Storm Drain Capacity: Pipe Cross-Section & Hydrograph (2D)

This is the 2D-native counterpart to the 3D storm-drain capacity simulator. Rather than orbiting a rendered street with an underground pipe, it plots the quantities that actually generate the physics: the pipe's own circular cross-section filling to its solved partial-flow depth, a scrolling hydrograph strip chart that races the Rational Method's inflow estimate against Manning's fixed pipe capacity in real time, and a crowned street gutter profile that ponds the same conserved backlog volume the way a cambered real street actually would. Dial up rainfall, imperviousness, pipe diameter or slope and watch the inflow trace climb toward — and, once it crosses — the capacity line, at which point the excess starts filling both gutters symmetrically until they flood together, exactly the mechanism behind urban flash flooding in undersized storm sewers.