Irrigation Systems, Wells, and Pumps of the Mississippi River Alluvium Aquifer of Southeast Missouri

Joseph C. Henggeler, PhD University of Missouri T.E. “Jake” Fisher Delta Center

Commercial Agricultural Program

Dedicated to Colonel (ret.) Francis J. Henggeler, USAF

Irrigation Systems, Wells, and Pumps of the Mississippi River Alluvium Aquifer of Southeast Missouri

Introduction Approximately 150 pumping plant evaluations were conducted on irrigation wells in the southeast Missouri (SEMO) area (Appendix I explains the method used during tests). The results from these tests provided information on both pumping plant efficiencies and aquifer characteristics, and were instrumental in developing this guideline on irrigation pump management for the Bootheel area. The evaluations gather information on both Static Water Level and Pumping Water Level (PWL), flow rate, operating pressure, and diesel use rate for engine driven systems and electric meter information for motor driven systems. From this collected data pumping plant efficiency, cost of water, and Specific Capacity (SC) could be determined. SC compares flow rate from a well versus how much the level of water is drawn down to obtain this flow (GPM/foot). In other words, it reflects the efficiency of a well; a high SC value produces lots of water with minimal drawdown. Units were tested under two sets of varying loads. First, both electric- and diesel-driven pumping units were tested under artificial increases in PWL simulated by applying back pressure to the system. This allowed the effect of dropping water table on pump performance and the cost of water to be understood. Secondly, the diesel-operated pumps were tested at various engine rotational speeds: 1250, 1350, 1450, and 1550 RPMs. The results of the tests indicated that the type of energy source (diesel versus electric) and the type of irrigation system (e.g., pivot, poly-pipe, basin, etc.) being used had their own best management practices (BMPs) specific to type of energy source/irrigation system. One startling fact gathered from tests was that initial well installation has a big impact on future irrigation energy costs.

Background Mississippi Alluvium Aquifer. This abundant water resource (officially designated as the Southeast Lowlands alluvial aquifer) underlies most of the Bootheel area on the west side of the Mississippi River and bounded to the west by the Ozark Encarpment (Figure 1). Well yield can be as high as 3,000 GPM with wells generally being only 100 foot in depth. The static water level during the irrigation season is generally 10 to 15 feet. Until recently, centrifugal pumps were commonly employed for pumping. The water surface declines during the summer with irrigation use, but recovers during the winter months. The Missouri Department of Natural Resources (MDNR) has nine automated observation wells into this aquifer, most of which have been collecting data for over fifty years, plus four addition observation wells that tap into aquifers underlying the alluvial aquifer (Figure 1). The average depth to the water surface for the nine wells over the course of the irrigation season is shown in Figure 2. The lines in the chart represent the mean values for the nine wells and includes: average depth on that day for each well for the period of record (blue line), for the shallowest depth on record for that day (green line), for the deepest recorded depth on that day prior to 2012 (yellow line), and the 2012 values (red line). 2012 was one of the driest years on record. The average depth (blue line) shows that water levels normally begin to decline in the beginning of May, reaching their lowest points during August and September; the drop of the water table’s surface during this period is approximately five feet. After that they begin to recover through April of the next year. It is important to remember that Figure 2 represents an average of nine wells. The results for individual wells all differ, especially regarding the recovery time frame. Also, while the drop in depth over the summer averaged 5 feet, it ranged from a low of 2 feet (Sikeston) to a high of 15 feet (Qulin). The five-foot drop in surface water table can affect the high-flow/low-head pumps used in furrow and basin irrigation within the SEMO area. Five feet of drop was used in a simulation study employing a pump curve from a typically used pump in SEMO and showed that the 2000 GPM pump reduced its flow to 1500 GPM Henggeler due to this 5-foot drop (2006). What’s more, while the surface of the Static Water Level (SWL) has dropped five feet, the PWL level will actually increase more than that due to the fact that the aquifer head is now smaller then before; head difference is the driving force for water to pass through the aquifer media, the gravel pack, and then the screen to enter into the well. The Darcy Equation was initially used to describe water flow in sand media and in wells (Darcy, 1856). The diminished flow Darcy discovered in wells became known as the falling head problem. Equivalent amounts of flow can be maintained following a drop in the water surface elevation, but by only increasing the amount of draw down such that the head difference

