IRRIGATIONS

1 INTRODUCTION.
Irrigation is one of the techniques that has been employed by the
man for the development of his agricultural activities with the purpose
to ensure the success of their harvests and thus meet their demand for
food for the purpose of ensuring their survival in their habitat, since
that this began to settle in a place or when it stopped being
nomad, reason why they sought to settle in the best
land extensions where they started to develop the
agriculture and livestock.
Thus, they were organized and gave rise to the towns or areas.
urban areas where they could carry out their daily activities, but
more and more they required food that came from the
fields of cultivation. In this regard, the increase in demand for the
food production forced farmers to produce more in
all seasons of the year regardless of seasonality or time
(Summer, autumn, winter or spring).
In response to these demands, the farmer began to develop techniques for
produce crops in adverse times, starting with
development of the irrigations. So much so that they started planning
a series of works or devices to transport water from the sources
from water (rivers, lakes, springs, etc.) to cultivated land.

In an irrigation project, the part corresponding to its

conception is defined by the agrological study and planning
hydraulic both are of vital importance, because it is there where it
determine the operating strategies of the system of
irrigation (collection, conduction - open channel or pressure,
regulation), therefore we will detail the scope of these
components:

AGRONOMIC OR AGROLOGICAL STUDY:

In the development of irrigation projects, the agronomic study has

vital importance because it will allow us to determine the needs
water needs of the crops depending on the behavior of each one
species during its vegetative development depending on the conditions
climatic, soil type, and geographical conditions where
develop the project.

The conclusion of this study will serve as a basis for:

 Quantify the volumes of water required for the project.
Determine the hydraulic characteristics of the different works
of the art of the irrigation system.
Determine the zoning of crops according to current use
(diagnosis).
It will allow planning the installation of crops according to capacity.
land use.
Determine the type of irrigation required for the land based on the
crop and soil type.
The design of irrigation in each plot.

HYDRAULIC STATEMENT.

To develop the hydraulic approach of the project, it is necessary to

implement the designs of the infrastructure identified in the stage
of the field, these will be designed based on the recommendations of the
agronomic study.

Currently, irrigation or irrigation projects consist of

CAPTURE STRUCTURES.
Fixed barrage weirs
Mobile barrage dams.
Mixed barrage gates.
Submerged barrage siphons.
CONDUCTING STRUCTURES.
Aductory canal.
Driving channel.
Channels or distribution lines.
Artwork
DISTRIBUTION STRUCTURES
Distribution channel.
Works of art.

IRRIGATION CHANNELS

The canals are infrastructures that are part of an irrigation project.

whose purpose is the conduction of a certain amount of water
in a certain time.
They are open channels through which water circulates due to the action
of gravity and without any pressure, given that the free surface of the
liquid is in contact with the atmosphere.

TYPE OF CHANNEL BY ITS GEOMETRY

Trapezoidal section canal.
Circular cross-section canal.

Rectangular cross-section canal.

DESIGN CRITERIA.

Geometric characteristics of the channel:

The geometric characteristics will define the type of section of a

canal (Rectangular, Trapezoidal, Circular). These elements are very
important and will be widely used in the calculation of flow.
The most recognized shape of the cross-section of a channel is the
trapezoidal, as shown in fig.

Most important geometric elements.

Water depth or flow depth

d: It is the vertical distance from the lowest point of a section

from the channel to the free surface, that is to say the maximum depth of
water in the canal.

Surface width or water mirror 'T':

It is the width of the free water surface, in m.

Slope 'm':
 "m" is the slope of the channel walls, value of the projection.
horizontal when the vertical is 1. It comes to be a function of the
angle of repose of the material and depends on the type of material in which
the canal is to be constructed, in order to prevent landslides and/or settlements.
For example, when it is said that a channel has a slope of 1.5:1, it means
to say that the horizontal projection of the side wall is 1.5 times
greater than the vertical projection which is 1, therefore the slope m =
1.5, this results from dividing the horizontal projection which is 1.5 by
the vertical that is worth 1.

Roughness coefficient (n):

This dimensionless value depends on the channel and the slope, given to the
nature of the side walls of it, vegetation,
irregularity and layout of the channel, hydraulic radius and obstructions in
the channel, generally when designing channels it is assumed that
the channel is recently opened, clean, and with a layout
uniform, however the initially assumed roughness value
it will hardly be preserved over time, which means that in
the practice will constantly face a continuous change of
the roughness.

For the consideration of these effects, the values will be taken:

Manning's coefficient
MATERIAL VALUE n
Land channels
Regular and smooth 0.025
Somewhat rough and coarse 0.030
Coated with stones 0.040
Channels in rock
Smooth 0.030
Rugged 0.040 - 0.050
Lined channels
Smooth concrete 0.012 - 0.016
Rough concrete 0.016 - 0.018
Masonry 0.018 - 0.020
Wooden channels 0.012
Iron plate channels 0.014

Pending (S):
Longitudinal slope of the channel alignment.
Hydraulic area (A):
 Surface occupied by water in a normal cross section
any, expressed in m2.
Perimeter wet (P) :
Length of the contour line of the wet area between the water and the
walls of the channel, expressed in m.
Hydraulic radio (R):
Quotient of hydraulic area and wetted perimeter. R=A/P, in m.
Mirror of Water (T):
Width of the free water surface, expressed in m.
Medium tie (dm):
Hydraulic area divided by the width of the free surface of the
water. dm = A/T, expressed in m.

