• Drains need to be maintained for a drainage system to continue operating
• All trench drains should be fenced on both sides to exclude livestock
• Weeds in drains should be sprayed in spring and autumn
• Keep machinery out of drains as ruts can stop water flowing
• Soil compaction is often an on-going problem that reduces drainage effectiveness

Drainage systems do not respond well to a set and forget approach. Attention must be paid to the maintenance needs of any drainage system if it is to continue functioning efficiently. Monitoring your drainage system is important to check for any decline in performance. Drains may become progressively blocked and wet areas reappear on the land surface. Drains need to be checked regularly to ensure that there are no blockages and water is flowing freely. Take a shovel with you on the ute or buggy and use it to get the water flowing. Place un-perforated plastic (PVC) pipe in the end of all underground ag-pipe drains, at least 1m in length, to protect the outlet from damage. Mark the end of every underground drain with a peg or permanent marker in the paddock (Figure 52). This will also make the drain easier to locate and maintain rather than have the end pipes broken. Headland culvert pipes can be easily broken by tractors and fertiliser spreaders. Outlet pipes can become blocked with weeds and plant growth or by dead vermin. End pipes should be checked before winter and any blockages cleared. Collapsed pipes or poor connectors may need to be dug up and replaced. If drainage pipes stop flowing in winter the pipe slots may have become clogged with iron ochre or dispersed soil, backfill gravels may have become clogged or the soil above the pipe may have become compacted. Soon after crop harvest is the best time to do any required maintenance on areas where wheels cross over drains. This includes machinery traffic as well as irrigator wheels. Trying to do drain maintenance after a crop is sown is often difficult for access and too late to prevent drainage problems occurring.

In the first year or two after installing a drainage system, it is often necessary to do some fine tuning after the first winter. Some wetter areas or seeps may not have been effectively drained and so supplementary drains may need to be installed. In flat areas blocked culverts and ditches can lead to waterlogging over large areas of land, restricting drainage upstream. This can cause flooding and soil erosion as the water backs up and tries to find an overland route to escape. Given the significant cost of installing a new field drainage system, cleaning trench drains and clearing outfalls is a simple, cheap and effective method of improving the effectiveness of existing systems. Surface waterways may need to be cleaned out with a spinner drainer during the growing season to cater for heavy rainfall events (Figure 71). One of the biggest movers of soil in a paddock is the lifting and dropping of cultivation implements at headlands and at the edge of surface waterways (Rob Tole pers. comm.). Over time this process can build up a ridge of soil that can prevent surface water moving into a shallow drain. Land planning or grading may be needed to move this built-up soil further away from the drain.

All trench drains should be fenced on both sides to exclude livestock. This prevents stock causing collapse of the sides and from damaging end pipes of underground drains. It can also protect water quality by preventing sediment and faecal contamination from livestock reaching streams and rivers, thus preserving water quality and ecology. Allowing stock access to trench drains shortens the life from 10 years plus down to only two to three years (Figure 72).

Spray weeds in open trench drains to allow water to flow freely and to reduce the rate of siltation. Drain weeds should be sprayed in spring and autumn. Only use appropriately registered chemicals and spray when water levels are at their lowest possible. Spraying once or twice each year is cheaper than hiring an excavator every second year. Drains should be cleaned out with machinery when clogged with growth or silt (Figure 73). When cleaning out trench drains with an excavator, the spoil can be spread over the adjoining land as it will be mostly organic matter that will dry down to a minimal amount of material that will be incorporated into the soil by livestock traffic and soil macro-fauna.

