464. Wells, pumps and related structures for irrigated land, October

Wells kumps And Related Structures

For Irrigated 1nds

Curl Rohwer

Irrigation by pumping from wells is a vital

factor in tne development of the arid and semi-arid

regions of the United States. in most of these

areas, tne water from streams has long been

complete-ly utilized for irrigation, or if surplus water Is

still available, the cost of bringing the water to

the lana is so great tnat it is not economically

feasible to use these sup lies at the present tie.

Where these conditions exist, pumping frost the great

reservoir of water stored in the **a- is the only

remaining source of auditionul water for irrigation.

-2-3ame idea of the importance of pumping from

wells for irrigation in the United 3tates can be

gained from the extent

or

the present use of water

for this purpose. In Arizona, two-thirds of all the

water used for Irrigation is derived from wells.

Of the

6s000s 000

acres irrig&ted in California,

4,700,000 acres receive all or u substantial portion

of the water applied for irrigmtion, from wells.

Colorado, which nas only recently begun to develop

its ground-water resources for irrigation, nas over

300,003 of its 3,0X3,000 irrigated acres supplied

by water pumped from wells. Texas, anotner newcomer,

nbAi 15,000 Irrigation wells In 1950. Ten years

be-fore there were 3,400 wells. Approximately 2,000,000

of

the 3,000,000

acres irrigated, use wells as a

primary or u supplemental source of water for

Irri-gation. Extensive use of ground water for

Irriga-tion is also made in any other states. No data are

available as to the total amount pumped for

irriga-tion each year, but it must be equal to a

substan-tial portion of the more than 100,000,000 acre feet

diverted annually for irrigation.

Many agencies have in the past studied the problems of pumping for irrigation and in recent years increasing attention has been given to these problems by the U.S. Department of Agriculture, State Experiment Stations, and other federal agencies. As

the result of these investigations much information is available to guide those concerned with t he

de-velopment and use of our ground-water resources so that prosperous and permanent agricultural communi-ties may be established.

The most Important Factors that have to be consider-ed in developing successful irrigation enterprises by pumping from wells, are the ground-water supply, the land, the well, the pump and accessories, the crops and the markets. First consideration must be given to the water supply. It is the limiting factor. If it is inadequate or if the quality is unsatisfact-ory there is no need to give consideration to the other factors. Next in importance is the land. It must be fertile and the topography must be

suit-able for irrigation. If the water supnly and the land are found to be satisfactory, then the remain-ing factors should be investigated.

ground-wuter supply that is adequate and

suitable for irrigation 19 usually harder to find

than land that 13 suitable for farming. Although

water exists beneuth tne surface of the ground in

most arid and semi-arid regions, too often

_conditions

are not favorable for the utilization of this supply

to irrigate crops. In some places the ground-water

is so far beneath the surfsce that the cost of

pum-ing is too grat; in others the formation in which

the whter occurs is so tlgnt that it does not yield

water readily or is so limited in extent that

the

supply would soon be exhausted; in many places the

rate of recharge of the ground-water reservoir

_{is too}

small to justify extensive development of the area;

and when an adequate water supply has been found,

_it

may be unsuitable for irrigation because of the

high

salt content.

Alluvial deposits containing thick layer of

water-bearing sand and gruvel are not favorable for

obtaining a good water supply. Broad alluvial

vel-leye, traversed by rivers or irri66,ted by a network

of canele, are ideal sites. The seepage from the

river

_{e and canals, und the deep eercolatien loss}

from irrigation, neerly alwaya aseure adequate

re-charge of the greuna-water reservoir. In theee

valleys

_{water table 13 usually quite close to}

the surface, an important feature from the

stend-point

_{of pumping costs.}

Ne hard and fat rules can be laid down as to

the depth to water beyond watch pumping is no longer

fealible for irrigation. It depends primorily on the

value of the crops produced. In California and Texas,

where fruits, cotton and winter vegetables are grown,

lifts of from 400 to 300 feet and more are common,

but in other areas wnere general farm crops are grown,

103 feet 13 probably the maximum, except under special

conditions. Wnere sprinkler irrigtion is practiced

the totsl pumping lifts can be

_{because the}

-6-The quality or the water in the zround.water

reservoir Is also important. It need not be

potable,

but it must not contain high concentrations

of soats

injurious to plants or soil. Sodium salts

sucn as

chlorides and carbonatas are especially bad. They

are toxic to plants and tend to puddle the

soil.

Al-though water containing 20)0 to 3000 parts per

mil-lion of sults has been successfully used for

irri-gation, concentrations of ov4r 1000 parts per million

usually CUL130

damage to all but the most resisti.at

crops. Tie Unger from the use of these alkaline

waters can be minimized by occasional hoof

irriga-tIons which wash the alkali out of the root zone

of

the plants. crops In porous soils

to uuthatand

higher concentrations or salt than those in heavy

soils. Date '.dalms, sugar beets and Bermuda xrass

are hignly resistant to alkali, alfalfa when once

established Is fairly resistant, but most fruits

and vegetables are susceptible to injury from

mod-erate concentrations of aLiall salts in the water or

soil. If there is any doubt 614 to the quality or the

water it should be tested to determine which alkalis

are present and the percentage of each.

tablisning the right to divert water for irrigution

from streams, but this is not true 01 tae right to

pump from underground sources. ke

laws governing

pumping from wells differ wideiy from state to state.

For this reason the legal right to pump should be

determined by consulting the stute engineer and it

tne priority or rignt to pump has to be established,

the necessary documents should be filed witn true

proper authorities.

Lana suitable for irrigation from surface

sources 18 also suitable for irrigation by

pump-ing from wells. The requirements are tne same.

Tne

soil should be deep, fertile, well drained and

fairly permeable, so that the soil will absorb

ir-rigation water readily. It should not contain alas,

-11 in excessive concentrations. The

of the

land should have gentle slopes; from 1 to 2 per

cent

slopes are ideal, but slopes up to 10 per cent

be irrigated if s,pecial precautions are taken and

If the soil is not too sandy. Flat lands, witn no

fall in any direction, are hard to Irrigate and also

hard to drain. Land covered with knolls and

depres-sions requirel extensive leveling before it can

be

Irrigated satisfactorily.

