Managing Aquatic Vegetation in Irrigation Canals Saves Water and Protects Infrastructure
Irrigation agriculture is the single biggest user of water in South Africa, consuming about 62% of the country’s total supply. Of the 1.4 million hectares that could potentially be irrigated, about 1 million hectares are currently under irrigation. Much of this water is transported through an extensive network of canals, which are vital for feeding the nation.
But these canals are also a source of water loss. Like all conveyance systems, they leak, spill, and lose water through evaporation. The problem becomes far worse when aquatic vegetation — algae and submerged plants — clogs canals and dams, reducing their carrying capacity and causing serious operational and economic challenges.
Why aquatic vegetation is a problem
According to Dr Kobus Du Plessis, managing director of Envirokonsult Scientific Services, aquatic vegetation can quickly grow into dense masses of biomass during warm summer months, fuelled by nutrients like phosphates and nitrates.
This rapid growth displaces water in the canals, leading to:
- Reduced canal capacity and spillage.
- Overestimation of water flows at measuring points.
- Flooding and damage to canal structures.
- Blocked sluice gates and clogged irrigation equipment.
In older schemes, water losses of over 50% have been recorded in some canals. Nationally, it is estimated that 20–30% of irrigation water is lost through leaks, spillage, evaporation, and vegetation.
The economic impact
The Department of Water and Sanitation’s Water Conservation and Demand Management Strategy highlights aquatic vegetation as a major contributor to water loss. Even a modest 10% reduction in current losses could save R120 million annually and release 550 million cubic metres of water for other sectors.
Traditional control methods
For years, farmers and irrigation managers relied on:
- Mechanical removal: labour-intensive, expensive, and often ineffective in peak summer.
- Chemical treatments: copper sulphate and diquat-based herbicides were once used, but they had serious drawbacks, including toxic residues, corrosion of equipment, and downtime for canals.
These approaches provided only temporary relief and often created new problems.
A new solution: MAGNACIDE™ H
A breakthrough came with the introduction of MAGNACIDE™ H Herbicide (L8655), an acrolein-based product widely used in the US, Australia, and Canada.
Key advantages:
- Can be applied while canals remain operational.
- Effective against both algae and submerged plants.
- Dissipates quickly into harmless carbon dioxide and water, leaving no residues.
- Restores canal capacity within 24 hours.
- Does not corrode structures or irrigation equipment.
Trials in Hartbeespoort and Roodeplaat canals showed impressive results, with water losses cut by 17–19%. In Hartbeespoort, the savings allowed enough water to support new mining operations worth more than R1 billion.
Integrated management for lasting results
Today, most irrigation schemes use Integrated Aquatic Vegetation Management Plans (IAVMPs) that combine:
- MAGNACIDE™ H applications in canals.
- Sterile Chinese grass carp introduced into balancing dams and reservoirs for biological control.
This combined approach has transformed aquatic vegetation from a persistent problem into a manageable maintenance task, ensuring reliable water delivery with minimal disruption.
Protecting South Africa’s water future
As Dr Du Plessis explains, keeping canals free of aquatic vegetation is not just about smoother operations. It’s about safeguarding water security in a country where every drop counts. By reducing losses and maintaining infrastructure, farmers and water managers can save millions of cubic metres of water annually — supporting agriculture, industry, and communities alike.Irrigation agriculture is the single biggest user of water in South Africa, consuming about 62% of the country’s total supply. Of the 1.4 million hectares that could potentially be irrigated, about 1 million hectares are currently under irrigation. Much of this water is transported through an extensive network of canals, which are vital for feeding the nation.
But these canals are also a source of water loss. Like all conveyance systems, they leak, spill, and lose water through evaporation. The problem becomes far worse when aquatic vegetation — algae and submerged plants — clogs canals and dams, reducing their carrying capacity and causing serious operational and economic challenges.
Why aquatic vegetation is a problem
According to Dr Kobus Du Plessis, managing director of Envirokonsult Scientific Services, aquatic vegetation can quickly grow into dense masses of biomass during warm summer months, fuelled by nutrients like phosphates and nitrates.
This rapid growth displaces water in the canals, leading to:
- Reduced canal capacity and spillage.
- Overestimation of water flows at measuring points.
- Flooding and damage to canal structures.
- Blocked sluice gates and clogged irrigation equipment.
In older schemes, water losses of over 50% have been recorded in some canals. Nationally, it is estimated that 20–30% of irrigation water is lost through leaks, spillage, evaporation, and vegetation.
The economic impact
The Department of Water and Sanitation’s Water Conservation and Demand Management Strategy highlights aquatic vegetation as a major contributor to water loss. Even a modest 10% reduction in current losses could save R120 million annually and release 550 million cubic metres of water for other sectors.
Traditional control methods
For years, farmers and irrigation managers relied on:
- Mechanical removal: labour-intensive, expensive, and often ineffective in peak summer.
- Chemical treatments: copper sulphate and diquat-based herbicides were once used, but they had serious drawbacks, including toxic residues, corrosion of equipment, and downtime for canals.
These approaches provided only temporary relief and often created new problems.
A new solution: MAGNACIDE™ H
A breakthrough came with the introduction of MAGNACIDE™ H Herbicide (L8655), an acrolein-based product widely used in the US, Australia, and Canada.
Key advantages:
- Can be applied while canals remain operational.
- Effective against both algae and submerged plants.
- Dissipates quickly into harmless carbon dioxide and water, leaving no residues.
- Restores canal capacity within 24 hours.
- Does not corrode structures or irrigation equipment.
Trials in Hartbeespoort and Roodeplaat canals showed impressive results, with water losses cut by 17–19%. In Hartbeespoort, the savings allowed enough water to support new mining operations worth more than R1 billion.
Integrated management for lasting results
Today, most irrigation schemes use Integrated Aquatic Vegetation Management Plans (IAVMPs) that combine:
- MAGNACIDE™ H applications in canals.
- Sterile Chinese grass carp introduced into balancing dams and reservoirs for biological control.
This combined approach has transformed aquatic vegetation from a persistent problem into a manageable maintenance task, ensuring reliable water delivery with minimal disruption.
Protecting South Africa’s water future
As Dr Du Plessis explains, keeping canals free of aquatic vegetation is not just about smoother operations. It’s about safeguarding water security in a country where every drop counts. By reducing losses and maintaining infrastructure, farmers and water managers can save millions of cubic metres of water annually — supporting agriculture, industry, and communities alike.
