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Storm hydrograph

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Why this lesson, and why the 3D

Storm hydrograph is a fifteen-minute projector lesson, not a homework packet and not a film with a quiz bolted on. Put this hook on the board before you dim the lights: Rain is the input. The river’s reply has a rising limb, a peak, a lag, a falling limb. By the end of the slot a pupil should be able to read rising limb, peak, lag and falling limb, and toggle urban versus rural to change the shape. Curriculum tags in the header (GCSE; A-level hydrology; APES) are filters, not a flag. The room is worldwide; SI first; International English. Ages on the card (GCSE, A-level, NGSS MS, APES) are a suggested band, not a gate.

Somerset Levels can sit on a falling limb for weeks after the rain has stopped. A paved UK high street and a US urban drain flash in hours. Same storm-hydrograph machine, different numbers. Lag time is why a village floods after the radar looks quiet, and why a city gully roars while the cloud is still overhead. Land use is a control, not a personality: impermeable roofs shorten lag and raise the peak; vegetated soil lengthens lag and fattens the falling limb. Environment Agency flood warnings and USGS stream gauges both plot this graph. The Levels are peat, clay and tide-lock; Katrina-Sandy urban flooding is a different surface on the same axes. Do not mix the two as one story. The graph is the reply of a catchment to a pulse of rain.

The 3D is a named, inspectable object. Click the part, not a caption. If the model will not spin, the Why panel still carries the mechanism, the two photographs, and the film. Do not apologise for the model. Drive it. A silent spin teaches a screensaver. A named mesh that changes under a slider teaches the process.

Fifteen minutes on the projector

Watch the storm input. Then the river’s reply: rising limb, peak, lag, falling limb. Lag time is rain peak to discharge peak. The hill has to drain. The river does not peak when the rain peaks. That is the misconception. Raise Urban cover. The hydrograph gets flashier: shorter lag, higher peak. Impermeable surfaces. Water cannot wait in the soil. Drop Urban cover toward rural. Fatter, later. Do not mix stage and discharge. Stage is height. Discharge is volume per time. Somerset Levels can sit on a falling limb for weeks. A flashy urban drain does not. Name rising, peak, lag, falling out loud before you leave the graph. Finish in Check.

Open the lab full screen (F). Labels on (L). Speak the first step before you touch a slider: Play the storm. Rain falls, then the river replies: rising limb, peak, lag, falling limb. Then the second: Raise Urban cover. The hydrograph gets flashier: shorter lag, higher peak. Drop it toward rural: fatter, later. Then the third: Lag is rain peak to discharge peak. The hill has to drain. Stage is height; discharge is volume per time.

The sliders that earn their keep are Urban cover; Rain. Space plays; arrows nudge time; R resets. Parameters the URL can remember: urban, rain. If you only have eight minutes, skip the last step and finish in Check. Projector layout (P) is for the back row: one idea, large type, the model still live.

Play the storm (space). Watch rain fall, then the river’s reply on the graph: rising limb, peak, lag, falling limb. Raise Urban cover toward 1 and run it again: shorter lag, higher peak, roofs instead of trees. Drop Urban cover toward rural and compare. Freeze on the peak and read the lag tag in hours. There is no labelled time slider — space still plays the pulse, arrows still scrub it. Name the four parts out loud before you leave the graph. Keyboard: space play, arrows scrub the storm, L labels, R reset. Urban cover lives in the bar. Finish in Check.

The in-site film is “How Water Shapes the Land: Crash Course Geology #9” (Crash Course Geology, about 10 min, Crash Course Geology / Complexly on YouTube. Standard YouTube licence. Educational embed, autoplay off.). Autoplay is off. Play one minute if you need a second voice; do not let the film eat the slot. The 3D still has to move under your hand.

What the third row will get wrong

You will hear the misconception before you have finished the first sentence. Write the false claim on the board and leave it there until the model has contradicted it. Do not skip this. A fluent pupil can recite the hook and still believe the false sentence.

“The river peaks when the rain peaks.” — no. Lag. The hill has to drain.

“Stage and discharge are the same thing.” — no. Stage is height. Discharge is volume per time. A narrow drain and a wide floodplain disagree.

“Urban land use stops flooding by putting water in pipes.” — no. Pipes and roofs shorten lag and raise the peak. The water still has to go somewhere.

Pitfalls to keep in your pocket: Mixing stage and discharge. Teaching the river as peaking with the rain. Calling every flood a flash flood — Somerset’s falling limb can last weeks. Do not let a pupil leave thinking the 3D is a photograph. It is a teaching model. Where vertical exaggeration exists, T collapses it and the caption says so. A labelled lie of scale is honest. An unlabelled one is a cartoon.

Two places, not a slogan

A storm hydrograph plots discharge against time after rainfall. Rain is the input. The river’s reply has four named parts: a rising limb as the catchment starts to contribute, a peak, a lag from rainfall peak to discharge peak, and a falling limb as the hill empties. The river does not peak when the rain peaks. The hillside, soil and channel have to drain. Urban cover raises the fraction of impermeable surface: water cannot wait in the soil, so lag shortens and the peak rises — a flashier graph. Rural cover does the opposite: fatter, later. Baseflow is the slow groundwater contribution under the storm pulse. Stage is height of the water surface; discharge is volume per time. Do not mix them. A high stage in a narrow urban drain is not the same discharge as that height on the Parrett. Somerset’s almost-flat long profile and saturated peat stretch the falling limb. A flashy urban drain does not. Throughflow and overland flow are the hill’s pipes; impermeable cover skips the slow ones. This lab holds storm size still so land use is the knob you turn. This lab is hours, not the year — that is the regime lab.

