was overbuilt - we'd driven a pickup across it a couple times and it flexed less than having someone stand in the middle and jump at the resonant frequency. It wasn't in the course of the big surge, but still, neither were most of those roadway culverts and bridges. Six 2x12 stringers a foot apart with full-height crossbraces between them every 18in and rough (that is, not planed thinner to provide a smooth surface) 2x10 deck planks, all held together by excessive numbers of those long wood screws you put in with an electric drill and anchored at the ends by a ten foot long pressure treated 8x8 buried sideways under the gravel ramp. Afterward, it was hauled out of the riverbed with a bulldozer, cut in two for transport, and turned into a deck. That bridge was a fucking masterpiece