410401V

Profitable crops must be grown on lami

Irriga-ted by :)umping from wells or the anterpr,se will

obviously fail. For a crap to be profitable, th,ere

should be a good marlet far it, iould tae land sh),Ald

be sult.ble for producing a high yield of good

qual-ity. Adequate trans2ortk.tion facilities should be

available so that the crops may be quice.ly and

econ-omicOly delivered ct the .uarit aaces. 3ecause

nf

_{the high return from fruita aaL v4getc.b1s, they}

are well suite. for irrig,ition by ,:uming from wells.

There Is an additional c.dvante In using wella for

the irrigation of these crops because the farmer

can opply the water for irrigation when needed, not

when it ia available in the canal ‘s frequently

hap-pens when the water is diverted from etre/Azle.

krigatIon Wel;s D;fler martedly from those

used to supply water for domestic purposes. Because

of the large volume of water that has to be pumped

from the well for irrigating even a small farm s

special equipment is required to put down these

wells. Heavy well drilling rigs must be used.

has to be designed to fit the matt:rial in the

aqui-fer(water beuring remotion), so that the tine aund

will be huld bacl4 without eausiht excess_ve hea4

losgss which increuse the lumping lift. The well

cusing u6t be strong t,nd duruble and or sufficiont

size to permit the instullution of u pump of the

re-quired capLcity. Me well nust be locuted le,Gre it

will tap a gooc water bearing fc.frLution but it should

u'ao be locuted if posaible, where It will serve the

entire area to he irrigi.ted with a minima* expense

!or the W.stribution system.

The usual practice is to try to find u site :or

the well at or near the h161-4 point of the lam to be

irrig.c,ted. From tnis locution all the land can be

served by gravity. ftout7ver, tne underlying water

bet...ring formation in tnts location my not be

satis-factory. Just what the formation is, cannot be

de-termlned without priliminary investigations. For

this rc,uson test noles are drilled. it the test hole

shows that the formution does not contain enough sund

and gravel to produce u good well, other te4t wells

are drilled.

-13-When a locution is fouad were taa water

baur.ng formation is suitable, thc irrigation well

put down at tilis point. It uay hot be the most

fhivoruble locatiln froa thu stuno.point of

Irr-ga-tIng the land, but thia 18 not

_{Important as}

set-a good well.

149st ,rrgatiop W0,1,, are drilled in

unconsoli-dated alluvial formations, and the rigs used to put

down tne wells are of tne type adapted to drilling

in soft materials. In California, the mud-scow,

method, is generally used. The mud-scow is attuched

to a special drill rig with sufficient power to

op-erate the equipment and to hoist the loaded scow to

the larface. Because of its great weight the

mud-scow can drill through layers of fairly :lard rock.

Double stove pipe casing is used to line the hole.

This casing is forced down with powerful hydraulic

j6CW4

_{as the drilling progresses. The wells}

dril-led by this method ure from 12 to 16 Inches in

dia-meter and may be more tnan 1000 rett-deep. hfter the

well is drilled to tne required depth, the casing is

perforated opposite the water bearing formations by

ripping slots or puncning holes with si,ecial

perofora-ting equipment. Thousands of successful wells have

put down w.th a sand bucket and ahy well drilling

rig with spudding aquipment. Lis mettloa Is used

aiostly for drilling small diameter weils. For

larger wells an orange peel buc4et

used to

re-rove the matcriul from the hole. Wells put down by

the3e two methods titre usuully

_{with lint weight}

giavanized pipe, muae by rolling 16 to 12 gage sheets

Into the .torm of u cylinder und then riveting the

neumA. The casing is forced down by means of levers

by louding t0

to of the c‘.zing with sand

exca-ii.

_{fro-1 the hole. :4,1;kJ cas.Lg 13 perforuted}

be-ron i is inatulled in the well. 4ris is one by

punch-lig holes or slots of th, rioluired size In tilt

metul sheets before they are roiled into cyllnders.

The tale of this method Qr drilling wells lo

restric-ted ta areas where no rock strKta are encountered.

Potiiry rigs of the type used in drilling oil

wells are sometimes used for putting down irrlgution

wells, but they are not well adapted for drilling in

unconsolidated material. They are effective where

lpyers of hardpan, calcareous clay, sandstone or

simi-lar ledimentary formations are encountered. The

drilling is done by rotating a bit attacned to a

hollow drill stem through wnich drilling mud is

forced at high pressure. The mud rises to the

sur-face on the outside of the drill stem and curries

the drillings with it.

The

_{heavy rigs required for}

tills method of drilling are too expansive to move

and install to justify their uae for drilling

shal-low wells.

the reverse-circulAtion rotiily method ht n come into

use in recent years, vhich is so effective in putting

(inwn lerge alameter wells in uncnn!3olidated material,

that It has nuperseded all others in many area,1 where

the welln are not more than 200 feet deep. It

oper-ates on the rt.

:Verse-circulation principle, that in,

the water uled in drillinc, in drawn up through the

hollow drill stem rather than being forced down through

it so is done in the stendard rotary method. The

material remnVed from the bottom of the well a9 the

drilling :rogressee, in carried to the surface by

this stream of vater. Since the water inside the

tItem la moving upwurd at a high Velocity, it can

curry out Irrger particles than the slow moving upward

flow of the water on the outside of the drill stem of

the standtrd rotrry rig. ThE Cisadvantage of the

standard rotary method in this respect becomes greater

re the size of the hole Increases, because the

vele-/,7r

city of the stream vcries oppreleemoktely as the squure

of the diameter or the well.

When the reverie rotary method is used, the

hole Is kept filled with water to prevent caving.

No casing is necessary while tne well is being

drilled. After the hole has been completed,

cas-ing Is installed, which Is smaller in diameter than

the well bore. The intervening space is filled with

selected gravel. The casing is perforated before

it

installed in the well. The area to be

per-forated is based on the location of the water

bear-ing formation as determined wails the hole was

be-ing drilled.

Wells drilled by the reverse rotary method

frequently produce larger yields for the

draw

down, than those drilled by other methods. tart

of the increase is due to the larger size of the

wells, but the fact that the gravel pack can be

more accurately placed in the well is probably a

more important factor. Also, since drilling muc is

not required to bring the excavated tutorial to the

surface, there is no danger of clogging the water

bearing formations with mmd.

Another reason for the higher efficiency of

these wells is the speed with which holes can be put

down by the method. Under favorable conditions 100

feet of hole can be drilled in 8 hours. Because of

the rapid progress of the drilling tne water

bear-ing formations are not disturbed as in other

dril-ling methods where the Jarring action of the bailer

or standard tools ccpapacts tne material and

conse-quently reduces the permeability.

