PROCEDURE FOR ASSESSING
AGRICULTURAL IRRIGATION WATER USE
Suwannee River Water Management District,
White Springs, Florida
BOB GRAHAM, GOVERNOR
Jerome Johns, Chairman
W. Jack Carlton
B. W. Helvenston, III
John M. Finlayson
Hilda S. Kressman
J. R. Miller
Jonathan F. Wershow
DONALD 0. MORGAN
Department of Planning and Operations
Kirk B. Webster, Director
JOHN L. SHOEMYEN
CARROLL J. GLYNN
TABLE OF CONTENTS
INTRODUCTION ----------------------------------------------------- viii
CHAPTER I--PREPARING FOR THE PHYSICAL INVENTORY------------------------ 1
Determining crop types and farm size------------------------ 2
Irrigation systems------------------------------------- 3
Basic units of the system----------------------------- 3
Types of irrigation systems--------------------------------- 4
Multi-sprinkler systems-------------------------------- 4
Single-gun systems------------------------------------- 6
Sources of information------------------------------------ 8
Designing the inventory form-------------------------------- 9
Designing the crop calendar-------------------------------- 11
Designing the public relations bulletin--------------------- 12
CHAPTER II--PREPARING FOR IRRIGATION SYSTEM INVENTORY------------------ 13
Preparing the work schedule-------------------------------- 13
Becoming familiar with the geographic area------------------ 14
Becoming familiar with the inventory equipment-------------- 15
Inventory form----------------------------------------- 16
Owner information--------------------------------- 16
Opinion questions-------------------------------- 18
Determining section, township, and range---------- 19
Determining 1/4 1/4 1/4 CD------------------------ 20
Other system uses--------------------------------- 26
Manpower form------------------------------------ 27
State Department of Transportation maps-------------- 28
Plat books--------------------------------------------- 28
Public relations bulletin------------------------------ 29
CHAPTER Ill--SITE SELECTION AND ANALYSIS------------------------------ 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------------------------------------- 37
Information to collect while interviewing the farmer-------- 38
Onsite analysis of the irrigation systems------------------- 39
CHAPTER IV--STATISTICAL SAMPLING----------------------------------- 42
Simple random sampling-------------------------------- 44
Stratified random sampling----------------------------- 44
Stratified nonrandom sampling-------------------------- 45
When to use stratified random sampling---------------------- 45
Planning a stratified random sample study------------------ 48
TABLE OF CONTENTS (Continued)
CHAPTER V-DETERMINING APPLICATION RATES-----------------------------
Vibration timer service log---------------------------------
Procedure for time measurement-----------------------------
Determining normal operating capacity----------------------
Framing square technique------------------------------------
System specific method--------------------------------------
Calculating the acreage irrigated per day------------------
Traveling sprinkler calculator------------------------------
CHAPTER VI--ESTIMATION OF IRRIGATION WATER RETURNED TO THE AQUIFER----
Components of a nomograph--------------------------------
Use of the nomograph for calculating percent evaporation
Calculating sprinkler system efficiency loss----------------
Tabulating efficiencies of various systems------------------
Collecting information at weather stations------------------
Determining consumption rates------------------------------
CHAPTER VII--INVENTORY UPDATE/DATA ANALYSIS HANDLING------------------
Irrigation dealer update-----------------------------------
Well-permit record check---------------------------------
Quality control and computer readiness----------------------
Basic data storage-------------------------------------
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 Cordes and Dr. Timothy Wyant for their time spent in reviewing
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
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
freshwater, not only for Madison
public supply, but for I / SRW Io
rural domestic, livestock, ------. 1
industrial, irrigation and / uwannee
thermoelectric purposes. ocolumbia
Water is now thought of as ayUor
a limited but renewable Lafayette.
resource. It is little i \ B
understood but immensely
important to man; as much as 5 ilchrli
the critically short I A Iac
1 Dixie V- -> A l |
supplies of fossil fuels. Dixie
Increased demands for
freshwater have created a
need to analyze the Levy
functions and uses of r -
this vital resource. When
efficient methods for con-
trol 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 fresh-
water 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: (1) 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
What types of
systems are found? Can we
~ o afford the
Field inventory preparation is Wcr are
an important part of any study since irrigated
care and time spent in actual prepa- Wil frmer
ration reduces the chance for future cooperate?
problems. Whether the study is based o o0
on a general inventory of the entire What type *
region or on a sampling technique, of samlingous "
take time to understand the local s* o
cultivation and irrigation practices a
before planning the inventory Is manpower How to design
strategy. available? inventory form?
Basic preparation includes
knowing the crop types and farm
sizes, understanding the commonly
used irrigation systems and de-
veloping inventory materials such
as inventory forms and public
Figure 1. 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
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.
Figure 3. A typical sprinkler irrigation system consists of four basic units:
(a) pumping unit and power unit, (b) mainline pipe, (c) lateral pipe, and (d)
one or more sprinklers
Types of Irrigation Systems
Two types of multi-sprinkler
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-cooling or frost protection.
