Big Rock Ranch dam
Big Rock Ranch
Big Rock Ranch, located in Nicasio, Marin County, California, is a privately owned Earth dam built in 2002 primarily for water supply purposes. The dam stands at a height of 45 feet and has a maximum storage capacity of 91.3 acre-feet, serving as a vital resource for the surrounding area. Situated along the Nicasio Creek Tributary to Lagunitas Creek, the dam plays a crucial role in ensuring water availability for both recreational activities and domestic use.
Despite its high hazard potential, Big Rock Ranch has been assessed to be in satisfactory condition, with regular inspections conducted by the state regulatory agency, Department of Water Resources (DWR), Safety of Dams. The dam's emergency action plan (EAP) was last revised in January 2021, emphasizing the importance of preparedness and risk management measures. With a drainage area of 0.52 square miles and a surface area of 7 acres, the dam contributes significantly to the water supply infrastructure in the region, highlighting its critical role in water resource management and climate resilience efforts.
Managed by private owners, Big Rock Ranch serves as a key asset in maintaining water security and supporting the local ecosystem. The dam's strategic location and design not only ensure adequate water storage but also contribute to the overall water management system in the area. With its strong enforcement, inspection, and regulatory measures in place, Big Rock Ranch stands as a testament to effective dam operations and underscores the importance of sustainable water resource management in combating the challenges of climate change.
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 Big Rock Ranch -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Novato C A Novato Ca | 0 cfs | → |
| Lagunitas C A Sp Taylor State Pk Ca | 15 cfs | → |
| Corte Madera C A Ross Ca | 4 cfs | → |
| Olema C A Vedanta Bridge A Olema Ca | 3 cfs | → |
| Lagunitas C Nr Pt Reyes Station Ca | 18 cfs | → |
| Petaluma R A Copland Pumping Station A Petaluma Ca | 90 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Big Rock Ranch.
⚓ Boat launches
- Steven Way 98, Marin County
- Calypso Shores 23, Marin County
- Sears Point Road 100-138, Novato
- Marin Rod And Gun Club Pier 2675, San Rafael
- Turney Street Boat Ramp
- Curtola Parkway 139-199, Vallejo
⛺ Campgrounds
- Camp Taylor
- Madrone Group Camp
- Orchard Hill Campground
- Five Brooks Horse Camp
- China Camp State Park
- Olema Campground
🎣 Fishing spots
- Lake Lagunitas
- Berkeley Yacht Harbor
- San Pablo Reservoir
- 9th Street Boat Ramp
- City Of Benicia Fishing Pier
- Lake Temescal
🛶 Paddle runs
- 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.
- Olema Ranch Campground To Caltrans Corporation Yard At Point Reyes Station
- Headwaters To Mouth
🛡 More reservoirs
More reservoirs →Track Big Rock Ranch 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 Big Rock Ranch
Where does the data for Big Rock Ranch 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 Big Rock Ranch.