Regulated–Unregulated Inflow Transform

[danmcgraw94]

Summary

Add support for a regulated–unregulated (reg–unreg) transform workflow within rfaR. This feature would allow users to sample regulated inflow-volume frequency and transform it back to an unregulated equivalent before routing, enabling frequency analysis in systems where observed inflows are influenced by upstream regulation.

Motivation

Many reservoir systems receive inflows that are already regulated by upstream dams or diversions. Conducting frequency analysis directly on regulated flows conflates hydrologic signal with operational influence. A reg–unreg transform step would allow rfaR to recover the unregulated flood signal and route it through the reservoir of interest, producing more physically defensible stage-frequency results.

Proposed Workflow

1. Sample regulated inflow-volume frequency — draw inflow volume samples from the fitted regulated frequency distribution (LP3 or GEV) using the existing stratified sampling framework.
2. Apply reg–unreg transform — convert regulated inflow volumes/hydrographs to their unregulated equivalents using a user-supplied transform relationship (e.g., regression curve, lookup table, or ratio-based correction).
3. Route — pass the unregulated hydrographs through the Modified Puls reservoir routing routine as in the standard rfa_simulate workflow.

Implementation Considerations

• Define the interface for the transform relationship (functional form vs. tabular input).
• Determine whether the transform is applied to peak flows, volumes, or the full hydrograph shape.
• Assess whether uncertainty in the transform relationship should be propagated (additional Monte Carlo dimension).
• Integrate cleanly with the existing stratified sampling and nested Monte Carlo structure.
• Add example data and a vignette demonstrating the workflow.

Related

• rfa_simulate()
• scale_hydrograph()
• Stratified sampling bin structure