remains the same as before. The well flow rate (GPM) divided by draw down (ft) needed to obtain the amount of flow is called specific capacity (GPM/ft). As water is pumped from deeper strata, SC decreases. That is to say, early in the season the draw down for the same amount of flow will be less. Late in the season, especially in droughty years, draw down for the same amount of water will be more. Evaluations on diesel engines during the study were performed at four different RPM values, thus producing four separate flow rates and PWLs. Figure 3 shows the relationship between SC and PWL. In short, for every increase in PWL the SC value decreases 2.5 GPM/ft. Thus, if the top of the water surface drops 10 feet, the SC decreases 25 GPM/foot. Specific capacity (SC) is influenced by head differences, but also by resistance to flow that water encounters traveling through the gravel pack and screen into the well. Things like improper gravel mixture and size, along with improper screen size, inadequate amounts of screen surface area, and screen blockage by scale, rust or bacterial slime all increase the amount of resistance. These all lead to lower SC values. Low SC values lead to greater PWLs, and PWL turns out to be paramount in how much money SEMO irrigators pay for their irrigation water.

Fig. 1. Map showing the Mississippi alluvium aquifer (Southeast Lowlands alluvial aquifer) located in southeast Missouri with its nine automated MDNR observation wells into that aquifer and four MDNR observation wells in the region that are tied into aquifers underlying the alluvium aquifer.

QUATERNARY SYSTEM(Alluvium)

TERTIARY SYSTEM(Wilcox & Midway Groups)

CRETACEOUS SYSTEM(Owl Creek &

McNairy Formations)

ORDOVICIANSYSTEM(Undifferentiated)

East Prairie

Sikeston

Delta

Duck Creek

MaldenNaylorQulin

Steele

Cardwell, #2

Cardwell, #1

Alluvium Observation Well

Non-alluvium Observation Well Caurthersville

Gideon

Bloomfield

Fig. 2. Average water table depths from nine MDNR observation wells in the Mississippi Alluvial Aquifer (Southeast Lowlands alluvial aquifer). Values represent the mean values of nine wells for each well’s average depth on that day for the period of study (blue line), for the shallowest depth on record for that day (green line), for the deepest recorded depth on that day prior to 2012 (yellow line), and the 2012 values (red line).

Fig. 3. Specific Capacity versus Pumping Water Level. Note as water is pumped from deeper depths the aquifer yields less.

2

4

6

8

10

12

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18

20

3/1 3/31 4/30 5/30 6/29 7/29 8/28 9/27 10/27

Dep

th t

o W

ater

Tab

le (f

t)

Date

Depth to Water TableBootheel of Missouri (1981-2011)

Avg

Shallowest

Deepest

2012

y = 0.1163x2 - 10.949x + 355.65R² = 0.9914

100

105

110

115

120

125

30 32 34 36 38 40 42

Spe

cifi

c C

apac

ity

(GP

M/f

t)

Pumping Water Level (feet)

Specific Capacity vs. Pumping Water Level

Power Units: Electric Motors versus Diesel/Propane Engines. One must be aware of the differences between an electric motor and a fossil fuel engine to understand the implications found in this study. One of the major differences between motors (electric) and engines (diesel/propane) is that the former rotates at a constant speed (RPM), whereas, engines are capable of rotating at various speeds. So motors, and thus pumps, must run at a fixed speed (normally, 1750 RPMs for deep well turbines).1 In comparison, an engine can be revved up or down to meet changing hydraulic needs. Thus, pumps driven by motors produce a single pump curve. When engines operate at different RPMs they, in effect, have many different pump curves – and thus can meet different hydraulic conditions. Therefore, engines are better capable at meeting changes in hydraulic conditions, such as the seasonal drop in water table depth or a slowly clogging well screen. In the case of furrow and basin systems, a motor driven pump will only be efficient at only one PWL, and this PWL depth must be known prior to installation. Even then the PWL in the alluvial aquifer in SEMO will change throughout the season, making the electric pump efficient some of the time, but less so at other times. In contrast, pivots which have operating pressures of around 40 PSI (equivalent to 92 additional feet of lift being tacked on to the PWL) are little affected by a few feet of change in PWL. This is especially the case when the pivot has an end gun and/or is not equipped with pressure regulators, as it acts as hydraulic shock absorber. Another disadvantage of electrical systems is that 3-phase service is not universally available, making either a phase converter be required, or paying to bring in 3-phase lines. On the positive side of electricity, its advantages over fossil fuel systems are:

A lower initial cost (excluding any charge to bring in power lines).

The cost of water is less ($0.76 vs. $1.71 per acre-inch).

