Rip Rap (ice)

[SMIAH]

I did a study to evaluate rip rap size to be put in a small stream to protect the slopes against erosion caused by the velocity of flow during floods.

So I did some calculation with HEC RAS to find the velocity during the peak flow (10-year). Doing so, and using the Corps of Engineer relationship (1991), the diameter size (D50) has to be = 6 inches (i.e. the velocity is relatively small in the stream as the flow is subcritical).

Then I know that the ice cover is approximately 20 inches right now on the stream and this is quite representative of the mean annual ice cover depth. I think that USACE's recommandation is to use a rip rap with a D100 = 2x(ice cover).

This would make the rip rap size very large.

Anything I'm missing?

 

[SMIAH]

For information this is from Guide to Bridge Hydraulics (2004) :

"It has been suggested that in severe conditions stones should have a diameter at least equal to the ice thickness. Another course of action is to design the rock sizes using conventionnal open water criteria, monitor the works for ice damage after construction, and undertake maintenance or upgrading if required. The amount of damage likely to occur in a single event is comparatively small"