Tag Archives: Irrigation

The Soggy South

knowledge
Soil Moisture Retention Over Time

The sky opened up and poured for an hour. In that 60 minute span a measured 1 inch of precipitation recorded.

The lawn was well soaked. Baseline moisture content before was 43% and by the end of the drenching it had risen to 85% where it peaked.

Heavy rain having ended, the moisture plot on the chart begins a steep descent. Over the course of 3 hours following the storm the moisture level begins to stabilize. The last data point in the chart is very quickly back down to 46%.

Soil moisture retention refers to a soil’s capacity to hold water and make it available to plants over time, which is crucial for healthy plant growth and reducing the need for frequent watering.

Analysis: The soil was already saturated before the event. The added rain rapidly percolated through soil (gravity) and the [type: sandy] soil was unable to retain the excess. Witness the plunge in the graph. The graph demonstrates that there is an ever broadening plateau that forms.

Takeaway: When the lawn sprinklers are turned on during dry spells, any irrigation above 40-45% is wasted water. The soil can’t hold it. Mileage may vary depending on soil type.

Soil Moisture Monitoring

Infrastructure

Our Irrigator uses an old school shovel; poking a hole, looking at dirt. With the installation of our new Irrometer IRROcloud IC-10 we can perform the same task and from afar — no shovel necessary.

An array of sensors buried in the active root zone measure soil water tension. A sensor is an electrode embedded within a specialized granular matrix. Water in the soil exchanges with the matrix, providing an electrical measurement of soil water tension expressed in centibars (or kPa). Sounds like magic. These sensor readings are captured by a data logger and uploaded via cellular to the Cloud allowing us a real-time inspection.

West Block – Muscat

This is actual output from 20 JUL through 01 AUG looking at the 1 foot depth sensors. Moisture is depicted on the Y axis. The X axis shows the individual days.

The [gray] line is an average of the moisture sensors in the root zone and the [blue] bar graph(s) are recorded irrigation events. The upper band of the chart equates to DRY and the lower scale WET. Observe that the typical peaks and valleys correspond to the heat of day and coolness of night. The significant dip (valley) concluding an irrigation set shows a dramatic increase in soil moisture.

The general idea of course is to manage the irrigation; keeping the moisture level within an ideal (white band) range. But, we shall quantify this with the following graphic:

example depicts the Loam soil type

10% depletion of available moisture will determine the WET reference value.
50% is a generalized recommendation for a DRY depletion threshold (point where a plant can not easily extract remaining moisture from the soil without stress)

Based upon our Sandy Loam soil one can use the graph to determine the desired moisture range. Entering the chart at 10% and dropping vertically to the correct soil type curve and then coming across horizontally the result would be: 14 centibars as the wetter threshold. Doing the same only entering at 50% on the dry end equates to 40 centibars. [see basics] in between 14 and 40 centibars (the white band) should yield vigorous thriving vines.

This next image is the irrigation tabulation showing the 5 data sets reference the bar chart atop.

Irrigation Sets
Green data line is a 1′ depth sensor
Blue data line is a 2′ depth sensor

This zoomed section shows an inefficiency during the 27-28 JULY irrigation event. The drip system was running for too long (18 hrs.) sending water below the root zone; wasted. The previous set on 26 JUL with a 6.8 hour duration was more elegant (excepting the 0.6 hour subsequent false start).

20-25 centibars might be a good upper end target to begin an irrigation. How did our Irrigator do? Keeping the moisture within an acceptable band was achieved albeit a tad on the wet side being careful perhaps. Not bad considering the shovel method.

Water Mandate (nitty-gritty)

Educational

up close with government acronyms

As previously briefed, we can expect a mandate reducing and ultimately prohibiting overdrafting of our aquifer supply. Legislation was signed into law in 2014 to be overseen by the California Department of Water Resources. Specifically, the Sustainable Groundwater Management Act ( SGMA ) is a compliance framework that delegates responsibility to local level management entities to develop and implement a plan toward that end.

Our farm property lays within the local jurisdiction of the McMullin Area Groundwater Sustainability Agency (MAGSA ) or GSA for short. The GSA is developing and implementing a plan to be approved and tracked by the state and will have the authority to assess fees, adopt rules and conduct enforcement. Our GSA must work collectively with other GSAs under the direction of a Joint Powers Authority GSA (Fresno County and its 2 Water Districts).

