by Ron Lyseng - 23 July 2015
The laser beam and tower-mounted RTK are already becoming obsolete as 3D GPS takes over the task of designing field drainage systems.
The topographical accuracy of GPS has evolved to the point that land-forming and surface modification can be performed with less earth movement and lower costs compared to laser and real time kinetic located on towers.
The OptiSurface Designer is one of the latest 3D tools available to producers and custom drainage contractors.
Developed by Graeme Cox of Davco OptiSurface in Australia, the program exploits the high resolution accuracy provided by the latest generation of GPS technology.
The OptiSurface process begins with a 3D GPS survey of the field to determine the elevation points and natural channels of water flow. At this point, the OptiSurface Designer differs from other programs in two ways:
- It relies solely on 3D topographical data provided by GPS.
- The use of infinitely variable grades (IVG) is the major departure from traditional drainage programs. Cox said that instead of trying to funnel all the water into an increasingly deeper, wider and wetter ditch to get it off the field, IVG uses small shallow water runs that drain slowly and displace little soil.
These IVG runs typically have only a small amount of drop, generally no more than the minimum needed to move water.
Slow moving water reduces erosion and enhances uniform water infiltration, which contribute to better yields.
In traditional land levelling, engineers take a prescribed slope and send it down the desired direction they want water to travel, even if it cuts through knolls and ridges, said Preston Marthey from OptiSurface’s office in Arkansas. That slope is expressed as the amount of fall every 100 feet from top to bottom.
“The problem is you’re moving more topsoil than needed to get water flowing off the field. In traditional land levelling, if the engineer says the water should run north, he designs the project so all the water channels will run north,” he said.
“In land-forming, on the other hand, you’re simply re-shaping the topography already there on your field. You eliminate potholes and ponding, but you do it without major changes to the landscape. We work with variable grades going all directions. It’s more like tuning your landscape. If we have an infinite number of slopes running in 360 directions, well, that’s OK.
“In one run we’ll have 4/10 inch per 100 feet, another at 1/10 inch per 100 feet and another might be one foot per 100 feet. The OptiSurface Designer looks at the raw map and determines what slope is required to move water out of that area of the field.”
Armed with this IVG design data, the program feeds instructions to the blade while ensuring it moves the minimal volume of soil.
Marthey said OptiSurface is strictly software that designs field drains. It is not a control system. The client exports the field design, which is compatible with a variety of machine control systems.
Cox said his 15 years experience designing drainage systems has taught him a number of lessons:
- Water rules. He said yield maps show that 80 percent of profit loss is because of too much water or too little water.
- Ponding kills. Water left standing 24 hours after rainfall or irrigation accounts for an eight percent yield loss per day, as well as further losses from nitrogen leaching and increases in disease and insect problems. Ponding also delays spraying and harvest operations.
- Tile drainage costs. It may be effective in some soil or in flat fields, but Cox said the return on investment is better with 3D GPS land-forming in most situations.
- Ditching takes cropland out of production, restricts machinery access and is a major reason for broken equipment.
Cox said the system deals only with the surface.
“We can’t solve subsurface issues,” he said.
“Some people in the tiling industry think we’re trying to eliminate tile drainage. Nothing could be further from the truth. If your water table is so high that your crop roots are drowning, then you need tile drainage. It’s that simple.”
For more information, call Precision Land Solutions in Winkler, Man., at 204-331-3003 or visit www.optisurface.com or contact Marthey in Arkansas at 870-340-2020.
Original Story: http://www.producer.com/2015/07/gps-used-to-design-field-drainage/