Paperlinx Green Shareholders' Group
Drains and Culverts
Factors which accelerate erosion by water are:
- removal of protective vegetation and roots
- disturbance of the soil
- concentration of water
- acceleration of water
- increase in slope
- soil type - some soils are specially sensitive to erosion by water
Much of the soil in West Gippsland and the Strzeleckis is very sensitive to erosion. When inadequate attention is given to drainage huge ditches, or underground tunnels, are the result.
The soil removed, together with its nutrients, ends up in the creeks, rivers, and ultimately the Gippsland Lakes.
The Code of Forest Practices, Section 1.2 Environmental Care Principles includes the following:
Planning and conduct of timber growing and harvesting operations must be such that:
c) water quality is protected by measures which minimise ..... sediment and nutrient input to streams from roads and harvested areas;
e) soil stability is protected by measures which regulate site disturbance and overland flow of water;
The more widely spaced drainage culverts are, the more water they concentrate into one small area. The smooth pipe beneath the road accelerates the water which then falls from the pipe end. This causes rapid erosion below the pipe outfall.
The culvert piping is undermined, by the flow falling from the lower end, and also by seepage through poorly compacted fill around the pipes.
Pipe sections then drop into the erosion gully that they have created beneath them, as we see here.
Photo Strzeleckis: Jeeralang North, Thompson Road, January 1977
Source: FOGB
Here is an interesting attempt to carry the water further from the pipe's end. Unfortunately it has further accelerated the water, and drops it from an even greater height.
The result is even faster erosion downstream, though the pipe may remain in position a little longer.
Effective erosion control requires a mechanism to break the water's fall, to slow it down and to spread the water out over a wider area.
Photo: Strzeleckis, Traralgon South, Red Hill Road, August 1997
Source: FOGB
This use of corrugated iron has ceased, and most culverts in this coupe, which has become something of a public example, now have beds of heavy bluemetal below their outfalls. This breaks the force of water and spreads it out somewhat, a good heavy duty solution.
Unfortunately there is no sign of the bluemetal or other energy dissipation structures below culverts in new coupes now being worked between Red Hill Road and Mt. Tassie and in other areas further west.
In this respect it is fortunate that we have had another exceptionally dry winter.