I Have a dirty question

[oldboot]

OH come on...wyvenhoe being overtopped.......another 6 hours of what rain and where........ nothing more than a throw away line......As I said before Wyvenhoe has not even been flowing on the spillway.

There are lots of people keen to beat the environmental catastrophy drum.........sorry, I wont have it.

As far as nutrients...there is a big difference between low water flows and highly active and disolved neutrients and high water flows and the sort of neutrients that come from mud and decomposing vegitation.

People talk about the poor current water quality in our rivers.....OH give me a break....the Brisbane River has not been in as good shape for over 50 years........in the 60's and 70s prior to the the 74 flood it was a stinking fetid hole......ya had factories off all sorts dumping, all sorts of untreated crap into the river industrial estates right down to the river edge, practicaly non-existent sewage treatment and constant dredging.

Remember too back in the 60's & 70's farmers were not into the carefull or reduced application of firtilisers or pesticieds.... they just used heaps......and there were all sorts of nasty chemicals being used that are no longer legal

In 74 ya had hundreds of acres in the brisbane river catchment under farmland that is now under nice sealed residential developments...and close to the river......so don't give me there is more silt today because of the development...its only unprovable speculation...if there is more silt this flood it is simply because of the greater waterflows......arround twice the 74 floods

The brisbane river always was and always will be a heavily silted river under strong inflows.......where do ya think all the sand that makes up the barrier islands ( moreton and stradbroke)and keeps the bay so shallow comes from.

I fell in the river in the toowong reach back in the late eighties while working on a boat.......river not in flood or any recent heavy rains.....I can tell you the water was gritty in my teeth.

Our moreton bay as we see it today is built on the silt droped out of the costal rivers

If ya want to get some idea of the silt that comes out of the brisbane river.......before white settlmemt much of the brisbane river was as shallow as 6 feet..as shipping was braught futher and further up the river it was dredged deeper and deeper first 20 then 30 feet deep up as far as the william jolly bridge.........lots of that silt was droped in the bay....... but lots of it was used for reclaim.........have alook at your referdex......everthing on the river side of kingsford smith drive from bretts wharf/ Race Course rd to the mouth is reclaim, most of it from constant dredging of silt to keep the river open for navigation.

Until the nineties, most of the sand and gravel for Brisbane came out of the river

Siltation deposits from one off large inflows like floods have a very different effect to the constant siltation that comes from continuous dredging, and low flow washdown......

The flood events are one off events and the evironment will soon recover.....the very banks that the seagrass grows on come from river sediment... creatures like yabbies and worms ( the bottom of the food chain) live on the washed down low value neutrients that come from decaying plant and animal matter in the mud.

As for algal blooms......if you recon there were no algal blooms prior to 74...dream on.

Besides the main triggers for algal blooms are stillness and water temperature....they do occur in nature......they just seem so nasty to us because they impose themselves on our human activities and our visual response.

Yeh disolved neutrients make them very much worse...... but I don't think you can associate algal blooms with high flow events...in fact these very high flow events are more likley to mitigate such things..... diluting and carrying away those nasty eliments that otherwise would enter our waterways in much more concentrated form where they would stay in the river systems far far longer.

Remember there are two common occurances of oysters...... often the same spicies......"rock oysters" and " dredge oysters"......dredge oysters live partialy burried in sand or mud.........

As far as the relationship between sand/ slit and coral........there will always be some association between sand and coral......how many small islands started out as coral outcrops, gathered sand and became islands......( hell look at green, st helena and mud) Coral has been dealing with sand and silt for thousands of years......I am sure it can manage a bit of a flood every 30 years or so.

It is the slow dribbling of human life that damages our marine environment... not the ripping cleansing flow of nature.



Remember nature always has a long term view....it is a mistake to try and impose our short term visualy motivated values on the marine environment.

This is the hipocracy of manny greenies, they look at and measure the environment by their feeble, inconsistent short term human life.

cheers

Cheers

[Ben D]

Hi Ben,

are you able to estimate any sort of time-frame with your professional background of when we might see the fishing recover to some extent in the river and bay?

also, have you got any idea of the impact this kind of inundation will have on the pelagic fishing around moreton bay in the medium term?

completely agree with your last statement, hopefully now the issues of agricultural runoff and sedimentation, and water quality flowing out of our catchments will be seriously addressed instead of being swept under the too hard rug

cheers
Dan

There are samples being taken and a research project being put together right now I understand that is designed to answer exactly that question. Surface salinity now around Bribie is 15ppt (9 ppt close to the island) and 23ppt on the surf beach with suspended solids and clarity that suggests pelagics will take a while to come back. The bottom sediments will be exposed to the same sort of muck that people have been sweeping out of flooded houses. Yes, its a one off event, but expecting recovery when the underlying problems with the bay remain unaddressed and unchanged is very optimistic and not at all realistic.

