OptiSurface was commissioned to analyze a 40 hectare center pivot on the Atherton Tablelands to optimize row direction with the aim of limiting risk of ponding, erosion down furrow and overtopping of beds.

A RTK GPS survey of the field was carried out. The data was imported into OptiSurface Designer, triangulate and contoured as shown below.   The surface was extended outside the black boundary using a simple extrapolation to eliminate any boundary effects on the further analysis.

Figure 1. Existing Topography.

Figure 2. Satellite Vegetation Index (NDVI) Map taken on 23/10/2015.

Drainage Analysis

The Drainage Analysis functionality in OptiSurface Designer allows you to calculate surface drainage characteristics such as:

• Ponding Depth Map,
• Catchment Area and flow direction arrows.

This analysis assumes enough rainfall occurs to overflow all depressions in the field. Ponding is the water that cannot drain away by flowing along the ground surface, so it needs to infiltrate or evaporate to be removed.  The effect of furrows and beds is also incorporated.

See http://support.optisurface.com/knowledgebase/articles/245285-3-4-4-drainage-analysis for more details.

The setting used for this study with a change in Furrow/Bed Bearing were:

Runoff Analysis

The Runoff Analysis functionality allows you to calculate runoff depth and velocity maps during a storm event (e.g. 1 in 10yr storm). The outputs allow the designer to assess the risk of erosion (high velocity) and overtopping of furrows (depth greater than furrow) for the existing topography or a particular landform design.

See http://support.optisurface.com/knowledgebase/articles/245286-3-4-5-runoff-analysis for more details.

The setting used for this study with a change in Furrow/Bed Bearing were:

Figure 3. Drainage Analysis on N-S furrow direction.

The results shown in Figures 4 and 5 that the velocities on the northeast part of the field has greater that 0.7 m/s. For bare soil, this would likely result in erosion.

Figure 4. Runoff Analysis on N-S furrow direction.

Figure 5 shows the velocity arrows on the Existing Topography contours.

Figure 5. Runoff Velocity on N-S planting direction (right) over Existing Topography (left).

The next step was to try different bed directions to try to reduce the erosion risk by lowering the runoff velocities.

Figure 6 shows the drainage analysis running east-west and the drainage problem on the north east still exist. However, the ponding issue on the south east has disappeared.

Figure 6. Drainage Analysis on E-W planting direction.

Figures 7 and 8 shows the runoff analysis for east-west bed direction. The erosion risk on the northeast has been eliminated, however, the area to the west is now showing up.

Figure 7. Runoff Analysis on E-W planting direction.

Figure 8. Runoff Velocity on E-W planting direction (right) over Existing Topography (left).

A number of bed direction was trialed. A rotation of 70° from north was found to offer the lowest runoff velocities and therefore lowest erosion risk.

Figure 9. Drainage Analysis on 70° bearing.

Figure 10. Runoff Analysis on 70° bearing.

Figure 11. Runoff Velocity on 70° bearing (right) over Existing Topography (left).

OptiSurface’s Drainage Analysis on this field highlighted some surface drainage problems (ponding). These can be fixed by ditching or landforming.

OptiSurface’s Runoff Analysis on this field highlighted some the areas with higher risk of erosion due to high water velocities. These can be reduced or eliminated by rotating the row direction to a bearing of 70 degree from north.