Environmental Flow: River Ecosystem Thresholds

Water Extraction

Extraction rate 0%

100% flow

0% extracted100% extracted

Ecological functions

🌾 Floodplain connectivityConnected

💨 Dissolved oxygenHealthy

🪨 Sediment flushingFunctional

🐟 Fish passageOK

Simulation

Speed 1.0×

How it works

A river doesn't just supply water to divide between people and "nature" — the river ecosystem itself needs a certain minimum flow for several separate jobs to keep working, and each job has its own threshold.

Floodplain connectivity — needs the river to reach and refill the adjacent wetland; the first to fail as extraction climbs.
Dissolved oxygen — slower, shallower water holds less oxygen and warms faster, stressing aquatic life.
Sediment flushing — occasional high-flow pulses are needed to scour fine sediment out of gravel spawning beds before it smothers eggs.
Fish passage — enough depth over shallow riffle sections for fish to physically swim upstream to spawn; the last, most dramatic failure.

Because these thresholds sit at different extraction levels, the river can look "mostly fine" on the surface long after some functions have already silently failed — and the final threshold crossing looks like a sudden collapse, even though it was building the whole time.

River channel Floodplain / wetland Riffle rocks Fish Sediment / gravel bed

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