Integrated Pest Management · Agriculture and Natural Resources
University of California
Irrigation recirculation and reuse
Agricultural runoff from surface irrigation is likely to contain sediments, nutrients, and pesticides that can harm the water bodies it is released into. A tailwater return system is a method of recirculating agricultural runoff (tailwater) back to the field. Tailwater is the water that runs off the lower end of the field after typical surface irrigation practices.
Benefits of reuse
Although there are various ways to manage tailwater, collection and recirculation has significant environmental and economic benefits.
- It reduces the amount of contaminants from tailwater and pesticides entering nearby waterways.
- It improves efficiency of water application.
- It reduces the amount of standing water in the field which can result in weed, bacteria, and pathogen growth.
- It may reduce overall water costs.
- It makes managing irrigation simpler for systems lacking an outlet for tailwater.
The tailwater return system consists of ditches for collecting runoff and carrying water to the tailwater pond, a flow pump and power unit (either an electric motor or a diesel engine), and a pipeline to transport water to its discharge point for reapplication to the field.
Consider the following when designing a tailwater return system:
- Excavation below ground allows gravity to fill the pond.
- Pond size depends on multiple factors, including how often it will be emptied, available land, cost, and maintenance. Five feet is the minimum depth to control aquatic weed growth.
- Consider lining the pond with a synthetic liner or clay to prevent seepage. If a lining is not installed, the pond water should be recycled frequently to minimize leaching of pesticides into shallow groundwater.
- A return flow pump can be automated using an electric probe sensor or float system that starts and stops flow when a preset water level is reached.