Interactive engineering model
Composite runoff coefficient parcel
Resize roof, asphalt, gravel, and lawn fractions to see how area weighting changes composite C and Rational Method discharge.
Preparing the 3D model...
Four adjacent land-cover slabs sit on one cutaway soil block. Each carries a conceptual budget arrow pair on one rate scale: upward is direct runoff C i, and downward is the remaining rainfall (1 - C) i represented by losses and storage. These arrows are not physical flow paths or a solved infiltration model. Sheet flow drains toward an exposed front collector channel whose normal depth follows the Rational Method discharge, and the parcel footprint follows the total area. Composite C is the sum of each area fraction multiplied by its runoff coefficient.
Diagram labels
Numbers match the callouts in the view. Drag to inspect the model; crowded callouts remain listed here.
Focus the 3D view and use the arrow keys to orbit, plus or minus to zoom, and Home to reset the view.
Text explanation and non-WebGL fallback
Four adjacent land-cover slabs sit on one cutaway soil block. Each carries a conceptual budget arrow pair on one rate scale: upward is direct runoff C i, and downward is the remaining rainfall (1 - C) i represented by losses and storage. These arrows are not physical flow paths or a solved infiltration model. Sheet flow drains toward an exposed front collector channel whose normal depth follows the Rational Method discharge, and the parcel footprint follows the total area. Composite C is the sum of each area fraction multiplied by its runoff coefficient.
The numeric controls and readouts remain usable if WebGL is unavailable. Drag or swipe the 3D view to orbit and use a wheel or pinch gesture to zoom. With the 3D view focused, use the arrow keys to orbit, plus or minus to zoom, and Home to reset. The complete numeric lesson is also keyboard-accessible in the adjacent controls and readouts. This model is an educational aid and does not replace applicable design standards or professional review.