North Australian FISH FINDER TM forums

SUSIE Q wrote:Matt the question of Deep divers potentially causing the banks to collapse ARE YOU FOR REAL or have you had more beers than I have? You cannot be serious or if you didnt query that I hope it wasnt a govt offical, what planet are they on? Lets just focus on buying back ALL THE NETS FIRST and worry about the minor details later.

i think you will find he is seriuos, i remember reading how a scientist did a study on the effects of deep divers removing sediment ect from bottom of river daly. Was causing huge problems in regards to damage, halco crazy deeps where the main culprit i think.
The goverment then paid a few of the high gloss mags to write up articles on high speed trolling down the middle and how good it was to encourage people away from dregding the bottom of the daly. Sum thing like if it continued for the next 20 years it would end up like the dredging in phillip bay and kill the river

The TO's want a 60hp outboard limit on all boats on the Daly.. Dont believe me ask them. I was told that from the horses mouth about 2 years ago.

If the results of the errosion trial come back in the negative towards boats causing it then mark my words this will be one of the things they ask for..

I reckon its a great Idea.. I run a 60hp Yammy

Ponyplay is right.

Suzie Q, it's not just deep diver bibs, but dense BRAID BALLS rolling up and down the bottom of the Daly with each set of tides, scouring the channel.

Some of these braid balls are full of deep-diver bibs!

Not to mention, fishos using high-powered bluewater sounders are disturbing the static charge holding sedimentary particles together, causing the particles to unclump and drift out to sea!

And the worst problem of all ... each time a fish is removed from the Daly the river level drops a fraction, exposing more of the critical river banks to boat wakes.

The situation is grim.

I propose the following rules ...

1. Row boats only
2. No bibbed lures
3. Biodegradable braid
4. Every fish taken requires release of a biodegradable "displacement equaliser device" in a size roughly matching the fish caught

But why would anybody propose such a study when the obvious has been stated? That being the amount of sediment scoured from the banks during the wet compared with what boats would cause is far greater.

It might be a matter of timing? When those big rain events change the course of rivers not only do they shift soil, they move it as well. Channels become deeper and sand banks a bit higher. A wet season can see 10 metres of bank disappear off one river bend, downstream a sand bar ends up so big it ends up with a bit of grass on it and before you know it has trees.

The wet moves soil on a huge scale redistributing it elsewhere from the nearest sand bar downstream out into the estuary. Then funnily enough the tides move much of that back up river again over the dry season slowly filling in the channels. The wet pushes all back out again and the system is in balance.

Throw into that other man made factors and things can go awry. A dam is a good example reducing those wet season flows allowing the estuarine channels to slowly close up from silt being pumped in by the tide from the estuary. A study was done on the Ord a few years ago with that scenario in mind.

Other man made things that affect the balance is fire reducing the vegetation cover over the landscape allowing water to flow off the country quicker taking with it much more soil that normal, monocultures of weeds on the river banks not allowing a grass understory to grow and hold together the banks.

Back to boats, we all know they create a wake and that wake will cause some erosion. Most of the boating activity happens in the dry when river flows are minimal so the soil would not be moved until the wet. Enough boats in one area and you may be able to measure a difference, particularly if the wakes inhibit the growth of bank side veg on the newly scoured wet season banks. What the knock on effect of that (if any) would be is uncertain. Then how do you compare that to the other man made influences on the system?

A study could either clear boats or condemn them, depends who does the study, their sentiments and how those guide the methodology and interpretation.

Having a sampling point within 50 metres of a popular boat ramp and constantly quoting the data from that one site and letting people assume that it's typical of all sites could do a lot of harm

Maybe they should look at the effects of all of the clear felling and deforestation of the catchment areas for cattle grazing, peanut growing and cropping. These stations provide a fair bit of employment for the NT and the farmers do a bl..dy tough job, so I am not saying ban the farming or cattle, just include all of the contributing factors in the study. Less vegetation in catchment areas means faster flow from those catchment areas, greater sediment erosion and a greater rate of bank destabilising.

Of course boat wakes impact the bank and move a bit of mud, sand sediment but nothing compared to natures flows and the man made enhancement of those flows. "9km/hr of current" flow (quoted by Mario on Tales from the Tinnie yesterday) is a fair whack of hydraulic earth moving power.

Cheers,

Doors Off

The hull type would be one of the variables when reaserch is conducted, a deep vee "blue water" boat creates a larger and more powerful wake than a flat bottomed hull. The increase in "blue water" type boats operating on the Daly is obvious. Waves in a waterway that normally does not have a constant wave action in it surely must be affected, the fish certainly seem to be, perhaps the fishing is good at night because there is no wave action from boats constantly travelling up and down the river.

WW,

I have noticed during the flooded period of the year that boat wakes can bring the fish on. Sitting anchored up alongside reedy, sheltered areas doing a bit of casting and strolling, that it will be quiet with near to zero boofing, then a boat comes past causes some wave action and the Boofing begins. I will always drag out the rod after a boat passes if I am having a feed or beer for a break. I think the night factor is to do with the Barra being optimised for low light hunting, not boat noise. Could be wrong but I don't mind a boat wake to help out the fishing.

A heavy, weighed down flat bottom punt style will chuck just as much wake about as a not so heavy weighed down "blue water" style boat. The displacement is probably the biggest factor but more weight in the boat and loading layout will have a big influence on the wake of the same hull.

Doors Off

Biggest problem for the Daly is going to be Neem Tree invasion ,which is already occurring on the Katherine River .
Sections of the Katherine river are almost choked with the mongrel tree.
The Govt both Federal and Territory are doing sweet f@@k all about it.
Kev.

daly flows at 30 cubic mt/sec dry season..Reckon the wet would near double that..boat impact is a piddle in comparison.

Love Matt's scientific approach, especially the level dropping with each fish taken. Makes me feel good that I dont contribute to the erosion very often. I think ALL factors should be considered, not just boats. But the answer to the question has to be yes.

In answer to the topic of this post ............NO!!!!
Let's see what the report returns and people, could we please apply logic and non bias opinion (in regards to the report)

Biggest problem for the Daly is going to be Neem Tree invasion, which is already occurring on the Katherine River.

Dead right Kev, same issue over here. You'll note that underneath them when they become a monoculture there is only bare soil and leaf litter. I saw that on The Wickham River nearly a decade ago. The result was some significant erosion and the river wider and shallower at that point, you could see where the banks used to be from the dead trees sticking out of the water.

Daly flows at 30 cubic mt/sec dry season.

Hey oldfart, multiply that by a thousand for big wet season flows .

Between the lines - The TO's agreed not to have a permit system, meaning the concept was on the table, Why? A permit is a form of revenue, where would that money go. It may provide funding for River Rangers to amongst other things check for compliance of the permit system. It may go elsewhere.

If the study was made to show some sort of impact and perceptions ruled the outcomes there will be renewed pressure for resources to protect the river and with that new restrictions. The muscle flexing is far from over.

Maybe we could all bring a bucket of sand in the boat and replace any diverts or errosion we may cause as they do on the golf course. Better still see if KON can get the funding to CONCRETE both sides of the bank all the way to the mouth. Problem solved.

That's a good one Suzie Q, then if we also concrete the bottom then deep divers and braid wont stir up or erode the bottom

if we also concrete the bottom

With a natural exposed aggregate finish. Which would make the water run clearer, and give spilt copper ore fewer places to settle - so improving the fishing - and fewer snags. Finally some sense in this debate!