River regime

Floodwater from the Stillaguamish River surrounds a picnic table and trees. — The South Fork Stillaguamish River in flood. Water spreads beyond the usual channel when discharge exceeds channel capacity.

A suggested lesson sequence

Use these stages at your own pace. Pause for students to sketch, compare observations or lead part of the demonstration.

01
Observe
Read the gold and blue annual discharge curves. Scrub through winter and locate water stored as snow.
Open Observe
02
Tinker
Follow the melt season and compare its flow peak with winter rain. Switch the dam on and compare the peak and delayed release.
Open Tinker
03
Explain
How does storing precipitation as snow shift the timing of river flow?
Open Explain
04
Check
Choose an answer and explain your reasoning. Each question includes feedback.
Open Check

Rehearse with the model

The same scene and controls as the lab. Load it when you are ready; use Start projector for the full classroom view.

Before the lesson

Compare annual patterns of river discharge and explain how rainfall, snowmelt and dams can change their timing.

Open the model before the lesson and choose a view that makes the important feature easy to see. Drag to rotate, and use the on-screen controls to change one variable at a time. The Controls panel explains the available keyboard shortcuts.

Pause the animation at a useful moment. Ask students what should happen next, then play it to test their explanation.

Guide the demonstration

Read the gold and blue annual discharge curves. Scrub through winter and locate water stored as snow.

Follow the melt season and compare its flow peak with winter rain. Switch the dam on and compare the peak and delayed release.

Discuss a common misconception

“A river’s seasonal flow pattern depends only on the amount of rain each month.” Rainfall matters, but snow accumulation and melt, evaporation, groundwater storage and reservoir operation can shift the timing of discharge. Water received in one season may reach the river in another. Explaining a regime therefore requires both the inputs and the processes that delay or remove water.

Build the explanation

A river regime describes the seasonal pattern of discharge. Rain may reach the river quickly, while snow stores water until melting; a reservoir can smooth and delay the resulting flow.

Follow the melt season and compare its flow peak with winter rain. Switch the dam on and compare the peak and delayed release.

Both catchments use invented repeating annual inputs, and the dam represents storage behaviour rather than an actual operating rule.

Teaching notes

Compare regimes across different climates rather than applying one annual pattern to every river.

Distinguish a monthly river regime from the short-term response shown by a storm hydrograph.

Use the graph’s stated scale and avoid assigning absolute discharge values to a normalised trace.

Check understanding

Open Check for 4 questions. Ask students to explain their choice before revealing the answer.

Return to the opening photograph. Ask students to identify one visible feature and explain which part of the model helps account for it.

Look more closely

Use these observations to connect the vocabulary to features students can identify.

Regime

A streamflow-gauging station beside Huey Creek in Antarctica's rocky McMurdo Dry Valleys. — USGS gauging station at Huey Creek, Antarctica, 12 December 2001. Repeated measurements of stage and discharge produce a river's hydrograph.

Read the definition

Nival

Melting snow patches and a stream near Fourth of July Lake in Idaho's Sawtooth Mountains. — Seasonal snowmelt feeds a stream near Fourth of July Lake, Idaho. A nival river regime is strongly influenced by snow accumulation and melt; this photograph shows a snowmelt source, not a measured annual hydrograph.