Authors: Reeta Vaahtera, Juha-Matti Välimäki, Tuure Takala & Eliisa Lotsari
Publication type: A1
Freshwater ice forms part of the cryosphere during winter. River ice cover changes the hydraulic resistance of a channel, affecting both water levels and flow velocity distribution. These changes in flow velocity and turbulence depend strongly on the ice characteristics, particularly its hydraulic roughness. However, ice-covered areas often remain understudied due to challenging conditions and limited access. This study presents an improved approach to assessing hydraulic roughness of river ice using a cost-efficient underwater drone platform equipped with camera systems. The developed method incorporates a photogrammetric approach, Structure from Motion. A key outcome is a workflow for reconstructing a digital elevation model of the ice underside. Manning’s roughness coefficient for the ice was derived from the photogrammetric reconstruction, yielding a value of 0.021 in mid-winter conditions. Results show that applying Structure from Motion to map the ice underside offers a practical mean to assess hydraulic roughness of river ice, which has broader potential for hydro-morphodynamic modelling in subarctic rivers under changing environmental conditions. Furthermore, underwater drones allow for more detailed and comprehensive observations of river ice compared to conventional methods.