Catch cups measure irrigation emitter flows: ALOT of variation can be found!
Greetings Fodder Followers! It won't be long before our foothill soil profile dries up and we start to irrigate. Are you ready for the season? Because when it comes to foothill water-and the irrigation systems that transport it-a little flushing can go a long way. Iron, bacteria, sediment, and precipitates can cause irrigation systems to become clogged-leading to major headaches when it's time to turn on your system.
Routine irrigation system maintenance, including flushing, can vastly improve system performance. That's what I learned last week when I met Brian Hockett, North West Kern County RCD, and Daniele Zaccaria, UCCE Irrigation Specialist, for a distribution uniformity check of our trial vineyard irrigation system.
Flushing of main lines, submains and laterals should be done while ensuring enough flow to flush out sediments (open only a few laterals at the same time) and continued until clean water flows out of the lines. How often should this be done? Most growers I've talked to said they do this once a year, but the amount of flushing required depends on your water quality-every few weeks may be needed to prevent problems building up at the emitter.
The quality of the water flushed will tell you what sort of problem you have. For example, precipitates forming on the emitters such as calcium carbonate may be an indication that acid injection is needed to keep the lines and emitters clear. Sulfuric acid or muriatic acid is used, it needs to stay in the system line for a period of time to work (read the labels for this information). Chlorine injections can work well Vineyard manager Felix Salbasa, Brian Hockett (NW Kern RCD Mobile Irrigation Lab), Daniele Zaccaria (UCCE Irrigation Specialist) and visiting scholar Sebastian discuss irrigation maintenance.
on algae and bacterial slime. Iron is pretty common in the foothills, it appears as a reddish stain. Iron levels of 0.5ppm or more in well water pose a risk of iron precipitate clogging. Acid injections will not solve iron precipitate clogging, instead, the recommendation is to aerate water by pumping it into a reservoir to settle out the iron. Alternatively, phosphonic acid, phosphonate, can be injected to help keep iron in solution so that it doesn't precipitate. This is a maintenance solution, not a clean up product.
Distribution uniformity (DU) is measured by collecting the flow from emitters throughout your field and finding the average flow rate. Then the lowest 25% of the emitters measured are averaged, and this number is divided by the overall average.
DU= Average flow (lowest 25%)/Overall Average Flow. A DU of 90% or greater is considered "excellent"; 85-89% "very good"; 80-84% "good"; 75-79% "fair" and below 75% distribution uniformity is considered "poor". Growers should shoot for at least a "good" (80% DU or above) rating in order to be more efficient with the water they use. Afterall, you want to make sure the water you're pumping from the ground is actually getting to your crop, right?
Measuring pressure, at different points (upslope and downslope), can tell you how flow changes across a block.
Pressure is also typically measured at points throughout the system. On foothill slopes, we can see big pressure drops downslope-on our trial site we saw a difference of 7 to 16 psi in pressure from the top of the slope to the bottom. According to Brian, this is not a big cause for concern as long as you are using "pressure compensating emitters". These "pc's" as Brian and Daniele called them, have a membrane that expands to compensate for pressure drops-making sure the right amount of water is delivered. Flushing maintenance is also good to maintain the flexibility of the pc membrane, according to Daniele. Brian commented that a Netafim dripper, a popular brand of emitter, can go 20-30 years if properly maintained!
Do you have an irrigation system problem? Do you know how much water you actuallyA flowmeter can tell you how much water you use, and if there's a problem
apply to your crop? Some would answer this according to what is stamped on the emitter...1/2 gallon an hour? Do you know this is what is actually being applied?! One relatively easy way to monitor your system and really know how much water you are using is to install a flowmeter. Flowmeters come in many sizes. A problem at the flowmeter can indicate a clogging problem downstream. Another way is to perform a self-evaluation of your system, which will involve measuring the flow rate from several emitters and calculating your DU. Hopefully, your irrigation system report card will be "Excellent"! and if not, you'll find resources here to help you correct the system before it's time to turn on the water.
Until next time...