Drainage Reuse Systems

What is a drainage reuse system?

Drainage reuse system

Drainage reuse systems are designed and constructed to collect excess irrigation and irrigation induced rainfall run-off water and nutrients from an individual property. The water is usually stored in a sump constructed to hold the water below ground level. However, some storages are constructed to hold water above ground. The water can then be pumped from the storage into the irrigation system on the property and used for irrigation, reducing the amount of water and nutrients leaving the property and reaching natural waterways.

Reuse systems may be constructed for several reasons. Some landowners require the earth from the dam to establish channel and lane pads during the construction of the irrigation system on their property. Others want to conserve water on-farm by directing irrigation and rainfall runoff to a storage sump where it can be reused for irrigation. Some landowners want to contain significant amounts of nutrients from applied fertiliser and animal wastes. The system ensures these nutrients are retained on-farm reducing the effects of nutrients on waterways.

What are the benefits of drainage reuse systems?

The major benefit of a reuse system is the capacity for the landowner to maximise the water use efficiency of the property through:

• greater flexibility in irrigation management - irrigation can start/stop at the irrigator s convenience,
• providing drainage for the property in areas where there is no Regional or Community Surface Drainage outfall available,
• providing “additional” water through collection of drainage flow before it is lost off the farm,
• allowing the irrigation of previously uncommanded land by pumping from the reuse system onto high ground,
• storing water from groundwater pump, drainage diversion or outfall from the supply system,
• providing a safety margin when using automatic irrigation,
• allowing reuse of nutrients (often fertiliser applied) before it is lost off the farm, and
• providing earth for channels and laneways.

When should I plan for the drainage reuse systems?

The best management practice for reuse system design is to design the reuse system as a component of a Whole Farm Plan for the property. It is through the planning process the most appropriate location is determined to catch, store and use the water. The Whole Farm Planning process provides details of the quantity of earth required for redevelopment and the area of the property that will be drained to the reuse system.

To determine watertable depth, groundwater salinity and suitability of the site and soils for construction, site investigations should be undertaken. The site investigations will provide a recommendation to the landowner of the suitability of the site for holding water in the reuse system to be constructed.

Where should I locate my drainage reuse system?

The reuse system should be located such that it collects drainage from the whole property. If this is not possible, priority should be for:

• area which can receive effluent (highest priority) or groundwater
• intensively irrigated areas, such as perennial pasture
• areas which tend to have more run-off eg., short bays and steep bays

How big should my drainage reuse system be?

The recommended drainage reuse storage capacity is 0.75 ML per 10 ha of perennial pasture or 0.38 ML per 10 ha of annual pasture. A practical consideration is to make the drainage reuse storage large enough to provide at least the amount of earth needed for channel and laneway pads.

Note the maximum capacity of new storages, as determined by the Victorian farm dams legislation, is 1 ML per 10 ha of irrigated land that drains to the storage.

What type of pump/motor should I use for my drainage reuse system?

The selection of a pump and motor should be determined by your Whole Farm Plan designer. Selection of the wrong pump or motor will lead to costly, inefficient pumping.

The selection of a suitable pump depends on the total head (both suction and lift) and the flow rate required. It is important to select the most appropriate pump to ensure maximum pumping efficiency and pump/motor life.

In typical low head applications, axial and mixed flow pumps are most efficient. Electric motors are preferred (ease of operation, less maintenance, quiet running, easily automated), but where electricity supply is not available, diesel motors are appropriate.

What are the best management practices (BMPs) that should be adopted to manage reuse systems?

1. The BMP for reuse system design is to design the reuse system as a component of a Whole Farm Plan for the property.
2. The BMPs for reuse system operation should be aimed at keeping the reuse system empty or as low as possible at the end of an irrigation. This will maximise the collection of water and reduce loss of water and nutrients off the property.
3. The BMP for high groundwater conditions is to operate the reuse system so the storage is not emptied below the watertable level in order to minimise groundwater inflow. In areas where saline water is entering the storage, the water salinity should be monitored regularly. If the water stored is moderately saline (1000 to 3000 EC), it should be shandied with fresh supply water.
4. The BMP for using water from a reuse system where a blue green algae bloom has occurred is to irrigate recently grazed paddocks, avoiding grazing the area for as long as possible, preferably after using fresh water for the subsequent irrigation or following rain, to remove toxins.
5. The BMP for maintenance is to regularly maintain the reuse system for efficient operation. Pumps and motors should be maintained as required to achieve reliable, efficient operation. Weed growth in drains should be controlled as required and sump desilting should be undertaken as required to maintain storage capacity.

What are some of the things I need to consider for constructing a reuse system on farm?

Drainage resuse system

Pump and motor installation:

Pump and motor should be installed as specified in the Whole Farm Plan. Pumps should be manufactured of non-corrosive material (cast iron casing fitted with stainless steel bolts, stainless steel shaft and impeller). Pump and motor must be coupled together and be fixed permanently in position.

Pump and motor shed:

A shed constructed from heavy duty materials should be provided to protect the pump and motor from the weather.

Fencing:

The reuse system should be fenced off to prevent stock damage to batters and structures. It also prevents stock from drinking reuse water which can become contaminated with algae.

Trees:

Tree belts along the reuse system can provide several benefits such as wildlife habitat, providing a windbreak, utilising groundwater and general aesthetic value of the farm.

Access:

Ease of access to the pump site is crucial for maintenance, fuel supply, and day to day operations. Where access is not convenient, a busy irrigator may not find time to start the reuse system and or check on the operation of the system.

Local government requirements:

Check whether your council requires a permit for the construction of a drainage reuse system.

Acknowledgements

Irrigation Survey and Designers Group

• Department of Agriculture, 1994, Re-use Systems in the Kerang Region, Kerang: Department of Agriculture.
• Lavis, A . and Lawler, D., 1998, Drainage Reuse Systems – Best Management Practices, draft report.