Lower maintenance costs.

Automating is easier to do. Irrigation Systems in SEMO. The studied showed that various types of irrigation systems (pivots, furrow, and rice basins) need their own distinct set of BMPs. For example, with a poly-pipe irrigation system and a diesel engine, the standard operating BMP would be to operate the engine at an RPM that allows the poly-pipe to remain “plumped up”, and change speed as needed even if the RPM used doesn’t produce the cheapest water ($/acre-inch). On the other hand, a diesel pump discharging into a rice basin to keep the flood up should be operated at the RPM that

1 Variable speed drives could be used to allow a motor's RPM to vary, however, they cost about $200-$300 per

motor HP. Additionally, rotational speed change could be had using drive belts having various diameter pulleys, but energy loss of 10% would ensue.

produces the cheapest water. Table 1 estimates the percentage for the various types of irrigation methods in SEMO.

Table 1. Irrigation Methods in SEMO

Irrigation Method Percentage of All Pivot 39%

Furrow, with poly-pipe 40% Rice basin 20%

Pivot systems. Fortunately, the efficiencies of pumping plant units associated with pivot irrigation systems are not adversely impacted by either the (a) type of energy source or (b) seasonal fluctuations the groundwater level. This is due, as explained earlier, to pivots having relatively larger TDHs. A pivot pump curve is also not nearly as flat as are furrow/basin pump curves. Since the farmer purchasing the pump will probably be relatively attuned to the PWL at the location and the local pump installer generally knows the water table behavior, the chosen pump will likely have flow/TDH characteristics close to the actual conditions. Unlike the electric furrow system where hydraulic conditions must be spot on, “Ball Park” is adequate for pivots. The only caveat needing to be mentioned is use sprinklers that are low-pressure.

Fig. 4. A SEMO center pivot.

Furrow with poly-pipe. The Polypipe was probably laid out during the period when the aquifer’s table was up. The number and size of the orifices were such that the pipe is full, but not over inflated. As the table drops the flow rate decreases and a good manager will increase the engine’s speed to compensate. Further drop in the water table will call for more RPM (but being careful not to create the unenviable job of having to patch a poly-pipe

blowout!). Pump affinity laws relate changes in pump RPM to created changes in flow rate (Q) and TDH. Q will change proportional to RPM changes. However, TDH changes exponentially. As mentioned before, a pump driven by an electric motor will only be efficient part of the time. Normally in electrical systems a direct linkage exists between the motor and pump. However, belt-drive linkage employing various pulley diameters is a means to provide hydraulic flexibility -- the catch being that belt-drive linkage will cost you 10% loss of your energy.

Fig. 5. Installing Polypipe. Various orifice size cutters are in cup. Types of pumps in SEMO. Centrifugal Pumps. A unique irrigation feature of the SEMO area, which separates it from irrigation throughout the world, is the use of centrifugal pumps to pull groundwater. While centrifugals may exist in other regions they are used to pull water from canals or lakes. The benefits of centrifugals are that they are cheaper to install (largely because they have no column pipe, drive shaft, or down-the-hole electrical wire) and have less intake pipe friction loss. Since the well casing serves as the column pipe, friction loss is at a minimum due to the large pipe diameters involved. The negative aspect of centrifugals is that they are harder to maintain and often need to be primed to be started. The fact they often need priming discourages owners in getting involved with load management programs offered by several of the local electric utilities. There is a maximum depth that water can be “sucked” up from using a centrifugal pump. Water at levels below this point will vaporize and cause cavitation in the pump. Elevation, barometric pressure, and hydraulic conditions of the pump influence this depth. For the SEMO situation the Pumping Water Level must be within 25 feet of the pump inlet. Again, we see how important SC is in SEMO irrigation. SC values in our study ranged from about 50 to 200 GPM/ft. Assuming that an irrigator desires 1000 GPM and the SWL during the summer was 15 feet. Draw down would be 20 and 5 feet, respectively, for the 50 GPM/feet

and the 200 GPM/ft case. This in turn would create PWLs of 35 and 20 feet, respectively. In the situation where SC was poor, a centrifugal pump could not be used, whereas in the other it could be. It turns out that the well would need to have a SC value of 100 or more GPM/ft. Because centrifugal users have to finely meet the challenges of a low water table depth they are the local go-to experts of on knowing the local water table situation. The vacuum they draw (most local farmers use gauges showing feet of water) indicates PWL since friction loss in those wells is very small. Turbine Pumps. As irrigators need to replace centrifugals they do so with turbine pumps. These do not need priming and are not normally affected by a lowered water table. Since the line shaft goes through the center of the column pipe decreasing cross-sectional area and increasing surface for drag to occur, higher levels of friction loss occur than in column pipe without line shaft. Since it was desirous to account for all energy sinks in our pumping plant evaluations, a special program was developed to calculate friction loss in column pipe with line shaft.

