Author(s): Harusha Abeynayake; Heli Yu; Jiahui Qiu; Epari Ritesh Patro; Ali Torabi Haghighi
Linked Author(s):
Keywords: Freeze-up; HEC-RAS; Ice-jam; Monte-Carlo; River ice; River1D; Subarctic rivers
Abstract: In northern regions of the world, seasonal river ice cover strongly influences winter hydrology and poses a significant flood hazard by forming ice jams. Several challenges remain for modelling ice-jam hydraulics due to limitations of data in subarctic rivers. The Oulankajoki River is a free-flowing subarctic river located in northeastern Finland and limited in historical ice observations. Considering it as a case study, this study applied an integrated framework combining statistical, empirical, and numerical modelling approaches to a 25 km river reach between the Oulanka Research Station and the Jäkälämutka bend. Freeze-up dynamics were first assessed using a Monte-Carlo-based statistical method following RIVICE guidelines to estimate cooling and supercooling lengths. Subsequently, the results were compared with physically based water-temperature simulations using the River1D model. In parallel, Stefan’s equation was solved using historical ice thickness observations, and ice cover development at the Jäkälämutka bend was quantified from estimated ice production and thickness. We also assessed the HEC-RAS ice model and cross-validated it with River1D under steady-state ice-jam conditions. A cooling-length of approximately 17 km downstream of the Kiutaköngäs Waterfall is obtained, with River1D independently reproducing freezing onset at 17–19km. The Stefan’s coefficient(α) was calibrated as 0.0126, which is consistent with values for other Finnish rivers. Ice-jam simulations of HEC-RAS indicated a potential upstream backwater rise of approximately 2.5 m. Although the sensitivity analysis revealed that internal friction angle (Ø) and ice-jam length exert the strongest control on upstream backwater elevation.
Year: 2026