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International Water Technology Journal, IWTJ Vol. 5 –No.3, September 2015

163

SIMULATION TECHNIQUES FOR SPRINKLER IRRIGATION DESIGN

SYSTEM AT ADIWANIYAH GOVERNMENT – IRAQ

Aqeel Al-Adili1, and Hasan H. Kraidi

1

1Building and Construction Engineering Department, University of Technology, Baghdad, Iraq.

e-mail: [email protected]

ABSTRACT:

In this research, several software models have been used to design and systemize management

of water resources with adopting meteorological data and measurements at field of the study area.

Soil-Plant-Air-Water (SPAW) computer model was used to analyze the type and properties of soil

of the study area, and then using the results of this model as input data for the CropWAT, 2008

model, to calculate the wheat crop water requirements, and hence irrigation requirements for a field

area of 54 donums with wheat cultivation, and a system of scheduling irrigation works was

designed, after proposing and designing a periodic hand move sprinkler irrigation system, to reduce

the capital cost for the project to enable land owners benefit from it by using (WaterCAD) model.

The results of the designed models were compared in terms of discharges with actually applied

discharge on the ground. This research has indicated that there is a big difference between the

applied discharges and water consumption by the plant. The final design of the system capacity is

76.56 m3/hr to irrigate area of 54 donums, within 9 days of 15 hours per day, while the average of

filed measurements of six fields of wheat in the same area showed that the existing applied

discharge is 327 m3/hr, with spending 10 days to irrigate 85 donums with not less ten hours per day,

so that will contribute to vivification and irrigate about 984400 donums of wheat lands.

Keywords; Simulation Techniques, Sprinkler, CropWAT, SPAW model, Irrigation. Received 10 December 2014.Accepted 27, July 2015

1 INTRODUCTION

The term "water resources systems" is comprised of water sources, means of their control and

transportation to water users. However, these sources are limited , and the competition for it is

increasing day by day. The Middle East is the scarcestwater region in the world. Worldwide, the

average water availability per person is close to 7,000m3/person/year, whereas in the Middle East

region, only around 1,200m3/person/year is available. One half of Middle East’s population lives

under conditions of water stress. Moreover, with the population expected to grow, per capita

availability of water is expected to halve by 2050, (FAO, 2012).Agriculture accounts for the vast

majority ofwater resources consumption in Iraq, withdrawing 92%of total freshwater for irrigation

and foodproduction, (Iraqi Ministry of Water Resources, 2012).

Adiwaniyah governorate suffers from network deteriorations of water resources and irregular

distribution of water, despite the multiplicity of sources, which led to the deterioration of

agricultural lands and poor in good soil in the province. Because of poor management of its water

resources and low efficiency of irrigation to less than 27%, thus, low productivity of donum that

significantly affected level of living for the people of the province. For the purpose of addressing

this situation and due to the fact that this province from the provincial agricultural and large core in

the country with a total of arable lands where up to 1.85 million donums, the data showed that the

largest proportion of planted area was 47% in 2008, so it became necessary to find a proper

management for the its water resources (Adiwaniyah Water Resources Directorate, 2012).

New methods to design water resources, irrigation systems, and management for decision

making are being developed which incorporate computer based capabilities with data management,

mailto:[email protected]


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analysis, and making decisions on operation and maintenance for better productions. Such tools is a

Water CAD as a Simulation Technique for Decision Support System (DSS), which is defined by

Sprague and Carlson, (1982) as “an interactive computer based system that helps decision makers

utilizes data and models to solve unstructured or under-specified problems.”

The aim of the research is to design and establish rational irrigation planning systems by

employing advanced scientific simulation techniques, and suggest a design management model to

estimate multiple irrigation water networks and scheduling systems at field level for Adiwaniyah

governorate agriculture lands.Thus, the hope is to lead to improving the water use efficiency in

agriculture and spreading of irrigation benefits to tail end areas.

2 IRRIGATION WATER REQUIREMENTS

Prior to design any irrigation project, it is necessary to calculate the project water requirements.

This means that exact (correct) amounts of water and correct timing of application should be

adopted. In addition, it will need more wide spread adoption of deficit irrigation, especially in arid

and semi-arid regions. Recent advances in new irrigation technologies will help to identify

irrigation scheduling strategies that minimize water demand with minimal impacts on yields and

yield quality, leading to improved food security. So, details about computed reference

evapotranspiration, crop water requirement, irrigation requirement, and soil investigation will be

discussed in detail.

3 EVAPOTRANSPIATION ESTIMATION MODEL

Evapotranspiration is one of the most important factors to be known prior to making and

implementing any decisions for the design and management of water resources systems.

Evapotranspiration varies day-to-day on the weather patterns and specific crop; therefore it is not

suitable to consider a fixed value. There are many methods proposed by different scientists and

organizations for estimating the evapotranspiration of a reference crop.