Study Results Study: Varying the Rotational Speed (RPMs). Irrigators with Polypipe normally increase the rotational speed of their engines during the course of the season to compensate for the diminished flow resulting from a dropping water table. Doing so allows the Polypipe to remain “plumped up” and allows the outlets at the far end to still receive adequate flow. Because of this, our pumping plant tests for engines included evaluations at 1250, 1350, 1450 and 1550 RPMs. Increasing RPM affected a whole host of pump and well hydraulic factors. As expected, with increased RPM, diesel use and flow rate always increased (Figs. 6a and 6b). However, the efficiency (Fig. 6c) and cost of water (Fig. 6d) did not necessarily track with RPM rate. On average, the 1350 RPM rate had the highest efficiency and lowest cost of water. The 1250 RPM rate was the least efficient by far (75% of the time it scored the lowest among the four speeds tested), but often it had the least expensive water. The 1550 almost always had the most expensive water, even though it was frequently the most efficient. It must be remembered that the reason the 1550 RPM rate was expensive was that it required more work – its PWL and friction losses were greater. In a similar fashion, the cheap nature of the 1250 RPM’s water was in great part due to that fact it performed less associated work (e.g., lift and friction). In the final analysis, a manager must sometime run his engine at a faster, albeit more expensive, RPM to meet the needs of his crop or irrigation system, such as in the case of poly-pipe that begins to water less evenly because it doesn’t have enough water.

y = -0.0021x2 + 8.0792x - 5644.7R² = 0.9866

1,000

1,200

1,400

1,600

1,800

2,000

1,200 1,300 1,400 1,500 1,600

Flo

w R

ate

(G

PM

)

RPM

Flow Rate vs. RPM

y = -3E-06x2 + 0.0079x - 4.9233R² = 0.7505

62%

64%

66%

68%

70%

72%

74%

76%

1,200 1,300 1,400 1,500 1,600

NE

PP

PC

(%

)

RPM

NE Pumping Plant Performance Criteria vs. RPM

y = 6E-06x2 - 0.0153x + 11.612R² = 0.9458

$1.50

$1.60

$1.70

$1.80

$1.90

$2.00

1,200 1,300 1,400 1,500 1,600

Co

st o

f W

ate

r ($/

acre

-in

ch)

RPM

Cost of Water vs. RPM

Figs. 6a-6d. As a function of engine RPM, (a) the average diesel use rate, (b) the average flow, (c) the average NE Pumping Plant Efficiency, and (d) the average cost of water for twelve tested diesel engines.

y = 5E-06x2 - 0.0098x + 6.0133R² = 1

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

1,200 1,300 1,400 1,500 1,600

Die

sel U

se R

ate

(gal

/hr)

RPM

Diesel Use Rate vs. RPMa b

c d

Since flow rate increases with RPM then friction loss in both the column pipe and the discharge head valve will also increase, as does the amount of draw down. All of these factors act to cause an increase in overall pump TDH with increasing RPM (Fig. 7).

Fig. 7. The average TDH for twelve diesel engines as a function of engine RPM.

One fortuitous thing that was discovered in the study occurs when engines and poly-pipe are used together. There is a relationship that describes changes in pump hydraulic output as RPM changes known as the Pump Affinity Laws. Flow rate increases proportional to RPM changes. Thus, doubling the RPM doubles the flow rate, as can be seen in Equation 1.

OLD

NEWOLDNEW

RPM

RPMQQ Eq. 1

However, the effect on the TDH is different; TDH increases by the square of the RPM ratios. Therefore, in the case of doubling the RPM, TDH increases fourfold! This could play havoc on Polypipe users as seen in Figures 8 and 9 since it bursts at low pressures. The bursting pressure for light mil and heavy mil Polypipe is 5 and 3 PSI, respectively.

