Difference between revisions of "San Antonio Dam"

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A [[Summaries of Environmental Topics in California's Central Coast Region|Environmental Topics]] summary by the [[ENVS 560/L Watershed Systems]] class at [[California State University Monterey Bay|CSUMB]].
 
A [[Summaries of Environmental Topics in California's Central Coast Region|Environmental Topics]] summary by the [[ENVS 560/L Watershed Systems]] class at [[California State University Monterey Bay|CSUMB]].
  
This page provides a brief overview of the history, purpose, design, and use-cases of the San Antonio Dam.  
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This page provides a brief overview of the history, purpose, and design of the San Antonio Dam.  
  
 
==Summary==
 
==Summary==
The San Antonio Dam was completed in 1967 and is owned by the Monterey County Water Resources Agency.The San Antonio Dam is located in Southern [[Monterey County]], about 16 miles northwest from Paso Robles, in Central California. It is 4.4 miles from the [[Nacimiento Dam]]. Both have been created for the purposes of flood protection, water conservation, recreation, and operation of the [[Salinas Valley Water Project]]. <ref name="MCWRA: Dams and Reservoirs"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/ MCWRA: Dams and Reservoirs] Updated 2020. </ref>
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The San Antonio Dam was completed in 1967 and is owned by the [[Monterey County Water Resources Agency]].The San Antonio Dam is located in Southern [[Monterey County]], about 16 miles northwest from Paso Robles, in Central California. It is 4.4 miles from the [[Nacimiento Dam]]. The San Antonio Dam creates the San Antonio Reservoir, which has the ability to store water from winter storms for the dry season. At an elevation of 780, the reservoir has the capacity to store 335,000 acre-feet of water when it is full. It is roughly 16 miles long, and has about 100 miles of shoreline available for recreation. The maximum flood stage elevation is 802 feet. The maximum temporary capacity during a flood event is 477,000 acre-feet, with a surface area of 7,500 acres. <ref name="MCWRA: Dams and Reservoirs"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/ MCWRA: Dams and Reservoirs] Updated 2020. </ref>
 
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The San Antonio Dam creates the San Antonio Reservoir, which has the ability to store water from winter storms for the dry season. At an elevation of 780, the reservoir has the capacity to store 335,000 acre-feet of water when it is full. It is roughly 16 miles long, and has about 100 miles of shoreline available for recreation. The maximum flood stage elevation is 802 feet. The maximum temporary capacity during a flood event is 477,000 acre-feet, with a surface area of 7,500 acres. <ref name="MCWRA: Dams and Reservoirs"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/ MCWRA: Dams and Reservoirs] Updated 2020. </ref>
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==Purpose==
 
==Purpose==
The primary functions of the San Antonio Dam include providing groundwater recharge for agriculture, controlling floods, conserving water supply from winter storms, and helping to slow [[Salinas Valley Seawater Intrusion| seawater intrusion in the Salinas Valley]]. [[Salinas Valley Seawater Intrusion| Seawater intrusion]] has been documented in [[Monterey County]] since the 1940s, and is caused by overdraft of groundwater. <ref name="Seawater Intrusion in Monterey County"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/programs/seawater-intrusion-monitoring Monterey County Water Resources Agency: Seawater Intrusion Monitoring] Updated 2020. </ref> Using more surface water lessens the reliance on groundwater, and the San Antonio Dam is instrumental in maintaining that supply.
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The primary function of the San Antonio Dam is to provide an instrument for groundwater recharge and flood control in the [[Salinas Valley]]. <ref name="Salinas Valley Water Project Engineer's Report"> Monterey County Water Resources Agency [https://digitalcommons.csumb.edu/cgi/viewcontent.cgi?article=1000&context=hornbeck_cgb_6_b Monterey County Water Resources Agency Engineering Reports] Updated July 21, 2017. </ref> The San Antonio Dam and [[Nacimiento Dam]] are also involved in the recently created [[Salinas Valley Water Project]] and they provide opportunities for water recreation in southern [[Monterey County]] and northern [[San Luis Obispo County]]. <ref name="MCWRA: Dams and Reservoirs"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/ MCWRA: Dams and Reservoirs] Updated 2020. </ref>  
 
