HomeMy WebLinkAboutppt flooding 010820AWater Quality Committee Presentation: Harbor Flooding Concerns
January 9, 2020
Lo w-Lying Areas Around the Harbor
National Flood Insurance ProgramSpecial Flood Hazard Areas
Seawall and Beaches provide flood protection
2100 Projected Sea Level
Rise Ra nge: 2.1’-6.7’
Astronomical High Tide Prediction: 6.4 feet Measured High Tide: 7.16 feet
3 feet of sea level rise (between 2080-2120)
Adaption Strategies:
1. Protect2. Accommodate3. Relocate
Ca p Ext e n s io n
Dra ina ge Syste m
•Gravity Drainage System Originally
Installed around 1930’s with
Seawall
•Originally Pipes with Wood Plugs
•Some interior pipes added.
Modified to current Manual Tide
Va lve Sys t e m
•Requires almost Daily Labor
attention, Supplemented by
Potable Pumping Units during High
Tides & Rain EventsTide Valves
34 Tide Valves Protects the Island from Flooding
due to High Tides. Currently Manually Operated
Manual
or Power
Assisted
Operation
Balboa Island - Thanksgiving Day 2019
12
Possible Big Island Drainage Concept
Storm Water Pump Station
Under Street (electric)
Green: 3 feet of sea level rise (between 2080-2120)
Go l d : 5 feet of sea level rise (between 2100-2150)
What if: 55” Sea Level Rise?
Flood Protection Actions
CURRENT
1.Increase height of seawall coping
2.Create automated tide gates and stormwater pumpstations.
3.Periodically build beach berms
LONGER TERM
1.Replace aging public seawalls wit h cantilevered seawalls where when the cap height can be periodically raised.
2.Create a master plan program to facilitate permitting of private seawalls.
3.Change General Plan to require higher finish floor elevations.
4.Address groundwater.