Study of Ice Formation/Jam Events on the Missouri River Using HEC-RAS

Northern rivers such as the Missouri River in Montana are hugely affected by river ice processes for a significant portion of the year causing river ice formation and ice jams. A flow analysis spreadsheet capable of automatically downloading hydrometric data available at the USGS gage stations from the Holter to Morony Dam was prepared which also downloads the visual crossing website weather data for historical and future (forecasting) periods for Great Falls to identify ice formation/jam events and organize input data for HEC-RAS temperature modeling. HEC-RAS model was developed for the ~100 river miles segment of Missouri River from Holter, MT, to Great Falls, MT, using the Lidar data and USGS data with the bathymetry data provided by Northwestern Energy Hydro. Holter flow hydrograph was used for the upstream boundary, stage hydrograph at the Great Falls was used for the downstream boundary, and depending on the availability of data three lateral inflow boundaries (Dearborn River, Pear Creek, and Smith River) were used. The model calibration and verification were carried out for two different events: summer 2020 and winter 2021. The simulated flow hydrographs and stage hydrographs indicated good agreement with the observed data at three different stations: Cascade, Ulm, and Great Falls within the modeled river reach. The water temperature simulation was then carried out for the calibrated model during the identified ice cover/jam events using the water temperature data at the upstream boundary, initial water temperature, and historical or forecasted meteorological data. The water temperature simulation results show evidence of ice cover/jam formation as the water temperature stays at 0^oC over many hours/days during the forecasted period. The HEC-RAS equilibrium ice jam simulations were also conducted without considering the dynamic process involved in river ice jam processes.