--Permanent set. The permanent set system is like the solid set except that
the sprinkler laterals are buried.
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
different rate of speed, which keeps the lateral in a straight line. Power
to operate the lateral may be hydraulic fluid drive, electric, or water
Figure 7. A center-pivot system
rotates about a swivel joint.
Water flows through the joint
to the sprinkler.
Figure 6. A well and pump supplying a
Water power is supplied by water
pressure from within the system which
turns a "spinner" or water turbine at
Electrically-driven systems have an
electric control panel at the pivot
point. Each tower has its own electrical
motor drive. Hydraulic fluid powered
systems use hydraulic motors at each
tower. Since the lateral travels in a
circle, special provisions must be made
to obtain an even distribution of water.
The sprinklers toward the pivot center
cover much less field area when making to
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
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) hand-moved, (2) tractor-
moved, and (3) self-propelled.
. FI:j .I U
Figure 9. Tractor-moved, gun
systems may be mounted on wheels
3. Self-propelled. Single-
sprinkler self-propelled guns move
continuouslyy from one end of the
field to the other while sprinkling.
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-
piston drive, water turbine or an in-
ternal-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.
Pair, C. H., et al., 1975, Sprinkler
Irrigation (4th edition): Maryland,
Sprinkler Irrigation Association,
Silver Springs, 615 p.
, ,, c a;~
1. Hand-moved gun systems are
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
moved to a new location.
2. Tractor-moved. Single-
sprinkler tractor-moved systems are
similar to hand-moved types, except
that the tractor-moved types have
larger sprinklers which are mounted
on wheels so they can be moved with
Figure 10. A "traveling gun"
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
necessary for producing a "crop calendar".
details on the planting schedules for crops
provide assistance and answer any questions
can provide crop-water demand figures, soil
can provide the information
The crop calendar contains
in the area. The researchers can
dealing with irrigation. They
information and water-use
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
(SCS), 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
1. Owner Information. Basic
information about the owners of
irrigation systems (the farmers) can \cr k 5 +
be compiled. The owners may be the
only individuals who have all the Ow\r In..rmaio~
the information on their specific
systems and irrigation practices. LTuL T 11EDIIII11 MIli
Agency information can be distributed to i I11 illJI
the farmers if their addresses and phone II11ll1 lIllll
numbers are kept up-to-date. The owners
SI I I i iltt1111
of the irrigation systems are not
necessarily the same individuals that
own the farm. Irrigation owners may Lo____io
lease the land.
2. Location of the systems. i 1 1111
Information on the location of
irrigation systems can be used for
future planning decisions. Farmers lIl II I I 1 -
often have more than one farm (and/ -!- --
or more than one system). In order
to locate the farmers for future data 11 I 11
collection efforts and dissemination
of information, the exact locations of
their systems must be known. I11 l l 1 I
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
JAN I FEB I MAR I APR MAY I JUNE JULY I AUG I SEPT I OCT | NOV I DEC
I I I I I
Water Use E::(I
Data Growth P
Network Period C
I I I I I I
rowth Senescence Harvest
Figure 12. A crop calendar provides a timetable for scheduling data collection
Designing the Public Relations Bulletin
A public relations bulletin should inform the public about the purpose
of the field inventory and the legal authority for conducting the survey.
Responses to questions asked in the survey should be treated as confidential.
Explain in the bulletin that the privacy of the individual will 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 SRWMD
What You Need
To Know About
Water Use And....
Q. What is Inventory '78?
A. It is an accounting of how much
water is used for industrial, home,
and agricultural purposes.
Q. Who wants to know how much water is
A. The Suwannee River Water Management
District (SRWMD). Established in
1973, the District covers all or
part of 15 counties in North Florida.
Under the direction of a nine-member
governing board, the District has
the responsibility to manage all
surface and ground water. The
Governing Board has the authority to
set standards and regulations for
water management purposes.
public relations bulletin is in
located; and (3) through "yard-
stick" weather stations located in
fields under different types of
irrigation systems (traveling gun,
center pivot, etc.).
IRRIGATION: A MAJOR USER OF WATER
The weather stations will provide
information on the amount of sun-
light (radiation), rainfall, water
applied by irrigation, and evapo-
Q. What do you mean by "fleld inven-
A. Beginning in early spring of 1978,
our staff will visit individual
farms throughout the District. If
you have an irrigation system, the
probability is good that you will
Q. What kind of questions will be
A. You will be requested to provide
information concerning the kinds of
crops you plant, how much water you
apply and how often, the type of
system you use, etc. Our field
personnel will be courteous and will
take up as little of your time as
Q. How will the Water Use Inventory
Figure 13. The public relations brochure explains the purpose of the field
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 for 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.