Plan development must be complete by year 2020. Coincidentally, our previous ranch manager, Don Cameron, is a director and co-chairman of the Raisin City Water District and thereby one of the five board members of the Joint Powers Authority GSA. He is a prominent voice and is active in the direction of GSA policy as you will note further on.

Responsibility

The MAGSA must determine its over-drafting responsibility for the region. Realize that the aquifer is vast and does not recognize political boundaries.  As you might surmise neighboring GSAs will make a case that “their” groundwater share is flowing into and being used up by ours.  It has been [unofficially] estimated that 125,000 acre feet of groundwater is over-drafted in the MAGSA each year.

This is Us

A solution (?)

A possible plan to achieve sustainability (Don Cameron’s) involves the idea of replenishment through the diversion of flood water flows when they naturally occur. These flows, which would otherwise be lost to the sea, would instead be funneled to select crop land holding areas within the GSA. Over time the standing water would join the aquifer through gravitational percolation or perhaps more quickly by way of dry wells — a reverse pumping concept or groundwater recharge. Funding for recharge study and actual testing have been conducted by Don Cameron as proof of concept. Phase I of his McMullin On-Farm Recharge Project on Terranova Ranch, Inc land holdings will be completed by the end of this year at a cost of $12 million in federal funding. Don Cameron holds title of Vice President and General Manager at Terranova. Phase I of the project is limited and specific to Terranova. It is not certain that there will be a Phase II or that our location in proximity might be included.

Outcomes

A recent idea, the concept of selling or transferring groundwater rights, is  gaining traction. Renewable Energy Credits (REC) have established a precedent which may be applied to irrigation supply. In theory, a farmer who fallows his field and discontinues pumping could sell his share credit as if it were a commodity. A buyer would use his purchase to offset or reduce penalties for what would otherwise be considered an overage.  In another example, Terranova might do the same by justifying that their recharge system experiment puts back more than they take out. They enjoy sustainability while marketing the excess credit.

We are hopeful that solutions and agreements can be achieved. Last year we used 993.4 acre feet of water. A scenario might have us reducing pumping by “x” percent in order to do our part. Agony would be GSA failure to meet SGMA established timeline goals and the state assuming restrictive control compounded with significant flowage derived monetary penalties/fees.

Extra credit for enduring the following PowerPoint Presentation:

Anticipating the Future

Educational

Some Clouds on Horizon

Our California farmland is an ideal environment for the crops that we grow with many sunshine filled days and until recently abundant water supply. California has been experiencing a protracted drought which we acknowledge as lengthy and significant. According to recorded statistics most droughts last only for a season or two or three. The previous record was way back in the dirty thirties . The current 2006-2017 drought has eclipsed this infamous Dust Bowl event by 3 years in length and counting.

Supply

  1. Natural rainfall, which occurs strictly during winter months and is of limited supply for sustaining annual range grass and desert shrub. It is not relied upon in our arid valley and must be augmented by irrigation.
  2. Managed resources imported from mountainous flows primarily to our North and East. This supply travels via canal and aqueduct, is subsidized and controlled by public government. It is used for flood control and is doled out to farmers and urban communities on an as needed basis. Cost effective but limited in scope.
  3. Natural aquifer aka ground water or the water table. This is our relied upon and only source option. Expensive but readily available.

…and Demand

These drought years coupled with growing needs have placed strain on the availability of surface water. With scarcity comes limits and many of those farmers who enjoyed the good fortune of cheap water in the past have been forced to drill wells for supplement as a matter of necessity.  This in turn has placed an unprecedented  burden on the aquifer.  Whereas, the water table had been reliably stable over time we are witnessing a certain fragility. The acceleration of diminishing water quantity and water quality degradation in terms of mineral content is cause for alarm.  Also, as an extreme, sea water ingress and land subsidence.

Reaction

Alarm bells have captured the attention of environmentalists, media, and regulators scrutinizing where water goes, who is to blame, and corrective ideas. Politics and economics are a complicated tangle but for sure, changes are afoot. In the short term we expect to see usage monitoring on a granular individual farm basis  e.g. registering number of wells and reporting of outputs. In the future, regulatory restrictions and [reduced] usage mandates.

On a routine basis we monitor our local water table for fluctuation, measure outflow usage, and sample water quality so we are well aware of these issues first hand.

So, while we are seeing darkening clouds on the horizon we are hoping that they will result in much needed rain. Our response must be to comply with the mandates and adapting as necessary to remain viable.