2

OLD

NEWOLDNEW

RPM

RPMTDHTDH Eq. 2.

y = -3E-05x2 + 0.1156x - 66.057R² = 0.9953

30.0

32.5

35.0

37.5

40.0

42.5

45.0

1,200 1,300 1,400 1,500 1,600

Tota

l Dyn

amic

He

ad (f

ee

t)

RPM

Total Dynamic Head vs. RPM

Fig. 8 and 9. Bursting of poly-pipe when pressure gets too high.

Using Equation 2 to examine our tests which started at a RPM of 1250 (producing an average TDH of 33.1 feet), then at a RPM of 1550 TDH should increase by a factor of 1.5, or to 43.8 feet. This is an increase of 10.6 feet, the equivalent of an additional 4.6 PSI –enough with the original pressure in the Polypipe to seemingly burst it. However, much of the increased TDH is used overcoming the additional friction loss and pulling the water from a deeper level. Thus, increases in friction loss and draw down as TDH increases with higher RPMs tend to put a lid on blow outs. When actual TDH and predicted TDH from affinity laws are examined stepwise as RPMs increased we see they are very close (Fig. 10).

Fig. 10. Actual TDH versus predicted TDH from pump affinity laws taken stepwise between the four RPMs tested.

As mentioned earlier, flow rate increased with RPMs. In addition, draw down increased with RPM. SC, you might recall, measures flow rate relative to draw down. Figure 11 shows that SC decreases with RPM. And even though flow rate and drawdown both increase as RPMs increase, the former does it at a slower rate, and therefore SC decreases with RPM, as expected based on the Darcy Equation. The effect of RPM on SC is a good segue into the next section of the study that concerns drops in the water table of the aquifer.

0

10

20

30

40

50

0 500 1000 1500 2000

TDH

(fe

et)

RPM

TDH

As Tested

Affinity Laws

Fig. 11. The average Specific Capacity for twelve diesel engines as a function of engine RPM.

Study: Dropping Water Table. The elevation of the water surface of the Mississippi alluvium aquifer changes throughout the season. When the change of water surface is downward, then the PWL increases and farmers pay more for water. In our tests added lift, which occurs when a water table drops, was simulated by squeezing a gate valve down to increase operating pressure. Each PSI of added back pressure is equivalent to the water level dropping 2.31 feet. Back pressures of 0, 5, 8 and 13 PSI were used in the test, corresponding to added depths of 0, 12, 18 and 30 feet. The results show that there is a linear increase in the cost of water for both diesel and electric (Fig. 12). The data are based on diesel fuel at $3.50 per gallon and electricity at $0.11 per KWH. As is common knowledge to SEMO irrigators, electric energy is cheaper to run. The cost incurred for every foot of water table drop is 4 ½ and 3 cents per acre-inch for diesel and electricity, respectively. For the electric system, the challenge that a dropping water table has is not so much the added water cost, but the drastic decrease in flow rate, especially for high-flow/low-head furrow systems. Figure 13 is the flow rate for a pivot and a furrow pump as influenced by water table drops. It can be seen that the flow rate for the furrow system drops precipitously with a drop in the water table. In reality, the water table drop in the alluvium aquifer probably would not exceed 15 to 20 foot. While the flow rate of the low-head

y = 0.0002x2 - 0.6021x + 581.14R² = 0.9996

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1,200 1,300 1,400 1,500 1,600

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cifi

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Specific Capacity vs. RPM

furrow pump system greatly decreased as the water table drops, the pivot pump is not as sensitive to a dropping water table. Figures 14 and 15 illustrate the percentage of flow rate decrease that occurs for the furrow and pivot systems, respectively. In the case of the former flow rate decreased 75%, while in the case of the latter the loss in flow rate was 11%.

Fig. 12. The average cost of water for diesel and electric systems as influenced by a drop in the water table surface.

y = 0.0463x + 1.8433R² = 0.9859

y = 0.0298x + 1.0116

R² = 0.8844

$0.50

$1.00

$1.50

$2.00

$2.50

$3.00

$3.50

0 5 10 15 20 25 30 35

Co

st o

f W

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r ($/

acre

-in

ch)

Additional Drop in Water Table (feet)

Cost of Water vs. Additional Drop in Water Table

Diesel

Electric

Fig. 13. The average flow rate for two electric pumping plants as influenced by a drop in the water table surface.

