It always disheartens me to see the lack of application of soil erosion principles to basic roadside stormwater drainage. Poor roadside runoff management, not unsurprisingly, ends up as unstable and eroding gullies alongside roads. Silt is moved into waterways and gullies become deeper, and may ultimately becomedangerous vehicle traps.
A case in point is the work that is now being undertaken alongside SH10 (Aurere and Oruaiti) where someone who does not appear to appreciate the basics of the combinations of length of slope, degree of slope and the benefits of vegetation in managing roadside drainage is now systematically destroying what were basically stable areas.
Previously these roadside verges and their drains had been correctly maintained by mowing to control vegetation, which provided the dual benefits of stabilisation and slowed runoff to safe velocities within the channel. The end result was an aesthetically pleasing and stable roadside verge, which in many places also provided a safe pull-off area.
However, someone who has not passed the basics of soil conservation and erosion control has decided the system needed 'improving' by arranging for these areas to be excavated, which has now destabilised the systems. As well as extending the excavation to the pavement, this has increased the verge slope so that drivers are no longer able to safely pull off the roadway.
The final touch seems to be to refill the channels with rocks to replace the lost benefits of the channel vegetation. Unfortunately rocks do not lend themselves to mowing, and will further compromise safety when a car enters the rock field in an emergency.
There is an old saying that goes "If it ain't broke don't fix it". Otherwise, whoever is responsible should please review their understanding of soil erosion principles and then proceed on a sustainable basis.