Land and Water Development Division of Food Agriculture Organization, (FAO) has developed

a software named CropWAT in 1992 to evaluate the irrigation water requirement, CropWAT (8.0)

(2009) which will be adopted in this research.

4 SPRINKLER IRRIGATION SYSTEM DESIGN

The study have been used Water CAD to model a sprinkler network as well as solving a

problem related to an irrigation system. The models consist of an optimization technique from a

network solver Water CAD used to reach the proposed scheme.

Water CAD (8.0) model was chosen, because it handles both steady state and extended period

simulation of water distribution network. This section presents discussions on Water CAD

simulation model using a sample model of a sprinkler irrigation system and a real irrigation system.

5 WATER CAD SIMULATION MODEL

Water CAD from Haestad method is a software application for construction of simple and

complex pipe networks. The Water distribution system program is developed by the U.S.A

Environmental Protection Agency’s Water Supply and Water Resources Division. It is compatible

with Geographical Information System (GIS) software, (Maksimovicand Prodanovic, 1996).


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Water CAD uses several equations to calculate the head loss along the pipes and through the

fittings and display it on each element of the model with color coding within the model, the head

loss equation frequently used is the Hazen-Williams formula. It is frequently used in the analysis of

pressure pipe systems (such as water distribution networks and sewer force mains). The formula is

as follows:

𝑸 = 𝑲.𝑪. 𝑨.𝑹𝟎.𝟔𝟑. 𝑺𝟎.𝟓𝟒 ………………… (𝟏) (WaterCAD user’s manual, 2008)

Where:Q= Discharge in the section (m3/s), C= Hazen-Williams roughness coefficient, A= Flow

area (m2), R = Hydraulic radius (m), S = Friction slope (m/m), k = Constant of the units (0.85 for SI

units).

The Hazen-Williams C-Factor is given by WaterCAD when the user selects a respective type of

pipe material, the lower the C-Factor, the rougher the inside of the pipe. In this research study, the

default value in WaterCAD was used for the water distribution model. For example, the default C-

Factors for PVC pipes and Cast Iron pipes of 150 and 130 were used, respectively.

The WaterCAD computer model used for water distribution network analysis is composed of

two parts: the input data file and the WaterCAD computer program.The data file defines the

characteristics of the pipes, the nodes (ends of the pipe), and the control components (such as

pumps and valves) in the pipe network. The computer program solves the nonlinear energy

equations and linear mass equations for pressures at nodes and flow rates in pipes. Simulation

carried out is presented to the user in a readable format on the GUI, (Figure-1).

Figure1. Water CAD Graphical User Interface.

6 METHODOLOGY OF THE SIMULATION TECHNIQUES

6.1 Study Area and Data Collection

Adiwaniyah governorate located at 180 km south of Baghdad, and lies between latitudes 31o 17'

18" – 32o 24' 24" and longitudes 44

o 24' 44" – 45

o 48' 6", Thus, the province occupies the site of the

center of Iraqi alluvial plain almost as it mediates the middle Euphrates region, as shown in Figure-

2.


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Figure 2. Study Area, Adiwaniyah Governorate.

The total area of Adiwaniyah governorate is 8366.443 km2, which represents 1.9% of the total

area of Iraq. The gross arable area of Adiwaniyah governorate does not exceed 4643.43 km2

(approximately 55% of the total area of Adiwaniyah governorate), (Figure -3).

However, the percentage of actually cultivated land was about 26% of the total area of

Adiwaniyah governorate (Adiwaniyah Agriculture Directorate, 2012), which represents 47% of the

arable land, due to limited and bad management for water resources and inequity of distribution of

water resource of the area, (Figure-3).


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Figure 1. Arableand cultivated land of Adiwaniyah governorate

Adiwaniyah governorate has a semi-arid to arid climate, which is characterized by the whole of

Iraq, a hot, dry summer and cool little rain in winter where characterized by high rates of

temperature domain the day, as well as, between winter and summer, with low humidity. The year

of the study area is divided into two prominent seasons; hot, dry weather during summer and the

winter season with a few rain and cold weather during the year. Table-1, shows the average climate

characteristics for the study area.

Table 1. The climate characteristics of the study area, average from 1978-2012.

Month Temp. Co Wind

speed m/s

Rainfall

mm

Evaporation

mm

Sun shine

hr.

