PROCEDURE FOR ASSESSING
AGRICULTURAL IRRIGATION WATER USE
Suwannee River Water Management District,
White Springs, Florida BOB GRAHAM, GOVERNOR BOARD MEMBERS
0 Jerome Johns, Chairman J. R. Miller
W. Jack Carlton Auley Rowell
B. W. Helvenston, III Doug Thomas
John M. Finlayson Jonathan F. Wershow
Hilda S. Kressman DONALD 0. MORGAN
EXECUTIVE DIRECTOR 1979
JOHN L. SHOEMYEN
CARROLL J. GLYNN TECHNICAL WRITER
TABLE OF CONTENTS
ACKNOWLEDGMENTS------.......... -- ....--.-..-. a ...--.-. ...--....--.-- a ..- ...-.- ..- vi
I NT O DU T ION .- ..- .a -..-...- -- -- - -. --....-..--- --- .. -- -....... ---- V I.II
CHAPTER I--PREPARING FOR THE PHYSICAL INVENTORY-------------------- 1..
Determining crop types and farm size---..----- -- ..--.--..-.--. 2
Irrigation systems-..-----.----- -.-.--.. a ......-..-...-..- -- - -..- 3
Ba s ic un it s of the sy s tem- -.-......-..--.. -.. --.. -..-..--.- --. 3
Ty pe s of i r rIg a tion sy s tems .................. ------- -.-.-..-.-. 4
Multi-sprinkler systems .....-.-..- ....-...-.-.......-..- .... 4
Single-gun systems --....-.- ...........-..... -.-.-...-......-. 6
So ur c es of in fo rmat ion -.a.--....-.- ..-.-..- ..- ..--.. -- .. .- - 8
Designing the inventory ---rm- ......-.- ......-- .......-.. ---- 9
Designing the crop calendar---..-- ......-... ---------....- 11
Designing the public relations bullet in----.----- ..........- 12
CHAPTER It--PREPARING FOR IRRIGATION SYSTEM INVENTORY-----..------- --.... 13
Preparing the work sceue...... ...... -- 13
Becoming familiar with the geographic area -.........- -..... 14
Becoming familiar with the inventory equipment-..--------- 15
I nv en t ory form--........a-..-.-....a.........-- - ....... 16
Own er in fo rm a t ion- - -- e.. .. ....... -... -. a --....-... 1 6
Location .- ...........- .............-- ............. 17
Opinion questions----.----.-.--.-..-. ....a..a - -- -- -- 18
Determining section, township, and rag ....- 19
Determining 1/4 1/4 1/4 CD------...--..---------.--. 20
S ys tema -....-.-. -a.-.--.-.....-a.-.-- ...--.- -- ..--.--....--. 21
S o ur ce --.--..-.a..-..-.-..-a..-a.--.a..-..-.--.--....-..a. a -.-..-..-. 25
Ot he r s ys tem uses g . ---a-fla------- -.. . . a ....-..-- ..- 26
Manpower form .....-- .....---- ....-.-.----------.....-. 27
State Department of Transportation maps ...-...------ .... 28
Plat books ..--.......- ... -- -- -- ---- - -- -. -.-.. 28
Public relations bulletin------.------------..----- ---... 29
CHAPTER Ill--SITE SELECTION AND ANLSS.. ---.... ...-- 30
Selecting the area to be inventoried---..------ -- -.. - - 31
Things to look for when locating irrigation systems---------. 32 What to do after locating an irrigation system-------------- 36
Interviewing the farmer -.-..-... a -...-......--..-. - .-..-......... 37
Information to collect while interviewing the farmer---..--- 38 Onsite analysis of the irrigation systems------------------.. 39
CHAPTER tV--STATISTICAL SAMPLING-- -- ---- --- -- --- ---- -.... -e- ---- 42
I nt r od u ction--- ---a ....a-.. -- ----- -- -------- -..-..- 42
S impl1e random sam pli ng---- -- -- -a- -- -- -.-..... ---a 44
Stratified random sampling-------. -_-____-_____-__-_-__-_--_-__-_ 44
O TABLE OF CONTENTS (Continued)
CHAPTER V-DETERMINING APPLICATION RATES------------------- ...-------- 57
Me a suring t im e~- ---- - -- -- -... ----- --- -- -- -- ---- .... 57
Int rin s ic me thod----- -- -- --- ---- ------ -.... --- -- .....- 57
Ex t rin s ic method--------- ----- --- -- -- -- -- -..- -a-_ 60
Vlb r a t ion timer s ervic e log- -- - ------ -- -....-.---- a- -- --- 64
Procedure for time measurement-----------------------------.. 66
Determining normal operating capacity-----------------------_ 68
P ip e s ched ul1e-- ------------ -- --a-- .-...--... --------.....- 69
I nvas ive met er s .-.... -- --- --- -- -------- -- --- ----- -.-....... 69
N on invas ivemt e..rs.------- ---- -- -- ------- ---- 71
F ram ing sq ua re t ec hnisqu e--- --- --- ---------- --- -a- -- -- -.- 73
S y stem s p ec If ic method----- ---- -- -- --- -------- ---- -- ..- 74
Calculating the acreage irrigated per day------------------. 77
Traveling sprinkler calculator----------------------...---- 78
CHAPTER VI--ESTIMATION OF IRRIGATION WATER RETURNED TO THE AQUIFER----- 79
The no mog r aph----- -..-. - ------ ---- --- -------- --- ... - --- -.. 80
C omp one n ts of a nom og ra ph---- ----- ---a------ --.-.- __- 81
Use of the nomograph for calculating percent evaporation
10os s ------ -. . -- -- --- -- ...-.. --- -.. -__-_ 84
Calculating sprinkler system efficiency loss--..---.--____--- 86
Q Tabulating efficiencies of various systems------------------_ 87
0 ~~~~We athe r s ta t ions----- -- --- -- - ----- ---...-... -- -- -.- 88
Collecting information at weather stations----..------------ 89
Determining consumption rates--------.-----------------------_ 93
CHAPTER VII--INVENTORY UPDATE/DATA ANALYSIS 1-ANDLING--------------...--_- 95
I r r igat ion deal er up da te-- -... -- -- -- -- -a- -- -.. -_-____-___-_--_ 95
Well-permit record check,-- -- ------- ------------------------- 96
Quality control and computer readiness----------------------9
B a sic d a ta s to rag e ......- --- -- ------- -. -- -- --- ----- -- ---9
P r oces s ing pr og rams- --- -... ---------- .... --- --9
SELECT ED RE FERENC ES .... -------a----- --------------- ... _____ 101
APPEND IX-- --a-- -- --- ---- .. _-__m_-_____-___-___-_-_- a a -_ 102
INDEX------- -.. --------a------- .... ---i- ----- ....- - --------1
The Suwannee River Water Management District wishes to acknowledge the assistance of the many individuals and organizations who helped in the preparation of this manual.
Many people assisted the Editor by reviewing the entire manuscript,
and offering many valuable suggestions. Special appreciation is expressed to Dr. Allen Smajstrla, Dr. Dalton Harrison, Dr. David Niddrie, Mr. Kirk Webster, Mr. David Fisk, Mr. Janos Shoemyen, Mr. Richard Musgrove, Mr. Glen Faulkner, Mr. Jack Weeks, Mr. Fred Ruggles, Mr. Aaron Higer, Mr. Ed Gordes and Dr. Timothy Wyant for their time spent in reviewing the manual.
The United States Geological Survey Cooperative-Water Use Program, through its support of water use investigations, has made invaluable contributions to the research effort that produced the manual.
Illustrations were prepared by Joyce Lottinville, photographs by John Shoemyen and our special thanks to Rhonda Howard for typing the final copy of the manuscript.
"Among these treasures of
our land is water -- fast becoming our most valuable, most prized, most critical resource, a blessing where properly used..."
Dwight D. Eisenhower
At one time water was
considered an inexhaustible resource, available for use in whatever quantities man desired. But as human
populations increased so r -~frsn -did demands and needs for rso Hmito
freshwater, not only for Madison
public supply, but for I f '-RWD I..
rua ~etc lvsok ) -------- B..aker I
ruaoetc ietca |I
industrial, irrigation and Su/l wannee' S L.
thermoelectric purposes. ko umb
Water is now thought of as I Uni on,
limited but renewable Laaete P ,n
resource. It is little k__ra.fo.d
understood but immensely Lr-
important to man; as much as ( gI~ichrI
the critically short // Alcu
supplies of fossllfuels. ey lLi__Increased demands for 2 /
freshwater have created a/ need to analyze the Lv
functions and uses of F
this vital resource. When efficient methods for control and distribution of
water have been determined,
then management strategies can be designed. Suwannee River Management District
~There are many demands for irrigation water. Approximately 46 percent
~of the water in the United States is used for irrigation. Irrigation
maintains high yield and high quality crops in areas where there is either
insufficient or unpredictable rainfall during the growing season. Irrigation
use, especially in the Southeastern United States, has increased rapidly in
recent years. The increase is due largely to the South's longer growing season; one of the most important climatic characteristics governing the
amount of water needed for crops. Irrigation is the largest user of freshwater in the State of Florida, where ambient temperatures and evaporation
rates are high. Irrigation in the state of Florida accounts for one third of
the total irrigation taking place east of the Mississippi River.
The Suwannee River Water Management District (SRWMD) has quantified
irrigation water use within the District which includes 15 counties. Crops grown in this region are representative of those grown in the Southeastern United States. The District also has a representative sample of most types of sprinkler irrigation systems. There are no ditch, border, or flood-type
systems found in the district.
The SRWMD irrigation water-use analysis is concerned with two major
assessments: (i) data on the amount of water withdrawn from ground or
surface-water. sources and applied to a crop, and (2) data on the amount of water returned to the sources. The volume of water applied and the amount returned is analyzed and classified by day, year, cropping season and many
other categories. The use of water for irrigation is also reported by county and hydrologic basin.
~The SRWMD manual is presented as an aid for the collection and analysis of agricultural water-use data. Several different strategies for collecting
the data are explained along with descriptions and instructions for using
equipment needed for the assessment.
Two methods for collecting data are described in the manual; a general
inventory technique which involves collecting information on every locatable
irrigation system in the area, and a random sample technique which involves the analysis of selected farms. The basic preparation, data collection and
analysis of the two techniques is similar. Differences are mentioned in the
manual when they occur.
The manual is designed in a loose leaf format. As equipment and
techniques are improved and updated, information can be added or deleted.
Every region will have different crops, agricultural practices and
irrigation systems. However, the basic procedures described in the manual
should still be applicable.
~Chapters I and II deal with preparing for the irrigation inventory.
Basic inventory systems, inventory forms, and maps needed for obtaining
information, and types of irrigation equipment to look for during the
inventory are described.
Chapter III deals with the actual field inventory and information to
collect while in the field. The random sample technique is discussed in
Techniques for collecting data and analyzing both applied and returned
water-use data are discussed in Chapters V and VI.
In Chapter VII inventory updates are described, and a general overview
of data analysis is presented.
The appendices of the manual contain SRWMD inventory forms and materials
and a list of sources. It must be stressed that the manual does not cover
every possible technique or problem but can be a guide to conducting an
irrigation system analysis.
