Study Area

UTREP study reaches in the upper Tuolumne River

The UTREP study area includes portions of the upper Tuolumne River mainstem and major tributaries regulated by the Hetch Hetchy Project, and has been delineated into seven reaches based on present-day operations and major tributary locations:

Hetch Hetchy Reach — Tuolumne River from O’Shaughnessy Dam (RM 117.5) to Kirkwood Powerhouse (RM 105.7). This reach is bypassed by Canyon Power Tunnel. Flows in this reach are affected by instream flow and reservoir management releases from O’Shaughnessy Dam and accretions from small tributaries. Roughly, the upper half of the Hetch Hetchy Reach is located within Yosemite National Park, the lower half within the Stanislaus National Forest. All other reaches within the study area are located within the Stanislaus National Forest;

Kirkwood Reach — Tuolumne River from Kirkwood Powerhouse to the Cherry Creek confluence (RM 103.8). Flows in this reach are affected by releases from O’Shaughnessy Dam, hydropower operations at Kirkwood Powerhouse, and small tributary accretions. Maintenance operations at Early Intake Diversion Dam occasionally affect flows in the reach; however, the diversion dam is typically operated as run of the river with no diversions;

Lumsden Reach — Tuolumne River from Cherry Creek confluence (RM 103.8) to Don Pedro Reservoir (RM 78.5). Flows in this reach are affected by the sum of Hetch Hetchy Project operations and accretions from several major unimpaired tributaries;

Upper Cherry Reach — Cherry Creek from Cherry Valley Dam to the Eleanor Creek confluence. Flows in this reach are primarily affected by instream flow and reservoir management releases from Cherry Valley Dam. The reach is bypassed by the Cherry Power Tunnel;

Eleanor Reach — Eleanor Creek from Eleanor Dam to the confluence with Cherry Creek. Flows in this reach are affected by instream flow and reservoir management releases from Eleanor Dam and tributaries;

Lower Cherry Reach — Cherry Creek from Eleanor Creek confluence to Holm Powerhouse. This reach is partially bypassed by the Cherry Power Tunnel. Flows in this reach are primarily affected by instream flow and reservoir management releases from Cherry Valley Dam and Eleanor Dam. Maintenance operations associated with the Cherry Creek Diversion Dam and Cherry Aqueduct occasionally affect flows in this reach; however, the Cherry Creek Diversion is typically operated as run of the river with no regular operational diversions;

Holm Reach — Cherry Creek from Holm Powerhouse to the confluence with the Tuolumne River. Flows in this reach are affected by releases from Cherry and Eleanor dams, and hydropower operations at Holm Powerhouse.