Modelling Ice-Dominated Deltas in the Laboratory: Exploring the Influence of Frozen Substrate on Delta Morphodynamics

Abstract

Ice-dominated deltas are shaped by the interplay of permafrost, seasonal discharge, river ice, and sea ice, concentrating geomorphic change into brief seasonal pulses. Thawing of frozen ground can alter erosion thresholds, sediment routing, and channel stability, yet its influence on delta evolution remains poorly constrained. This gap limits our ability to model and anticipate change in systems that support northern communities, ecosystems, and infrastructure.

This thesis presents the first controlled laboratory flume experiments to isolate the effects of frozen ground on delta morphodynamics. Experiments used a fine-sand substrate subjected to repeated seasonal freeze–thaw cycles and compared two hydrological regimes: a constant flow representing a simplified active season and a variable flow mimicking Arctic river hydrographs. Delta evolution was recorded with time-lapse imagery for continuous planform tracking and periodic elevation surveys for topographic change.

Frozen substrates promoted persistent bifurcated channels, suppressed progradation, and enhanced sediment retention and redistribution within the delta plain—especially under constant flow—resulting in smaller planform extents than unfrozen controls. Under seasonal hydrographs, frozen deltas diverged from controls after peak discharge, often reactivating progradational channels, whereas unfrozen deltas shifted toward internal redistribution and channel infill with little further growth.

These results link process-level changes to substrate state, providing a framework for interpreting Arctic delta field observations and improving morphodynamic models. They highlight the sensitivity of delta behaviour to cryohydrologic interactions and the need for process-based understanding to inform adaptation as environmental and geopolitical pressures in the Arctic intensify.