More efficient drips take water to the world

Engineering expertise and evolution algorithms have been applied to drip irrigation, reducing the energy and costs of this water-saving method of growing crops.

Engineering expertise and evolution algorithms have been applied to drip irrigation, reducing the energy and costs of this water-saving method of growing crops.

In drip irrigation, water is pumped through long thin tubes that stretch across farm fields. Hundreds of drippers along the length of each tube trickle water directly onto a plant's base. This allows the farmer to control the timing and amount of watering, delivering only as much water as required by the crop.

Comparatively, the traditional way of growing crops in developing parts of the world, through flood irrigation, requires farmers to flood fields with redirected river or groundwater. This is an inexpensive method, but presents little control over when and how much to water their crops. In areas where water is at a premium, this is also inefficient, as most of the water not taken up by plants either evaporates or drains away.

Drip irrigation can reduce a farm's water consumption by as much as 60 percent, and increase crop yield by 90 percent, compared to conventional irrigation methods. However, drip irrigation systems are also expensive to install, particularly in off-grid environments common in developing countries.

A team from Massachussets Institute of Technology (MIT), has developed a way to make drip irrigation systems accessible to farmers in developing countries.

"Low-cost drip systems could help them increase their yield and income, so they can get out of the cycle of poverty," said team leader Amos Winter, an assistant professor of mechanical engineering at MIT.

"The main cost driver is the pump and power system. That laid the foundation for our research project: Could we make drippers that operate on much lower pressures, and thus cut the pumping power and the capital costs?"

The engineers at MIT started their optimising efforts by looking at the drippers. By modifying the drippers' dimensions in a way that significantly reduces the pressure required to pump water through the entire system, while still delivering the same amount of water, they were able to cut the cost of solar-powered drip systems by half, and also halve the pumping power required for irrigation, thus lowering energy bills.

To do this, the researchers characterised the behaviour of existing “pressure compensating” drippers. These drippers are designed to maintain a constant flow rate, regardless of the initial water pressure that is applied, allowing every dripper along a tube to deliver the same water flow throughout a farm field, and regardless of the distance each individual dripper is from the central pump.

The team generated a model of these pressure-compensating drippers in MatLab, studying the dynamics of water flowing through the modelled dripper, then came up with a mathematical description to explain how a dripper's internal features affect fluid flow and water pressure.

They then coupled the mathematical model with a genetic algorithm, which stimulates the evolution of various parameters in the dripper. The team selected a range of dimensions for certain features and tested their flow behaviour in simulation. They discarded those dimensions that produced undesirable water pressure, and kept the better performers, which they fed back into the algorithm with a new set of dimensions.

After several generational iterations, this process yielded features and geometries that delivered good performance, while eliminating features which reduced performance.

This new, evolved dripper has dimensions and geometries that produce an optimal flow rate with an initial pressure as low as 0.15 bar. In contrast, most conventional drip irrigation systems are designed to operate the drippers at a pressure of at least 1 bar.

Using these optimal dimensions, the team fabricated a few dripper prototypes and tested them in the lab, with results that matched their simulations.

Winter is now working with the United States Agency for International Development (USAID) and Jain Irrigation, a major manufacturer of drip irrigation systems, to test the optimised drippers in Morocco and Jordan, where he says there is a push to shift farmers to drip irrigation.

“With these drippers, poor farmers can now grow higher-value crops, like off-season crops that they couldn’t grow unless they had rain, and make more money to try to get out of poverty,” Winter says.

Next, the team plans to optimise the rest of the drip irrigation system, which will further reduce the system’s cost.

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[An example of a current drip irrigation system. Photo: MIT]