THE ENVIRONMENTAL ASPECTS OF EDUCTOR DREDGING

[RKC]

THE ENVIRONMENTAL ASPECTS OF EDUCTOR DREDGING

Eductor dredges are small portable machines that vacuum gravel from the bed of a river or stream, pass the gravel through a floating recovery system and then return the gravel directly back into the waterway. Eductor dredges simulate, on an extremely small scale, the natural movement of alluvial gravel in times of flooding. The total disturbance of a waterway by eductor dredging represents only a small portion of the geological processes that occur naturally – whether or not any eductor dredging was carried out!

The auriferous deposits contained within waterways are formed by the relatively constant movement and sorting of gravels over extremely long periods of time. Without this movement and gradual concentration of valuable minerals, economic deposits could not form and there would be no reason to mine them.

If the movement of small quantities of alluvial gravel is to be considered as pollution, then the constant repeating processes of natural erosion must be regarded as a massive degradation of the environment. All rivers and streams could then be said to be polluted to an incredible extent. The "pollutants" are natural substances that have always been present, and always will be.

The geology of all rivers and streams involves a natural movement of gravel, a constant replacement process that is very much a part of the river environment. And at times of heavy run off, the movement is very pronounced. A rivers aquatic life forms, from the smallest invertebrates to full grown fish, survive this natural movement of gravel during floods.

In comparison with natural processes, the disturbance caused by an eductor dredge is insignificant, lasts no longer than the following high flow and has no long term effect whatsoever. No other mining, forestry or farming method can assure a complete and natural rehabilitation as eductor dredging can.

Concerns

a)Turbidity

The main environmental concern which arises from the use of eductor dredges is the direct disposal of tailings after processing.

Most river gravel processed by an eductor dredge is sufficiently coarse to cause it to fall almost instantaneously to the river bed after processing. Some fine material can remain in suspension for varying lengths of time, before settling out. It is this turbidity which can be of concern.

Variables such as the amount of colloid material in a stream, the size and number of eductor dredges in use, the waterways velocity and volume, and the width of the waterway, all influence the amount of turbidity created. In effect, changes in turbidity caused by eductor dredging are highly variable – dredging river gravels containing only sand and gravel causes very little change in turbidity, whereas dredging clay deposits can cause noticeable turbidity increases.

In an eductor dredging trial conducted on the Mulgrave River in Far North Queensland (Australia) for various state government departments, it was recorded that a 5-inch eductor dredge caused marginal discoloration at the tailings discharge, with the discolouration precipitating very rapidly and not being discernible 30 meters downstream from the dredge.

Turbidity is an expression of the optical properties of water that causes light to be scattered rather than transmitted through it. In simple terms it is a measurement of how "muddy" the water is, and is measured in nephelometrie turbidity units (NTU).

During an eductor dredging test carried out by the California Department of Fish and Game on the north fork of American River, it was concluded that turbidity was greatest immediately downstream, returning to ambient levels within 100 feet. Referring to 52 eductor dredges studied, Harvey (1982) stated "...generally rapid recovery to control levels in both turbidity and settable solids occurred below dredging activity."

Hassler (1986) noted "...during dredging, suspended sediment and turbidity were high immediately below the dredge, but diminished rapidly within distance downstream." He measured 20.5 NTU 4 meters below a 5-inch dredge which dropped off to 3.4 NTU 49 meters below the dredge. Turbidity from a 4-inch dredge dropped from 5.6 NTU 4 meters below to 2.9 NTU 49 meters below with 0.9 NTU above. He further noted "...water quality was impacted only during the actual operation of the dredge...since a full day of mining by most Canyon Creek operators included only 2 to 4 hours of dredge running time, water quality was impacted for a short time." Also "...the water quality of Canyon Creek was very good and only affected by suction dredging near the dredge when it was operated."

During 1997 the US Geological Survey and the Alaska Department of Natural Resources conducted a survey into eductor dredging on Alaska’s Fortymile River, which is a river designated as a wild and scenic corridor. The study stated, "One dredge had a 10-inch diameter intake hose and was working relatively fine sediment on a smooth but fast section of the river. The other dredge had an 8-inch intake and was working coarser sediments in a shallower reach of the river. State regulations require that suction dredges may not increase the turbidity of the river by more than 5 nephelometric turbidity units (NTU), 500 feet (=150m) downstream. In both cases, the dredges were well within compliance with this regulation."

