The sediment tongue is not low in both Cs-137 and Be-7 and it is inferred that
erosion is not from a gully wall. The interpretation here is that it is not from a cut bank of the
snig track. Furthermore the result is seen as confirmation of the inference from assumption one.
These considerations in relation to the Burch assumptions have an emphasis on
comparisons between features in endeavouring to source the sedim ent in the tongue. Next
consideration is given, again in relation to the Burch assumptions stated above, to the activity
levels in the sediment tongue.
The Cs-137 values are generally constant down the tongue for the coarser
fractions indicating that these fractions are either from one source ( in this case a feature) or are
from several sources ( features ) and well mixed. There seems little doubt that these coarser
fractions could come only from the snig track where the existing surfaces would have been at
deeper profiles at the time of bomb tests and Cs-137 assimilation. The Cs-137 concentrations
for the finer fraction present difficulties for interpretation because of the variability. That, on
average, the concentrations are higher than on the snig track and at the water bar means that
some fine material has been derived from either undisturbed areas or the dump. The higher
levels would not have come from sampling 'undisturbed' material underneath the tongue
the coarser fractions as well. It is reiterated in this context that care was taken to obtain surface samples at all times.
A simple pro - rata of the Cs-137 values in the sediment tongue as compared to the snig track and the dump site indicates
1. that if the fine material is coming from the snig track and the dump site then about 86% of the material is from the snig track.
2. that if the fine material is coming from the snig track and the undisturbed areas then about 97.5% is from the snig track.
4. 10. R ev iew
One aim of this study was to assist in developing methods for the study of sediment tongues on logged areas, using radio isotopes, by differentiating into fraction sizes the particles at site features of sediment tongues. In this study particles less than 1.00 mm in size were differentiated into three fractions >500 urn, 63-500 urn, <63um.
The concentrations of both Cs-137 and Be-7 show a consistent pattern of dependence on the fraction size with higher concentrations on finer particle sizes. However more variability was found in the finer particle sizes than in the coarser. It is concluded that measurement of concentrations of Cs-137 and Be-7 for both of the coarser fraction sizes (63- 500 urn and >500 urn) is unnecessary, that is separation into the two classes is not warranted. The view is taken that because of the variability of concentrations of both Cs-137 and Be-7, on the finer fraction it is necessary to undertake further research to determine the utility of measuring concentrations on the finer fractions where eroded material may move only short distances. Nevertheless there are indications that studies of Be-7 on the movement of fine material down sediment tongues may provide information to assess the movement of fine material off sediment tongues by overland flow. It is suggested that initial studies should define the variability of Be-7 concentrations on fine particles as a consequence of both rainfall patterns
and the movement of the fine particles over only short distances during some but not other storm events.
The major objective of the study was to verify the field observation that the source of sediment in the tongue was rilling on the snig track. It is clear that the material in the sediment tongue was not from the undisturbed area. Furthermore only very small amounts of material from the dump site has reached the sediment tongue. The strong inference is that the source of the sediment tongue material is the snig track.
C H A P T E R F IV E
SU M M A R Y R E V IE W
Field measurements to assess the effectiveness of buffer strips, as Filter strips to
trap sediment on granite soils in the Eden Woodchip Area, have established the frequency with
which sediment tongues occur around the drainage lines of logged coupes, the length of the
sediment tongues and the longevity of the sediment tongues as active erosion sites. The lengths
are compared to the provisions for the widths of buffer strips.
The inspections also established the point source of the sediment tongues. A
secondary study was undertaken to determine if these sediment tongues contained material from
the undisturbed logged areas.
The monitoring studies on the stability o f sedim ent tongues indicated that a
rainfall intensity of about 50 mm.hr’ * causes erosion leading to the formation and extension of
sediment tongues.
Two diverse sets of techniques and analytical procedures were adapted for the
investigations. They are seen as promising for studying and monitoring erosion mitigation on
logged areas.
1. Field measurements were made of the lengths of sediment tongues and their
point source by simply walking around the boundaries of randomly selected logged coupes.
The measurements are therefore associated with normal logging practice. The extension of
sediment tongues was again a field study. Randomly selected sediment tongues were inspected
after rainfall events.
Statistical analysis indicated that the lengths of sediment tongues are not related
to the slope on which they occur.
2. The radio isotopes Cs-137 and Be-7 were used to study the source of the
the nearby undisturbed area, the dump site served by the snig track, the snig track and the water
bar forming the drain. Surface soil samples collected at the features of the site were analyzed for
radio activity by three classes of particle size distribution.
The results of the field inspections and monitoring studies on sediment tongues
showed that sediment tongues stabilize about one year after logging. It was concluded that a
width of buffer strip of 20 metres is very effective and conservative on slopes up to 20 .
Sedim ent tongues were observed to penetrate to the drainage line along
unbuffered drainage lines, but rarely (one for every 2.4 km of drainage line). It is inferred that
reducing the width of the protective strip along the buffered drainage lines and increasing it
along unbuffered would be a marginal improvem ent in term of decreasing the number of
sediment tongues reaching drainage lines.
