Category Archives: Sandshed Science

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King Tides

King Tides and Future Sea Level Rise

Check out the great memorandum put out by my friend Dave Revell, with Revell Coastal, explaining King Tides. I urge you all to get out early on Sunday and Monday (January 20 and 21, 2019) to experience the king tides at the coast near you. Remember, this is a good way to experience how a "typical" tide will flood surrounding areas with ~1.5 feet of sea level rise on a routine high tide, which is a reasonable estimate for sea level rise in the next 20 years.

You can also be a part of the California Coastal Commission's active citizen science project and submit your own pictures of the king tide. Follow this linkhttps://www.coastal.ca.gov/kingtides/ to learn more about king tides and submit your pictures.

Date: January 19, 2019
To:    Interested Citizens of Southern California
From: Potential King Tide Photo Spots in SoCal in December 2018

Purpose

To respond to many requests from respected colleagues and news outlets interested in helping to monitor potential sites that are likely to be exposed to flooding from an extremely high “King” tide. The highest high tides follow the full moon cycle and are predicted to occur on the mornings of January 20th and 21st, 2019.

Background

A “King tide” is also known as a perigean spring tide, when the moon in the winter reaches its nearest orbit to the earth and thus exerts its largest gravitational pull on the ocean water levels.

A king tide with no storms identifies places that will be routinely vulnerable to sea level rise first. A king tide with high waves can cause extensive wave flooding and coastal erosion. A king tide with a rain event can also back up stormwater during rain events and cause increased ponded flooding. No large wave or rain events are predicted with this king tide series.

On the US West Coast erosion and coastal hazards are caused by large storm wave events and total water levels not only high tides. Total water levels are the combination of wave run-up, and high tides, NOT storm surge (which can be 20 feet in a major hurricane on the East and Gulf Coasts versus 3 feet on the West Coast). A king tide provides a good example of what would be flooded by ~1.5 feet of sea level rise on a routine high tide and is about 1.5 to 2 feet above a normal high tide (Mean High Water is the average of all high tides over a 19 year period is the public-private boundary in CA). High tides though do play an important role in beach ecology affecting where certain species can safely nest, overwinter, and lay eggs. In locations where coastal armoring (seawalls and revetments) are prevalent, king high tides can flood beaches, inundate unprotected stormwater and wastewater systems which tend to be gravity fed and restrict access and coastal recreation.

Forecast

This high king tide series in December is forecast to have minimal wave energy during this tide series which makes this less exciting yet still important to document. The key locations to document impacts would be those that will be routinely impacted by sea level rise in the next 20 years. My prediction based on wave conditions is that there will not likely be large flooding or coastal erosion, but rather certain areas will be flooded and highlight areas that will pose future transportation bottlenecks, nuisance property flooding, illustrate future loss of beaches in areas of heavy coastal armoring and illustrate critical infrastructure that will likely be isolated from maintenance and emergency repair crews.

What to look for

Missing beaches that have coastal armoring on the backshore which demonstrate the impact of coastal squeeze (loss of beach due to coastal armoring and sea level rise = loss of our public trust resources)

Flooded roadways or runways that may hinder future evacuation

Completely full estuaries that show little to no vegetation around the edges (while this is an important process to accrete sediment, it demonstrates there is nowhere left for these ecosystems to evolve)

Open mouthed lagoons are affected by tides and thus inland development fringing those lagoons (probably delayed by an hour or two from peak high tide). If a barrier beach is present then probably not worth the time.

Locations in southern California (Imperial Beach to Point Conception) South to North

Specific locations (* potentially dramatic and news story worthy)

San Diego

Imperial Beach

South Sea Coast Drive*

Bayview School  and the South Bay Bikepath on San Diego Bay

Helicopter Base in Tijuana River Valley

North County lagoons

Beaches on Del Mar* (important to show the loss of beach amidst the controversy around managed retreat)

Low lying beach areas in Coronado, Mission Bay, Encinitas, Carlsbad, and Oceanside

 

Orange County

Beaches in San Clemente

Capistrano Beach

Newport Bay – Balboa Island*, upper Newport Bay

Huntington Beach Wetlands including access to the rebuilt power plant and proposed Desalination Plant site*

Seal Beach wetlands (Sunset and Los Alamitos Bay) and fronting development

 

Los Angeles County

Long Beach and LA Harbors

Ballona Wetlands

Venice Beach Canals*

Malibu Beach Adamson House

Broad (No) Beach*

 

Ventura

South County PCH particularly state park beaches at Sycamore Cove, and campgrounds at Point Mugu State Park