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The San Antonio Dam stores water during the winter and releases it during the summer. Water released from the dam travels down the San Antonio River to join the [[Salinas River]] groundwater system, which contributes to the [[Salinas Valley]] water supply.<ref name="Nacimiento Dam Report #79"> CalWater [https://www.yumpu.com/s/KIull25otL6gJKwn Nacimiento Dam Report #79] Published 2014. </ref> The [[Salinas River Diversion Facility]] captures some of this released water, and creates an artificial dam near the mouth of the [[Salinas River]].  <ref name="MCWRA: Dams and Reservoirs"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/ MCWRA: Dams and Reservoirs] Updated 2020. </ref> This timed-release and gradual groundwater recharge helps to slow the rate of [[Salinas Valley Seawater Intrusion| seawater intrusion in the Salinas Valley]]. <ref name="Seawater Intrusion in Monterey County"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/programs/seawater-intrusion-monitoring Monterey County Water Resources Agency: Seawater Intrusion Monitoring] Updated 2020. </ref>
Since the enactment of the [[Salinas Valley Water Project (SVWP)]] in 2003, the San Antonio Dam has played a part in storing water during the winter and releasing it during the summer. Water released from the San Antonio travels down the San Antonio River to join the [[Salinas River]] groundwater system, which contributes to the [[Salinas Valley]] water supply.<ref name="Nacimiento Dam Report #79"> CalWater [https://www.yumpu.com/s/KIull25otL6gJKwn Nacimiento Dam Report #79] Published 2014. </ref> The [[Salinas River Diversion Facility]] will capture some of this released water, and creates an artificial dam near the mouth of the [Salinas River].  <ref name="MCWRA: Dams and Reservoirs"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/ MCWRA: Dams and Reservoirs] Updated 2020. </ref>
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==Statistics==
 
==Statistics==
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==Current Issues==
 
==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. <ref name="Dam spillway near SLO County has significant cracks"> Vaughan, Monica. [https://www.sanluisobispo.com/news/local/article233132051.html Dam spillway near SLO County has significant cracks] Published August 1, 2019. </ref>
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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.” The San Antonio Dam is currently classified as an “Extremely High” downstream hazard by the Division of Safety of Dams of the California Department of Water Resources. <ref name="Monterey County Office of Emergency Services"> Monterey County Office of Emergency Services [https://www.co.monterey.ca.us/government/departments-a-h/administrative-office/office-of-emergency-services/ready-monterey-county/hazard-ready/dam-failure Monterey County Dam Safety] Updated 2020. </ref> 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. [[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. <ref name="Dam spillway near SLO County has significant cracks"> Vaughan, Monica. [https://www.sanluisobispo.com/news/local/article233132051.html Dam spillway near SLO County has significant cracks] Published August 1, 2019. </ref>
  
==Use Cases==
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The peak flow through the breach is estimated to be almost 1,500,000 cubic feet per second (cfs) and is estimated to occur 2.75 hours after the dam begins to fail. Models predict that almost all the reservoir would be drained within one day, and that the flood wave would take about one day to reach the mouth of the [[Salinas River]]. At the mouth, the flow rate is projected to be 90,000 cfs. The towns of Bradley, Spreckels, San Ardo, King City, [[Salinas]], and Castroville would experience full or partial flooding. <ref name="Monterey County Office of Emergency Services"> Monterey County Office of Emergency Services [https://www.co.monterey.ca.us/government/departments-a-h/administrative-office/office-of-emergency-services/ready-monterey-county/hazard-ready/dam-failure Monterey County Dam Safety] Updated 2020. </ref>
===Operational Pools===
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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. <ref name="MCWRA: Dams and Reservoirs"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/ MCWRA: Dams and Reservoirs] Updated 2020. </ref>
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==Dam Safety==
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==Dam Subdivisions==  
===Overview===
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In the San Antonio Dam, operational pools refer to management of water being stored in the reservoir. There are a few different operational pools related to storage, release, and conservation.
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.<ref name="Monterey County Office of Emergency Services"> Monterey County Office of Emergency Services [https://www.co.monterey.ca.us/government/departments-a-h/administrative-office/office-of-emergency-services/ready-monterey-county/hazard-ready/dam-failure Monterey County Dam Safety] Updated 2020. </ref>
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*Physical minimum pool - maximum height: 645 feet. At this elevation or lower, water cannot flow out of the reservoir.
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*Operational minimum pool - maximum height: 666 feet. Any water below this elevation is reserved for fish habitat.
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*Conservation pool - maximum height: 774.5 feet. Water is "conserved" to be later released into the [[Salinas River]].
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The conservation pool can store 305,000 acre-feet of water. There is one more pool known as the flood pool, with a water elevation of 780 feet and 335,000 acre-feet of storage. The flood pool is meant to provide protection from a historic flood event, and water can flow from the flood pool to the spillway. <ref name="MCWRA: Dams and Reservoirs"> Monterey County Water Resources Agency [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/ MCWRA: Dams and Reservoirs] Updated 2020. </ref>
  
===Dam Failure Simulation Results===
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==San Antonio Dam Measurements==
 
