Mine Rehabilitation Handbook - Mining and Blasting

C. When using jute mesh
PLACE MESH OVER
SEEDED AND FERTILISED
TOPSOIL. BURY THE TOP
END OF THE JUTE MESH
STRIP IN A TRENCH
150mm IN DEPTH
LAY MESH AND ENSURE
CONTACT WITH SOIL AT
ALL TIMES
Figure 5.6
• Encouraging Infiltration
This is often, but not always, most effectively achieved by ripping the
disturbed area parallel to the contours. In addition to increasing
infiltration, ripping relieves soil compaction, “keys” topsoil to subsoil,
increases the volume of soil readily available to plant roots and
provides places for seeds to lodge. Important considerations when
ripping include:
- always rip precisely along the contour - this will normally require a
surveyed line;
- rip the area following development of the post mining land form;
- ripping should normally be as deep as possible 0.8 - 1.8m
depending on the material, available equipment and subsurface
conditions;
- spacing of rip-lines should be approximately equal to ripping depth;
- do not rip when soil conditions are too wet to allow the soil
to shatter;
- a “winged” ripping line may be more effective in moist
soil conditions;
- take care when ripping sodic materials, as they are prone to tunnel
erosion (piping); and
- avoid drawing large rocks to the surface whilst ripping.
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SECURE MESH WITH
U-SHAPED WIRE STAPLES
• Managing Water Leaving the Site
Water, which is discharged from the site, or is diverted away from the
site, will generally have been controlled and the flow concentrated.
Diversion of established drainage lines or watercourses would
normally require specific approval from the State/Territory water
authority. Similarly, diversion or discharge of runoff may have legal
implications and necessary approval or permits should be obtained.
Unless the water can be utilised by the mining operation, it must be
managed to avoid pollution due to erosion and sediment deposition,
either at the point of discharge or further downstream. As a guide:
- Sediment dams are most commonly used to control and retain
sediment laden runoff prior to discharge.
- Most sediment will be carried by the infrequent high intensity
rainfall events. Dams and spillways must be designed to
accommodate these events or they will not function at the most
critical times. Seek advice from appropriate authorities or detailed
references for design techniques (refer Appendices 1 & 3).
- Ensure that construction materials are suitable. Leakage from the
dam may in itself not be critical but consequent instability of the
dam wall due to tunnel erosion (piping) may result in failure.
- Locate dams so that runoff from undisturbed catchments can be
diverted to natural waterways. Ensure that channel gradients are
not excessive and the need for protective measures within the
channel is minimised.
- In many dams, sediment levels greater than half of the total dam
capacity will significantly reduce sediment removal rated. In these
circumstances, sediment should be removed (refer figure 5.7).
- In saline areas, be aware that the head (pressure) of a dam on a
slope may cause salt scalding downslope of the dam.
Figure 5.7
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