So, to recap, we have the following equipment in use on this photograph:
The Secret Sauce
There are two secrets to this photograph: 1) the neutral density filter and 2) the leveling base. Let's explore why...
To create the flowing water effect and the swirl in the bottom of the image, I need to take a long photograph. That long image exposure will allow the sensor to see things - like the swirls - that are not really perceptible with the human eye. It takes some practice to spot things like the pools of water that will swirl in a long exposure, but it is doable with the naked eye. Anyway, in daylight, the only way to get the camera to take a long photograph and not have the image washed out is by putting a pair of sunglasses on the camera - known as a neutral density filter. Like sunglasses, this darkens what the camera sensor sees, and thereby makes the exposure time required to get a properly exposed image longer. I stacked two filters to give a really dark effect - resulting in exposures of over a minute.
Not all tripods are created equal, and this photograph is a great example for why investing in good gear matters. I knew this was going to be a panorama, and the only way to ensure a level plane as you rotate the camera is with a leveling base. Let's explore.... Set up your tripod in your house and purposefully make it a little uneven by putting a book under one leg of the tripod. You can remove that un-level-ness by making the ball head level. But now if you loosen the rotation on the tripod head and move the head left to right, you'll see that the head doesn't stay level.
A levelling base sits below the ball head on the tripod. Once you level that, you can rotate the ball head portion and the whole things stays flat. Compared to the price of a great tripod and head, the leveling base is cheap, and it's a must have if you plan to shoot panoramas.
Planning the Shot
The goal was to get a swirl of water at the base of the waterfall - the trick was how. I walked around the falls taking some test shots for a few minutes before eying this pool of water. I knew it'd be prefer to make my swirl, so I setup my tripod.
Unfortunately, there was no way I could get the image I had in my head in a single capture. The 24mm focal length of my lens meant I'd have to aim down toward the pool of water, and I wanted the image to feel more straight on. Thankfully there is a solution to this problem - shoot the image as a vertical panorama.
When most people think of making a panorama, they mistakenly orient their camera horizontally because they want the final image to be wide. But you actually get a better final product by taking vertically oriented images and stitching those together to get a wide final image (see photos below to illustrate this point).