Water Meters: Formatting the Data for Use

Water meters are a necessary tool to determine water applications to the orchard. Having access to this near-real-time data can provide insight into the irrigation practices by helping determine if the proper amount of water was applied to a block. Furthermore, a deeper analysis of this information can assist with managing field variability by improving distribution uniformity and even estimating yield.

Before diving deeper into the data from water meters, it is important to format the data into a consistent value across the operation. Even though water meters are sold in all shapes and sizes, there are generally two types: totalized flow (reporting the total amount applied to the field) or current flow meters (reporting the current flow of volume). Knowing which type of meter is present within the orchard is required to understand the application of water to a particular block.

Due to manufacturing differences and meter types, data may be reported differently. Common units used within the United States are gallons (gal), acre inches (a.i.), acre feet (a.f.), cubic feet per second (CFS), or gallons per minute (GPM). Within the rest of the world, the metric system is used and reporting is either in liters or cubic meters (cbm) with flows reported as liters or cubic meters by time (second, minute, hour). Totalized meters will report as a number of a particular unit applied. This value has to be subtracted from the previous measurement to determine how much water was applied over a period. Current flow meters report the flow of water and reports it as a measurement over time (e.g. gallons per minute). This data has to be multiplied by the irrigation set time to determine the amount of water applied.

After the initial data is collected, it is then needed to format it into a common unit across the operation. Within the US, it is common for most people to use either a.i. or a.f. To assist with getting data into this form, use the following equations:

U.S. Standard:

Gallons to acre inches:

____ gal x 0.000037 ac-in

Acre inches to acre feet:

____ ac-in/12 = ____ ac-ft

GPM to ac-in

____ gpm x ____ irrigation set time (minutes) x 0.000037 = ____ ac-in 

CFS to ac-in

____ cfs x ____ irrigation set time (minutes) x 0.0165 = ____ ac-in

Metric:

Liters into cubic meters (cbm):

____ liters / 1000 liters = ____ cbm

Once the total amount of water applied is calculated into either ac-in or cbm., it should be divided by the area in which it was applied. Keep in mind that US Standard units should be discussed in ac-in per acre, while metric discussions will be cbm per ha.

Converting between these two systems is not really needed unless you are visiting a country with a different system. As an example, an almond producer from Spain or Australia may find it difficult when discussing water with an almond producer in California, and vice-versa. To help with that process, a few different equations are required to do the conversions as both the water applied and the land area in which it was applied have to be adjusted accordingly.

ac-in to cbm:

____ ac-in x 102.79 = ____ cbm.

Acre to ha:

____ acre / 2.47105 = ___ ha

This means that to apply the equivalent depth of water as ac-in/acre to cbm./ha, the following equation would take place:

____ ac-in/acre x 102.79 x 2.47105 = ____ cbm./ha

To further illustrate, the amount of water it takes per ha to provide the equivalent depth of 4 ac-in/acre (i.e. the amount of water it would take to cover a hectare in four inches of water)=

4 ac-in/acre x 102.79 x 2.47105 = 1,016 cbm./ha – or roughly 1,000 cbm//ha.

So, if hearing a farmer discussing the application of 1 acre feet per acre, that is roughly the equivalent DEPTH of applying 3,000 cbm/ha.

For a reference and potential use, here is a sheet to collect water meter data: