Estimating Stage-Frequency Curves For Engineering Design In Small Ungauged Arctic Watersheds

The design of hydraulic structures in the Arctic is complicated by unique runoff processes caused by shallow terrain relief which promotes 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 to allow snowmelt runoff flows through a proposed coastal revetment. Snowpack accumulation and ablation were modeled using SnowModel which was used to force a physically based hydraulic runoff model (HEC-RAS) to estimate runoff hydrographs arriving at the lagoons. We discuss the approach used to develop stage-frequency curves with uncertainty using a volume-driven Monte Carlo simulation. This approach accounts for uncertainty in snow-damming and refreeze processes which affect the arrival time of snowmelt inflow peaks to the subject lagoons. This methodology is adaptable and can be applied in other similar environments where secondary runoff processes which are challenging to model directly may be dominant.