Rainwater Harvesting and Reuse System at Narrandera Sports Ground, NSW

In November 2008, Think Water Leeton was commissioned to supply and install a rainwater harvesting and reuse system at the Narrandera Sports Ground to irrigate the playing fields.

Project Details:

To allow for stormwater catchment at the stadium, a stormwater network was installed to channel the roof water to an 8,100 litre Taylex concrete underground tank (2 tonne rated lid).

The main roof area of the stadium is approximately 1,280m2, for e.g. if there was 12.0mm of rain in 15 minutes this would equate to a total of 15,360 litres, assuming 100% catchment (there would normally be some losses) The pump is capable of moving this amount of water in slightly over 12 minutes and with the 8,100 litre buffer, it will make easy work of a deluge of this nature.

A 1.5kW 415 volt Grundfos Storm water pump, pumps the water through approximately 300m x 160mm OD poly line to the new 113,000 litre underground concrete reservoir (8 tonne rated lid). Narrandera Shire Council excavated the hole required to approximately 11 meters x 11 metres and with the tank measurimg 2230mm high, the depth was approximately 2430mm.

The tank required an overflow that was plumbed to the town storm water drain system running parallel to the street. Narrandera Shire Council already had a pump that was purchased a few years previously for another project that didn’t eventuate so it was de-staged and used on this project instead. It is now a Grundfos CR32 5-2.

The pump draws water from the tank which is a shandy of potable town water and stormwater and provides a reliable, steady flow of water and pressure to operate the irrigation system at the ovals. No backflow prevention is required as there is an air gap in the tank to protect the Narrandera town supply, with a suitable sized overflow positioned within the tank.

A pressure transducer was installed on the discharge pipe work downstream of the pump. This is to regulate the speed at which the pump is running according to what water is being used at that time. This will reduce the power consumption of the pump, especially when the peripheral areas outside the ovals are being watered by a few hoses and sprinklers.

A ring main was used to balance the system resulting in a reduction in pipe sizing. The oval uses 13 stations. There are 4 stations located around the outside of the ground and another 9 stations (2 watering zones per station) across the playing area. The stations are controlled by a Hunter Pro-C programmable controller which is weather sensor compatible, able to be used with wireless remote station on/off as well as also being IMMS Compatible which means it is compatible with a remote link up if required in the future through a computer system linked back to the parks foreperson

Hunter I31 Sprinklers were used that have a stainless steel stem and also carry a five year warranty. The tops of the sprinklers are small and have a heavy duty rubber cap which will withstand football boots and keep the playing field safe.

The sprinklers will be placed in what is called a triangle configuration; the purpose of the design is to reduce the impact the wind has on the distribution uniformity of the sprinklers. The I31 sprinklers have a larger droplet size which also reduces the effect of wind.

The way the system is designed and now works is that the irrigation controller would switch on each of the 22 zones as programmed into the system, for e.g. 40 minutes. If the soil moisture level at the sensor is drier than -28kpa then the soil active line from the irrigation line will be passed to the solenoid, turning on the station as programmed.
Alternatively if the soil moisture level at the soil moisture sensor is wetter than -14 kpa (after rain or when irrigation has reached the sensor depth at typically 100mm) then the active line from the irrigation controller will open, effectively isolating the solenoid from the controller and so leaving the station off, the next station will start after the allotted time with the same sequence of events taking place. The GB switch from MEA (Measurement equipment Australia) and its associated watermark sensors are both buried in the oval, there are no user adjustments required. This will ensure only the water required for adequate irrigation is used. Meaning that the watering time may be reduced to 20 minutes which will equate to a 50 % saving in water.

Options not taken up here included a weather station that can be set up to provide a web page that shows interested people daily evaporation, temperature, rainfall etc. No human intervention is necessary. The weather station can also provide the information (when connected to a pulse water meter) to actually show water savings that have been had as a result of the installation of the GB switches.

All in all this was a satisfying project that will help save water; it was partly funded by the community water Grants programme as well as some state government funding. It has provided a state of the art irrigation system and oval for the Narrandera community to use for many years to come. 

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