In American studies, average turbidity levels have been shown to be between 5 and 15 NTU 5 meters below dredges. But even the maximum turbidity level measured in a clay pocket (51 NTU) fell below 10 NTU within 45 meters. Turbidity increases, from even large eductor dredges on moderate sized streams, have shown to be fairly low, usually 25 NTU or less, and to return to background within 30 meters. The impact is localized and short lived; indicating minimum impact on moderate and larger waterways.

Within any waterway, sediment is primarily carried in suspension during periods of rainfall and high flow. This is an important point, as it indicates that an eductor dredging operation has less, or at least no greater effect on sediment mobilisation and mobility than a rain storm.

b) Immediate habit changes

Eductor dredging involves moving river gravel, with a number of operational circumstances dictating to what depth the gravel is moved. In some rivers only the top ½ meter of gravel needs to be moved, while in other rivers all of the gravel down to bedrock is moved. Rocks too large to enter the dredge are moved by hand, by being rolled aside (usually laid on bedrock). Larger boulders are rolled over or they can be left in place to be dredged around. The auriferous sand and gravel small enough to enter the dredge is moved by suction through the dredge to the recovery system, where the gold and some other heavy materials are retained. The coarse gravels settle immediately upon leaving the dredge. The smaller particles travel further downstream before settling. Therefore the habit for benthic organisms is removed from the dredge hole, and covered up with sand downstream.

c) Effect on invertebrates

In a river or stream bed, invertebrates are found in the spaces and cracks between unembeded rocks, or rock surfaces. Eductor dredging impacts on these invertebrates by displacing them from the dredged area, and by burying suitable habitat downstream from the dredge. The buried habit does not continue downstream indefinitely, nor is the effect from bank to bank, and not all invertebrate species are equally affected.

During eductor dredging, food (invertebrates) is stirred up and becomes accessible to fish which feed from the dredged area and from the wash of the dredge.

A longer term effect is that a greater area of gravel is aerated; therefore giving a much larger habit to the invertebrates, which then provides fish with food well after the dredging has been completed. Insects are no exception to the general hypothesis that diversity increases with habitat complexity. In American studies, and from the observations of Australian dredgers, it has been found that fish can do much better in rivers and streams that have been eductor dredged, than they do in areas where there was no such activity.

River and stream invertebrate populations are not severely impacted during eductor dredging, as the impact is local, not harmful to all invertebrate species, and mildly beneficial to some. And, the most important point is that recolonization of dredged areas by invertebrates is rapid!

In an American study (J.S. Griffith and D.A. Andrews, 1981) it was stated in a paragraph titled "Recolonization of Dredged Areas", that "...the dredged sample plots in Summit Creek were substantially recolonized by benthic invertebrates after a 38-day period. A comparison of numbers between orders in the populations of these two areas showed no significant difference. Similarly there were no significant difference among numbers of the five taxa that together accounted for 80% of the invertebrates in both areas." Thomas (1985) noted that recolonization was substantially complete one month after dredging, and Harvey (1986) stated, "Insects recolonized the sand and gravel deposited by dredging at Butte Creek fairly rapidly."

[RKC]

d) Effect on fish

In Australia in the 1980s an extremely vocal minority of anglers in the state of Victoria objected to allowing any eductor dredging. Their criticisms against eductor dredging were entirely conjecture, with the claims made that dredging "clouds out" fish and that dredging reduces fish numbers, and that fish go "off the bite". And there were even objections to the temporary "holes" sometimes left in a river after dredging, with the fanciful claim made that anglers would fall into these holes and drown.

In New Zealand in the mid 1990s the recreational fishing lobby claimed that the "siltation caused by dredgers could smother developing trout eggs and kill young fish". Also, it was said that dredges have the "potential to silt up brown trout spawning beds and wipe out a generation of trout" and "silt discoloration also created unfavourable conditions for anglers, it can effect the ability to spot fish and stop fish from seeing lures...anglers want to fish in clear water." And these general criticisms were made, "while silt is non-toxic it is harmful to aquatic systems" and (an eductor dredge) "was harmful to fish life and the aquatic insects on which fish feed."