The cost of drilling irrigation wells varies

with the diameter of the hole, the depth, the nature

of the formation, the diameter and thickness of the

casing, and the type of well screen and gravel envelope.

The cost of a 36-inch well with 18-inch sheet metal

casing is from ,

;15 to $20 per foot wren drilled by

the reverse rotary method. This price includes the

gravel pack. Test holes in alluvial formations which

are usually drilled by the standard rotary method,

cost from "0.50 to $1.00 per feet. No casing is

re-quired. Drilling in rock is more expensive. More

ac-curate samples of the underlying formations can be

ob-tained if the test hole Is drilled with a sand buciiet.

This method is more expensive because the hole has to be

cased and because progress is slow, but if there is any

question as to the suitability of the formations, this

method should be used.

-16-DevelorAng The Well is necessary to obtain the

_{capacity from tne well for a given drawdown.}

The developing process removes the fine material from

the formation near the well screen, thereby opening

up the passages so that the water can enter the well

more freely. If prolA3rly done, developing the well

may increase the capacity of the well up to 50 percent.

The customary method of developing a well is by

means of a surge block wrilch is pumped up and down

opposite tne waterbearing sand witn tae drill rig.

Another metnod of developing tne well is to use

the test pumi.;.

_{By alternately starting ana}

stop-ping the pump, a surging action is produced which

washes out the fine material from the formation.

Air-lift rumps are smetimes used for developing

wells.

Dry ice is also used. It is dumped into the

well in chunks. The rapid conversion of the dry

ice into as in the water causes a violent

distur-bance in the well which washes out the fins material.

Sometimes the well is capped when dry ice is used.

This procedure builds up pressure in the well and

forces water out through the screen. Releasin8 the

pressure by opening a valve in the cap causes the

water to flow back into the well. This reverse flow

washes the fine material out of the formation into

the well. After the surging is completed by any of

these methods, the fine material remaining in the

bottom of the well is removed with a sand bucket.

Each of these methods will produce satisfactory re

-suits if the work is properly done. However, the

well should always be developed by an experienced

well driller, because in7,roper methods may ruin

the well.

-18-A Capacity Test should be made on every

ir-rigation well before the pump is purchased, because

the pump must be accurately fitted to the well in

order to obtain a plant with the maximum efficiency.

The teat should determine the water level before

pumping starts, and the drawdown at several

dis-charge rates. The maximum rata tested should

ap-proximate the rate at which the pump is to be

oper-ated. The discharge at each pumping rate should be

accurately measured with an acceptable measuring

device, such as a weir, end orifice, Parshall flume,

or Pitot tube. The well tholild be pumped at each

rate until the drawdown becomes fairly constant.

If the drawdown continues to increase materially

after several hours of pumping, it is an indication

that the capacity of the well is being exceeded.

The increased drawdown may be due to the fact that

the Lravel pack or screen has becorle clog&ed with

sand or that the formation does not bive up water

readily. Sometimr.

,

4

it is due to the small size of

the ground..water reservoir.

The well test is usually made by the well

driller because he has his drilling rig on the site

and can install the test pump without bringing in

additional equipment. Most drillers own a test pump.

Ube of a new pump for the purpose is not recommended

because most new wells pump some sand which wears

the Impellers and may ruin the bearings. This

re-duces the efficiency of the pump, which would be a

serious matter if the pump to be permanently

in-stalled in the well, were used for the tests.

Be-cause the test pump is used for short periods only,

high efficiency is not important.

The Hydraulics Of_HatIT_AlLEL that is the

theory of flow of water from the water bearing

form-ation into the well under different conditions is not

clearly understood. There are however so-le established

principles, which are helpful in designing irrigation

wells. The capacity of a well is proportional to the

permeability of the water bearing sand and it is

ap-proximately proportional to the thickness of the

formation and to the drawdown. The capacity increases

as the diameter of the well increases, but at a

much slower rate and it decreases ONO,

as the area

influenced by pumping the well increases. The effect

of the area of influence is small.

-20-Although increasing the diameter of the well

should increase the discharge only slightly,

actual-ly however, there are decided advantages in choosing

a large diameter well. The velocity of the water

through the sand and gravel surrounding the well is

less and therefore the danger of washing sand into

the well is reduced. An adequate number of

perfor-ations can be made in the screen without danger of

materially weakening it, because the screen can be

made larger. There is less danger of clog6ing a

large screen having adevate perforations. There

is also less possibility of deposits of chemicals

from the water forming on the screen or in the sand

and gravel when the velocity of the water is snail,

because the oressiire changes which cause the

de-posits are reduced. ?amps of large size which have

large capacities, high efficiencies and operate at

low speed can be installed in a large well.

The discharge of wells in artesian formations

is directly proportional to the draw-down, but

in

non-artesian formations, the rate of increase of the

discharge with the draw-down varies. Three-quarters

of the maximum discharge of the non-artesian well

will be obtained when the draw-down is equal to

one-half the depth of water in the well before pumping

started. IncreasinL the draw-down from the half-way

point to the bottom of the well will increase the

discharge by only one-quarter of the capacity of the

well. 7or this reason it is usually not feasible to

draw down the well below the mid depth of the water.

To obtain the maximum flow from a given water

bearing formation, the well should be drilled to

the bottom of the formation. If the well is drilled

half-way through, the yield for a vixen draw-down

will be one half the capacity of the formation.

Increasing the depth of penetration of the formation

is one of the best ways to increase the capacity

of a well.

-22-When wells tapping the same formation

_are

dril-led too close together, they interfere

_{with each}

other and the capacity of each well is reduced.

_If

the wells are more than 1000 feet apart,

_the

inter-ference will usually not be serius.

_{Small capacity}

wells, iv:eh an used in batteries, wLere

_the

water-bearing sand is only a few feet in thickness,

_{may be}

drilled closer together. The itsual

_{spacing of these}

wells if from 50 to 100 feet, but sometimes

_smaller

spacings are used. When such a battery

_{of wells is}

pumped, the capacity of each well may be reduced

₁₀

to 20 percent by the interference.

_{The smaller the}

spacing the greater will be the reduction

_in

capa-city. Because of the interference

_{in battery wells,}

and the difficulty in pumping a series

_{of wells with}

the same pump, more efficient results

_{can often be}

obtained by putting down widely spaced

_{small wells,}

which are pumped independently.