Fig. 14. Flow rate and additional drop in water table for an electric FLOOD irrigation pumping plant. A 30 foot drop would cause a 75% reduction in the original flow rate.

y = -30.046x + 1279.5R² = 0.9677

y = -2.7448x + 548.79R² = 0.7111

0

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800

1,000

1,200

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Flo

w R

ate

(G

PM

)

Additional Drop in Water Table (feet)

Flow Rate vs. Additional Drop in Water Table:Furrow & Pivot System with Electric Motor

Furrow

Pivot

y = -30.046x + 1279.5R² = 0.9677

0

300

600

900

1,200

1,500

0 5 10 15 20 25 30 35

Flow

Rat

e (G

PM)

Additional Drop in Water Table (feet)

Flow Rate vs. Additional Water Table Drop for an Electric Pumping Plant:

FURROW SYSTEM

75% reduction

Fig. 15. Flow rate and additional drop in water table for an electric PIVOT irrigation pumping plant. A 30 foot drop would cause a 11% reduction in the original flow rate.

Analysis: 1) What Drives the Cost of Water?

The most significant fact gleaned from this study was that it allowed us to be able to identifying the most important factor (other than fuel or system type) in the price of irrigation water for the SEMO area. Pumping plant efficiency which one would assume to be the prime driving force in irrigation energy costs, turned out in the SEMO study to be poorly related to the cost of water at all as seen in Figure 16 (R2 = 0.18) which represents the diesel tests. The correlation for the electric units had R2 = 0.16. The average pumping plant efficiency for all units (69.5%) was only fair. However, even if full improvements were made on all of them, the average savings for the farmer would be only about $5-7 per acre. It turns out that the most significant factor in the cost of water for the systems was the pumping water level (PWL). Figure 17 shows the correlation for cost of water and PWL for the diesel systems (R2 = 0.71); the electric units had a correlation of R2 = 0.44.

y = -3.3826x + 551.2R² = 0.769

400

450

500

550

600

0 5 10 15 20 25 30 35

Flo

w R

ate

(GP

M)

Additional Drop in Water Table (feet)

Flow Rate vs. Additional Water Table Drop for an Electric Pumping Plant:

PIVOT SYSTEM

11% reduction

Fig. 16. The cost of irrigation water for diesel systems versus the NE Pumping Plant Efficiency.

Fig. 17. The cost of irrigation water for diesel systems versus the Pumping Water Level.

y = -4.5182x2 + 4.0883x + 1.4775

R² = 0.1791

$0.00

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$1.00

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30% 40% 50% 60% 70% 80% 90% 100%

Co

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/acr

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)

NE Pumping Plant Efficiency (%)

Cost of Water vs Pumping Plant Efficiency:Diesel

y = 0.0005x2 - 0.0074x + 1.3739R² = 0.7065

$0.00

$0.50

$1.00

$1.50

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20 30 40 50 60 70 80

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Pumping Water Level (ft)

Cost of Water vs Pumping Water Level:Diesel

Analysis: 2) Well Efficiency.

Identifying PWL to be important in determining the cost of water led to analysis of well efficiency in the SEMO area. Little can be done about the annual drop in the water table surface, the SWL. However, the PWL can be minimized with efficient wells. A good estimate of well efficiency is its specific capacity (SC), which compares flow rate versus how far the water level is drawn down to get his flow (GPM/foot). In other words, an efficient well produces lots of water with a small amount of drawdown. SC values in the study ranged from 60 to 220 GPM/ft, making some wells in the study 250% times more efficient than others. Wells with PVC screens seemed more efficient than ones with steel screens (140 GPM/ft versus 90 GPM/ft). SC can be affected by the type of gravel pack and well screen used in the well. While the type of gravel pack and well screen used in municipality wells are often based on sieve analysis of the media in the water-bearing strata of the wells, irrigation wells are generally installed with generic gravel and well screens. The difference between a SC of 200 versus one of 100 GPM/ft represents a savings of $7,200 over the 20-year life of a well. This is an area that demands more study in future years and work with SEMO area farmers, irrigation dealers, and well drillers.

Fig. 18. The cost of irrigation water for diesel systems versus the well’s Specific Capacity.

y = -3E-06x2 - 0.0032x + 2.1891R² = 0.4491

$1.00

$1.20

$1.40

$1.60

$1.80

$2.00

$2.20

$2.40

0 50 100 150 200 250

Co

st o

f W

ate

r ($

/acr

e-i

nch

)

Specific Capacity (GPM/ft)

Cost of Water vs Specific Capacity:Diesel

Conclusions Energy Source/Irrigation Systems.

Electricity remains cheapest form of energy. Its biggest drawback is that it produces a single RPM. This limitation affects furrow/flood systems, but not pivots because of the higher TDH that is used.