Fish are affected by eductor dredging if their specific habitat is impacted. Of particular concern is the potential for the destruction of fish spawning beds. Fish species require sized gravel with good porosity and proper water flow in which to deposit their eggs. Eductor dredging can impact spawning areas in two ways. Spawning beds immediately in front of the dredge can be sucked up and removed, and downstream from the dredge can have tailings or sand deposited on top of them.

American studies have shown that the impact arising from the deposition of silt on spawning areas downstream from the dredging operation is extremely variable. It was found that silt deposition ranges from being harmful to having no detrimental effect. Spawning areas are naturally restored after dredging, following the flushing of the next flood which will remove the silt.

In California it has been noted that intergravel permeability was increased by dredging. Porous gravels left after dredging can be washed downstream a short distance during high flows, adding to spawning beds, thus improving them. In America, sieved gravel from bucket dredge tailings have been added to creeks for spawning gravel as part of an improvement project. An American study (Hassler 1986) has stated that "...dredge tailings are often referred to as good salmon spawning subtract," and "...in the Trinity River Chinook salmon have been observed spawning in the tailing piles of suction (eductor) dredges."

Gravel bars formed downstream of eductor dredging operations provide excellent spawning beds for fish – because the gravels are lose and uncompacted. The fish eggs can be laid and covered more easily than in compacted gravels.

Even dredging fish eggs from a stream bed does not necessarily mean the destruction of those eggs...as would seem logical. In an American study (J.S. Griffith and D.A. Andrews 1981) it was stated that "...a substantial proportion of the eyed cut-throat and rainbow trout eggs survived passage through the dredge. In these eggs, the vitelline membrane has been replaced by layers of cells and they can withstand the shock created by turbulent flows through the dredge." There can be considerable variation in mortality among fish eggs after passing through a dredge."

Trout follow seasonal migration patterns. The majority of adult fish move upstream to shallow gravel spawning streams during the winter months, then return downstream into lakes where possible, for the summer.

The spawning sites chosen are in the remote headwaters of a river system, with the preferred sites within a creek, in rapids, or in the tail or sides of pools. One exception to this is in streams with swept bedrock, or larger boulder stream beds, where fish spawn in small patches of gravel located on the downstream side of larger boulders.

Obviously, the critical aspects of protection of fish spawning sites will vary by stream, fish species, presence of suitable sites, water flow characteristics, ect, ect.

On any eductor dredging claim where spawning is known to occur, dredging could be restricted during the spawning period as a condition of the claim. Such a condition should be designed to prevent dredging only during the period when life stages are present, and excessive buffer periods need not be imposed long before spawning occurs, or long after fry should have been expected to have emerged. There is no reason for closing to dredging any rivers or streams not used for spawning.

During eductor dredging there is a short period when food (invertebrates) is stirred up and made accessible to fish. In American studies, and from what has been experienced during a great deal of dredging activity in Australia, it has been found that fish do better in areas that have been eductor dredged than they do in rivers where there has been no such activity.

In a study done by marine biologists from the prestige’s Scripps Institute in California rivers, it was found that in the second year of dredging activity, the life cycle of the biological life that fish feed upon is actually sped up with their access to room and feed. Stirring up the gravel by dredging speeds up these life cycles. The food available to fish is increased, and the actual finding on record is that fish count can be increased by up to 40%.

The American state of Oregon, by actual fish count determined that the effect of eductor dredging is negligible on aquatic life. A fish count study was made on Cow Creek, which was an excellent area due to the fact that they were able to count the fish prior to the opening of that area for eductor dredging. Up until 1978 Cow Creek was virtually closed, and there was little or no activity by gold dredgers. The area became popular during the 1980-81 season by dredgers, in that there were between 50 and 60 dredges in a 10 mile area of the stream. The actual fish count during that time improved by as much as 15 to 20%.

Studies generally have concluded that no adverse effects upon fish numbers result from eductor dredging activity.

e) An annoyance to fish.

Fish do not take fright from the noise of the dredge motor, or the diver in the water, and all dredgers have experienced fish swimming about as the miner works. Fish react defensively to movements above the water surface -- as any angler will be well aware of. Fish have no fear of a diver in their own element. Were this not a fact, fisheries biologists could not conduct mask and snorkel studies (drift dives) without scaring away the fish.

