Mansons Landing: Shoreline Of The Spit Is Eroding

The shoreline of the spit, in Manson’s Landing Park, is eroding. Last summer BC Parks brought in Northwest Hydraulic Consultants Ltd (NHC) to investigate the causes and to develop viable engineering options to reduce erosion. On February 25, Grant Lamont of NHC unveiled his findings at a Friends of Cortes Island (FOCI) meeting at Mansons Hall.

The shoreline of the spit, in Manson’s Landing Park, is eroding.
Mansons Landing – Roy L Hales photo

Threat To The Spit

It was the kind of meeting that Cortes should see more of. While opinions widely differed, they were presented in a civil manner and the overall focus was finding solutions.

In their report, MANSON’S LANDING PARK COASTAL ENGINEERING OPTIONS FOR SHORELINE PROTECTION, NHC states (p 22):

“Coastal spit features tend to grow where there is a supply of sediments and a net long-shore transport of sediments that feeds the spit. Instabilities in spits, in which storm waves overtop or breach the spit and carry sands to the inner side of the spit are natural processes that help to widen the spit over time. If the supply of sediments to the beach spit is in balance with the loss of sediments then the spit will remain stable.” 

Removing The Dock 

The most controversial issue was the government wharf, built in 1947 and enlarged in 1964/65. Lamont described the dock and three associated floats as a breakwater, which is halting the flow of sentiment northward. This has resulted in a large bulge of sediment on the lee-side of the docks. 

“North of that sediment bulge, there is a sediment deficit. You do not have the supply of sediment coming in, that you do in other parts of the beach or that historically happened and … it is just leading to erosion and a deflation of the beach.”

On page 28 of their report, NHC states: 

“ … Removal of the pier and dock structures in their entirety would thus have the greatest effect of restoring the natural longshore transport processes at the site …” 

A few listeners were quick to endorse this view, pointing out that Mansons Landing was designed as a park.

A More Acceptable Option

However the pier and floats are outside of the park, predate it, and are owned by the Department of Fisheries and Oceans. They are managed by Harbour Authority Cortes Island (HACI)

One of the audience claimed the boats tied up at the floats were abandoned, which prompted the exclaimation, “That’s not true.”

After the meeting ended, Bob Katzko, President of HACI, stated, “Mansons Landing is probably the most used recreational facility [on Cortes Island]. When I go to Mansons, I just hang out on the docks. There are people strumming away there, they are drinking, barbecuing. People just go there and sit; they watch the sunset; they have regattas. It is heavily used by recreational boaters and seaplanes … There are fish being sold off the dock, and shellfish being used there …”

The author’s of the report were aware the dock is popular and suggest: 

“A more acceptable option may be to remove the existing floats and replace them with one short float (as small as 7 m in length, similar to the small float at Teakerne Arm Marine Park) to be used only for temporary docking of small tenders to allow public access ….”

The shoreline of the spit, in Manson’s Landing Park, is eroding.
Opposite the Floats in Mansons Landing – Roy L Hales photo

Changing The Shape Of The Dock

Someone who has observed the build-up of sediment opposite the floats since the 1950s, suggested the solution was to switch the floats from the north to the south side of the wharfhead. 

Lamont responded, “In the short term, ten to fifteen years, you are going to open up the north side. That wave action is going to come in and remove the bulge, which is going to help reduce the erosion happening to the north – because a bunch of that sediment is going to start moving northwards. It is going to start nourishing that eroded area. You will greatly reduce the erosion towards the north end of the spit …” 

However, even if Lamont’s estimate is too conservative, a new bulge would eventually form where the floats were moved. So, at best, this seems like a partial solution.  

Building Up The Spit?

One of the possible solutions NHC offers, in their report (p 31), is: 

“ … placement of a large volume of sand and gravel/cobble at strategic locations to provide an additional source of material for the longshore transport system. This size material is known to be very effective at absorbing and dissipating wave energy and would match the natural aesthetic of the site. Gravel/cobble beaches are generally constructed at a slope of 6:1 (H:V) or milder; however, because the existing beach slope is already relatively steep, a steeper beach fill would be required to tie into the existing slope (approx. 4:1), and the design would be such that the beach nourishment would be placed and then it would be expected that natural forces would reshape the beach over time.” 

Their design is expected to “have a service life of 10 to 20 years.” 

What About Using Sand?

“ … There is no engineering reason you couldn’t take the sand in front of the beach and use it. What we usually run into is major headaches in permitting, especially if there is fisheries concerns. There are often sub-tidal habitats that are quite valuable and their can be shellfish and spawning areas,” said Lamont.

Someone confirmed that there are spawning grounds in front of the spit.

Lamont’s suggestion, if Cortesians want to use sand, they should import it from another location. For half a million dollars, he guesstimates they might buy another 10-20 years for for the spit. 

Value of 10-20 Year Remediations

[Twenty years] “ … Buys you time to then have a broader community discussion, to get more funding, to follow more sea level rise science and whether all the countries are going to start addressing climate change, or whether we are on a high emissions scenario and whether some of the scientific theories about Greenland and Antarctic Ice sheets unravelling more quickly than we think are true,” said Lamont.

Sea level Rise

One of the unknown factors is the amount sea levels will rise over the decades to come. The current worst case scenario is described on page 37 of the report

“ … Potential SLR levels of between 1.4 m and 1.6 m have been suggested for the BC coast by year 2100 under enhanced scenarios. We note this to put into context that half a metre of SLR can be accommodated, but that two metres of SLR will radically alter Manson’s Landing. The existing spit will transform into an intertidal sand-bar with two metres of SLR, with the loss of the existing upland vegetation on the spit. Given this, a long-term plan for the park may involve retreat of human structures (docks, roads) and creating space for a natural response of the park to rising sea levels.”    

Human Traffic

The shoreline of the spit, in Manson’s Landing Park, is eroding.
Fence in the park – Roy L Hales photo

BC Parks is already fencing off some of the park’s sensitive areas. A recommendation  on page 30 of the report states: 

… minimizing pedestrian access to some areas of the spit and lagoon should be considered. Methods to accomplish this include improved signage, additional fencing, relocation of the parking lotand walking trails further south, and disallow storage of small boats/kayaks on the beach crest. Despite the obvious negative impact to recreational usage of the site, this management technique would be low cost and help protect the ecological and cultural values of the park. Further, the park is relatively large and there would remain other areas for public access.” 

Human foot traffic, along the edge of the spit, pushes the sand down and adds to the erosion. 

The shoreline of the spit, in Manson’s Landing Park, is eroding.
The Inner Lagoon – Roy L Hales photo

Vehicle Access To The Inner Lagoon

The road on the inner side of the lagoon is in the inner tidal area and on page 30 it says:

Vehicle access may have the dual effect of actively mobilizing sediment and inhibiting vegetation growth, which may otherwise help to stabilize the shoreline. Vehicle access on the foreshore also increases the potential for petroleum products or other pollutants to be introduced into the ecologically sensitive lagoon. As such, it is recommended that BC Parks considers eliminating vehicle access to the foreshore. Removing vehicle access would also have the effect of reducing boat traffic within the lagoon, which may both reduce erosion and provide ecological benefits.

There are allegedly headlights in the inner lagoon, every night, when oysters are being harvested. Most of the listeners were in favour of barring them from the lagoon, a dissenting voice pointed out that would be depriving Cortes Islanders of employment.  

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