Linear Move Drainage

Fixing Drainage Problems With Only 138 m³/ha (73 yd³/ac) Of Earthworks

Farmer: David Wright
Location: Queensland, Australia
Field Area: 65 ha or 160 acres
Irrigation Method: Linear Move Irrigation
Crops: Cotton and Grain

OptiSurface User Satisfaction Rating:
10 out of 10


Problem

A linear move irrigator was installed on 65 ha (160 ac) running across the slope as shown in the Existing Topography below.

Problem was the topography was very flat in the direction of the linear move and in the cross slope direction.   With these low slopes, a ridge created by wheel tracks of only 15mm (0.6in) high can pond water up from wheel to wheel across the span of the linear move.  See Drainage Analysis image below.

Figure 1. Existing Topography (left) and Existing Drainage Analysis (right). Drag white slider left or right to view each.

Solution

In this case, the earthworks required to drain from one end to the other in the direction of the linear move was too high.  It was decided the best solution was to provide drainage along the direction of the linear move however with cross drains every 400m (1300ft), approximately.

OptiSurface 2Way is a Surface Type in OptiSurface which can drain in two opposite directions (2Way). This suits crops grown in furrows or even minor wheel tracks where water needs to drain along the furrows or direction of travel but it can drain out to either end of field or at some distance along the furrow using cross drains. The location of the high point in the field is defined using a subzone with the Subzone Type setting of 'Ridge'.  The location of the cross drain is defined using a Subzone Type setting of 'Valley'.  All furrows will have positive slopes falling away from the 'Ridge' subzone to either the edge of the boundary or to a 'Valley' subzone.

Figure 2. Existing Topography (left) and Proposed Topography (right). Drag white slider left or right to view each.

Below shows how special subzones like Ridges and Valleys are used in OptiSurface Designer to tell OptiSurface's unique algorithm to optimize the surface.

Figure 3. Example Valley Subzone

Below is the Cut/Fill Map required to achieve the Proposed Design. The earthworks were 138 m³/ha (73 yd³/ac).

Figure 4. Proposed Cut/Fill Map

Figure 5. Profile View along the length of the field.

Figure 6. Water Flow Path Direction Map

Conclusion

Below is David happy with the design of his field with earthworks ending up at 138 m³/ha (73 yd³/ac) and gave a User Satisfaction Rating for OptiSurface of 10 out of 10.

Figure 7. David Wright revealing his field after the earthworks were completed and a number of seasons have passed.

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