Screens Are Installed in wells so that the water may flow into the well with a minimum of interference and still keep sand from coming into the well. To do this the screen should have an adeluate area of openings and the size of the openings should be such that only the smaller particles of sand in the aqui-fer (water-bearing formation) can pass through the openings.

Tests by the Division of Irrigation of the U. S. Department of Agriculture, on screens one foot in diameter show that the head loss through the screen increases rapidly if the percentage of openings in the screen drops below 20 percent. However, in-creasing the percentage of openings beyond 20 per-cent does not decrease the head loss. This limi-ting percentage remains constant regardless of the discharge and also regardless of the size of the gravel in which the screen is installed. If the screen is larger or smaller than one foot in di-ameter, the limiting percentage remains the same but a different length of screen is required.

Another characteristic

_{characteristic of well screens}

disclosed by these tests, is that most of the water

enters the well thri_u6h the screen opposite the

inlet of the suction pipe of the pump. Par this

reascn the suction pipe should be perforated so as

to distribute the inflow along the full length of

the suction pipe. Otherwise, high velocities may

occur in the sand opposite the suction inlet and

large quantities of sand may be drawn into the

well.

asuklamtL2021

are used in conjunction with

well screens to help hold back the sand in the

water-bearing formation and also to reduce the

head loss. The gravel for this purpose is

screen-ed to a size that will hold back the sand found in

the formation. The gravel should be of uniform

size so that the porosity will be a maximum. The

diameter of the gravel particles (50-percent size)

should not be more than 5 or

6

times the 50-percent

size of the sand, if the gravel pack is to be

ef-fective in holding back the sand.

ing the gravel, the head loss will be small. If

the pack-aquifer ratio is greater than

6,

sand may

be carried into to gravel, thereby reducing the

pore space and increasing the head loss. If the

pack-aquifer ratio is too small, this also will

increase the head loss. ,fost well drillers use

gravel for the Lravel pack that is too coarse.

If the waterbearing sand is well graded

(con-taining particles of a large range of sizes) no

gavel envelope is required. Developing the well

will form a natural gravel envelope under these

conditions.

141-.en a gravel envelope is used, the

perfor-ations in the screen are designed to hold back the

gravel and not the water-bearing sand. Large size

perforations which reduce the head loss, arc used.

The width of the openings need be only slightly less

than the diameter of the gravel particles.

-26-The CgalsAALff -26-The

-Ilse

required to irrigate

the acreage served by a well, depends on the number

of acres to be irrioted, the crops to be grown, the

diversity of the crops, the length of the growing

season, the te,

_{.perature, and the rainfall. The}

pump is desi!_ned to supply the deficiency between

the water requirements of the crops and that

pro-vided from other sources such as rainfall and in

some cases water from streams or reservoirs. As

the acreage to be irri6ated incrcases: the (pm

(L:allons per ninute) capacity of the pump

requir-ed per acre decreases. This is true because the

crops are more diversified and do not all have to

be irrigated at the same time. Crops grown where

the average tenperature is high, require more water

than those grown in a temperate climate, because

the evaporation and transpiration rates are higher.

Where the growing season is long, the pump can be

operated for a longer time to deliver the water

needed. Under average conditions; small tracts

require a pump capacity of 15 to 20 gpm per acre,

small farms (80 acres), 10 to 15 gpm per acre, and

large farms (160 acre or more)

5 to

10 gpm per acre.

Another factor, that must be considered

in

deciding the capacity of the pump,

is the supply

available from the well as shown

by the well

cap-acity test. If the water requirement

of the crops

exceeds the amolnt the well is

capable of

produc-ing with a reasonable draw-down,

the acreage to be

irritated will have to be reduced

or another well

may have to be drilled.

Several Types Of T'umps are available

for use

in wells, each of which is adapted

for specific

conditions. The horizontal centrifugal

pump is the

cheapest, but its use is limited

to wells where

the slctIon lift does not exceed

25 feet at sea

level and less at higher altitudes.

It must he

primed before it will start pumping.

Piston rumps

can be used for small flows and hich

lifts. They

are however, no longer used extensively

in wells for

irrigation. Other types of pumps

are -lore

satis-factory.

-28-'cost irrigation wells are equipped with deep

well turbine pumps. Priming is not required to

start them. There are three main types --

centri-fugal, mixed flow and propeller pumps. The

class-ification is based on the kind of impeller used in

the pump. The centrifugal type has a small capacity

but will pump against maximum heads with high

ef-ficiency. The propeller type has a large capacity

and hih efficiency at low heads. It cannot be

used for high heads. The mixed-flow type turbine

has an impeller that combines some of the

character-istics of both the centrifugal and the propeller

types. It has a fairly large capacity and can be

installed in wells with casing too small for the

centrifugal type.

Deep well turbines may be either oil or water

lubricated. Whichever type is used, the

instruc-tions should be carefully followed so that the

pump will always be adequately lubricated. Turbine

pumps with submersible motors are also available.

All types of deep well turbines will give long and

efficient service when used under the proper

condi-tions.

Each deep-well turbine pump is designed to

operate at maximum efficiency at a definite head,

discharge and rate of rotation. These factors are

inter-related and if one is charved all the others

are affected. If the conditions under wLich a

pump is operating are different from those for which

it was designed, the pump will continue to deliver

water hut at a lower efficiency. Fowever, the

ef-ficiency can be improved by changing the speed,

the diameter of the impeller or the type, and if

the change in head is large, by adding a stace

(an additional impeller). For small changes in

speed of c-entrifugal type pumps, the discharge is

proportional to the speed; the head is proportional

to the sivare of the speed; and the horsepower is

proportional to the cube of the speed. T.,e

character-istics of mixed-flow and propeller pumps do not

fol-low these rules.

.30-The manufacturer has conplete information

_on

the characteristics of each type of pump he

makes

and can supply a pump that will fit the conditions

at practically any well. To do t.is, the

manu-facturer must know how rluch water is required,

_the

draw-down of the well at different discharges,

the elevation of the land to be irrigated

_with

re-ference to the static water level in the well,

ami

the size and length of the pipe line, if one

is

required to carry the water to the high point

of

the land.

numps made by different manufacturers

_{may fit}

the requirements of the pumping plant, but they

may

vary considerably in price and efficiency.

