Take home messages

• Drainage planning software using accurate elevation data can drastically improve the effectiveness of drain installations.
• Data from global navigation satellite systems (GNSS) underpin all collection systems.
• Better drain planning leads to better installations.
• The same software tools can often also be used to redesign paddock surfaces and address both surface and subsoil drainage.
• Such modern technology can make drains more accurate and more effective.

Introduction

Waterlogging is one of the main causes of crop loss in higher rainfall zones. The issues caused by waterlogging can be direct, from stress on plants that stunts growth or causes plant death. The issues can also be indirect, creating conditions that increase the ability of pathogens to impact the plant. There are also a wide range of associated logistical impacts, such as bogging, making operations like spraying and harvesting difficult or impossible. Even small, waterlogged areas with shallow puddles can lead to crop losses, since the site will always end up sitting saturated for longer.

Actions that reduce waterlogging risk make sense for broadacre cropping systems in higher rainfall zones and are particularly important for irrigated crops. Not only does the likelihood of waterlogging increase with irrigation, but the value of crops (and by extension, the financial impact from crop loss) also tends to be higher under irrigated cropping systems.

The most fundamental tool in reducing waterlogging is improved drainage. Installing drains on farms isn’t new, and there is evidence that it has been around for almost as long as agriculture itself. While drainage may be almost as old as the hills, that doesn’t mean our techniques haven’t changed and improved over time. Technology has increased the accuracy and efficiency of many parts of our lives, and drainage is no exception.

Better elevation data

Drainage planning software can drastically improve the effectiveness of drain installations. All versions of this type of software need accurate elevation data, and technological advances have made several options available for data collection.

LiDAR sensors on aircraft allow regional mapping of elevation at high levels of accuracy. LiDAR is much like RADAR, but instead of recording the echo of a transmitted radio wave, LiDAR uses lasers. LiDAR data have been collected for much of Tasmania and can be freely accessed for most areas within the agricultural region.

The data collected is very accurate, with one important caveat. As LiDAR uses light, the map it provides will be an accurate record of the visual surface of the ground, this means it can be impacted by crops and other dense vegetation levels. However, when the ground cover was minimal at the time of capture, it is a great resource for drain planners.

Drones can generate elevation data as well. Sometimes this will be via LiDAR sensors, but more commonly, it is done using a technology called photogrammetry. Hundreds of images are compared and the change in location of objects due to changing camera angles as the drone flies allow a 3-D model to be constructed. Drone mapped elevation has two main sources of error. The first source is the same issue faced by LiDAR – it is recording the visual surface, not the hard surface. The other is the need for accurate georeferencing, that is, being able to tie the surface onto known points on the ground. This step takes a few extra skills on the part of the operator.

GNSS

Data from global navigation satellite systems (GNSS) underpin all collection systems. GPS is the most well-known, but other systems include Galileo, Beidou, GLONASS and QZSS. When uncorrected, this data is fine for a general location but not suitable for drainage – they’ll get you within a few metres, but drainage planners need to be within a few centimetres at the worst.

Correcting GNSS data is simple – a base station sits at a known location and sends data out on variation in the incoming GNSS signals. Since the base isn’t moving, this variation is the error in the signal. The base sends the correction to the rover, and accuracy jumps from within a few metres to within a few centimetres.

There are a wide variety of ways this can be configured. Solutions include a base station set up in the field to transmit directly to a rover; a network of base stations across a region and the rover receives corrections via the internet; or base stations that communicate directly with satellites that then provide a correction directly to the rover.

The preferred method for collecting elevation data is to simply drive across a paddock with a GNSS receiver, logging points as we go. We use a base station in the field to ensure our data correction is as local as we can make it. The elevation surface is created using what is essentially a 3-dimensional dot-to-dot puzzle.

Better drain planning

Once the elevation data is loaded into the drain planning software, several extra layers of data can be generated. These include location and depth of puddles, where water accumulates, and the slope.

At its most basic level, a plan can be created by simply tracking where the water would naturally want to run. Layering in more data allows other factors to be taken into account, including pivot wheel locations, outfall locations, soil texture changes, and the impact on surface flow of planting or bed direction.

The output can be a line to follow, either for manually steering or for loading into an autosteer-enabled tractor. With the appropriate drainage gear, the options are much more powerful. The plan can define the depths of cut needed, gradients that drains will run at, and even the cross-section shape of the drain.

One other freely available tool for drainage planning is satellite imagery. Google Earth as a desktop program allows growers to see images captured in the past, not just the image displayed by default. Often, the available imagery will include the paddock in a wet season – being able to back up the modelled water flow with observed crop damage greatly increases the confidence in the plan.

Better installations

Very similar positioning systems to those needed to collect elevation data can be used on the machinery installing the drains. Fitting a rover antenna to the top of a drainage machine means the height of the machine can be very accurately controlled, and a rover antenna on the tractor towing the drainage gear keeps the machine exactly where it is needed.

The impact of this control is drains can be installed on much flatter gradients than would be achievable by eye. For example, we have installed drains successfully with a 0.1% grade, that is, a fall of 10cm over 100m. It also means drains can be installed much faster, since the operator can enter the paddock already knowing where the drains will go. This means they don’t need to spend time thinking and planning, while a large and expensive tractor sits idle.

Beyond drains – Landshaping

A drain fixes a hole by digging another hole. The surface of some paddocks can be so full of holes that if drains were used to eliminate wet sites, the field would be more drain than paddock. Instead of drains, a much better solution is often filling the holes. This inevitably involves moving soil around, which can become an expensive operation. In shallow duplex soils, it can also become a counter-productive solution, if it leads to excessive removal of topsoil.

The same software tools that are used to create drainage plans can often also be used to redesign paddock surfaces. Implements such as land planes or laser buckets can carry the same implement control systems as the drainage gear, providing very accurate control over depths of cut and heights of fill. The software allows all planning to get the maximum impact from the soil movement with the maximum efficiency, and without creating cuts that are deep enough to lead to soil damage.

Beyond the surface

Of course, not all drainage is across the surface. Subsoil drainage works under the ground, removing water from saturated soils. The same GNSS controls are used to ensure that drains are installed at grade, and where they were planned.

Subsoil drainage is substantially more expensive than surface drainage, however, it has many advantages. Surface drains, for instance, are rarely effective if the source of the water is under the ground (such as a spring or a soak). Subsurface drains can be extremely effective at removing such water. Subsurface drains need lower maintenance than surface drains (although they aren’t maintenance free), and don’t impact on your activities on the paddock surface. Surface drains don’t like to be cultivated and can get fouled by machinery or pivot wheel rutting.

Conclusion

All strategies to improve drainage rely on one marvellously consistent feature of water – it will always flow downhill, until something stops it or pumps it. There is a myriad of tactics to harness this power that gravity has over water, and, just like growers on the banks of the Nile 4,000 years ago, a grower wanting to install drains needs to make decisions about what the best solution will be. Even though the fundamental problem is ancient, using modern technology can make drains more accurate and more effective.

Contact details

Reuben Wells
Ag Logic Pty Ltd
27 Redwood Crescent, Youngtown TAS 7249
info@aglogic.com.au
0448 947 286