BACKGROUND FOR ThE
Field inventory preparation is an important part of any study since 'i amr
care and time spent in actual prepa- 0 ooerte
ration reduces the chance for future a 0
problems. Whether the study is based ,,'--., on a general inventory of the entire
region or on a sampling technique,.menatosyofamin O,
take time to understand the local cultivation and irrigation practices o
before planning the inventorymnpwr '
Basic preparation includes
knowing the crop types and farm -sieunderstanding the commonly used irrigation systems and de- (" .
veloping inventory materials such\ i--... "
as inventory forms and public relations bulletins.
Figure i. There are many decisions to be made when planning for an irrigation inventory
Figure 2. Winter rye grown under center pivot irrigation
Determining Crop Types and Farm Size
Knowledge of the regional cropping practices is useful when attempting to locate irrigation systems. Certain crops are irrigated more frequently than others. Examples of commonly irrigated crops in the district are corn, tobacco, peanuts, soybeans, and various truck, ornamental and forage crops.
The types of irrigation systems and amounts of water used to irrigate
are related to farm size. For example, large farms tend to have complex and costly irrigation systems that irrigate large amounts of land. Smaller farms may not be able to afford these expensive systems because of the amount of
capital investment involved and may lend themselves to other types of irrigation systems.
W There is a wide selection of irrigation systems developed to meet a
variety of needs, systems also differ regionally. Several of the most common
types are discussed in this section.
Basic Units of the System
All sprinkler irrigation systems consist of four basic units.
Familiarization with these units will aid in defining and analyzing
irrigation systems found in the region. The units are as follows:
1. Pumping and Power Unit. The pumping unit brings water from the
source and makes it available under pressure to the system. The unit usually
is driven by an electric motor or internal-combustion engine.
2. Mainline Pipe Unit. The mainline pipe unit delivers water from the
pumping unit to the lateral pipe unit.
3. Lateral Pipe Unit. The lateral pipe unit delivers water from the
mainline pipe unit to the sprinklers.
4. Sprinkler Unit. The sprinkler unit is normally an impact drive
mechanism that rotates by the force of water action.
Types of Irrigation Systems
Two types of multi-sprinkler i systems are: (1) hand-moved (including
portable set, solid set and permanent set) and (2) self-propelled.
1. Hand-moved systems are designed so they can be moved by hand labor. This may mean moving parts of the system, such as the laterals and sprinklers from one setting to another throughout the irrigation season. The entire system may be moved from field to field. Other types may be installed at the start of the crop season and not moved until the end of the season. There are two types of multi-sprinkler, hand-moved systems: portable and solid
--Portable set. The portable-set type system was the first to make sprinkler irrigation popular. It consists of a mainline and one or more laterals which are spaced according to the effective diameter of the sprinkler Figure 4. A portable set system used.
--Solid set. The name "solid-set" came into use because the system consists of enough laterals with sprinklers to cover the entire field. Small to
medium-sized sprinklers are used. Once the complete system is in place it is not moved until the end of the irrigation season. Then it is taken up and stored until the next season. The solid-set system may be used for crop-coor'rlirng or frost.4 pvrotionn.n
2. Self-propelled systems move continuously while sprinkling. They represent developments in sprinkler systems directed toward reducing the labor requirements for irrigation. The most common type in this area is the center pivot. This type of system has a single lateral which rotates about a center pivot (a swivel joint). It uses low or high volume sprinklers. The lateral is supported by mobile towers (A-frames on wheels) which are located approximately every 100 feet along the lateral. The length of the lateral may vary from 500 to 1500 feet. When in operation, the lateral rotates continuously about the center-pivot, irrigating a circular area of 20 to 250 or more acres. The amount of area irrigated depends on the length of the lateral. Water is supplied at the center pivot from a well located near the pivot point or from a mainline supply.
Figure 5. A center-pivot system
The lateral is self-propelled, driven by a series of power units, one at each tower. Separate power units are necessary to power each tower at a
Figure 6. A well and pump supplying a center-pivot system
.= Water power is supplied by water ~pressure from within the system which ~turns a "spinner"* or water turbine at
Electrically-driven systems have a ~electric control panel at the pivot
point. Each twrhas its electrical
W m motor drive. Hydraulic fluid powered
i systems use hydraulic motors at each
tower. Since the lateral travels in a circle, special provisions must be made
~Figure 7. A center-pivot system to obtain an even distribution of water.
rotates about a swivel joint. The sprinklers toward the pivot center
Water flows through the joint cover much less field area when making to
to the sprinkler, one revolution than the ones toward the
outer end. This is accomplished by varying the size or spacing of the
sprinklers (larger ones or closer spacing toward the outer end), producing
higher volumes of water.
Gun systems operate under i
enough pressure to irrigate a
large area, approximately 1 to
6 acres per sprinkler. Gun
systems discussed here are: Figure 8. Portable gun system
(1 hn -e,()tatr
O 1. Hand-moved gun systems are
S so named because both the lateral
and sprinkler are moved from one location to another with hand labor. Only one gun is normally operated per lateral on this type of system. The sprinkler remains in one location while irrigating. After the required amount of water has [ been applied, the gun system is
a- moved to a new location.
2. Trco ovd Snl
* ,~. tht*h trator-mu~ved typehv
larger sprinklers which are mounted on wheels so they can be moved with
Figure 9. Tractor-moved, gun a tractor.
systems may be mounted on wheels
3. Self-propelled. Singlesprinkler self-propelled guns move
continuously from one end of the
O field to the other while sprinkling.
S This unit uses a flexible hose lateral
which is dragged across the field by
the same power that propels the
sprinkler. The power may be a water-r
piston drive, water turbine or an internal-combustion engine. A steel
cable anchored at the opposite end of
the field pulls and guides the sprinkler
as it moves. The "hose pull" machines (fig. 20) use the hose lateral to move
the hose up on a large reel.
Sources of Information
Irrigation dealers can provide information about the types of systems they sell and the types that are used regionally. Dealers are valuable sources of information, since they can describe the actual systems that are seen in the field. They can determine equipment design specifications such as the capacities of certain center pivot systems. These specifications are needed for analyzing inventory data. Many types of irrigation systems can.be inspected at the dealerships.
Researchers at land-grant universities can provide the information necessary for producing a "crop calendars. The crop calendar contains details on the planting schedules for crops in the area. The researchers can provide assistance and answer any questions dealing with irrigation. They can provide crop-water demand figures, soil information and water-use information.
Agricultural Extension Agents
Agricultural Extension agents should be able to provide information on
the types of irrigation systems and irrigated crops found in the area. They may be able to estimate the numbers of farms that irrigate crops and assist in the development of a crop calendar.
Other sources of information include the Soil Conservation Service
(SGS), and the Agricultural Stabilization and Conservation Service (ASCS).
Designing the Inventory Form
A field inventory form is used to collect the necessary water-use
information. The form should be designed to cover information on crops, irrigation systems, and owners of the systems. Specific details concerning completion of the inventory form are discussed in Chapter II. The following list contains examples of some items that may be included on the inventory form:
1. Owner Information. Basic
information about the owners of _______________irrigation systems (the farmers) can A Aoc Wi tc&cA S ta
be compiled. The owners may be the only individuals who have all the ow t ltvorn%*on
the information on their specific
systems and irrigation practices. NTV t tt !IiIii
Agency information can be distributed to tlliti ~
the farmers if their addresses and phone IIIIIIilliII
numbers are kept up-to-date. The ownersru of the irrigation systems are not necessarily the Same individuals that ______________own the farm. Irrigation owners may lao J rn
lease the land.
2. Location of the systems. [1:1-information on the location of 'L~f r
irrigation systems can be used for'' future planning decisions. Farmers
often have more than one farm (and/ L
or more than one system). In order t
to locate the farmers for future data -- -collection efforts and dissemination of information, the exact locations of their systems must be known. ~~J~t,
Figure 11. An inventory form is used to collect water-use
3. Opinion Questions. Opinion questions can vary depending on the
research information desired. For example, farmers can be asked why they
purchased an irrigation system.
4. Crops and irrigated acreage. To determine water use, the acreage of
each crop and the number of inches of water applied in that year must be
determined, as well as the type of system irrigating each crop.
5. System information. Analyze irrigation systems as to their
capacity. To calculate capacity, check such items as the sprinkler nozzle
size, system operating pressure, pump capacities and operating time.
Determine how many systems a farmer has and the types of systems used. The
following chapters will deal with the above factors.
6. Source. Whether water used for Irrigation is withdrawn from surface
water such as a lake, or ground water such as a well, ascertain the source
for each irrigation system.
7. Origin. The origin of irrigation water indicates whether the water
used for irrigation is transferred (conveyed) across county or basin
8. Other system uses. This section can be used to collect specific
information of interest to an agency. Examples might include waste disposal
*through irrigation systems, the application of fertilizer or herbicides ~through irrigation systems.
* Designing the Crop Calendar
The crop calendar provides a timetable for scheduling data collection
during the growing season. It contains information necessary for
inventorying irrigated crop acreages and monitoring irrigation system usage
in the region.
Information contained in the crop calendar includes types of irrigated
crops, planting and harvesting dates, and periods of plant growth. This
information can be obtained from university extension services, county agents
and state agricultural agencies. Development of the crop calendar is
essentially a one time effort that will require only slight modifications
from year to year at the beginning of the irrigation season.
To have the highest success with locating irrigation systems, it is
important to do the field work during a peak growth period. During
senescence (the period of vegetative die back) and harvest, little irrigation
occurs and portable systems may already be removed from the field.
SRWMD FIELD CROPS CALENDAR
SJANJI FEB I MAR I APR IMAY JUNE IJULYI AUG SEPT IOCT I NOV I DEC
OSet Up0 00
Water Use :..
Data Growth Peak
Network Period Growth __ Senescence Harvest
Designing the Public Relations Bulletin
A public relations bulletin should inform the public about the purpose
of the field inventory and the legal atoiyfrcnutn h uvy
Responses to questions asked in the survey should be treated as confidential. Explain in the bulletin that the privacy of the individual wilt not be violated. It should also detail the ultimate use of the data, and more
importantly, how the farmers will benefit.
An example of the complete SRWPID public relations bulletin is in
located; an~d (3) through 'yardstick" weather stations located irn
W hat Y u Needfields under different types of
W hat You eedirriqat ioin systems (travelimq gun,
To Know About
Water Use And....
* i ,i l' l l lIRRIGJATION: A MAJOR USER OF WATER
The weather stations will provide
information on the amount of sunlight (radiation) rainfall, water
applied by irrigation, and evapotranspiration.
Q. What do you moan by 'field inventory"?,
A. Beginning in early spring of 1978,
- What is Inventory '78? our staff will visit individual
farms throughout the District. If
A. It as an accounting of how much you have an irrigation system, the
water is used for industrial, home, probability is good that you will
and agricultural purposes. be contacted.
