Modelling stranded river ice using LiDAR and drone-based models

Abstract

Grounded and other remnants of ice in rivers influence flow and alter instream conditions in the period the ice is left in the river channel. Modelling the flow effects of ice have been difficult in the past due to difficulties in measuring the ice geometry both with regards to time needed to cover the ice formation and since moving on the ice for measurements can be difficult or even dangerous. The detailed river geometry could also be a challenge to find. Recent development in remote sensing from aerial vehicles have changed this and new technologies exist to capture such data. Here we show how the combination of a green LiDAR based river bathymetry can be merged with drone-based ice measurements to form a new river geometry suited for hydraulic modelling. The LiDAR bathymetry is collected from a plane and processed into a digital elevation model (DEM) covering the riverbed and the adjacent areas. The drone geometry is captured using a simple quadcopter with camera and processed into a DEM using structure from motion. Ground Control Points and randomly placed control points are measured with an RTK-GPS and used for georeferencing and to control the accuracy of the ice model. Using the drone for measurements provides a simple and efficient way to capture ice without the need for entering the ice to do traditional measurement campaigns using total stations or GPS software. The DEM representing the ice is merged with the LiDAR bathymetry in a GIS system, and the combined elevation model is used as input to the HECRAS 2D hydraulic model and the flow patterns for typical late winter discharges is simulated with and without ice to compare the impact of the grounded ice formations on the flow 25 th IAHR International Symposium on Ice Trondheim, November 23 to 25, 2020 1. Introduction Development and release of river ice can have large impacts on several important processes in rivers related to physical and ecological factors (Prowse 2001b; Prowse 2001a). Of this, breakup of ice with the associated transport and potential jamming of ice can lead to flooding and changed hydraulic conditions in rivers with potential damage to infrastructure, altered morphology and severe effect on instream flora and fauna (Prowse and Culp 2003; Beltaos 2009). Establishing a relation between how ice behaves during the breakup period and the river hydraulics is therefore necessary to quantify important processes for understanding the dynamics and environment of river systems.