Well No. 1 – 100 HP as new installation – 1962

 

 

 

 

Giving it Meaning and with Emphasis

Infrastructure

Modern Irrigation: We track a handful of metrics. Some of them are constants e.g. the pricing rate of energy. There are data points such as pump operational hours that are logged in tabular form. All of this information can be spun with a spreadsheet yielding useful intel.

Recall a previous post on scientific irrigation? It made reference to how much moisture a plant needs to maximize the photosynthetic process and thus crop harvest yield. Too much water is a waste and not enough is detrimental. The task then is to compute how much water are we putting down.

A first thing to understand is the concept of irrigation sets. Each of the vertical bars indicates a set. Think of an irrigator person adjusting or setting the flow so that he can leave for a few hours or attend to other jobs. (He needs to do this precisely because if the flow is too high then flooding occurs) The month of June requires a lot of water. It’s a vigorous growth period. Here you can see that the irrigation set can last for multiple days and extend into a 24hr interval.

Were’d this data come from? In times previous the reporting was scattered and usually furnished in an end of month statement summary. For example the utility company would tell us the energy total for the month and at the end of the period a field hand would read a flowage meter and pass along a reading. Knowing the previous months reading we could find the difference and figure out a total. Bare bones basic and lacking any detail, right? Did I mention that the report dates rarely coincide.

These days, we have smart meters and telemetry that will allow us near real time data collection. A side effect is that the quantity of data can become immense and we’re back to square one trying to make sense of it.

Gathering the data is a first challenge. It comes from scraping an online file and of course it is in a format that doesn’t present in any concise way.

This is just a snippet. It has 3,500 rows and that is just for half the year and only one of the wells! So next step is to fold, spindle or mutilate that raw data to give it meaning.

Observe that each row is a  00 :15 minute window. A daily output however is sufficient granularity. Further we need to convert the energy usage for presentation in layman’s terms. We want to know for how many hours the pump motors ran, on what days, and what proportional share of energy they each used to move “x” amount of water.

“X” amount of water: As said, the water flow meter is our primary tool but only a monthly itemization. There are some known constants that will break this down into a daily amount. We know the pumping capacity based on recent testing and now that we have the daily usage (above) we can formulate the output. More variables and constants and arithmetic that we use:

  • output in GPM is 1,792 and when multiplied by 60 converts to gallons/hour
  • 32,585 gallons == 1 acre foot (an old school agricultural unit of measure)
  • divide 32,585 by our gallons per hour determines how many hours of pumping
  • energy consumption rate expressed in kWh is 169
  • multiply hours of pumping times 169 to find energy per acre foot
  • cost of energy is $0.19 per kWh
  • multiply cost x energy results in cost per acre foot
  • 1 acre foot x 12 converts to acre inches
  • acre inches divided by 220.62 gives us inches of water applied

You get the idea. We can discover all kinds of things; cost per hour, which well and pump delivers the water for less, etc. By studying the data we find how the wells are managed.

We had three wells: #1, #2, #3; oldest to newest. #1 has been retired from service (but could be recalled for emergency use).  Our irrigator has the ability to select between them. It was interesting to observe (from the data) his pattern (not that it made any sense 😉 The irrigation sets are managed by timer clock. It is typical that Well 2 will operate throughout the night — shutting off automatically at 06:45 when Well 3 is brought online. Both wells are rarely operated simultaneously even though we have that capability. Hmmm, answers lead to more questions sometimes.

More enlightenment: In September (2017) there was a system problem. The irrigator finally remedied but this telling data trend would have caught it. The recordation value of .08 is below par and the interval is unusual. This pattern repeats many times.  What is happening is that the motor is attempting an auto startup but failing in the attempt. Evidently the irrigator’s timing of his inspection rounds was such that he missed the momentary start|stop anomaly.  

Irrigation Old Time: The Irrigator is practically redundant. See how much we can do from the remote office? Still, we need someone to establish the Sets. I remember when the Irrigator carried and actually used a shovel. The long handle was convenient for leaning upon 😉 Rubber [Irrigator] boots, and a cowboy hat to block the hot sun completed the look. The Irrigator made his set and watched for water that was getting away or (more hopefully) about to… It was a learned procedure — kind of like the more meaningful methods of today.

