Terry Gaasterland | Chair, Sea Level Rise Technical Advisory Committee
In 2015, Del Mar launched local planning for sea level rise. Del Mar’s citizens, staff, and council members worked hard for 3 years to learn about flooding and erosion risks to our beaches, wetlands, homes, and public and private infrastructure. The result: a Sea Level Rise Adaptation Plan adopted by Council on May 21, 2018. It is intended to lay out risks, and tools Del Mar can use in planning for those risks, on a very long-term basis, through 2100. Risks and tools differ from wetlands and river to beach and bluff.
The plan points to five highest priorities to protect Del Mar from erosion, river flooding and storm surge:
• Replenish sand on all beaches on a regular basis.
• Protect beach access points.
• Raise sewer lift station above flood levels or waterproof the pump.
• Relocate or flood-proof public works offices, garage and work areas.
• Relocate or flood-proof fire station.
For beach neighborhoods, the roads and bridges, tennis and basketball courts, parking lots, and low lying beach neighborhoods will experience new or increased flooding as river sediment accumulates, as rainstorms drop larger amounts of water, or as windstorms surge more forcefully from the sea. Options to address beach-level vulnerabilities include:
• Replenish sand on the beaches.
• Dredge the river channel.
• Improve upstream reservoirs for more flood protection.
• Build levees.
• Elevate structures.
• Relocate public infrastructure.
• Raise and improve sea walls and revetments.
For Powerhouse Park, the plan points out a trade-off: armor the bluffs along the Powerhouse and lose some beach; or let the bluffs erode and lose some grassy areas. With enough sea level rise, Del Mar may one day face this choice. In the short run, Del Mar can continue to build sand berms each winter to protect the low bluffs, and start planning now to ensure replenished sand each year.
For bluff neighborhoods, bluff erosion from rising seas may expand the number and size of local collapses and put the railroad at risk. Reinforcing the railroad will lead to narrower beach below the southern bluffs. Removing the railroad and allowing natural bluff erosion will replenish sand to some extent, but eventually may imperil other infrastructure along the bluff top and possibly some bluff top homes. Water drainage from east and uphill compounds bluff erosion. Tools range from immediate to long-range:
• Replenish sand on beaches below the bluffs.
• Improve surface water drainage east and uphill of all bluffs.
• Improve groundwater drainage along bluff edges and faces.
• Reduce landscape irrigation throughout Del Mar.
• Relocate sewer lines and fiber-optic cables off the bluff.
• Add railroad crossings and pathways down the bluffs to reduce foot traffic.
• Re-vegetate worn-down footpaths.
• Relocate the railroad off the bluff.
The San Dieguito wetlands will experience “habitat creep” with new flooding due to sea level rise. The marshes will drown if they cannot migrate upstream or expand. Some tools to respond may be feasible in Del Mar; some may not, but the plan lists them as options:
• Place sediment to preserve wetland elevations relative to tide levels.
• Place wetland vegetation seeds at higher elevations as tide levels rise.
• Create protected spaces for wetlands to transgress, upland and upstream.
• Create spaces for the wetlands to expand.
• Create new wetlands through “restoration.”
Keeping sand on the beaches is the first protection for beach and bluff neighborhoods. Del Mar’s Adaptation Plan gives highest priority to sand management. Sand management and retention tools to start thinking about include groins, breakwaters, artificial reefs, “living levees” and future technologies. The Plan recommends creating a Beach Retention Advisory Committee.
What started all this planning? What’s next? The California Coastal Act requires us to address hazards in our Local Coastal Program (with our current LCP not specifically addressing sea level rise), and California’s Senate Bill 379 requires every city to update its “safety element” to plan for new fire and flood vulnerabilities due to climate change. Del Mar will add the Sea Level Rise Adaptation Plan in some form to our safety planning documents. On May 21, Council asked the City Attorney and staff to study the pros and cons of adding the Adaptation Plan to Del Mar’s certified LCP or to our Community Plan.