Q.Who wants to know how much water is Q. What kind of questions will be
A. The Suwannee River Water Management A. You &ilI be requested to provide
District (SRWMD) Established in information concerning the kinds of
1973, the District covers all or crops you plant, how much water you
part of 15 counties in North Florida. apply and how often, the type of
Under the direction of a nine-member system you use, etc. Our field
governing board, the District has personnel will be courteous and will
the responsibility to manage all take up as little of your tame as
surface and ground water. The possible.
Governing Board has the authority to
set standards and regulations for Q.How will the Water Use Inventory
water maanagem~ent purposes, benefit moe?
O PREPARING FOR THE
IRRIGATION SYSTEM INVENTORY
Whether the study is a general inventory or the application of random
sample techniques, basic preparation is necessary. Prepare equipment and materials f or the inventory before beginning the study. Field work is the
most important part of the inventory and entails a considerable investment of
money and manpower. To ensure that fieldwork runs as smoothly and
economically as possible, one must become familiar with the inventory
materials. Be prepared for problems that may occur during the inventory and
learn how to cope with them.
*Preparing the Work Schedule
It is beneficial to assign personnel to specific geographic areas to
reduce transportation costs. Develop the personnel work schedule before the
field inventory begins. Sufficient vehicles should be available and
scheduled for field work.
D'44. K, -akrCo.-7
Figure 14. A work schedule should be developed before the inventory begins
O Becoming Familiar with the Geographic Area
Depending on available resources, aerial photographs or other remotely
sensed data (such as satellite imagery) should be studied. Analyzing these
materials can help identify forest and wetland locations and agricultural
areas. In arid regions requiring irrigation for productive crops, remotely
sensed data can be effective for agricultural area verification. .Center
pivot sites can be easily located using aerial photographs (see figure 15).
If field personnel are highly trained, the aerial photographs can be used for measuring field sizes and crop types. When new field personnel are hired, It
is beneficial to take them on several field trips for familiarization with
the geographic area. However, if personnel are familiar with the region,
such field trips may not be necessary.
] .. .... ... ,; ... .
. .... ... .. ..U r4Ai :p %
A F.. .
O Becoming Familiar with the Inventory Equipment
The inventory form should be understood before conducting the study.
The form is designed so that inventory information can be easily entered into
the computer. During the initial data collection, most of the information
necessary for data analysis can be obtained. If the inventory form is
designed in the manner described on the following pages, most information
needed for updates and random samples (discussed in later chapters) will be
While interviewing farmers, collect as much information as possible to
complete the inventory forms. When collecting data on irrigation systems and
crops, correlate each crop with the system or systems used on the crop.
Assign each system a system number. In subsequent years, use this number
when referring to a specific system.
For example, the farmer interviewed during the initial study has 2 traveling guns and 1 center pivot. The traveling guns are numbered #i and
#2, and the center pivot is numbered #3. In 2 years the farmer is revisited.
He has sold traveling gun #i and has acquired another center pivot. The new
pivot is numbered #4. That is, the new system has a new number, while the
old system retains the old number in the file and can be retired or evicted
*from the tile.
O A sample field inventory form is discussed on the following pages.
Questions included on the form may vary depending upon individual needs.
The SRWMD inventory forms described below can be used as an aid in developing
a form. The SRWMD form is discussed by section, and each item is explained
Transaction Add Evict Replace Update
3 9Y Y N! N D)I
Transaction -- The "transaction" indicates whether the particular inventory
form under consideration contains any additions (ADD), evictions (E) O (completely deleted), replacements, or updates.
Rec. No. -- This number is automatically printed by the computer and is used
by the computer for cataloging.
Farm Numiber -- Farms should be numbered consecutively. The first two blanks
can be filed in with the first two letters of the county name, followed by
the designated number. For example, the first farm surveyed in Baker County
would be BAO0l. The 316th farm surveyed in Columbia County would be 00316.
Note: If there are duplicate county abbreviations, the first three
letters in the county name or the first and last letters of the county name
can be used.
Date -- Indicate on the form the date the irrigation information was
collected. Make sure all field personnel place the month and day numbers in
Cell No. -- For a random sample study, indicate the cell number of the farm.
Cell number refers to the stratification or cell that the farm has been
placed in for the sample (see Chapter IV).
Active -- Fill in this blank, if the farm is used for the random sample study
Owner's Name ii III i I [ i I H I ] I I I
Adres[l ilL ] I I KlHT Tl l]]l
Owner Name -- Record the irrigation system owner on the form. Enter the owner's last name first and do not use title (Mr., Mrs., etc.). Entering
names in this fashion will permit easy access on the computer.
Number and Street, City, State, Zip and Phone -- Indicate the address (or rural route) and phone number of the irrigation system owner on the form.
Location I- II
I I /I /iI [
1 -H--AB5Topo Map No. [ jj --I-- -I- -- -4-- --
11asin No8LJ County No. [Jl 12I- /-- ------I I I
/ I /i l I i I
Topographic Map Number -- Look at topographic sheets and record the number of
the sheet where the system is found.
Basin Number -- Look at U.S. Geological Survey (USGS) Basin Maps and assign a
basin number to an irrigation system. The basin map has basin boundaries
marked. The boundaries can be superimposed onto a Department of Transportation (D.O.T.) County map, or each system can be located on the basin
map. After determining the basin number for the system, indicate the number
"System Located By" -- The initials of the technician conducting the inventory are filled in the blanks.
Section, Township, Range -- An example of how to determine the Section, Township, and Range is on the following page.
1/4 1/4 1/4 CD -- An example of how to use the 1/4 1/4 1/4 CD section subdivision system is on Page 20. The section, township, range and Basin
Number should be written in the blank provided.
Remarks -- Any unusual occurrences should be indicated. A well without a pumping unit, or a portable unit that is used at several sites on the farm are examples. Use this blank also to designate an uncooperative farm.
Transaction Add Kviot Replace Update
Rec. No. Fax. No. _ _ _
1. Do you think there will ever be a shortage of water for
Yes/No (Y/N) Unsure (U)
2. Do you think that droughts are becoming more frequent?
Yes/No (Y/N) Unsure (U)
3. Did you decide to purchase your first system after aYe/o L
drought or after a poor growing season?
4. In wat year was the worst "1
5. ]How important was the advice of friends or neighbors
in your decision to install on irrigation system?
None (N) Some CS) Major Importace (Ml
If N or 5: What then was the major factor that made you decide to install irrigation inystem?
6. Has the system improved your yield as expected? Yes/No (Y/N)
Thei opinion qunestions secti n of t-he 4inntry fnrn should be cnsidered
Determining Section, Township, and Range
A township usually contains 36 sections of land each approximately 1
square mile. However, civil or political townships may be smaller or larger. Township strips may be either north or south of the base line. Range strips may be either east or west of the principal meridian. Each township and range strip is assigned a number to indicate its position to the initial point. Thus, a township measures 6 miles on a side and is easily identified by a notation such as T2N, R3E (read as "township 2 north, range 3 east"). The notation identifies the township that is formed by the convergence of the second township strip north of the base line and the third range strip east of the principal meridian. Figure 16 illustrates this example.
-. _...._. ---"" C
Determining 1/4 1/4 1/4 CD In order to describe where an irrigation system is located, it is necessary to further subdivide the township. Descriptions of these
subdivisions are from the smallest to the largest unit and are generally based on a set of halves.
When describing a piece of land, you should always read from either the north or the south first, such as "northwest" or "southwest".* The descriptions are never read as "westnorth" or "eastsouth". It is simple to determine where a tract of land is located, if you read the description backwards from the smallest to the largest units.
Section 21 Township 2 North Range 3 East
6 5 4 3 2 1
7 8 9 10 11 12
18 17 16 15 14 13
19 20 J,..
- A _____________ YSTI'M I NFORMATIONeCc. NO. [%J Farm No. System No.
style liii]- Center Pivot OH Overhead Sprinklers
T- Traveling Gun TS Turf Sprinklers
SG Stationary Gun DT Drip/Trickle 11 Hand Move SS Seepage/Surface
II_ H l l lll ll ll
Maximum ___ __ __Nozzle Size 46 ,,, ozl _ __
Capacity L.. gpm Large Guns Pressure ][ Tray.
System Number Number each system consecutively. Use one page for information on each system.
Farm Number -- The farm number is the same number previously assigned to the farm.
Type Indicate the type of irrigation system.
Manufacturer -- Indicate the name of the irrigation system manufacturer, indicate the number of sprinklers in operation at one time (for hand-moved systems). For center pivot systems indicate the model number and number of
Maximum Capacity (in gallons per minute, gal/min) -- Maximum capacity depends on the system. It may be calculated in the office (this will be explained in Chapter V). Occasionally system capacity information can be obtained in the field.
Nozzle Size -- Indicate the size (inside diameter) of the sprinkler orifice (in inches or in fractions of an inch).
Nozzle Pressure (in pounds per square inch, psi) -- The nozzle pressure is the operating pressure. This measurement is taken at the nozzle of the gun.
Travel Speed (in feet per minute, ft/min) -- Travel speed will only apply to self-propelled systems like the center pivot or the traveling gun. Travel speed is the speed at which the system moves across the ground in feet per minute (normally 12-60 in/min). A traveling speed calculator, described in Chapter V, can be used to calculate travel speed.
Pump Manufacturer [H lT_ _l ILL ilif Ill!
Sial Iii IIJJJ RP 7J 7I ELIJJI TDHJJI If
[jrc24 Electricity (E) LP (L) Diesel (D) Gas (G)
Effeciency __ ___LOSS gpm
Area Irrigated 2 1 1[Date of33YY M
Per Day Acres Installation
Pump Manufacturer -- Indicate the name of the pump manufacturer on the survey form. Also indicate the type of pump (horizontal, centrifugal, deep well turbine, vertical centrifugal, or submersible).*
*Tmpeller-type pumps are used for sprinkler irrigation. Included
in this classification are (1) horizontal-centrifugal pumps, (2)
deep-well turbine pumps, vertical centrifugal and (3) submersible
1. Horizontal-centrifugal pumps are used for surface water sources
or where dependable ground water is available from depths of less than
2. Deep well turbine pumps are used where irrigation water is
obtained from depths of more than 20 feet. There are many pumps
included in this category. The pumps are suspended by the discharge column which contains the drive shaft. The power units are above the
ground, and can be internal combustion with gearhead or electric.
3. Submersible pumps have a power unit that is close-coupled to
the pump below the water level. Submersible pumps are electrically
Refer to the previous page to locate the following information on the inventory form.
Pump Serial Number -- The serial number can be found on the inspection plate which is located on the pump. This number should be copied on the form.
RPM -- RPM indicates the revolutions per minute of the gearhead and pump. The number can be found on the inspection plate or the gearhead.
CPM -- GPM indicates the operating discharge in gallons per minute of a pump.
TDH -- These initials stand for the "Total Dynamic Read". The number may be found on the pump inspection plate (optional).
Power Source -- Indicate the appropriate initial of the power source, whether it is electric CE), Liquid propane (Lp), diesel (D), or gasoline (G).
Efficiency Loss in GPM's -- The efficiency loss figure in gallons per minute is calculated in the office and will be discussed in Chapter VI.
Hours System Operated During Season -- Indicate the number of hours the systems operated based on the results of the survey.
Total Gallons Pumped -- The total gallons of water pumped through the system during an irrigation season.
