New Outdoor Experimental River Facility to Study River Dynamics

Abstract. The Outdoor Experimental River Facility (OERF) is a new large-scale, semi-natural research facility designed to study river dynamics at scales that bridge small laboratory models and natural rivers. The facility comprises a 50 m long, 20 m wide floodplain corridor and is designed to sustain discharges up to 800 L s^-1, allowing subcritical, fully rough flow with field-like Reynolds numbers approaching 10⁵ – beyond values typical of small-scale planform experiments constrained by Froude similarity. In an initial 338 h (~14 days) straight-channel run without upstream sediment feed, a bi-modal gravel–sand bed (initial D₅₀ = 10 mm) progressively armoured to ~22 mm, and reach-scale planform change remained modest despite a width-to-depth ratio of ~12 and a transport stage τ₀/τ_c ~ 1.2. A three-phase, mathematically designed inlet bar–pool perturbation increased local velocities by 8–27 % and produced limited lateral bank erosion (~2.5–7.5 cm) but did not initiate meandering. The results delineate a narrow operational window for sustained bar growth and migration, long adjustment times, practical constraints of outdoor operation, and the moderating role of bank-material strength and toe armouring. Together, these findings show that field-like hydraulics are achievable within the facility while clarifying what limits mobility at this scale; they also motivate future experiments that couple hydrodynamic similarity with controlled sediment recirculation or feed and refined boundary controls to advance understanding of the controls on planform evolution.