Scientific Irrigation

Horticulture

I should think that a green thumb, who through tried and true experience  — knowing the synergy between plant, sun, and water — could dig down a few inches grasp and squeeze soil in his hand, look at the plant and say needs or does not need irrigating. To obtain this cosmic sense one would have to be mentored as an apprentice and have years of hit/miss experience. Naturally the goal is to have healthy and productive growing and have more hits than misses but there is an [upward] trending motive and that is one of ecological conservation. Also, water is an expensive resource. Here is the short course using Wateright – a scientific tool from the Fresno State University. What comes first the discussion or the explanation of terminology? Feel free to skip around to get a handle on it. It is some interesting stuff if you’ve wondered (scientifically) when to irrigate and for how long. Hope you don’t find it too dry (sorry)

Disclaimer : I don’t pretend to fully comprehend the interpretation of the output from the formulae or the strategic use of moisture control for plant yield and pest control. Follows is an exercise in learning discovery. I’ve gathered definitions of terms and immersed myself in the science of irrigation using one of several scheduling tools available to farmers. My primary presentation is how soil holds water (see available water) and how plants consume water (see Transpiration).

In this 2017 Wateright Water Balance tabulation for the Section 30 Ranch, weather data from Five Points/WSFS USDA is utilized to calculate ETo (see below) . This station is part of the California Irrigation Management Information System network (CIMIS). It is a network of standardized weather stations scattered throughout California which report weather data (emphasis is sun exposure / air temperature) on an hourly basis and a reference point for evaporative demand for our micro-region.

A Water Balance FORM used data from the CIMS e.g. Potential ETc column is pre-populated. There were some constants, such as soil type, irrigation efficiency, and canopy coverage assumptions that I had to configure. Otherwise, the only daily inputs to the form by the farmer is Gross Water Applied in inches and Rain minus Runoff in inches. The tabulation output i.e all other columns are then presented in the printout follows: Wateright Moisture Balance 2017 (download link)

Interpretation: The farmer would like to have the actual ETc match the potential ETc for maximum plant performance. He doesn’t want to see the Volumetric Water Content go much below MAD

Explanation of Terms that will help interpret the Water Balance tool.

ET is Evapotranspiration — the process by which water is transferred from the plant leaf to the atmosphere by evaporation. for most of the growing season, the majority of the seasonal ET is from transpiration. Transpiration losses are usually high and are directly linked to plant growth and productivity. This is because the pathway for transpiration in plants is the same one that allows for plant intake of carbon dioxide. Both exchange processes occur through pores called stomates on the leaf surface. Stomates are fully open when plants receive enough water through the soil and when both transpiration and photosynthesis are occurring at maximum rates. If soil water becomes limiting, stomates begin to close causing a decrease in transpiration and photosynthesis i.e. growth production

ETo is simply a reference number which represents an estimate of evapotranspiration (ET) from an extended surface of 3 to 6 inch (8 – 15 cm) tall green grass cover of uniform height, actively growing, completely shading the ground, and not short on water. All of the CIMIS weather stations throughout the state are situated within a small grass field which is optimally irrigated. Thus, instruments attached to the weather station datalogger measure weather parameters that would directly affect ETo estimates such as solar radiation, air temperature, humidity, wind and rain. This data is incorporated within the weather station’s database and calculates a reference evapotranspiration (ETo) number every hour.

ETc is calculated by multiplying reference evapotranspiration (ETo) by the actual crop coefficient (Kc actual), ETc = ETo * Kc actual. The daily ETo values are from the CIMIS weather station, and daily actual Kc values are calculated based on dates and values entered in the ‘field setting’ multiplied by a water stress coefficient (Ks), Actual ETc = ETo * Kc * Ks.

Potential ETc is calculated by multiplying reference evapotranspiration (ETo) by the crop coefficient (Kc), ETc = ETo * Kc. It is the best case scenario for the plant to operate at 100%

Actual ETc is calculated by multiplying reference evapotranspiration (ETo) by the actual crop coefficient Kc * Ks

Kc or crop coefficient is a numerical factor that relates to the ET of an individual crop. Tall grass has a different Kc than a tree as an example. The Kc might vary through out the growing cycle e.g. as the tree canopy becomes fuller.

Ks values range from zero to one (0 to 1) and reduce the value of Kc when soil water is not adequate to sustain potential ETc. When the soil water level is above Management Allowed Depletion (MAD), Ks is equal to one, and Actual ETc = Potential ETc. When the soil water level declines below MAD, plants begin to experience water stress, Ks values are less than one, and ETc will not occur at potential rate, Actual ETc<Potential ETc. The Ks values become increasingly smaller as soil dries below MAD.