Timer -- Record the number found on the vibration timer case. The timer is one method of calculating the hours the system operates in season. However, other methods may be used to determine operating time (see Chapter V).
Area Irrigated Per Day -- The area irrigated per day is calculated in the office and will be discussed in Chapter V.
Date of Installation The date of installation is an estimate of the month and year the system was installed. Obtain this information during the interview with the farmer.
CROPS PER SYSTEM AND IRRIGATED ACRES
rnti saictiot Add E'vict Recplace Update
Recc. No. Farm No. System Year Crop Irrigated Yield Mount Applied' in Inches
NmberY PA T casAres Pe Acr Farmerans
Ti i 8 BE]c Crops PE -2 14aut TU Tur (G--ouss
indcatd. f con1ntbac are2ron, indFict rhtti farm asftw
rop tye.Ls h rp grownLfo each irigtonsstm The form
crops/cmmo to the eia.e ofthe mol comopropschoul e ited onr thn e inventory frm.efamr
Tot Irriaed Ances The total numert of iriated acrle plntie to ea Yield/Acresughnostitto the toalprdutine irrigate esnsoledtried. Ae canhe
foItewae RVrc -o ier systSinhol
WellN~b -- illi theevosi, rWng -n seltolf h elto
Sell Weol Pe__tNber --_ Yi neld gprnel Permit ~e. Tis7 Basin N. r umero Wh11 Coun to. wellD oae
Wautr Soure -- Fille in the appopritwe nitials. Ths sldecmlee
for the wter sourerforyeahmsystem
Well Numere il intet owipngeandesectiondofethelwel, notiiofs testdem fom eftg wts right.aple hruhanirgainsyt cans bepped fretom the we ifanwdn te"te ytUe"sin
OThIER SYSTEm USSe
HISTORICAL CELL INFORMATION Transaction Add Evict Replace Update
Rec. No. 1W I
Cell No. LO L[ [j 1/
FUTURE ACREAGE INFORMATION
I [--]A. About the same acreage.
B. Increase acreage. C. Decrease acreage. D. Discontinue. Decreased byare
Historical and future acreage information is important when conducting a long-term study since farms can be recalled from the file quickly and their past water-use patterns can be determined.
SAMPLE MANPOWER FORMDa[7j]111111
Miles TraveledI Kil h
Farm No. I "'"
Initial Contact Form Completedl-- Clock Installed II
Callback Install Clock I Complete FormI3"f Remove Clock ELI
The "Manpower Form" is used for determining the number of miles driven
in one work-day, the number of farms contacted, the percentage of work
completed during the initial visit, and the number of callbacks* necessary to complete the form. At the end of the inventory, manpower costs and the total
number of miles driven for the study can be calculated. An estimate can be
made of the number of callbacks expected in future studies. The form can be
added to the regular inventory form if desired. Each sheet contains information on 5 or 6 farms. Information on the SRWMD form includes:
Date: Date of travel.
* Miles Traveled: Total miles traveled that day.
Farm No: Number of farm being surveyed.
Initial Contact: If the initial interview and all parts of the inventory
form are complete, check "Form completed." If the timer is installed, check "Timer installed." Circle "Initial Contact" even if the form is not complete
and/or the timer is not installed. If initial contact is made but the farmer
does not allow installation of the timer, write a note to that effect.
*Gallback: Indicate whatever tasks are accomplished during the callback; "Install Timer", "Complete Form", or "Remove Timer"*. Continue to use the
callbackk" line each time the farm is visited until all the necessary work is complete. If the farmer is not located after two visits, attempt to call him
on the telephone. It should be stressed that there is a strict time limit
involved. The timers must be in operation before irrigation begins.
Otherwise, the accuracy of the study will be reduced.
*In this manual "callback" is used to denote a return visit or any other
secondA ntactn wirth1 the farmer by the interviewer.
e State Department of Transportation (D.O.T.) Maps
D.O.T. maps are available from State Department of Transportation and
State Topographic offices. These maps are important field inventory aids
because they are drawn in detail to large scale proportions. The maps
include topographic features, secondary and primary roads, and unimproved and
During the field inventory every accessible private and public, road in
the area is traversed in search of irrigation systems. The degree of detail
found on the D.O.T. maps is essential for locating these roads. The
topographic and cultural features included on the D.O.T. maps are superimposed over township and range grid patterns with numbered sections.
Township and range coordinates are written in the margins of the map, making
it easy to locate irrigation systems.
Plat books can be obtained from the county courthouse. The books are
prepared by private publishing companies and must be purchased. Some
sparsely populated counties may not have plat books.
-- LACA'OA C04UNTyZoc z
" -- oIoA
0 il,0 Al/GR-- --* 'C -, ---o /' /," r7 aaSiAREONd> too .
PA~sp at. aGRAoT
O County indices must be identified in the plat books before the farms can
be located. These indices will refer to township maps. Parcels of land are
delineated in the plat books, and individual owners' names are included on
the maps. An index to land owners can be found in the back of the plat
books. The owner information is useful after an irrigation system is
Public Relations Bulletin
The public relations bulletin, described in Chapter I, is an important
document to study, since it may represent the first contact an agency will have with the farmers. The bulletin should be comprehensive and used when farmers and other interested persons ask questions. The bulletin should be placed in farm stores, irrigation dealerships and other places that farmers
BASIC INTERVIEW TECHNIQUES
Keep some basic interview techniques in mind when approaching the farmer to obtain irrigation information.
1. Be courteous and considerate.
2. Ask the farmer for voluntary cooperation, do not demand information.
* 3. Clothes and overall appearance should be neat and
4. Be careful not to destroy any personal property.
5. Be sure to introduce yourself and the agency you represent.
6. Present a brochure to the farmer when introducing yourself.
7. Tell the farmer what information will be. available to him after the inventory and explain how this information will be useful to him.
8. Mfter the irrigation survey is complete, you must maintain contact and provide the farmer with the results of your study. Information should be disseminated that will be helpful to the farmer and help to maintain his continued cooperation.
SITE SELECTION AND ANALYSIS
Field analysis of irrigation sites iks an essential part of any irrigation water-use survey.
The purpose of the inventory, the study approach, and survey materials should be developed and understood by all project members before field work begins. Chapter III is designed to aid the field technician in the location of irrigation sites, the analysis of irrigation equipment and in basic interview techniques.
Figure 20. Tree plantations can often be eliminated
from the study
Selecting the Area to be Inventoried
The geographic area for the field inventory will have to be selected, no matter what sampling technique ts used. This chore can be reduced by taking
an initial look at maps and aerial photographs. Areas such as swamps, state preserves, wildlife management areas and tree plantations, are not likely to be irrigated and could be eliminated from the maps. Check with county Extension agents, the Soil Conservation Service, and other agencies for information on nonirrigated areas in the county. After determining the parts of the county that are not irrigated, select the work area from remaining portions of the map. If a general inventory technique is used, every public and private road is traversed. Hark areas off the road as they are covered to avoid possible redundancy.
Things to Look for When Locating Irrigation Systems
An irrigated field may be overlooked by the casual observer or the
inexperienced eye. However, there are certain clues for locating irrigation systems. Get used to looking for these clues while driving down the road. Every system does not need to be located for the random sample technique. These suggestions are most helpful when conducting a general field inventory.
Irrigation Equipment. The most
obvious sign to look for during the field inventory is a piece of irrigation equipment; a pump, sprinkler, or pipe line.
Figure 22 k portable gun irrigation system
Irrigation Pipe. Irrigation pipe can often be seen joined together in the field or stacked near the farmer's house, barn or equipment shed.
. .. -~ t t
Figure 24. Certain crop types are commonly irrigated and should
Crop Type. One indicator of an irrigated field is the type of crop
grown. Ninety percent of all tobacco crops and all nurseries are irrigated. If there are tobacco fields or truck crops in the area, stop and investigate.
Figure 25. Spacing of crop rows often indicates an
irrig ,naedn crop
Tire or Skid Marks. Watch for tire or skid marks, especially in watermelon fields. Approximately 60 percent of all watermelon fields are
irrigated with a self-propelled or :'
hand-moved single sprinkler system, which leaves tire marks. Do not confuse these tire marks with those made by spraying equipment. i44
Figure 26. Watch for tireorsi
! marks when searching for irrigation
Fuel Tanks and Oil Cans. If fuel tanks or olcn r
evident in a field, assign the parcel of land a farm number and check the plat book for the landowner's name. If you cannot find the owner's name, return to the site
several times during the next few weeks to find someone at .... jthe site.
hi oW W
* hi ~
~ Mg a' O CD
O What to Do After Locating An Irrigation System
Getting your Bearings
When an irrigation system its found, mark the location on a map using a farm number. Also mark the initials of the system on the map (for example, mark
"TG" for traveling gun").
Analyze the system and interview the farmer. If the farmer cannot be located
at the time, find his name on a mailbox from a neighbor or the plat book.
Fiue31 oae h wero ht.rgtonsse
Itisimoran t etrmnewh on te .rlgt onsstmbeaue4h
owne ofthesysem illnotalwas b th sae idivdua tht ws h
lad.Ocainal a adwe il es u i paclt- are h a
Interviewing the Farmer
No matter what sampling method is used, the basic interview techniques will be the same. Before beginning the interview, introduce yourself and your agency. The farmer will need to know the purpose of the interview. Stress that his responses to the questions will be kept confidential. Explain the purpose of the inventory and ask the "owner information"' questions discussed in Chapter II. Ask any opinion questions included on the inventory form. A cooperative farmer may allow his equipment to be examined, eliminating the need to ask a large number of questions during the interview.
Information collected out in the field will have to be analyzed in the office. If the basic equipment is available and the correct procedures are followed, the analysis can be relatively simple.
Information to Collect While Interviewing the Farmer
Information obtained from the interview will be more accurate if the equipment is actually seen. Be sure to have information on the following.
1. Kinds of crops planted.
2. Amount of irrigated acreage.
3. Amount of water applied to the crop by individual applications
and/or season (in inches).
4. Irrigation period (April, Nay, June, etc.).
5. Number of irrigation systems.
6. Nozzle size of sprinkler unit.
7. Nozzle pressure in pounds per square inch (psi).
8. Travel speed of system.
9. Installation date.*
10. Types of power used for operating the irrigation system (lp, gas,
*Note: For example, a farmer has a traveling gun which uses a well as
its water source. The complete system (well and traveling gun) was installed in 1974. Indicate "1974" as the installation date.
A farmer installed a pump in 1972, bought one traveling gun in 1972 and
another in 1974. In addition, both systems use the same pump. A form should
be completed for both of the traveling guns, indicating the installation date for each. The information about the pump will be the same for both systems and should only be completed on the first form. On the second form (for the second traveling gun), simply write "same as system number 1" under the pump information.
Occasionally there may be incorrect information on the inventory forms. Look up the owner' s address and telephone number in the city directory or telephone book, to verify whether the information is accurate. In addition,
it is important to check the farm numbers to see that none have been used
more tharoe Makesur tha unfr frm ltter an nubr arued
Onsite Analysis of the Irrigation Systems
It is important to learn to gather information about the irrigation
system while at the site, so that return visits are kept to a minimum. The owner can be interviewed later if he is not present during the initial visit.
