Erosion explained: recognising risks, preventing problems and protecting your soils and waterways

Small-scale erosion and ground cover:

What can I do myself about minor erosion?

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Start by fencing stock out, as a simple fence fixes about 70% of erosion. Then build up ground cover with what's on hand:

• Coir logs or pegged square bales across rills, or in a horseshoe shape to trap sediment

• Brush or sticks to stop stock and kangaroos tracking through

• Composted mulch, about 40% coarse and 60% fine

• Meadow hay from your own property, about 30–40 mm thick

• Jute mesh

• Repurposed rock over small headcuts

Always add seed to mulch or hay, as many areas have lost their seed bank.

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How do I know if my erosion is getting worse?

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Monitor it. Put a couple of pegs at the top of the headcut and take a photo across them each year. An app like Context Camera records the date, time and location, so you can compare the same view year on year.

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When do I need expert help?

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Early, small-scale erosion can often be fixed quickly with fencing, small scale erosion control techniques, mulch and seed. Get help for large-scale erosion, which we define as anything deeper than about 500 mm. Examples include gullies with unstable floors, sideways (lateral) movement, undercut creek banks, landslips, and widespread salinity. A poor fix at this scale can make things worse, and costs rise quickly once erosion passes its tipping point.

Millet:

Is millet seed okay?

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Yes. Millet is a summer-growing seed, so it's a good choice for repairs done now. We often recommend sterile ryecorn because it suits more times of year. It grows vigorously for one season, then dies back into a green mulch that lets slower seeds come through.

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Where can I get seed for a perennial native pasture?

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Try your local seed stores or Greening Australia in Canberra. In a native area you may need a native seed mix rather than an improved pasture. We would still add sterile ryecorn, as it only lasts one season.

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Is there a native grain I could use for seeding?

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Here is a fact sheet about native grains that may help: https://agrifutures.com.au/product/fact-sheet-native-grain-species/  
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Your seed supplier is also a good place to ask.

Salinity:

How can I tell if I have a salinity problem or just erosion?
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Look for:

• Bare or dying patches below dams, or where a slope flattens out (the break of slope), while the hills above stay green

• Salt crystals glistening on bare ground, especially from now through to December

• Very clear water in dams

If you're unsure, get your water tested.

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My dam is crystal clear. Is that good water?

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Not necessarily. Very clear water can be a sign of high salt. Stock will drink it, but they'll drink less than they need. A cow needs about 70–80 litres a day but might drink only 50. Get a water quality test done.

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Can pool salt test strips check water salinity?

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Yes, take your results to Local Land Services or an agronomist to find out whether the salt levels are high and whether the water is suitable for stock.

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Can a dam make salinity worse?

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Yes, all dams leak, and a dam in a saline area holds water high in the landscape. That raises the water table and kills grass below it. Options include filling the dam in and watering stock from troughs and header tanks instead, fitting a plastic liner.

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Does it matter what type of stock I use for the hay-and-molasses method?

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No – sheep, cattle or goats all work. They break up the crust, add manure and trample the hay into mulch. Add seed and the bare patch should start to heal.

Soils:

What role do sodic soils (high ESP) play in erosion?

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Soil with more than about 7% sodium is generally considered high in sodium. When sodic soils get wet they disperse, which makes them very erodible. Sodic soils, high-magnesium soils and some granites are all fragile and need extra care. Alan covered this in detail in Webinar 3, and the SoilsWest and Soil Quality Knowledge Base resources above explain it further.

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What's a phreatic line?

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A phreatic line, also called a seepage or saturation line, is the top boundary of saturated soil inside an earthen structure such as a dam wall or bank. Below it the soil is saturated; above it, it isn't. On sodic soils, water held in a bank can seep through and pop out below it, causing erosion.

Structures and larger repairs:

Is it risky to bank water away from a headcut?

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Yes, on larger catchments. Our rule of thumb in the Crookwell and Goulburn area is to treat the water where it flows once a catchment is above about 50 hectares, because diversion banks that size tend to fail. At that size, soft fixes like coir logs, branches or hay won't hold either, and you need a hard structure such as rock, logs or concrete. Check above and below the site too, so you don't just move the problem somewhere else.

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Can I slow an active headcut with branches, rocks or coir logs?

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On a small catchment, yes. In the webinar example, the headcut had an 80-hectare catchment and was moving 15 metres a year, which is too much water for soft structures. The options there were a dam with a safe outlet, or a designed hard structure such as a rock ramp or flume, plus fencing and revegetation.

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Why is a flume so smooth? Won't that speed the water up?

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Yes, and that's deliberate. A flume is designed to move water quickly from a higher point to a lower one. The pond at the bottom, sized to a set length and depth, is what takes the energy out. The velocity leaving the structure ends up close to the velocity entering it.

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Can you retrofit a trickle pipe to an existing dam?

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Yes, a trickle pipe keeps the spillway dry so grass can establish and stock don't churn it up. One pipe is usually enough. Start at 150 mm PVC, because smaller pipes can be blocked by turtles. Your contractor should size it to the catchment and the trickle flow coming in.

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Do I need to check salinity before installing landscape rehydration structures?

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Yes, structures that hold water can raise the water table, so check salinity, rainfall, slope and hydrology before acting. Rehydration structures in streams also need fish passage now. Fencing, trees and vegetation can rehydrate a landscape without structures, and usually without needing approval.

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Is there a point where land is too saline for this kind of work?

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There's always something you can do to make it better. Small changes, such as planting trees, mulching, seeding or removing a dam, you can often do yourself. Large-scale problems need expert help.

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Do I need approval for erosion control works?

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It depends on the site and the type of works. An erosion control structure on a second-order stream may need approval, but a dam built under harvestable rights may not. In-stream structures may also need DPIRD Fisheries approval for fish passage. Other things to check include Crown land, sediment control plans and WHS requirements for contractors. Webinar 2 with NRAR covered approvals in detail, and it's always worth checking before you start.

Wombats:

What can I do about wombats?

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Wombats are native and protected, so there's not much you can do yourself. To do anything about a wombat or its burrow, you need approval from NSW National Parks and Wildlife Service.