Net

radiation

Mj/m2/d

Jan. 10.7 2.9 24.9 84 6.6 11.6

Feb. 13.3 3.2 17.5 120.8 7.5 14.7

March 18 3.4 14.7 195.5 7.8 17.9

April 24.5 3.5 14.3 300.9 8.6 21.4

May 30.2 3.2 4.1 429.2 9.5 23.9

June 33.9 4.1 0 557.7 11.6 27.4

July 35.7 4.1 0 614.6 11.7 27.2

August 35.1 3.4 0 731.1 11.7 26.1

Sep. 32 2.7 0.5 430.6 10.2 21.8

Oct. 26.1 2.4 3.5 291.6 8.4 16.5

Nov. 17.9 2.4 14.6 165 7.3 12.7

Dec. 12.6 2.6 18.9 102 6.3 10.6

Remarks Ave.=

24.2

Ave.=3.2 ∑=113 ∑=4023 Ave.=8.9 Ave.=19.3

6.2 Selected Field Network

The total area to be irrigated is 56 donums, (0.135km2), (450 m * 300 m), located at north of

Adiwaniyah governorate (Figure-2). This area can be configured according to proposed irrigation

system (sprinkler irrigation system) and the planted crop wheat. AutoCAD 2013 was used to draw

the networks and hence export them as DWX file to the WaterCAD to design it hydraulically.

Wheat is the main plant which will be considered in this research, due to wheat being a very

essential crop in Iraq and widely farmed in the study area.

The general steps to be followed for periodic-move system are presented diagrammatically in

Figure-4.


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Basic

Farm Data

Map of Design

Area

Weather & CropsSoils

Peak Water useDepletionRote Zone

Depth

Water Holding

Capacity

Application

Rate

Amount Per

Application

Irrigation

Interval

Sprinkler Spacing and Move of

Laterals

Irrigation Period

Determination of Pipe

SizeSprinkler Selection

System CapacityTotal Dynamic

Head

Selection of Pump

Operation Instruction

Figure-4; Design flow chart of periodic-move sprinkler systems.

6.3 Net depth of water application

The depth of water application is the quantity of water,which should be applied during irrigation

in order toreplenish the water used by the crop due toevapotranspiration,

CropWAT (8.0) model is based on FAO Penman-Montieth method (1992) (Eq.2) for calculating

the reference crop evapotranspiration:-

𝑬𝑻𝑶 =𝟎. 𝟒𝟎𝟒 𝑹𝑵 − 𝑮 + 𝜸

𝟗𝟎𝟎

𝑻+𝟐𝟕𝟑𝑼𝟐(𝒆𝒂 − 𝒆𝒅)

∆ + 𝜸 𝟏 + 𝟎. 𝟑𝟒𝑼𝟐 …………… . ……… 𝟐 (FAO, 1992)

Where: ETO = Reference crop evapotranspiration (mm/day).RN =Net radiation at crop surface

(MJ-2

/day).G = Soil heat flux (MJ-2

/day).T = Average temperature (oC).

U2 = Wind speed measured at 2 height (m/s).(ea-ed) = Vapor pressure deficit (kPa).

∆ = Slope vapor pressure curve (kPaoC).γ = Psychometric constant (kPa

oC).

900 = Conversion factor for daily-basis calculation.

The available data of wind speed at the meteorological station of the study area measured at 10

m height, so it must be converted toCropWAT(8.0) models format by using the following

formula(eq.3) (Shariati 1997),

𝑼𝟐 =𝟒.𝟖𝟔𝟖

𝒍𝒏(𝟔𝟕. 𝟕𝟓𝒁 − 𝟓. 𝟒𝟐)∗ 𝑼𝒁 ……………………………………… . … (𝟑)

Where:U2 = Wind speed at two meters.Uz= Wind speed in Z meter elevation, and Z= altitude of

measured wind speed.

The result of ET0 of CropWAT (8.0) has been validated with Blaney-Criddle which is modified

by N. Kharofa (1985) Eq. (4). ETo = C P Tc1.3 ……………………………………… (4)


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Where:C = coefficient calculated for the local site, Kharofa (1985) fixed it by 0.34 for the middle of

Iraq.P= the percentage of the number of daylight hours in the month relative to the number in the

year.Tc = average monthly temperature (Co).

By applying the meteorological data of Adiwaniyah meteorological Station which discussed

above in CropWAT (8.0), the results of ETo as in table-2. Table 1. ETo At Adiwaniyah Meteorological Station

This variation in ETo values is attributed to combined effects of temperature, sun shine hours,

radiation, wind speed and humidity. The increase in ETo during May to Sep. in the study area can

be related to the change in temperature and wind speed.

In specific case, the computation of the net depth ofwater application requires additional inputs

corporate CropWAT (8.0) model as the following:

a. The available soil moisture [FC - Permanent Wilting Point (PWP)].

b. The allowable soil moisture depletion (P) as a percentage from the available soil moisture.

c. The effective depth of root zone of the crop (RZD).

Soil survey and tests should be done to determine the field capacity (FC) and permanent wilting

point (PWP) of the soil. Reports and data from Huriyah-Daghara Project's field laboratory were

used to estimate the soil texture, FC, PWP and P. by using SPAW computer model simulate. The

difference between the field capacity and permanent wilting point will give the available soil

moisture (water holding capacity), which is the total amount of water that the crop can use.

Depending on the crop sensitivity to stress, the soil moisture should be allowed to be depleted only

partially. For most field crops, a depletion of 50% of the available moisture is acceptable.

