Title: Seepage irrigation for pastures
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00084333/00001
 Material Information
Title: Seepage irrigation for pastures
Series Title: Seepage irrigation for pastures
Physical Description: Book
Creator: Harrison, D. S.
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
 Record Information
Bibliographic ID: UF00084333
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 227365753

Full Text
o7 CIRCULAR 309-C


MAY 1974


ION


SEE I
























Photos show pastures under seepage irrigation and examples of clover,
clover and grass, and grass. Lower photos are lateral views showing ditches.


















i'I















*- *



7. .. ... V W .. ..





.-e
V i Tii L-






SEEPAGE IRRIGATION FOR PASTURES
D. S. Harrison, J. M. Myers
and D. W. Jones1


Seepage irrigation is a method of
applying water beneath the ground
surface through a series of ditches,
rather than on the surface as is the
zase for other methods.
The physical systems for seep-
age irrigation consist of a water
source, pumping facility (not need-
ed if free-flowing artesian water is
available at the highest elevation
in the field), distribution ditches
and grade control structures. The
network of field ditches may also
function as drains for surface run-
off when excessive rainfall occurs.
Either a suitable gravity flow out-
let or a low lift pumping station is
a basic requirement for the system
before it will function for drainage
purposes. Because of the dual func-
tional capability of the ditches,
seepage irrigation is sometimes re-
ferred to as "water control" or
"water management."
The quantity of moisture present
in the soil is often a limiting factor
in the production of high quality
pasture forage at a uniform pro-
duction rate. While Florida's an-
nual amount of rainfall is adequate
for a fairly high level of forage
production, distribution leaves
something to be desired. Several
droughts of short duration and at
least one drought of 25 or more
days duration are expected each
year.
The labor requirement for seep-
age irrigation is very low. Where
this method is adaptable, it is prob-


ably the most efficient type of irri-
gation from the standpoint of labor
required.
Seepage irrigation is usually less
efficient than sprinkler irrigation
in utilization of water. If the water
supply is limited or has greater
than normal value, or if looses due
to vertical seepage in substrata
are great, a sprinkler system may
be the best choice even though the
land meets all the physical require-
ments for seepage irrigation.

Physical Requirements
for Seepage Irrigation
At least five physical require-
ments must be satisfied if seepage
irrigation is to be successful and
practical.
The topography of the land sur-
face must be of gentle slope (not
greater than one percent) and suf-
ficiently level to preclude the need
for an excessive number of grade
control structures. Also, if the sur-
face is not reasonably level, the
lower areas will be over irrigated
and higher areas will be under ir-
rigated. Sometimes it is feasible
to level the land prior to installing
a seepage irrigation system.
The hydraulic conductivity (ability
of soil to conduct water) of the
surface soil must be medium to
high. This soil factor has a pro-
found effect on the rate at which
water will move from the water
supply ditches into the soil that is


'Agricultural Engineer, Florida Cooperative Extension Service; Agricul-
tural Engineer, Florida Agricultural Experiment Stations; and Agrono-
mist, Agricultural Extension Service, Institute of Food and Agricultural
Science, University of Florida, Gainesville.





being irrigated. The rate of hy-
draulic conductivity depends large-
ly on the soil's texture, with lighter
(sand ) soils having the higher rate
and the heavier (loamy sands or
sandy loams) soils having the
lower rate.
The hydraulic conductivity for
the surface soil layer should be 20
inches per hour or more. Also, it
is desirable for the highly perme-
able surface layer to be at least 18
inches deep. Some examples of soil
types that meet this requirement
are Leon, Ona, Adamsville and
Blanton fine sands. The hydraulic
conductivity of a particular soil
can be determined in a soil labora-
tory or estimated by agricultural
specialists of the Agricultural Ex-
tension Service and the Soil Con-
servation Service.
There should be a confining layer
in the soil profile at a reasonable
depth (two to four feet) which will
form a barrier against excessive
vertical loss while the water moves
laterally into the field. In the ab-
sence of a confining layer, a suc-
cessful seepage irrigation system
may be installed if there is a per-
manently high natural water table
on which an artificial water table
can be built.
There must be adequate water
for irrigation. A supply rate of
eight gallons per minute per acre
of irrigated pasture is usually ade-
quate. If the water source is a
shallow well, free-flowing artesian
well, pond, lake or stream, pump-
ing costs are much lower than for
a deep well water source. Some-
times the lower cost water sources
are not strategically located with
respect to the highest ground ele-
vation within the pasture. Since
the water must be distributed from
the highest point, consideration