Gross applied water is equal to net applied water divided by our irrigation efficiency. We know how many acre/feet are applied in a given month but we don’t know exactly how it is proportioned (which Field). I make the assumptions that all fields receive the same amount. Convert the acre/feet (from our meter) to acre/inches and then divide the result by 220.62 acres gives the number of inches applied. Also, I don’t know what specific day the irrigation is applied; so I can only input the monthly total. That’s why is shows up on the last day of the month as a lump sum in the tabulation.

Gross irrigation deficit is the amount of water needed to bring the soil back to ‘field capacity’. It is given as depth (inches) of irrigation water and hours of running the well pumps. (Another constant I entered during tool setup. i.e. number of drip system emitters per tree and flow rate/per)

By default no runoff is assumed. Rain minus runoff is weather station data. I’ve added rainfall totals to the tabulation form using a nearby Personal Weather Station (PWS) at Kerman, CA

Available Water is the amount of water that is held by the soil between Field Capacity (FC) and Permanent Wilting Point (PWP) that crops can extract from the root zone. Water held between FC and PWP is considered to be 100% of available soil water. Soil water above FC cannot be retained and will be lost by drainage.

Not all the water between FC and PWP is Readily Available Water (RAW) to crops. When the soil water drops below a threshold value known as Management Allowed Depletion (MAD), crops begin to experience water stress and actual crop ETc falls below potential crop ETc. Moisture below PWP is strongly bonded to the soil and cannot be extracted by roots.

AW = available water
FC = field capacity
RAW = readily available water (to the plant) — MAD * AW
PWP = permanent wilting point
MAD = management allowable depletion — Default MAD value is 50%. MAD usually ranges from 40% to 60%

The Available Water measured in Inch/Foot refers to the holding ability of Sandy Loam. At FC this soil type can hold 2.6 inches per foot soil depth. Any greater than 2.6 inches and gravity overcomes and the excess percolates through.

So, how did our year turn out? Note that the monthly irrigation meter reading is sum totaled on the last day of the month, thus the spike in the graph below. We know how many acre/feet (from the meter) are applied in a given month but we don’t know exactly how it is proportioned (which Field). I make the assumptions that all fields receive the same amount. Convert the acre/feet to acre/inches and then divide the result by 220.62 acres gives the number of inches applied. 

Executive Summary: As a rough guideline and continuity check, generic almond trees require about 38″ of water during their growth season. We had:

  • 8″ of rainfall to date
  • 44 3/4″ of applied irrigation (as of 8/31)
  • …for a total of 52.76″ gross applied water

On some dates the moisture content was above FC. This was primarily due to winter and early spring rainfall but was a good thing. Our fields do require periodic leaching to remove salinity and other accumulations that are naturally occurring in our aquifer sourced water.

Hmmm.  It would appear that in March the irrigation got a little bit behind… Observe that the Estimated Water Storage was slightly below MAD. I’m not making a judgment. This may have been purposeful. As I say there’s much to learn!

It’s the Water

Horticulture

Irrigation water contains soluble (dissolved) mineral salts. Overtime, these salts can build-up in the plant root zone. Excess salinity creates osmotic stress. A plant must expend competitive energy to absorb water from a saline soil. In addition to total salt content we are concerned about specific salts such as sodium, chloride, and boron. For the most part, roots normally exclude between 95-99% of the dissolved mineral salts applied. The tree sucks up the water leaving the salt behind. At some point however, the concentration of salts exceeds the tree’s ability to exclude them. The salt is then picked up by the tree, moves to the leaves, and burn occurs. Leaf burn reduces photosynthesis.

Leaf Burn

… not to be confused with Leaf Scorch, a biological cause

Water sources are not created equal. For example, our new Well #3 has sweeter water than our Well #2. We have this awareness because we test for water quality annually. The agricultural laboratory with which we contract, scientifically measures the salinity by electrical conductivity (EC) in units of decisiemens per meter (dS/m) Water salinity of up to 1.0 dS/m and average root zone soil salinity 1.5 dS/m is a-okay. [source]

The 2016 lab water analysis report:

  • Well #3 Soluble Salts @ 0.53 dS/m
  • Well #2 Soluble Salts @ 0.83 dS/m

But, specific salts (Sodium, Chloride, Boron) accordingly are well above optimum range.

There is relief! We cannot easily procure a better water source but we can dissipate the salts from the soil through leaching. Essentially, the soil can hold water moisture up to a point at which time, thanks to gravity, its ability to retain is overcome and water passes through** flushing the salts with it.

