Understanding the effects of floodplain shade on hyporheic and stream channel temperature cycles

Abstract

River reaches with coarse-grained alluvial floodplains have a breadth of lateral interaction between the channel and surrounding landscape, yielding extensive riparian zones and high rates of gross water exchange between the channel and substrate (i.e., hyporheic exchange). The lateral hyporheic zone on floodplain rivers is often near the ground surface, allowing for heat exchange between the atmosphere, unsaturated sediments, and hyporheic zone. We hypothesized that floodplain shade overlying lateral hyporheic water influences the conductive heat flux through unsaturated sediments, thus influencing hyporheic temperatures and temperatures in associated stream channels. We conducted simulation modeling experiments to test the potential effects of floodplain shade on hyporheic and stream channel temperatures. We found that scenarios with floodplain shade led to cooler hyporheic and stream temperatures than scenarios lacking floodplain shade under a variety of realistic floodplain conditions. We conclude that floodplain forest shade is a novel consideration for riparian management on floodplain river reaches and may be crucial in managing and maintaining cold-water habitat into the future.