_Godd

pumps have efficiencies of 70 to 80 percent.

_The

pump with the highest efficiency sho Ad be chosen

if it can be purchased at a reasonable

_price.

Whether the price is reasonable can be determined

by computing how much the power bills will be

re-duced by using the most efficient pump.

Peep-well turbine and centrifugal pumps

op-erate at the hichest efficiency when the suction

lift is a minimum. For this reason the bowls

of a

turbine pump are installed so that the impeller

will

be submerged when the pump is runninE. The suction

lift will also be reduced if the suction inlet

is

equipped with a strainer ad a bell entrance.

root

valves, which are sometImes used on centrifugal

pumps to prevent the water from running hack

into

the well When the pump is shut off, increase the

suction lift. Gate valves do not increase

the

suction if the valve is of the same size

as the

suction pipe and is kept fully open. The

loss

through the valve increases rapidly if it

is lees

than one-half open.

Check valves which are frequently installed

in

the discharge pipe of pumps, may cause

considerable

resista,]ce to the flow of watdr in the pipe

es-pecially if the velocity is low. Pipe sizes should

be adequate because friction in pipes increases

rapidly as the diameter decreases.

-32-The power required to drive a pump depends on the discharge, the total head against which the water has to be pumped, and the efficiency. Ex-pressed as a formula

Horsepower - gallons per minute x total head 3960 x efficiency

Total head is the difference in elevation between

the water level in the well when the pump is operating, and the land to be irrigated, plus the friction loss in the pipeline, if one is used. The efficiency as here used, ia—t14-overall efficiency and is the pro-duct of the pump efficiency and the drive (belts or gears) efficiency.

The Choice Of 'Dower Unit to drive the pump is usually restricted to electric motors ad internal combustion engines. Steam engines are seldom used because of the high cost of operation. Windmills do not provide sufficient power, except for small plants, such as used to irrigate gardens. The power depends on the wind and it may fail at a critical time. A dependable source of power to drive the pump is important.

electric current is available and the power rates

are reasonable. Electric motors are dependable and

they are economical to operate. They give long and

trouble-free service. They are practically

auta-a-tic. Electric motors of the type used for pumping

plants operate on alternating current and rlui at a

constant speed. ti!ost motors are made to run at

1760 revolutions per minute but -notors with speeds

of

3475,

1160 and 870 revolutions per minute are

also available. motor driven numns are usually

direct connected and are designed to operate

ef-ficiently at one of these speeds. If the pump has

to run at a different speed to fit the conditions,

then a belt or gear drive must be provided with the

proper pulley or gear ratio to produce the

.34..

Electric motors can be desiEned to operate in

either the horizontal or the vertical position.

The vertical motors are especially effective for

use on deep well turbine pumps because the motor

can be direct connected to the pump -- the motor

and the pump head makin

8

_{a single compact unit.}

Electric motors will operate satisfactorily

_with

a continuous overload of up to 10 percent and at a

hiEher overload for short periods. PumpinL plants

should be desiLned so that the motor is at least

rally loaded because it improves the efficiency

of the plant and also reduces the demand charge

for

power.

Internal combustion engines are used to drive

pumping plants if electric current is not available

or where it is too expensive. Them are three common

types of internal combustion engines: gasoline,

diesel and butane. Gasoline and butane

_enEines

operate on the scre principle. A mixture of gas

and air is ignited by means of an electric

_spark.

They use volatile fuels such as gasoline or butane

and sometimes natural gas.

distillate. The mixture of distillate and air is

united by the heat due to compression of the

mixture in the cylinders of the engine. These

engines, regardless of type, will all give

de-pendable service but they require more attention

than electric motors.

Oasoline engines, with slight changes can be

made to operate on butane or natural gas. These

engines run at high speed, and since the

horse-power prodliced is directly proportional to the

speed, the weight of the engine for the

horse-power produced, can be kept low. For this reason,

also the cost of gasoline engines per horsepower

is relatively low.

Diesel engines have a much higher compression

ratio than gasoline engines and consequently must

be made stronger. They do not operate

satisfac-torily at high speeds. For these reasons, a diesel

engine of the same horsepower as a gasoline engine,

Is usually larger and heavier than the gasoline

engine of equivalent horsepower. It is also

con-siderably more expanaive. However, the hie,h

ini-tial cost is counterbalanced by the higher

ef-ficiency or the diesel engine and the low cost of

the type of ruel used. niesel encins are harder

to start than gasoline engines and require an

auxiliary solArce of power such as a largo storage

battecly, compressed air or a small gasoline engine

for this purpose.

Internal combustion engines, when used as

power units, are =Ado to drive a shaft in a

hori-zontal position. They can be direct-connected to

horizontal centrifugal pumps, but for deep-well

tlrbine pumps Which have a vertical shaft, a sear

or belt drive must be used. Highly efficient sear

and belt drives are available for this purpose.

Be-cause t'le

be varied

seriously

the ape

3d

sl?ead of internal combustin ell6ines can

t'lrough a considerable range, without

reducing the efficiency of the engine,

can be adjusted so as t make the pump

operate at maximum efficiency even though the

con-ditions, which the pump was orisinally designed to

fit, way have changed. They are rore flexible than

electric motors in this respect. Internal

com-bustion engines should not bo overloaded. They

wear out rapidly when loaded beyond their rated

horsepower.

Pipe Lines must be provided for pumpine plants

if the water has to be delivered at a higher point

than where the well is located. Steel, concrete,

vitrified clay, or coi.position pipe s:ch as

tran-site or plastic, may be used.

.38.

Steel pipe is adapted for use on

_high

pres-sure lines. It is resistant

to shocks, such as

those caused by starting the pump

_{or by the sudden}

closing of a valve. Deflection

_{of steel pipe caused}

b.j settling of the soil under the

_{pipe will not}

crack the pipe or cause leakage.

_{steel pipe is}

ade in a large range of sizes and

_weic,hts

suita-ble for any discharge or pressure

_{that may be}

required for the pumping plant.

_{However, steel}

pipe is expensive and rusts rapidly

_unless

oil-vallized or coated with a durable

_{paint such as}

coal-tar enamel or similar

_material.

Concrete pipe is extensively

_{used for pump}

discharge lines. it is :)est suited

_{for conditions}

w:Iere the pressure is low and where

_{the danger of}

shock is small. It is relatively

_{cheap and is}

dur-able except in soils containing

_{a high percentage}

of salts, particularly sulfates.

