3.4.6 Furrow Irrigation Optimization (OptiIrrigate)

Last Updated: 11 April 2018          For: OptiSurface Designer V2.5

Overview:  The Irrigation Optimization function allows the designer to calculate Irrigation Infiltration Depth Map, Irrigation Cutoff Time Map and Irrigation Inflow Rate Map.  The output allows for analysis of optimized furrow irrigation.

Watch this video as Graeme discusses this new feature.  You can watch it on youtube for better resolution up to 720p.

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3.4.6.1 Topography

Surface:  The surface to carry the analysis out on.

Calculation Grid Spacing (m or ft):  The cell spacing of the grid that the drainage analysis is calculated on. 10m or 30ft is a typical useful value. Be careful not to go too small, calculation will increase dramatically as the grid spacing is reduced.

3.4.6.2 Water Application

Furrow Inflow:  The rate of water added to the start of the furrow.

Min. (L/s): Minimum flow rate used when Optimize check box is ticked ON.

Rate (L/s): Flow rate used in the simulation of the Irrigation Analysis. If Optimize check box is ticked ON, it will come up with an optimum flow rate between the Min. (L/s) and Rate (L/s).

Cutoff: This is when you stop the inflow at the start of the furrow. Select one from Furrow Distance (%) or Time (hr).

Furrow Distance (%): Distance along the furrow in percentage. ie 50% means the water is stopped at the start of the furrow when the water had progressed 50% of the way down the furrow.

Time (hr): Duration of running the water at the start of the furrow.

Target Irrigation Depth (mm or in): The infiltration depth of water being aimed to be applied along the furrows.

3.4.6.3 Furrow Geometry

Furrow Direction (deg):  The direction of the furrows relative to north. Use the ‘Pick’ button to click two points to define the direction or type a number in.

Furrow Spacing, W (m or ft):  The spacing between the furrows/bed. i.e from one crest to the other as shown in the diagram on the dialog box.

Furrow Height, h (m or ft):  The height of the intended furrows in the field. The water will build up in the furrow and only spill across the furrow when it exceeds this depth.

Furrow Side Slope (?h:1v):  The side slope of the furrow as shown in the diagram on the dialog box. This is the horizontal distance per 1 vertical. eg 1 mean 45% gradient and 3 would mean 33% gradient.

Furrow Bottom Width, b (m or ft):  The width of the bottom of the furrow as shown in the diagram on the dialog box.

Hydraulic Roughness (n):  This is the same as Mannings ‘n’ used commonly in engineering calculations. Here are some values as measured by Chow (1959):

3.4.6.4 Soil Infiltration Parameters

NRCS Intake Family: In the absence of localized ﬁeld data the US Department of Agriculture–Natural Resources and Conservation Service (USDA–NRCS) intake families have often provided sufﬁcient information for preliminary design, evaluation, or management of surface irrigation systems.

Soil intake families are designated 0.1, 0.3, 0.5, 1.0, 1.5, 2.0, and 3.0 with the lowest number designation representing the slowest intake.  These designations relate generally to the intake rate of the soil in inches per hour after several hours of water intake.

Modified Kostiakov Formula: This is another way of representing soil infiltration characteristics. Please see this for more information.

3.4.6.5 Water Values

These water values allow the optimization of the irrigation settings.

Inflow Cost (\$/ML):  This is the cost of the water delivered at the inflow to the furrow. It typically includes supply charges and pumping cost to get the water to the top of the furrow.

Root Zone Value (\$/ML):  The value of the water placed in the root zone (essentially it is getting the value of the crop). To estimate this, calculate the value of the increase in crop through irrigation. e.g For sugarcane, if the crop increases 50 tons per hectare due to irrigation and 5ML per hectare is used by the crop to produce the 50 tons and the sugarcane is worth \$50 per ton then the Root Zone Value is: (\$50/ton * 50tons/ha) / 5ML/ha = \$500/ML.

Similar number can be calculated for other crops. It is important to only use the increase in crop yield and the actual water used by the crop to estimate this number.

Deep Drainage Value (\$/ML):  The value of the water that drains below the root zone. This value maybe a negative value. e.g. If rising ground water is a problem and causing salinity issues and it's costing you to deal with that water then this maybe a negative number

Runoff Value (\$/ML):