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| Surfers Point Managed Retreat Protective dunes December 11, 2015 |
December 11, 2015 marked the first real test of the Surfers Point Managed Shoreline Retreat project. Things have been relatively calm since the project was constructed in 2011. But last week, the first sign of this year's much-publicized "El Nino" materialized, coinciding perfectly with the new moon and morning high tide. The swell registered 25ft at 17 seconds from 295 degrees on Harvest buoy. Although the predicted tide was 6.2 ft above "mean sea level," sea level has been recorded up to 1 foot higher this year due to warm surface waters throughout the Pacific Ocean. A tsunami gage recently installed at the Ventura Harbor recorded sea levels over 8.2 feet! Storm surge combined with
Coastal Flooding, Hanover Lane, Pierpont Beach
Ventura CA Dec 11, 2015
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The Surfers Point Managed Shoreline Retreat project combines restoring adequate setback with an engineered cobble berm and vegetated dunes to enhance coastal resiliency. This first test proves this concept quite dramatically. (It is ironic that the dunes at Surfers Point were constructed with sand from dunes that were removed from Pierpont beach due to beachfront homeowners objections to losing their views and recreational space!)
The photo below shows that although the seaward edge of the dunes was eroded, overtopping was kept to a minimum. The loss of the seaward edge of these dunes was expected, and they will grow back during the summer months. This illustrates the value of "retreat." Allowing space for the beach, dunes, and cobble to come and go naturally is a welcome change from the crumbling asphalt and concrete that were removed from this site.
The photos below are shown to illustrate the difference between the Managed Retreat project area and the parking lot that remains until Phase 2 is funded. Although there was no damage to the bike path and parking lot this time, the entire area got wet with overtopping waves.
The following sequence illustrates the function of the buried cobble berm. The summer waves bring sand back to the beach every year, completely burying the exposed edge of the cobble berm. Winter swells remove this sand and expose the cobble beneath. The cobble naturally forms a berm which is very effective at absorbing wave energy. Note that this site is on the Ventura River Delta where cobble is a feature of the natural beach. Also note that the hard escarpment is a result of "sand" that was imported from an inland source during construction. Despite engineering specifications that limited the percentage of fine sediment in this material, there was enough fine silt and clay to firmly cement this layer. Erosion events like this will remove this fine material over time leaving a more natural sand and cobble beach.
The photo below shows that although the seaward edge of the dunes was eroded, overtopping was kept to a minimum. The loss of the seaward edge of these dunes was expected, and they will grow back during the summer months. This illustrates the value of "retreat." Allowing space for the beach, dunes, and cobble to come and go naturally is a welcome change from the crumbling asphalt and concrete that were removed from this site.
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| Surfers Point Managed Retreat Foredune erosion and overtopping December 11, 2015 |
The photos below are shown to illustrate the difference between the Managed Retreat project area and the parking lot that remains until Phase 2 is funded. Although there was no damage to the bike path and parking lot this time, the entire area got wet with overtopping waves.
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| Surfers Point Managed Retreat overtopping downcoast of retreat zone December 11, 2015 |
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| Surfers Point Managed Retreat overtopping at phase 1 boundary December 11, 2015 |
The following sequence illustrates the function of the buried cobble berm. The summer waves bring sand back to the beach every year, completely burying the exposed edge of the cobble berm. Winter swells remove this sand and expose the cobble beneath. The cobble naturally forms a berm which is very effective at absorbing wave energy. Note that this site is on the Ventura River Delta where cobble is a feature of the natural beach. Also note that the hard escarpment is a result of "sand" that was imported from an inland source during construction. Despite engineering specifications that limited the percentage of fine sediment in this material, there was enough fine silt and clay to firmly cement this layer. Erosion events like this will remove this fine material over time leaving a more natural sand and cobble beach.
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| Surfers Point Managed Retreat Summer beach profile Sept 18, 2015 |
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| Surfers Point Managed Retreat Winter beach profile December 2, 2015 |
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| Surfers Point Managed Retreat Extreme event response December 11, 2015 |
These next two photos show how much sand was removed during the large swell of December 11. Also compare the degree of overtopping during the high tide of December 2nd vs that of December 11. (Remember that this cobble berm will once again be buried in sand next summer.) The rocks in the right foreground are the "spur groin" on the end of the Ventura River levee. This structure focuses wave energy onto the cobble berm, which was the cause of greatest erosion prior to construction of the managed retreat project.
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| Surfers Point Managed Retreat Cobble berm from the west December 2, 2015 |
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| Surfers Point Managed Retreat Cobble berm from the west December 11, 2015 |
It is also interesting to compare those areas with established dunes versus a flat beach. Although the dunes were slightly overtopped or wetted in the low spots, large surges of seawater completely flooded the recreation area used by kite boarders. (Note that this flat area was not part of the original plan, but was modified during construction. While this actually enhances this "living laboratory" opportunity, it is clearly the weak link in the project.) Also note the blown sand in the foreground of the second image: this is the only location where sand is not captured by vegetation, often resulting in sand blown onto the bike path.
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| Surfers Point Managed Retreat Dunes vs flat beach December 11, 2015 |
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| Surfers Point Managed Retreat Dunes vs flat beach December 11, 2015 |
The Surfers Point Managed Shoreline Retreat project performed as designed during the first significant swell since construction. We shall continue to maintain and monitor the site to demonstrate the advantages to this approach to coastal management compared to the hard structures of traditional coastal engineering.
Special thanks to all the partner agencies who made this project possible!
More on this blog: Surfers Point
More project history: SurfersPoint.org
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