R interface and control unit for the RAINDROP hydrodynamic planning tool: long-term simulation of blue-green infrastructure (swale-trench elements) driven by real climate series, plus two cost optimisers that find the cost-minimal design per allowed overflow frequency — a deterministic bisection-based coordinate descent whose search order is derived from the construction cost rates, and an assumption-free simultaneous search (penalised Nelder-Mead, differential evolution and Halton sampling) as cross-check.

The proprietary calculation engine ("Regenwasserbewirtschaftung", © Tandler.com GmbH) is not part of this archive; it is downloaded on demand from the companion repository kwb.raindrop.binaries.