OpenHydroTwin v1.0.0 — Initial public release This is the first public release of OpenHydroTwin, an open-source digital twin framework for stormwater infrastructure built on the OpenHydroQual process engine. The release accompanies the manuscript: Shakouri, B., Kiriazes, R., and Massoudieh, A. (2026). OpenHydroTwin: A Generic Digital Twin Framework for Stormwater Infrastructure. Submitted to Environmental Modelling & Software. What's included Framework source code in C++ (C++17, Qt 6.8+), consisting of the forward simulation loop, the streaming data-assimilation loop, the meteorological forcing-ingestion layer, and the snapshot-based hot-restart mechanism. WebAssembly viewer for browser-based monitoring of deployed twins, served alongside the simulation outputs. OpenHydroQual model files for the bioretention case study reported in the manuscript, including the configuration files and visualization specification. Deployment configuration examples for both standalone Linux deployment and reverse-proxied multi-deployment setups under nginx. Build scripts and a sample systemd unit file for running OpenHydroTwin as a long-lived service. Capabilities Continuously running, wall-clock-synchronized simulation of any system that can be represented in OpenHydroQual, including bioretention cells, rain gardens, stormwater ponds, constructed wetlands, drywells, and other engineered practices. Live ingestion of meteorological forcing (precipitation, temperature, humidity, wind, shortwave radiation) from public web services. Streaming parameter estimation through a genetic-algorithm-based maximum-likelihood objective with a kernel-weighted observation likelihood, supporting tracking of slowly evolving physical parameters as new sensor data arrive. Joint estimation of physical parameters and channel-specific residual standard deviations, supporting automatic diagnosis of model–data mismatch. Snapshot-based hot-restart for fault-tolerant continuous operation across planned restarts, crash recovery, and operating-system maintenance. HTTP-served outputs (rolling time series, model snapshots, SVG visualization) for monitoring and consumption by downstream tools. Requirements Linux (tested on Ubuntu 22.04 and 24.04). Qt 6.8 or later. OpenHydroQual shared library (libOHQLib.so). A recent C++17-capable compiler (GCC 11+ or Clang 14+). Optional: nginx for serving published outputs over HTTP. A typical deployment runs on a small Linux virtual machine with two CPU cores and 4 GB of RAM. Getting started See the repository README for build instructions, deployment configuration, and an annotated walkthrough of the bundled bioretention example. License OpenHydroTwin is released under the GNU Affero General Public License v3.0. See LICENSE for the full text. Users who run OpenHydroTwin as a network-accessible service are required by the AGPL to make their source modifications available to users who interact with the service. Citation If you use OpenHydroTwin in academic work, please cite both the software and the accompanying manuscript. The software citation is provided by the Zenodo DOI minted with this release. Acknowledgments OpenHydroTwin builds on the OpenHydroQual simulation engine. Development of OHQ and OHTwin has benefited from collaborations with DC Water and the District Department of Transportation. Known limitations This is an initial release intended for academic and demonstration use. Field deployment against real sensor telemetry has not yet been undertaken, and the framework's robustness to real-sensor pathologies (drift, fouling, dropouts) remains to be characterized. Bayesian Markov chain Monte Carlo posterior sampling for parameter uncertainty quantification — supported by the underlying engine for offline use — is not yet integrated into the streaming loop and is planned for a future release. Feedback Issues, feature requests, and pull requests are welcome through the GitHub issue tracker.