The effective root zone depth of the crop under consideration can be established from specified

tables. Some tests and measurements for root depth of wheat crop at the field of the study were

taken and compared with measurements of Agriculture Directorate of Adiwaniyah Governorate,

these tests and measurements showed that the RZD of wheat is (0.8-1m), so that it was taken as 1m

as the worst case for this research.


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The maximum net depth to be applied per irrigation will be at the maximum root zone depth at

the mid-season of the crop depending on the crop cycle, can be calculated, using the following

equation, (FAO, 1992):

𝒅𝒏𝒆𝒕 = 𝑭𝑪 − 𝑷𝑾𝑷 ∗ 𝑹𝒁𝑫 ∗ 𝑷……………………………… (𝟒)

Where:dnet = Readily available moisture or net depth of water application per irrigation for the

selected crop (mm), FC = Soil moisture at field capacity (mm/m), PWP = Soil moisture at the

permanent wilting point (mm/m), RZD = the depth of soil that the roots exploit effectively (m), P=

the allowable portion of available moisture permitted for depletion by the crop before the next

irrigation.

Depending on Huriyah-Daghara’s field laboratory data and the SPAW model results with

applying equation-4in CropWAT model, the maximum dnet for the area of the case study is 60.4

mm.

In order to express the depth of water in terms of the volume, eq.5 calculated this volume, the

area proposed for irrigation must be multiplied by the depth:

𝑽𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒘𝒂𝒕𝒆𝒓 𝒕𝒐 𝒃𝒆 𝒂𝒑𝒑𝒍𝒊𝒆𝒅 (m3)= 𝟏𝟎 ∗ 𝑨 ∗ 𝒅…………… . (𝟓)(FAO,1992)

Where:A = Area proposed for irrigation (ha), d = Depth of water application (mm), 10 = Conversion

factor.

For the field of the study area of an area of 54 donums (13.5 hectare), depending on the results of

CropWAT (8.0) model and using equation -5,a net application of 8154 m3of water will be required

per irrigation to bring the root zone depth of soil from the 50% allowable depletion level to the field

capacity at worst case within the period between 16 November and 30 of April.

6.4 Crop Water Requirements

The amount of water required to compensate the evapotranspiration loss from the cropped field

is defined as crop water requirement. Although the values for Crop evapotranspiration under

standard conditions (ETc) and crop water requirement are identical, crop water requirement refers

to the amount of water that needs to be supplied, while crop evapotranspiration refers to the amount

of water that is lost through evapotranspiration, (CropWAT 8.0 Manual, 2009).

Crop evapotranspiration per decade was calculated by multiplication of the number of effective

crop days. To convert monthly rainfall data to decade values, a linear interpolation was carried out.

Values for first and third decades of each month were respectively calculated by interpolation with

the preceding and successive months.

Crop water requirements were then calculated as the difference between the crop

evapotranspiration and effective rainfall, (Table-3).

Table 2. Wheat crop water requirements results.

mk:@MSITStore:C:\ProgramData\CROPWAT\helpfiles\CROPWAT8_English.chm::/html/hs1150.htm




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7 IRRIGATION FREQUENCY AT PEAK DEMAND AND IRRIGATION

CYCLE

The peak daily water use is the peak daily water requirement of the crop determined by

subtracting the rainfall from the peak daily crop water requirements. Irrigation frequency(If) is the

time it takes the crop to deplete the soil moisture at a given soil moisture depletion level.The

following equation determine If, (Irrigation Manual, 2001):

𝑰𝒓𝒓𝒊𝒈𝒂𝒕𝒊𝒐𝒏 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 (𝑰𝑭) = 𝒅𝒏𝒆𝒕

𝑬𝑻𝑪…………………………… . ……… (𝟔)

Where:IF= irrigation frequency (days), dnet= net depth of water application (mm), ETC= peak daily

water use (mm/day)

According to CropWAT (8.0) model result, the peak water demand of wheat at Adiwaniyah

meteorological station was estimated to be 6.38 mm/day. Therefore, using equation 4 will give

irrigation frequency IF equal to 60.4/6.38=9.47 days.

The system should be designed to provide 60.4 mm every 9.47days (113.64 hours). For practical

purposes, fractions of days are not used for irrigation frequency purposes. Hence, the irrigation

frequency in this case should be 9 days, with a corresponding dnet of 57.42 mm (6.38 x 9), and by

using equation-4,the moisture depletion should be 34%.

7.1 Gross Depth of Water Application

The gross depth of water application (dgross) equals the net depth of irrigation divided by the farm

irrigation efficiency. It should be noted that farm irrigation efficiency includes possible losses of

water from pipe leaks.


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The gross depth can be calculated from equation (7), (Irrigation Manual, 2001):

𝒅𝒈𝒓𝒐𝒔𝒔 =𝒅𝒏𝒆𝒕

𝑬…………………………………… . 𝟕

Where:E= the farm unit irrigation efficiency

The farm irrigation efficiency of sprinkler systems varies from climate to other as in table (4),

(FAO, 1992).