Figure 14. A work schedule should be developed before the inventory begins
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
is beneficial to take
the geographic area.
such field trips may
and crop types. When
them on several field
However, if personnel
not be necessary.
new field personnel are hired, it
trips for familiarization with
are familiar with the region,
Figure 15. Aerial photographs may be used to locate large irrigation
systems such as center pivots
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 #1 and
#2, and the center pivot is numbered #3. In 2 years the farmer is revisited.
He has sold traveling gun #1 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 file.
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
Y Y M M D D
Rec. No. J Farm No. Date
Cell No. IActive Y/ 22Y Y
Transaction -- The "transaction" indicates whether the particular inventory
form under consideration contains any additions (ADD), evictions (E)
(completely deleted), replacements, or updates.
Rec. No. -- This number is automatically printed by the computer and is used
by the computer for cataloging.
Farm Number 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 BA001. The 316th farm surveyed in Columbia County would be C0316.
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
that year (Y=Yes, N=No) (see Chapter IV).
Year -- Fill in the blank with the year that the farm was surveyed (see
49I 64 I r
" II a I I
Phone I I I I I I I I I 80
Phone I I
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.
I r r T -r 1 -r
14 II I I I
System located by 26 [
] I I I
-- --- .---
I I a I
I--- -4-- -.-..-- -+--
t It I I
SI I I I
I I I I
i i L
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 Trans-
portation (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
on the inventory form.
County Number The county number can be assigned based on the USGS
Topo Map No.
"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 Evict Replace Update
1 11-111--- 1-1--r--I-- I
Rec. No. [ 5 Fa'm 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 a
drought or after a poor growing season?
Yes/No (Y/N) 11 0
4. In what year was the worst 12
5. How important was the advice of friends or neighbors
in your decision to install an irrigation system?
None (N) Some (S) Major Importance (M)
If N or S: What then was the major factor that made you decide to install
an irrigation system?
6. Has the system improved your yield as expected? Yes/No (Y/N)
The opinion questions section of the inventory form should be considered
to be optional. In the SRWMD it was used to collect data that was important
to the study. For example, the major reasons why farmers installed their
irrigation systems or whether the systems improved the yield as they had
expected can be analyzed.
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.
3W 2L W IW IE
o) O B se
^/c ^^ z
^ / ^---^ a
Figure 16. The X identifies the township that is formed by the convergence
of the second township strip north of the baseline and the third range strip
east of the principal meridian
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
north or the south first, such as "northwest" or "southwest". The
descriptions are never read as "westnorth" or "eastsouth". It is simple
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
Figure 17. The description of the tract of land above should
read 1/4B, 1/4B, 1/4C or the NE 1/4, NE 1/4, SW 1/4, of the section
A ____YSTI'IM INFORMATION
ec. No.1I Farm No. System No.
Style -11 CP Center Pivot OH Overhead Sprinklers
LJ TG Traveling Gun TS Turf Sprinklers
SG Stationary Gun DT Drip/Trickle
H2 Hand Nove SS Seepage/Surface
Maximum 42 Nozzle Size 46 Nozzle 49--- psi. 52
Capacity gpm Large Guns Pressure Trav.
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
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
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 1 11 15 20
Power Source24 D Electricity (E) LP (L) Diesel (D) Gas (G)
29 33 Y Y M M
Area Irrigated 29 Date of
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).*
*Impeller-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
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.
GPM -- GPM indicates the operating discharge in gallons per minute of a pump.
TDH -- These initials stand for the "Total Dynamic Head". 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 (E), 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
'runsa1ctlio Add Evict Replace Update
Rec. No. Farm No. System Year Crop Irrigated Yield Amount Applied' in Inches
Number Y Y T Acres Per Acre Farmer SRS
3 8 -10 C 12 14 T19oa 24 O26
0 3 8 10 312 14 24 26
E 3 8 10 12 M 14 19 24 26M
I M 3 8 M -10 12M 14 -H 19 24 26
RY Rye PA Pasture SB Soybeans
TC Truck Crops PE Peanuts TU Turf (Golf courses)
The crop calendar (see Chapter I), should be used to produce a list of
crops common to the area. The more common crops should be listed on the
Number of Crop Types The number of crops the farmer grows should be
indicated. If corn and tobacco are grown, indicate that this farm has two
crop types. List the crops grown for each irrigation system. The form
should be changed to reflect the crops grown in your region.
Total Irrigated Acres The total number of irrigated acres planted to each
crop type should be designated on the form. The farmer will have this
Yield/Acres -- An estimate of the total production per irrigated acre can be
obtained from the farmer.
Amount Applied in Inches The total amount of water applied in inches to a
crop throughout the entire irrigation season should be determined. Ask the
farmer how much he applied and indicate under Farmer. Then, when the study
is complete, indicate what the analysis of the water applied revealed (SRWMD
used the stratified random sample technique). With this data, increases and
decreases in irrigation use can be noted. Crop growth and drought or the
amount of rainfall can be correlated to irrigation water use for future
1 LP Lake or Pond PQ Pit or Quarry
after Source RV River SH Sinkhole
RR Reservoir WW 1ell
3' 13 SReI.D 18
Well No. I_ l___ __I Yield I .Permit
County No. 27
Water Source -- Fill in the appropriate initials.
for the water source for each system.
