A Dryland River Transformed: The Little Colorado

The Little Colorado River (LCR) occupies a highly sinuous alluvial channel with numerous historical meander cutoffs and avulsions in the reach between the city of Winslow, AZ, and the Navajo Nation community of Leupp. Over the past century, regional changes in long-term average temperature and precipitation have been notable. As a consequence, many formerly perennial streams in the LCR drainage basin are now ephemeral. While groundwater discharge sustains negligible base flow near Winslow, streamflow is ephemeral as the LCR meanders toward the Navajo Nation. From 1936-2010, there was a decrease in average channel width from 380 to 33 meters. Concurrently, 96% of the channel was abandoned as a result of lateral migration. Yet flood events and channel migration continue to impact a growing population; for example, water spread for nearly 3 km across the floodplain during a recent and relatively minor flood event. During the same flood event, erosion was locally significant. A well-vegetated meander that had been relocated by a flood in 2008, was eroded an additional 100 m at the bend axis between June 2010 and June 2011. A reduction in channel carrying capacity through narrowing has likely increased the risk of overbank flooding and lateral instability, thereby escalating the risk to nearby communities.