Figure 32. The initial serial Figure 33. The pumping pressure in
numbers are needed for determi- pounds per square inch (psi) can be
ning the capacity of the system read from the pressure gauge if the
(see Chapter V). Locate the system is operating. This reading
serial numbers on the base of is often needed to determine the
the pump housing, capacity of the system (see
Figure 36. The water source (whether ground water or
surface water) is often important informati-on for
Figure 37 Identify the pump Figure 38 and the irrigation
manufacturer (the identifiea- system manufacturer (identitln ms rlocae nn the npump fication plates are attached
. % r, ..I 1
~Sequence Diagram for
Select Geographic Area Site Selection
Examine aerial photos and
maps to eliminate nonirrigated areas
I Assign farm number.
t Mark number on map
Locate Irrigation Systems and inventory form
SFarmer present. Farmer absent.
Conduct interview Collect all possible
and complete inven- system information
Officetory form Data Computer ________Check Ask
plat book neighbors,
fom located _____
Stratified random sampling can greatly reduce the cost of data
collection and maintain reliable estimates of water use. Stratified random sampling techniques provide precise water use estimates when time, budget and available equipment are too limited to permit analyzing each and every water user. SRWMD selected 100 of 600 irrigating farms in the district for its sample. With the careful use of stratified random sampling, it is possible to obtain reliable water-use estimates from samples of 50 to 200 farms, depending on what level of accuracy is needed.
Sampling saves time and money. In addition, having fewer farms in the
sample may permit more accurate data collection from each farm. For example costly equipment such as time and flow meters can be installed. Water use data can be collected for each system on a farm rather than combining farm water use as a whole. Processing a smaller set of data not only takes less time, but can be accomplished with fewer errors.
Figure 41 and the accompanying tables illustrate the techniques and principles of stratified random sampling.
Simple Random Sampling
Assume you must estimate the total water used by the four farms in
figure 41's example district, but you can only monitor two. Two farms can be sampled at random from the four in the example district and the average of the po~ible estimates will be the actual amount of water applied (see Table 1). This is always true of simple random sampling. But if you know: (a) which farm grows corn and (b) that corn may require far more water than tobacco, the reliability of the total water-use estimate (see tables 2 thrnugh 4) will be increased by "stratifying".-
(U TOBACCO CROP
Farm 1 11 MgaI water pumped
19 MgaI water pumped
3 MgaI water pumped Farm 3
I CORN CROP
38 MgaI water pumped
Table 1.-Random sampling in the example district
* Two farms are selected at random from the four.
(estimate of total district water use) = 4 x (average water use in sample)
All equally likely samples of 2 farms
Estimate of district Error
Farms in sample water use (Mgal) (Mgal)
1,2 4 x (19 + 11)/2 = 60 -11
1,3 4 x (19 + 38)/2 = 114 +43
1,4 4 x (19 + 3)/2 = 44 -27
2,3 4 x (11 + 38)12 = 98 +27
2,4 4 x (11 + 3)/2 = 28 -43
3,4 4 x (38 + 3)/2 = 11 +i1
Stratified Random Sampling
"Stratifying" means separating the farms with similar water-use
characteristics into groups (strata). In the following examples, one stratum
contains the tobacco farms. The other contains only the corn farm.
If two farms are selected for the stratified samples, the one corn farm
is chosen deliberately (see Table.2), and one of the three tobacco farms is
chosen at random. The water applied by the tobacco farm is assumed to be
O typical of all three tobacco farms in the district. The stratified random
sample always includes the one farm in the corn stratum. In general, when some strata contain considerably higher volume water users, it is advisable to sample these strata more intensively, sometimes sampling all the members.
As a rule, there is more variability in water use in a stratum with high water users, and it takes a larger sample to produce a reliable estimate.
Also, some very large users may account for a large proportion of total water
use. In the example district, the one corn farm applied more than half the
total irrigation water. Including such farms in the sample increases the
reliability of the overall water-use estimates.
Table 2.--Stratified random sampling in the example district
The four farms are stratified by crop type. The one farm in the corn
stratum is randomly selected for the sample, and one of the three farms in
the tobacco stratum is randomly selected.
(Estimate of total district water use) =
(Water use on corn farm) + 3 x (water use on sample tobacco farm)
Stratification divides the population into internally similar groups.
The greater the internal similarity of a group, the smaller the sample needed to adequately characterize water use for the group. The greater the similarity within groups and dissimilarity between them, the more stratified random sampling increases the reliability of the water use estimates.
Stratified Nonrandom Sampling
In the final example (see Table 3), a field worker chooses to select the sample farm from the tobacco stratum closest to the main road rather than randomly selecting one of the three tobacco farms. Unfortunately, in this example district, high water users tend to live closer to main roads. The field worker's nonrandom selection procedure guaranteed a high bias in estimating total water applied in the example district. Such correlations between water use and arbitrary selection criteria are common. Random sampling within strata (except as in the corn stratum, where all members are selected) protects against this kind of bias.
Table 3. --Stratified nonrandom sampling in the example district
Stratified nonrandom sampling is similar to stratified random sampling, but instead of selecting the sample tobacco farm randomly, the tobacco farm closest to the main road is chosen. Note that there is only one possible sample, and the overall water-use estimate is 24 Mgal high.
Farms in Estimate of district Error
sample water use (Mgal) (Mgal)
1,3 38 +3 x19 =95 +24
When to Use Stratified Random Sampling
Stratified random sampling can increase the reliability of estimates
based on sample "en"(see figure 42). The technique is used when there
are known groups with particular water-use habits (corn or tobacco growers, for example). Stratified random sampling works well when certain groups use much more water per member than others (very large farms, for example).
Stratified random sampling can also be used to make water-use estimates for special groups. For example you may need to estimate water use for irrigation by peanut farmers. Grouping peanut farmers into a stratum insure the inclusion of some of the farmers in the overall sample.
Another reason for stratifying is if some farms are more expensive to sample, you may want to place these farms in a separate stratum. Sampling less intensively in this stratum may greatly reduce costs, but will reduce the reliability of the water-use estimate for this group.
Table 4.--Comparison of the 3 sampling methods in the example district
Average error Average absolute
Method (Mgal) error (Mgal)
Simple random 0 20
Stratified random 0 16
Stratified nonrandom 24 24
~ A64r~c~4 ~ &a~rrftS
~ (su~wo-( taeo.4tr ~ ~ ~ ~ In
14t(so.n~pia rr~e&n) 4ts44n~oAe of icAcd wo&tV wsc tt~ or
Figure 40. Total water-use estimates based on sample means
* Planning a Stratified Random Sample Study
Planning and carrying out a stratified random sampling study i. Determine objectives.2. Decide what to sample and make up lists.
3. Design the inventory form.
5. Decide on sample sizes.
6. Sample allocation.
7. Examine the sampling strategy.
8. Select the sample.
9. Design a public relations bulletin 10. Collect the data.
11. Make estimates.
O Determine Objectives
If estimates of total district water use are desired, sample heavily among large users, lightly among small users. If estimates of average use
among small users are desired, reverse this sample allocation. That is,
sample heavily among small users; lightly among the large users. If
estimates of water used to irrigate okra are desired, make sure okra growers are included in the sample. No one sampling strategy can satisfy all needs,
and there often must be compromise.
Decide What to Sample, and Make Up Lists
The SRWMD samples farms and and monitors all irrigation systems on each farm in the sample. Since SRWMD organizes its inventory data by farm, this method was best. Other agencies might sample systems, entire counties, or
Whatever units are chosen, compile a complete list of the units from which to draw a random sample. The SRWMD chose its sample from the basic
inventory of farms, described in Chapter III.
O Stratifying entails classifying farms into groups with similar water-use
patterns and sampling from each group. The example opening this chapter showed how this can increase the reliability of water-use estimates from
samples. Farms can be classified in many different ways, depending on the
objectives of the study and the required information. Usually information on
several factors thaL relate to a farm's water use is available. This may
include geographic locations, water use in previous years (if a basic
inventory like SRWMD's is compiled), acreage, types of crop, and types of
irrigation system. Any or all of these factors can be used to stratify farms
into groups with roughly similar water use levels.
When estimating total water use, much of the gain from stratifying
comes from selecting extremely high-volume users for special attention in the
sampling effort. The SRWMD basic inventory showed that 33 percent of 1977
irrigation water was applied by only 20 farms through 5 percent of the
district's irrigation systems. These farms were all sampled in 1979 (figure
43). Large users can be identified by means other than basic inventories.
In some areas large water users may have the most acreage or may be
identified by personnel who are familiar with the region.
If several factors can be used to stratify, it may be desirable to
compromise between using those factors with the strongest influence on water
use and those that can be checked and updated for future sampling studies.
The type of the principal irrigation system on each farm at the SRWMD, center
pivot, traveling gun, hand-moved sprinkler, etc., proved from the basic
O inventory to have a stronger relation to past water use than factors such as
acreage or geographic location. Irrigation system information can be
verified and updated through equipment dealers and field checks.
The SRWND stratified farms into three classes based on principal system
types, center pivot, traveling gun, and "other" This illustrates another
rule of thumb for effective stratification course divisions on a factor
achieve most of the gains for stratification. The SRWMD could have created
at least nine classes of farms based on district system types, but used only
Of course, more than one factor can be used to stratify. Redundant
factors should not be used. If one county uses mostly center pivot systems,
and another mostly traveling guns, stratifying by either county or system
type is equally effective. Stratifying by both types is superfluous.
The SRWMD used both system type and principal crop for stratifying.
Figures 44 and 45 show how effectively these divisions separated the
district's tobacco and watermelon growers into similar water-use groups. The figure indicates that this stratification was worthwhile. SRWMD attempted to
stratify using several other sets of factors, but the combination of system
tvne and nrincinal crone seemed the best choice based on 1977 water use. A
Top 201977 irrIgators Top 20 1977 Irrigators
make up 20% of the (3%) applIed 33% of
1979 sample 1977 Irrigation water
40- E I
- 0) 0 6.
C C 4"
E E N
6. 6. N
CU (U a)
U.. LL. r
= Celn 0u ytm
0:jte 8 Jsytm
Fiue4.Patwtrue ytbcoan aemlo rwr0ndctdta th RMDsol srtf b ytmntb cut. (Telrercne pio ytesaesedmuedo hsecos
0-40 by any'
"-" farm in'
E stratu m
Li..--.p rf r
4-0-- 0 id l
C 50% o
Figre43.Coparso ofirigaio water use tbcoadwtreo+am
usln tOthern sysesan other systems Trsiniavelin guns sTravlcainun
* Decide on Sample Sizes
Usually, budget or equipment limitations determine the total sample size
for a water-use study. Different strata in this sample can be divided in
many ways. Sampling the same proportion of users from each stratum
guarantees that the sample will be a close miniature replica of the overall
population. More reliable estimates can often be obtained by sampling higher
proportions of users from strata where water use is variable. These strata
generally contain large users.
