SB County Flood Control presentation from the March 15 BEACON Board Meeting. Agenda Item # 9.
This presentation was given at the BEACON Board Meeting on Friday, March 15, 2019. The Powerpoint has been converted into a video:
King Tides are predictable, larger than normal high tide events that occur a few times a year when the moon is closest to the earth. A more scientific name is perigean spring tides. King Tides are interesting because they help to illustrate what more normal high tide events will look like in the future as sea level rise becomes more pronounced.
Part 2 Maureen Spencer Santa Barbara Flood Control
Dan Hoover USGS, Glen Shepard Ventura County Wathershed Protection District, Matt Roberts City of Carpinteria
The Coast and River Report
Sandshed: The Sand Is on the Move!
There is a constant flow of sand from the land into the ocean. Watershed run-off and bluff and hillside erosion bring sand to the beach. Sand grains travel southward down the coast, while finer particles of sediment are carried and deposited further out to sea.
Along the way, sand is washed ashore, temporarily resting on beaches, until it is re-suspended in the ocean by wave action or wind. The one-way journey down the coast ends when sand is blown inland forming sand dunes, or more commonly, when it flows into a submarine canyon. This deep underwater feature is essentially the dead end of a littoral cell, where sand is deposited for the long-term and, for practical purposes, lost.
A littoral cell is a distinct area of the coastline where sand enters the ocean, flows down the coast, and then is removed from the system. Permanent loss of sand occurs at the end of the littoral cell when it flows into a submarine canyon or, less frequently, when it accumulates on shore as part of a sand dune. The amount of sand available to…
Credit: Dave Hubbard and UCSB Sea Grant Team
A Beach Nourishment Opportunity
Beach Erosion Authority for Clean Oceans and Nourishment
Sequence of Events
- Thomas Fire – December 2017
- Montecito Debris Flows – january 9, 2018
- Perhaps 500,000 cy made it to the beach
- About 70,000 cy deposited on public streets & flood control channels
- About 400,000 cy deposited in local debris basins
- Perhaps 1,000,000 cy deposited on private property
- Street & f/c channel sediment taken to Goleta & Carpinteria Beaches
- Debris basin sediment taken to Buellton & Santa Paula landfills
- Private property sediment remains in place
What Does Debris Flow Look Like?
Montecito Debris Flows Stats
- 25 people killed
- Over 100 homes destroyed & more than 300 damaged
- Widespread damage to property & infrastructure
- About 2M cy of sediment released from foothills
- Sediment mostly composed of sand (80%) along with rocks, logs, etc.
- Sediment largely uncontaminated
Impact to Beaches
- Sediment sorted rapidly by waves with finer material moving offshore & coarser material onshore
- Rocks & boulders deposited at creek mouths – logs & other floating debris scattered along coast
- Nearby beaches grew wider – new sand blended in well with existing
- Trucked sediment at Carpinteria & Goleta Beaches had similar effects
- Water quality impacts significant but short-term
Fernald Point – April 2017
Fernald Point – January 2018
Fernald Point – February 2018
Loon Point – April 2017
Loon Point – January 2018
Loon Point – March 2018
Carpinteria Beach – April 2017
Carpinteria Beach – January 2018
Carpinteria Beach – March 2018
Goleta Beach – June 2017
Goleta Beach – January 2018
Goleta Beach – February 2018
Goleta Beach – March 2018
Predicted Shoreline Response
Unique Opportunity for Beach Nourishment
- Large volume of sediment available on private property
- Significant benefit if sediment taken to beaches
- Sediment must be sorted & stored for placement in Winter/Spring
- Comprehensive SCCBEP-type program needed to:
- Establish sorting/storage areas
- Identify beach receiver sites
- Establish testing, placement & monitoring protocols
- Secure environmental permits
- Identify/develop funding mechanism
“Where is the mud and debris from Montecito going” by Oscar Flores
Source: KEYT online
Carpinteria Beach and other local beaches are the preferred locations for receiving excess sediment from the recent extreme flood event. Normally this sediment would have made its way to the coast in a controlled manner over the course of many years. But in the present case, heavy rainfall coupled with burned hillsides caused the sudden release of a large amount of sediment and debris leading to widespread flooding and damage.
When sediment arrives at the beach either by stream or by truck, natural wave action sends the finer material (clays and silts) offshore leaving the coarser material (sand, gravel and cobbles) nearshore. Further wave action mixes the gravel and cobble fractions downward into the beach face where they eventually form a hidden protective layer. The remaining sand fraction stays in the nearshore helping to nourish the beach profile.
Ash Avenue is an excellent receiver site for the excess storm sediments. Located at the end of a long rock revetment, it is the first to lose its sand during storm wave attack and the last to recover its sand during milder conditions. Placing excess storm sediment on the beach widens it providing added protection against storm wave attack and creates space in local debris to combat future flooding events.
Jim Bailard, Ph.D.
BEACON Technical Advisor
USGS Coastal Erosion Report May 19, 2017 by Dan Hoover, Lead Researcher.
Report given during BEACON Board of Directors Meeting, Carpinteria, CA.