The first place to land is Somerset Levels. The second is Shanghai / Huangpu. Same process, different rock or climate. If a pupil can only name one place, they have a postcard, not a mechanism. Atlas entries for those names are a click from the case list; send them back to the lab with one sentence they can say in Check.

Do not flatten the comparison into “this country versus that country.” Name the landform. Holderness is till, not chalk. Hawaii is a hotspot, not an island arc. Yosemite is a glacial trough, not a river canyon. The 3D is allowed to be schematic; the place names are not allowed to be sloppy.

Figures and the film

Field photograph: A hydrograph: rain then discharge against time. A hydrograph: rain then discharge against time. A hydrograph plots rainfall then river discharge against time. Source: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC. Credit: Wikimedia Commons / NASA / USGS / NOAA, public domain or CC.

Mechanism photograph: Field or official figure for teaching Storm hydrograph. A second photograph for the projector script — not the lab cover. Credit: Wikimedia Commons / NASA / USGS.

Two photographs, two jobs. The field picture is the place. The mechanism picture is the process. Do not run the lesson on a single Apollo Earth disc. A carbon-cycle class is a forest and a seam, not a blue marble. An ENSO class is a Pacific temperature map, not Africa from Apollo 17.

Words they must be able to say

Say these out loud once while you click the matching mesh. If a word has no mesh, it still has a photograph in Terms.

Hydrograph: Discharge plotted against time after rain. A storm hydrograph is hours; a regime graph is the year. Lag time: Time from peak rainfall to peak discharge. The hill has to drain. Rising limb: The increase in discharge as the catchment starts to contribute. Peak discharge: The highest discharge in the storm reply. Falling limb: Discharge declining after the peak as the catchment empties. Baseflow: Slow groundwater contribution under the storm pulse. Stage: Height of the water surface. Not the same as discharge. Discharge: Volume of water per time passing a point. Cubic metres per second in school units. Exam language also accepts “Q”.

Exam-language toggle (the Teacher tab) swaps UK/US pairs where they exist — levée/levee, arête/arete — so a mixed room is not punished for spelling.

Close the slot

Without the 3D view: rain is the input; the river replies after a lag. Rising limb, peak, falling limb. Urban surfaces shorten lag and raise the peak. Rural catchments are fatter and later. Stage is height; discharge is volume per time. Somerset can sit on a falling limb for weeks. A hydrograph is hours. A regime graph is the year. Impermeable roofs skip the soil store. Baseflow sits under the pulse. The hill is a schematic catchment, not a traced Parrett.

Finish in Check — ten questions, not a mood. The bank mixes definition, process, the misconception you just killed, a named place, and a read-the-model item (click the part; T). If a pupil can only recite the hook, they have not used the geometry. Wrong answers still show the one-line explain. Do not skip the explain.

Sources on the Teacher tab are the trail, not a bibliography to copy. UKCEH; USGS NWIS.

Link back to the live lab and keep the same slug. Do not invent a parallel worksheet that contradicts T, SI, or the named parts.

This note is worldwide. Curriculum tags (GCSE; A-level hydrology; APES) are filters, not a flag. A class in Nairobi, London, or Shanghai can use the same 3D. Ages (GCSE, A-level, NGSS MS, APES) are a suggested band. If a sentence only works in one exam board, rewrite it before you project it.

Write these three lines on the board before you dim the lights. One: Rain is the input. The river’s reply has a rising limb, a peak, a lag, a falling limb. Two: the misconception “The river peaks when the rain peaks.”. Three: the named parts they must click. Then drive the model. Check is ten questions covering definition, process, the misconception, a place, and a read-the-model item. Do not skip the explain on a wrong answer.

Board, units, and what not to say

SI first. Metres, kilometres, degrees Celsius, metres per second. A conversion in brackets is courtesy, not a second system. Do not let a pupil leave thinking the 3D is a photograph. It is a teaching model. Where vertical exaggeration exists, T collapses it and the caption says so.

Do not say “teaching mesh”, “sprinkle”, or “thin free surface not a fat pipe” out loud. Say the landform. Seasons are ~23.44° of axial tilt, not Earth–Sun distance. The outer core is liquid; S-waves do not pass. Yosemite is a glacial U-trough. San Andreas is a transform. Hawaiʻi and Yellowstone are hotspots. Florida is not a glacial trough.

If the room is noisy, projector layout (P) is the back-row setting: one idea, large type, the model still live. Full screen (F). Labels (L). Space plays. Arrows nudge time. R resets. The URL can remember urban, rain. Send them home with the same link; there is no login.

In-site film

How Water Shapes the Land: Crash Course Geology #9. Crash Course Geology. Crash Course Geology / Complexly on YouTube. Standard YouTube licence. Educational embed, autoplay off. Autoplay off.