Circle S dam
Circle S
Circle S is a privately owned dam located in Napa, California, along the Tr Milliken Cr river. Built in 1979, this earth dam stands at a height of 28 feet with a hydraulic height of 24.7 feet, serving primarily for water supply purposes. With a storage capacity of 131 acre-feet, Circle S has a significant hazard potential but is currently assessed to be in satisfactory condition as of September 2017.
Managed by the Department of Water Resources (DWR) and regulated by the Safety of Dams agency, Circle S undergoes regular inspections, with the last one conducted in December 2019. Its location in a high-risk earthquake zone raises concerns, but the dam meets guidelines for emergency action plans, although specific details on preparedness and risk management measures are not outlined in the data. Despite its age, Circle S continues to play a vital role in irrigation, recreation, and water supply within the region.
For water resource and climate enthusiasts, Circle S presents an intriguing case study of a crucial infrastructure in California's water supply network. Its design and construction details, along with regulatory oversight and hazard assessment, offer valuable insights into the challenges and responsibilities associated with maintaining dams in earthquake-prone regions. As the debate around water resource management and climate change intensifies, understanding the complexities of structures like Circle S becomes increasingly important for ensuring the safety and sustainability of our water systems.
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 Circle S -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Napa R Nr Napa Ca | 27 cfs | → |
| Napa R Nr St Helena Ca | 8 cfs | → |
| Putah C Nr Winters Ca | 548 cfs | → |
| Sonoma C A Agua Caliente Ca | 10 cfs | → |
| Nathanson C A Sonoma Ca | 0 cfs | → |
| Sonoma Creek A Kenwood Ca | 2 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Circle S.
Boat launches
- Knoxville Road 1601, Napa County
- Napa Valley Vine Trail, Napa
- Cuttings Wharf Road 3175-3337, Napa
- Cuttings Wharf Road 3270, Napa
- Chaparral Cove Napa County
- North Camino Alto Vallejo
Campgrounds
- Steele Canyon Camp Site
- Lupine Shores - Lake Berryessa - Usbr
- Lupine Shores Camp Site
- Foothill Pines - Lake Berryessa - Usbr
- Spanish Flat Camp Site
- Spanish Flat Camp Site Office
Fishing spots
- Lake Berryessa
- Berryessa Lake
- Lake Ralphine
- 9th Street Boat Ramp
- City Of Benicia Fishing Pier
- San Pablo Reservoir
Paddle runs
- Cache Creek
- Olema Ranch Campground To Caltrans Corporation Yard At Point Reyes Station
- Headwaters To Ends One Quarter Mile South Of Bear Valley Road Bridge Segment 1: Ends 1/4 Mile South Of Bear Valley Road Bridge Segment 2: Caltrans Corporation Yard At Point Reyes Staton.
- Headwaters To Mouth
More reservoirs
Track Circle S 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 Circle S
Where does the data for Circle S 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 Significant 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 Circle S.