The radio isotope studies showed that sedim ent in the sedim ent tongue was
produced almost entirely on the snig track. The associated studies of activity level of Cs-137
and Be-7 in respect of particle size distribution indicate that intensive study of activity levels of
Be-7 at a site may provide information on the m ovem ent of fine material from sediment
Appendix 3.1
Erosion mitigation practices in the Eden Woodchip Area 1. General
1. These conditions for mitigation of erosion shall apply to all logging and forest operations controlled by the Forestry Commission o f New South Wales in the Eden Native Forest M anagem ent Areas, Badja management area, M onaro South managem ent area and Bombala exotic management area.
2. These conditions incorporate the'A m ended Standard ErosionM itigation Condition for logging in New South W ales - June, 1984' with supplem entary prescriptions made in respect of local conditions.
3. Notwithstanding the requirements of these conditions, in catchment of major water storages and in areas where the erosion hazard so warrants, restrictions on the method and intensity of all Forest operations may be imposed by the Forestry Commission.
4. No logging or clearing operations shall take place within 100 metres of the top water level of any major water storage.
5. No tree shall be destroyed, lopped or topped within 20 metres of a prescribed stream as defined under the water Act, 1912, without prior authority of the Catchment Areas Protection Board.
2. Conditions for logging
2.1. Roading
Roads and minor roads shall be located where practicable on ridges. They shall not intrude into filter strips beside streams except where the road crosses the stream.
2.1.1 Roads
(1) Roads shall be properly formed and they shall be gravelled if the density of traffic so warrants and this is specified.
(2) All batters shall be constructed to a stable slope. Consolidation may be necessary on fills to minimize subsequent slumping and erosion of fill batters. Revegetation of batters nay be required on some roads, and his shall be carried out when specified.
(3) Adequate pipe drainage shall be provided in roads consistent with sound engineering practice so that erosion of the road surface and table drains is minimized. Pipes should discharge water onto undisturbed vegetation.
-Appendix 3.1 continued-
(4) The use of borrow pits for the provision o f extra material during road construction should be kept to an absolute m inim um . W here use of a borrow pit is unavoidable, topsoil shall be stockpiled and subsequently replaced to aid revegetation. The bottoms of pits
should be graded and levelled, sides should be battered and shaped to conform to the surrounds and the replaced topsoil fertilized and seeded where necessary to establish a vegetative cover.
(5) Maximum grades on roads shall be kept below 10 degrees.
(6) Bridges and culverts on roads shall be designed to transmit peak discharges consistent with the standard of road. Bridge approaches shall be stabilized and revegetated where necessary following construction. Culvert outlets should be located or designed to minimize scour and erosion.
(7) Immediately after operations have ceased on roads which have been damaged and on which use is to be permanently or temporarily discontinued, the damage shall be repaired by re-grading off if conditions are too wet for this to occur, temporary crossbanks shall be constructed. In this latter instance, regrading shall occur as soon as conditions allow.
(8) M aintenance grading shall be carried out only w here necessary and disturbance of vegetation should be minimized.
2.1.2. M inor roads
(1) Operations shall be planned systematically so that the number of roads open at any one time will be kept to a minimum.
(2) Wherever the type of operations permit and as far as practicable, minor roads should be constructed with cross fall drainage to the fill batter of approximately 3 degrees. There shall be no water table drain on the cut side and no windrow on the fill side of the road. All cut batters shall be vertical. When wheel tracks form as a result o f compaction of loose materials, outlets shall be constructed at the spacing specified in 2.1.4, to ensure that run-off will be diverted off the track before erosion occurs.
(3) Grade - The grade of minor roads is to be kept as gentle as practicable with a maximum o f 8 degrees. As far as is practicable long lengths of unbroken grade shall be avoided.
(4) Immediately after the logging operation has ceased in and section (even if it is planned to use the road at any time in the future) the road shall be drained by cross banks unless
-Appendix 3.1 continued-
otherwise specified. The channel of these banks must be constructed with a minimum gradient sufficient to ensure that there is adequate lateral drainage onto the surrounding vegetation. Cross banks must not direct water directly onto other tracks or roads. The exits of these banks must allow water to escape readily from the road. The spacing of these banks will depend on the erosion hazard-
Average hazard - 40 metres High hazard - 20 metres
The height of the cross banks shall be at least 60 cm consolidated.
(5) Immediately after operations have ceased on minor roads the surface material shall be replaced as far as practicable, and the roads shall be drained by banks unless otherwise specified. Seeding and/or fertilizing of minor roads shall be specified where necessary.
(6) The use of borrow pits should be kept to an absolute minimum and if employed, should be dealt with as under 2.1.1 (4).
(7) Minor roads shall not cross streams which are running unless a causeway, bridge or pipe culvert designed to transmit peak flows has been provided. Excepting where the erosion hazard is very high, minor roads may cross dry stream beds via causeways, temporary culverts or log crossings, provided there is a minimum disturbance to the surrounds.Where the erosion hazard is very high all stream bed crossing shall be kept to an absolute minimum and shall be as prescribed above for running streams. At the completion of operations the sites of temporary crossings shall be restored as closely as possible to their original condition.
