Large irrigation reservoirs can play an important role in maintaining a reliable water supply for golf courses, agriculture and other irrigation systems. However, during warmer periods, changes within the reservoir can affect water quality and create challenges for irrigation management.
One of these challenges is thermal stratification.
What happens during stratification?
When a reservoir becomes stratified, the water can separate into different layers based on temperature and density. The deeper water may become isolated from the surface, reducing the natural transfer of oxygen.
As dissolved oxygen levels decrease near the bottom, conditions around the sediment can change. This may contribute to the release of substances such as phosphorus, iron and manganese into the water.
For irrigation reservoirs, this can become particularly important when the water is continuously circulated through the irrigation system and drainage water is returned to the reservoir.
Why does dissolved oxygen matter?
Maintaining adequate dissolved oxygen throughout the water column can help support more stable water quality conditions.
Low oxygen conditions near the sediment can contribute to internal phosphorus loading. When phosphorus becomes available in the water, it can contribute to conditions that support excessive algae growth.
Low-oxygen conditions can also affect the behaviour of iron and manganese in the reservoir. Once oxygen is introduced, dissolved iron may oxidise and form precipitates. While this may be beneficial for reducing dissolved iron, the resulting solids can increase the loading on downstream filtration systems.
This is why oxygenation should be considered as part of the overall reservoir and irrigation system rather than as an isolated treatment.
Diffused aeration and nanobubbles
For a large reservoir, bottom-diffused aeration can be used to promote circulation and help reduce stratification. By releasing air from diffusers positioned near the bottom, the rising bubbles can move water upward and encourage circulation through the reservoir.
Nanobubble technology can provide another approach to oxygenation.
Rather than relying on nanobubbles to circulate an entire large reservoir, a nanobubble system can be used as a targeted recirculation system. Water can be drawn from a deeper section where dissolved oxygen is low, treated with oxygen-rich nanobubbles, and returned to the same area.
This creates the potential for the two technologies to work together:
- Bottom diffusers provide the main circulation and destratification.
- Nanobubbles provide targeted oxygenation in areas where additional oxygen may be required.
- Monitoring helps determine whether the desired oxygen conditions are being maintained.
Monitoring is an important part of the solution
Before selecting an oxygenation system, understanding what is happening inside the reservoir is important.
Continuous dissolved oxygen and temperature monitoring at different depths can help identify when stratification occurs and how oxygen levels change throughout the water column.
This information can then be used to determine where additional oxygenation may be required and to optimise the operation of the system.
Rather than treating the reservoir based only on its total volume, understanding its depth profile, circulation patterns and seasonal water-quality conditions can provide a more practical basis for system design.
A balanced approach to reservoir management
There is no single oxygenation method that is suitable for every reservoir.
For large irrigation reservoirs experiencing seasonal stratification, a combination of circulation, targeted oxygenation and water-quality monitoring may provide a more practical approach than relying on a single technology.
The objective is not simply to add oxygen, but to understand where oxygen is needed, how the reservoir circulates and how changes in water chemistry may affect the wider irrigation system.
At IGS Water, we look at these factors when assessing water-quality and oxygenation applications, with the aim of developing solutions that suit the specific conditions of each system.
Smart Water. Greener Results.