Table 4. Farm Irrigation Efficiencies for Sprinkler Irrigation in Different Climates

Climate Farm irrigation efficiencies

Cool 80%

Moderate 75%

Hot 70%

Desert 65%

According to FAO classification, the climate of Adiwaniyah governorate is considered as

moderate at winter season, so that the farm irrigation efficiency would be 75%, and applying

equation-7, the gross depth of irrigation should be 76.56 mm (57.42/0.75).

7.2 Preliminary System Capacity

The next step is to estimate the system capacity. The system capacity (Q) can be calculated using

equation -8, (Irrigation Manual, 2001):

𝑸 =𝟏𝟎 ∗ 𝑨 ∗ 𝒅𝒈𝒓𝒐𝒔𝒔

𝑰 ∗ 𝑵𝒔 ∗ 𝑻………………………………………… (𝟖)

Where:Q = System capacity (m3/hr.), A = Design area (ha), d = Gross depth of water

application (mm), I = Irrigation cycle (days), Ns = Number of shifts (movement) per day,T =

Irrigation time per shift (hr.).

For the area of 13.5 ha, in order to achieve the maximum degree of equipment utilization, it is

desirable, but not always necessary, that the irrigation system should operate for 15 hours per shift

at one shift per day during peak demand and take an irrigation cycle of 9 days to complete irrigating

the 13.5 ha. Substituting the values in equation-8gives a system capacity of 76.56 m3/hr.

8 DESIGN CRITERIA

8.1 Design Steps for Periodic-Move System

Once the preliminary design parameters are obtained, the design adjustment can commence. The

adjustment allows for the revision of the preliminary design parameters, in order to suit the

physical, human, financial, and equipment performance limitations or impositions. The next design

step is to select the Sprinkler system design and the spacing.

8.2 Sprinkler Simulation

Sprinklers are devices associated with junctions that model the flow through a nozzle or orifice.

In these situations, the demand (i.e., the flow rate through the sprinkler) varies in proportion to the

pressure at the junction raised to some power. The constant of proportionality is termed the

discharge coefficient. For nozzles and Sprinkler heads, the exponent on pressure is 0.5, and the


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manufacturer usually states the value of the discharge coefficient as the flow rate in CMH through

the device at a 1 psi pressure drop.

Emitters are used to model flow through sprinkler systems and irrigation networks. Users can

also be used to simulate the leakage in a pipe connected to the junction (if a discharge coefficient

and pressure exponent for the leaking crack or joint can be estimated) and compute a flow at the

junction. In the latter case, a very high value of the discharge coefficient e.g., 100 times the

maximum flow expected can be used.

When both an emitter and a normal demand are specified for a junction, the demand that Bentley

Water CAD reports in its output results includes both the normal demand and the flow through the

emitter.

The flow through an emitter is calculated as; (WaterCAD user’s manual, 2008):

𝑸 = 𝒌𝒑𝒏 ………………………………… . . … (𝟗)

Where:Q = Flow (m3/hr), k = emitter coefficient (property of the node), P = Pressure (n/m

2), n = is

the emitter exponent and is set globally in the calculation

Options for the run; it is dimensionless but affects the units of k. The default value for n is 0.5

which is a typical value for an orifice, (WaterCAD user’s manual, 2008).

8.3 Sprinkler Irrigation Scheme Plan

The field which was chosen as the study area consists of two neighboring pieces of lands for two

famers; each one has dimensions of 150m*450m. The main pipe of the system is supposed to be laid

on the center line between the two lands, but the laterals which are carrying the raiser and sprinklers

must be installed perpendicularly on the main line.

Figure-5, shows that, the designed sprinkler network consist of the main line of 445 m in length,

three pairs of laterals are laid perpendicularly on the main line; each lateral pipe is 135m in length,

the distance between two laterals is 135 m as well, and 66 Sprinklers carried by the laterals with 11

sprinklers per lateral.


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Figure 5. Proposed Sprinkler Irrigation Scheme

The selection of the correct sprinkler depends on how the best fit spacing with a certain pressure

and nozzle size can provide the water at an application rate that does neither cause runoff nor

damage the crop and at the best possible uniformity under the prevailing wind conditions.

In this study, where a precipitation rate of 6.44 mm/hr of chosen sprinkler is compatible with the

soil and wheat crop, there are several nozzle size, pressure and sprinkler spacing combinations to

choose from (Table-5), so there is another aspect to consider in selecting a sprinkler which is the

energy cost.

Table 5.Sprinkler manufacture table

Lower pressures are preferable as long as the uniformity of application is not compromised. The

coefficient of uniformity (CU) is a measure of the uniformity of water application. A value of 100%

indicates perfect uniformity, which means that the water is applied to the same depth at each point

in the field. As a rule, the selected sprinkler should have a CU not less than 85% or more. It is

advisable to avoid using the lowest pressure since usually this is the pressure that corresponds to

low CU values,(Naser, 2003).