The fact that the water table of the alluvium aquifer fluctuates during season and from year to year causes electric driven furrow/basin pumping plants to be at top efficiency only part of the time they are being used.

In electric furrow/flood systems, drops in the water table of just five feet can reduce flow rate 25%.

For Polypipe, diesel and propane units will need to be run at higher RPMs as the water table drops. The operating management strategy is to keep the Polypipe “plumped up.”

o For electric systems, variable frequency drives for electric motors may

be advantageous

For basins, diesel units need to be run at the RPM that produces the cheapest water. Determining diesel rate is simple to do using graduated cylinders and a stop watch. Determining the water flow rate is more problematic. NRCS and Extension offices should have impeller flow meters on hand to lend out.

o Low cost flow meters need to be developed.

The pumping plant efficiency for both electric and diesel systems has little bearing on the costs of irrigation water.

Wells.

The most significant factor in the cost of irrigation water for furrow/basin systems in the SEMO area is the PWL.

o The method by which a well is initially installed is very important in PWL, thus in the future cost of water.

o The Specific Capacity of the well (GPM/foot of draw down) influences what the PWL will be and thus what the cost of water will be.

A small test well should be drilled prior to the well being installed. Gravel and sand from the main water bearing strata should have a sieve analysis done on it. The results of the sieve analysis should dictate gravel pack and screen slot size.

The operator and/or the irrigation company should try to determine what the likely flow rate and PWL will be by investigating close-by wells.

When the final well development is being done, information on the flow rate and PWL should be determined. The pump chosen should match those hydraulic conditions.

Since the water table will be changing, pump selection should consider the crop that generally will be planted and when most applications will likely occur.

Water Table. -pipe

The University of Missouri’s Center for Applied Research and Environmental Systems (CARES) division should begin mapping water table surface for the Mississippi alluvium aquifer.

All stakeholders (i.e., farmers, irrigation dealers, pump installers and agency personnel) should learn more about water table depth; this information will help them become more efficient at keeping energy use and pumping costs down.

o Installing an air line at the time of pump installation needs to become common practice.

“A smoke detector in every home, an air line in every well.”

References Darcy, H. 1856. Les Fontaines Publiques de la Ville de Dijon, Dalmont, Paris. Henggeler, J. 2006. Change in Water Table Depth Affects Pump Efficiency. Delta Farm Press Hla, Aung K., Thomas F. Scherer. 2001. Operating efficiencies of irrigation

pumping plants. American Society of Agricultural Engineers Paper No. 01-2090. St. Joseph, MI 49085.

Kranz, W. 2010. Updating the Nebraska Pumping Plant Performance Criteria. In proc. of the

22nd Annual Central Plains Irrigation Conference. Kearney, NE., February 23-24, 2010. CPIA: Colby, Kansas.

Acknowledgements I would like to acknowledge Representative JoAnn Emerson for the assistance in providing funding to support this project and other irrigation projects in southeast Missouri. This study supported with funds from the ARS/MU SCA. I would especially like to acknowledge the farmers below who allowed their irrigation pumping plants to be tested: who allowed tests to be conducted on their pumps:

Lewis Rone

Steve Watkins

F.E. “Jake” Fisher Delta Center

Dennis McCrate

Scott Wheeler

Scott Crumbpecker

James Hann

Lester Blanchard

Bob Benoit

Brant Barley

Leon Phipps

Bunton brothers

Jay Braker

Mark Larson

Carl, Larry & Robert Compton

Dale Schnelle

.

Appendix I

Testing Irrigation Pumping Plant Efficiency A pumping plant efficiency test compares energy in to energy out. The term “pumping plant” refers to the combination of power unit, pump, and linkage mechanism (i.e., drive train) connecting the former and the latter. Energy in is the amount of electricity, diesel, propane, etc. being consumed; when the energy source is electricity it is sometimes referred to as wire horsepower. Energy out is the energy created by the pump, sometimes referred to as water horsepower, includes both flow rate and Total Dynamic Head (TDH). TDH includes pumping water level (PWL), pressure losses downstream of pump outlet, and operating pressure. Normally in evaluations a category termed miscellaneous losses is used estimating other minor losses (say 2% of other TDH). However, when high-flow/low-head pumping units are being evaluated, and due to their flat pump curve, it is important to attempt to specifically account for all minor losses since small differences in TDH impact flow rate and efficiency. To be as exact as possible our tests also took into account velocity head, thrust horse power, and motor efficiency vis-à-vis applied load. The energy losses experienced during pumping occur because the pump, the power unit, and the drive train are all subject to efficiency losses. Final pumping plant efficiency is the product of power plant efficiency x drive train efficiency x pump efficiency as shown in Equation 1.