Template (b):
Base of the channel whose measurement is expressed in m., the sizing of
this characteristic of the channel in the case of flow channels
minimums will be predetermined by the type of tool that it will be
used for maintenance purposes.
Free Board or free board (Lb):
Distance from the free surface of the water to the crest
from the edge, is expressed in m.

Flow (Q): Volume of water that passes through the section in the unit.
of time, and is expressed in m3/s.
Average speed (V):
Speed of water flowing in the channel, expressed in m/s. During
the design or planning process will take into account the
minimum and maximum speeds.

Conditions for the design of the channel section:

Among the conditions for the selection of a section of a

one must take into account the following:

Typical cross section of a channel:

 Where:

T = Upper width of the channel

b = Template

z = slope

C = Road berm, it can be: 0.5; 0.75; 1.00 m.

V = Width of the surveillance road, it can be: 3; 4 and 6 m.(

in some cases, the monitoring path can go along both margins

H = Height of the box or depth of the channel's bottom.

CRITERIA FOR THE CHANNEL TRACE.

Topographic survey.
It represents one of the main activities for the design of the stroke of
a channel and it must be oriented towards information gathering,
within which we can detail:
Cartographic information of the area (Old maps, chart
national, aerial photographs, satellite information, studies
geological, etc...) that will allow us to perform the primary evaluation of
likely strokes.
Field visits with preliminary measurements (geo-referencing)
in the field) of the likely proposed infrastructures.
Carrying out a detailed topographical survey.
the main characteristics of the land where it was planned
with the above information.
Once obtained thedataprecise, we proceed to work on
cabinet generating a preliminary axis, which will be redefined in
 field, where the necessary final adjustments are made,
obtaining the definitive line.

Geometric design.

For the tracing of a channel axis, it is the same as considered for the tracing.
from a road, since it must be taken into account that this
hydraulic infrastructure during its construction phase will require
the access of people, equipment, vehicles, and materials, as well as
also after the construction process access will be required
teams and people for the operation and maintenance phase.

Achieve the highest hydraulic efficiency and safety of the works with the
lower cost.

Reason that should be taken into account during the layout and re-planning.
all the curve elements necessary in the layout of a track must be
must necessarily contain the following:

Progressive
Land quota
BMs (every 500 or 1000 m)
Defined height
Pending
Indication of the stroke's deflections with the curve elements
Location of the artworks
Hydraulic section or sections of the canal, indicating their mileage
Soil type
Frame with geometric and hydraulic elements of the design

Elements of a curve.
 Where:

A = Arc, it is the length of the curve measured in chords of 20 m.

C = Long chord is the chord that subtends the curve from PC to PT.

ß = Deflection angle, formed at the PI.

E = External is the distance from PI to the curve measured on the bisector.

F = Arrow, perpendicular drop from the midpoint of the curve to the chord.

G = Degree is the central angle.

LC = Length of the curve that connects PC with PT.

PC = Beginning of a curve.

PI = Turning point.

PT = Tangent point.

PSC Point on curve.

PST = Point on tangent.

R = Radius of the curve.

ST = Sub tangent, distance from the PC to the PI.

Minimum radios in open channels for Q < 20 m3/s

Capacity of Radio
channel minimum
20 m3/s 100 m
15 m³/s 80 m
10 m³/s 60 m
5 m3/s 20 m
 1 m³/s 10 m
0.5 m3/s 5m
Source: Ministry ofAgriculturey FoodTechnical Bulletin N- 7
General Considerations on Trapezoidal Channels" Lima 1978.

It is important to keep in mind that during the design of the axis

from a channel we must take into account that the excess of
tight curves would extend the final length of the channel with
the consequent disadvantage of the high cost of the work.
Determination of the slopes of a channel:
The inclination of the side walls of a channel depends
of various factors but especially of the type of terrain
where they are hosted, the U.S. BUREAU OF RECLAMATION
Recommend a unique slope of 1.5:1 for your channels.
function to different experiences have been developed
recommendations regarding slopes suitable for
different types of material, of which we detail the following
frame:

Maximum and minimum permissible speeds.

The minimum permissible speed is that speed which does not
it allows sedimentation, this value is very variable and does not
it can be determined accurately, when the water flows
without a limit this value is insignificant, but the decrease
speed promotes plant growth, in channels
of land. The value of 0.8 m/s is considered as the
appropriate speed that does not allow sedimentation and
It also prevents plant growth in the channel.
maximum allowable speed, something quite complex and
it is generally estimated using local experience or the
engineer's trial; the following tables provide us with values
suggested.
Free board or frivolous.
It is the space between the crown height and the surface of the
water, there is no fixed rule that can be accepted
universally for the calculation of the free edge, due to the fact that
the fluctuations of the water surface in a channel, are
it can originate from uncontrollable causes. Therefore,
we will assume a modality based on the flow.