Referring to the sprinklers manufacture tables, there area number of spacing fits on the land of

the case study, such as 12*12m, 12*15m, 12*18m, and 15*15m. The next step is to find out how

the winds will affect the spacing between two sprinklers and laterals. For this purpose, the mean

wind velocity of the windiest month of the year is considered. Most designers set the maximum

spacing of sprinklers based on the information of table-6. It should be noted also that in the

rectangular pattern, better distribution is obtained when the lateral is placed across the prevailing

wind direction.

Table 6. Maximum sprinkler spacing as related to wind velocity, rectangular pattern

Average Wind Speed (km/hr) Spacing as Percent of Wetted Diameter

Up to 10 40% between Sprinkler

65% between laterals

10-15 40% between Sprinkler


Above 15 30% between Sprinkler


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In the case of the research, where the average wind velocity in June is 4.1 m/sec (14.7 km/hr)

and in March is 3.4m/sec (12.2 km/hr), the sprinkler spacing should be based on 45% of sprinkler

wetted diameter (D) for square pattern, and 40% of D∗ 60% of D for rectangular pattern.

From table-5, the sprinkler of the 4 mm nozzle at 350 kPa with 30.50 m of wetted diameter and

6.44 mm/hr precipitation rate was chosen for this design. From table-5,the spacing for a rectangular

pattern for 14.7 km/hr wind speed (10-15 km/hr), 40% of D and 60% of D for the 12 m x 15 m

spacing are 12.2 m (> than 12 m sprinkler spacing) and 18.3 m (> than 15 m lateral spacing),

respectively. Therefore, the wind requirements are satisfied the 12 m x 15 m spacing.

Therefore, 6.44mm/hr sprinkler precipitation rate is less than infiltration rate of the soil of the

study area (7.26mm/hr), so it is compatible with the infiltration rate, and the 4 mm nozzle can be

considered.

It is advisable to determine whether the sprinkler with a 4.0 mm nozzle would satisfy the wind

requirements at the 12 m x 18 m spacing at 300 kPa. At this pressure, the wetted diameter is 26.60

m. 40% of D and 60% of D are 10.64 m (< than 12 m sprinkler spacing) and 15.96 m (< than 18 m

lateral spacing), respectively. For the 15 m x 15 m spacing, 45% of D is 11.9 m (0.45 * 26.60),

which is less than the sprinkler and lateral spacing of 15 m each. Therefore, the 4.0 mm nozzle

operating at 300 kPa pressure does not meet the wind requirements either under 12 m x 18 m

spacing or 15 m x 15 m spacing as the wetted diameter is too small compared to the desired spacing

requirement.

8.4 Design of Periodic Move Sprinkler Irrigation System

According to previous discussed data of the case study, the 12 m *15 m spacing for the 4 mm

nozzle operating at 350 kPa pressure and delivering 1.16 m3 /hr at an application rate of 6.44 mm/hr,

was accepted as a potential spacing.

The next step is to determine the set time (Ts), which is the time each set of sprinklers should

operate at the same position in order to deliver the gross irrigation depth, and establish whether it is

acceptable. So, it can be found out according to equation 10,

𝑻𝒔 =𝒅𝒈𝒓𝒐𝒔𝒔

𝑷𝒓……………………………… . ……… (𝟏𝟎)(FAO,1992)

Where:Ts= Set time (hr), Pr= Sprinkler precipitation rate (mm/hr), Substituting the values in

Equation (4.6) gives:-

Ts= 76.56/6.44=11.8 ≈12hours.

Hence, each set of sprinklers should operate at the same position for 12 hours in order to deliver

the 76.56 mm gross application per irrigation for nine days. If it is assumed that the design is a

permanent system, as in (Figure-6), this would have been ideal, because it will have full utilization

of the equipment by having two sets per day. However, if the design is a semi-portable system, as in

(Figure-7), where the laterals have to be moved from one position to the next, there would be time

available to move the laterals between each of the two shifts for the next day during the peak water

demand period. In this case, the following choices will be adopted:

1. To increase twice the number of operating laterals so that extra laterals are moved while the

other laterals are operating, or

2. To re-assess the moisture depletion level, or


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3. To use a different sprinkler with the same or different spacing, nozzle, pressure and

precipitation rate.

Figure 6. Permanent sprinkler irrigation system.

Figure7. Semi-portable sprinkler irrigation system.

As a rule, it is more economical to look into alternative 2 or 3 than to follow alternative

1.Alternative 2, involves re-adjusting the moisture depletion level. The effect will be re-adjustment

of dgross and consequently the set time. In the case, may assume that, during each irrigation cycle,

the net equivalent depth to 9 days of consumptive use could be applied. This would amount to a net

application depth of 57.42 mm (9 x 6.38), which is equivalent to 34% (57.42/ (170 x 1)) soil

moisture depletion, with an irrigation frequency of 9 days. Allowing one day for cultural practices,


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the irrigation cycle would be 9 days. In order to apply the 57.42 mm net per irrigation, the gross

application at 75% efficiency should be 76.56 mm (57.42/0.75).