Eductor dredging does not disturb mature size fish, and can attract fish, especially juveniles, to the working dredge. These juveniles will quickly dart in and out of the dredged hole feeding on the invertebrates displaced as the dredger moves rocks. Fish will also feed on dislodged invertebrates as they are expelled from the dredge. Juvenile fish benefit greatly from this feeding and will increase in length and weight as a result. American studies have mentioned rainbow trout feeding in a dredge outfall at turbidity levels of 25-30 NTU, and that the eductor dredge caused turbidity had little effect on the feeding fish.

f) Cumulative or additive effects.

Several studies have been conducted in California to determine what, if any, are the effects of many larger dredges. Harvey (1986) studied six 6-inch and smaller eductor dredges on a 2 km long section of Butte Creek. Some dredging occurred in 85% of all pools and rapids in the 2 km study section. The study stated, "If there were a cumulative effect of dredging, an increasing number of taxa should have declined in abundance after June at downstream stations" -- no such decline appeared in the data. The study concluded "Fish and invertebrates apparently were not highly sensitive to dredging in general, probably because the streams studied have substantial seasonal and annual fluctuations in flow turbidity and subtract...in May 1982, no subtract changes caused by dredging in Butt Creek during the previous summer was evident...along with rapid temporal recovery of insects seen in the study, these results suggest that suction dredging effects can be short lived on streams where high seasonal flows occur."

Harvey (1982) examined the additive effects of 40 dredges on a 11 km section of the Yuba River in 1981. In the conclusion he states, "No additive effects were detected on streams where a number of dredges were being operated."

McLeneghan and Johnson (1983) studied the impact of 270 eductor dredges with up to 10-inch intake, and stated, "Subjective in stream and riparian assessments of habitat damage revealed that few suction dredge miners surveyed caused adverse impacts" -- no additive effects were mentioned. And they point out, "The physical characteristics of the stream will also regulate dredge size to some extent. Stream bed subtract is probably the most selective parameter...relatively shallow foothill streams will generally exclude the larger dredges."

g) Mercury disturbance.

Eductor dredging is carried out in rivers and streams where miners have preceded them. And in many rivers and streams during the late 1800s and early 1900s, mercury (quicksilver) was commonly used in various mining processes. Mercury has an affinity for gold and silver, absorbing them, and was used by earlier miners in sluice box’s and on copper plates to assist in the recovery of the smaller gold particles.

Due to inefficient processing, various quantities of mercury were lost to the system, to settle into the gravel of the rivers and streams downstream of the processing site. An example of this is in New Zealand’s Lyell Creek immediately downstream from the Alpine stamper battery. And in Victoria (Australia) significant amounts of mercury have been found by eductor dredge miners in the Ledederg River.

In the early 1980s when eductor dredging activity was at its height in Victoria (Australia), concerns were expressed whether disturbance of sediments through the use of these dredges would result in the increased mobilisation and biological availability of mercury. These concerns arose after studies done on Australia’s most heavily eductor dredged river, The Goulburn River, revealed that mercury levels in both water and sediment were high by world standards.

A report compiled by the Environmental Protection Authority of Victoria in 1983 showed that the Goulburn River had severe mercury contamination of surface waters, sediment and edible tissues of large fish. The report indicated that the dredgers regularly found quantities of inorganic mercury in the stream bed.

It was found that there are two main sources of mercury in the Goulburn river system. Firstly the Jamison area is a known area of mercury mineralization. Mercury was first discovered there in 1893, along what was to become known as Quicksilver Creek, where globules of mercury could be obtained by breaking up the slate and washing it. Free mercury could be seen in cavities in the quartz, along with small patches of sulphide of mercury, or cinnabar.

The second source was more significant and more widespread, and resulted from the standard procedure in use by the early miners for the extraction of fine gold from crushing by passing the slurry over mercury coated plates. Very high levels of mercury were found in river sediment at the A1 and Morning Star lode mines, confirming historical evidence that mercury had been discharged at these mines.

A production eductor dredge removes mercury from the mercury contaminated river bed as the mercury forms an amalgam with the gold on entry to the dredge. And as a means of solving the problem of mercury contamination of streams, an Australian study (EPA study, 1984, publication: 195) recommended dredging to remove the (mercury) contaminated sediments. A production eductor dredge can therefore have a positive effect by removing any dangerous mercury from a stream environment.

[RKC]

h) Stream bank erosion.

Eductor dredging has the potential to contribute to stream bank erosion by either the undercutting of stream banks or in the construction of roads for access.