Our Sandy Loam soil type has a water holding capacity of .07 to 1.4 inches per foot of soil. Rainfall is nature’s way of cleansing (and it costs very little) but we must assist the leaching process with remedial applied irrigation.

How much is needed? For Well #3, that has irrigation water with electrical conductivity of 0.53 dS/m; the percentage of water that needs to pass beyond the root zone is 7% or 3.9 inches of water. This is in addition to Evapotranspiration* (what the trees ordinarily need to drink). The requirement for Well #2 is double at 14% and nearly 9 inches of extra water. So a takeaway is to favor Well #3. [source]

When? We like to leverage the leaching period with the rainy winter months when trees are dormant and soil fertilization (Nitrogen) has not been applied. This year we had abundant rainfall.  The CIMIS estimates 11.45 inches since the first of the year. Whoohoo!

*Evapotranspiration is the loss of water through soil surface evaporation and transpiration through openings in the leaves.

**assumes no barrier e.g. hardpan we rip the soil before planting

The Cost of Water

Infrastructure

The PG&E Energy Statement comes every month and it is a major slice of our annual expenses. Dissecting the utility bill while solving for ‘X’ may provide some clarity.

Constants (known assumptions)

  • kWh == kilowatt hours – a measure of energy consumption
  • Well #3 produces 1,792 GPM at a consumption rate of 169 kW
  • Well #2  produces  780 GPM at a consumption rate of 77 kW
  • Booster has a consumption rate of 41 kW
  • Booster Pump must be run during operation of either well.
  • 325,851 gallons == 1 acre foot

Rates for Energy Charge (reference the PG&E document: Large Time of Use Agricultural Power – Schedule AG5B )
Summer
Peak:            $0.20775 12:00 noon to 6:00 p.m. Monday through Friday
Off-Peak:       $0.08974
Winter
Partial-Peak:  $0.10984 8:30 a.m. to 9:30 p.m. Monday through Friday
Off-Peak:       $0.08143

Calculations showing my arithmetic
1792 gpm * 60 min = 107,520 gal/hr so 325,851 / 107,520 = 3.03 hrs to produce 1 acre foot
780 gpm * 60 min =   46,800 gal/hr so 325,851 /  46,800 = 6.962 hrs to produce 1 acre foot

Billing breakdown explanation
There are primarily three types of charges on an electric bill: fixed charges, energy charges and demand charges.

  • Fixed Charges are usually small fees that do not change from month to month. ~$40/month
  • Energy Charges is based on the amount of electricity in kilowatt-hours (kWh) consumed over the entire billing cycle and vary depending on time of use.
  • The amount of electricity being consumed at any single moment is known as Demand (kilowatts).  Demand Charge is a calculation using the maximum energy consumption flow rate seen during the billing period.  For each 15-minute period in a billing cycle, the average demand is calculated. Typically, a motor startup will result in this peak flow rate value but the average over the 15 time interval helps to mitigate somewhat. The utility billing amount for Max Demand is $5.95 and Well #3 has a typical Max Demand of 168 kWh so the product of the 2 would be $1,000.00

Billing summary based upon actual averages
All of this boils down to real world average billed costs (including meter charges, demand charges, etc.) of:
$0.13 kWh  for Well #2
$0.20 kWh for Well #3
$0.12 kWh for the Booster Pump

Usage sample (July / August )
Well #3 running for 3.03 hours produces 1 acre foot of water with an energy usage of 512 KWh with the Booster Pump using 125 KWH for a total of 637 KWh. Cost per acre foot == $117.40 ((512 x .20) + (125 x .12))

Well #2 running for 6.962 hours produces 1 acre foot of water with an energy usage of  536 KWh with the Booster Pump (req’d) using 285 KWH for a total of 821 KWh. Cost per acre foot == $205.25 (821 x .25)

 Takeaway after solving for X

  1. Turning on a well when irrigation is not planned as if only to fill a truck water tank or perform a well test would cost a grand just to throw the switch! See the PG&E service period 11/17/2015 to 12/15/2015 and also PG&E service period 1/15/2016 to 2/16/2016 for Well #2
  2. Well #3 is the more efficient. This Well uses more energy as it is throwing more water (working harder) but it takes less time to get to the finish line.
  3. Off Peak usage is much cheaper. During some summer months the Well(s) must run ’round the clock so the ability to take advantage of rate incentives is limited.

Apologies if you found that topic to be DRY (and sorry for the pun), but water is a critical ingredient for we farmers. I promise future articles on this important resource.