This should be completed
Well Number -- Fill in the township, range and section of the well, not of
the system from left to right.
Yield (gallons per minute) Indicate the gallons per minute of water that
can be pumped from the well, if known.
SRWMD Well Permit Number SRWMD noted the well permit number. This
information allows easy access to the files.
Basin Number -- Number of the basin the well is located in.
County Number Number of the county where the well is located.
Other System Uses
If there is interest in knowing whether liquid fertilizer, herbicides,
pesticides or sewage wastes are being applied through an irrigation system,
this type of question can be answered in the "Other System Uses" section.
OTI1F.R SYSTEM USES
Liquid Fertilizer n Y/N Acre 2 Pesticide Y/N Acrs
11 12 16
Herbicid I ^/N Acres waste Disposal 1 Ac r17
HISTORICAL CELL INFORMATION
Transaction Add Evict Replace Update
Rec. No. 1
Cell No. 10
Active [ YIN
FUTURE ACREAGE INFORMATION
Next year what changes are expected in the acreage of land you intend to irrigate?
A. About the same acreage.
SB. Increase acreage.
C. Decrease acreage.
Increased or acres
Decreased by ac
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 FORM
Datero1- 5 EDM f M
Miles Traveled I [I 3'
Farm No. Islo I
Initial Contact Form Completed \- Clock Installedl|
Callback Install Clock j Complete Forml|Ij Remove Clock E
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.
*Callback: Indicate whatever tasks are accomplished during the callback;
"Install Timer", "Complete Form", or "Remove Timer". Continue to use the
"callback" 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
second contact with the farmer by the interviewer.
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 super-
imposed 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.
Figure 18. Section from a plat book
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
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
6. Present a brochure to the farmer when introducing
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. After 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
SITE SELECTION AND ANALYSIS
Field analysis of irrigation sites is 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
~~gdl.. .Ic -.C
A. ;~10~z"- M. -
Figure 19 A hose-pulling traveling gun irrigation system
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 is 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. Mark areas off the road as they are covered
to avoid possible redundancy.
Figure 21. Wildlife preserves will not have irrigation
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
Figure 22 A portable gun
Irrigation Pipe. Irrigation pipe can often
be seen joined together in the field or
stacked near the farmer's house, barn or
Figure 23. Irrigation pipe stacked
near a farmer's house
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
Row Spacing. The spacing of crop rows often indicates irrigation. A
corn field may have a wide space in every 70th or 90th row. This space could
be a lane for a traveling gun irrigation system.
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, O
which leaves tire marks. Do not
confuse these tire marks with those
made by spraying equipment.
Figure 26. Watch for tire or skid
marks when searching for irrigation
Fuel Tanks and Oil Cans. If
fuel tanks or oil cans are
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
Figure 27. Fuel tanks, oil cans and pump
power units may be signs of an irrigation
Figure 28. Irrigation pipe can often be seen
in a culvert
Figure 29. ...or a wooded
Figure 30. ...or loaded on a pipe wagon.
What to Do After Locating An Irrigation System
Getting your Bearings
When an irrigation system is 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.
12 .~, .2
-. L -..'.
"' `.- -,
Figure 31. Locate the owner of the irrigation system
It is important to determine who owns the irrigation system, because the
owner of the system will not always be the same individual that owns the
land. Occasionally a landowner will lease out his parcel to a farmer who has
his own irrigation system.
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
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, May, 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 (Ip, 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
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 than once. Make sure that uniform farm letters and numbers are used.
The most important thing to remember is: BE CONSISTENT.
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
numbers are needed for determi-
ning the capacity of the system
(see Chapter V). Locate the
serial numbers on the base of
the pump housing.
Figure 34. Measure the nozzle
diameter of the sprinkler
orifice. This measurement can
be used to determine the
capacity of the system if the
nozzle operating pressure is
known (see Chapter V)
Figure 33. The pumping pressure in
pounds per square inch (psi) can be
read from the pressure gauge if the
system is operating. This reading
is often needed to determine the
capacity of the system (see
hN "^sri t^
Figure 35. The power source for
the system should be determined.
It is necessary to know the source
when deciding what method to use
for measuring time (see Chapter V).
Figure 36. The water source (whether ground water or
surface water) is often important information for
Figure 37 Identify the pump
manufacturer (the identifica-
tion is located on the pump
serial number plate)
Figure 38. and the irrigation
system manufacturer (identi-
fication plates are attached
to the machinery). These
identifications are necessary
when using the system specific
methods for determining
capacity (see Chapter V)
Sequence Diagram for
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 possible estimates will be the actual amount of water applied (see Table
1). This is always true of simple random samping. 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
through 4) will be increased by "stratifying".