Included in sampling textbooks are precise formulas for allocating samples. This can be accomplished with practice by sampling in proportion to the total expected use in a stratum. In fact, all that is needed to estimate
is how much more water the farms in one stratum will use than the farms in
another stratum, not how much (such as 1000 Mgal?) each will use.
Example: Sample sizes for some SRWMD Strata
The SRWMD basic inventory showed that among traveling gun users, the 46 watermelon growers used together the same amount of water in
1977 as the 94 tobacco farmers. A good rule of thumb would be to
sample the same number of farms in each group for 1979. The SRWMD
used a formula from a sampling textbook based on water-use variability
in each group. This formula indicated samples sizes of 13 for tobacco farms
and 16 for watermelon farms.
Designing a Public Relations Bulletin
It is helpful to design a public relations bulletin for the stratified random sample study, similar to the bulletin described in Chapter I. The pamphlet should explain the random sample and the general functions of the agency. The bulletin can be designed for indefinite use. The public relations bulletin used in the basic study referred to a particular sampling project and was essential to the success of the inventory. However, the public relations bulletin for the random sample can be more general and should only deal with the random sample.
Designing a Letter to the Farmers
Before beginning the random sample study, write a letter to the
farmers in the area included in the sample: The letter
should contain four main components.
1. A brief description of the random sample technique.
2. Notification to farmers that they are randomly selected from the
file and that their cooperation is strictly voluntary.
3. An explanation of the equipment used for the study and
what the equipment measures.
4. An explanation of the information needed from the farmers.
* Examining the Sampling Strategy
An infinite number of stratifications and sample allocations can be devised in any water use study. Choosing among them requires judgments by
all who will use or collect the water-use data. A good practice is to
construct two or three sensible sample designs and discuss their pros and
cons among all people concerned before the field work begins.
Selecting the Sample
Randomly select the farms in each stratum by assigning a random number to each farm on the list. Use published random number tables or random
number-generating computer programs. Take the farms in each stratum with the lowest random numbers until reaching the predetermined size for each stratum.
Replacement farms for those who refuse to cooperate with field personnel can
be selected in similar fashion.
If the list of farms is in random order with respect to water use for example, using the farmer's middle initials a systematic sample serves
well. That is, if you want to sample 20 percent of the farms in one stratum,
choose every fifth farm on the list. Even if the farms are ordered by
categories such as acreage, a systematic sample will usually work and may be
easier to select than a strictly random one.
The important thing to remember is to prevent field personnel or supervisors from constructing their own subjective or arbitrary selection
Methods. The example at the beginning ofthis chapter ilsrtsthe
dangers of such an approach.
Collect the Data
Make a list of farms refusing to participate. After the study, check to see whether the uncooperative farms are from a particular group in each
stratum the largest farms, for example. This would make the sample nonrandom.
Efforts should be made to collect data for every farm in the original sample. However, randomly selected alternative farms should be available, so
that non-cooperation by farmers does not deter field work.
To estimate total water use in a stratum, the "expansion estimate"* is usually used (see figure 42):
Nx (sample mean) = total use estimate.
O "Miscellaneous" Classes
Finally, it is often necessary to have a "miscellaneous" class for farms that will probably not contribute much to total water use. In other words,
water use on these farms is relatively insignificant. Farms within the
"miscellaneous" class will usually differ in their water-use habits; farms in the other classes should have similar water-use habitats. Estimates of water
use within the miscellaneous class will be imprecise. Make sure that large
and important water users are not included in the miscellaneous category.
Then even if the water use estimate is imprecise, it will have little effect
on the overall water use estimates for the region.
DETERMINING APPLICATION RATES
An important part of the irrigation analysis is determining the amount of water applied to the crops. The amount is calculated by determining the length of time farmers irrigate, and by calculating the normal operating capacity of the irrigation systems (average flow rates at which the system operated).
There are three primary ways to measure time; intrinsic (involving a
permanent component of the power unit), and extrinsic (involving the use of a vibration timer), or by getting the farmers estimate of operating time.
The type of power unit the farmer uses to operate his pump must be determined for the intrinsic method. The unit is either an internalcombustion engine (powered by diesel, gasoline, or Lp fuel), or an electric motor.
1. Electric. If the unit is electric, determine the operating time by reading the kilowatt hour meter that monitors the electrical energy consumption, which is attached to a nearby utility pole. Using this method is accurate, if the kilowatt meter measures electricity used only by the irrigation system. However, if a circuit breaker or junction box with electric outlets is nearby, it is necessary to determine whether the meter is also measuring usage by additional equipment. If this is the case, the meter will give inaccurate readings since it will include the power used by the
Read and record the kilowatt hours shown on the dials. Return to the farm at the end of the cropping season and read the kilowatt hours. Directions for calculating time of operation are presented on the following page. A picture of a kilowatt meter identifying various parts is below.
Observe for a few minutes the dial that moves the fastest, that dial should be the last dial read.
-~ ~ ----' .ta~~Ja~~k la .,.t
a-,.- .,: N
Calculations for time of operation of well pumps
Definitions of Terms
Scale factor = A multiplication factor Site ID ________________for the meter reading. Well No. 05J3 21/1
Kh = Conversion factor; printed on face Owner ______________________of meter.
Pole Number __ __ __ __ ___!Rev = Revolutions of meter disc.
Meter Number Cce-- J 24g,7oK Tsec = Time in seconds.
Account Number ____________KWhr = Kilowatt hours; computed from
meter readings. Power Company Ftc 44 /ZL> cS'2
KWi = Instantaneous kilowatt demand. Date __/_______ Irr. System Typec'irt'v'
TO = Computed time of pump operation; Measurements By y!d -J
HPd = Computed horsepower demand. HPr = Rated horsepower of pump motor.
Procedures Dial Reading Scale Reading
1. Multiply beginning and present dial i. Present-'37V /6> = //c
readings by Scale Factor printed on B .ginin.72 6. 7
meter face, if necessary, to get a
correct meter reading. 2.Kh it2
2. Subtract beginning meter reading from
present meter reading to get KWhr. 3. Kh =/VY
3. Record Kh factor from meter face. 4. Rev =/
4. Time meter disc for at least 10 Tsec = 33 O
revolutions; and then record time
and number of revolutions.
5. Compute KWi using the formula:Ki=/// = 7Rev Kh 3.6 ,
KWi = Tsec 6. TO = 4-__/ = '-6. Compute TO using the formula: /7o3
TO=KWhr 7 HPd = /73 x /,S = 2
TO =KWi_ __
7. Compute HPd using the formula. 8.% = 9-3.' *1i00 = 2-3
* 2. Diesel or Liquid propane.
If the unit operates on diesel or Lp power, determine whether there is
an hour meter located on the unit.
Gauges that record water temperature, oil pressure, and revolutions per
minute are often included on the plate. In most instances there will be
an "hours" meter that records the length of time the system is in operation
by hours and tenths. Before using the meter, try to determine whether it
is operating correctly. Record the hours from the meter at the beginning and
end of the cropping season.
Figure 47. The hour meter is found within the tachometer in the center of the picture
1. Timer (vibration timer)
If the previous methods mentioned are not available or if consistency from one system to the next is important in the study, use an external timing
device. A timer (vibration timer) has been developed for this purpose. It
Is deige to moio vitions andreor thrnnn tim of equpmnt
At the end of the irrigation season, the timer is placed on a read-out"t machine which will calculate the hours the system operated. SNR
The timer should be mounted at a l.
point on the power unit where NUMBER OT
there is sufficient vibrationto activate the timer. ISALDA vibration meter is used toREOD determine the best location for the timer. The system should be in operation while the vibration meter is in use. Determine which part of the pumping unit will vibrate sufficiently to activate the timer. Avoid placing the timer in locations that are sub- Figure 48. A timer can be used to
ject to climatic extremes. measure the amount of time the
system is in operation
figure 50. Mother type of vibration sensing meter
Design specifications will vary according to the types of timers used.
Distinctive specifications are included with the timers.
Use epoxy putty on the mounting bracket and attach it to the selected
site. Indicate the date and time installed on the front of the timing
device. Then, slip the timer in the mounting bracket.
Some locations to consider when deciding where to place the timer are:
., Figure 53
~The motor or
" discharge pipe,
Vibration Timer Service Log
The Vibration Timer Service Log is used when installing, checking and removing the timers. Information on the log includes. Manufacturers Date: Indicate the month and year the timer was manufactured. This information is important because timers have limited battery lives, and the timers should not be allowed to run down in the field. Serial Number: Indicate the serial number of the timer. Installation: Indicate the date and time the timer is installed.
VIBRATION TIMER SERVICE LOG 1 52
Manf. Date Serial No.
Date: ______ Date.:_____INSTALLED REMOVED
Time: ____ AM PM Time. AM PM
Cant.:_______Pos.:_____OPER. MODE MOUNTING
Inter.:______Dispi.:.___SERVICE TIME: hrs. (est.) READOUT TINE: hrs.
Figure 56. Vibration timer service log
Operating Node: Check to see whether the pump operates continuously or if it is interrupted. Most of the pumps will probably be interrupted unless they are located in nurseries.
Service Time: Indicate the estimated time that the pump has operated during the irrigation period.
nRmoed: TnAicate rhe date anA time the tifmer is reoved.no
*Displacement: Indicate the amount of vibration that occurs at the site where the timer is mounted. The measurement will be in millimeters of deflection, and it is determined from the vibration meter. This measurement can act as a check for the timer at the end of the irrigation season and help identify faulty equipment.
Readout Time: Indicate the hours that the system was in operation. The hours are determined from the timer after it is brought back in the office and placed in a read-out" machine.
Service Location" Indicate the farm and the serial number of the pump in this space. Include the system number, if there is more than one system. Indicate the well number, if the system is on a large farm and the farmer has a well in several different sections.
Remarks: Problems encountered while servicing the timers can be noted in the "Remarks" section. Also, indicate where the timer is mounted--whether on the gearhead, pump, etc. Note the crop or crops that are being irrigated by the system. On the back of the card indicate whether the system is a diesel, Lp, electric or gasoline-powered unit. Record the operating hours from the "Hours" meter. Record the hours when the timer is first put on and again when the timer is removed. These hours should be compared to those read from the timer.
*In this manual "displacement" refers to the degree of vibration measured at the timer mounting site during normal pump operation.
* Procedure for Time Measurement
Internal CombustionElcrcRod Power Unit Unit Hours
Unit has no Unit has mmm,,., Calculate Hours
"Hours In operation' "Hours in operation Record
meter meter Hours
Prepare necessary 1Use vibration meter
equipment for m uno to select
attaching timer System appropriate site
Attach Fill In Timer
Mounting ,,, Attach Timer Log Card
Figure 56. Flow-chart on the methods to use for measuring time
Determining when to install the timer or other time measuring equipment
is based on factors such as the irrigation periods and the types of crops
An irrigation analysis can be based on irrigation periods.
i. Spin Iriaio eio.Tgta acurtewaerus nmbr all.
2. Summer Irrigation Period. It will be necessary to remove the timers from those farms which are planting a summer crop, and replace them with fresh timers. This chore should be done between the spring and summer periods. A new timer can be used or the original one cleared and used again. In many instances it maybe difficult to determine when the spring irrigation period ends and the summer irrigation period begins. Ability to determine the difference depends on the type of irrigation system and the kinds of crops the farmer grows.
