HydroPlan was engaged by the City of Fremantle to evaluate and upgrade the irrigation system at Fremantle Park, the popular destination known as “Freo Park” adjacent to the Aquatic Centre.
Freo Park has two distinct active sports turf areas, plus passive areas of lawn and large trees. The passive areas have steep slopes and some outcropping of the underlying limestone rock through relatively shallow sandy soil. The winter sport of football and the summer sport of cricket share the larger sports area in the eastern part of the site. Soccer is played on the smaller sports area in the western part of the site.
Independent evaluation is an important part of proper planning processes, particularly when certainty is important, money is tight and scrutiny is high. Whilst there was a known history of pipe failures and poor turf quality, the facts needed to be investigated and documented, and the best value from capital expenditure had to be determined.
HydroPlan’s site audit and assessment report of the existing irrigation infrastructure clearly identified it was underperforming because it was nearing the end of its life cycle. Analysis also revealed the laterals and sprinklers could not be modified to achieve current best practice for Distribution Uniformity (DU) so replacement of this component was necessary. This would represent around 60% of the cost of a new system, so questions were raised about remaining life of the other 40%.
A number of other considerations were identified through community consultations and the City’s own internal review process. Of particular note was the need for the design to take account of two recently constructed geo-thermal bores and associated re-injecting pipe works which were installed as part of recent improvements to the Aquatic Centre. The construction phase of the project would need to be managed in such a way as to avoid damage to this infrastructure.
The water supply for the Park was provided by a single ground water bore which also served to fill the Aquatic Centre pool. The City’s water use strategy suggested that the water supply used for irrigation purposes within the Park should be differentiated from that used to fill the Aquatic Centre pool. As a result the irrigation design should call for the construction of a new irrigation bore to take water from the superficial ground water aquifer.
The City’s particular interest in improving water use efficiency determined that the new irrigation system should be designed to be consistent with hydrozoning principles. Accordingly the irrigation design provides for the active turf areas of the playing fields to be separated from the passive turf areas associated with the landscaped surrounds. This provides for an efficient and flexible scheduling of the irrigation cycle in response to seasonal variations and changes in weather conditions.
The resulting design is based on a ring main aligned to skirt the main playing area with back-to-back sprinklers controlled from separate solenoid valves at the interface between active and passive turf areas. Moisture sensors have been included to monitor soil moisture levels in both active and passive turf areas. The sensors measure and relay a live soil moisture status to the electronic irrigation control system which is used as the basis for irrigation scheduling.
Design and documentation of the new irrigation bore and watering system was undertaken by HydroPlan in consultation with the City. The scope was split into two tenders so specialist contractors could compete. The new irrigation bore was constructed and tested during January 2014 by RBM Drilling Contractors. The contract to construct the new irrigation system was awarded to Horizon West with work commencing on site during the latter part of April 2014. Construction works included installation of a submersible pump and associated head works and a TII SD 2-wire decoder controller. Welded polyethylene (PE) mainline pipework was installed to supply Bermad solenoid valves serving solvent cement jointed (PVC) laterals and Hunter PGP and I25 sprinklers.
In WA the use of PE (polyethylene) pipe is not as common as PVC but Council agreed to the rationale for adopting PE in this instance. Pipe and fittings were joined using a technique commonly referred to as electrofusion. Each and every pipe fitting has an inbuilt heating element which when connected to the welding equipment results in the PE material of which they are made melting and the adjacent surfaces of the pipe and fitting fusing together. It is a technique which requires skill, good work practices and the correct equipment. Timing and temperature during the fusion process is of the utmost importance. The critical parameters are pre-programmed during the manufacture of individual fittings. The welding equipment reads the pre-programmed data which is in turn displayed on a monitoring screen where it must be confirmed by the welding operator in order to initiate the weld.
This is an example of a successful outcome of a medium scale irrigation project where the design objectives were realised and the project was completed within the prescribed time and budget.