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Crown Harbor Homeowner Association

Rip Rap

Rip rap is rock or other material used to armor shorelines, streambeds, bridge abutments, pilings, and other shoreline structures against erosion. It is made from a variety of rock types, commonly granite or limestone, and occasionally concrete rubble from building and paving demolition. Much of Alameda's rip rap is remnants from freeways destroyed by earthquakes affecting San Francisco. It can be used on any waterway or water containment where there is potential for water erosion.

The information below (Climate Change, San Francisco Bay, City of Alameda, and City of Alameda Response) was culled from "Climate-Change Denial in Alameda" by Sarah Phelan, Oakland Magazine, March 2017.

climate change

Climate Change

  • Scientists have been warning for decades that many human activities increase atmospheric conditions of heating trapped gases, causing the planet to warm. Rising temperatures warm the oceans, which expand as temperatures increase, causing more polar ice to melt adding more volume to the oceans.
  • 2016 was the Earth's hottest on record for the third consecutive year.
  • Climate experts estimate that sea levels could jump as much as 8 feet by 2100 as ice sheets in Greenland and Antarctica sheer off and fall into the ocean.
san francisco bay

San Francisco Bay

  • Water levels in the San Francisco Bay have elevated by more than 8 inches in the last century.
  • The San Francisco Bay shoreline in Oakland and Berkeley is steeper and less prone to flooding than the shoreline in Alameda.
  • Two-thirds of modern-day Alameda, including Bay Farm, South Shore, and Alameda Point, are built on former marsh or fill. Fill area is the most vulnerable to high tide.
  • When storms coincide with king tides, rip rap vulnerability is increased.
surge map

City of Alameda

  • Other than a plan for Alameda Point, Alameda has yet to form any city-plans for sustainable solutions.
  • Unlike Bay Farm's western shoreline, which is heavily armored with large boulders known as rip rap, the north shore has low areas that are vulnerable to flooding.
  • In 2009, the U.S. Army Corps of Engineers reported that high waves from storms in December 2005/January 2006 damaged Bay Farm's northern dike, incurring $500,000 in emergency repairs.
  • In 2015, FEMA (Federal Emergency Management Agency) identified several flood risk zones on Bay Farm Island and parts of Alameda's main island.
  • According to the city of Alameda's analysis of the FEMA flood zone maps, 2,000 parcels of property in Alameda reside is what FEMA considers to be the 100-year floodplain, but FEMA floodplains are based on past flooding and not the dramatic seal level jump that climate experts predict.
  • FEMA's maps showed heavily impacted areas including (among others):
    • Ballena Boulevard
    • Cola Ballena
    • Tideway near Encinal High School
    that are adjacent to Crown Harbor.
  • FEMA's estimates that there will be 1 foot to 3 feet of flooding, yet elevating homes in flood zones is often not possible due to height limits.

City of Alameda Response

  • Since water levels in the San Francisco Bay have elevated 8 inches in the last 100 years, water levels will elevate 8 inches in the next 100 years — not 8 feet as climate experts predict.
  • According to a 2015 letter from the city to residents, "There is a 1 percent chance that in any one year, at-risk property will experience flooding from extreme high tides and storm activity."
  • Skeptics contend that FEMA's floodplain maps are an attempt to get more homeowners to purchase flood insurance to help recoup costs from Hurricanes Katrina and Sandy.
  • The city of Alameda has decided to appeal FEMA's floodplain maps.
rip rap map

rip rap height

Crown Harbor Association



  • Today, though tides vary the level of the bay water with respect to the rip rap, it never reaches the top of the rip rap:

    Tide Average Height
    Low 12.3 feet below the top
    High 6.5 feet below the top
    King 5.0 feet below the top
  • A king tide is when the Earth, Moon, and Sun are aligned to result in the largest tidal range seen over the course of a year. A king tide typically happens once a year around January 2.



  • The typical wave height in Alameda is 1.3 feet.
  • In addition to the tides, the waves reduce the clearance from the top of the rip rap.
  • Based on the dampening effect of the Ballena Bay breakwater, the wave height during a storm near Crown Harbor may be in the neighborhood of 2.0 feet.


  • During bad weather, sea levels rise of about 1 foot due to localized pressure from storms.
  • Long periods of atmospheric river (Pineapple Express) events could cause a temporary build-up in the bay of 0.5 feet.
Download spreadsheet


  • Based on the estimates used in these calculations:
    • Crown Harbor rip rap (12.3 foot height),
    • tides (7.3 foot swing),
    • waves (1.3-2.0 feet),
    • Pineapple Express weather anomalies (0.5 foot rise), and
    • storms (1 foot increase),
    if the expected 8-foot sea level rise by 2100 is linear, for normal weather conditions:
    • Crown Harbor would not have a problem on a normal day with a king tide until 2054.
    • There will be issues at every high tide with average waves in 2070.
    For stormy weather conditions:
    • Crown Harbor would not have a problem on a stormy day with a king tide until 2031.
    • There will be issues at every high tide for stormy days with waves starting in 2047.
  • For planning purposes, 2047 is a good target date since storms on the same day as a king tide after a Pineapple Express period are unlikely, but at least one stormy day in a year is almost certain, and high tides on any day are for certain.
  • The climate change problem will not be solved by Crown Harbor. As a group of 76 owners, the association can work with city of Alameda officials to do what we can to mitigate the problem; however, we have time.

More Info

In Support of Addressing Climate Change

In Opposition of Addressing Climate Change

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