Any risk of undercutting stream banks can be prevented by restricting all mineral recovery to the wet perimeter, and by specifying that the boundaries of an eductor dredging claim follow the natural contours of the waterway. Stream bank disturbance is highly visible and lasting; therefore such mining conditions would be easily enforced.

Most erosion in a waterway occurs naturally due to the direction of flow or obstacles in the river or stream bed. The build up of gravel bars after flooding usually indicates a choking effect in that section of the waterway. Eductor dredging of the inside of a river bend can help reduce stream bank erosion, as these gravel bars can force the river to carve a new course out of the adjoining bank. Dredging of other areas of gravel build up could help containing the waterway in its original channel.

Eductor dredging also helps stabilize the river bed by locating the heavy material on bedrock and then binding these larger rocks with the finer sand and gravel.

It is not necessary to construct roads to gain access to a river or stream for eductor dredging. All sizes of eductor dredges can be dismantled for transportation to the river or stream to be dredged. It would be practical to specify, as a condition of an eductor dredging claim, the appropriate means of access.

Helicopters are a practical and widely utilized means of accessing a dredge directly into a waterway without disturbing the surrounding vegetation. Also, dredging sites, especially in the larger rivers, can often be accessed from the closest point of road access by the use of jet boats or canoes. Walking tracks used by hikers and anglers are common alongside rivers and can be used by dredgers when accessing a dredging site on foot.

i) Impact on flora.

Because of the nature of an eductor dredging operation (water required to permit dredging) and when dredging conditions applying to an eductor dredging claim prohibit any interference with the banks of a watercourse, no impact on any flora would occur.

j) Impact on fauna.

There is potential for eductor dredging to impact on native and introduced fauna through disturbance to the bed of a river or stream and associated turbidity. The noise from an engine which powers a dredge may also impact on fauna.

The fauna likely to be impacted on by eductor dredging include fish, water-dwelling macro invertebrates and also birds and ducks.

The impact on fish and invertebrates has earlier been examined. Birds and ducks can be disturbed by the noise emanating from a dredge motor, or the noise produced while paddling a canoe, or the operation of a power boat that is used to access a dredging site, or even while walking along a river bank. The noises produced by a helicopter can also temporally disturb birds and ducks.

k) Noise pollution.

Noise is produced from the engine/s on the dredge which is used to power the pump/s and air compressor. Low rpm four stroke motors are used on eductor dredges and are all fitted before sale with efficient noise suppression devices (mufflers) which conform to regulations.

Professional dredgers tend to purchase motors that have a higher horse power rating than is actually required to run their dredges with sufficient suction. They do this to avoid running the motors at a high rpm which would significantly reduce the operating life of the motors. These motors are run at about ¾ power which has the added advantage of a lowering of noise levels. Production dredges can have noise levels further reduced by the addition of extra noise suppression devices, for use in areas where noise levels are at issue.

l) Impact on man-made features.

Any man-made feature contained within an eductor dredging claim such as vehicular crossings, fords, bridge footings, piers, domestic pumps, water supply take offs, ect, ect, can be protected by introducing conditions preventing dredging within a specified distance of the feature. Consequently no impact on these features would occur.

m) Petrol in the river environs.

Dredgers are particularly careful when handling petrol and any spillage is most unlikely. The only time when there is a potential for a spill is when pouring petrol into the motor on the dredge. Care is always a necessity when handling fuel near a dredge as any spillage of fuel onto a dredge sluice box can reduce its effectiveness, and result in costly downtime cleaning the spill. Any petrol spills onto a hot muffler or onto a sparkplug, can have disastrous consequences. A spill of fuel onto a neoprene wet suit can cause a severe burning of the miner’s skin because of a resulting chemical reaction between the neoprene and the petrol, and damage to the wet suit would also result.

n) Visual impact.

There is a visual impact arising from the operation of an eductor dredge in that the dredge can be viewed in the river or stream. There is a minority of people who would object to the introduction of any man-made feature, no matter how temporary, into a "natural" environment. However, most people who come across a dredge are interested and curious about the operation, which they often enquire about. Anglers will keep on fishing – and if they are aware that eductor dredging attracts fish they will throw a line in just a little downstream of the operating dredge.

