Saving Valuable Topsoil With One Of The First OptiSurface Designs

Location: DAVCO Farming, Queensland, Australia
Field Area: 85 ha or 210 acres
Irrigation: Drip
Crops: Sugarcane


OptiSurface was specifically developed By David & Graeme Cox for the new irrigated farm development called 'Oaky', covering 5000 ha (12,500 ac). This field is in that farm and was one of the first fields that OptiSurface was applied to back in 2009.

This farm was being converted from pasture to drip irrigated sugarcane. Furrows and beds were to be used to maximize crop yield from improved micro-drainage and harvester efficiency. The problem with furrows and beds is that they restrict drainage to one direction (along the furrow).

Landforming is required to ensure that continuous fall occurs along the furrow so that the water will drain out the end of the furrow.

Also this farm typically has topsoil that is quite thin (e.g. 200mm or 0.2ft) and below it is a subsoil with high sodium and magnesium which restricts water infiltration rates and rooting depth. Any movement of the topsoil can dramatically reduce yield for many years so OptiSurface was developed to minimize the topsoil movement but enable optimum surface drainage of the fields.

Existing Topography

Existing Topography Drainage Analysis

The drainage analysis shows where water will pond in the furrows if the furrows/beds were formed along the bearing 68.88 degrees from North.  The map shows where 25% of the field would be affected. This would reduce yield in these areas and also create problems with machinery access for planting, spraying and harvesting.

Design Inputs

Proposed Topography

Proposed Cut/Fill Map

Long Section for Single Plane Design

For comparison, here's the Long Section for a Single Plane Design in the same location.  The earthworks for the single plane design is 750 m3/ha which is 490% higher than OptiSurface Design.

An OptiSurface 1Way design was calculated to drain water down the field to the northeast direction following the natural topography of the field. Significant smoothing was applied in the main slope and cross slope directions and maximum grades were limited to 0.3% for the main slope while 0.2% for the cross slope.

This resulted in smooth design surface with earthworks of 147 m3/ha (80 yd3/acre).

If this was done with the traditional design methods available (multiple planes) at the time, the earthworks cost and topsoil movement would have been 200% to 300% larger.

Video Explanation

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