San Antonio Dam

From CCoWS Wiki
Revision as of 23:14, 8 April 2020 by DanL (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, purpose, design, and use-cases 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. Both have been created for the purposes of flood protection, water conservation, recreation, and operation of the Salinas Valley Water Project. [1]

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 functions of the San Antonio Dam include providing groundwater recharge for agriculture, controlling floods, conserving water supply from winter storms, and helping to slow seawater intrusion in the Salinas Valley. Seawater intrusion has been documented in Monterey County since the 1940s, and is caused by overdraft of groundwater. [2] Using more surface water lessens the reliance on groundwater, and the San Antonio Dam is instrumental in maintaining that supply.

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.[3] The Salinas River Diversion Facility will capture some of this released water, and creates an artificial dam near the mouth of the [Salinas River]. [1]

Statistics

  • The San Antonio Dam is located at 35°48′25″ N, 120°54′00″ W. [4]
  • 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 [5]

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. 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. [6]

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]

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.[7]

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. [7]

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. [7]

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. ↑ 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: Seawater Intrusion Monitoring Updated 2020.
  3. ↑ CalWater Nacimiento Dam Report #79 Published 2014.
  4. ↑ USGS Feature Report: Lake San Antonio USGS Feature Report: Lake San Antonio
  5. ↑ California Data Exchange Center CDEC: Dam Definitions Updated 2017.
  6. ↑ Vaughan, Monica. Dam spillway near SLO County has significant cracks Published August 1, 2019.
  7. ↑ 7.0 7.1 7.2 Monterey County Office of Emergency Services Monterey County Dam Safety Updated 2020.

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.

Retrieved from "http://ccows.csumb.edu/wiki/index.php?title=San_Antonio_Dam&oldid=26397"