Hetch Hetchy Valley: History, Dam, and Pipeline System

Introduction

Hetch Hetchy Valley, located in Yosemite National Park, is a region steeped in natural beauty and contentious history. Its glacial origins carved a landscape reminiscent of Yosemite Valley, with sheer granite walls and a flat, fertile floor. Once home to indigenous peoples and teeming with biodiversity, the valley became a battleground over water rights and conservation in the early 20th century.

Geology and Indigenous Peoples

The Hetch Hetchy Valley shares a geological history with Yosemite Valley, both shaped by ancient glaciers that sculpted their dramatic granite features. Indigenous peoples, including the Miwok and Paiute tribes, called this valley home for thousands of years, relying on its abundant resources for sustenance. They referred to it as "Hetch Hetchy," a term believed to reference edible seeds found in the valley.

The Battle to Preserve Hetch Hetchy

In the early 1900s, San Francisco sought to dam the valley to secure a reliable water supply following the devastating 1906 earthquake. Conservationists, led by John Muir and the Sierra Club, fiercely opposed the project, arguing it would destroy a natural wonder. Despite their efforts, Congress passed the Raker Act in 1913, allowing the valley to be flooded. By 1923, the O’Shaughnessy Dam was complete, creating the Hetch Hetchy Reservoir.

Pipeline and Power Infrastructure

The Hetch Hetchy system not only provides water but also generates hydroelectric power. After passing through the dam and powerhouses, the water flows into a 167-mile aqueduct crossing the Central Valley. While much of the pipeline is buried, segments can be seen where it traverses uneven terrain or reservoirs. In Fremont, the aqueduct splits into four Bay Division Pipelines (BDPL), each varying in capacity, to distribute water across the Bay Area.

Hetch Hetchy water is among the cleanest in the nation, sourced from Sierra snowmelt and filtered naturally through granite. This exceptional quality exempts San Francisco from federal filtration requirements, although the water is disinfected and rigorously tested.

Ongoing Debate and Future Prospects

Calls to remove the Hetch Hetchy Dam persist, with proponents arguing for ecological restoration and improved biodiversity. Critics, however, point to California’s ongoing droughts and the vital role the reservoir plays in water security. While other dams in the western U.S. have been decommissioned, Hetch Hetchy remains operational, balancing environmental concerns with urban demands.

1. Hetch Hetchy Valley

Feature Type: Glacial valley
Elevation: Approximately 3,800 feet at the valley floor (pre-dam), now submerged under the Hetch Hetchy Reservoir.
Still Visible: Partially. The flooded valley floor is no longer visible, but the surrounding granite cliffs remain intact.
Comparison to Yosemite Valley: Similar in its glacially carved U-shape with towering granite walls, often referred to as a "mini-Yosemite Valley."

2. Kolana Rock

Feature Type: Granite monolith
Elevation: 5,772 feet
Still Visible: It towers prominently over the reservoir.
Comparison to Yosemite Valley: Comparable to El Capitan for its prominence and steep granite face, acting as a gateway sentinel to the valley.

3. Tueeulala Falls

Feature Type: Seasonal waterfall
Elevation: Drops approximately 880 feet.
Still Visible: Visible during spring and early summer when snowmelt feeds the falls.
Comparison to Yosemite Valley: Similar to Bridalveil Fall for its elegant, slender cascade and seasonal flow.

4. Wapama Falls

Feature Type: Perennial waterfall
Elevation: Drops approximately 1,080 feet in multiple tiers.
Still Visible: It remains a major feature of the valley and is accessible via a trail along the reservoir’s edge.
Comparison to Yosemite Valley: Comparable to Yosemite Falls, though Wapama Falls is more consistently flowing due to the Tuolumne River.

5. Tuolumne River

Feature Type: River
Elevation: Varies; enters the reservoir at approximately 3,800 feet.
Still Visible: Partially. The upper reaches are visible upstream of the reservoir, but much of the river's course within the valley is submerged.
Comparison to Yosemite Valley: Comparable to the Merced River, which winds through Yosemite Valley and feeds its ecosystem.

6. La Conte Point

Feature Type: Granite promontory
Elevation: Approximately 4,000 feet
Still Visible: Partially. Its base is submerged under the reservoir, but its upper reaches are visible.
Comparison to Yosemite Valley: Comparable to Cathedral Rocks for its position as a striking granite feature on the valley rim.

7. Features Lost to Flooding

Feature Type: Meadowlands, forests, and smaller granite formations
Elevation: 3,800 feet (valley floor)
Still Visible: No, the valley’s once-lush floor is now entirely submerged under the reservoir.
Comparison to Yosemite Valley: Similar to the meadows of Yosemite Valley, such as El Capitan Meadow or Cooks Meadow, which were teeming with biodiversity and provided habitat for wildlife. Unique rock formations and cultural sites, such as Miwok Native American settlements, were also lost to flooding.