Bankless Bay Irrigation Design Made Easy
Location: Queensland, Australia
Field Area: 126 ac or 51 ha
Irrigation: Bankless Bay Irrigation
"The ability to get a seamless design from the top of the field to the bottom is great."Jason Hubbard
Hubbards Contracting Group
The Hubbard's purchased a new farm and it was furrow irrigated with siphons and a head ditch. The map below shows the Existing Topography which was irrigated from the bottom edge of the image to the top edge. They wanted to convert it to a bankless channel irrigation system, irrigating from the right edge to the left edge.
The drainage map (right map of image below) shows where the water would pond if they didn't do any earthworks and switched the furrow direction around.
Figure 1. Existing Topography (left) and Existing Drainage Analysis with furrows (right).
OptiSurface Designer was used to design the new layout. The block was divided into four bays 130m wide allowing steps between the bays as shown in the figure below.
The dead level sill areas for each bay is shown on the right side. The bankless channel is cut into these sills using a simple offset done by the operator on the machine control system. The sill areas then automatically transitions back into the field topography based on defined slopes and allowable rate of change (smoothing).
Figure 2. Existing Topography (left) of the block and Proposed Topography (right) divided into four bays.
Subzones are used to define a minimum slope in each section as you move down the bay as shown in the figure below. The smoothing factor allow for a smoother transition between slopes.
Figure 3. Proposed Topography (left) and Main Slope Map (right).
Figure 4 below shows a long section down one bay. The sill is shown in the right side then transitions smoothly to the field with defined slope ranges. Each of the four sill area is about 50m of 0% main slope and cross slope.
Figure 4. Bay long section showing the Proposed Topography Profile (purple).
Figure 5. Cross section showing the sill areas steps down 200mm at a time for each bay.
The resulting earthworks is about 115 m³/ha (61 yd³/ac) which is very reasonable to convert this field to bankless channel which is more labor and water efficient.
Figure 6. Proposed Cut/Fill Map.
OptiSurface Designer is perfect for this types of design. It allows design of channels with breaklines and design of the sill areas with subzones and set slope requirements on each subzone and all the sections of the design matches up automatically at the edges and allow smooth transition of slopes.
Jason said, "I don't know how you would do this without 3D design software like OptiSurface. The ability to get a seamless design from the top of the field to the bottom is great."