Low Head Dams: Not as prevalent in the Western U.S., but they are a concern in other parts of the country. I am not sure about around the world. These two videos are dated, but the visuals and info are relevent to the kayaker, boater, rafter on rivers with such dams/spillways. If you run rivers or know those who do watch the videos or share. Low Head Dam Info & Another Low Head Dam Tragedy
Here is a nice overview of stream structure, hydraulics and where fish might hold to feed or seek safe shelter. Reading the water is critical to your presentation. The structures of streams dictate where insects and baitfish hang out or migrate too. And, in turn, where trout will be to dine and dash.
Today, I was perusing a book by Darrell Mulch called Reading Water, An Illustrated Guide to Hydrodynamics and the Fly (2001). The book has a lot to contemplate while presenting materials about the holding patterns of fish in various hydraulic scenarios.
On the very last page, a section entitled The Beginning, there’s a passage that I thought interesting: “However, in a store, flies are usually tied to either attract fish or fishermen. That is, they are made to look like a specific insect or they are made to appeal to the fishermen’s understanding of beauty. Ugly flies, though, are constructed to interact and relate to the characeristics of moving water to produce an animate behavior. The image they present to the fish is dynamic; it is seen as a cinema (a sequence of events), instead of a snapshot (a moment frozen in time).”
The ‘Ugly Fly’ patterns in the book are scraggily, wavy patterns that move upon and under the water’s ‘roof’ as Mulch calls them. I like the Cinema (fluid movements) vs. the Snapshot (static) idea. I have long suggested the impressionistic pattern is preferable to the perfect replica pattern on many occasions. Rather than being my excuse for sloppy tying, perhaps Mulch has given me even another reason to tie my unkempt patterns.
So in light of my last post about fish above waterfalls or natural barriers: so how do they jump up those waterfalls?
“Good leaps depend on the pool below the falls. The deeper the pool, the better the take-off angle, and the faster the fish can go. Consequently, “the higher the fish can leap,” says education coordinator Jonathan Lyman of the Alaska Department of Fish and Game.
Also, water falling from a ledge above hits the water surface below, and continues to plunge deep below the surface. Then — under pressure from more plummeting water — the water rushes back up to the surface. The continuing falling water acts as a hydraulic jack, squeezing the water back up to the surface. Fish use the “hydraulic jump” water to boost their initial leap, says Webb.
Among Pacific salmon, Lyman says, Coho and steelhead (rainbow) trout are the best leapers because they seek the high river source to spawn. The chum salmon is the poorest leaper. The Atlantic salmon is the best leaper of all salmon.” (source)
Water depth of the pool below the falls and the hydraulic push of the plunging water back upward combine to propel the determined fish.