11 Mgal water pumped
19 Mgal water pumped
3 Mgal water pumped
38 Mgal water pumped
Figure 39. Example of district of 4 farms
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)/2 = 98 +27
2,4 4 x (11 + 3)/2 = 28 -43
3,4 4 x (38 + 3)/2 = 11 +11
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
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)
All equally likely samples of 2 farms
Estimate of district Error
Farms water use (Mgal) (Mgal)
1,3 38 + 3 x 19 = 95 +24
2,3 38 + 3 x 11 = 71 0
3,4 38 + 3 x 3 = 47 -24
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 x 19 = 95 +24
When to Use Stratified Random Sampling
Stratified random sampling can increase the reliability of estimates
based on sample "means" (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.
If these conditions--separate groups, large users, special interests,
different costs--do not apply, stratification is unnecessary. Random
sampling may be unwise with very small samples, and deliberately chosen
"representative" farms may give better estimates. Finally, more intricate
statistical techniques than simple or stratified random sampling, such as
regression and ratio estimation, might be used. Many standard textbooks on
sampling describe these techniques in detail.
Table 4.-Comparison of the 3 sampling methods in the example district
N O AxS
Figure 40. Total water-use estimates based on sample means
Sample me< = me CsunoA w u04 r osA by t1 e 5 fcvA, /V
Planning a Stratified Random Sample Study
Planning and carrying out a stratified random sampling study
1. 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.
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.
Design the Inventory Form
The SRWMD stratified random sample inventory form is described in
Chapter II. SRWMD sampling emphasizes estimation of total water use by
county and basin for a given year. Crop, acreage, and yield information are
collected for each system.
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
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 SRWMD 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
type and principal crop seemed the best choice based on 1977 water use. A
great deal of effort should not be spent attempting to obtain perfect strata.
There will always be some overlap between the resulting groups.
Additional special strata may be needed for special groups of farms
which may be atypical, or which water-use estimates are particularly needed.
The SRWMD sampled the district's experimental farms separately. Experimental
farms are atypical operations that accurately monitor their own water use,
and so provided a check on SRWMD measurements.
Top 201977 irrigators
make up 20% of the
Figure 41. Concentrate sampling on large irrigators
Top 20 1977 irrigators
(3%) applied 33% of
1977 irrigation water
c r gun systems
_2 / other
Figure 42. Past water use by tobacco and watermelon growers indicated that
the SRWMD should stratify by system, not by county. (The larger center
pivot systems are seldom used on these crops)
c water used
40- by any
E" farm in
z water use +
0 per farm
Tobacco farms Watermelon farms Tobacco farms Watermelon farms
Other systems Other systems Traveling guns Traveling guns
Figure 43 Comparison of irrigation water use by tobacco and watermelon farms
using traveling guns and other systems. This indicates that stratification
by both crop and system may increase the reliability of water-use estimates,
despite the overlaps
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 of this chapter illustrates the
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 non-
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.
The district water-use estimate is the sum of these stratum estimates.
Sampling text books provide additional formulas for estimating precision and
for making water-use estimates across strata (by county, for example).
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.
Figure 44. Experimental farms exhibit atypical water-use patterns
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
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 internal-
combustion engine (powered by diesel, gasoline, or Lp fuel), or an electric
Figure 45. Electric power unit
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.
Figure 46. Kilowatt meter
In this example the dials should be read from right to left.
example above, 2565 x 80 = 20,520 kwh.
Calculations for time of operation of well pumps
Definitions of Terms
Scale factor = A multiplication factor
for the meter reading.
Kh = Conversion factor; printed on face
Rev = Revolutions of meter disc.
Tsec = Time in seconds.
KWhr = Kilowatt hours; computed from
KWi = Instantaneous kilowatt demand.
TO = Computed time of pump operation;
HPd = Computed horsepower demand.
HPr = Rated horsepower of pump motor.
Well No. 5 /3 2 -
Owner /YL:/ /1-'4f?
Pole Number /
Meter Number Gcr-c 2 -S 7o x(
Power Company /A-, A4 /cLL-_a
Date Z////" Irr. System Type,1e-'r/.'v/
Measurements By 2d y -/,_
1. Multiply beginning and present dial
readings by Scale Factor printed on
meter face, if necessary, to get a
correct meter reading.
2. Subtract beginning meter reading from
present meter reading to get KWhr.
3. Record Kh factor from meter face.
4. Time meter disc for at least 10
revolutions; and then record time
and number of revolutions.
5. Compute KWi using the formula:
K. Rev Kh 3.6
6. Compute TO using the formula:
TO = K
7. Compute HPd using the formula:
HPd = KWi 1.34
8. Compute % difference between HPd
and HPr using the formula:
% = 100
If % difference is less than 80
or more than 120 recheck all
measurements and calculations.