must be given to the cost of supply
lines and/or canals, and the corre-
spondingly more expensive pump-
ing unit that will be required.
The inherent productive ability
of the soil must be good enough to
assure a favorable response to irri-
gation water. Response must be in
terms of increased value of forage
produced. Potential response to
improved fertility and manage-
ment practices must be relatively
high.

Operation of a'Seepage
Irrigation System
The seepage system is one of
the simplest types of irrigation
systems to operate. Water is intro-
duced into a network of distribu-
tion ditches at the point of highest
elevation in the irrigated area. The
force-of gravity causes water to
flow down a main distribution
ditch until its flow is retarded by
the flashboards or a grade control
structure.
Because of the flow retarding
structure, water will backup and
flow into the field distribution
ditches until they are filled. As the
depth of water in the main ditch
increases it will reach a depth
where it will overflow the flash-
boards and begin filling the next
reach of the main distribution
ditch. The process continues until
all the ditches in the irrigated area
are filled. Water will then seep
laterally into the land areas be-
tween the field ditches.
Water is held in the field ditches
until the area is irrigated. The
water supply is then turned off or
diverted to another section of the
irrigated area. Water held by the
field ditches at the completion of
an irrigation cycle is usually not





drained, but allowed to evaporate
and continue seeping into the soil.
There may be exceptions to this, as
water should not be allowed to re-
main in the field ditch long enough
to injure the pasture plants grow-
ing in the ditches.
The major duties of the system
operator are to start and service
the pumping unit (if one is used)
and to manipulate the gates
(valves) at the distribution box.
Maintenance of a properly de-
signed seepage irrigation system is
generally lower than it is for other
types of systems. Ditches may
need some reshaping every two to
three years and occasionally un-
desirable water tolerant native
vegetation may displace grass and
clover in the ditches when pas-
tures are kept too wet.

Facilities for Seepage
Irrigation
A seepage irrigation system will
usually consist of the following
components:
Water supply
Pump
Power unit
Distribution box
Main distribution ditches
Field ditches
Stage control structures
The water supply must be ade-
quate, dependable, economical and
free from harmful quantities of
salts or other impurities.
The pump and power unit to-
gether make up the pumping plant.
In comparison to sprinkler irriga-
tion, the original and operating
cost for the pumping plant is lower
for seepage irrigation. Two fac-
tors contributing to these lower


costs are low operating heads and
more hours of operation per day.
The discharge pressure at the pump
is practically zero for seepage irri-
gation systems, since the water
is allowed to fall freely into the
distribution box. Pump discharge
pressure for sprinkler irrigation
systems will range between 30 and
120 pounds per square inch. Lower
discharge pressure results in lower
power requirement and less fuel
or electric energy consumption for
pumping a given quantity of water.
Because of the simplicity of op-
eration, it is usually practical to
operate a seepage system on a 24-
hour-per-day basis. When the
pumping unit is equipped with a
group of automatic devices to pro-
tect the engine and the pump from
damage should a malfunction oc-
cur, it is not necessary to have an
attendant at the pumping station
on a continuous basis when the
unit is pumping.
The distribution box, shown in
Figure 1, is needed to receive the
water from the pump and direct it
into the desired distribution ditch.
The box should be constructed of
concrete, concrete blocks, brick or
some other construction material
that will not be eroded away by
the energy of turbulent water. The
structure must have the capability
of discharging water calmly into
the ditches at a velocity that will
not erode the soil around the dis-
tribution box and the pumping
unit.
The distribution box may have
several gated outlets so that water
can be discharged into any of sev-
eral main ditches leading to differ-
ent parts of the irrigated area.
Figure 2 is a schematic drawing
showing a typical layout for main






DISTRIBUTION BOX
ISOMETRIC VIEW


Figure 1

SEEPAGE IRRIGATION SYSTEM FOR IMPROVED PASTURE
(on slightly sloping land)


NOTE
STRUCTURES (rT-) ARE
USED FOR GRADIENT
CONTROL AND FOR SUB-
SURFACE IRRIGATION
CONTROL.


