Managed Retreat Threshold Simulator — 2D NPV View

Coastal communities facing sea-level rise usually pick one of three strategies: protect the shoreline, accommodate the water, or retreat inland — and the "right" choice is really an economic threshold, not a fixed answer. This 2D companion to the 3D town scene strips the decision down to its actual finance: the same Gumbel extreme-value model turns rising freeboard into an annual probability of the seawall being overtopped, and each year's expected protection cost is discounted back to present value and added to a running curve. Compare that curve against the flat, one-time, undiscounted cost of buying out and relocating every household, and watch for the exact year the two lines cross — computed live from the sliders, never asserted.