Constructing a netting fence above a dam can reduce the amount of organic material entering during and after a storm.
Agriculture Victoria land management extension officer, Clem Sturmfels, said while thunderstorms can produce needed runoff, they can also result in large amounts of dry grass, manure, soil and other material being swept into dams.
“If left unattended, these materials will sink to the bottom and decompose, impacting water quality,” Mr Sturmfels said.
“Netting fence sediment traps are quick and easy to erect and can be made using second-hand materials.
“Netting fences slow the speed of water and trap large organic materials.
“As the water slows, heavier sediments drop to the bottom while the organic materials trapped on the fence act as a filter for finer materials.”
He said to be most effective, the netting fence needed to be well supported with steel posts and follow the contour of the land.
“By making the base of the fence follow a level path, the water can spread out in both directions along the fence.
“The longer the fence, the more material that will get trapped.
“The ends of the fence need to be turned uphill to increase capture of materials.
“Commercial geo-fabric silt fences are great for trapping finer materials, however they transmit water very slowly and are not
recommended for concentrated flows of water.
“Clean straw bales placed tightly together and pegged down with steel posts can also be used to create an effective sediment trap.”
Alternatives include synthetic silt fences, sediment ponds or a simple diversion bank with drop boards to manage flows into the dam, but regardless of design, all sediment traps should be regularly inspected, maintained and emptied following major storm events.
Mr Sturmfels said sediment traps could only do so much to prevent dam pollution, and the best strategy was to ensure good ground cover was maintained and all larger dams were fenced out.
“Stock access to water can be maintained using a hardened access ramp or by pumping to a tank and trough arrangement,” he said.
For more information, visit the AgVic website.
