HISTORICAL FLOOD REGIME VARIABILITY IN MISSOURI RIVERS

Improving our understanding of flood magnitude and frequency informs flood loss control and ecological management planning. In this study, flood frequency analysis is used to evaluate flood regime variability in Missouri rivers since 1922. Annual maximum peak discharge time series were collected at USGS gages from two eco-regions, including five gages from the Ozark Highlands and three from the Northern Dissected Till Plains, with drainage areas ranging from 1036 km² to 7615 km². For each gage site, separate 30 year time series were obtained starting in 2012 and were lagged successively by five years ending in 1952. The records were analyzed using USGS PeakFQ software. The magnitude of the 1-2 year flood increased by more than 20% at 6 stations since the 1950s, suggesting that geomorphic adjustment to larger bankfull floods may be occurring in largely rural watersheds in Missouri. There is a general trend of increasing 50-100 year flood magnitudes over the past 20 years at most gages, however, behavior differs greatly between eco-regions. The most urbanized watershed showed increasing magnitude for all recurrence intervals over the past 30 years.