Effective management of overland flow water
Overland flow is the water that runs across the land after rainfall, either before it enters a watercourse or after it leaves a watercourse as floodwater.

In line with best practice measures it is essential for the biosecurity of your property that feed for animals is:

Overland flow is a vital source of fresh water for streams, rivers and underground reserves. It also naturally irrigates bushland and grasslands.

However, overland flow has the potential to erode soil, elevate soil nutrient levels, produce sediment deposits, transport pests, weeds and disease directly into water bodies creating a potential biosecurity risk

The management of water from overland flow is an ever increasing challenge for property owners, local communities and jurisdictions to strike the right balance between water used for irrigation, agriculture, town water supplies, stock or domestic requirements - while also ensuring the long-term health of waterways and the users.

When fertile topsoil is lost, nutrients and organic matter needed by crops are often removed along with it. Erosion tends to remove the less dense soil constituents such as organic matter, clays and silts, which are often the most fertile part of the soil.

Off-property impacts occur when the eroded soil is deposited elsewhere, along with nutrients, pesticides or pathogens that may be attached to the soil.

Soil eroded by overland flow has effects such as:

• eroded soil deposited in depressions and adjacent fields
• decreased water quality downstream
• decline of downstream aquatic ecosystems because of sedimentation and the addition of nutrients (nitrogen and phosphorus), pesticides and bacteria
• clogged drainage ditches.

Methods land owners employ to slow-down or prevent overland flow erosion will vary depending on property location and geography and may include:

• planting of cover crops
• grassed waterways in fields where land forms natural depressions
• contour cultivation
• strip cropping
• conservation tillage
• no till
• drainage banks.

Water from overland flow also has the potential to carry seeds, weeds and plant fragments for kilometres away from the source onto properties and into waterways. Plant fragments and seeds remain viable through this process and once settled, can grow into new weeds and thrive. It is recommended that all landowners develop an integrated weed management plan that uses a variety of techniques to keep weeds under control by maintaining weed densities at manageable levels. For more information on developing an integrated weed management plan, contact your local state or territory Department of Primary Industries or Department of Agriculture.

Keeping livestock out of waterway margins and overland flow areas such as, gullies, drains, seeps and wetlands, will reduce their exposure to overland flow which may carry faecal matter, fertilisers, pesticeds and herbicides and can be dangerous to livestock health.

Faecal matter contamination in particular can cause the transmission of diseases such as Johne's disease. Cattle, sheep, goats, deer and alpacas can become infected with Johne's disease by eating pasture or drinking water contaminated with faeces carrying the bacteria from infected animals. Good on-farm biosecurity practices will minimise the risks of livestock contracting these diseases.

The cleaning of vehicles and equipment is an important biosecurity consideration and visitors, staff, contractors and family should always wash down cars, trucks and machinery that may contain any potential pest, weed or disease in one easily managed area. However, care should be taken that run-off water does not collect with overland flow. The wash-down area should have a sump or water collection area. The sump and area surrounding the wash-down facility should be checked regularly for the presence of weeds, new pests or chemicals and dealt with appropriately.

Wash-down areas should:

• be readily accessible and located between the driveway and farm roads
• be well away from crops
• have access to power and water
• have a sealed or gravel surface
• not drain into a waterway or crops
• have a sump or collection area for easy inspection.

Overland flow water management plays an important part in good on-farm biosecurity, which will in turn secure your farm and secure your future.

If you see anything unusual on your property call the Emergency Animal Disease Watch Hotline on 1800 675 888 or the Exotic Plant Pest Hotline on 1800 084 881.

SOURCES: The State of Queensland (Department of Natural Resources and Water), Rangeland Watershed Program and Government of South Australia Primary Industries and Resources