3. Winter Irrigation Period. If there is a winter irrigation period,
switch the timers in October or November and leave these last timers on until the following spring.
Example: Farmer #1 grows tobacco and peanuts and uses a traveling gun system. He will still be irrigating the tobacco at the same time he begins to irrigate the peanuts. There will not be an interlude when the timers can be changed. However, Farmer #2 has a spring-crop of corn followed by soybeans in summer and rye in winter. Farmer #2 has a harvest period and also has to replant. In that 2 to 3 week interlude, the timers can be changed.
Timer retrieval for determining total water use should be based on the crops grown by the farmer. In the example above, the timers would be collected from Farmer #1 after the peanut harvest. However, to determine total water use for Farmer #2, the timers would not be collected until the end of the winter irrigation season.
To determine crop-specific water use, Farmer #2 timers will have to be
collected, analyzed in the office, and returned to the field betweeen crops. Farmer #1l's timers can be collected at the end of the spring irrigation season. At this time Farmer #I will have to be interviewed to determine how long the system was running on his summer crop. You can then put on a fresh timer and leave it on for the rest of the season. There may be inaccuracy due to the overlap in the latter part of the spring irrigation season. The problem occurs because Farmer #Il may not know the number of hours he irrigated his summer crop. In addition, he may not be cooperative.
After determining the amount of time a farmer irrigates during the
cropping season, the length of time the system operated can be analyzed. Enter the hours under "Hours System Operated" in the System section of the inventory form. After analyzing the system and calculating the maximum capacity, enter this capacity (in gallons per minute) under "Maximum Capacity"~ in the System section of the inventory form. The computer will analyze the data and calculate the total water use by irrigation system for the cropping season.
A Determining Normal Operating Capacity
Operating capacity is the flow rate at optimum pump speed. There are many methods for determining the capacity, some of which depend on the type
of system being analyzed. Invasive meters, noninvasive meters, framing square technique and system-specific methods will be discussed in this
Information Needed for Invasive and Noninvasive Flow Meters It is necessary to obtain certain information before installing invasive meters and measuring water flow using noninvasive meters including:
1. The pipe material (i.e., aluminium, pvc, or steel),
2. The outside diameter (O.D.) of the pipe, 3. The inside diameter (I.D.) of the pipe,
4. A rough idea of the rated capacity of the system in
* gallons per minute.
There is a special steel tape designed to measure the diameter of a pipe so that the O.D. can be calculated. However, the type of pipe and the
schedule (wall thickness of pipe) must be known.
* Pipe Schedule
The pipe schedule or class can found on the outer walls of the pipe,
(i.e., "schedule 180, schedule 160"). A sonic thickness gauge is also
available to measure the pipe wall. Perhaps the farmer can provide the
1. Tube Meters. There are several types of tube meters designed for irrigation or other types of low pressure service (up to 100 pounds per
square inch). The meters are installed so that a propeller mechanism inside
the pipe is in contact with flow of water. The meters can be installed by
cutting and welding into the main line irrigation pipe, drilling a hole,
inserting the propeller, and clamping the meter to the pipe externally. The
meters are calibrated at the factory at certain pipe 0.D.?s, I.D.'s or
thicknesses of the pipe material. The meter includes a totalizer with a
center sweep dial. The dial shows accurate readings for timing purposes in
determining flow rates. The totalizer records gallons, cubic feet, acre feet
or any other standard liquid measuring unit.
2. Open-flow meters. Open-flow meters are designed to give accurate timed
incremental flow readings of open canals and ditches. Installation is
relatively easy. The meters need to be attached to any vertical structure which allows the propeller to be in the center flow of the measuring area.
The open-flow meter has a sweep hand on the totalizer to give accurate
internal flow readings. The totalizer keeps track of the total gallons of
water that flow.
It should. besrssdta uigi-ln outdmtesaeexesv
an uualyrqurecopicte istlatonprcdues Uin hee etr
alorqme ra ea fcoerto rm-h amr
Figure 60. Sonic flowmeter
Sonic flowmeters measure the amount of water flowing through the pipe. There are two basic types of sonic meters (1) Doppler meters, and (2)
transient time meters.
Doppler meters have a transducer which is mounted externally on the irrigation pipe. A transmitting crystal sends a continuous ultrasonic pulse
into the water. When the transmitted frequency is reflected back to the
transducer from an air bubble or other particle, the frequency change will be
proportional to the velocity of the moving object (see figure 64). A
transmitter will measure the difference between the transmitted and reflected
freauencies and display this difference in feet per second on a flow rate
offlw Th ae rcs -srpae gis h lwdrcinh
difference between the two travel-imeispootonlt h li
-- - - - - - -- - - - - - -- - - - - - -- - - - - - -- - - - - - -- - - - - - -- - - - - - -- - - - - - -- - - - - --.
Framing Square Technique
The framing square technique is a method for taking flow measurements.
The diameter of the open discharge pipe must be known before the technique is used.
The gpm flow from pipes may be approximated by measuring the distance "X" in inche when the vertical distance is 12" (or 6", see note below table)
and find value in Table 15.
FOR PIPES FLOWING FULL
Horizontal Pipe Inclined Pipe
TABLE 15. GALLONS PER MINUTE
Dia. Horizontal Distance = "X
Pipe =.D 12" 14" 16"J 18" 20"L 22" 24" 26" 28" 30'
2" 41 48 55 61 68 75 82 89 96 102
3" 90 105 120 135 150 165 180 195 210 225
4" 150 18 27 32 25 284 310 336 361 387
6" 352 410 70_28 58 645 705 762 821 880
0"960 1120 1280 1440 1600 1760 1920 2080 2240 2400
_2_178 167 83 2032 2300 2521 2760 2980 3210 3430
APPROXIMATE FLOWS FROM PIPE RUNNING FULL IF 6" VERTICAL DISTANCE IS USED MULTIPLY GPM BY 1.4
FOR PIPES FLOWING PARTIALLY FULL
Flow from partially filled pipes. Divide 'E' by "D" for percent factor. Multiply flow for full pipe of 'D" diameter (Table 15) by factor obtained from Table 16. E Measure = l_ EASUE-"""of empty portion of pipe. D -Measure of inside
- diameter of full pipe.
- -Qx -__- _- TABLE 16
E ED Factor E D Factor
\\\X \N i0 0.95 50 0.50
\\ ~20 0.86 60 0.38
System Specific Method
O The following techniques are based on the "system"~ section of the
inventory form. Please refer to that section when necessary.
1. Rand-moved systems
Information needed for the analysis of water use by hand-moved systems include the following:
(a) Style of system--Indicate whether the system is a hand-moved portable
set, a hand-moved solid set, etc.
(b) Manufacturer--Indicate the name of the manufacturer of the system.
(c) Number of sprinklers in operation--This information is unique to
(d) Nozzle diameter (in inches)--Obtain this information from a sprinkler
specifications book, from actual observation or from interviewing the farmer.
(e) Nozzle pressure (in pounds per square inch)--Obtain this information by
interviewing the farmer or by viewing the system in operation.
Find the performance chart for the specific system in question. Based
on the nozzle size and the nozzle pressure, the performance chart for the
O system will indicate the capacity of the system in gallons per minute (gpm).
Figure 63. Identifying the
number of sprinklers in
operation is important
* 2. Single-sprinkler or multi-sprinkler self-propelled systems
Information needed for system analysis of single-sprinkler or self-propelled systems includes the following.
(a) Style--The style of the system.
(b) Manufacturer--The manufacturer of the system.
(c) Nozzle diameter--This can be obtained from a specification book,
interviewing the farmer, or from actual observation in the field.
(d) Nozzle pressure--This can be obtained from interviewing the farmer or from viewing the system ~in operation.
(e) Travel speed (in feet per minute) (indicate for traveling
guns only)--Information on travel speed can be supplied by the farmer. It can also be determined ~by measuring 12 inches of land near
the system and observing the length of time it takes for the gun to O move the 12 inches. Mother wyto
determine travel speed is to ask the farmer how many hours it takes for his traveling gun to complete a 1/4 mile run. Then the travel speed can be calculated from his Figure 64. A traveling gun system answer (see illustration below).
In order to determine the maximum capacity of the system, simply look up the nozzle size and nozzle pressure on the performance chart for the
If a farmer said it took 8 hours for his traveling gun to make a 1/4 mile run, then:
8 hours/l/4 mile run x 60 mmn/hour = 480 min/i/4 mile run
* 3. Center Pivot Systems
Center pivot manufacturers design center pivots with differing nozzle sizes along the laterals that produce certain discharges at certain
pressures. Therefore, on a center pivot system, determine only the model number, the nozzle pressure and the travel speed of the system. The model
number can be found by looking it up in the operator' s handbook and finding
the number on the system in the field.
The manufacturers' book will give the gallons per minute capacity of the center pivot system at a certain number of pounds per square inch. The
farmer will have to indicate the travel speed of his center pivot system.
Which Method is Best?
Decide which method for determining the irrigation capacity will be most suitable for your area. Initial capital expenditures for the "framing
square" and "system specific techniques"* are lower, but the two methods
require a great deal of cooperation from the farmer and more field
technicians than if the noninvasive devices are used.
Farmers in some areas frequently use open discharge systems. Sonic
meters will not work well in those regions. Make sure to tailor the methods
used to the irrigation systems and the money available.
O Again, remember to indicate the maximum capacity and the time on the
inventory form. The computer will then determine the total water withdrawn.
In Chapter VI methods for determining the amount of water returned to the
source are discussed.
Calculating the Acreage Irrigated Per Day
SRWMD calculated the "acreage irrigated per dayt by different systems in the District. Calculating the irrigated acreage is optional, but the method is presented here:
VOLUME GUN MODEL 550
Use a performance chart, 01W
as in Figure- 65, to 0) CD W Q WO
calculate irrigated acreage. N= <
Performance charts for 0 "4'H 0 1-4 .= H
specific irrigation systems
can be obtained from manu- 70 188 300 1.62 .256
facturer' s irrigation system 1" 75 195 308 1.71 .251
manuals. Estimate the normal 80 202 314 1.77 .250.
length of an irrigating day 85 208 324 1.89 .242
in the area to calculate the average number of inches of7025281926 water the farmer is trying to1-1/8" 80 253 346 2.15 .259
apply to his crops every time802346.125 he irrigates. These facts 85 260 354 2.26 .253
will depend on soil types and region of the country. For702532.223 example, if the farmer 1-1/4" 75 297 360 2.34 .280
operates a system that applies803872.427 500 gallons per minute, 85 317 380 2.60 .269
covers 3.03 acres and puts
down approximately 1/3 inch 70 355 366 2.41 .326
(.365) of water an hour. 1-3/8" 75 368 380 2.60 .313
The farmer will need to 80 380 390 2.74 .306
irrigate 3 hours to apply 1 85 392 400 2.88 .301
inch to 3 acres. If the
normal irrigation period is 70 425 390 2.74 .343
12 hours, the farmer will 1-1/2" 80 455 412 3.068.329
irrigate 12 acres per day with8045123632 this system if he wants to 85 470 420 3.18 .327
apply 1 inch to his crops.
