Irrigation Talk
– By Austin Goodfellow

Periodically we will provide the community with updates on the oval maintenance program at Grass Roots. Maintaining the oval is an essential aspect of the project, as it will ensure the validity of research outcomes.

Sprinkler Uniformity Testing

By checking the system's "vital signs", we can determine if it is performing at peak efficiency and uniformity.

• Efficiency is the ratio between how much water the grass uses compared to how much water the system applies.
• Uniformity is how evenly the sprinklers deliver water over the oval. Non-uniform systems create areas that are too wet or too dry which results in problems with irrigation scheduling (see Figure 2).

Figure 1.	Figure 2.

A healthy system leads to improved soil-moisture uniformity, reduced run-off and water wastage, easier irrigation scheduling and healthier grass that is more resistant to pests and disease.

Sprinkler uniformity testing at Grass Roots — Thursday 20th July 2006

One way of measuring the uniformity of coverage is by a statistical parameter called the distribution uniformity (DU). The DU depends on the spacing of sprinklers and the spray pattern of the specific type of sprinkler equipment chosen. Wind direction, wind speed, water pressure and interception by plants can also affect the distribution pattern. As a general rule sprinkler irrigation systems should have a DU of at least 75% (IAA.CIAL Reference Manual).

The 'catch can' uniformity test
Pressure testing sprinkler nozzles

The uniformity testing was carried out using 60 catch cans strategically placed on a grid. Sprinklers covering the area were all run for an equal amount of time. Nozzle sizes were checked and operating pressures were noted. Wind was from the southeast and varied between 0 – 10 km/hr.

The DU test results came back at 73%. Whilst this was not quite up to scratch it should be noted that the following changes will be made to increase the efficiency:

1. Increase nozzle size to increase droplet size so less water is lost in windy conditions. An analysis of the hydraulics and pressures available must be carried out prior to the nozzle changes.
2. Irrigate with sprinklers at night only to reduce the effect of wind.
3. Match up all sprinkler pressures; some sprinklers were set too high causing significant misting. This has had a large effect on the uniformity.

Overall the uniformity of the system as it stands could be considered as "fair". Once these identified modifications are made the uniformity will be better than 75% bringing the system back into "best practice" guidelines.

Monday 16 October

When viewing the information on Grass Roots LIVE it is important to please note the following:

1. A very warm dry October has forced the project to put on more water than would usually be applied at this time of the year. Daily evaporation rates are nearly twice that of average years.
2. The Sir Walter (Section 5) is only just coming out of dormancy therefore does not require a lot of water. This is similar to the Trans Continental Couch (Section 1). Unfortunately as the Trans Continental Couch is overlaid across many irrigation sections it cannot be irrigated separately as with the Sir Walter therefore will always be perceived to be using more water, where as in fact we believe it will use similar if not less water than the Sir Walter. It will be interesting to see how the Trans Continental Couch performs in comparison to the other grasses on those irrigation areas as the season progresses and we start to really put the squeeze on these irrigation sections as far as irrigation is concerned.
3. Irrigation Sections B C and D are currently receiving higher than usual amounts of water, as these areas have not established as well as the other sections. Higher irrigation volumes than usual will be applied over the coming weeks to these areas.
4. All drip irrigated areas are currently being only water once a week.
5. Sprinkler areas are receiving multiple 3 to 12 minute irrigation cycles.

Wednesday 17 January 2007

Like the rest of the Canberra Region, Grass Roots is being hit hard by the continuation of the extreme “lack of moisture”. Due to current Stage 3 water restrictions we have wound back the watering on all blocks from the original suggested application rates, so that Grass Roots is in line with the 35% reduction strategy being employed by similar sites within the community.

The most satisfying outcome at this point in time is that the fescues are holding up well under sprinklers utilising as little as 47% of current evaporation rates. This is a massive 37% saving in water compared to traditional suggested watering rates.

However, under the current very stressful conditions we have found some limits with the varieties planted and the watering methodology.

The current watering schedules for sections F and G are way below that of being sustainable. The Fescues are dying and the Sir Walter whilst still alive is really struggling. These areas are being watered at approximately 20% of the evaporation. The stressed lots can be seen in the image below.

However, at 40% of evaporation the Sir Walter and the Trans Continental Couch is performing quite well.

We are currently experiencing some soil/moisture related problems in some of the drip and sprinkler areas that are causing a decline in turf population. This is particularly noticeable in the drip section. One recent observation whilst viewing the original site through “Google Earth” is that there may have been long term issue with these areas that can actually be seen using this software.

Wednesday 9 January 2008

NO IRRIGATION AT GRASSROOTS

Grass Roots has not been irrigated since mid November. Soil moisture probes have been monitoring water availability at different levels throughout the root zone of the turf. At two points over the previous two months moisture levels fell below the refill points, these were observed from 18 to 22 November and 16 to 20 December. At these two points the turf had basically run out of water. Weather forecasts predicted showers, so we opted to switch irrigation off during these periods until the showers arrived. Both dry events were followed by significant rainfall, 26mm (23 Nov) and 34mm (20-23 December) just at the point when we were to initiate an irrigation event.

Moisture levels have since fallen, and with increases in evaporation and dryness of the turf, irrigation has been switched back on. This has been an interesting couple of months. By utilising some innovative technology we have saved considerable amounts of water and managed our way through rain events. It is interesting to note that leading turf managers in the region have indicated that they too have been able to manage their water efficiently between rain events. One manager in particular has saved 15 Megalitres over the last month by regularly monitoring soil moisture levels.