Barely beating: Pulsed flows in the Dolores River below McPhee Reservoir restore habitat connectivity and suppress water temperatures

Natural streams in the western United States fluctuate daily in response to snowmelt, transpiration/infiltration, or meteorological events.  Dams alter the historic flow patterns of a stream by capturing snowmelt and either releasing it downstream in an unnaturally high baseflow scenario or transporting it out of the river basin of origin, leaving unnaturally low baseflows for much of the year; this is the case in the Dolores River below McPhee Reservoir.  This year, 56% of the allocated water for downstream releases was available.  We used a pulse flow operating plan to release flows ranging from 15 to 75 CFS, with a 5-day minimum (15-25 CFS) and a 2-day maximum (50-75 CFS).  Compared to a similar water year (2018; 67% allocation), preliminary analysis suggests water temperatures in the Dolores River from June 1-August 31 were cooler under the pulsed flow regime (mean 69.0°F, STD 3.0°F) than under a static flow regime (mean 70.5°F, STD 5.7°F).  The pulsed flow also allowed fishes to move between pools during high-flow periods and scoured fine sediments.  Seven out of the last ten years have been no-release or shortage years in the allocated pool for fishes out of McPhee Reservoir.  Given these shortage years, we believe introducing dynamic flows will reap ecological benefits over the current static delivery of water below McPhee Dam.