This paper presents a method to quantitatively assess the impact of ice-affected hydraulics on hydropower operations using the widely used Hydrologic Engineering Center River Analysis System (HEC-RAS) hydraulic model. The model was used to identify historical periods where downstream river ice growth reduced the net head on a US Army Corps of Engineers dam on the Pend Oreille River in Idaho, USA. The model was used to create curves of projected stage impacts based on border-ice and continuous bank-to-bank ice formation scenarios. The temperature modelling capabilities in HEC-RAS were used to hindcast ice formation periods on the river that were validated with shore-based webcam data. These results provide a framework that can be applied to other rivers with hydropower generation, particularly sites where an open-water HEC-RAS model exists.

The design of hydraulic structures in the Arctic is complicated by shallow relief, which cause unique runoff processes that promote snow-damming and refreeze of runoff. We discuss the challenges encountered in modeling snowmelt runoff into two coastal freshwater lagoons in Utqiaġvik, Alaska. Stage-frequency curves with quantified uncertainty were required to design two new discharge gates that would allow snowmelt runoff flows through a proposed coastal revetment. To estimate runoff hydrographs arriving at the lagoons, we modeled snowpack accumulation and ablation using SnowModel which in turn was used to force a physically-based hydraulic runoff model (HEC-RAS). Our results demonstrate the successful development of stage-frequency curves by incorporating a Monte Carlo simulation approach that quantifies the variability in runoff timing and volume. Our process highlights the complexities of Arctic hydrology by incorporating significant delays in runoff onset due to localized snow accumulation and melting processes. This methodology not only addresses the uncertainty in snow-damming and refreeze processes which affect the arrival time of snowmelt inflow peaks, but is also adaptable for application in other challenging environments where secondary runoff processes are predominant.