Domain: Natural Science — Geology & Geophysics
Target concept: Erosion simulation: Water flow over soil and gravel

Video generation prompt: A small tray with a slight inclination contains soil and small pebbles. Water is continuously poured from the higher end, causing the water to flow across the tray and exit from the lower side.

Evaluation guide:
(i) Target concept: Fluvial erosion driven by gravity-driven surface runoff on an inclined sediment bed.
Minimum mechanism: Water must exert shear stress sufficient to overcome sediment cohesion/friction; soil must be unconsolidated and erodible; pebbles must be small enough to be entrained by flow at observed velocity; inclination must provide unidirectional flow vector.
(ii)Storyline: [Phase 1] Dry tray with static soil+pebbles establishes baseline state. [Phase 2] Water introduced at higher end initiates wetting front propagation. [Phase 3] Wetting front reaches soil → reduced cohesion → particle detachment. [Phase 4] Flow velocity increases downslope → pebbles begin rolling/sliding. [Phase 5] Sediment transport concentrates near lower exit → visible accumulation/channel incision. Perspective: Fixed frontal/slightly elevated view showing full tray length; no occlusion; all phases visible in sequence without cuts or viewpoint shifts.

Manual:
Experimental Procedure
1. Place a rectangular tray on a stable surface with slight, fixed inclination (higher end raised).
2. Spread a layer of dry soil evenly across tray bottom, then scatter small, rounded pebbles over soil.
3. Pour water continuously from a fixed point at the higher end, allowing it to flow down the tray and exit solely at the lower end.
Observation of Experimental Phenomena
- Water advances as a coherent wetting front from higher to lower end.
- Soil particles detach and move downstream with flow.
- Pebbles roll or slide in direction of flow, not against it.
- Erosion intensifies near lower end; sediment accumulates or channels form there.
Summary of Experimental Principles
Water flow over inclined soil and gravel demonstrates fluvial erosion: gravitational potential energy drives flow, shear stress mobilizes sediment, and transport capacity depends on flow velocity and particle size.

Prompt Grounding rubric:
level_1: No tray is shown; or the tray holds neither soil nor pebbles; or no water is ever poured onto it; or the tray sits flat/level or is tilted with the intended pour end lower than the exit end (reversed incline); or poured water never leaves the tray by any route (it just pools or fully soaks in with no outflow visible).
level_2: The tray and its incline are visible, but only one of soil or pebbles is present on the surface (not both); or water is poured but no continuous wetted trail crosses the tray from the raised end toward the lower end; or the outflow happens from a side edge or the middle of the tray instead of concentrating at the designated lower end.
level_3: The tray is visibly tilted with a raised pouring end and a lower end; a layer of soil and small pebbles covers the tray floor together; water is poured continuously at the raised end and visibly runs the length of the tray to exit at the lower end; the tray's position and dimensions stay the same throughout the clip.
level_4: All 3-point conditions are met, and: soil and pebbles are mixed together across the surface rather than sitting in separate soil-only and pebble-only patches; the poured stream keeps flowing without stopping or leaving gaps for the whole clip; the raised (pour) end and lowered (exit) end stay unambiguous from the tray's visible tilt; no hands, tools, or other objects intrude into the shot.
level_5: All 4-point conditions are met, and: the water lands at the same spot on the raised end for the whole pour rather than drifting or restarting elsewhere; the soil and pebbles keep a visibly grainy, particulate look (never fully submerged into a smooth slurry) until they are eroded away; the lower end is the only place water leaves the tray, with no dripping, splashing, or overflow at the sides or the raised end.

Scientific and Causal Correctness rubric:
level_1: Water moves uphill or sideways with no net downhill progress; or soil and pebbles shift position without ever being touched by water; or the wetting front vanishes before reaching the lower end; or pebbles appear to float above the tray surface; or soil is seen eroding at a spot before water has reached that spot.
level_2: Water reaches the soil and pebbles but nothing moves in response; or only the pebbles roll while the soil bed never budges (or the reverse: soil washes away while no pebble ever shifts); or the stream flows across the tray but leaves the soil looking completely dry; or pebbles are seen rolling back up toward the pour end against the current.
level_3: Water advances from the raised end toward the lower end; soil visibly detaches in grains or clumps and moves downstream once the wetting front passes over it; pebbles roll or slide in the direction of flow, not against it; the wetted region grows continuously toward the lower end without a dry gap reappearing behind it.
level_4: All 3-point conditions are met, and: soil comes away as discrete grains or small clumps rather than as one continuous sheet peeling off; pebbles are seen rolling or sliding rather than bouncing or drifting as if weightless; the wetting front stays a single continuous advancing line rather than isolated wet spots skipping ahead; visibly more sediment collects (or a small channel starts to cut) near the lower end than near the pour end.
level_5: All 4-point conditions are met, and: soil grains are visibly carried along inside the moving water rather than merely nudged forward and left behind; pebbles only start moving after the soil around them has already begun washing away, preserving the cohesion-loss-before-entrainment order; no soil or pebbles pile up above the wetting front: everything that moves ends up further downstream, never back toward the pour end.

Spatiotemporal Consistency rubric:
level_1: The tray jumps to a different position or angle between frames; soil or pebbles are visible in one frame, missing in the next, then back again later; the water stream cuts on and off or suddenly changes thickness for no visible reason; the scene's lighting flips (e.g., bright to dark) with no change in light source; the tray's rim visibly bends, warps, or folds.
level_2: The tray stays in place but rotates or tilts on its own during the clip; the point where water lands at the raised end jumps sideways between frames; the number of visible pebbles changes from one frame to the next; shadows swing to point in a new direction without the light source moving; the soil's surface flips between a dry granular look and a smooth wet look with no visible wetting shown in between.
level_3: The tray's position, tilt, and size stay constant for the whole clip; the same soil-and-pebble layout is visible throughout with no pieces vanishing or duplicating; the water stream stays visibly connected from the pour point to the exit without breaking into disconnected segments; shadows keep the same direction and strength across the clip; a pebble that sits behind soil in one frame does not jump to appearing in front of it without visible motion causing that change.
level_4: All 3-point conditions are met, and: the stream's width stays steady rather than suddenly narrowing, splitting, or merging without a visible cause; the wet area on the soil spreads outward gradually rather than new wet patches appearing far ahead of the wetting front; pebbles only shift position when the water visibly reaches them, never sliding on their own; the sequence never runs backward (e.g., water never appears to retreat into the tray before it was poured).
level_5: All 4-point conditions are met, and: pebbles roll with a visible turning motion rather than sliding as if frictionless; the water surface shows small ripples or turbulence rather than looking like a perfectly flat sheet; soil detaches mainly where the flow visibly narrows or speeds up, not at random uneroded spots; no object's outline flickers, doubles, or jumps between adjacent frames.