All,

The Nashua River watershed received nearly 5 inches of rain in two days from the recent Hurricane Ida, so I hiked the spillway to see first hand to what heights the discharge reached.

It did not disappoint, not only was the water deeper in the channel but it was moving a lot faster than at normal times.

This video is of the whole channel from top to bottom and around the bend. At the low end it demonstrates how the velocity control measures carved into the rock at the low end effectively slow the flow down before it can hit the millpond and erode the opposite shore.

Refer to the series “Hidden Hydraulics at the Dam” for a good writeup on how the engineers accomplished it.

Thanks,

Paul