8.5 Allowable Pressure Variation

Pressure differences throughout the system or block or subunit should be maintained in such a

range, so that a high degree of uniformity of water application is must achieved.

(Addink, et al., 1989) and (Keller and Bliesner, 1990 ) suggested that for practical purposes, the

allowable pressure loss due to friction can be estimated at 20% of the required average pressure. In

design case of the 12 m * 18 m spacing for the 4.5 mm nozzle operating at 350 kPa, the allowable

pressure variation in the system should not exceed 20% of the sprinkler operating pressure, which is

70 kPa (350 x 0.2) or 7 meters water head.

8.6 Pipe Size Simulation

Pipe size simulation involves selecting the type and diameter of the pipe that would be used in

the system, which can carry a given flow at or below the recommended velocity limit. The velocity

limit for PVC pipes is about 2 m/s (Kuo et al.,2000). PVC pipes range in diameter from 12 to

600mm.The PVC pipes normally come in 6 meters lengths. And come in pressure ratings of 40

meters (Class 4), 60 meters (Class 6), 100 meters (Class 10) and 160 meters (Class 16).

Laterals in a semi-portable system are PVC pipes with multi-outlets (sprinklers) along their

length. The friction losses were simulated and calculated by WaterCAD model with Hazen-

Williams equation, the model corrects the pipe diameter, since the flow reduces along the lateral.

While the class 6 pipe is used for surface irrigation, the most commonly used classes for

pressurized irrigation systems are the class 12.

8.7 Total Head Requirements

The total head requirements are composed of the pump suction lift, the friction losses in the

supply line, the friction losses in the main, lateral and fittings, the riser, the sprinkler operating

pressure and the difference in elevation. The suction lift is the difference in elevation between the

water level and the eye of the pump impeller plus the head losses in the suction pipe. The head

losses of the suction pipe comprise the frictional losses of the pipe, fittings and the velocity head.

The velocity head is equal to, (Chow, 1982);

𝐯𝟐

𝟐𝒈……………………….. (11)

Where: v = Water velocity (m/s), g = Acceleration due to gravity (9.81 m/s2)

Keller &Bliesner, (1990) recommended that for centrifugal pumps the diameter of the suction

pipe should be selected such that the water velocity v<3.3 m/s in order to ensure good pump

performance. Assuming this maximum velocity for the flow and applying the above formula, then

the velocity head corresponding to the minimum diameter of the suction pipe that can be selected to

satisfy this condition is 0.56 m (3.32/ (2 x 9.81)).

Considering that the water level is at 18.00 m, so there will be no difference in elevation between

the water level and the eye of the impeller (located at 18 m elevation). Since the maximum velocity

head is 0.56 m, the suction lift is 0.56 m (0 + 0.56). Assuming minor losses in fittings and a short

suction pipe, the suction lift is rounded up to 2 m.

The elevation difference is obtainable from the contour map and is approximately 0.5 m.The

length of the supply line is 25 m. The friction losses for the supply line are computed as follows:


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Q = 76.56 m3/hr, L = 25 m, D = 200 mm, HL = 0.0035 x 251 = 0.88 m.

The friction losses in the riser could be assumed about 0.25 m per m of riser, and for fittings, it

is usually taken 10% of the total head losses. Additionally, the height of the riser should be included

in the calculations. This was assumed to be 2 meters in this design, to cater for tall crops, such as

maize/corn. So that the total head requirement in the system must be not less the minimum

operation sprinkler pressure.

9 RESULTS OF FIELD MEASUREMENTS & DESIGN

9.1 System Capacity

The final design of the system capacity is 76.56 m3/hr to irrigate area of 54 donums, within 9

days of 15 hours per day, while the average of filed measurements of six fields of wheat in the same

area showed that the existing applied discharge is 327 m3/hr, and spending 10 days to irrigate 85

donums with not less ten hours per day. This means each donum gates 385 m3 per irrigation, while

this present study showed that each donum requires only 150 m3 per irrigation. So the application of

sprinkler irrigation will assist to double the area of cultivation by about 2.5 times, in case of wheat

crop.

9.2 Main Line Pipe Sizing

The schematic display of WaterCAD model output annotates all the model results on each

element, such as pipes inner diameters, carried discharge on each pipe, velocity of flow, unit head

lossand other details.

The main line of the system consists of three parts according to diameter, carried discharge and

unit of the head losses along each part of the pipe, part one (main line -1) includes pipes 1,2 and 3

with diameter of 150 mm and operation discharge of 76.56, 76.56, 63.8 m3/hr,respectively. Main

Line -2 includes pipes 4 and 5, which are 125 mm in diameter with operation discharges of 51.04

and 38.2m3/hr, respectively. Pipe 6 and pipe 7 form main line 3 which has diameter of 100 mm and

discharge of 25.52 and 12.76m3/hr. respectively, (Figure-8),(table-7).

