jlillywh/STREAM-1D — reverse-engineered prompt

Build me a small open channel hydraulics solver I can use from Python, with a fast core under the hood if that makes sense. I want to define a single river reach by passing in cross sections, roughness, and boundary conditions, then get back water surface elevation, discharge, velocity, and structure diagnostics.

It should handle steady gradually varied flow well, plus a beta unsteady routing mode for one reach over time. Please include optional inline culverts and bridges, and one steady tributary junction if that is already supported. Keep the scope honest, no GUI, no project database, and no HEC RAS file import.

I would also like simple examples for a basic steady run and an unsteady hydrograph run, support for loading geometry from JSON, tests, and a verification notebook or script that compares results against known reference cases. Make it easy to install and use from Python on normal machines, and look up current docs online if you need to fill in details.