O`Shaughnessy dam
O`Shaughnessy
O`Shaughnessy, also known as Hetch Hetchy Reservoir, is a gravity dam located in Moccasin, California, on the Tuolumne River. Built in 1923, this impressive structure stands at a height of 312 feet and has a storage capacity of 360,000 acre-feet. The primary purpose of this dam is to provide water supply for the region, serving as a critical source for both hydroelectric power generation and water distribution.
Managed by the local government and regulated by the California Department of Water Resources (DWR) and Safety of Dams, O`Shaughnessy Dam is considered to have a high hazard potential. However, recent inspections have deemed its condition as satisfactory. The dam plays a crucial role in water resource management in the area, with a drainage area of 459 square miles and a surface area of 1972 acres. Despite its age, O`Shaughnessy continues to operate efficiently, meeting the water needs of the surrounding communities.
With its historic significance and vital role in the local water supply infrastructure, O`Shaughnessy Dam stands as a testament to engineering excellence and resource management. As climate change continues to impact water resources, structures like O`Shaughnessy play a crucial role in ensuring a reliable water supply for both current and future generations. The dam's construction, maintenance, and regulatory oversight highlight the complex interplay between water management, climate resilience, and infrastructure development in California.
Dam data reference
Condition Assessment
- Satisfactory
- No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
- Fair
- No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action.
- Poor
- A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency.
- Unsatisfactory
- A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
- Not Rated
- The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Hazard Potential Classification
- High
- Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
- Significant
- Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
- Low
- Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
- Undetermined
- Dams for which a downstream hazard potential has not been designated or is not provided.
Plan around the weather
Same NOAA / yr.no feed Snoflo's iOS app uses. Watch the precipitation column on the meteogram -- rain on the basin upstream typically lifts inflow 24-72 hours later.
Next 5 days, hour by hour
Temperature line with weather symbols on top, snow + rain accumulation as columns, humidity as a dotted line.
5-day forecast table
Every 3 hours, broken out across temperature, snow, rain, humidity, and wind. Each cell is colour-coded relative to the column min/max.
| Time | Condition | Temp (°F) | Snow (in) | Rain (in) | Humidity (%) | Wind (mps) | Wind dir |
|---|---|---|---|---|---|---|---|
| Loading detailed forecast… | |||||||
15-day temperature & precipitation
Daily temperatures, snow, and rain projected over the next two weeks.
Nearby streamflow gauges
USGS streamgauges around O`Shaughnessy -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Tuolumne R Nr Hetch Hetchy Ca | 912 cfs | → |
| Eleanor C Nr Hetch Hetchy Ca | 204 cfs | → |
| Lk Eleanor Div To Cherry Lake Nr Hetch Hetchy Ca | 1 cfs | → |
| Cherry C Bl Valley Dam Nr Hetch Hetchy Ca | 6 cfs | → |
| Tuolumne R A Grand Cyn Of Tuolumne Ab Hetch Hetchy | 1,440 cfs | → |
| Tuolumne R Ab Early Intake Nr Mather Ca | 1,000 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near O`Shaughnessy.
Boat launches
Campgrounds
- Hetch Hetchy Backpackers Camp
- Lake Eleanor Campground
- Dimond O Campground
- Diamond O
- Cherry Valley Campground
- White Wolf - Yosemite National Park
Fishing spots
Paddle runs
- Headwaters Near The Tuolumne And Mariposa County Lines To Western Boundary Of Yosemite National Park
- Clavey River From 3n01 To Cottonwood Road
- Clavey River At Confluence Of Bell And Lily Creeks To 3n01
- Lilly Creek (Source At Chewing Gum Lake And Y Meadow Lake) To One-Tenth Mile Downstream Of Coffin Hollow
- One-Tenth Mile Downstream Of Coffin Hollow To Confluence With Bell Creek And Clavey River
More reservoirs
Track O`Shaughnessy in the Snoflo app
Save this dam as a favorite and get the local NOAA / yr.no forecast plus regional flow context wherever you are.
About O`Shaughnessy
Where does the data for O`Shaughnessy come from?
Structural and regulatory data come from the U.S. Army Corps of Engineers' National Inventory of Dams (NID). Weather forecast comes from NOAA / yr.no -- the same feed Snoflo's iOS app uses.
How often is the report updated?
NID structural data refreshes annually as the Corps publishes updated assessments. The weather forecast refreshes throughout the day.
What does the High hazard rating mean?
The Corps of Engineers' hazard potential classification grades probable consequences if the dam fails: High = probable loss of human life; Significant = no probable loss of human life but possible economic loss / environmental damage; Low = no probable loss of human life, only minor economic / environmental losses. See the Dam Data Reference card above for the full definitions.
What's "% of normal"?
The current storage value compared to the historical average storage on this calendar day. 100% = right on average; values above 100% mean above-normal storage (wet year); values below mean below-normal (dry year or drought).
Can I get alerts when storage crosses a threshold?
Yes -- alerts are managed in the Snoflo iOS app. Favorite this dam, set a threshold, and you'll get a push the moment conditions cross.
Other water bodies near here
Snoflo-tracked reservoirs and dams within driving distance of O`Shaughnessy.