Effect of King Island on swells hitting Victoria????

indo-dreaming's picture
indo-dreaming started the topic in Wednesday, 14 Apr 2021 at 3:18pm

Being a Victorian surfer something that has always surprised me when looking at a map of Australia is how King island doesn't seem to have any obvious effect on our swells (Coast from the Otways to Wilson Prom), no matter the size or direction there never seems to be any blocking or swell shadow effect, and our lines of swell seem to come in as long straight lines and not broken or criss crossed or anything weird and many of our beach's still get almost as much swell as exposed beach's of Vic far west coast or Tassies West Coast. (i said almost yes i know Johanna etc gets more as do beach's on Tassie West coast, but it's not a huge difference, its still rare for Gunnamata, Woolamai, Kilcunda etc to go flat or even close)

So why doesn't King Island seem to cause any issues for us?

And what actually happens when swells pass by it, anyone who knows a little about King Island knows swells wrap up both sides and can met and crisscross at it's tip, but the swell that keeps going past on both sides what happens?

Surely the swell line cant join up again, do the swells kind of criss cross where they met but we don't notice it as there isn't one point as such where this happens (when hit the coast)

Is there a side of the island most of the swell passes?...When you look at a map and take a standard SW swell direction it looks like the swell that passes on King islands West side would hit the West coast and Peninsula and the swell that passes the East side of King island would roughly hit Phillip island to the Prom, but i assume its not that simple.

To help with visuals.

PS. Sorry if it's affect rather than effect, grammar is not my strong point.

JQ's picture
JQ's picture
JQ Wednesday, 14 Apr 2021 at 8:18pm

I wonder if this has something to do with the ratio of the size of the island to the distance from aforementioned coast?

Also, wonder if this has any parallels with the mechanism that sorts waves into sets as a swell develops.

southey's picture
southey's picture
southey Thursday, 15 Apr 2021 at 12:55am

Hi ID .

I disagree on it having an effect . Swell is definitely slightly bigger at Gunnamatta than say Woolamai and definitely bigger than around Liptrap and Wilsons Prom depending on swell direction with small variations from SW . I also think that there are also south swell shadowing on the Surf coast also . But to less of an influence as obviously KI is skinny . One thing is for certain KI itself and the shape of the the north west tassie coast and Surf coast to Cape Otway defintely combine to effect the tidal flows . And to this extent we defintely know that tidal flow effects swell refraction into Bass strait . I'm not going tp say anymore as some readers don't deserve a leg up .

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming Thursday, 15 Apr 2021 at 7:27am

Hi Southey

Maybe you miss read my post, Im not saying it does have an effect, i agree it doesn't seem too, im just surprised that it doesn't or like to know why it doesn't, its like King island is not there.

I get what JQ is suggesting the further out an island is the less influence it has on shadowing etc, but there is still land on each side Vic one side Tassie the other, which creates two swell windows that swell for swell to come through and the Island must break up the swell changing direction of the swell that passes each side etc..

Hmmm interesting you speak of tidal flows of heard someone suggest this before, i don't understand this aspect outside of the entrances of say Westerport bay, to be honest where i live (Phillip Island) i mostly surf the beachies so its more about right tides for a bank so i these kind of things aren't any issue, unlike say guys on the west coast who want swells to reface into their favourite waves.

But i did live on Tassies NW coast as a grommet where very large swells of the right direction and period can wrap right in, some of my best mates still live there (mostly surfing down west coast) nobody i seem to know has ever worked out everything to a science there, and even though i don't surf there anymore i still think about aspects that influence swells getting in to certain spots, I've though about the influence of possible tidal flows there affecting refraction around Tas NW tip.

freeride76's picture
freeride76's picture
freeride76 Thursday, 15 Apr 2021 at 8:47am

heard a few people mention the effect of tidal flows on swells in (shallow) Bass Strait and entrance to Bass strait.

don't give away anything Southey, but if you wanted to talk generally I'd be really interested.

hope all's well with you.

udo's picture
udo's picture
udo Thursday, 15 Apr 2021 at 9:11am