San Antonio Dam

From CCoWS Wiki
Revision as of 20:05, 6 April 2020 by TedR (Talk | contribs)

Jump to: navigation, search
Image 1. San Antonio Dam.

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

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

Summary

The dam was completed in 1967 and is under the jurisdiction of the California Department of Water Resources.[1]

The Nacimiento Dam is located at 35°48′25″ N, 120°54′00″ W. [2]

San Antonio Dam and its reservoir, San Antonio Reservoir, are located in southern Monterey County, about 16 miles northwest from Paso Robles, in central California. [3]

When the reservoir is full (elevation 780 feet), which is the crest of the spillway, it has a maximum storage capacity of 335,000 acre-feet, is 16 miles long, and has about 100 miles of shoreline. The maximum elevation during flood stage is 802 feet, with a maximum temporary capacity of about 477,000 acre-feet and a temporary surface area of about 7,500 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: STO,FC,DOM,IRR,MUN - Storage, Flood Control, Domestic, Irrigation, Municpial [4]

Purpose

The primary function of the San Antonio 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).[5] 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 San Antonio travels down the San Antonio River to join the Salinas River groundwater system, which contributes to our region's water supply.[6]

Current Issues

An audit of the 60-year-old dam found significant cracking in the concrete surface of the spillway, and the integrity of the understructure has been compromised by erosion and clogged drainage pipes — a “poor condition” that the state Division of Safety of Dams said in an April 2019 letter is “unsafe for use under high flow conditions.” Failure of the spillway would lead to massive flooding downriver, first hitting the community of Bradley. Backwater in the Salinas River could also cause inundation at Camp Roberts, including in San Luis Obispo County. Now, Monterey County has five years to completely overhaul the spillway or replace it at a cost that will likely reach above $40 million, some of which San Luis Obispo County might have to pay. [7]

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 minimum pool to elevation of 774.5 feet, 305,000 acre feet of storage, 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 conservation pool to the spillway elevation of 780 feet, 335,000 acre feet of storage. 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.[8]

Dam Safety

Overview

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 San Antonio Dam is classified as “Extremely High” downstream hazard potential dams by the Division of Safety of Dams of the California Department of Water Resources.[9]

Dam Failure Simulation Results

The peak flow through the breach is estimated to be 1,498,000 cubic feet per second (cfs) and is estimated to occur 2.75 hours after the dam begins to fail. It is estimated that almost all the reservoir would be drained within one day, and that the flood wave would take about 24 hours to reach the mouth of the Salinas River where the flow rate would be an estimated 90,000 cfs. The entirety of the towns of Bradley and Spreckels would be flooded, as would portions of San Ardo, King City, Salinas, and Castroville. [10]

Spillway Failure Simulation Results

The peak flow is estimated to be 9,140 cfs and estimated to occur 7 minutes after failure begins. An estimated 38,000 acre-feet of reservoir storage will be discharged within 7 days of failure, and the flood wave would take about 5.5 days to reach the mouth of Salinas River. The peak flow there would be about 5,500 cfs, or about the same flow as a 2-year flood event. In contrast to a failure of San Antonio dam, most of the flow would remain within the Salinas River channel and FEMA100-year flood plain.[11]

Data

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)

References

  1. https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/
  2. https://geonames.usgs.gov/apex/f?p=gnispq:3:::NO::P3_FID:254200
  3. https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/
  4. http://cdec.water.ca.gov/misc/damInfo.html
  5. https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/
  6. https://www.yumpu.com/s/KIull25otL6gJKwn
  7. [1]
  8. https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/
  9. https://www.co.monterey.ca.us/government/departments-a-h/administrative-office/office-of-emergency-services/ready-monterey-county/hazard-ready/dam-failure
  10. https://www.co.monterey.ca.us/government/departments-a-h/administrative-office/office-of-emergency-services/ready-monterey-county/hazard-ready/dam-failure
  11. https://www.co.monterey.ca.us/government/departments-a-h/administrative-office/office-of-emergency-services/ready-monterey-county/hazard-ready/dam-failure

Links

Disclaimer

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.