Mugu wetlands and the Naval Base Ventura County runways, beaches, and wetlands*

Oxnard J Street Drain

City of Port Hueneme Beaches

Channel Islands Harbor (inside) – South Victoria Avenue near Lakeshore Ct. (evacuation route)

Pierpont Bay Community

Sanjon Barranca (if open)

Surfer’s Point restoration versus Ventura Promenade (managed retreat vs hold the line)*

Rincon Parkway (no beaches)

Rincon Creek

 

Santa Barbara

Contrast the beach between City of Carpinteria Beach with Sandyland Cove*

Carpinteria Salt Marsh

Potentially inundation on the North End of Ash Avenue

Beach fronting Sand Point Road with unpermitted revetment

Beach in front of Channel Drive in Montecito

SB Waterfront (in particular Laguna Channel and the tide gate)

Goleta Beach County Park (now completely armored)*

Goleta Slough (if open) and the airport

Devereux Slough (if open) and the new restoration*

Bacara Resort and the emergency revetment fronting the bathhouse*

Sea Walls along Gaviota Coast protecting the railroad (beach narrowing)

Refugio Beach State Park

Hollister Ranch and the under litigation public access point at Cuarta Beach*

Large wave event near the Pierpont neighborhood in Ventura, California

What is the littoral cut-off diameter?

Very fine-grained sand, ranging from 0.0625 to 0.125 mm in diameter (4ø to 3ø), typically doesn’t remain on the exposed (dry) portions of most California beaches due to the high-energy wave environment. An investigation of littoral transport processes and beach sand in northern Monterey Bay (Hicks, 1985), discovered that there is a littoral cut-off diameter, or a grain-size diameter, characteristic of any particular segment of coast. The cut-off diameter serves as a functional grain size boundary in that very little material finer-grained than this diameter actually remains on the exposed beach. The cut-off diameter along any particular beach or stretch of coast is primarily a function of wave energy at that location. Studies along the coast of northern Santa Cruz County, which is a relatively high-energy, exposed coast, determined a littoral cut-off diameter of ~0.18 mm (2.5ø) for this stretch of coast, with very little finer sand remaining on the exposed beaches. In southern California, where much of the coast is protected from strong wave action by the sheltering effect of the Channel Islands, the littoral cut-off diameter is smaller, typically around 0.125mm (3ø). When estimating or calculating inputs to a sand budget or planning a beach nourishment project, it is important to consider the littoral cut-off diameter. Sand placed on the beach or entering a littoral cell that is finer than the littoral cut-off diameter will not remain on the dry beach.

What is Littoral Drift?

Researchers have learned that sand is in constant motion along California’s coastline, and only resides “temporarily” on an individual beach. An alongshore or littoral current is developed parallel to the coast as the result of waves breaking at an angle to the shoreline. This current and the turbulence of the breaking waves, which serves to suspend the sand, are the essential factors involved in moving sand along the shoreline. As waves approach the beach at an angle, the up-rush of water, or swash, moves sand at an angle
onto the shoreface. The backwash of water rushes down the shoreface perpendicular to the shoreline or a slight downcoast angle, thus creating a zigzag movement of sand. This zigzag motion effectively results in a current parallel to the shoreline. Littoral drift refers to the movement of entrained sand grains in the direction of the longshore current.

Littoral drift can be thought of as a river of sand moving parallel to the shore, moving sand from one coastal location to the next and so on until the sand is eventually lost to the littoral system. Littoral drift or transport in California can occur alongshore in two directions, upcoast or downcoast, dependent on the dominant angle of wave approach. Along the California coast, southward transport is generally referred to as downcoast and northward transport is considered upcoast. If waves approach perpendicular to the shoreline, there will be no net longshore movement of sand grains, no littoral current, and thus no littoral drift. Longshore transport for a reach of coast will typically include both upcoast and own coast transport, often varying seasonally.

What is a Sandshed?

Sandsheds form the framework for our understanding of the sources, sinks, transport, and storage of sand along the coast in conjunction with the processes and factors shaping the economic, recreational and ecological health of beaches. Similar to a watershed which delineates the boundary of land draining into a particular river, a sandshed physically encompasses the land and nearshore zone affecting the sand supply and overall health of our sandy beaches in a particular beach compartment or littoral cell. In California, a beach compartment or littoral cell typically begins at a rocky headland and terminates into a submarine canyon with sand transported along the shoreline in the direction of the predominant waves. Managing the coastline with a sandshed-based approach is a beach-centric, interdisciplinary method that assesses sand supply and processes within a regional landscape to evaluate the stability and condition of our beaches in a holistic way to minimize hazards and maximize the recreational, geomorphological, ecological, and cultural value of the beach.

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