(8) "Blading-off" on minor roads shall be permitted only where damage is minimal and subsequent drainage and repair is possible. Each "blading-off operation must be specifically approved.
(9) The use of minor roads shall be minimized during wet weather. They should carry no traffic at times when there is runoff from the surface.
2.2. Streams, drainage lines and other wet areas 2.2.1. Filter strips
A filter strip shall be retained on a stream or drainage line downstream from the point where its catchment exceeds the area listed below.
-Appendix 3.1 Continued-
Average grade of catchment Maximum catchment area Erosion hazard
Average High
Less than 15 degrees 50 ha 40 ha
15 degree - 20 degrees 45 ha 35 ha
Greater than 20 degrees 40 ha 30 ha
The filter strip shall be a minimum of 20 metres each side of the watercourse for slopes under 18 degrees. Where the fall into the watercourse is over 18 degrees the filter strip shall be a minimum of 40 metres each side of watercourse. The width and upstream extension of the strip may be increased as considered necessary by the forester.
2.2.2. Drainage lines
Where a filter strip is not being retained, machines shall not be taken within 5 metres of any drainage lines except with the specific approval of the supervising forester.
2.2.3. Swamps, surface seepage and poorly drained areas
Machines shall not be taken within 5 metres of the border of any swamp or area showing surface seepage or poor drainage. Vegetative indicators shall be accepted as defining such areas in periods of dry weather. Access tracks may be constructed through these areas only in circumstances where they can be adequately drained, as specifically approved by the supervising forester and marked on the harvesting plan, construction must be to a standard adequate to carry the traffic. This may require corduroy or stone.
2.3. Felling
(1) No trees shall be deliberately or negligently felled into a stream within a filter strip, except as provided in 2.3(2).
(2) In conifer filter strips, trees may be felled into a stream when approved by the supervising officer, so as to avoid possible later windthrow. Approval will be given where the tree can be removed with minimal disturbance to the stream.
(3) Crowns of conifer trees felled into streams must be removed and such removal must result in minimal disturbance to the bed and banks of the stream.
-Appendix 3.1 continued-
(4) Trees may be felled into a filter strip but shall not be fallen within a filter strip unless they have been authorised for felling by the Forestry Commission supervising officer, with the exception of those planted within the filter strip after 25th May 1983. Extraction machinery shall not enter a filter
strip to remove logs, except that in conifer plantations with conifer filter strips, extraction machinery may enter the filter strip to within 5 metres of the bank of the stream with the authorisation shall only be given where machinery is not likely to cause damage to the soil surface of the filter strip and the bed and bank of the stream.
(5) Logging operations shall be carried out so that there is minimal disturbance within any drainage line.
(6) In conifer plantations, wherever possible, slash shall be retained on extraction tracks and harvesting machinery shall operate over it.
2.4. Snigging and timber extraction
(1) As far as is practicable snigging and timber extraction shall be directed away from creeks and drainage lines to dumps located on ridge tops. In any event downhill movement of timber shall not be practice in areas with high erosion hazards or as specified.
(2) No snig track shall be constructed if it can not be adequately drained. 2.4.1. Drainage of tracks
(1) The drainage of snig or timber extraction tracks shall be carried out in the same way as for minor roads. The height and spacing of the cross banks shall be specified. The following table shows the maximum bank spacing required for each grade and degree of erosion hazard. These maximum spacings may be varied where difficult or inappropriate disposal areas are encountered. Any variation requires the concurrence of the supervising forester.
-Appendix 3.1 continued-
G rade o f sn ig track
M a x im u m sp acin g o f banks alon g sn ig track or road
Extraction track and m inor road (D e g re e) A verage erosion hazard H igh erosion hazard 1. L e ss than 15 d egree 6 0 m 3 0 m 2 . 15 - 2 0 d egree 4 0 m 2 0 m
3. 2 0 - 25 d egree 2 0 m n o track a llo w a b le
W here there is a high erosion hazard, the grades of snig tracks, extraction tracks and minor roads shall be limited and shall be specified according to the erosion hazard, and in any event shall not exceed 20 degrees. Where the erosion hazard is less, the grade shall exceed 20 degrees only where specified.
(2) Where there is a high erosion hazard, snigging and extraction of timber from areas with slopes over 25 degrees shall not be permitted if track construction is required. The maximum grade of any track constructed under these conditions shall be 20 degrees. There is less erosion hazard, snigging and extraction of timber from areas with slopes over 35 degrees shall not be permitted if track construction is required. W here specifically approved by the supervising officer, tracks may be constructed on slopes in excess of these limits where it is necessary to traverse these slopes for short distances to enable timber to be extracted from areas o f lesser slope.
(3) W herever possible in hardwood logging the dispersed system of logging shall be used with a minimum of high-use tracks and this requirement should be specified by the forester in the harvesting plan. The dispersed system shall always be used on low load bearing soils.
(4) As far as is practicable, slash shall be retained on extraction tracks, timber