_{roncrete pipe im}

brittle and will break if the foundation

_settles

or if it is subjected to heaving

_{caused by frost}

action. Temperature changes and sudden

_{wetting of}

the pipe may crack it. To avoid

_{these possibilities}

the pipe is usually laid in the

_{sprin6 or fall and}

is kept wet while it is bein6

_{installed. A surge}

pipe or air chamber must be installed

_{near the pump}

to reduce th,,I danger of sudden

_shocke.

Vitrified clay pipe, commonly known

sewer

tile, is highly resintant to corrosion. It is

practically indestructible in this respect. It

is not affected by moisture or temperature chances,

trIt it is brittle and must be protected from shocks

by a surge pipe or air chamber if used in a pipe

line for a pumping plant. Fewer tile is made in

short lengths with bell ane spigot joints. The

joints are usually sealed with concrete, but a

flexible sealing compound, is recommended if there

Is any -/anger of settlement Or heaving. sower tile

should not be used where the pressure will exceed

10 feet of water, unless it is installed under

competent engineerinE supervision.

Special pipes such as transits and plastic are

sometimes used for pumping plant discharge lines.

Before choosing one of these special pipes, the

advantages and disadvantages of usine it, should be

carefully investiLated.

-40-The resistace to the flow of water in a pipe

depends on the -van

_{tity pumped, the rou6hnoss of}

the pipe and the diameter. Tables are avilablo

that show the feet of head revired to drive

vari-'pas vantitles of water through steel, concrete

and vitrifiod clay pipes of different diameters.

Tits frietion head rut

be added to the difference

in elevation between the water level in the well and

and the land where the watar is dischareel, in

com-putinz the horsepower reluired to operate a

pump-ing plant. If the pipe lii is long the friction

head may be the major portion

or

the total head

azainst which the pump has to operate. Care in

desl.gn of the pipe line is therefore important.

Sinee the friction head for a given discharge

varies inversely as the fifth power of the diameter

of the pipe, it is obvious that the proper size of

pipe should be chosen. Purtherrlore, the additional

cost of the pipe as the size increases a;711 tb.

fric-tion head decreases has to be balanced against the

saving in the cost of pumping. An engineer should

be consulted to be sure that the rost economical

size is chosen.

charges -- interest, depreciation and taxes; and

the operattnE costs -- power, repairs, lubricants

and attendance.

he fixed charces mist be paid

Whethi)r the punp is operated or not. OperatIng

costs however, are directly proportional

to the

total quantity 7.7.mped or the hours of operation

each season. If tha pump is operated for only

a short period, the fixed charges will be the

major item in the cost, and since the total

van-tity pumped will be small, the cost per acre foot

of water per foot of lift may be excessive. The

lowest unit costa will be ilbtCned if the lant

operates for a lo

n3 period each snason. For such

plants the cost of cower is the major item 7.-4*

expense. A modarn plant When operated 1010 hours

or more per season should pump water at a total

cost of ab ,-It 5

cents per acre-foot per foot of

lift. If the plant in old and inefficient

or if

the plant is run for only a short perir)d each

season,

the total cost may be doubled.

-424

'

Well irrigation pumping plants are expensive.

They may cost between a300 and 410,000 and

some-times muck: ore, if the lift is high and the

capa-city is lar66. Saah expensive e4uipment

_deserves

isuod care. Aet.,lect of the plant may cause

failure

at the critical time when water is most

_{needed for}

the crops. 3y the time the plant is repaired,

_it

may be too late. Water applied after the

critical

time will be largely ineffective.

_{For maximum}

;field of high-quality crops the water must

_be

ap-plied wizen it is needed most.

Carl Rohwer has been engaged in irrigation

research for the Division of Irrigation, USDA,

since 1914. His work has been chiefly on water

measurement and utilization, evaporation from

reservoirs, pumping for irrigation, and seepage

from canals. During most of his professional

career he has been stationed at Colorado

Abricul-tural and Mechanical College. He has degrees in

civil engineering from the University of Nebraska

and Cornell University.

For further

_{further reading on pumping from wells for}

irrigation:

W. E. Code: Equipping a Small Irrigation

Pumping Plant,

Colorado Agricultural Experiment Station

Bul-letin

_{435, 55}

Pages, 1936.

Carl Rohwer: Putting Down and Developing

Wells for Irrigation, USDA

Circular No. 546, 87 pages, 1941.

Carl Rohwer: Design and Operation of Small

Irrigation Pumping Plants, UFDA

Circular No. 678, 78 pages, 1943.

F. W. Bonnison, Ground Water, Its Development,

Uses and Conservation, Edward E.

Johnson, Inc., St. 'aul,

Min-nesota, 509 pages, 1947.

Ivan P. Wood: Pumping for Irrigation, USDA

Technical Paper 89, 40 pages, 1950.

Tom 0. Meeks, Developing and Testing Irrigation

Wells, Soil Conservation Service

Regional Bulletin

_{114, 44}

_{pages, 1952.}

Jack S. Petersen, Effects of Well screens on Flow

into

wells,

with Carl Rohwer and

M. L.

Alberton,

American Society

of Civil Engineers Proceedings

Separate No. 365, 24 pages,

_1953.

Recommendations for further research:

Effect of uniformity coefficient of gravel

used in gravel pack for irrigation wells on

flow of sand into wells.

Effect of distribution of inflow throujiout

length of suction pipes on flow of sand into wells

in fine-brained aquifers.

Ane

,

Well rumps And Related Structures

For Irrigated Lands

Carl Rohwer

Tiite—kirop.oitlui-ilmekmal—Lor irrigation by pumping from wells is

a vital factor in the uevelopment of the arid and semi—arid re:ions of the United States. In most of ihose areas, the water from streams has long been completely utilizee for irrigation, or if surplus water is still available, the cost of bringing the water to the land is so

great that it is not economically feasible to use these supplies at the present tic. There these conditions exist, pumping from the great

reservoir of rater stored in the soil is the only reraaining source of

au itional water for irrigation.

(6cme idea of the importance of pumping from wells for irrigation in the United States can be gained from the extent of the present

use of water for this purpose. In Arizona, two—thirds of all the

water used for irr'gation is oerived fron. wells. Of the 6,0001000

applied for irrigation, from wells. Colorado, which lies only recently

begun to develop its ground-water resources for irrigation, hes over

300,000 of its 3,000,000 irrigated acres supplied lyr water pumped fron 1•\

ci

wells. Texas, another newcomer, n.whas-15,000 irrigation wellsAWMO.