For electrical systems, the motor efficiency value used was the maximum efficiency value stamped on the nameplate (usually, 88.5%), adjusted based on the load the motor was under. Since there is no energy loss in direct linkage used in electrical units, all other losses are assumed due to pump efficiency. For engines, a 5% loss is assumed to occur in the gear head (10% if belt-driven), and the remaining losses are jointly attributed to engine efficiency and pump efficiency. Inserting a dynamometer in the drive shaft linkage would have allowed apportioning the loss between the engine and pump. In the cases where the overall pumping plant efficiency was high, then it is known that both items must have high efficiencies. It is only in cases of low overall efficiency that a dynamometer is needed.

Table Ia. Information collected during pumping plant evaluations broken into the three categories of Energy Out, Energy In, and Other.

Information Collected to Calculate Energy Out

(Water Horsepower)

Information Collected to Calculate Energy In

Other Information

Flow rate(GPM).

Pumping water level (feet).

Operating pressure (PSI).

Column pipe diameter (inches.

Discharge head size (inches).

Line shaft diameter (inches).

Depth pump set at (feet).

Diesel

Diesel use rate

Electric

Motor efficiency from plate.

# of disk revolutions of electric meter.

Time for disk revolutions.

Kh, TF, and KW values from electric meter.

Voltage between legs.

Amperage between legs.

Standing water level (feet)

Screen pipe material.

Age on installation.

Installer.

Water sample to test iron content.

Gear head information.

Energy Out, Water Horsepower. Flow Rate. Flow rate was calculated using a 8-inch inline flow meter (McCrometer, Inc., Hemet, CA) installed near the pump outlet as shown in Figure Ia. Flow rate was calculated by using the flow accumulator, “odometer” part of the meter, and timing the amount of time between two accumulated gallon values. The flow rate test was repeated for each pumping plant evaluation for the four tested RPMs and the four tested drops in water table. Fig. Ia. Timing water meter to get pump flow rate during a pumping plant evaluation.

Pumping Water Level. Pumping Water Level, as well as, Static Water Level, were measured with a e-line depth sounder () as shown in Figure Ib. The sounder was dropped into the space between the column pipe and the well casing. Depth was measured in feet to the closest inch. In cases where there was no access to drop a sensor between the column pipe and casing, or it was too tight to drop down, then only the SWL was measured using secondary access into the column pipe while the pump was off (Fig. Ic).

Fig. Ib. Measuring the distance to the water surface.

Fig. Ic. Sounding a well’s Static Water Level by removing an air relief valve and dropping e-line into the column pipe while the pump is off.

Operating Pressure. The pump operating pressure was remeasured by a pressure gauge near the pump outlet. Under open discharge conditions operating pressure was considered as zero.

Energy In. Diesel Systems. The rate of diesel consumption was calculated with a graduated cylinder and stop watch. The fuel line leading to the engine was disconnected from the diesel tank and submerged into a five-gallon container of diesel. If a return flow line existed it likewise was inserted into the bucket. After the engine was started up and reached the correct test speed, the ends of the lines were transferred to a 3000-ml graduated cylinder and a stop watch was started. The engine was allowed to run for three to five minutes during which time flow rate and PWL were measured and then lines were removed and placed back into the bucket of diesel and time recorded. Figure Id shows Whenever possible, engines were tested at various speeds (RPMs: 1250, 1350, 1450, and 1450) to develop a complete efficiency curve. Also, artificial increases of PWL were tested (PWL+: 0, 12, 18, 30 feet).

Fig. Id. Measuring the amount of diesel fuel removed from the 3000-ml graduated cylinder during a pumping plant efficiency test.

Electric Systems. The rate of electricity use in KWH was measured by collecting/recording appropriate data from the electric meter face, identifying/recording transformer factors, and then timing a set number of revolutions on the electric meter. In some instances input energy was gathered by measuring system voltage and amperage.

Appendix II

Nebraska Pumping Plant Performance Criteria (NPPPC)

The Nebraska Pumping Plant Performance Criteria (NPPPC) was used to make evaluations (Kranz, 2010). Electric motors were to be tested for energy consumption using electricity meters, or with a power meter if needed. To be supplied later.