Garrison Dam Paleoflood Hydrology Discharge Estimation Analysis

摘要

Paleoflood hydrology studies analyze large flood events that occurred before direct measurement and stream gaging networks were established. As part of the hydrologic hazard assessment (flood frequency analysis) for Garrison Dam, preliminary peak discharge estimates were derived from paleoflood geomorphic data. Garrison Dam is located in North Dakota along the Missouri River, which presents unique challenges for paleoflood analysis due to the occurrence of flood inducing ice jams, a wide floodplain, and an alluvial river bed. For each paleoflood terrace, estimates of the minimum discharge required to exceed the terrace elevation were made. Preliminary discharge estimates ranged from at least 110,000 cfs (1952 flood deposit) up to 550,000 cfs (Quaternary non-exceedance bound). Sensitivity simulations were performed to estimate the uncertainty in the initial discharge estimates, including variations in Manning's N values and modifications to channel geometry.