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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. <ref name="Monterey County Office of Emergency Services"> Monterey County Office of Emergency Services [https://www.co.monterey.ca.us/government/departments-a-h/administrative-office/office-of-emergency-services/ready-monterey-county/hazard-ready/dam-failure Monterey County Dam Safety] Updated 2020. </ref>
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===Spillway Failure Simulation Results===
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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. <ref name="Monterey County Office of Emergency Services"> Monterey County Office of Emergency Services [https://www.co.monterey.ca.us/government/departments-a-h/administrative-office/office-of-emergency-services/ready-monterey-county/hazard-ready/dam-failure Monterey County Dam Safety] Updated 2020. </ref>
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==Data==
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===Current 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 [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/historical-data (MCWRA Reservoir Data)]
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The [[Monterey County Water Resources Agency (MCWRA)| Monterey County Water Resources Agency]] 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.). They also include historical data from 1958-present for the same parameters. This information can be found at [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/historical-data (MCWRA Reservoir Data)]
 
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===Historical Data===
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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 [https://www.co.monterey.ca.us/government/government-links/water-resources-agency/projects-facilities/dams-and-reservoirs/historical-data (MCWRA Reservoir Data)]
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==References==
 
==References==

Latest revision as of 14:11, 12 April 2020

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, purpose, and design of the San Antonio Dam.

Summary

The San Antonio Dam was completed in 1967 and is owned by the Monterey County Water Resources Agency.The San Antonio Dam is located in Southern Monterey County, about 16 miles northwest from Paso Robles, in Central California. It is 4.4 miles from the Nacimiento Dam. The San Antonio Dam creates the San Antonio Reservoir, which has the ability to store water from winter storms for the dry season. At an elevation of 780, the reservoir has the capacity to store 335,000 acre-feet of water when it is full. It is roughly 16 miles long, and has about 100 miles of shoreline available for recreation. The maximum flood stage elevation is 802 feet. The maximum temporary capacity during a flood event is 477,000 acre-feet, with a surface area of 7,500 acres. [1]

Purpose

The primary function of the San Antonio Dam is to provide an instrument for groundwater recharge and flood control in the Salinas Valley. [2] The San Antonio Dam and Nacimiento Dam are also involved in the recently created Salinas Valley Water Project and they provide opportunities for water recreation in southern Monterey County and northern San Luis Obispo County. [1] The San Antonio Dam stores water during the winter and releases it during the summer. Water released from the dam travels down the San Antonio River to join the Salinas River groundwater system, which contributes to the Salinas Valley water supply.[3] The Salinas River Diversion Facility captures some of this released water, and creates an artificial dam near the mouth of the Salinas River. [1] This timed-release and gradual groundwater recharge helps to slow the rate of seawater intrusion in the Salinas Valley. [4]

Statistics

  • The San Antonio Dam is located at 35°48′25″ N, 120°54′00″ W. [5]
  • 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 [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.” The San Antonio Dam is currently classified as an “Extremely High” downstream hazard by the Division of Safety of Dams of the California Department of Water Resources. [7] 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. 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. [8]

The peak flow through the breach is estimated to be almost 1,500,000 cubic feet per second (cfs) and is estimated to occur 2.75 hours after the dam begins to fail. Models predict that almost all the reservoir would be drained within one day, and that the flood wave would take about one day to reach the mouth of the Salinas River. At the mouth, the flow rate is projected to be 90,000 cfs. The towns of Bradley, Spreckels, San Ardo, King City, Salinas, and Castroville would experience full or partial flooding. [7]

Dam Subdivisions

In the San Antonio Dam, operational pools refer to management of water being stored in the reservoir. There are a few different operational pools related to storage, release, and conservation.

  • Physical minimum pool - maximum height: 645 feet. At this elevation or lower, water cannot flow out of the reservoir.
  • Operational minimum pool - maximum height: 666 feet. Any water below this elevation is reserved for fish habitat.
  • Conservation pool - maximum height: 774.5 feet. Water is "conserved" to be later released into the Salinas River.

The conservation pool can store 305,000 acre-feet of water. There is one more pool known as the flood pool, with a water elevation of 780 feet and 335,000 acre-feet of storage. The flood pool is meant to provide protection from a historic flood event, and water can flow from the flood pool to the spillway. [1]

San Antonio Dam Measurements

Current Data

The Monterey County Water Resources Agency 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.). They also include historical data from 1958-present for the same parameters. This information can be found at (MCWRA Reservoir Data)

References

  1. 1.0 1.1 1.2 1.3 Monterey County Water Resources Agency MCWRA: Dams and Reservoirs Updated 2020.
  2. Monterey County Water Resources Agency Monterey County Water Resources Agency Engineering Reports Updated July 21, 2017.
  3. CalWater Nacimiento Dam Report #79 Published 2014.
  4. Monterey County Water Resources Agency Monterey County Water Resources Agency: Seawater Intrusion Monitoring Updated 2020.
  5. USGS Feature Report: Lake San Antonio USGS Feature Report: Lake San Antonio
  6. California Data Exchange Center CDEC: Dam Definitions Updated 2017.
  7. 7.0 7.1 Monterey County Office of Emergency Services Monterey County Dam Safety Updated 2020.
  8. Vaughan, Monica. Dam spillway near SLO County has significant cracks Published August 1, 2019.

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.