Murray CMA Erosion design implementation

Case Summary

Client - Murray Catchment Management Authority

Task - 2009/10 Erosion incentive design and implementation fee for service agreement

Value - $645,000

Date - 2009/10 financial year

Background

The Murray Catchment Management Authority allocated $645,000 for projects targeting the treatment and control of actively eroding gullies for the 2009/10 financial year. This may typically involve a combination of remedial earthworks to control water flow, revegetation to stabilise the site and fencing to prevent renewed degradation. The SCS was awarded the contract to design and construct effective and efficient erosion control works to mitigate gully erosion and contribute to achieving Murray CMA investment program milestones of:

• 50km gully treated
• 2500ha catchment/hill slope erosion protected
• 200ha revegetation

Objectives

SCS staff meet with the landholder, assess the site, determine a cost effective solution and then design, survey and implement the necessary work. A typical case in point is the property "Colonsay", a property 20km west of Albury on the Howlong Road, An active gully system was directing sediment directly into the Murray River. It required earthworks to direct water around the site, shape the gully and revegetate it and fence it out.

Works Undertaken

Diversion works above an actively eroding gully system were installed to divert overland flows. The gully area was then shaped using bulldozers. Because of the highly dispersive nature of the underlying clay, the site was treated with 2.5 tonnes of gypsum per hectare which was incorporated into the upper layers to help stabilise the site and aid the revegetation process and mitigate against potential tunnel failure. Adequate compaction during construction was also important to further reduce the risk of tunnel failure. A plastic membrane was installed in the wall of the GCS to reduce the risk of tunnel railure. A 225mm PVC trickle pipe was installed to help convey the trickle flows safely to the gully floor and a designed spillway was constructed to handle the larger flows. As the area had a significant rabbit problem the bulldozers ripped the warrens and a follow up baiting program was undertaken in the autumn months by the landholder. 

Outcomes

A severely eroded site was stabilised and all sediment retained on site. These works form part of a series of works that have been installed on "Colonsay" over three years with additional works to be undertaken in 2010. This work is an example of a catchment wide project designed to assist landholders to treat badly eroded land on their properties which would not otherwise be undertaken without funding by Murray CMA.

Referee

Client Contact

Dale Stringer

T: 0428 409 680

SCS Contact

Chris Bootsma

T: 0427 481 132