Ten years Itg5 there Ivor. 3,400 wells. Approximately 2,000,000 of the A

3,000,000 acres irrigated, use wells as a primary or a supplemental

source of water for irrigation. Extensive use of ground water for

irrigation is also made in many other states. No data are available

as to the total amount pumped for irrigation each year,iair-the-United

States but it must be morporeaft a substantial portion of the more than

100,000,000 acre feet applied annually for irrigation.

The rate at which our ground-water reserves are being depleted by

the increase in pumping for irrigation and other uses, is causing grave

concern to the state and federal agencies responsible for the

conserva-tion of our naconserva-tional resources. Unrestricted exploitaconserva-tion of our

grolnd-water resources will lead to disaster in all but the most favored

areas, whereas a wise use will make possible the permanent reclamation

of extensive areas of once desert land.

Hany agencies have in the past studied the problems of pumping

for irrigation and in recent years increasing attention haa been given

to these problems iv the U. S. Department or 1.grioulture, State

Experi-ment Stations, and other federal agencies. As the result of these

•2_

with the development and use of our ground water resources so that

prosperous and permanent agricultural communities may be established.

The most imporlE0 factors that heve to be considered in

develop-ing successful irrigation enterprises by pumpdevelop-ing from wells, are the

ground water supply, the land, the well, the pump and accessories, the

crops and the markets. First consideration must be given to the water

supply. It is the limiting factor. If it is inadequate or if the

quality is unsatisfactory there is no need to give consideration to

the other factor. Next in wiz importance is the land. It must be

fertile and the topography must be suitable for irrigation. If the

water supply and the lend are found to be satisfactory, then the remaining

factors should be investigated.

r +-CA 1i? Co

A ground_mater supply that is sati-graotery for irrigation is usually

harder to find than land that is suitable for farming. Although ground—

water exists exists beneath the surface of the ground in Ulls_ 711 portions

most arid and semfKarid regions too often conditions are not favorable

for the utilization of this supply to irrigate crops. In some places

the ground water is so far beneath the surface that the cost of pumping

is too great; in others the formation in which the water occurs is so

tight that it does not yield water readily or is so limited in extent

that the supply would soon be exhausted; and in many places the rate of

recharge of the ground-water reservoir is too small to justify extensive

If the rate of recharg is small, unrestricted pumping soon

lowers the ground-water level to the point where the cost of pumping is prohibitive. This unfortunately is occurring in many pumping areas

of the United States at the present time. This condition is partly due

to the long series of dry years whioh have reduced recharge and accelerated

pumping, but it is due also to over developrent of the areas.

tlluvial deposits containing thick layers of water leaving sand

and gravel Iltmost favorable for Obtaining a good water supply. Broad

allurial valleys, traversed by rivers or irrigated by a network of canals

are ideal sites. The seepage from the rivers and canals, and the deep

percolatioL TOW from irrigation, assure adequate recharge of the

ground-water reservoir. In these valleys the ground-water table is usually quite close

to the surface, an important feature from the standpoint of pumping costs.

No hard and fast rules can be laid down as to the depth to water

beyond which pumping is no longer feasible for irrigation. It depends

primarily en the value of the crops grown. In California and Texas,

where fruits and ,Anter vegetables are grown, lifts of from 400 to

500 feet and more are common, but in other areas where general farm

crops are grown, 100 feet is probably the maximum, except under special

conditions. Where sprinkler irrigation is practiced the total pumping

Asedsaoan be higher because the amount of water required is usually less.

The quality of the water in the ground-water reservoir is also pc-/e-ftde,

important, It need not be potable, but it must not contain high

oonoen-trations of salts injurious to plants or soil. Sodit).m salts such as

-5-and tend to puddle the soil. Although water containing 2000 to 3000 e(4r A-Sfer .

ed

=u=2 of salts has been successfully used for irrigation, concentrations ppc,r,

of over 100043porusually cause damage to all but the most resistant crops.

The danger from the use of these alkaline waters can be minimized by

occasional heavy irrigations which wash the alkali out of the root zone

of the plants. Crone in porous soils seem to withstand higher

concentra-tions of salt then those in heavy soils. Date palms, sugar beets and

Rermuda grass are highly resistant to alkali, alfalfa when once established

is fairly rest,tant, but most fruits and vegetables are susceptible to

injury from moderate concentrations of alkali salts in the water or soil.

If there is any doubt as to the quality of the water it should be tested ;Which

to determine/alkalis are present and the percentaTe of each.

'40st states nave definite procedures for establisning the right

to divert water for irrigation from streams, but tnis is not true of the

right to pump from underground sources. The governing pumping

from wells differ widely from State to State, For this reason the

legal right to pump should be determined by consulting the State Engineer

and if the priority of right to pump has to be established, the necessary

documents should be filed with the proper authorities. if there are

no lows in the State resprding the right to pump from wells, for irriga-0=6

tion any conflicting which may later arise will have to be settled

Land suitable for irrigation from surface sources is also suitable

for irrigation by pumping from wells. T43,a_requirements_are the same. The

soil should be deep, fertile, well drained and fairly permeable, so that

the soil will absorb irrigation water readily. It should not contain

alkali in excessive concentrations. The surface of the land should

+-have gentle slopes; from 1 to 2 per,gentIMIX ideals but slopes up to

10 percent can be irrigated if special percautions are taken and if the

soil is not too sandy. Flat lands, with no fall in any direction are

herd to irrigate and also hard to drain. Land covered with knolls and

depressions requires extensive leveling before it can be irrigated

satisfactorily.

Pesert vegetation is a good indication of the fertility of the

soil and also of the presence of alkali. The plants that indicate these

conditions differ in different regions, depending on the altitudes

latitts limate. ehe local County Extension Agent should be consulted

as to which plants are good indicators in a area. He will a1s be able

to furnish much useful information regsrding\the potentialities of the

-7..

Profitable crops must be grown on land irrigated by pumping

from wells or the enterprise will obviously fail. For a crop to be

profitable, there should be a good market for it, and the land should

be suitable for producing a high yield of good quality. Adequate

transportation facilities should be available so that the crops may be

quickly and economically delivered at the market places. Fruits and

vegetables, because of the high return from them, are well suarbet for irriger4iew

tntarprices-Irliftated by pumping from wells. There is an additional c/chroge_

in using wells for the irrigation of these crops because the farmer

can apply the water for irrigation when needed, not when it is available

in the canal as frequently happens when the water is diverted from

streams.

