Even Coverage and Precip. Rates

THE MOST IMPORTANT ASPECT OF DESIGNING AND INSTALLING A SUPERIOR IRRIGATION SYSTEM OF ANY SIZE IS EVEN COVERAGE OVER THE ENTIRE WATERING AREA.

Across much of the country it's easy to think that you don't need full coverage because you get rain and everything may look "green enough" to you. Many people think that sprinklers are just supplementing rain water, and for places like South Florida or Seattle they may be right. The rest of the country, however, should stick to the principals of Full Coverage if they want the absolute best lawn on the block. Our reasoning is simple: if you are going to install any sprinklers at all, with all the digging, valves, wire, controller, fittings, etc., why not go head-to-head the first time? Contractors or homeowners who stick a couple of sprinkler heads here or there just don't get it: the point of a sprinkler system is superior turf.

What's the best way to get full coverage? First of all, you are going to have to install head-to-head. This means that the edges are going to need sprinklers too, shooting from the edge inwards. Every good quality sprinkler head will have a variety of nozzles to choose from that shoot different amounts of water over different distances. If the heads can be spaced at 12' apart nozzles over the whole lawn, get nozzles which shoot 12 feet. It's that simple. Nozzles are available in 1/4, 1/2, 3/4 circle, adjustable part circle, full circle, etc., etc. If you're serious about your landscaping you will not be getting the bottom-of-the-barrell sprinkler heads that do not have a variety of nozzles to choose from.

What about the "left-over" areas that do The heads don't fit perfectly with lawn measurements?

Okay, you've got everything sketched out on paper or flagged in the field on a perfect grid. Now you have discovered a 10 foot wide area at the end of everything and a curved area looking like it needs something. What are you going to do? First of all, start your sprinkler head layout near buildings, roads, cart paths or other edges. That way you'll be leaving the odd-spacing areas to spots way out in the field. At the 10 foot wide spot, put in sprinklers with 12 foot nozzles and don't worry about the overlap. A little overlap is perfectly fine and much better than a little under-coverage. At the curved spot, use a sprinkler with an adjustable part circle nozzle. It may spray just a little on the pavement or might not get every inch of turf.....but you'll be getting it as good as it possibly could be. For golf courses the leftover areas are larger but the principles of full coverage are the same.

Trust us, the irrigation experts at Golf Engineering Associates, Inc., full coverage is the pathway to superior turf.

Precipitation Rate: the amount of water applied over an irrigated area, usually expressed as inches per hour. For those of you who want more advanced knowledge of irrigation, we offer the following equation to determine precipitation rate:

Total GPM = total flow from all sprinklers in the given area in gallons per minute.
PR = precipitation rate in inches/hour.
96.25 = constant for conversion of area and flow into common units.

Example: The average PR for a lawn which is approximately 40 feet wide by 20 feet deep, watered by 15 sprinklers putting out a total of 12.59 gpm:

To find the total GPM, first find out what pressure you have. Next, add up all the different nozzles, i.e. full circles, 1/2 circles, 1/4 circles (each has a different GPM number) and see what GPM value the sprinkler manufacturer's chart gives you. For instance, if you have 3 full circles at 1.57 gpm/head, 4 quarter circles at .39 gpm/head and 8 half circles at .79 gpm/head for the above example, that all equals 12.59 GPM for 15 pop-up sprinkler heads. For golf courses, use GPM flow information from your sprinkler manufacturer charts and estimate how much pressure you have at each hole.

Figuring out how long to water: Let's say you have a PR = 1.51"/hr., as above. If you know the Evapo-Transpiration rate for your area in the middle of the hot Summer is 3" per week, you also know that you'll have to water for approximately 2 hours per week to keep the turf/landscape healthy. (2 hours x 1.51"/hr = 3") Over a 7 day watering schedule, you now know that you have to water for 18 minutes per zone per day. (2 hours = 120 minutes; divided by 7 days = 17.15 minutes per day) For an every other day schedule, this equals about 35 minutes per cycle, although we would add a few minutes for wind factor.

What is Evapo-Transpiration Rate, and where can I find this out? ET rate is a measure of evaporation and transpiration of water through plant tissue which relies on temperature, solar radiation and wind. It is determined by agricultural exension services, county ag agents, universities, etc., and is calculated for every region of the United States. It varies greatly from location to location and throughout the months of the year. Most major newspapers will have this information daily in a section titled "how much to water your lawn" or "weather statistics", or a similar feature. If not, call your county or state agriculture department. If that fails, go to the library and look up Evapo-Transpiration rates for your area. If you've come this far, consider yourself an advanced irrigation person. Anyone using ET rates to determine their optimal watering times for various times of the year is conserving our water resources and managing their landscape or turf in a very efficient manner.

Maximum Monthly ET Rates for Sample Cities
in Inches per Month Moisture; 30 year average