Studies of cores from 400 year old corals shows that sedimentation during floods was historically not a problem up until around 1870, after which european land use practices (tree clearing, agriculture and urban development) in river catchments along the QLD coast resulted in increased in sedimentation (around an order of magnitude or more) higher than historical backgrounds prior to european settlement, resulting in sedimentation problems that stifle coral, oyster and other biogenic reef habitat. These issues continue to get worse as population grows and development progresses. Same for toxic Lyngbya blooms, they were not recorded before the late 1990's but since then have increased in frequency and severity, due to increased nutrient availability (mainly P) and also increased availability of complexed iron (the latter from disturbance of acid sulphate oils by development).

re: Moreton and Stradbroke Islands, Ward (1978) shows they were actually formed during the previous glacial period and represent holocene drowning of mainly Quaternary sediment deposits that were many miles inland, not due to sediments from the river. Oldboot, you could do worse than look at
http://espace.library.uq.edu.au/eser...rd-dgp-8-2.pdf

Oh, and if waterflows were twice as much as the 1974 floods, why was the river height at the brisbane city gauge around a meter less than 1974 ? Yes, rainfall may have been twice as much, but the river flows were mitigated by Wivenhoe dam. And re: the dam, the engineers don't lie, you could clearly see looking at http://www.bom.gov.au/fwo/IDQ65389/I...0177.plt.shtml how close it got, and you could track how once the level exceeded 74 meters, they opened up the dam fully and even then, the height climbed for a while before the rain slowed down and they got control back. That is why they have a fuse plug in the dam to form a secondary spillway as a safety valve - when it rains very heavily in such a large catchment it is possible for dam inflows to exceed the outflow capacity of the 5 gates, and the dam is not designed to be overtopped. It is also very clear and widely covered in the media they were releasing water from all 5 gates (partially open) in the leadup to the severe rain events of the 10 and 11 jan, check it out here http://www.seqwater.com.au/public/dam-levels , select wivenhoe and go to a month timescale to see the releases leading up to the severe rain event.

[oldboot]

Firstly the flows in the river and out of wyvenhoe are not the main source of the sedements in the water......this is obvious in the colour of the water in the dam.

The sedements suspended in the water come from the catchment...a catchment that has produced inflows twice that of the 74 period.

twice as much rain hitting the ground, twice as much errosion in the catchment.......easily twice the sedement in the water, maybe more.

As for the claim that development and increased agriculture has increased siltation particular to this sort of event....still don't buy it.

At 74 the lockyer and also nearer was pretty well exploited to the max for farming.

Thousands of acres that was under cultivation in 74 has now been developed into residential yes.... that results in stable surfaces of roofing, sealed roads and established grass...it may have resulted in more rapid outflow and more solid manufactured rubbish, but increased sediment loads..sorry don't buy it.

And soil disturbance during development and acid sulpate soil leaching will be shot lived...and realy insignificant in comparing the flood event 74 to now

As for the lockyer valley being more intensely farmed.....don't buy that either.....in fact, As I have been driving thru those areas, I see farm after farm left idle and or unstocked due to the drought and other reasons......in the last year or two these areas have been looking greener than they have been for years..... better ground cover.......less errosion.......but yet to be stocked or cultivated......add that to more and more farmers going to low till and cover crop farming methods... I recon on ballance the farming land would yeild less sediment under the same circumstances.

However...... when you have huge ripping inflows like went thru Grantham, the water will rip huge holes in the land, regardless of the surface condition.

so main dfference between 74 and 2011......dogs balls obvious......very much higher and more concentrated rainfall that is the culpret.

cheers

[snapperbasher]

[quote=Ben D;1243747]There are samples being taken and a research project being put together right now I understand that is designed to answer exactly that question. Surface salinity now around Bribie is 15ppt (9 ppt close to the island) and 23ppt on the surf beach with suspended solids and clarity that suggests pelagics will take a while to come back. The bottom sediments will be exposed to the same sort of muck that people have been sweeping out of flooded houses. Yes, its a one off event, but expecting recovery when the underlying problems with the bay remain unaddressed and unchanged is very optimistic and not at all realistic.

Studies of cores from 400 year old corals shows that sedimentation during floods was historically not a problem up until around 1870, after which european land use practices (tree clearing, agriculture and urban development) in river catchments along the QLD coast resulted in increased in sedimentation (around an order of magnitude or more) higher than historical backgrounds prior to european settlement, resulting in sedimentation problems that stifle coral, oyster and other biogenic reef habitat. These issues continue to get worse as population grows and development progresses. Same for toxic Lyngbya blooms, they were not recorded before the late 1990's but since then have increased in frequency and severity, due to increased nutrient availability (mainly P) and also increased availability of complexed iron (the latter from disturbance of acid sulphate oils by development).

Ok well i'm with Oldboot on this one.... I have been fishing the flood waters over the last week and have seen an explosion of snapper/ squire on the close reefs off brisbane (even in coffe brown nearly fresh water). and i think it will only get better from here. It is a natural event and it will have no adverse affects on the bay, seagrass or reefs in the long term.

Ben, Do you not think that the increased frequency of Lyngbya blooms has been caused by the drought not flood??? look at the timing.... it took from 74 to the late 90's (drought) to increase and i believe we will see the same effects now after this flood. it can only mean good things in the future for us.

as for the pelagics off the coast for the short term they will head to wider cleaner water but before long they will be back closer to the coast when it all settles down feeding on the baitfish which will now thrive off the nutrient rich water. the whole food chain has just had a massive kick start and all i can say is it is game on on the fishing front!!!!!!!!!!!!