INFLUENCE OF BEAVER-INDUCED CHANNEL AND FLOODPLAIN GEOMORPHIC COMPLEXITY ON CATCHMENT SCALE HYDROLOGIC FLUX IN COLORADO MOUNTAIN STREAMS

Beaver meadows (complexes of multiple beaver dams and ponds) influence storage and attenuation of water at reach and catchment scales. Over the last century and more, removal of beaver has transformed the hydrology and geomorphology of mountain West streams from multi-thread channels in wet valleys to single-thread channels in drier valley bottoms. Less complex stream and floodplain geomorphology transport water rapidly downstream and minimize storage and attenuation at reach scales. We hypothesize that although beaver meadows occupy a small fraction of mountain stream catchment area, their increased channel and floodplain geomorphic complexity means they have a disproportionate influence on retention and attenuation of catchment scale hydrologic flux. We predict a beaver meadow’s influence on catchment fluxes depends on the meadow size, beaver activity level, and meadow position within the stream network. We test these relationships with complexity metrics and hydrologic data for 22 beaver meadows in the Colorado Rocky Mountains. Preliminary indications are that larger meadows, with more beaver activity, store more water and have greater attenuation than smaller meadows, or meadows with less beaver activity. In addition, beaver meadows positioned near the outlet of a catchment tend to have less influence on overall catchment scale hydrologic flux than beaver meadows in or near the catchment headwaters.