Effects of flow regulation and drought on geomorphology and floodplain habitat along the Colorado River in Canyonlands National Park, Utah

Streamflow regulation compounded by regional drought has resulted in up to 22% reduction in channel width, changes in channel planform, expansion of riparian vegetation, and alterations to floodplain habitat on the Colorado River in Meander Canyon, Utah. Although some changes in channel width occurred between the 1940s and 1980s, coinciding with major phases of upstream water development, larger decreases in channel width occurred between 1993 and 2006 during periods of exceptionally low annual floods. These findings illustrate that low runoff associated with regional drought and climate change may cause changes in river channel form that accelerate and compound the effects of upstream water development. Declining peak flows have also resulted in disconnection between the wetted channel and floodplains, where inundated back-levee depressions provide habitat used by two species of threatened and endangered native fish. Despite this disconnection, some back-levee depressions on the floodplain continue to be inundated by ~1.5-year recurrence floods via connections created by tributary mouths, floodplain outflow channels, and levee breaches excavated by resident beaver. These changes are shown by analysis of aerial images, high-resolution bathymetric and topographic measurements, and 2-dimensional streamflow modeling.