SEVERAL wild and wet weather events across northern Victoria have compounded damage already caused by December’s that included soil erosion on farm roads, tracks and driveways.
While some of the massive falls, which dumped 100mm-plus in a few hours, not days or weeks, would overwhelm most systems, Agriculture Victoria land management extension officer Clem Sturmfels said the key to controlling this damage was drainage.
“Good surface drainage, wide stable table drains and closely spaced run-offs to direct the water away from the roadway are vital,” Mr Sturmfels said.
“Additionally, the roadway needs to have stable, well drained foundations and a hard-wearing gravel, concrete or bitumen surface.”
Class 1 and Class 2 materials – a mix of quarry dust and larger aggregate – make for a very stable and hard-wearing surface without the need for a surface seal.
“Roadways can be constructed on quite steep slopes using these techniques,” he said.
“A well-built road should only require occasional grading and a top dressing with gravel every few years.
“And roadways cut into the side of a hill will need regular culverts or other forms of cross drainage.
“A simple speed hump or roll-over is a cheap and easy way to divert water.
“Wherever possible, roads, tracks and driveways should follow ridgelines to minimise the need for cross drainage.”
Mr Sturmfels suggested the best way to create good surface drainage was by crowning up the centre of the roadway.
The crown needs to be high enough to rapidly shed water away from the centre of the road. An alternative method, commonly used on bush tracks, is to slope the road surface into, or away from the side of a hill.
Roadside table drains should have a flat base to spread and slow the speed of the water, and ideally will have a good cover of grass to protect them from erosion.
“A well-established grass table drain can safely carry a similar flow of water to a typical rock lined drain.
“If using a rock lined drain, it’s important to make it wide and deep enough to carry the anticipated flow.
“Run-offs or cut-off drains are used to take water from the table drain to a safe disposal area. They should be spaced 50 to 100 metres apart on gently sloping roadways, but only 15 to 20m apart on steep roads, tracks and driveways.”
If you have any questions, Mr Sturmfels said he was happy to answer them at clem.sturmfels@deeca.vic.gov.au.
