Monday, September 13, 2021

Stepped Spillway

I've walked around the Ashland Reservoir hundreds of times, yet I only just learned the "correct" name and reason for the physical structure used for the water to leave the reservoir. It is properly called a "stepped spillway".

Furthermore, because of the shape and location of the dam used to create this particular reservoir, the designers chose to create a stepped spillway that also turns around a gentle curve to give the water a path to flow out of the reservoir. What I hadn't thought about - and thank you, Wikipedia, for this observation - is the reason for the steps, as opposed to a smooth incline, aka chute. It is to help dissipate all the "kinetic energy of the descending water." "Failure to dissipate the water's energy can lead to scouring and erosion at the dam's toe (base). This can cause spillway damage and undermine the dam's stability." Quoted phrases are from these two articles: and

On a recent walk, I noticed the spillway flow to be quite loud and dramatic, since we'd just had several days of rain. I've got one still photo, and one video below, both taken with my cell phone, to show the power of the descending water.

Roaring Spillway

Since I'm usually a still photographer, I had fun taking and post-processing the video below. I used the "slow motion" mode setting on my cell phone to take the video, then post-processed it with Blackmagic Design's excellent DaVinci Resolve software to perform essentially two modifications: add a "ramped" speed change during the clip, and remove a non-kid friendly word written on the stone on the side.

Resolve (Studio version) is used to create professional movies. Go to and watch all the really cool trailers at the top of their web site. It's a very powerful tool to apply to my very low budget and limited resolution cell phone video. Nevertheless I'm hopeful you get the basic idea that the amount of water flow was impressive! And that slow motion turbulent water is kind of fun to watch:)

Warning: geeky stuff follows...

As mentioned, part of my video post-processing challenge was "removal" of a moving object. This involves cloning a different part of the scene over the portion to be removed, so that it appears the object is not present. After reviewing several YouTube instructional videos, I finally figured out how to do this. Resolve has a tab called "Fusion" which allows the user to design their processing steps using a map of connected nodes. Here is the Resolve Fusion node map I created to perform the "moving object removal" task. As you can see, this is not a simple operation. As I understand it, there's a more automated way to remove objects from videos in the non-free Studio version of the software, but that would take all the fun out of it:)

 All photos © 2021, all rights reserved.  Contact for licensing or to order prints.

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