Dial Reading Scale Reading
1. Present ,y/y /O = 3j//V/O
Beginning,77 3 /o =-.2793
KWhr = ,b/
Kh = / ./
Rev = //
Tsec = ,3 0
. KWi = /// // /x 8. = / 7
6. TO = C /' = "2-7
7. HPd = //J x /.3/ = 3 2_
8. % = 3 3- *100 =
Diesel or Liquid propane.
the unit operates on diesel or Lp power, determine whether there is
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 designed to monitor vibrations and record the running time of equipment.
This device indicates the amount of time an irrigation system is in operation
during the season.
At the end of the irrigation
season, the timer is placed on a
"read-out" machine which will cal-
culate the hours the system operated.
The timer should be mounted at a
point on the power unit where
there is sufficient vibration
to activate the timer.
A vibration meter is used to
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-
ject to climatic extremes.
Figure 48. A timer can be used to
measure the amount of time the
system is in operation
Figure 49. A vibration meter is used to determine the
best location for the timer
Figure 50. Another 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.
Figure 51. The mounting bracket is placed on the
gear head with epoxy. The timer is then placed
in the mounting bracket
Some locations to consider when deciding where to place the timer are:
The motor or
or pump casing
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
SERVICE TIME: hrs.(est.)
Time: AM PM
READOUT TIME: hrs.
Figure 56. Vibration timer service log
Operating Mode: 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.
Removed: Indicate the date and time the timer is removed.
Mounting Position: Indicate whether the timer is mounted horizontally or
*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
*In this manual "displacement" refers to the degree of vibration measured at
the timer mounting site during normal pump operation.
Procedure for Time Measurement
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.
1. Spring Irrigation Period. To get an accurate water use number, all
farms in the sample should be contacted, and the timers should be in place by
the time spring planting begins. Depending on the size of the sample and the
number of field technicians, field work may begin a month or more in advance
so that all timers can be installed.
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
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 col-
lected 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 between crops.
Farmer #1's timers can be collected at the end of the spring irrigation
season. At this time Farmer #1 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 #1 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.
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.
Figure 57. Tape used to measure pipe diameter
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 O.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.
Figure 58. Tube impeller flow meter
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.
"'xrl~lflllll\ \\\ .
TrlO T ALIE
**^y **L F
Figure 59. Open-flow meter
It should be stressed that using in-line mounted meters are expensive
and usually require complicated installation procedures. Using these meters
also require a great deal of cooperation from the farmer.
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
frequencies and display this difference in feet per second on a flow rate
indicator. A simple calculation based on the indicated flow rate and known
pipe diameter gives the gallons per minute reading.
Figure 61. A Doppler meter reflects frequency change in proportion to the
velocity of moving objects
The transient time meter transmits a series of ultrasonic sound pulses
through the pipe walls and the water to a receiver. The sound beam velocity
increases in proportion to the velocity of the flow of water in the direction
of flow. The same process is repeated against the flow direction. The
difference between the two travel times is proportional to the fluid
Figure 62. The transient time meter transmits a beam of ultrasonic sound
through the pipe
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
The gpm flow from pipes may be approximated by measuring the distance
"X" in inches when the vertical distance is 12" (or 6", see note below table)
and find value in Table 15.
FOR PIPES FLOWING FULL
TABLE 15. GALLONS PER MINUTE
Dia. _Horizontal Distance = "X"
Pipe = D 12" 14" 16" 18" 20" 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" 150 181 207 232 258 284 310 336 361 387
6" 352 410 470 528 587 645 705 762 821 880
8" 610 712 813 915 1017 1119 1221 1322 1425 1527
10" 960 1120 1280 1440 1600 1760 1920 2080 2240 2400
12" 1378 1607 1835 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
- ---MEASURE = X"J
0 OJ -----------
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
of empty portion of pipe. D -Measure of inside
diameter of full pipe.
E/D Factor E/D Factor
10 0.95 50 0.50
20 0.86 60 0.38
25 0.81 65 0.31
30 0.75 70 0.25
35 0.69 80 0.14
40 0.63 90 0.05
45 0.56 100 0.00
System Specific Method
The following techniques are based on the "system" section of the
inventory form. Please refer to that section when necessary.
1. Hand-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
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
(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
move the 12 inches. Another way to
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 min/hour = 480 min/l/4 mile run
Since there are 1320 feet/l/4 mile,
1320 480 = 2.75 ft/min travel speed
* 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 manufacturer's 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.
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 day" by different systems
in the District. Calculating the irrigated acreage is optional, but the
method is presented here:
Use a performance chart,
as in Figure 65, to
calculate irrigated acreage.
Performance charts for
specific irrigation systems
can be obtained from manu-
facturer's irrigation system
manuals. Estimate the normal
length of an irrigating day
in the area to calculate the
average number of inches of
water the farmer is trying to
apply to his crops every time
he irrigates. These facts
will depend on soil types and
region of the country. For
example, if the farmer
operates a system that applies
500 gallons per minute,
covers 3.03 acres and puts
down approximately 1/3 inch
(.365) of water an hour.