70 500 410 3.03 .365
1-/"75 518 420 3.18 .360
1-/"80 532 432 3.36 .350
85 550 440 3.49 .348
1-3/4" 85 650 460 3.81 .377
* 9 9
9 49 9 *9 :9 *9 9
99 09 .*9 :99 *99 9,
* 9 S a ~9 I
S S S '.9 S. 9
- :9 99 S S
* 3 *9
S. ** 99'
9*. '*9 5* 9
9* S - 9,
.9 -S *9 9
I S '9t S 9 9 '*9 *
:9 9 5* 1
. 99 *
* 9 9
* S *
* S 9, 9 .9.
* S. I 99
* 9~ 9. .9*! 9*.
* 0* 9 A a I a 0 4 S aS
a 0 S 0 a a a S I a S S
n a 0 0
S I- II .s~ -. 0 0b S S 0 a a 0 3 4 a a
- a B~~@ 0 -ml a II,- a *a -* I- 0 I~ 4.
ESTIMATION OF IRRIGATION
WATER RETURNED TO THE AQUIFER
The previous chapter described how to determine the operating capacity of an irrigation system and how to calculate the total amount of water applied to crops through irrigation. This chapter will describe how to use the applied water use information determined in Chapter V for calculating the percentage of water returned to the system.
.. Not all of the water applied by irrigation is used by the crop.. "Consumption" is the amount of water lost through wind drift and evaporation in addition to the amount of water used by the crop. After the amount of water consumed is determined, the remaining water returns to the ground or surface water source, such as a lake or an aquifer. This water is known as irrigation return water.
Water returns to the source in several ways; through surface runoff
into nearby lakes, ponds or streams from which it was pumped or through deep soil percolation to recharge an underground aquifer. To determine how much water is recharged, first calculate how much water is consumed and subtract this amount from the amount of water applied to the crop. Therefore, the percent evaporation loss of the irrigation systems, the crop water demands (evapotranspiration), and the amount of water applied (determined in Chapter V) should be calculated. This will reveal the amount of water consumed.
This chapter will describe the Frost and Schwalen nomograph and its use in calculating evaporation loss. Estimating recharge water from this data will also be discussed. Later in the chapter, there is a section on the use of meterological data for estimating crops demands. The data is collected at weather stations.
Q ThE NOMOGRAPH
A nomograph can be used to analyze the several factors that contribute
to evaporation loss from irrigation systems. A suitable nomograph used for
this purpose was developed by K. R. Frost and H. C. Schwalen (in Sprinkler
Irrigation, page 133). The amount of water lost depends on specific weather
conditions, temperature, wind movement, water droplet size, sprinkler size, and system operating pressure. The more water lost from a system, the less
efficient the system is. Therefore, system efficiency increases with
increases in nozzle diameter and humidity, and during times of low
temperature and low wind speed.2
2McCulloch, Allan W., and Schrunk, John F., 1975, Sprinkler Irrigation,
(Third Edition): Maryland, Sprinkler Irrigation Association, 675 p.
Moisture loss by:
Moisture gain by Evapotranspiration
by irrigation.- .--
--- -soil-moisture belt ": J '
Components of a Nomograph
The percent evaporation loss is determined from a nomograph, its use is
discussed later. The data required to estimate percent water loss on any
given day are (1) percent relative humidity, (2) air temperature, (3) wind
velocity, (4) nozzle diameter, and (5) nozzle pressure. The additional
variables on the nomograph are calculated from this basic data. The two
pivot lines (pivot A and pivot B) are added as a calculation aid.
'cc 4 10
oi -t '40 +
ot~ 2 $11
01 ~ 0- il
-4- Ala AD 0 .5
t -, 40 i.IO
4, p 0
S oG C
04-4- t SSO IC
on V L 4 7
-% \oO 5 L4~ Ito
70 03" 0-~ II 'S
1% AM 3% 25
1,0 -r t ~ .29
9) 4*3 0. I)
ci N 3
0 0 30 -o
0- ado ni a
05 N C
2o -~ -# a
00 10 0
Figure 68 The nomograph
A brief description of the basic data required to estimate percent
* water loss follows:
1. Percent Relative Humidity. Relative humidity is the amount of
moisture contained in the atmosphere relative to the potential water holding capacity at that temperature. The water holding capacity of air increases as
the temperature increases.
For example, the air temperature may be 560 Fahrenheit (F), and the
relative humidity may be 79%. If the air temperature increased to
700F then the water holding capacity of the air would increase and the
relative humidity would decrease to about 50%. Estimate what the average
relative humidity will be for the region in any given day, during the period
in which the majority of irrigation takes place.
air temper-at~re 8
, I 45
Fiuea9 eaiehmdt ste muto osuecnandi h
atopeerlaiet h ptnilwte odn apct tta
temperature_2. Ai8eprtr (ndgesFhrnet.Etmaetenra
tmeaueta ocusdrn th rwnperid rirrgtonprod _h
3. Wind Velocity (in miles per hour). Estimate the average wind
* velocity of the region during the irrigation season.
Beaufort Class Observable Velocity in Equivalents
Nube o eaursmi/hr., in kilometers
Wind f etue 2O ft above prhu
Wind ~ground prhu
0 Calm Smoke rises vertically Less than!I Less than 1.6
Moderate Raises dust 8a loose
SBreeze paper, small branches 13 to 18 20.9 to29.O
7 Moderate Whole trees in motion,
gale incovenience felt in 32to 38 51.9 to6IJ1
walkin9 a ~ainst wind.
Figure 70. There are numerous ways to determine wind velocity
4. Nozzle Pressure (in pounds per square 5. Nozzle Diameter
inch, psi). This is the operating pressure (in inches). This is
of the sprinkler during irrigation the diameter of the
*sprinkler nozzle orifice
e Use of the Nomograph for Calculating Percent Evaporation Loss
A. Determining Vapor Pressure Deficit
9Draw a line connecting the Estimated "percent relative C humidity" with the estimated "air
" temperature". For example, the
90 estimated relative humidity is 10%
9_ and the air temperature is 90F.
4/ 4 5 Draw a line to intersect these two
80 points. The extension of this
"z 70 straight line reveals the vapor.
907- 3 pressure deficit to be 6.25 lb/in2.
"u 0 B. Estimate Nozzle Diameter
10After determining the vapor
--- ,_- 12-. pres sure deficit, estimate the
- 6 14nozzle diameter of the sprinkler
-4 0 16 heads in use. In this example the
.C diameter is 12/64 of an inch. Note
-- 20 the nozzle diameter on the scale,
3.,then draw a line to connect the 24- vapor pressure deficit with the
C nozzle diameter. Nnote where this
sC. Determine wind velocity
70~ 13 Next, find the wind velocity
11line and place a point on the
90 appropriate wind velocity. In this
8I example the wind is 5 miles per
50 7.c hour. Next, indicate the
6.0 appropriate nozzle pressure on the
6o.nozzle pressure line. .Then, 40- ------- connect the wind velocity on nozzle
354E pressure. Note where the line crosses
35 C pivot B.
50 -0 1>.rtonos
"30 7 D eezePretEao
0 lie iteriect P ercent o
70 i __ evpration ls le ntl
Ath atsher pon onpot B.ure ti
COMPLETED NOMOGRAPH INDICATING EVAPORATION LOSS
c m 0i
0. 2. 8* 'C 0z
a 0 '3
* w -' -'
* o~ /
57 C 0 /
* 0~- 09
(4 4, W 0 0
as' S 0z 08 S
r 2. *0 C
o 09 91 / 5
C 01 K
II 09 0? ___ '3 90
LI 02 0 01 (a 20
SI W 08 60
98 8 01 00!
B. Calculating Sprinkler System Efficiency Loss
To determine the efficiency loss for a particular system, multiply the percent
evaporation loss (from the nomograph), by the operating capacity, using methods
from Chapter V.
For example, if the maximum capacity for a hand-moved system Is 470 gallons
per minute, and the percent evaporation loss is 9.0%, multiply 9.0 by 470 for the
efficiency loss (in this case, 42.3 gallons per minute).
C. Tabulating Efficiencies of Various Systems
In order to evaluate the efficiency of different sprinkler systems,
develop a table where the climatic variables are held constant and only the nozzle pressure and nozzle diameter vary. Choose any "representative" relative humidity and air temperature to determine the "representative"~ vapor pressure deficit. Also choose a representative wind speed for the calculations. Using these measurements, vary the nozzle diameter and nozzle pressure to represent all the systems in use in your area. The table can be developed from the data.
Table 5.--Evaporation and Wind Drift Losses
1/2 inch nozzle 60 psi = 5.2% 70 psi = 6.0%
80 psi 7.1%
center pivot, average losses 1000 gpm 60 psi = 12% 70 psi = 14%
80 psi = 16%
1 inch nozzle traveling gun 60 psi = 2.6% 70 psi = 2.8%
80 psi = 3.2%
* Weather Stations
As mentioned, crop water demands are determined by using the data
collected at weather stations. Therefore, various components of weather stations will be discussed. Adverse weather conditions (such as drought) are the most important factors in the farmers decision to buy irrigation systems. Weather conditions determine when farmers irrigate and how much they irrigate. Therefore, weather conditions should be monitored and any
fluctuations should be noted.
Figure 72. Weather station
Installing Weather Stations
The best time for setting up weather stations is prior to the spring
planting, in winter or early spring. In some areas, one station for the
L = 1 1 1 l L 1 1 1
Collecting Information at Weather Stations
* The following are examples of factors that can be monitored at weather
stations and equipment that can be used. The information and equipment may
vary, depending on regional needs. Weather stations at the SRWI4D are
serviced once a week.
1. Radiation Data. A radiometer is
used to measure total radiation, both
direct and reflected. Radiation data
is important in determining soil
moisture, humidity, and evapotranspiration.
Evaporation -When water from "moist" i
surfaces is absorbed into the
atmosphere asavapor. :
Transpiration When a plant gives up
moistur through it ueus leaves. ..
Evapotranspiration -The combined
process of evaporation and evapotranspiration.
Figure 73. Radiometer
2. Temperature and Relative Humidity.
A hygrothermograph is used to measure
temperature and relative humidity.
This information is important because
the rate of evapotranspiration is
partially determined by humidity and
3. Rainfall. Rainfall is one of the most important meterological characteristics that needs to be monitored. A digital-recording rain gauge can beiiii-used for this purpose. It can be set l
to record rainfall at any time interval desired. Since irrigation is supplemental to rainfall, monitoring rainfall will be an essential ingredient for irrigation scheduling and crop water demand modeling, which will be discussed later.
Figure 75. Digital recording rain gage
4. Wind Velocity. An anemometer is used to measure wind speed. Wind speed can affect the rate of evaporation of water from soil and plant surfaces, thereby affecting irrigation needs (see figure 76).
5. Volume of Water Pumped by Irrigation System. The amount of water pumped by the system needs to be measured. This measurement is not a weather station data measurement. Use an instrument such as one of the flow meters mentioned in Chapter V to monitor water use by the farmer at the weather station site.