There can be an additional visual impact arising from the distribution of tailings in the river or stream. Under most conditions there would be no visual impact as all tailings would be contained below water level, and it is only during the low water conditions of the late summer months that some small gravel islands of tailings may appear above the surface. Because of the lose packed nature of these tailings, soon all signs of tailings and any unfilled holes are totally removed by the following high flow. River and stream gravels are never flat or even, nor do they remain static. They consistently change with holes appearing and disappearing naturally, purely as a result of the force of nature.

o) Characteristics of river water.

A Victorian study (T.J. Doeg, 1985) found that the charactistics of river and stream waters are unaffected by eductor dredging. In a study area on Victoria’s (Australia) Goulburn River being eductor dredged, all values for temperature, conductivity and dissolved oxygen were found to fall within the range of values normal for that area. Also chemical compositions reflected the values expected.

In an American study (USGS Fact Sheet FS-154-97, October 1997) of two production dredge operations (a 10-inch dredge and an 8-inch) it was stated that "...suction dredging appears to have no measurable effect on the chemistry of Fortymile River within the study area."

p) Examples of eductor dredged rivers.

In Victoria (Australia) the second most heavily eductor dredged river is Big River (a tributary of the Goulburn River). It is a typical wild and scenic mountain river located in State Forest well away from any substantial human habitation. This river was very intensively eductor dredged from the late 1970s up until the 1989/90 season. And during this period this river produced excellent returns of gold for the professional miners who were experienced and willing to put in the necessary hours each day when weather conditions permitted dredging. There was also a great deal of recreational dredging carried out in the same period.

Although this river was very heavily eductor dredged over nearly its entire length for more than 10 years, there is no evidence, immediately visible or otherwise, to indicate any eductor dredging ever occurred. Trout still thrive, as they did before and during the years of dredging activity, and each weekend during summer anglers still congregate along the river as they always have.

In a report dated August 1985, published by the Biological Survey Department of the Museum of Victoria that investigated concerns about the possible effects of eductor dredging activity on biological aspects of four main catchments draining into the southeastern arms of Lake Eildon, it was stated that "...from the results presented in this report, there is no evidence to suggest that the macro invertebrate communities at sites where eductor dredging has been carried out have been seriously altered by this activity. This is particularly so in Big River which has been fairly heavily dredged over the past four years and is minimally affected by other aspects of human activity. The macro invertebrate populations in this river are typical of those found and expected in relatively undisturbed rivers in the transitional zones between upland and foothill sections of rivers. Such undisturbed areas are characterized by a high species diversity and the presence of representatives of many groups that appear to be associated with clean waters."

Victorias (Australia) Big River can be regarded as an example; as good as any, that eductor dredging has no lingering or any long term detrimental environmental impact on river and stream ecosystems. Also, Australia’s most heavily eductor dredged river, the upper Goulburn River (Victoria), can be similarly regarded – taking into consideration that the upper Goulburn River environs have been significantly impacted by the construction of bank side holiday houses and picnic areas, and the cultivation of river flats, which have added sewage seepage, rubbish and fertilizer residues into the river. And because of easy access the Goulburn River is heavily fished which significantly impacts on fish numbers.

In Queensland the two most heavily eductor dredged rivers in that state are the Palmer and Mitchell Rivers in the far north. Many other rivers have been eductor dredged in Queensland including the Russell River which was first dredged in the 1960s (in the Golden Hole), and the Mulgrave River.

Numerous rivers in New South Wales (Australia) have been eductor dredged, including the Mongalow River, the Turon River and the Sholhaven River. Only a few rivers have been eductor dredged in Tasmania as this state lacks the rich alluvial gold deposits typically found in the other eastern states of Australia.

In New Zealand numerous rivers and streams have, and are being, eductor dredged. The Arrow River has been eductor dredged, almost exclusively by recreational dredgers, since the 1960s. The Lyell Creek was intensively eductor dredged until recent years by a professional dredger (who produced between ½ and 3 ounces of gold a day). The Clutha River, the Mangles River, Winding Creek, Wakamarina River, Foster Creek, Kawarau River, Bannockburn Creek, Alfred River, Waikaia River, Moonlight Creek (on the West Coast), Pell Stream, Waimangaroa River, Little Keyburn River, Pomahaka River, Nevis River, Skippers Creek, Floodburn Stream, Shielburn Stream, Baton River, and the Tadmore River, have also been eductor dredged. The Buller River was extensively eductor dredged in its middle reaches by a few professionals, and many recreational dredgers, during the 1980s, and is presently being eductor dredged on a commercial scale.

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