rains-putting-more-pressure-on-landslipsThe Strzelecki hills are renowned for landslip erosion as evidenced by this slip near Mirboo North. Heavy rain, poor drainage and a lack of deep-rooted vegetation cover can lead to land slippage and a loss of valuable farm land. m022614

IT’S not just the farmers in the hills who have to deal with the impact of landslips.
Local shire councils and Vicroads also have to be mindful of the effects of landslips on the roads network and are constantly attending to such problems affecting country roads.
Typically, you’ll see what’s known as a Gabion basket, a large wire-mesh basket filled with crushed rock, to stabilise the roadside above and below a landslide.
It’s not so simple to deal with a landslip on the farm.
And, after recent heavy rains, Department of Environment and Primary Industry staff are concerned that we don’t see a repeat of the situation which occurred in the winter of 2012 when there was a proliferation of landslips in the local area.
“When slips do occur or when people have concerns about landslips, DEPI can assist with soil erosion planning and in the past year we completed 30 such plans across the Corner Inlet, Bunurong and Latrobe catchment areas,” said Nick Dudley, a team leader at the Leongatha DEPI office.
“We are happy to receive calls and we’ll come out on site and have an inspection and work with the landowners on the best way to manage the situation. These plans can also be partially funded by the West Gippsland Catchment Management Authority.
“If this rain keeps up, I would expect we’ll get a number of calls and we’d welcome that (phone 5662 9900).
Vegetation plays an important role in reducing erosion and stabilising soil to minimise the risk of landslip.
A landslip can occur when the ground is not strong enough to support its own weight, causing a slope to collapse. Land slippage can result in significant damage to land and buildings, both on and below the landslip area.
The removal of vegetation, particularly deep-rooted, long lasting trees and plants that have a large root system, can increase landslip risk and locally, this has been going on since the time of European settlement.
It’s another reason why tree-planting projects, like those supported by Landcare are necessary.

How to manage a landslip

To manage a landslip site, the water in and around the affected area must be managed. Two main methods of managing water are by erecting physical works designed to enhance drainage and increasing water use by increased vegetation cover.
Where possible, use surface or sub-surface drains to redirect water flow away from the slip. Construction of small diversion banks above the slip is one way of diverting water. Water should be diverted to a well vegetated stable site away from the slip area to help minimise further erosion activity.
Often the soil surface is severely broken up immediately after a landslip has occurred. Where grading is possible it will help reduce infiltration, assist surface drainage, prevent ponding and allow for revegetation works.
If possible, batter back head escarpments and steep faces which are prone to further slipping. Excess material available from the ‘head’ after grading, could be added to the toe of the slope to provide added support.
Establish a good grass cover over the disturbed area. Support structures at the toe of the slip can be constructed if needed, but engineering advice may be required.

Important points

• Don’t construct dams on old slips or slip-prone hillsides as this will increase water pressure in the soil.
• Maintain a well-managed pasture and do not overstock.
• Avoid excess cultivation of slip-prone areas as this can adversely affect soil structure and organic matter levels and lead to greater erosion risk and increased infiltration.
• The aim of landslip control is to see a return to stability and productivity of the area. A combination of short term solutions (such as drainage works) and long term remedies (such as planting deep rooted trees/pastures) may well be the best approach.
• For effective landslip control the cost of the works, their likely success rate and off-site benefits must all be evaluated.
For further advice and information contact your local office of the Department Environment and Primary Industries on 5662 9900 or 136186.