Irrigation Wenn diffent markedly from those used to supply

water for domestio purposes. Because of the large volume of water

that has to be pumped from the well for irrigating even a small farm,

special equipment is required to put down these wells. Heavy well

drilling signs must be used. The well screen or the gravel paok2 if _{?Cot i 410,1}

elAtv Peer rosy v

required, has to be designed to fit the material in the sivart, so that

the fine sand will be held back without causing excessive head losses

which increase the pumping lift. The well oasing must be strong and

durable and of sufficient size to permit the installation of a pump

of the required capacity. The well must be located where it will

tap a good water bearing formation but it should also be located if

minimum expense for the distribution system. bum=

The usual practice 10 to try to find a site for the well at or

near the high point of the land to be irrigated. From this location

all the land can be served by gravity. However the underlying water

bearing formation in this location may not be satisfactory. Just

what the formation is cannot be determined without priliminary

investi-gations. For this reason test holes are drilled to-find-out what the

underlying_formati_on. are. If the test hole shows that the formation

does not contain enough sand end gravel to produce a good well, other

thest yells should be drilled. When a location is found where the

water bearing formation is suitable* the irrigation well should be

put down at this point. It may not be the most favorable location

from the standpoint of irrigating the land, but this is not so

im-portant as getting a good well.

Most irrigation wells are drilled in unconsolidated alluvial

forma-tionsj and the rigs used to put down the wells are of the type adapted rneitkoca to drilling in soft materials. In California, the mud.seaw,

4.1 A CV/ac 4 czy e sard

ivehei

large-heevy-beeer, is generally used. The mud semis attached to a

special drill rig with sufficient power to operate the equipment and

Because of its great weight the mudsoow

m drill throu layers of fairly hard

rook. to hoist the loaded scow to the surfaoe./At uouoie stove p casing

is used to line the hole. This casing is forced down with powerful

hydraulic jacks as the drilling progresses. The wells drilled by this

method are from 12 to 16 inches in diameter. Wells over 1,000 feet

deep can be put down by the California mud-scow method. After the

well is drilled to the required dept, the casing is perforated opposite

the water bearing formations by ripping slots or punching holes

with special perforating equipment. Thousands of successful wells

have been dulled in California and elsewhere by this method.

Shallow wells up to 100 feet in depth can be put down with a

sand bucket and any well drilling rig with spudding equipment. This

method is used mostly for drilling small diameter wells. For larger

wells an orange peel bucket is used to remove the material from the

hole. A standard rig is required to operate the bucket. Wells put

down by these two methods are usually cased with light weight galvanized

pipes made by rolling 16 to 12 gage sheets into the form of a cylinder /0 acite)el and then riveting the seams. The casing is forced down by 4tA1sig the

top with sand excavated from the hole. The casing is perforated before

it is installed in tne wells by punching holes or slots of the required

size in the metal sheets before they are rolled into cylinders. The

use of this method is =du restricted to areas where no *ink rook

strata are encountered.

Rotary rigs of the type used in drilling oil wells are sometimes

used for putting down irrigation wells, but they are not well adopted

for drilling in unconsolidated material. They are effective where

layers of hardpan calcoreaus clays sandstone or si ilar sedi-,entary rt e9 7--ae rtf formations are encountered. The drilling is done with a rotstril

but which is attached to a hollow drill stem through which drilling

mud is forced aViligh pressure. The mud ;Wet° the surface on the

The heavy rigs required for this method of drilling are too expensive to move and install to justify their use for drilling shallow wells.

A new method of drilling irrigation wells known as the reverse

rotary method has come into use in recent years, which is so effeotive in putting down large diameter wells in unconsolidated material, that

it has superseded all others in many areas where the wells are not more then 200 feet deep. It operates on the reverse rotary principle,

that is, the weter used in drilling, is drawn up through the hollow

drill stem rather than being forced down through it as is done in

Pr-f /fin er Pr7

the standard rotary method. The material removed from the bottom of

the well as the drilling progresses, is carried to the surface by

this stream of water. Since the water inside the drill stem is moving

upward at a high velocity, it can carry a heavier load of material

than the slow moving upward flaw of the water on the outside of the

drill stem of the standard rotary rig. The disadvantage of the standard

rotary method in this respect becomes greater as the size of the hole

/ 'c, / •

increases, because the velocity of the stream varies gmatelll

square of the attantaxxisapttax diameter of the well.

When the reverse rotary method is

with 'rater. This prevents caving and

sary while the well is being drilled.

casing is installed, which is smaller

the intervening space is)(filled with

as the

used the hole is kept filled

consequently no casing is neces..

Ifter the hole has been completed,

in diameter than the well bore and

dgh-

-11-kept filled with waterwitirle-setttng-the-catiing and 15aarintii-g-1110- hole

wfthwrillter/ to prevent caving while this work is being done. The

casing is perforated before it is installed in the well. The area

to be perforated is based on the location of the water bearing

formation as determined while the hole was being drilled.

Wells drilled by the reverse rotary method frequently produce el

lerger yields for the same drawdown, than those dulled by other methods.

Part of the increase is due to the larger size of the wells drilled

by this method, but the fact that the gravel pack can be more accurately

placed in the well is probably a more important factor. Also, since

drilling mud is not required to bring the excavated material to the

surface, there is no danger of clogging the water bearing formations

with mud. Another reason for the higher efficiency of these wells

ia the speed with which holes can be put down by the method. Under

favorable conditions 100 feet of hole can be drilled in 8 hours.

Because of the rapid progress of the drilling the water bearing

for-,Jarr,

mations are not disturbed as in other drilling methods where the javing

action of the bailer or standard tools compacts the material and

conse-quently reduces the permeability.

The cost of drilling irrigation wells varies with the diameter of

the hole, the depth, the nature of the formation, the diameter and

thickness of the casing and the type of well screen and gravel

envelope. The cost of a 36-inch well with 18-inch sheet metal casing

is from $15 to $20 per foot when drilled by the reverse rotary method.

itg

This prioe includes the gravel pack. holes in alluvial

forma-tions which are usually drilled by the hydraulic rotary method, cost