It is not only important to contain and control weeds on your property, but also an obligation of all landholders to actively control or eradicate any declared weeds on their property under the Tasmanian Weed Management Act 1999. A list of declared weeds and identification material can be accessed at nre.tas.gov.au

One of the most common on-going soil management problems in relation to drainage is soil compaction. Soil compaction prevents water entering the drainage system. Compaction occurs mostly when soils are wet and can be caused by both machinery and heavy stocking rates such as strip grazing forage crops in late winter/early spring. Headlands and gateways are often badly affected (Figure 74). Compaction needs to be correctly diagnosed as the problem and the depth of remediation determined. Shallow compaction can be relieved by chisel ploughing or running a coulter seed drill over the ground without any seed in the drill. Deeper compaction can be relieved using a winged tyne ripper in order to re-establish drainage pathways down fissures and cracks. It pays to prevent compaction by digging root crops early in the autumn and using low pressures in machinery tyres. Hump and hollow drained areas require a smooth surface to operate effectively. If the surface becomes pugged, a heavy roller may be required in the spring to smooth the surface. The hollows in hump and hollow drainage systems may need to be cleaned out with a spinner drainer if they have become pugged due to heavy stocking.

Maintaining laneways in good condition will help alleviate pugging, hoof health problems and stress on the farmer. Side drains should be constructed to stop water entering paddocks and a fence installed on the lane side of drain (Figure 75). In the summer when laneways are dry, they may need to be regraded, have new metal applied and compacted.

Gateways can become severely pugged (Figure 76). Side drains to stop water entering paddocks can help. Use of wider gateways can take the pressure off narrow access points and if necessary, a section of electric fence can be dropped and used as a temporary gateway. Also, keep the water trough well away from the gate.

Under intensive grazing systems, such as dairy, livestock management options can be an alternative to installing expensive drainage systems but good livestock management to minimise soil pugging should be considered as best management, even with a drainage system installed. If prolonged wet periods are not common, adopting an on-off grazing strategy to reduce pasture damage caused by pugging and compaction is a relatively cheap option. Cows can be stood on a laneway or in the dairy shed yard for short periods. However, the more severe the waterlogging, the better the stand-off facilities must be to cope with animals being off pasture for longer periods. This may require building a feedpad or loafing-pad and extra machinery such as feed out wagons may be needed as well. A feedpad is like a sacrifice paddock as it allows the cows to be removed from the paddocks (Figure 77). The advantage is that no paddocks need to be taken out of the round to be “sacrificed”. This eliminates the cost of re-grassing as well as increasing the available feed on the farm. Allow 2m2 per cow for standing. A solid base to the feedpad allows for regular cleaning. Any feedpad requires an effective effluent management system in order to keep the effluent on the farm and out of waterways.

Other grazing strategies than can assist with minimising soil compaction include:

• Start the winter with more grass cover which gives more flexibility and greater soil protection.
• Low-lying wet paddocks should be grazed early to save having to graze them on a long round in winter.
• Known dry paddocks should be targeted for later grazing.
• Try a later calving date.
• Back fence so that cows can’t pug grazed areas. Back fencing not only prevents cattle moving over grazed areas and damaging them, but also increases pasture growth rate. Back fencing is an important strategy when long rotations are in place.
• On-off grazing. Cows can eat their daily ration within 3 hours. Remove the cows onto a feed pad, sandy bank, laneway or sacrifice paddock for the remainder of the day.
• Feed out hay or silage on sandy banks.
• Use a sacrifice paddock for feeding out or standing the cows on. Sacrifice paddocks reduce the damage on the rest of the farm by localizing the problem on one part of the farm. Paddocks targeted for pasture renovation may be ideal for this role. Follow up by cultivating and growing a spring turnip crop or new pasture.
• Give the cows a bigger break in wet weather.
• Ignore them. Don’t ignore the problem as this will prove disastrous, but rather ignore the cows. Once you have made your decision have faith in it. Do not go visiting the cows and giving them an excuse to walk up and down the fence and pugging the soil.
• Agistment. Wintering stock off the property can reduce the problems of wet soils as well as building up pasture cover for calving. By having stock off the farm it can also reduce the stress on the farmer.
• Adopt more than one strategy and remain flexible. In any given situation it may be better to use a combination of these strategies rather than depend on one alone.