Figure 8. Main line pipe design.

Table7. Pipes Sizes and Carried Discharges

Pipe Type Length m Diameter mm Discharge m3/hr

1 Main 10 150 76.56

2 Main 25 150 76.56

3 Main 135 150 63.8

4 Main 15 125 51.04

5 Main 120 125 38.28

6 Main 15 100 25.52


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7 Main 135 100 12.76

9.3 Lateral Pipes Sizing

The designed system has 6 laterals, each lateral consists of 11 pipe’s segment of 50 mm in

diameter of each pipe (pipe 8 to pipe 72) with different discharges after each node (sprinkler),

starting by 12.76 m3/hr and ending by 1.16m

3/hr. Figure-9, shows the laterals design.

Figure 9. Lateral pipes design.

10 WATERCAD PRESSURE SIMULATION IN THE SYSTEM

It is desired that the pressure in the system should not be below the sprinkler operating pressure

of 350 kpa. Assuming 20% pressure variation (FAO, 2009), between the lowest point and the

highest point is allowed, the variation then should not exceed 7m (20% of 350 kpa Sprinkler

Operation Pressure), so that a high degree of uniformity of water application is achieved.

From WaterCAD model calculation, the maximum pressure in the system is 395 kPaoccurring at

the first sprinkler on the field(Figure-10), whilst the minimum pressure is 351 kPa occurring at the

last sprinkler (Figure-11). Thus, the pressure variation is within the constraints limits.


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Figure 10. First sprinkler node, max pressure in the system.

Figure 11. Last sprinkler node, min pressure in the system.

CONCLUSION

The main concern in the design water resources system of pressurized irrigation networks

is to achieve an optimal solution which satisfies the constraints of the network, especially if

the network is large.The following conclusions were derived from the present study as follows;

1- The designed models employed and applied to irrigate about 368200, 304370 donums of

wheat and barley respectively at winter seasons, and to irrigate about 17485, 46543 donums

of maize/corn and sorghum respectively, at summer season, to save more water quantities

to vivification and irrigate about 984400 donums of heathy land.

2- The final design of the system capacity is 76.56 m3/hr to irrigate area of 54 donums, within

9 days of 15 hours per day. While the average of existing filed measurements of six fields

of wheat in the same area showed that the existing applied discharge is 327 m3/hr, and

spending 10 days to irrigate 85 donums with not less ten hours per day. This means each

donum gates 385 m3 per irrigation.

3- This study showed that each donum requires only 150 m3per irrigation, so that the

application of sprinkler irrigation will assist to doublicate the area of cultivation by about

2.5 times, in case of wheat crop.

4- This study revealed the ability of applying these models on other regions inAdiwaniyah and

other Iraq governorates.Itis recommended due to the efficiency and compatibility of such

simulation especially if the network is large.

5- The model was able to simulate water management, the calibration, and validation results

with Kharoofa formula indicated that the results were compatible.

6- However, this study recommend the possibility of employing this simulation model on

other crops such as barley, maize, andsorghum can be achieved to assess the irrigation

system.

REFERENCES

Addink, H. and Bytat, 1989. “Design and operation of farm irrigation systems”, ASAE,

USA, 31(3):pp. 821-829


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Bentley Systems, Incorporated Haestad Methods Solution Center 2008, “Bentley

WaterCAD V8i User’s Guide”, New York, USA.1289p.

Chow, V. T., (1982): Open Channel Hydraulics, 3rd

ed. McGraw-Hill Book Co.,New York,

USA, 680p.

FAO, (1992). A framework for land evaluation. Soils Bulletin 32. FAO, Rome,Italy. FAO,

(2009). Data Base. Food and Agriculture Organization of the United Nations, Rome., Italy.

Haestad Press, 2002. “Computer Applications in Hydraulic Engineering”, Fifth Edition,

Waterbury, Connecticut.297p.

Keller, J. and Bliesner, R. D., 1990. “Sprinkler and Trickle Irrigation”, Chapman and Hall,

New York, USA.

Kuo, S. F. Merkley, G. P. and Liu, C. W. 2000. “Decision support for irrigation planning

using a genetic algorithm”, Agricultural Water Management 45: pp. 243-266.

Naser, Shetha Abdul-Kader, 2003.“Spray Losses in Sprinkler Irrigation Systems in Iraq”,

M.Sc. Thesis, Dept. of Building and Construction Engineering,

University of Technology. Baghdad, Iraq. Sprague, R. H. Jr. and Carlson, E. D. 1982.

“Building effective decision support systems”, Prentice-Hall, Englewood Cliffs, N.J. USA,524p.

Shariati, M.R., 1997. “Water Requirement Estimating of Main Crops Part 1”, Soil and

Water Research Org., Karaj, IRAN, 432p.

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