OpenHydroQual models of an edge-of-field subsurface-flow vegetated bed (CIG system, Ohio)

Abstract

This record contains the OpenHydroQual model files and input data for an edge-of-field treatment system in a 78-ha row-crop catchment in the Upper East Fork of the Little Miami River watershed, southwest Ohio, USA. The system is a USDA NRCS Conservation Innovation Grant site. An in-channel detention area and a riser divide runoff from a grassed waterway between a subsurface-flow vegetated bed (SVB) and a high-flow bypass. The models cover the first monitoring year, 1 December 2014 to 30 November 2015, at a 15-minute time step, and accompany the paper by Alfaqih, Nietch, Davison and Massoudieh (2026), “Modeling an Edge-of-Field Subsurface-Flow Vegetated Bed: Nitrogen Process Identification, Uncertainty, and Design Evaluation,” submitted to the Journal of Irrigation and Drainage Engineering. The models represent the detention area, the bypass, the SVB and the outlet channel as diffusion-wave channel segments. Weirs divide the flow, and the subsurface beneath the channels is represented by an aggregate storage layer and variably saturated soil (Richards equation, van Genuchten retention). Nitrogen is represented by three species, ammonia, nitrite+nitrate and organic nitrogen, with first-order transformations and a temperature factor. Water-quality observations are storm event mean concentrations compared with flow-weighted modeled event means under a log-normal error model. The archive contains 61 models: hydraulic calibration, full-year and MCMC setups;every candidate model of the stepwise nitrogen process selection by the Akaike information criterion;the selected nitrogen model (ammonification, organic-nitrogen loss and nitrification with a shared temperature factor) and its MCMC setup;32 design scenarios, combining four bed geometries (as built, twice as wide, twice as long, thicker aggregate), with and without an outlet riser, and four flow-split variants;an as-built model extended with dissolved oxygen, reaeration and DO-inhibited denitrification.Each model’s parameters are set to the values reported in the paper. The data folder holds the forcing time series (upstream and lateral inflow, inflow concentrations, air temperature), the observed 15-minute flows at the SVB influent, the SVB effluent and the system outlet, and the storm event windows and measured event mean concentrations. All file paths are relative. After unpacking, the models run directly in the OpenHydroQual graphical interface or command-line interpreter, version 2.1.1 or later. They can be recalibrated with its genetic algorithm, Levenberg–Marquardt and MCMC tools. The README lists each file and explains the naming of the models and data. The monitoring data originate from the USEPA data release (USEPA 2023; Nietch et al. 2024). This work was supported by the DC Water Resources Research Institute through the U.S. Geological Survey (award number G21AP10603-05).