Fish Ladder Hydraulics Simulator

Weir & Pool Geometry

Head drop per pool ΔH 0.30 m

Slot width b 0.45 m

Pool width W 1.60 m

Migrating Species

Live Hydraulics

Jet velocity v

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Flow rate Q

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Dissipation ε

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Pools for 3 m rise

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How it works

Water dropping ΔH between two pools accelerates through the weir's vertical slot. Treating the slot as a submerged orifice/weir gives the jet velocity from Torricelli's law and the volumetric flow from the orifice equation:

v  = Cv · √(2 g ΔH)
Q  = Cd · b · s · √(2 g ΔH)
ε  = ρ g Q ΔH / Vol_pool   [W/m³]

Cv ≈ 0.90 (velocity coefficient), Cd ≈ 0.85 (discharge coefficient), s = 0.60 m (submerged slot depth), and Vol_pool = pool length (1.8 m) × pool width W × water depth (1.0 m).

ΔH — the head each weir must dissipate; a bigger drop means a faster, harder-to-swim-through jet.
b and W — slot width raises flow Q (more water moving); pool width raises volume, which spreads the same turbulent power out and lowers ε.
Fisheries design guidance keeps ε below roughly 150 W/m³ for salmonids so the pool stays calm enough to rest in between jumps.
A fish can only ascend a slot if its burst swim speed exceeds the jet velocity v — below v it gets swept back downstream no matter how many times it tries, which is exactly what the release button demonstrates.

This is the pool-and-weir / vertical-slot fishway built alongside almost every modern hydroelectric dam to let anadromous fish reach spawning grounds upstream of the barrier.

Pool water Weir jet Migrating fish

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