Within flood plains stockpiles will be constructed with a regular profile and the surface compacted to minimise the potential for erosion by flowing water.


11.6 Dry Open Cut Watercourse crossings 156


157


The following sections outline a generic method for wet open cut crossings of watercourses by the onshore cable route.


Dry open cut techniques create a dry section of the river bed, temporarily diverting flow from the channel. This can take two forms:


A flume pipe crossing An over-pumping technique.


11.6.1 Plant and Vehicle Access 158


In most instances, temporary flume pipe(s) or bridges are installed at watercourse crossings as described in section 11.5. In all cases, vehicles will be prohibited from driving through watercourses.


11.6.2 Flume Pipe Technique 159


In this method, water flow is maintained using temporary “flume” pipes installed in the bed of the watercourse.


160 Soil would be stripped from the areas adjacent to the watercourse banks and grading the banks down to bed level. The stripped topsoil will be stacked separately from subsoil within the working area.


161


The cable trench will then be excavated below the flume pipes. The trench excavation will be checked for sufficient depth of cover through the crossing.


162 Spoil from the trench excavation will be stored in the working width areas next to the crossing or removed by dump truck along the working area. River bed material will be stored separately from the bank materials and replaced following installation of the ducting.


163 De-watering, using appropriate sediment control techniques and/or trench supports may be used to facilitate safe excavation. If pumps are used, the discharge hose will be directed through a filtering medium to remove silt, before the pumped water is allowed to percolate back into the watercourse.


Outline Code of Construction Practice. Version 3. Page 50


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