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Erosion at Topanga Beach in August 2021

California Coastal Commission staff presented two important items regarding sea level rise in coastal cities like Malibu at the commission’s September meeting last week.

The commission is urging local communities to get proactive in planning how they are going to deal with sea level rise and adapt to its effects on infrastructure like roads, wastewater systems and stormwater drainage. Some of these changes and the funding for them need to be planned out years in advance.

To that end, the commission has released a draft version of what is basically a handbook for local governments to use in developing their own guidelines and policies. The 224-page document— “Critical Infrastructure at Risk—Sea Level Rise Planning Guidance for California’s Coastal Zone”—was made public on Aug. 16. Comments are still being collected through Sept. 24.

A study that analyzed 4.6 feet of sea level rise by 2100—which is what many experts predict—found that hundreds of miles of highways and railways statewide would be threatened or damaged by flood events. Flooding and rising groundwater would threaten at least 28 wastewater treatment plants in California, as well as wastewater and water supply distribution systems. In addition, flooding would increasingly threaten stormwater systems throughout coastal communities and seawater intrusion would threaten freshwater supplies in some areas.

That is why cities need to start planning now, they say, as a way to avoid future damage and loss of service. The commission document explains how existing infrastructure can be flood-proofed, elevated and relocated. New infrastructure can be sited in areas safe from hazards or replaced by newer systems. Natural green systems can be restored or enhanced in combination with constructed features.

The commission emphasized that adaptation and change is not expected to happen all at once; adaptation plans can be phased in gradually over time as sea levels rise.

But the 4.6-foot rise is just the beginning—the document recommends cities evaluate the expected impacts to critical infrastructure that would be caused by approximately 10 feet of sea level rise by the year 2100.

The document was developed in coordination with Caltrans, state and regional water boards, and other agencies; it consists of advisory guidelines, examples and recommendations—not regulations. Commission staff want cities to use that information to help modify their own local coastal programs (LCPs) with plans on how they intend to be resilient to climate change and sea level rise.

To read the draft document, go to bit.ly/SeaLevelRisePlanning.

 

Rising groundwater marks ‘paradigm shift’

California Coastal Commission staff also released a new statewide model predicting how sea level rise will cause groundwater to rise in the shallow groundwater tables of coastal communities. This is a new threat that had not been considered before as a consequence of sea level rise. This would be a particular concern for areas in Malibu where high groundwater levels have always been a problem, including most of the Civic Center area.

Coastal commission climate change analyst Kelsey Ducklow indicated groundwater was expected to rise so much in some places that “dry land will turn into wetlands.”

Patrick Barnard, PhD, research director for the Climate Impacts and Coastal Processes Team of the United States Geological Survey in Santa Cruz, leads the study.

He stated that California’s coastal communities will experience the impacts of groundwater rise in a number of ways: emergent flooding and ponding, foundation damage, pollutants, impacts to septic systems and their leach fields, increased liquefaction risks, saltwater intrusion farther and farther inland, drainage problems, and roadbed damage.

Barnard also emphasized that it is not just seal level rise itself that will cause damage and problems—sea level rise in combination with storms will result in much higher tides, storm surges, flooding and erosion, all of which put people and property at higher risk.

“Groundwater rise may possibly cause greater damage and exposure to risk than surface flooding,” he commented at the meeting. “The research is still ongoing and we’re still assessing the cascading effects of sea level rise.”

Donne Brownsey, vice chair of the California Coastal Commission, said after hearing the presentation, “The idea that it’s not just sea level rise, but also groundwater rise, is a paradigm shift for what communities will start facing. It’s critical for our own staff as well as officials to understand what’s at stake.”

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