The farmer will need to
irrigate 3 hours to apply 1
inch to 3 acres. If the
normal irrigation period is
12 hours, the farmer will
irrigate 12 acres per day with
this system if he wants to
apply 1 inch to his crops.
VOLUME GUN MODEL 550
~.m o e u o
-0( 0 PU C 0
N C N :3 ) P4 ca k > W U P.
Z P4 cE P4i Pi C: 0U H U -Hl pL4 -4 P
70 188 300 1.62 .256
75 195 308 1.71 .251
80 202 314 1.77 .250
85 208 324 1.89 .242
70 235 328 1.94 .267
1-1/8" 75 244 338 2.06 .260
80 253 346 2.15 .259
85 260 354 2.26 .253
70 285 352 2.23 .283
1-1/4" 75 297 360 2.34 .280
80 308 372 2.49 .273
85 317 380 2.60 .269
70 355 366 2.41 .326
1-3/8" 75 368 380 2.60 .313
80 380 390 2.74 .306
85 392 400 2.88 .301
70 425 390 2.74 .343
1-1/2" 75 440 400 2.88 .338
80 455 412 3.06 .329
85 470 420 3.18 .327
70 500 410 3.03 .365
1-5/8" 75 518 420 3.18 .360
80 532 432 3.36 .350
85 550 440 3.49 .348
1-3/4" 85 650 460 3.81 .377
1-15/16" 85 1030 500 4.51 .503
Figure 65. A performance chart
7719 N Pioneer I r.ar
Peori.l Illhnois 61614
Phon,.: (309) 691.0080
SOUTHEAST DISTRICT .
P.0 Box 1325 A. A Ad4V.d'i
3616 Solh5 We.st Are.h.r Road Id/ ,
G,.linsvl:;'. Florda, 32601
Phon..: (904) 372 8W5d 7j -
1 NOZZLE TYPE AND SIZE
OPERATING HOURS G 8 10 15 20 24
PER DAY I I II III IIlII(
I I III Ill 11 "1Illi "ll 'i"I 'I"I"llll l I( I 'II I I'l'I I l l '
ACR 0 40 50 60 80 100 150 200
300 400 500 600 800 1000 1500
____ GPM IlI IIll jII ll I lii llill l li i I II l li p l jill I I l lh
MOISTURE REQUIRED I11 I I I 1
N./AY .10 .15 .20 .3 .4 .5
400 420 440 460 480 500 550 GI
. '. I I .. ... .
S' 80 90 100 110 120 130
F200R 1I" 1I"
F200T 1.3" 1.4"
Set GPM at operating pressure PSI.
ReI.il noz/. l i and si/,i nearest arrow
Set ,i res of aind errv.l",telt .t oIlperting
hours per day.
Rr syt ,yist, l IMn pi n elll rfelir.-n t G.t
sIt eross dl.sy mostret iJ r-rirf. d
' onfs lt-riti ifrmip. ft f-fr is-n' v
F full circle
P full or part circle
R ring nozzle
T taper bore nozzle
() WETTED DIAMETER
MODEL F OR P200T
NOZZLE SIZE 5
WETTED DIAMETER 400 410
PRESSURE PSI l I 1
( AVE. APPLICATION RATE
(Full Circle Only).
APPLICATION RATE .30 .31
IN. PER HR.
420 430 440 450
00 110 120 130Il
100 110 120 130
.32 .33 .34
() SPACING BETWEEN TRAVEL LANES
MODEL F OR P200R
NOZZLE SIZE I',. 2"
WETTED DIAMETER 480 490 500 510 520 530
FT. Ili iI I I I l i I I I I .
PRESSURE PSI Iill l I'i"!"'" i"I
80 90 100 110 120 130
Set ( no/ll-" se:' I:t l irrow Re.Iel weittetd (l.er 't(l r :1t Uop r.ltln): press !i'
NOZZLE SIZE 1;.-
APPLICATION RATE .44 .45
IN. PER HR.
Set nozzle sl/' at arrow Re'ad houlrly a;pplic,tion rtce at traijctory ,ingle.
.46 .47 .48 .49
I I I
WETTED DIAMETER I : :
FT. 450 500 550 600
LANE SPACING 260 280 300 350 400
%OF Wlill I E 0; l55 60 5ill 7' ill75
WETTED DIAMETER 50% 55% 60%; 65% 70% 75%
Figure 66. TRAVELING SPRINKLER CALCULATOR. A "traveling sprinkler calculator" should be available
at a local irrigation dealer's office. The calculator can be used to calculate the "gallons of
water per minute" applied to a crop through an irrigation system. It can also be used to calculate
the travel speed of the system and the number of acres irrigated per hour per day
S.-t wltfdl diatmleter .it ,irrn.v
Roald .nte sp,.eing t ;-r**r-
of Vwttfd di;rm-t* r
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
evapotranspirationn), 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 meteorological data for estimating crops demands. The data is collected at
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.
