ASSESSING HYPORHEIC EXCHANGE IN AN ARID, SPRING FED STREAM SYSTEM, BRIGHT ANGEL CREEK, GRAND CANYON NATIONAL PARK, AZ

Bright Angel Creek, a major tributary to the Colorado River within Grand Canyon National Park exhibits substantial variability in discharge as it flows through gravel deposits in the Phantom Ranch area, near the confluence with the Colorado River. This stream has been selected for the reintroduction of native fish species; variability in habitat conditions play a major role in the viability of these reintroduction efforts. This study quantifies the variability of flow and documents the relationship between available unconsolidated deposits, and discharge variability. We measured discharge at thirteen sites, using standard methods, in order to assess where water was being lost to the surrounding gravels. The overall surface areas of gravel deposits between sites were calculated using GIS software. During high flow periods, sites showed decreased discharge in areas that contained a greater area of gravel bars, indicating higher infiltration rates and increased recharge through the hyporheic zone into the gravels in these sections of the creek. Low flow periods showed an overall increase in discharge from the gravels and a different relationship, likely related to individual aquifer characteristics. The dynamics of this hyporheic exchange acts as a mechanism for habitat protection in the regulation of baseflow. Without these gravel bars, the habitat would have higher high flow events and a lower baseflow, negatively impacting habitat stability for native fish species.