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Secchi Disk Marine Project e-News

Welcome to the the Secchi Disk Project e-news. The Secchi Disk Marine Project is a citizen science project investigating water turbidity in Gulf St Vincent. Along with nutrient discharges, turbid inputs into the Gulf have the greatest impact of coastal water quality and seagrass health. The project is managed by the Friends of Gulf St Vincent with support from Adelaide and Mt Lofty Ranges NRM.

                                                                               

News and upcoming events

World Oceans Day: June 8th 2019
World Oceans Day has been celebrated since 2002 on June 8th to educate the community on the importance of our oceans and how to protect them. Oceans provide over half the oxygen we breath, are a major source of food and medicines and are one of the main sinks for carbon dioxide helping to regulate our climate. Ensuring they maintain these functions is vital for our future.
https://www.worldoceansday.org/
 


 
Extra protection for Port River dolphins

In the Port River, 11 out of 13 calves born over the past two years have died. In an attempt to reduce these deaths as well as injuries, the Government dropped boating speed limits on the 28th of March from unlimited to 7 knots in key areas of the Adelaide Dolphin Sanctuary.

You can read more on the decision and new laws at
https://premier.sa.gov.au/news/speed-limits-reduced-in-adelaide-dolphin-sanctuary

 
Funding for sand replenishment at West Beach

The State Government have allocated $48.4 million to the Adelaide coastline over four years. This will include $20 million for around half a million cubic metres of "newly sourced" sand and $28.4 million for building the sand pipeline from Semaphore to West Beach. Further funds are allocated for revegetation to help stabilise dunes.

https://www.environment.sa.gov.au/news-hub/news/articles/2019/06/west-beach-funding

 
Living shorelines better at protecting our coast than walls
A recent article in Scientific America has described how living shorelines are better at protecting the coast from extreme storm damage than man-made rock walls. Living e shorelines are natural communities such reefs and marshes. Oyster, rocky and coral reefs limit wave erosion by acting as natural offshore breakwaters. Other living shorelines such as samphires, mangroves (as well as offshore seagrass) disperse and cut out up to 50 percent of storm energy

America loses 89 hectares of coast every day and it's believed 40% of their coastline is being eroded.

The research on coastal resilience was based on damage following Hurricane Irene. Three quarters of standard rock walls were damaged whereas natural mash shorelines had lost no sediment and the vegetation bounced back within a year. Their research found that 93 percent of the damage to stormwater properties was "protected" by bulkhead style walls.
Coastal erosion is only going to worsen as our climate continues to change further.
You can read about the research at
https://www.scientificamerican.com/article/rebuilt-wetlands-can-protect-shorelines-better-than-walls/?redirect=1
 
If you're interested in living shorelines you may want to also check out the Living Shorelines project.run by The Estuary Care Foundation SA.
https://estuary.org.au/category/living-shorelines/
 
 
Google Earth Timelapse
With all the recent discussion in the media about beach and coastal erosion and how best to prevent it, some of you may be interested in checking out Google Earth Timelapse. This is a fascinating app that lets you see changes in satellite images since 1984. The changes are quite evident in some areas, but even along Adelaide's coastline you can see small changes when you zoom right in. Here is a comparison between 1984 and 2018 along the coast between the Torrens and Patawalonga outlets. You may be able to see that the width of sand was once relatively consistent and smooth along the whole coast before various structures were built.

   

https://earthengine.google.com/timelapse/
 

Turbidity trends: recent trends and hot spots around Gulf St Vincent
Turbidity in early Autumn remained good before the rains commenced in May. The average secchi depth along the Gulf during the entire Autumn period (March - May) was 231cm. In early Autumn, clear water was common. Granite Island had secchi depths up to 380cm, Port Noarlunga had a maximum of 474cm, Semaphore had up 363cm, Outer Harbor up to 522cm, and Edithburgh up to 452cm and Brighton and Grange both got over 300cm which doesn’t happen often. Decent rains started in mid to late May and water clarity  reduced with the brown inshore water line lingering for a few days at Grange (a secchi reading of 150cm), Largs Bay (105m) and Henley (96cm).
 

Sampling Site Spotlight

A closer look at secchi sites: Glenelg jetty
Volunteers monitor at the end of the jetty. The first jetty at Glenelg was built in 1857 and was originally 381 metres long. A lighthouse was built in 1872, but after it caught fire it was demolished at sea and the whole jetty rebuilt in 1874. Other structures were built on the jetty including public baths, kiosk, aquarium and tea rooms. A cyclone hit the jetty in 1948 and resulted in the jetty we have today being complete in 1969 which is sonly 215 metres in length.

Glenelg Jetty has only been monitored since 2015. The current average secchi depth is 277cm and readings have ranged from a very low 63cm to a maximum of 539cm. Water is generally clear at this site but there have been a slight decline in the last couple of years.

The average secchi depth in 2015 was 303cm, which is quite clear compared with other metropolitan waters. However in 2017 the average was 238cm and 2018 only 220cm. The progressive decline can be seen in the linear regression below where the slope is -0.0463.

In practical terms, this means that the secchi depth reduces by 0.046 cm every day, or the visibility into the water column is almost 17cm less each year. This is quite substantial especially when you consider that most other monitoring sites are showing that water clarity is stable or improving a tiny amount.

There are many potential reasons for this, but the only other site showing similar increases in turbidity is Brighton and there have been a number of personal comments from locals at Brighton about the effect of the sand pipeline on water clarity with the pale brown turbid line caused from the sand lasting for extended periods after the pipeline has been in operation. It makes sense that sites immediately north (i.e. Glenelg) which are affected by the northern littoral drift would be affected by pumping sand into the water at Brighton, especially if that sand is fine and easily transportable. These measurements have also become more variable and it would be interesting to see if low secchi depths correlate to periods when the sand pipelines are in operation.

More data will certainly assist in determining the impact of these sand protection measures on water quality both a Glenelg and Brighton, but also around West Beach.

If you'd like to see more trends and averages visit our website:
www.secchi.org.au
 
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Secchi Disk Marine Monitoring Project · Secchi Project · Adelaide, South Austrlia 5000 · Australia

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