Figure 67. The hydrologic cycle
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.
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.
Figure 69. Relative
humidity is the amount of moisture contained in the
to the potential water holding capacity at that
2. Air Temperature (in degrees Fahrenheit). Estimate the normal
temperature that occurs during the growing period or irrigation period in the
region. One way to determine this is by averaging the monthly high
temperatures during the irrigation period.
401 I I I I I
) II', 1 / a
Midnight 6am Noon 6pm Midnight
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
Number of mi/hr., in kilometer
uWind Features 20 ft above
Windground per hour
0 Calm Smoke rises vertically Less than I Less than 1.6
Moderate Raises dust 8 loose
SBreeze paper, small branches 13 to 18 20.9 to29.0
7 Moderate Whole trees in motion,
gale inconvenience felt in 32to 38 51.9 to61.1
walking against wind.
Figure 70. There are numerous ways to determine wind velocity
4. Nozzle Pressure (in pounds per square
inch, psi). This is the operating pressure
of the sprinkler during irrigation
5. Nozzle Diameter
(in inches). This is
the diameter of the
sprinkler nozzle orifice
Figure 71. The nozzle diameter (in
inches) needs to be known before
evaporation loss can be determined
Use of the Nomograph for Calculating Percent Evaporation Loss
90 y 6
' \\ / 4 s
S 80 N A
I 70 3 3
5 60 '0 .4-
* 50 10 2 a
K 40 50< '
S30 / \0 1 I
0 0 >
A. Determining Vapor Pressure
Draw a line connecting the
estimated "percent relative
humidity" with the estimated "air
temperature". For example, the
estimated relative humidity is 10%
and the air temperature is 900F.
Draw a line to intersect these two
points. The extension of this
straight line reveals the vapor
pressure deficit to be 6.25 lb/in2.
B. Estimate Nozzle Diameter
After determining the vapor
pressure deficit, estimate the
nozzle diameter of the sprinkler
heads in use. In this example the
diameter is 12/64 of an inch. Note
the nozzle diameter on the scale,
then draw a line to connect the
vapor pressure deficit with the
nozzle diameter. Note where this
line crosses pivot A.
10 M <
Sq -0_ 8-
1 C2 40
9 0 o 48-
0 > Z 64
40--- --- -.--..
35- ;4- |E
20- Z 0 0- o
C. Determine Wind Velocity
Next, find the wind velocity
line and place a point on the
appropriate wind velocity. In this
example the wind is 5 miles per
hour. Next, indicate the
appropriate nozzle pressure on the
nozzle pressure line. Then,
connect the wind velocity on nozzle
pressure. Note where the line crosses
D. Determine Percent Evapo-
Now connect the point on pivot
A with the point on pivot B. This
line intersects the percent
evaporation loss line. In this
example about 8% of the applied
irrigation water will be lost to
the atmosphere and not returned to
Percent Relative Humidity
0 8 0 0 10,lo
N- prs .c 0 I b .pe 1 O0
Vapor pressure Deficit in Ibs. per sq. in.
o tm N -
S0 0 0 0o P M 0 C
-- I ^-000
N ol M M / O 0
0 1o 0. o ? o
0 N u .
I0 00 T0
I I I l l
7 1 4-
0 0 Co
0 > a
Wind Velocity in Miles per hour
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 calcula-
tions. 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%
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
entire region would be satisfactory. In other areas where there are
variations in climatic, crop and soil conditions, several weather stations
might be necessary. Permanent monitoring setups may be necessary for
monitoring weather changes within a crop season.
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 SRWMD 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 evapotrans-
Evaporation When water from "moist" ,
surfaces is absorbed into the.
atmosphere as a vapor. I N
Transpiration When a plant gives up
moisture through its leaves.
Evapotranspiration The combined
process of evaporation and evapo-
transpiration. 3 a
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
Figure 74. Hygrothermograph
3. Rainfall. Rainfall is one of the
most important meteorological charac-
teristics that needs to be monitored.
A digital-recording rain gauge can be
used for this purpose. It can be set
to record rainfall at any time inter-
val 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
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
SRWMD decided to provide irrigation schedules as a service to farmers
after the initial field inventory. Many farmers requested information on how
they could best and most efficiently use their irrigation systems. The data
collected at the weather stations can be applied to develop ET models like
Blanney-Criddle, or it can be used to develop models best suited to local
conditions. Land-grant institutions may be able to assist in the development
of models or irrigation schedules.
Irrigation scheduling will benefit the farmers and help them get the
most efficient use from their irrigation systems. In addition, irrigation
scheduling benefits water use monitoring in the area.
-. 1.C~7' ~ ,,
.*~~ c ~- 9
Figure 76. Many farmers do not use their systems efficiently,
note the high wind drift losses due to irrigating during
adverse wind conditions