The Central Arizona Project (CAP) is a large canal system that traverses hundreds of ephemeral stream
channels in the Sonoran Desert. This longitudinal barrier alters flow during runoff events, causing water
to pond behind the canal's wall. We asked: How has riparian vegetation of the ephemeral streams
changed over the course of 35 years in response to canal construction? We compared field data (vegetation
volume, woody plant stem density and size, and herbaceous cover) collected in distinct zones
located upstream and downstream of the canal to unaltered controls.
By ponding water and inducing sedimentation of fine particles, the canal has created areas that
support dense vegetation. The wettest zone has the greatest vegetation volume and plant height, and
supports densities of Prosopis velutina that are six times greater than in the control zone. Larrea tridentata
and other desert shrubs are displaced to the border of the wettest zone, but have greater height and stem
diameter than typically occur in the desert owing to increased frequency of soil wetting in the canalassociated
anthropogenic-floodplain. This research aids in understanding the impacts of canal barriers
on desert riparian vegetation, and can be used to predict future outcomes of proposed canals in desert
environments.