Brisbane Lagoon Watershed Sea Level Rise Adaptation Plan Sea Level Rise Subcommittee Update #2
March 30, 2026
Agenda
• Project Overview and Background Refresher
• Partners
• Community Outreach
• Hydrology & Hydraulic Summary
• Approaches and Measures
• Proposed Alternatives
• Draft Evaluation and Input
• Questions
Project
Overview
The goal of the project is to develop and
adopt a Brisbane Lagoon Watershed Sea
Level Rise Adaptation Plan (Plan).
The Plan will identify solutions that:
• Protect Brisbane residents and
Highway 101 from flooding impacts
related to climate change
• Enhance lagoon resilience to sea level
rise, while supporting natural systems
• Improve ecological function and habitat
continuity
• Explore opportunities to improve
existing public access
Project Linkage to Oneshoreline
https://oneshoreline.org/wp-content/uploads/2025/12/BrisbaneLivingShoreline_2pager_20251218.pdf Project Linkage to RSAP
$750,000
California
Ocean
Protection
Grant
Project Advisory Committee
• Association of Ramaytush Ohlone
• Baylands Development Inc.
• BCDC
• California High Speed Rail Authority
• Caltrain – Peninsula Corridors Joint Powers Board
• Caltrans D4
• OneShoreline
• San Mateo County Department of Emergency Management
• Sierra Point Owners Association
Project Advisory Committee Role
• Provide feedback on planning process – PAC Meeting 1
• Review comments from the public – PAC Meeting 2
• Guide implementation of proposed activities – PAC Meeting 3 • PAC #3 Goal – provide input on three (3) alternatives and evaluation criteria for upcoming community meeting April 30th Project Timeline
10.16.25 12.16.25
10.21.25 4.30.26
3.12.26 11.18.25
3.30.26 Brisbane SLR Subcommittee
Community Outreach
• Art contest online
• Through April
• $50 gift cards
• Photo will likely be cover of report
• Community Meeting April 30th at
library 5:30-7:30pm
Analysis Overview
Flood Hazards Analyzed
Hydrologic and Hydraulic Results
Scenario
10yr Storm, 100yr Tide
Lagoon Peak Water Surface
Elevation (ft, NAVD)
100yr Storm, 10yr Tide
Lagoon Peak Water Surface
Elevation (ft, NAVD)
Existing 10.0 8.9
2050 10.8 9.8
2100 LOW 13.2 12.1
2100 HIGH Overtops Highway 101 Overtops Highway 101
TIDES > STORMS
Brisbane Lagoon
Watershed
January 3rd 2026
• Existing condition roadway is underwater
• Jan 3rd was about 1-ft lower than 100-yr tide
• Increasing tides will get worse
Curtesy of Brisbane Resident Emmett
Marsh Under Water on December King Tide
Hydrologic and Hydraulic Summary
• Lagoon water surface is drive by the tide
• The twin culverts have capacity to drain out the lagoon • The lagoon is not significantly overwhelmed by 100yr runoff • The lagoon fills and drains delayed from tide about 1.5hr • Mid Century - lagoon water surface elevation about 1-ft higher • At around lagoon elevation 8.5-ft a portion of Sierra Point Parkway is underwater • End of century, water is overtopping highway 101
Approaches
Adaptation Approaches
PROTECT ACCOMODATE RETREAT
Primary Measures: Lagoon/Coastal Flooding
Protect: Raise Edge Protect: Tide Gate
Accommodate: Raise
Infrastructure (Roads/Rail)
Accommodate: Pump station Retreat: Repurpose street/naturalize Raise Edge: Flood Wall
Hazard: Lagoon/Coastal Flooding
Strategy: Raise Edge
Vinyl Sheetpile at SFO
Adaptation Approach: Accommodate
Hazard: Lagoon/Coastal Flooding
Strategy: Raise Infrastructure (Roads/Rail)
Section Elements
BAY TRAIL
DFE
ADAPTATION ZONE
Repurposed Street/Retreat
Hazard: Lagoon/Coastal Flooding
Strategy: Abandon infrastructure/naturalize
Measures
Engineering Measures
Tide Gate Flood Walls Raise Trail Pump Station Increased Detention Complementary Measures +
Nature-Based Features
Erosion:
Lagoon Beach
Erosion:
Naturalized Edge
Erosion:
Ecological armoring
Mitigation:
Enhance/preserve
Existing wetlands
Stormwater:
Green infrastructure
Alternatives
Proposed Flood Mitigation Alternatives
1. Do Nothing 2. Manage Bay Water 3. Raise Lagoon Edge 4. Pump Station Do Nothing
Do Nothing
Marsh Habitat AS SEA LEVELS RISE, MARSH HABITATS
WILL MIGRATE UP IN ELEVATION
TRANSITION MARSH WILL DROWN
OUT OVER TIME AS LOW MARSH AND
HIGH MARSH EXPAND UPLAND
Manage Bay Waters
ADD
TIDE GATE
INCORPORATE
ECOLOGICAL ARMORING
SLOW DROWNING OF
EXISTING WETLAND
Manage Bay Waters
Open and shut tide
elevations can be
managed https://www.youtube.com/watch?v=cW300UkNCQo
Future Design Considerations
• Regulatory
• Lagoon vs bayside
• Permitting timeline
• Frequency of closure, need to close around 8-ft tide
• Change to salinity in the lagoon
• Maintenance responsibility of tide gate
Raise Lagoon Edge
RAISE
ROADWAY
NATURALIZED EDGE +
LAGOON BEACH
WETLAND
ENHANCEMENT
Raise Lagoon Edge
Future Design Considerations
• Amount of beneficial fill
• Protect to end of century or adapt by mitigating tides • Fisherman Park considerations
Pump Station
CLOSE CULVERT,
INSTALL PUMP STATION
INCORPORATE
ECOLOGICAL ARMORING
Pump Station
Future Design Considerations
• Change in habitat to freshwater
• Location for large pump station
Evaluation Criteria
Evaluation Criteria
Ecological Benefit Permitting/
Design Duration
Benefit to Existing
Public Access
Cost
Legend
Low
Habitat Benefit
Medium
Habitat Benefit
High
Habitat Benefit
0-5 years
to permit
5-10 years
to permit
>10 years
to permit
<$5m
project costs
$5m - $15m
project costs
>$15m
Project costs
Low Public
Access Benefit
Medium Public
Access Benefit
High Public
Access Benefit
Ecological Benefit
Permitting/
Existing Public Access Design Duration Cost
Evaluation - DRAFT
Raise Lagoon Edge
Pump Station
Questions