Nacimiento Dam

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Image 1. Nacimiento Dam.

A Environmental Topics summary by the ENVS 560/L Watershed Systems class at CSUMB.

This page provides a brief overview of the history, purpose, design, and use-cases of the Nacimiento Dam.


The dam was completed in 1957 and is under the jurisdiction of the California Department of Water Resources. [1]

The Nacimiento Dam is located at 35°45′31″ N, 120°53′6″ W. [2]

Nacimiento Dam and its reservoir, Nacimiento Reservoir, are located in northern San Luis Obispo County, about 20 miles from the coast, in central California. [1]

When the reservoir is full (elevation 800 feet) it has a maximum storage capacity of 377,900 acre-feet, is 18 miles long, and has about 165 miles of shoreline. The maximum elevation during flood stage is 825 feet, with a maximum temporary capacity of 538,000 acre feet and a temporary surface area of 7,149 acres.

Dam Type as determined by the California Department of Water Resources: ERTH - Earth

Dam Usage as determined by the California Department of Water Resources: FC,DOM,IRR,MUN,POW - Flood Control, Domestic, Irrigation, Municpial, Power [3]


The primary function of the Nacimiento Dam is to provide groundwater recharge for agriculture, control floods, conserve water and to contribute to the water supply in the Salinas Valley in accordance with the goals of the Salinas Valley Water Project (SVWP). [1] The secondary function of the Nacimiento Dam is to provide a recreation area for boating, fishing, and camping. The Nacimiento Dam is owned and operated by the Monterey County Water Resources Agency (MCWRA). Water released from the Nacimiento Dam percolates into the Salinas River groundwater system, contributes to our region's water supply. [4]

Current Issues

According to a 2019 report and independent audit done by GEI Consultants, Inc., Monterey County’s Nacimiento Dam safety program is seriously deficient with an outdated program document, insufficient staff and a long list of outstanding dam safety repairs and maintenance estimated to cost more than $50 million that needs to be addressed in short order. The report noted that staff is overworked and undertrained, accompanied by a myriad of workload and funding issues. Additionally, the safety program is inadequate for a structure built more than six decades ago. The Nacimiento Dam is identified by the state Division of Safety of Dams as “extremely high hazard.” [5].

Use Cases

Operational Pools

Operational pools have been created to aid in the management of water being stored in the reservoir. The conservation pool which extends from the minimum pool to the concrete spillway elevation of 787.75 feet is the operational pool used to store water for later release to the Salinas River for groundwater recharge, fish passage, and the operation of the Salinas Valley Water Project (SVWP). The flood pool extends from the concrete spillway to an elevation of 801 feet or 1 foot above the top of the inflated Obermeyer spillway gate. The flood pool is intended to provide winter flood protection by maintaining the ability of the spillway to pass the Probable Maximum Flood without overtopping of the dam. [1]


A 4-megawatt powerplant is constructed at the right dam abutment. The plant contains both large and small turbines that operate in the range of 25 cfs to 400 cfs. To maximize power production, two sets of runners have been provided. One set is used at low reservoir elevations and the second at high reservoir elevations. [1]

Dam Safety


A dam failure is the structural collapse of a dam that releases the water stored in the reservoir behind the dam. A dam failure is usually the result of the age of the structure, inadequate spillway capacity, or structural damage caused by an earthquake or flood. The Nacimiento Dam is classified as “Extremely High” downstream hazard potential dams by the Division of Safety of Dams of the California Department of Water Resources. [6]

Dam Failure Simulation Results

The peak flow through the breach is estimated to be 3,300,000 cfs and is estimated to occur one hour after the dam begins to fail. It is estimated that ZZZ of reservoir storage above the TTT-foot level will be discharged RRR days after failure begins. The flood wave would take an estimated 24 hours to reach the mouth of the Salinas River where the flow rate would be approximately 700,000 cfs. The simulation predicts flooding in portions of Camp Roberts and San Miguel, Bradley, the San Ardo oil field, San Ardo, portions of King City, Spreckels, portions of Salinas, and portions of Castroville and Moss Landing. [6]

Spillway Failure Simulation Results

The peak flow is estimated to be 216,000 cfs and estimated to occur 6 minutes after spillway failure begins. An estimated 205,000 acre-feet of reservoir storage will be discharged within 3.5 days of failure, and the flood wave would take about 2 days to reach the mouth of Salinas River. The peak flow there would be about 40,000 cfs. Most of the flow would remain within the Salinas River channel and the FEMA 100-year flood plain, and most of the flood plain would drain within one week after failure. The simulation predicts a community adjacent to San Lorenzo Park in King City may experience some flooding, mostly in the streets, and there would also likely be shallow flooding along the southern edge of the City of Salinas. [6]


Current Data

As of April 6th, 2020, the Monterey County Water Resources Agency (MCWRA) publishes observed data for preceding 10-day periods for the following metrics: Percentage of Capacity, Elevation(feet), Depth(feet), Storage(acre-feet), Lake Surface Area(acres), Length of Lake(miles), Releases(cfs), Rainfall Past 24 hours(in.), Rainfall to Date Last year(in.), and Total Rain Last Season(in.). This information can be found at (MCWRA Reservoir Data)

Historical Data

As of April 6th, 2020, the Monterey County Water Resources Agency (MCWRA) publishes historical data from 1958-present for the following: Elevation Graph, Daily Elevation Data (PDF), Daily Elevation Data (text), Storage Graph, Daily Releases. This information can be found at (MCWRA Reservoir Data)


  1. 1.0 1.1 1.2 1.3 1.4 Monterey County Water Resources Agency MCWRA: Dams and Reservoirs Updated 2020.
  2. USGS Feature Report: Nacimiento Dam USGS Feature Report: Nacimiento Dam
  3. California Data Exchange Center CDEC: Dam Definitions Updated 2017.
  4. CalWater Nacimiento Dam Report #79 Published 2014.
  5. Johnson, Jim. Monterey County’s Nacimiento Dam Needs Safetey Upgrades Published July 18, 2019.
  6. 6.0 6.1 6.2 Monterey County Office of Emergency Services Monterey County Dam Safety Updated 2020.



This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.