Figure 2
6






TRAPEZOIDAL OR FIELD LATERAL DITCH
NATURAL
GROUND
SP IL SPOIL BERM - ~
d SPOIL_ 4-( BERM- SPOIjL
SIDE SLOPES PCT


WITH SPOIL SPREAD


V- TYPE DITCH










Figure 3


and field ditches. The arrangement
and spacing are designed to facili-
tate distribution of water to all
parts of the irrigated area. A ty-
pical cross section of both types of
ditches is shown in Figure 3. In
the layout design, main ditches run
down the slope and lateral ditches
are level (along the contour). Dis-
tance between field ditches will
range from 80 to 150 feet depend-
ing on hydraulic conductivity of
the soil and the slope of the ground
surface.
Stage control structures facili-
tate the regulation of water levels
in the ditches. While these struc-
tures are usually fabricated from
steel or culvert pipe, other con-
struction materials-like concrete,
concrete block and lumber are
sometimes used.


Normally, grade control struc-
tures are located along the main
ditch at points coinciding with
each 6-inch change in vertical ele-
vation. Flash boards in the struc-
tures are used to regulate the depth
of water in the ditches. When all
the flash boards are removed, flood
water can flow unrestricted down
the ditches to low points in the
field for discharge into flood water
channels.


Cost of Seepage
Irrigation
Compared with other types of
irrigation systems, seepage is the
lowest in both initial and operating
costs. Initial cost of seepage irri-
gation systems varies widely. Vari-


WITH SPOIL STACKED





ation in all physical requirements
previously discussed influences the
initial cost of seepage irrigation.
A range of costs for different com-
ponent parts of a seepage irriga-
tion system is presented in Table 1.

Table I. Range of Costs of Component
Parts of a Seepage Irrigation System1
Range of Cost,
Dollars
Component Part Per Acre
Water Supply
Pumped well $25 $70
Surface impoundment $ 5 $15
Structures, Stage Controls $ 4 $20
Ditches $10 $12
SInformation furnished by Field Engi-
neers of Soil Conservation Service

It is unlikely that a seepage irri-
gation system would cost less than
25 or more than 100 dollars per
acre. A cost estimate for any par-
ticular proposed system can be
obtained from an engineer special-
izing in the design of irrigation
systems.
Direct operating costs include
the cost of maintenance of ditches
and structures, operation and
maintenance of the pumping unit,
and labor for regulating the flow
and water level during actual irri-
gation. On large systems annual
direct operating costs have run as
low as five dollars per acre where
the water supply was from a flow-
ing artesian well. Costs are con-
siderably higher if pumping is in-
volved.


Benefits from Seepage
Irrigation
Seepage irrigation can be in-
fluential in producing high quality
forage over a longer part of the
year and without risk of crop fail-
ure as a result of drought. Earlier
grazing in the spring season, par-
ticularly from clovers, may be
expected during most years. Ani-
mal-carrying capacity of irrigated
pastures is more uniform through-
out the year.
Greatest benefits will be realized
by using well adapted forage plants
with high production potential, by
giving careful attention to fertili-
zation, and by managing the graz-
ing practices.
Seepage irrigation can be in-
strumental in increasing average
forage production and animal-
carrying capacity by as much as
50 percent. Production increases
during short periods of time can
be even greater.

Summary
Seepage irrigation of pastures
in Florida is recommended if the
land meets all the physical require-
ments discussed in the second sec-
tion of this bulletin and if the for-
age crop and livestock that are
being produced are of high quality.
The seepage irrigation system is
simple to operate and the cost is
low when the system is properly
designed.


This public document was promulgated at an annual cost of
$461.32, or 41/3 cents per copy for the purpose of informing
ranchers on seepage irrigation for pastures.

6 10M 75

COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, IFAS, University of Florida
and United States Department of Agriculture, Cooperating
Joe N. Busby, Dean




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs