Tuesday, February 21, 2017

Surf science



The LA Times reports that last winter's  El Niño triggered unprecedented erosion across California's coast.

The article highlights research analyzing last year's El Nino storm track that brought us one of the best winter surf seasons on record. 





This new research confirms what we observed in Ventura: the combination of large waves and drought drove unprecedented levels of winter shoreline retreat.


the "cove" at Surfers Point in Ventura
post El Nino winter beach, 5-6-2016


the "cove" at Surfers Point in Ventura
summer beach, 6-28-2016


The drought is just one factor in sand-starved beaches.  “...we dam the rivers for flood control and say, ‘Holy crap, the sand’s not getting to the beaches anymore.”

But last year another force was in play; rising sea levels.  The paper states that "Water levels anomalies of 7–17 cm above normal were measured across the US West Coast during the El Niño winter of 2015–2016, similar to anticipated global mean sea-level increases expected within the next few decades."

This El Niño may have been a big one, but it may become “the new normal”

Which raises the question;

How will rising sea levels affect surfing in the future?

This topic is explored in a new paper titled Using local knowledge to project sea level rise impacts on wave resources in California published in the journal Ocean & Coastal Management.

This research concludes:
Map of California surf-spot vulnerability, Reineman et al

  1. Sea level rise will likely impact the quality of surf-spots; in California that impact will be a net reduction in overall wave quality at current surf-spots. 
  2. Vulnerability of surf-spots to sea level rise varies geographically, with some surf-spots and some regions experiencing more significant reductions in wave quality; due to sea level rise, roughly 18% of surf-spots evaluated here are Threatened by drowning and 16% are Endangered; 5% could improve. 
  3. Surfers' local ecological knowledge of waves constitutes a measureable source of data about environmental condition and variation. 


As sea level rises locally, surf-spots that break at low tide, or medium tide, or high-tide will be increasingly and sequentially inundated: the water will simply be too deep for them to experience their best conditions.

And perhaps most relevant to our local situation, in areas where landward migration of the beach is not permitted, either through seawalls or natural marine terraces, the beach will be "drowned."

Factors influencing surf-spot vulnerability, Reineman et al


This research relied upon surveys of thousands of surfers, who often have the best understanding of local conditions.  The paper concludes that;

Given the vast economic and cultural importance of surfing, these conclusions suggest that coastal managers should not only give credence to the wave knowledge of surfers, but also take wave quality and vulnerability into consideration, especially when planning coastal armoring, beach nourishment, or other developments, whose impacts to natural coastal processes could affect waves.


On this blog:

Surfer Magazine cover
C-St Ventura - cobble and erosion Dec 2015
Surfers Point - first real test
Surfers' Point emergency revetment


References:

El Niño triggered unprecedented erosion across California's coast, LA Times Feb 14, 2017

Extreme oceanographic forcing and coastal response due to the 2015–2016 El Niño.  Barnard, P. L. et al. Nat. Commun. 8, 14365 doi: 10.1038/ncomms14365 (2017).
http://www.nature.com/articles/ncomms14365


Using local knowledge to project sea level rise impacts on wave resources in California, Dan R. Reineman, Leif N. Thomas, Margaret R. Caldwell, Ocean & Coastal Management. Volume 138, 15 March 2017, Pages 181–191


Monday, February 20, 2017

Matilija Dam, after the storm...

Matilija Dam, Feb 18, 2017
flow  3,500+ cfs

2-day rainfall totals Feb 18, 2017
http://www.vcwatershed.net/fws/gmap.html


The storm of Friday, February 17, 2017 delivered 9-10" of rain to the Matilija Canyon watershed.  Flows in Matilja Creek peaked at 4pm with approximately 7500 cfs (cubic feet per second) flowing over the dam.  The Ventura River at Foster Park peaked over 20,000 cfs later that evening.   


The hydrograph below shows flows in Matilija Canyon exceeded 3000 cfs for more than 48 hours.  This is the perfect scenario for flushing the fine sediments from the reservoir to the ocean, as required in order to physically remove the dam.  (See Matilija Dam stakeholders select local project)

Hydrograph for February 2017 storm showing flows at
Matilija Canyon and Ventura River at Foster Park
USGS Current Conditions for USGS 11118500 VENTURA R NR ...
Studies completed last year determined that the minimum high flow event on Matilija Creek that is assumed to be able to transport the large quantities of fine sediment over a short period of time is a storm having an average daily flow of at least 1,700 cfs, corresponding to a peak daily flow of about 3,000 cfs (Stillwater Sciences, 2014b). This is approximately a 4‐year recurrence interval on Matilija Creek.

Although much work remains until the project is ready, a storm like this will exceed that required for the eventual removal of Matilija Dam.



In the News:


“What it really demonstrates is the tremendous energy that the Ventura River has when we get these types of flood events,”


On this blog:


References:


Matilija reservoir upstream of the dam, Feb 18, 2017
The main flow currently enters the reservoir along the right bank (far side in this photo)




contrasting graffiti decorates the obsolete Matilija Dam 



Tuesday, February 7, 2017

Surfers' Point emergency revetment


In February 2016 the City of Ventura constructed a rock revetment  to protect the promenade at "C-St."  Public concern about the city’s response to erosion led to the formation of the Surfers Point
C-St emergency revetment shortly after construction
March 9, 2016
Coalition who collectively commented on a draft alternatives analysis for the emergency permit.  The coalition is working to ensure the final permit addresses potential alternatives and that any future work has the least impact to the recreational and aesthetic values of our beach.

Background:

Surfrider had contacted the City engineering department in October 2015, warning that erosion was imminent given the predicted el Nino winter surf.  Then, as predicted, on December 11, 2015, a large palm tree planter collapsed into the surf during what turnout to be the largest event of the season.  (more here: C-St Ventura - cobble and erosion Dec 2015)

Then just 7 days later, on Dec 18, 2015, the Coastal Commission issued an emergency permit to the City of Ventura.  The permit application stated :

  • an unexpected occurrence in the form of shoreline erosion is threatening to undermine and damage a portion of the Promenade, and continued erosion in addition to predicted El Nino event storm action would undermine and damage the Promenade. This occurrence requires immediate action to prevent or mitigate loss or damage to life, health, property or essential public services. 14 Cal. Admin. Code Section 13009.”
In further communications, Surfrider voiced concerns that shoreline armoring would adversely impact the beach and the high value recreational opportunities at the famed "C-St" surf break.  


Construction of the revetment was initiated on February 3, 2016 and completed on March 4, 2016.  (Note that this was AFTER the biggest swells of the season which typically arrive December-February.)


Surfer's Point Promenade Emergency Repairs
Constructed Condition (ESA Oct 3, 2015)



C-St emergency revetment March 9, 2016

C-St emergency revetment January 23, 2017

In the year it has been in place the rock revetment has already shown some wear.  This is mentioned in the Draft Alternatives Analysis document:

  • The currently-constructed condition alternative requires no change from current conditions, described in Section 2. Since construction, cobble transport to the east and degradation of revetment design under subsequent storm has occurred. A site visit on June 6, 2016 showed that the fine-grained fill at the top of the revetment had been weathered enough to expose the filter fabric and large voids in the revetment. Further images from September, 2016 indicate that erosion has continued in this area. Additionally, some shifts in the rock revetment had occurred as a consequence of wave action.   (ref: Draft Alternatives Analysis pg19)


Emergency Permit:

Under the Coastal Act, an emergency permit is conditional and requires that the permittee follow up and apply for a final permit which, among other things, requires an alternative analysis.  The city initiated this process which has so far included two "stakeholder" meetings.

Several people who had contacted the City to voice their concerns were included in these meetings, which led to the formation of the Surfers’ Point Coalition.  These stakeholders include local surfers with many years experience at Surfers’ Point, as well as expertise in ocean engineering, engineering design, project permitting, and “real world” water time.

The Coalition submitted comments to a draft Alternatives Analysis which is currently under revision.  Compatibility with the US Army Corps of Engineers requirements required an extension of the timeline, and subsequent withdrawal of the permit application.  The project will require both an Army Corps and Coastal Commission permit.

The current schedule anticipates an opportunity to review the updated analysis in April with final permit applications submitted to Corps and Coastal Commission in May.






Alternatives:

The Surfers' Point Coalition proposed a modification to one of the alternatives presented in the analysis.

  • As noted in our comments on the Alternatives Analysis, there is merit in developing a strategy to retain cobble on the beach face at Surfers’ Point.  While the past cobble nourishment provided effective shore protection, the benefit is unfortunately short lived due to the high rate of longshore transport at the point.  The attached concept modifies the profile of the Low-Profile Groins with Cobble Nourishment alternative to better match the shoreline dynamics while minimizing the regulatory footprint.  These structures should be designed with large enough boulders such that they will withstand extreme surf conditions, serving to establish semi-permanent “pocket beaches” backfilled with cobble.  The spacing and elevation shown on the drawing should be considered a starting point for further design.




  • As the Alternatives Analysis points out, the City of Ventura has been very proactive in experimenting with alternative shore protection strategies.  Given this history, it would be appropriate at this time to develop an engineering solution that would provide multiple benefits without adversely impacting the aesthetic and recreational qualities of Surfers’ Point.  If this experimental solution proves viable, it can be duplicated along the remainder of the beach fronting the promenade as needed in the future.

This could look something like this:






What's at Risk?

Aerial view of erosion resulting from the
1991 Surfers' Point emergency revetment
History, science, and personal experience has shown that emergency responses to beach erosion can lead to piecemeal coastal armoring.  This was evident at Surfers' Point during the last erosional cycle of 1991-1995, shortly after the bike path was extended along the beach at the fairgrounds.  The emergency revetment placed in 1991 exacerbated erosion on the adjacent shoreline resulting in the closure of a damaged section of parking lot for 15 years until the managed retreat project was constructed. 

A holistic approach that considers the shoreline as a contiguous system is required to effectively manage the coast.  Otherwise the public beach will slowly be replaced with progressively larger rocks in response to each erosion episode, forever changing the character of this valued resource.    



More information:

On this blog:
C-Street, Ventura - more cobble berms
C-St Ventura - cobble and erosion Dec 2015